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5.16.1.1.1 Immediate messaging procedure to registered Public User Identity
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Figure 5.47: Immediate Messaging procedure to registered Public User Identity
1. UE#1 generates the multimedia content intended to be sent to UE#2.
2. UE#1 sends the MESSAGE request to P‑CSCF#1 that includes the multimedia content in the message body.
3. P‑CSCF#1 forwards the MESSAGE request to S‑CSCF#1 along the path determined upon UE#1's most recent registration procedure. Before forwarding, if P-CSCF#1 has received the MPS for Messaging indication for the UE as set (enabled), P-CSCF#1 sets the Resource-Priority information in the MESSAGE to a value appropriate for MPS.
4. Based on operator policy S‑CSCF#1 may reject the MESSAGE request with an appropriate response, e.g. if content length or content type of the MESSAGE are not acceptable. S‑CSCF#1 invokes whatever service control logic is appropriate for this MESSAGE request. This may include routing the MESSAGE request to an Application Server, which processes the request further on.
5. S-CSC#1 forwards the MESSAGE request to I‑CSCF#2.
6. I‑CSCF#2 performs Location Query procedure with the HSS to acquire the S‑CSCF address of the destination user (S‑CSCF#2).
7. I‑CSCF#2 forwards the MESSAGE request to S‑CSCF#2.
8. Based on operator policy S‑CSCF#2 may reject the MESSAGE request with an appropriate response, e.g. if content length or content type of the MESSAGE are not acceptable. S‑CSCF#2 invokes whatever service control logic is appropriate for this MESSAGE request. This may include routing the MESSAGE request to an Application Server, which processes the request further on.
For example, the UE#2 may have a service activated that blocks the delivery of incoming messages that fulfil criteria set by the user. The AS may then respond to the MESSAGE request with an appropriate error response.
9. S‑CSCF#2 forwards the MESSAGE request to P‑CSCF#2 along the path determined upon UE#2's most recent registration procedure.
10. P‑CSCF#2 forwards the MESSAGE request to UE#2. After receiving the MESSAGE UE#2 renders the multimedia content to the user.
11–16. UE#2 acknowledges the MESSAGE request with a response that indicates that the destination entity has received the MESSAGE request. The response traverses the transaction path back to UE#1.
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5.16.1.1.2 Immediate messaging procedure to unregistered Public User Identity
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Figure 5.48: Immediate messaging to unregistered Public User Identity, service control invoked
1-5. The same actions apply as for when the Public User Identity is registered, see step 1-5 in clause 5.16.1.1.1.
6. I‑CSCF#2 interacts with the HSS as per the terminating procedures defined for unregistered Public User Identities in clause 5.12.1. If the Public User Identity has no services related to unregistered state activated the interaction with HSS would be as per the procedure defined in clause 5.12.2.
7. I‑CSCF#2 forwards the MESSAGE request to S‑CSCF#2.
8. Based on operator policy S‑CSCF#2 may reject the MESSAGE request with an appropriate response, e.g. if content length or content type of the MESSAGE are not acceptable or the UE#2 does not have a service activated that temporarily hold the MESSAGE request in the network.
S‑CSCF#2 invokes whatever service control logic appropriate for this MESSAGE request. This may include routing the MESSAGE request to an Application Server, which processes the request further on.
For example, the UE#2 may have a service activated that allows delivery of any pending MESSAGE request. The AS may then hold the MESSAGE request and deliver the MESSAGE request when the UE#2 becomes reachable. In this case, depending on user settings UE#2 controls the delivery of the pending MESSAGEs.
9-12. The MESSAGE request is acknowledged with an appropriate acknowledgement response. The acknowledgement response traverses the transaction path back to UE#1.
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5.16.1.2 Immediate messages with multiple recipients
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IMS users shall be able to send a single immediate message to multiple recipients, as specified in TS 22.340 [29a]. The following means are supported to achieve this:
- A PSI identifying a new group is created in the appropriate Application Server and members are added to this group (e.g. by the user via the Ut interface or by the operator via O&M mechanisms). Immediate messages addressed to this PSI will be routed to the AS hosting the PSI and this AS shall create and send immediate messages addressed to a group member of the group identified by the PSI.
- The user can send an immediate message by indicating the individual addresses (Public User Identities for IMS recipients) of the intended recipients as part of the immediate message. The AS of the user shall then create and send immediate messages addressed to each one of the intended recipients.
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5.16.2 Session-based Messaging
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5.16.2.0 General
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This clause describes architectural concepts and procedures for fulfilling the requirements for Session-based Messaging described in TS 22.340 [29a].
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5.16.2.1 Architectural principles
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Session-based IMS messaging communications shall as much as possible use the same basic IMS session delivery mechanisms (e.g. routing, security, service control) as defined in clause 4 and 5 of this document. For session based messaging the session shall include a messaging media component, other media components may also be included.
As the messaging media component usually does not require QoS beyond best-effort, use of the preconditions mechanism as defined in IETF RFC 3312 [41] is not required for session based messaging establishment that only includes a messaging media component.
NOTE: Pre-conditions mechanism may still be required for session establishment with additional media components that require the establishment of additional IP‑CAN bearers.
Once the session containing a messaging media component is established, messages in the session are transported between the session participants as per the parameters defined in the messaging media component part of the session description (SDP).
The invited UE shall host the message session (accept a connection for the message session from the other endpoint). In order to host the message session the UE needs an appropriate IP‑CAN bearer, on which it can accept the connection for the message media component. This IP‑CAN bearer may be e.g. a general purpose bearer available prior to starting the session initiation or a dedicated bearer that is established during session establishment. Messages within a message session should be transported over a connection-oriented reliable transport protocol. Message sessions may be either established end to end between two UEs or may involve one or more intermediate nodes (e.g. a chat server for multi party chat or an Application Server to perform per message charging).
For addressing chat-group-type session based messaging the concept of Public Service Identities is used.
Session based messaging is available for users that are registered in the IMS.
The session based messaging shall be able to provide the following functionality:
- Per-message-based charging, as well as content- and size-based charging.
- Operator-controlled policy to be set on the size and content of the messages.
- Support for indication of maximum message content size that a UA will accept to be received.
- Support for a messaging media component as part of a session where other media components are also included.
- Support for messaging-only sessions.
If charging mechanisms like charging based on the message content, message type or number of sent and/or received messages (see TS 22.340 [29a]) are required, then an intermediate node (messaging AS) shall be involved, which is able to inspect the SIP signalling as well as the exchanged messages and their content. Such an intermediate node may also provide support for time- and/or volume based charging.
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5.16.2.2 Procedures to enable Session based Messaging
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5.16.2.2.0 General
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IMS users shall be able to exchange session-based messages with each other by using the procedures described in this clause. These procedures shall allow the exchange of any type of multimedia content (subject to possible restrictions based on operator policy and user preferences/intent), for example but not limited to:
- Pictures, video clips, sound clips with a format defined in the respective access specific documents.
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5.16.2.2.1 Session based messaging procedure to registered Public User Identity
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The following procedure shows the establishment of a message session between two registered UEs where the UEs are able to exchange messages end-to-end. The signalling flow is based on the general flow shown in clause 5.7a of this specification.
Figure 5.48a: Message session establishment
1-30. These steps are identical to the steps 1 to 30 in the flow of clause 5.7a. After that the message session is established. For session based messaging the SDP offer in the first INVITE request may indicate the maximum message size UE#1 accepts to receive and the 200 OK (Offer response) to the INVITE request may indicate the maximum message size UE#2 accepts to receive.
For MPS for Messaging, the following exception at step 3 in the referenced flow applies: If P-CSCF#1 has received the MPS for Messaging indication for the UE as set (enabled), P-CSCF#1 sets the Resource-Priority information on the INVITE request to a value appropriate for MPS.
31. UE#1 establishes a reliable end-to-end connection with UE#2 to exchange the message media.
32. UE#1 generates the message content and sends it to UE#2 using the established message connection.
33. UE#2 acknowledges the message with a response that indicates that UE#2 has received the message. The response traverses back to UE#1. After receiving the message UE#2 renders the multimedia content to the user.
Further messages may be exchanged in either direction between UE#1 and UE#2 using the established connection. The size of the messages exchanged within the session shall be within the size limits indicated by UE#1 and UE#2 respectively.
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5.16.2.2.2 Session based messaging procedure using multiple UEs
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Session based messaging between more than two UEs require the establishment of a session based messaging conference.
Within session based messaging conferences including multiple UEs (e.g. multiparty chat conferences) an MRFC/MRFP or an IMS AS shall be used to control the media resources.
When MRFC/MRFP are used, then conferencing principles are used to provide the chat service:
- MRFP must be able to establish message connections with all involved parties.
- MRFC/MRFP must be able to receive messages from conference participants and to distribute messages to all or some of the participants.
- In order to enable the UE managing information related to the session based messaging conference the MRFC may be co-located with an IMS AS.
- MRFC/MRFP roles and interactions with an AS are described in more detail in clauses 4.7, 5.14.1 and 5.14.2.
- The interface for session based messaging between MRFC and MRFP is not standardised in this release. When an AS is used, then the IMS service control architecture is used to provide the chat service. Both signalling and user plane are then supported by the AS. For more details, see clause 4.2.
The following flow shows the originating session based messaging set up using an intermediate server for a chat service. In this case the intermediate chat server is addressed by the UE#1 using a PSI. It is assumed that UE#1 is the first UE entering the chat session.
NOTE: Interactions between MRFC and MRFP are not shown in the flows below since these interactions are not standardized. An optional ringing response from MRFC/AS to the UE is not shown in the following procedure.
Figure 5.48b: Session based messaging using a chat server
1. UE #1 sends the SIP INVITE request addressed to a conferencing or chat PSI to the P‑CSCF. The SDP offer indicates that UE#1 wants to establish a message session and contains all necessary information to do that. The SDP offer may indicate the maximum message size UE#1 accepts to receive.
2. P‑CSCF forwards the INVITE request to the S‑CSCF.
For MPS for Messaging, before forwarding, if the P-CSCF has received the MPS for Messaging indication for the UE as set (enabled), the P-CSCF sets the Resource-Priority information on the INVITE request to a value appropriate for MPS.
3. S‑CSCF may invoke service control logic for UE#1.
4. S‑CSCF forwards the INVITE request to the MRFC/AS.
5. 6. and 8. MRFC/AS acknowledges the INVITE with a 200 OK, which traverses back to UE#1. The 200 OK (Offer response) may indicate the maximum message size the host of the PSI accepts to receive.
7. Based on operator policy P‑CSCF may instruct PCRF/PCF to authorize the resources necessary for this session.
9.-11. UE#1 acknowledges the establishment of the messaging session with an ACK towards MRFC/AS.
12. UE#1 establishes a reliable end-to-end connection with MRFP/AS to exchange the message media.
13. UE#1 sends a message towards MRFP/AS.
14. MRFP/AS acknowledges the message.
A1. Another UE (UE#2) sends an INVITE request addressed to the same conferencing or chat PSI. The initial SDP indicates that the UE wants to establish a message session and contains all necessary information to do that.
A2. MRFC/AS acknowledges the INVITE request with a 200 OK.
A3. UE#2 acknowledges the 200 OK with an ACK.
A4. UE#2 establishes a reliable end-to-end connection with MRFP/AS to exchange the message media.
A5. MRFP/AS forwards the message to all recipients, e.g. all participants in the chat room.
A6. The recipients acknowledge the message towards MRFP/AS.
B1. and C1. Further INVITE requests from new possible participants may arrive at any time.
Further messages may be exchanged in either direction between the participating UEs using the established connection via the MRFC/MRFP or AS. The size of the messages exchanged within the session shall be within the size limits indicated by UE#1 and the host of the PSI respectively.
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5.16.2.2.3 Session based messaging procedure with an intermediate node
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The following procedure shows the originating session based messaging involving an intermediate node. An optional ringing response from AS to the UE or vice versa is not shown in the following procedure.
Figure 5.48c: Session based messaging with an intermediate node
1. UE#1 sends the SIP INVITE request addressed to UE#2, containing an initial SDP, to the P‑CSCF. The SDP offer may indicate the maximum message size UE#1 accepts to receive.
2. The P‑CSCF forwards the INVITE request to the S‑CSCF along the path determined upon UE#1's most recent registration procedure.
For MPS for Messaging, before forwarding, if the P-CSCF has received the MPS for Messaging indication for the UE as set (enabled), the P-CSCF sets the Resource-Priority information on the INVITE request to a value appropriate for MPS.
3. Based on operator policy the S‑CSCF may reject the INVITE request with an appropriate response. S‑CSCF may invoke whatever service control logic is appropriate for this INVITE request. In this case the Filter Criteria trigger the INVITE request to be routed to an Application Server that acts as an intermediate node for the message session.
4. The S‑CSCF forwards the INVITE request to the AS. The AS may modify the content of the SDP (such as IP address/port numbers). Based on operator policy the AS may either reject the session set-up or decrease the maximum message size indication.
5. The AS sends the INVITE request to the S‑CSCF.
6. The S‑CSCF forwards the INVITE request to the destination network. The destination network will perform the terminating procedure.
7–8. UE#2 or AS in the terminating network accepts the INVITE request with a 200 OK response. The 200 OK response is forwarded by the S‑CSCF to the AS. The 200 OK (Offer response) may indicate the maximum message size UE#2 accepts to receive, possibly decreased by the AS.
9‑10. The AS acknowledges the 200 OK response from the terminating network with an ACK, which traverses back to UE#2 or AS in the terminating network via the S‑CSCF.
11. The AS initiates the establishment of a reliable end-to-end connection with UE#2 or the AS in the terminating network to exchange the message media. This step can take place in parallel with step 12.
12, 13 and 15. The AS accepts the message session with a 200 OK response. The 200 OK response traverses back to UE#1.
14. Based on operator policy P‑CSCF may instruct PCRF/PCF to authorize the resources necessary for this session.
16‑18. UE#1 acknowledges the 200 OK with an ACK, which traverses back to the AS.
19. UE#1 establishes a reliable end-to-end connection with the AS to exchange the message media.
20. UE#1 generates the message content and sends it to the AS using the established message connection.
21. The AS forwards the message content using the established message connection with the terminating network.
22. UE#2 or AS in the terminating network acknowledges the message with a response that indicates the reception of the message. The response traverses back to the AS.
23. The AS forwards the message response back to UE#1.
Further messages may be exchanged in either direction between UE#1 and the terminating network using the established message connection via the AS. The size of the messages exchanged within the session shall be within the size limits indicated by UE#1 and UE#2 respectively, possibly decreased by the AS.
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5.16.2.2.4 Session based messaging release procedure
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The following procedure shows the release of a message session, which was established between two UEs. It is assumed that UE#1 is the session host.
Figure 5.48d: Message session release procedure
1–6. UE#1 indicates its intent to terminate the message session by sending a BYE request to UE#2. UE#1 stops sending messages and tears down the message connection on the transport level and destroy local state for the message session. The UE#1 may use the IP‑CAN bearer for some other services; hence it keeps the bearer activated.
7-8. UE#2 agrees to end the session and tear down the message connection on the transport level and destroy local state for the message session. The UE#2 may use the IP‑CAN bearer for some other services; hence it keeps the bearer activated.
9-13. UE#2 acknowledges the BYE request by sending a 200 OK to UE#1, which traverses back the signalling path.
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5.16.2.2.5 Session based messaging release procedure with an intermediate node
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The following procedure shows the release of a message session, which was established between two UEs via an intermediate node. It is assumed that UE#1 is the session host.
Figure 5.48e: Message session release procedure with intermediate node
1–4. UE#1 indicates its intent to terminate the message session by sending a BYE request to UE#2, via the AS. UE#1 stops sending messages and tears down the message connection on the transport level and destroy local state for the message session. The UE#1 may use the IP‑CAN bearer for some other services; hence it keeps the bearer activated.
5. The AS forwards the BYE request to the UE#2.
6-9. The AS tears down the message connection on the transport level and destroys local state for the message session. The AS acknowledges the BYE request by sending a 200 OK to UE#1, which traverses back the signalling path
10. The AS receives the acknowledgement from UE#2 to end the session.
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5.17 Refreshing sessions
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The active sessions in stateful network elements (e.g. CSCFs, ASs) may need to be refreshed periodically. This allows these stateful elements to detect and free resources that are being used by hanging sessions.
This SIP‑level session refreshing mechanism is to be used to allow removing session state from the stateful elements of the session path upon unexpected error situations (e.g. loss of radio coverage, crash of application in the UE, etc…). The refreshing period is typically in the range of several tens of minutes / hours. The mechanism is intended as a complementary mechanism for the "Network initiated session release" described in clause 5.10.3. Whether the session refresh mechanism is used for a particular session is negotiated between the endpoints of the session upon session initiation.
IMS entities acting as User Agents as defined in IETF RFC 3261 [12] should support the refresh mechanism of SIP sessions. This includes support for the negotiation of the session refresh details upon session initiation and the initiation of session refresh requests.
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5.18 Void
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5.19 Support for Transit scenarios in IMS
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5.19.1 General
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This clause presents some high level flows to describe the procedures for supporting IMS transit network scenarios.
The IMS Transit Functions perform an analysis of the destination address and determine where to route the session. The session may be routed directly to an MGCF, BGCF, or to another IMS entity in the same network, to another IMS network, or to a CS domain or PSTN. The address analysis may use public (e.g. DNS, ENUM) and/or private database lookups and/or locally configured data. As described in clause 4.15 there are various transit configurations possible that may be supported.
For the case where an operator is providing transit functions for other operators and/or enterprise networks, the configuration is as shown in Figure 5.49. The configuration in Figure 5.49 is also intended to cover scenarios where an operator routes traffic from other IMS- or SIP-networks to CS domain or PSTN customers through the IMS transit network. In this case the terminating network as shown in the figure indicates the operator's CS domain or PSTN.
Figure 5.49: IMS transit network
For the transit operator in Figure 5.49, ISUP messages that arrive at a configured MGCF, are translated into SIP and are passed to the IMS Transit Functions. SIP messages may arrive directly at the configured entity supporting the transit functions or first pass through an IBCF before arriving at the IMS Transit Functions. The IMS Transit Functions determine whether to route directly to an MGCF, BGCF, or to another IP entity on the path (e.g. an IBCF). In this transit operator configuration, the IMS Transit Functions might reside in a stand-alone entity or might be combined with the functionality of an MGCF, a BGCF, an I‑CSCF, an S‑CSCF or an IBCF. When residing in a stand-alone entity the IMS Transit Functions shall be able to generate CDRs.
For the case where the operator is the terminating network operator handling a terminating service for its own customers, the configuration and operation may be more complex as shown in figure 5.50.
NOTE 1: In the case of Fixed Broadband Access to IMS the term "CS domain" in the following text and in figure 5.50 may be replaced by the term "PSTN".
Figure 5.50: Terminating IMS network with transit support, Transit Functions first
For the operator in figure 5.50, ISUP messages arriving at an MGCF may be destined for an IMS or a CS domain customer (see clause 4.15). The ISUP messages are translated into SIP.
The operator can choose whether to route all traffic through the IMS Transit Functions, which subsequently route to the I‑CSCF for IMS terminating call scenarios or to an MGCF for the case of CS domain subscribers as described above. This is depicted in figure 5.50. In this case, there may be an additional delay for terminating sessions destined for IMS subscribers.
NOTE 2: In this case, the IMS Transit Functions perform selection of the appropriate domain to terminate the call to, followed by routing to the CS domain (for CS domain destined traffic).
As an alternative, the operator may choose to route all traffic to the I‑CSCF directly and then identify those sessions that are not destined to IMS subscribers based on an HSS query. Based on the response from the HSS, sessions are either routed to an S‑CSCF or to the CS domain (optionally via Transit Functions). In this case there may be an additional delay for terminating sessions destined for the CS domain subscribers.
NOTE 3: If in this case, the I‑CSCF becomes aware that the call is not destined to an IMS subscriber and forwards it to the Transit Function for further routing, then the Transit Functions only perform routing to the CS domain.
It is the operator's choice to determine which way to route the SIP messages, first through IMS Transit Functions or first to an I‑CSCF. This may depend on whether the majority of the sessions that enter the IMS network, are destined to IMS or CS domain subscribers.
NOTE 4: In either configuration of the terminating network scenario, once it is determined that the call is not destined for an IMS subscriber, it is necessary to verify that the call is destined for a CS domain subscriber rather than to a ported number or to a wrong number. At which stage of the session establishment this decision is made is FFS.
In the terminating network configuration shown in figure 5.50, the IMS Transit Functions might reside in a stand-alone entity or might be combined with the functionality of an MGCF, a BGCF, an I‑CSCF, an S‑CSCF, or an IBCF. When residing in a stand-alone entity the IMS Transit Functions shall be able to generate CDRs.
For the case where an IMS network serves as a transit network and as a terminating network (depending on the destination of the session), the configuration and operation resembles that of the previous case as shown in figure 5.50a and figure 5.50b.
Figure 5.50a: Terminating/Transit IMS network, Transit Functions first
Figure 5.50b: Terminating/Transit IMS network, I-CSCF first
For the operator in figure 5.50a and figure 5.50b, ISUP messages arriving at an MGCF may be destined for the own IMS network of for a succeeding network. The ISUP messages are translated into SIP. This is not depicted in figure 5.50a and figure 5.50b.
The operator can choose whether to route all traffic through the IMS Transit Functions, which subsequently route to the I‑CSCF for sessions destined for subscribers of the own IMS network, to the own CS domain for sessions destined to subscribers of the own CS domain, or to a succeeding network for sessions not destined for subscribers of the own IMS network or the own CS domain. This is depicted in figure 5.50a. In this case there may be an additional delay for sessions destined to subscribers of the own network.
NOTE 5: In this case, the Transit Functions perform selection of the appropriate domain to terminate the call to, for subscribers of the own network, followed by routing to another network (if the session is not destined to the own network).
As an alternative, the operator may choose to route all traffic to the I‑CSCF directly and then identify those sessions that are not destined to IMS subscribers of the own IMS network based on an HSS query. Based on the response from the HSS, sessions are either routed to an S‑CSCF of the own IMS network or to Transit Functions. The Transit Functions subsequently route the session to either the CS domain of the own network or to a succeeding network. This is depicted in figure 5.50b. In this case there may be an additional delay for sessions not destined to subscribers of the own IMS network.
It is the operator's choice to determine which way to route the SIP messages, first through IMS Transit Functions or first to an I‑CSCF. This may depend on whether the majority of the sessions that enter the IMS network, are destined to subscribers of the own IMS network or not. This operator's choice may be implemented as a functionality of an entry functions such as an IBCF.
In the terminating/transit network configuration shown in figure 5.50a and figure 5.50b, the IMS Transit Functions might reside in a stand-alone entity or might be combined with the functionality of an MGCF, a BGCF, an I‑CSCF, an S‑CSCF, or an IBCF. When residing in a stand-alone entity the IMS Transit Functions shall be able to generate CDRs.
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5.19.2 Providing IMS application services in transit network scenarios
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This clause provides an overview of how IMS application services in transit network scenarios are provided.
Figure 5.50c: IMS application services in transit network
The procedure for IMS application services in transit network is as follows:
1. The Transit function receives an incoming request from a preceding network.
2. Based on local configured Transit invocation criteria, the Transit function determines whether one or more services are to be performed.
If the preceding network is the served network, for which special services are invoked, the invocation criteria will trigger and invoke the related services based on the origination of the request.
If the succeeding network is the served network, for which special services are invoked, the invocation criteria will trigger and invoke the related services based on the termination point of the request.
The related service(s) are invoked.
3. The Transit function performs the transit routing according to clause 5.19.1 and forwards the Session Request towards the succeeding network.
NOTE: An AS that acts as a B2BUA can decide to not route back the call to the transit function. In this case, it will use the terminating UA mode of operation for request from the Transit function. It can apply originating UA procedures according to TS 23.218 [71].
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5.20 Procedures for Assigning, Using and Processing GRUUs
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5.20.1 UE
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5.20.1.1 Obtaining a GRUU during registration
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A UE shall indicate its support for the GRUU mechanism in the registration request and retain the GRUU set (P‑GRUU and T‑GRUU) in the registration response. The UE may retain some or all of the previous T‑GRUUs obtained during the initial registration or previous re-registrations along with the new T‑GRUU or the UE may replace some or all of the previous T‑GRUUs with the new T‑GRUU. The UE shall generate an instance identifier that is a unique identifier for that UE. The UE shall include an instance identifier in all registration requests. Instance identifiers shall conform to the mandatory requirements for instance identifiers specified in RFC 5627 [49] and RFC 5626 [48].
If the registered Public User Identity is part of an implicit registration set, the UE shall obtain and retain the GRUU sets for each implicitly registered SIP URI sent by the S‑CSCF in accordance to RFC 5628 [50].
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5.20.1.2 Using a GRUU
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When sending SIP requests from an explicitly or implicitly registered Public User Identity for which a UE obtained P‑GRUU and at least one T‑GRUU, the UE should use the corresponding retained P‑GRUU or a T‑GRUU as a Contact address.
When responding to SIP requests where the identification of the called party is a registered Public User Identity for which a UE obtained a GRUU, the UE shall use the corresponding retained P‑GRUU or T‑GRUU as the Contact address when addressing that UE.
If the UE has obtained GRUUs for its Public User Identity being used in a request or response and the user does not require privacy the UE should use the P‑GRUU as the Contact address.
A UE may learn a GRUU of another UE using mechanisms that are outside the scope of this specification, (e.g. a UE may learn a GRUU from the contact header of a request, from presence information, or by other mechanisms).
If a UE that receives a notification from the S‑CSCF indicating that an implicit registration has occurred for a contact the UE has registered, then the UE shall retain the GRUUs included in the notification for future use.
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5.20.1.3 Using a GRUU while requesting Privacy
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When a UE sends a request or response containing a GRUU and it wishes to block the delivery of its Public User Identity to an untrusted destination, the UE shall use a T-GRUU as the Contact address.
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5.20.2 Serving‑CSCF
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5.20.2.1 Allocating a GRUU during registration
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The S‑CSCF, when receiving a registration request from a UE that includes an instance id, shall allocate a GRUU set. If the UE indicates support of GRUU in the REGISTER request, then the S‑CSCF shall return the GRUU set in the registration response and associate that GRUU set with the registered contact information for that UE.
NOTE: As long as the instance id provided in the register request is the same, the resulting P‑GRUU in the GRUU set will always be the same for a given Public User Identity. The T‑GRUU will be different from those returned during previous re-registrations. All T‑GRUUs that are allocated continue to remain valid until that UE Instance ID and Public User Identity pair are deregistered.
If there are implicitly registered Public User Identities, the S‑CSCF shall generate a GRUU set for each implicitly registered Public User Identity and include the corresponding GRUU set with the notification of each implicitly registered Public User Identity
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5.20.2.2 Using a GRUU
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The filter criteria in the service profile may check for the presence of a GRUU in the Request URI or related parameters of a request.
For originations, the S‑CSCF shall validate the GRUU conveyed in the contact header of the SIP request and pass the SIP request with the validated GRUU to Application Servers based on the filter criteria.
For terminations, the S‑CSCF may validate the GRUU conveyed in the Request URI header of the SIP request and pass the SIP request with the validated GRUU to Application Servers based on filter criteria.
Application servers may then apply services to the GRUU.
If the SIP message is destined to a GRUU, then the S‑CSCF shall associate the request with the corresponding Public User Identity. The S‑CSCF will not fork this request, but will direct the call to the identified instance.
S‑CSCF shall provide an indication to UE that the SIP request was targeted to a GRUU.
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5.20.3 Interrogating‑CSCF
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When routing requests addressed to a GRUU to the terminating S‑CSCF, the I‑CSCF uses the contents of the Request URI when querying the HSS. Requests routed to the terminating S‑CSCF are addressed to the GRUU.
5.20.3a HSS
The HSS shall remove the P‑GRUU as part of the canonicalization process of SIP URIs, to obtain the Public User Identity for identity look-up as it is defined in TS 29.228 [30].
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5.20.4 Elements other than UE acting as a UA
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5.20.4.1 Using a GRUU
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It shall be possible for other IMS elements other than UEs, that act as UAs (e.g. MGCF, Application Server) to use a GRUU referring to itself when inserting a contact address in a SIP message. The MGCF and MRF are not required to store GRUUs beyond a session. If the incoming contact address that is being replaced by the B2BUA functionality contains a GRUU, then the replacement URI in the outgoing SIP message should also contain a GRUU.
If an element so uses a GRUU, it shall handle requests received outside of the session in which the contact was provided.
Routing procedures amongst IMS elements other than UEs that act as UAs are unchanged when GRUUs are in use.
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5.20.4.2 Assigning a GRUU
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The GRUUs shall either be provisioned by the operator or obtained by any other mechanism. The GRUU shall remain valid for the time period in which features addressed to this URI remains meaningful.
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5.21 IMS Multimedia Priority Services Procedures
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The IMS Multimedia Priority Service provides Service Users access to IMS services in a prioritised manner.
Based on regional/national requirements and network operator policy, the P-CSCF should handle the IMS registration from an MPS-subscribed UE with priority.
NOTE 1: How the P-CSCF determines that an IMS registration signalling is to be handled with MPS priority for a UE is implementation specific. As an example, all IP packets including IMS messages from MPS-subscribed UEs can be marked by the P-GW or SMF/UPF with a designated DSCP value (per clause 4.4.3.3 of TS 23.401 [70] and clause 5.8.2.7 of TS 23.501 [93]), therefore, the P-CSCF can detect an MPS-subscribed UE and apply priority to the IMS registration. Another example to distinguish MPS traffic would be by directing it to a dedicated IP address-port number on the P-CSCF.
After detecting an MPS-subscribed UE, as described in NOTE 1, the P-CSCF should add Resource-Priority information with a value appropriate for MPS in the IMS registration signalling.
The P-CSCF shall control the priority of IMS based MPS sessions, using PCC procedures. The P-CSCF shall permit any authorised Service User to originate an IMS based MPS session. The detection of MPS sessions is handled by the P-CSCF at the originating network.
The P‑CSCF may send an MPS for Messaging indication to the PCRF/PCF using PCC procedures to request the PCRF/PCF to modify the IMS signalling bearer/QoS Flow for MPS for Messaging, as described in TS 23.203 [54] and TS 23.503 [95] when it has received the MPS for Messaging indication from the S-CSCF (at the time of initial IMS registration, or when the indication is changed in the HSS).
PCC shall always be enabled in a network supporting IMS Multimedia Priority Services.
The HSS shall store the IMS Priority Indication, the Priority Level and the MPS for Messaging indication as part of the subscription information/user profile.
The P-CSCF at the originating end shall determine whether the INVITE message requires priority handling based on the user profile as stored during the registration procedures or as subsequently updated and/or the MPS code/identifier provided by the INVITE message. For MPS Session-based Messaging, the P-CSCF shall determine whether the INVITE message requires priority handling based on the MPS for Messaging indication. If the session is determined to require priority handling, then the P-CSCF inserts/replaces the MPS priority indication in the INVITE and, if the Service User's priority level is known, may include it and forwards the INVITE to the S-CSCF.
The P-CSCF uses the MPS priority indication and Service User's priority level, if available, to derive Resource-Priority information as further described in clause 4.11 of TS 24.229 [10a].
If the Service User's priority level is not known, the P-CSCF includes the priority indication without the Service User's priority level. The S-CSCF routes (using initial Filter Criteria set for the MPS code/identifier) the INVITE to the AS for authentication/authorization for MPS (if needed) and the AS adds the Service User's priority level if it is not in the INVITE already. The AS or the S-CSCF may assert the authorization for priority in the INVITE. The AS then forwards the INVITE (with MPS priority indication and the Service User's priority level) to the next entity in the network via the S-CSCF as part of the normal IMS routing. All subsequent SIP messages carry both MPS priority indication and the Service User's priority level.
NOTE 2: Only one entity is configured to perform assertion of the authorization for priority of a request.
When the P-CSCF at the originating end determines that priority handling is required, the P-CSCF shall derive session information and interact with the PCRF/PCF providing the session information. The derived session information shall indicate the priority of the MPS session, which depends on whether the Service User's priority level is known at this stage. The PCC interaction between the P-CSCF and the PCRF/PCF is described in TS 23.203 [54] and TS 23.503 [95].
The P-CSCF at the terminating end shall determine whether the INVITE message requires priority handling based on MPS priority indication and the originating Service User's priority level received from the originating network. If priority handling is required, P-CSCF shall derive the session information based on the Service User's priority level to indicate the priority of the MPS session and interact with the PCRF/PCF providing the session information.
For IMS Immediate Messaging, the P-CSCF at the originating end shall add Resource-Priority information to the MESSAGE request and shall handle this request with priority if the MPS for Messaging indication is set (enabled) in the originating UE subscription information.
The P-CSCF at the terminating end shall handle the MESSAGE request with priority whether or not it contains Resource-Priority information, if the MPS for Messaging indication is set (enabled) in the terminating UE subscription information.
The P-CSCF shall adjust the priority treatment of transactions or dialogs according to the most recently received authorized MPS priority indication.
When the terminating user is a Service User, while the session request is from a normal user, the IMS signalling bearer/QoS Flow may be given priority treatment when operator policy and MPS (IMS) priority subscription indicates so. For a Service User originating a non-priority session, the IMS signalling bearer/QoS Flow may be given priority treatment when operator policy and MPS (IMS) priority subscription indicates so. For IMS media, priority treatment is not required in these cases.
If so configured by the operator, a P-CSCF or an IBCF shall prohibit the negotiation of ECN during SDP offer/answer exchanges and shall not invoke ECN (as described in clause 4.22) for IMS based MPS sessions.
NOTE 3: Disabling ECN in an IBCF does not prevent a P-CSCF (IMS ALG), subject to roaming agreement, from applying ECN over the access network between a UE and the P-CSCF (IMS ALG) / IMS AGW.
A conferencing AS, if enabled by local policy, shall permit an authorized host with an MPS (IMS) priority subscription (i.e. the Service User that established the conference) to request an upgrade of the host itself, specific participants, or all participants including the host in the conference, whether participants have an MPS subscription or not. Once the conference has been upgraded, the AS will upgrade new participants to MPS without explicit host invocation. For MPS conferencing sessions, upon request from a host to upgrade an existing conference, the AS shall first authenticate/authorize the host for MPS.
NOTE 4: The procedure for the AS to authorize the host for MPS is either based on internal AS information or via access to an MPS database or HSS; and is left to operator implementation. The procedure used by the host to initiate the upgrade request is out of scope.
NOTE 5: The AS decides on the MPS priority level to use for participant UEs in the conference for the purpose of the upgrade.
The session upgrade of UE conference participants is based on existing IMS routing procedures, including interaction between the P-CSCF and PCRF/PCF for that purpose.
For E-UTRAN access, priority support for an EPS bearer is described in TS 23.401 [70].
For 5GS, support of Multimedia Priority Service is described in TS 23.501 [93].
IMS Immediate Messaging and IMS Session-based Messaging delivered with MPS priority are further described in clause 5.16.
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5.22 Support of Overload Control
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5.22.1 Next-hop monitoring of overload
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The following figure depicts an example information flow for the overload control mechanism based on feedback.
Figure 5.22.1-1: Information flow for Overload Control with next-hop monitoring
1. During a past INVITE, the SIP IMS entity 1 obtained a percentage by which the load forwarded to SIP IMS entity 2 should be reduced.
2. During a past INVITE, the SIP IMS entity 1 obtained a percentage by which the load forwarded to SIP IMS entity 3 should be reduced.
3. Incoming INVITE from Originating side (network or UE). The SIP IMS entity 1 determines that the INVITE has to be forwarded via SIP IMS entity 2.
4. With the information obtained in step 1, the SIP IMS entity 1 either:
5a. refuses the INVITE request because of overload situation, or
5b. forwards the INVITE to SIP IMS entity 2 (5b1). The Reply to the INVITE (5b2) can contain updated overload control information.
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5.22.2 Filter based Overload Control
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The following figure depicts an example information flow for the filter based overload control mechanism. NOTE: The applicability of the filter based overload control mechanism is not restricted to the IMS entities mentioned on this figure. Figure 5.22.2-1 Information flow for AS Overload Control using a filter based mechanism 1. Upon initialization or restart, AS/S-CSCF subscribes to overload event notification of AS-1 and receives overload control filters (1c). 2. Upon initialization or restart AS/S-CSCF subscribes to overload event notification of AS-2 and receives overload control filters (2c) 3. An INVITE comes to AS/S-CSCF. 4-5. The AS/S-CSCF determines where to forward the message (AS-1 in this example), then evaluates whether the contents of the INVITE matches the filters received from AS-1: - If the request does not match any filter, the AS/S-CSCF forwards it to AS-1 (5b1); - Otherwise, depending on the throttling algorithm, the AS/S-CSCF either: - refuses the INVITE request because of the overload situation (5a), or - forwards the INVITE to AS-1 (5b1). Annex A (informative): Information flow template This clause describes the template used in developing information flow (IF) procedures. X.Y.Z "Name of procedure (e.g. Terminal location registration)" In this clause, provide a brief prose description of the service or network capability. The "X.Y.Z." refers to the clause heading number. Figure A.1: Information Flow Template This clause consists of subparagraphs each dedicated to one information flow of the IF diagram. For each information flow, a detailed description is provided on the information flow name, certain information elements (IEs) within the information flow, whether the IE is mandatory or optional (M/O), in the sequence as shown in the IF diagram. FE actions (FEA) are also provided in this clause. This clause format is proposed as follows: 1. Initial information flow: One should normally describe the initiating FE Action (FEA) leading to the first flow. Any information that is specifically required to support the operation should be mentioned (e.g. this flow conveys the user identity to the HSS). 2. Each paragraph should contain a brief description of the flow and any specific start and end FEAs. When information to be conveyed is optional, the conditions for its inclusion should be specified and the response to its presence when received should also be specified (e.g. Include IP Address when condition xyz occurs). For an information flow that is required, the description should indicate whether a response is required based on successful outcome to the received IF, failed outcome, both or neither. e.g. "Response is required indicating Success or Failure". 3. Flows may occur in either direction but not both at the same time. To indicate a shorthand for multiple flows, use a procedure box as in flow 5 or 6. 4. Flows that are an optional part of the procedure should be shown as dotted arrows as in flow 4. These may appear in either direction. 5. A set of flows, representing a common procedure, is shown by a box. The procedure should be numbered and named with a name that corresponds to the procedure as described elsewhere. The location of the box on an entity represents the start of the common procedure regardless of the number of the entities involved in the procedure. 6. An optional set of flows is represented as a dashed box. Otherwise the use is the same as in flow 5. 7. A small number of alternative flows may be shown within a dashed box. The alternatives are shown by a letter immediately following the flow number, e.g. 7a, 7b, 7c, etc. Where a single alternative results in multiple flows, they must be shown with an indication of the proper sequence, e.g. 7b1, 7b2. The subparagraph describing the information flow must describe the decision process taken in choice of alternatives. 7a. Alternative (a) is described. If alternative (a) is a single information flow, the contents and purpose of that information flow is included here. 7b. Alternative (b) is described. 7b1. The first information flow of alternative (b) is described 7b2. The second information flow of alternative (b) is described. Etc. 8. The final flow in a procedure may provide additional information regarding other procedures that might follow it but such information is not required. The general characteristics of the information flow template are as follows: - All relevant functional entities are contained in the flow diagram. Only relevant entities need be shown. - When an element occurs only in an information flows for which several alternatives exist, the description box for the functional entity and the vertical line shall be dashed lines. - The specific network affiliation of functional entities may be shown using a labelled bracket over the specific entities as shown in the figure (e.g. Home Network). Such labelling is not required unless the flow would not be clear without it. - The number associated with each flow provides a "handle" to the functional entity action (FEA) executed by the FE receiving the flow. This number is known only within the scope of the specific information flow diagram. The description of this functional entity action (FEA) immediately follows the information flow description. - Common Procedures described elsewhere can be used in the information flows in order to simplify the diagram. These may be either required or optional. - Each common procedure is treated as a single action and therefore is given a unique number. - An optional flows (flows 4 and 6) are indicated by a dashed arrow or box. - Co-ordinated flows or flows that illustrate parallel actions are indicated by the flow text description. For example one might see a description such as: "flows 5 and 6 may be initiated any time after flow 3". - Sequential operation is assumed unless indicated otherwise. Annex B (informative): Void Annex C (informative): Void Annex D (informative): Void Annex E (normative): IP-Connectivity Access Network specific concepts when using GPRS and/or EPS to access IMS E.0 General This clause describes the main IP-Connectivity Access Network specific concepts that are used for the provisioning of IMS services over GPRS and EPS system using GERAN and/or UTRAN radio access and/or E-UTRAN (using EPC only). When using GPRS-access, the IP-Connectivity Access Network bearers are provided by PDP Context(s). When using EPS the SGSN is responsible for mapping PDP Context(s) to EPS bearers, i.e. the UE (using GERAN/UTRAN) is using PDP Context(s) whereas EPS bearers are used from the SGSN towards the S‑GW/P‑GW. However, throughout this annex PDP context(s) are used when referring to an IP‑CAN bearer for GPRS networks and when a UE is connected to EPS via GERAN/UTRAN access. When GGSN/P‑GW is shown, it represents either a GGSN or a P‑GW for a specific UE connection towards a PDN. E.1 Mobility related concepts E.1.0 General The Mobility related procedures for GPRS and EPS are described in TS 23.060 [23] and TS 23.401 [70] respectively and the IP address management principles are described in TS 23.221 [7]. As specified by the GPRS/EPS procedures, the UE shall acquire the necessary IP address(es) as part of the PDP Context activation procedures for GERAN/UTRAN access and Attach (or PDN connectivity)/EPS bearer activation procedure(s) for E-UTRAN. If the UE changes its IP address due to changes triggered by the GPRS/EPS procedures or according to TS 23.221 [7], then the UE shall re- register in the IMS. If the UE acquires an additional IP address, then the UE may perform an IMS registration using this additional IP address as the contact address. If IMS registration is performed, this IMS registration may co-exist with the previous IMS registration from this UE and the UE shall be notified that this IMS registration results in multiple simultaneous registrations. NOTE: The UE can acquire an additional IP address that can be used for registration to the IMS only outside of the EPS. When a routeing area update or tracking area update is not performed due to the Idle mode Signalling Reduction feature being active (see TS 23.401 [70] for more information), then the UE shall also not perform an IMS re registration because of such routeing area and tracking area change. Similarly, the UE shall not perform an IMS re registration because the UE has moved between GERAN and UTRAN cells that share the same RAI. When the PLMN changes and the attempt to perform an inter-PLMN routeing area update or tracking area update is unsuccessful, then the UE should attempt to re-attach to the network using GPRS/EPS procedures and register for IMS services. Typically this will involve a different GGSN/P‑GW. In Dual Connectivity with EPC case, the UE shall use the access network information based on the primary cell of the Master RAN node that is serving the UE for network location information when the UE interacts with IMS, regardless whether the IMS traffic is routed via the Master RAN node or the Secondary RAN node or both. E.1.1 Procedures for P‑CSCF discovery E.1.1.0 General This clause describes the P‑CSCF discovery procedures applicable for GERAN/UTRAN access. All the procedures described in clause 5.1.1 apply with the following additions: P‑CSCF discovery shall take place after GPRS/EPS attach and after or as part of a successful activation of a PDP context (in the case of GERAN/UTRAN access) and EPS bearer (in the case of E-UTRAN access) for IMS signalling using the following mechanisms: a. For GERAN/UTRAN access: Transfer a Proxy‑CSCF address within the PDP Context Activation signalling to the UE, as described in clause E.1.1.1. The UE shall request the P‑CSCF address(es) when activating the PDP context. The GGSN/P‑GW shall send the P‑CSCF address(es) to the UE when accepting the PDP context activation. Both the P‑CSCF address(es) request and the P‑CSCF address(es) shall be sent transparently through the SGSN/S‑GW for GERAN/UTRAN. b. For E-UTRAN access: Transfer a P‑CSCF address within the EPS Attach or PDN Connectivity Procedures to the UE, as described in clause E.1.1.1. The UE shall request the P‑CSCF address(es) in the EPS Attach or PDN Connectivity request. The P‑GW shall send the P‑CSCF address(es) to the UE when accepting the EPS Default bearer activation. Both the P‑CSCF address(es) request and the P‑CSCF address(es) shall be sent transparently through the intermediate network entities (e.g. MME/S‑GW). When using DHCP/DNS procedure for P‑CSCF discovery (according to the mechanisms described in clause 5.1.1.1) with GPRS/EPS, the GGSN/P‑GW acts as DHCP Relay agent relaying DHCP messages between UE and the DHCP server. E.1.1.1 GPRS/EPS procedure for P‑CSCF discovery This alternative shall be used for UE(s) not supporting DHCP. This may also be used for UE(s) supporting DHCP. Figure E.1: P‑CSCF discovery using PDP Context Activation signalling 1. The UE requests establishment of a PDP context according to clause 4.2.6 (QoS requirements for IM CN subsystem signalling). The UE indicates that it requests a P‑CSCF IP address(es). The indication is forwarded transparently by the SGSN to the GGSN in the Create PDP Context Request or to the S‑GW/P‑GW in the Create Default Bearer Request. 2. The GGSN/P‑GW gets the IP address(es) of the P‑CSCF(s). The mechanism to do this is a matter of internal configuration and is an implementation choice. 3. If requested by the UE, the GGSN/P‑GW includes the IP address(es) of the P‑CSCF(s) in the Create PDP Context Response or in the Create Default bearer response. The P‑CSCF address(es) is forwarded transparently by the SGSN to the UE. After reception of the IP address of a P‑CSCF the UE may initiate communication towards the IM CN Subsystem. NOTE: This request of a P‑CSCF IP address(es) and response is not transparent for pre-R5 SGSN when using the Secondary PDP Context Activation Procedure as defined in TS 23.060 [23]. E-UTRAN access only: The procedure for E-UTRAN access applies to both Initial E-UTRAN Attach and PDN Connectivity Request. Figure E.2: P‑CSCF discovery using EPS bearer activation signalling 1. During Initial Attach/PDN Connection Request, the UE indicates that it requests a P‑CSCF IP address(es). 2. The MME sends a Create Default Bearer Request to the S‑GW. 3. The S‑GW forwards the request to the P‑GW and the P‑GW gets the IP address(es) of the P‑CSCF(s). The mechanism to do this is a matter of internal configuration and is an implementation choice. 4. If requested by the UE, the P‑GW includes the IP address(es) of the P‑CSCF(s) in the Create Default Bearer Response. 5. The S‑GW forwards the response to the MME 6. Completion of procedures, as described in TS 23.401 [70]. After reception of the IP address of a P‑CSCF the UE may initiate communication towards the IM CN Subsystem. E.1.2 Support for Enhanced Coverage for data centric UEs Support for Enhanced Coverage (CE) for data centric UE is specified in TS 23.401 [70]. If the UE's usage setting is set to "data centric" as defined in TS 23.221 [7] and it is operating in CE mode B then IMS PS voice/video services are not to be used in this IP-CAN. If the UE's usage setting is set to "data centric" and it is operating in CE mode B, then the UE shall reject any SIP invite for IMS PS voice/video services as per the existing IMS procedures. In addition, the UE may deregister from IMS PS voice/video services. When the UE determines that the radio conditions are suitable for IMS PS voice/video services (e.g. UE is in normal coverage or in CE mode A) then UE may (re-)register for IMS PS voice/video services. NOTE: How UE determines that the radio conditions are suitable for voice/video services is left up to the UE implementation. E.2 QoS related concepts E.2.1 Application Level Signalling for IMS E.2.1.0 General When the UE uses GERAN/UTRAN-access for IMS services, it shall be able to establish a dedicated signalling PDP-Context for IM CN Subsystem related signalling or utilize a general-purpose PDP context for IM Subsystem signalling traffic. When the UE uses E-UTRAN access for IMS services, it shall be able to request establishment of a default or dedicated EPS bearer for IM CN Subsystem related signalling. E.2.1.1 QoS Requirements for Application Level Signalling It shall be possible to request prioritised handling over the GERAN/UTRAN radio for IM CN Subsystem related signalling by including the Signalling Indication in the QoS IE of the PDP Context to be used for this traffic as described in clause E.2.1a.1. It shall be possible to request prioritised handling over the E-UTRAN radio for IM CN Subsystem related signalling by including the appropriate QCI value for signalling traffic as specified in TS 23.203 [54], clause 6.1.7, Standardized QCI Characteristics, Table 6.1.7. E.2.1.2 Requirements for IM CN subsystem signalling flag The IM CN Subsystem Signalling flag is used to indicate the dedicated signalling PDP context for IMS signalling. If the network operator does not support a dedicated signalling PDP context or the UE does not include the IM CN Subsystem Signalling flag, the network will consider the PDP context as a general purpose PDP context. The IM CN Subsystem Signalling flag is used to indicate EPS bearer dedicated for IMS signalling. If the network operator does not support a dedicated signalling EPS bearer or the UE does not include the IM CN Subsystem Signalling flag, the network will consider the EPS bearer as a default or dedicated bearer according to TS 23.401 [70]. A PDP context/EPS bearer dedicated for IM CN Subsystem signalling provides dedicated IP-Connectivity Access Network bearers for IM CN subsystem signalling traffic, hence architectural requirements described in clause 4.2.6 for the usage of dedicated bearer resources shall be applied. The UE is not trusted to implement these restrictions, therefore the restrictions are enforced in the GGSN/P‑GW by the operator of the GGSN/P‑GW. If the PDP context request/EPS bearer is initiated by the IP‑CAN, then the GGSN/P‑GW may provide a set of UL filters for the PDP context/EPS bearer used for IM CN Subsystem Signalling. The UL filters provide the UE with the rules and restrictions applied by the GGSN/P‑GW for the dedicated IM CN Subsystem signalling IP‑CAN bearer. The GGSN/P‑GW may in addition provide the IM CN subsystem signalling flag to explicitly indicate to the UE the intention of using the PDP context/EPS bearer for IM CN Subsystem related signalling. Policy and Charging Control functionality can be used to provide additional charging capabilities for dedicated signalling PDP context/EPS bearer dedicated to be used for IMS signalling (as well as for a general-purpose PDP context) as described in clause 4.2.6. Whether the network is configured to support IM CN signalling flag or Policy and Charging Control functionality or both, is dependent on the operator configuration policy. The requirements described above also apply in the case of E-UTRAN access and for GERAN/UTRAN access using EPS supporting dedicated bearer for IM CN Subsystem Signalling traffic and where appropriate filters are configured in the P‑GW and PCRF as applicable. E.2.1.3 Application Level Signalling support for IMS services In order to receive different level of support for application level signalling in a PDP context/EPS bearer, the UE may choose one of the following options: - Include both the IM CN Subsystem Signalling Flag in the PCO IE and the Signalling Indication in the QoS. This indicates to the network (radio & core) the requirement of using the PDP context/EPS bearer for application level signalling after it has been negotiated with the networks, to provide prioritised handling over the radio interface (as described in clause E.2.1.1), with rules and restrictions applied in the network (as described in clause E.2.1.2). - For GERAN/UTRAN access the UE includes the IM CN Subsystem Signalling Flag in the PCO IE and the Signalling Indication in the QoS IE in the PDP context activation or the Secondary PDP context activation procedure. - For E-UTRAN access the UE includes both the IM CN Signalling Flag in the PCO IE and the appropriate QCI value for signalling traffic in the UE Requested Bearer resource Modification procedure. NOTE 1: When the UE Requested Bearer Resource Modification procedure is used the IM CN Subsystem Signalling Flag in the PCO IE should be sufficient to trigger the network to provide UL packet filters to the UE, i.e. the UE is not required to provide any meaningful filter information related to the IMS signalling. - Include the IM CN Subsystem Signalling Flag in the PCO IE in the PDP context activation or the Secondary PDP context activation procedure for GERAN/UTRAN access and for E-UTRAN access in the Attach, PDN Connectivity request or the UE requested bearer resource modification procedure. This indicates to the GPRS/EPS network the requirement of using PDP context/EPS bearer for application level signalling with restricted handling as described in clause E.2.1.2, after it has been negotiated with the networks. NOTE 2: If the PDN connection is not limited to IMS based services only and the Default EPS bearer is used to support application level signalling for IMS, the UE request for establishment of a general purpose EPS bearer (i.e. a Dedicated non-GBR EPS bearer with a filter set appropriately for a general purpose EPS bearer) might be rejected by the network. - Utilize a general purpose PDP Context/default EPS bearer with a negotiated QoS profile (this includes the possibility of having the Signalling Indication in the QoS IE for GERAN/UTRAN and the QCI for E-UTRAN. In the case of E-UTRAN access, when referring to the appropriate QCI for the signalling traffic, the functions described above are fulfilled as specified in TS 23.203 [54] using EPS bearers. The IM CN Subsystem signalling flag is used to reference rules and restrictions on the PDP context/EPS bearer used for application level signalling, as described in clause E.2.2. The Signalling Indication in the QoS IE or the appropriate QCI for signalling traffic provides prioritised handling over the radio interface. The Signalling Indication in the QoS IE is detailed in TS 23.107 [55] and clause E.2.1a.1 and the appropriate QCI for signalling traffic is detailed in TS 23.203 [54]. Depending on the operator's policy, one or more of the above combinations may be allowed in the GPRS/EPS network. E.2.1a PDP context/EPS Bearer procedures for IMS E.2.1a.1 Establishing PDP Context/EPS bearer for IM CN Subsystem Related Signalling It shall be possible for the UE to convey to the network the intention of using the PDP context/EPS bearer for IM Subsystem related signalling. For this purpose it uses the mechanism described in this clause and Application Level Signalling in clauses E.2.1.1, E.2.1.2 & E.2.1.3. When the bearer establishment is controlled or a bearer establishment is requested (in the case of EPS) by the UE, in order to establish a PDP context/EPS bearer for IM CN Subsystem related signalling, the UE shall be able to include the IM CN subsystem signalling flag in the PDP context activation/UE Requested Bearer Resource Modification procedure. This indicates to the network the intention of using the PDP context/EPS bearer for IM CN Subsystem related signalling. For GERAN/UTRAN access: To establish a PDP context for IM CN Subsystem related signalling with prioritised handling over the radio interface, the UE shall be able to set the Signalling Indication in the QoS IE in the PDP context activation procedure and the Secondary PDP context activation procedure. The Signalling indication in the QoS IE indicates to the radio and core networks the requirement for enhanced handling over the radio interface, once it has been negotiated with the networks. A request for a general purpose PDP context having the "signalling indication" within the QoS IE may be accepted or downgraded according to operator policy configured at the GGSN using the usual QoS negotiation mechanisms described in TS 23.060 [23]. It shall not be possible to modify a general purpose PDP context into a dedicated PDP context for IM CN Subsystem related signalling and vice versa. For E-UTRAN access: The (default or dedicated) EPS bearer for IMS signalling may be established from network side at Attach/UE Requested PDN connectivity Request time, in which case the appropriate QCI for signalling traffic and the packet filters will provide the necessary QoS and any restrictions applicable on packets sent over this EPS bearer. A request for an EPS bearer having the appropriate QCI for signalling traffic according to TS 23.203 [54], may be either accepted or rejected according to operator policy configured at the P‑GW i.e. there is no QoS negotiation mechanism used in EPS. In order to establish a Dedicated EPS bearer for IM CN Subsystem related signalling, the UE shall be able to request the appropriate QCI for signalling traffic as specified in TS 23.203 [54] in the UE Requested Bearer Resource Modification procedure. This indicates to the radio and core network the requirement for enhanced handling over the radio interface, once it has been accepted by the network. It shall not be possible to modify an existing EPS bearer in order to convert it to be dedicated for IM CN Subsystem related signalling and vice versa. For all 3GPP accesses: The IM CN Signalling Flag in the PCO IE is used to reference rules and restrictions on the PDP context/EPS bearer used for application level signalling, as described in clause 4.2.6. Based on operator policy the "Signalling Indication" in the QoS IE or the appropriate QCI for signalling traffic may be allowed only if the "IM CN Subsystem Signalling" flag is present in the PCO IE. The IM CN subsystem signalling flag and the Signalling Indication in the QoS IE or the appropriate QCI for signalling traffic may be used independently of each other. E.2.1a.2 Deletion of PDP Context/EPS bearer used to transport IMS SIP signalling If the GPRS subsystem deletes the PDP Context used to transport IMS SIP signalling, then according to clause 5.10.3.0 the UE or GGSN shall initiate a procedure to re-establish (or modify where possible) a PDP Context for IMS signalling transport. If there are any IMS related PDP contexts active, the re-establishment of the PDP context to transport IMS signalling shall be performed by using the Secondary PDP Context Activation Procedure (or the Network Requested Secondary PDP Context Activation Procedure if initiated by the GGSN) as defined in TS 23.060 [23]. If the EPC system deletes the Dedicated EPS bearer used to transport IMS SIP signalling, then according to clause 5.10.3.0 the UE or PDN Gateway shall initiate a procedure to re-establish (or modify where possible) an EPS bearer for IMS signalling transport. If there are any IMS related EPS bearers active, the re-establishment of the EPS bearer to transport IMS signalling shall be performed by the UE using the UE Requested Bearer Resource Modification procedure or the PDN Gateway using the Dedicated bearer activation procedure as defined in TS 23.401 [70]. The failure in re-establishing the ability to communicate towards the UE results also in the P‑CSCF/PCRF being informed that the IMS SIP signalling transport to the UE is no longer possible which shall lead to a network initiated session release (initiated by the P‑CSCF) as described in clause 5.10.3.1 if any IMS related session is still ongoing for that UE. Additionally, the P‑CSCF shall reject subsequent incoming session requests towards the remote endpoint indicating that the user is not reachable, until either: - the registration timer expires in P‑CSCF and the user is de-registered from IMS; - a new Register message from the UE is received providing an indication to the P‑CSCF that the PDP Context/EPS bearer used for IMS SIP Signalling transport for that user has become available again and session requests can be handled again. E.2.2 The QoS requirements for an IM CN subsystem session E.2.2.0 General The selection, deployment, initiation and termination of QoS signalling and resource allocation shall consider: - the general requirements described in clause 4.2.5. for E-UTRAN access, the QoS handling is described in TS 23.401 [70], TS 23.203 [54]. - for GERAN/UTRAN access, the requirements described in this clause so as to guarantee the QoS requirement associated with an IM CN subsystem session for IMS services. 1. QoS Signalling at Different Bearer Service Control Levels During the session set-up in a IM CN subsystem, at least two levels of QoS signalling/negotiation and resource allocation should be included in selecting and setting up an appropriate bearer for the session: a. The QoS signalling/negotiation and resource allocation at the IP Bearer Service (BS) Level: The QoS signalling and control at IP BS level is to pass and map the QoS requirements at the IP Multimedia application level to the UMTS BS level and performs any required end-to-end QoS signalling by inter-working with the external network. The IP BS Manager at the UE and the GGSN is the functional entity to process the QoS signalling at the IP BS level. b. The QoS signalling/negotiation and resource allocation at the UMTS Bearer Service Level: The QoS signalling at the UMTS BS Level is to deliver the QoS requirements from the UE (received from the GGSN in the case of IP‑CAN Bearer Control) to the RAN, the CN and the IP BS manager, where appropriate QoS negotiation and resource allocation are activated accordingly. When UMTS QoS negotiation mechanisms are used to negotiate end-to-end QoS, the translation function in the GGSN shall co-ordinate resource allocation between UMTS BS Manager and the IP BS Manager. Interactions (QoS class selection, mapping, translation as well as reporting of resource allocation) between the QoS signalling/control at the IP BS Level and the UMTS BS Level take place at the UE and the GGSN which also serve as the interaction points between the IM CN subsystem session control and the UMTS Bearer QoS control. UMTS specific QoS signalling, negotiation and resource allocation mechanisms (e.g. RAB QoS negotiation and PDP Context set-up) shall be used at the UMTS BS Level. Other QoS signalling mechanisms such as RSVP at the IP BS Level shall only be used at the IP BS Level. It shall be possible to negotiate a single resource allocation at the UMTS Bearer Service Level and utilise it for multiple sessions at the IP Bearer Service Level. E.2.2.1 Relation of IMS media components and PDP contexts/EPS bearers carrying IMS media All associated media flows (such as e.g. RTP / RTCP flows) used by the UE to support a single media component are assumed to be carried within the same PDP context/EPS bearer. E.2.3 Interaction between GPRS/EPS QoS and session signalling E.2.3.0 General The generic mechanisms for interaction between QoS and session signalling are described in clause 5.4.7, the mechanisms described there are applicable to GERAN/UTRAN/E-UTRAN-accesses as well. This clause describes the GERAN/UTRAN/E-UTRAN-access-specific concepts. At PDP context/EPS bearer setup the user shall have access to either GPRS/EPS without Policy and Charging Control, or GPRS/EPS with Policy and Charging Control. The GGSN/P‑GW shall determine the need for Policy and Charging Control, possibly based on provisioning and/or based on the APN of the PDN connection. For the GPRS/EPS without Policy and Charging Control case, the bearer is established according to the user's subscription, local operator's IP bearer resource based policy, local operator's admission control function and GPRS/EPS roaming agreements. For the GPRS/EPS with Policy and Charging Control case, policy decisions (e.g. authorization and control) are also applied to the bearer. The GGSN/P‑GW contains a Policy and Charging Enforcement Function (PCEF). E.2.3.1 Resource Reservation with Policy and Charging Control Depending on the Bearer Control Mode, as defined in TS 23.060 [23], selected for the GPRS IP‑CAN session, resource reservation shall be initiated either by the UE or by the IP‑CAN itself. IMS media which require resource reservation is always mapped to a dedicated bearer, i.e. a dedicated EPS bearer or a PDP context activated using the Secondary PDP Context Activation Procedure. For IP‑CAN initiated resource reservation, the PCRF has the responsibility to ensure that a dedicated bearer is used for media which require resource reservation. For GERAN/UTRAN the UE initiates the activation or the modification of an existing PDP Context for the media parameters negotiated over SDP using the procedures for Secondary PDP-Context Activation and MS-Initiated PDP Context Modification respectively as defined in TS 23.060 [23] subject to policy control. Otherwise, the GGSN/P‑GW within the GPRS IP‑CAN initiates the activation or the modification of an existing PDP Context for the media parameters negotiated over SDP using the procedures for Network Requested Secondary PDP Context Activation and GGSN/P‑GW-Initiated PDP Context Modification respectively as defined in TS 23.060 [23]. For E-UTRAN, the UE initiates the resource reservation request for the media parameters negotiated over SDP using procedure UE Requested Bearer Resource Modification procedure as defined in TS 23.401 [70] subject to policy control. Otherwise, the P‑GW within the EPS IP‑CAN initiates the activation or the modification of an existing Dedicated EPS bearer for the media parameters negotiated over SDP using the procedures for Dedicated bearer activation and PDN GW initiated bearer modification with or without bearer QoS update as specified in TS 23.401 [70]. The request for GPRS/EPS QoS resources may be signalled independently from the request for IP QoS resources by the UE. At the GPRS/EPS BS Level, the PDP Context activation / UE Requested Bearer Resource Modification shall be used by the UE for QoS signalling. At the IP BS Level, RSVP may be used for QoS signalling. E.2.4 Network initiated session release - P‑CSCF initiated E.2.4.0 General In the event of loss of coverage for GERAN/UTRAN access, TS 23.060 [23] defines the Iu or RAB Release procedures. In the case of PDP context/EPS bearer with streaming or conversational class the maximum bitrate of the GTP tunnel between SGSN and GGSN or between SGSN and S‑GW/P‑GW is modified to 0 kbit/s in up- and downlink direction. This is indicated to the P‑CSCF/PCRF by performing an IP‑CAN session modification procedure (see TS 23.203 [54]) as shown in Figure E.3. This procedure also applies to PDP Contexts/EPS bearer used for IMS SIP Signalling transport. For loss of coverage in the case of other PDP contexts/EPS bearer (background or interactive traffic class), the PDP context/EPS bearer is preserved with no modifications and therefore no indication to the P‑CSCF/PCRF. In the event of loss of coverage for E-UTRAN access, TS 23.401 [70] defines the S1 release Procedure. This procedure releases the EPS bearers. This is indicated to the P‑CSCF/PCRF by performing an IP‑CAN session modification procedure (see TS 23.203 [54]) as shown in figure E.3. The UE will become aware of the release of the GBR bearer the next time it accesses the E-UTRAN network via the procedures as described in the clauses 5.3.3 and 5.3.4 of TS 23.401 [70]. E.2.4.1 Network initiated session release - P‑CSCF initiated after loss of radio coverage Figure E.3: Network initiated session release - P‑CSCF initiated after loss of radio coverage 1. In the case of GERAN/UTRAN access, in the event of loss of radio coverage for a PDP context with streaming or conversational class the maximum bitrate of the GTP tunnel between SGSN and GGSN and between SGSN and S‑GW /P‑GW is modified to 0 kbit/s in up- and downlink direction. The P‑CSCF/PCRF receives an indication of PDP context/EPS bearer modification or EPS bearer removal. This also applies to PDP Contexts/EPS bearer used for IMS SIP Signalling transport. In the case of E-UTRAN access, loss of radio coverage causes the GBR bearers to be released in the network and P‑CSCF/PCRF is notified appropriately. 2. It is optional for the P‑CSCF/PCRF to deactivate the affected bearer and additional IP bearers (e.g. an IP bearer for chat could still be allowed). If the P‑CSCF decides to terminate the session then the P‑CSCF/PCRF removes the authorization for resources that had previously been issued for this endpoint for this session (see TS 23.203 [54]). 3. The P‑CSCF decides on the termination of the session. In the event of the notification that the signalling transport to the UE is no longer possible, the P‑CSCF shall terminate any ongoing session with that specific UE. If the P‑CSCF decides to terminate the session then the P‑CSCF/PCRF removes the authorization for resources that had previously been issued for this endpoint for this session. (see TS 23.203 [54]). The following steps are only performed if the P‑CSCF/PCRF has decided to terminate the session. When receiving an indication that bearer resources are not available for a voice media negotiated in a multimedia session that is in pre-alerting phase e.g. due to weak E-UTRAN coverage, the P-CSCF performs the procedures according to clause 6.2.1.3a or clause 6.2.2.3a in TS 23.237 [67]. 4. The P‑CSCF generates a Hangup (Bye message in SIP) to the S‑CSCF of the releasing party. 5. The S‑CSCF invokes whatever service logic procedures are appropriate for this ending session. 6. The S‑CSCF of the releasing party forwards the Hangup to the S‑CSCF of the other party. 7. The S‑CSCF invokes whatever service logic procedures are appropriate for this ending session. 8. The S‑CSCF of the other party forwards the Hangup on to the P‑CSCF. 9. The P‑CSCF/PCRF removes the authorization for resources that had previously been issued for this endpoint for this session. This step also results in a release indication to the GPRS/EPS system to confirm that the IP bearers associated with the session have been deleted for UE#2. 10. The P‑CSCF forwards the Hangup on to the UE. 11. The UE responds with an acknowledgement, the SIP OK message (number 200), which is sent back to the P‑CSCF. 12. The IP network resources that had been reserved for the message receive path to the UE for this session are now released. Depending on the Bearer Control Mode selected for the IP‑CAN session, the release of previously reserved resources shall be initiated either by the UE or by the IP‑CAN itself. The UE initiates the release of the IP‑CAN bearer resources as shown in figure E.3. Steps 12 and 13 may be done in parallel with step 11. Otherwise, the GGSN/P‑GW within the GPRS/EPS IP‑CAN initiates the release of the bearer PDP context/EPS bearer deactivation after step 9 instead. 13. The GPRS/EPS system releases the PDP context/EPS bearer. The IP network resources that had been reserved for the message receive path to the UE for this session are now released. This is initiated from the GGSN/P‑GW. If RSVP was used to allocated resources, then the appropriate release messages for that protocol would invoked here. 14. The SIP OK message is sent to the S‑CSCF. 15. The S‑CSCF of the other party forwards the OK to the S‑CSCF of the releasing party. 16. The S‑CSCF of the releasing party forwards the OK to the P‑CSCF of the releasing party. E.3 Address and identity management concepts E.3.1 Deriving IMS identifiers from the USIM If the UICC does not contain an ISIM application, then: The Private User Identity shall be derived from the USIM's IMSI, which allows for uniquely identifying the user within the 3GPP operator's network. The format of the Private User Identity derived from the IMSI is specified in TS 23.003 [24]. - A Temporary Public User Identity shall be derived from the USIM's IMSI and shall be used in SIP registration procedures. The format of the Temporary Public User Identity is specified in TS 23.003 [24]. It is strongly recommended that the Temporary Public User Identity is set to barred for SIP non-registration procedures. The following applies if the Temporary Public User Identity is barred: - A Temporary Public User Identity shall not be displayed to the user and shall not be used for public usage such as displaying on a business card. - The Temporary Public User Identity shall only be used during the SIP initial registration, re-registration and mobile initiated de-registration procedures. - The implicitly registered Public User Identities shall be used for session handling, in non-registration SIP messages and may be used at subsequent SIP registration procedures. - A Temporary Public User Identity shall only be available to the CSCF and HSS nodes. NOTE: If a Temporary Public User Identity is used, the user can not initiate any sessions until the implicitly registered public identities are available in the UE. In order to support a pre-Rel‑5 UICC accessing IMS services, a Temporary Public User Identity is generated using an appropriate identity related to the subscriber's subscription (e.g. in 3GPP it shall use the IMSI). When a Temporary Public User Identity has been used to register an IMS user, the implicit registration will ensure that the UE, P‑CSCF & S‑CSCF have Public User Identity(s) for all IMS procedures after the initial registration has been completed. E.4 Void E.5 IP version interworking in IMS A PDP context & its associated additional PDP contexts (i.e. PDP contexts associated to the same IP address/prefix) support either PDP type IPv4 or IPv6 or IPv4v6. For communication with the IMS, the UE establishes an IPv4 PDN connection or an IPv6 PDN connection or an IPv4IPv6 PDN connection via PDP contexts/EPS bearers. Termination of this PDP context/EPS bearer will normally trigger de-registration of IMS application first. Hence, the PDP context/EPS bearer that has been established for IMS communication must be retained for the UE to establish a SIP session via the IMS with an IPv4 SIP client. As such, any interworking on IP version on the application level (i.e. IMS & SIP) need to work with the architecture requirement from GPRS/EPS of maintaining the IP connectivity over GPRS/EPS by maintaining the PDP contexts/EPS bearers. For IMS perspective, a user may be connected either to a home GGSN/P‑GW or a visited GGSN/P‑GW depending on the configuration as specified in TS 23.221 [7]. E.6 Usage of NAT in GPRS/EPS There should be no NAT (or its existence should be kept transparent towards the UE) located between the GGSN/P‑GW and the P‑CSCF, which is possible as they are either located within the same private network and share same address space, or both the UE and the P‑CSCF are assigned globally unique IP addresses (see Annex M). NOTE: If the UE discover a NAT between the UE and the P‑CSCF, the UE might send frequent keep-alive messages and that may drain the UE battery. E.7 Retrieval of Network Provided Location Information in GPRS/EPS Information related to the location of the user provided by the access network may be required in IMS in order to comply with regulatory requirements (e.g. data retention, lawful interception) and/or in order to enable certain types of added value services based on the user's location. Depending on usage scenario, the following mechanisms are defined and can be used to retrieve the user location and/or UE Time Zone information from the access network when using GPRS and/or EPS to access IMS: - The P‑CSCF can retrieve the user location and/or UE Time Zone information using PCC mechanisms as specified in TS 23.203 [54] and in TS 29.214 [11]. Operator policy determines whether to provide the user location and/or UE Time Zone information from the access network in the INVITE request, a MESSAGE request, or within a subsequent message of the dialog. - When the user location and/or UE Time Zone information is required from the access network but not already available (e.g. when required in an INVITE request, when it is needed prior to session delivery, or when call is broken out to a MGCF), an IMS AS can trigger the retrieval of the user location and/or UE Time Zone information from the SGSN/MME via the HSS as specified in TS 29.328 [79] and as described in clause 4.2.4a. Operator policies at P-CSCF and IMS AS need to be coordinated in order to ensure that the appropriate method to retrieve the user location and/or UE Time Zone information is used for specific scenarios according to operator's preferences. The IMS entity that retrieves the user location and/or UE Time Zone information shall have the capability to further distribute the information to other IMS entities once it has been retrieved. User location and/or UE Time Zone information provided in the signalling by the network shall be possible to distinguish from user location information provided by the UE. The transfer of the user location and/or UE Time Zone information within IMS signalling shall not affect the transfer of any UE provided user location information. Information flows on how user location and/or UE Time Zone information can be further distributed within IMS depending on the alternative mechanism used can be found in Annex R. The level of granularity of user location information may be changed at network/trust boundaries. Thus, the level of user location information granularity that can be retrieved by an IMS AS via the HSS-based procedures in roaming scenarios depends on inter-operator agreement and needs to be aligned with policies in the P-CSCF. Information related to the location of the user provided by the access network may be required in IMS in order to comply with regulatory requirements for SMS over IP. The P-CSCF applies the above mechanisms upon reception of a MESSAGE including the distribution of received information to other IMS entities. E.8 Geographical Identifier The Geographical Identifier identifies a geographical area within a country or territory. It may be described in a geospatial manner (e.g. geodetic coordinates) within a country or territory or as civic user location information (e.g. a postcode, area code, etc.), or use an operator-specific format. It is assumed that a given cell cannot belong to more than one area identified by a Geographical Identifier. A network which requires the Geographical Identifier to be generated in the IMS may implement a mapping table between an (E)CGI (received as part of Access Network Information) and a Geographical Identifier. The P-CSCF or an IMS AS may then, based on operator policy, use this mapping table to convert the user location into a Geographical Identifier and insert the Geographical Identifier in the SIP signalling, thus enabling routing decision in downstream IMS entities or interconnected network. E.9 Support for Paging policy differentiation for IMS services As a network configuration option, where P-CSCF and P‑GW are located in the same PLMN, it shall be possible for the P-CSCF for terminating signalling to identify conversational voice as defined in IMS multimedia telephony service, TS 22.173 [53]. NOTE 1: This feature may be extended for other IMS services if so desired as long as the same principles are reused. P-CSCF may support Paging Policy Differentiation (as defined in TS 23.401 [70]) for a specific IMS service by marking packet(s) to be send towards the UE related to that IMS service. For such an IMS service, a specific DSCP (IPv4) value and/or a specific Traffic Class (IPv6) value are assigned by local configuration in the P-CSCF. NOTE 2: The packet marking used for Paging Policy Differentiation can also be used for determination of the Paging Cause, for the Multi-USIM UE support, by the relevant EPS node. When Paging Policy Differentiation is deployed in a PLMN, all P-CSCF entities of that PLMN shall homogeneously support it and shall be configured with the same policy for setting the specific DSCP (IPv4) and/or Traffic Class (IPv6) values used by P-CSCF for that feature. NOTE 3: It is assumed that the DSCP / Traffic Class header is not rewritten by intermediate routers between the P-CSCF and the P‑GW. E.10 Support of RAN Assisted Codec Adaptation RAN assisted codec adaptation is a functionality that assists codec rate adaptation for Multimedia Telephony based on access network bitrate recommendation (ANBR) messages that the UE receives in the access stratum of the 3GPP access network (E-UTRA RAT). The functionality is defined in TS 26.114 [76] and affects the following system entities: UE, RAN, P-CSCF and PCRF/PCF. During SIP registration or emergency registration if the network supports ANBR as specified in TS 26.114 [76] and RAN-assisted codec adaptation as specified in TS 36.300 [99] and TS 36.321 [100], the P-CSCF indicates 'anbr' support to the UE. NOTE: When IMS services are provided in deployments with home routed traffic a supporting P-CSCF does not indicate its capability to handle the 'anbr' SDP attribute unless it is configured to know that the roaming partner supports RAN assisted codec adaptation with access network bitrate recommendation. As specified in TS 26.114 [76]: - support for RAN assisted codec adaptation can be used only if it is supported end-to-end. - support for RAN assisted codec adaptation is assumed to be homogeneous in a PLMN i.e. all affected system entities in a PLMN including equivalent PLMNs need to support it. RAN support is required on E-UTRA. - the UE includes the 'anbr' attribute in the SDP offer only if the P-CSCF has indicated its ability to handle it. - the P-CSCF forwards the 'anbr' attribute if it has received it in the SDP offer from the UE. - when the 'anbr' attribute is successfully negotiated end-to-end, the PCRF/PCF uses MBR>GBR setting for the corresponding IP-CAN bearer relying on RAN assisted codec adaptation. A UE supporting Multimedia Telephony and RAN assisted codec adaptation shall support the procedures described in TS 26.114 [76]. Annex F (informative): Routing subsequent requests through the S‑CSCF This annex provides some background information related to clause 5.4.5.3. The S‑CSCF is the focal point of home control. It guarantees operator control over sessions. Therefore IMS has been designed to guarantee that all initial session signalling requests goes through the Home S‑CSCF on both terminating and originating side. A number of tasks performed by the S‑CSCF are performed either at registration time or immediately during session set-up, e.g. evaluation of initial filter criteria. However, there are tasks of the S‑CSCF, which require the presence of the S‑CSCF in the signalling path afterwards: - Media parameter control: If the S‑CSCF finds media parameters that local policy or the user's subscriber profile does not allow to be used within an IMS session, it informs the originator. This requires record-routing in the S‑CSCF. For example, change of media parameters using UPDATE would by-pass a S‑CSCF, which does not record-route. - CDR generation: The S‑CSCF generates CDRs, which are used for offline charging and for statistical purposes. A S‑CSCF, which does not record-route, would not even be aware of session termination. If the CDRs at the S‑CSCF are needed, then the S‑CSCF must record-route. - Network initiated session release: The S‑CSCF may generate a network-initiated session release, e.g. for administrative reasons. For that purpose a S‑CSCF needs to be aware of ongoing sessions. In particular it must be aware of hard state dialogs that are required to be terminated by an explicit SIP request. - If a UE registered to the S‑CSCF uses a Globally Routable User Agent URI (GRUU) assigned by the S‑CSCF as a contact address when establishing a dialog, then the S‑CSCF needs to remain in the signalling path in order to translate mid-dialog requests addressed to that contact address. The above criteria are particularly important for "multimedia telephony" type peer-to-peer communication. - Media parameter control guarantees that the user does not use services he or she did not pay for. - For telephony type services the session charging component is the most important one. - If a subscriber is administratively blocked, the network shall have the possibility to terminate ongoing communication. More generally, all the tasks are needed; thus they need to be provided elsewhere if the S‑CSCF does not record-route. On the other hand there are client-server based services, which may be offered by the home operator. An example of such service available today where the no record route principle is applied, is Presence, where notifications need not go through the S‑CSCF. Another example could be where the UE initiates a session to an Application Server (AS) in the home operator's domain, e.g. video download. In such cases: - The server implementation (or the server's knowledge of user subscription data) may limit the allowed media parameters. - Charging will be mostly event-based charging (content charging) and depends on the information provided from the AS. - The AS can terminate sessions. And the dialogs may be soft state dialogs, which are not required to be terminated by an explicit SIP request (e.g. SUBSCRIBE dialogs). However not in all cases the AS would receive the necessary information, which usually triggers session release (e.g. for administrative reasons). Thus, for some client-server based services, it might not be necessary to keep the S‑CSCF in the path. It may be desirable for an operator to avoid the load in the S‑CSCF and control the service from the AS. For such services "no record-routing in S‑CSCF" may be configured together with the initial filter criteria, as defined in clause 5.4.5.3. Annex G (normative): Reference Architecture and procedures when the NAT is invoked between the UE and the IMS domain G.1 General This clause specifies concepts of IMS service provisioning for the following scenarios: 1. When a device or devices that perform address and/or port translation are located between the UE and the P‑CSCF performing translation both of signalling and media packets. 2. When IP address and/or port translation is needed between the IP‑CAN and the IMS domain (e.g. different IP versions) on the media path only. This scenario covers the case when a device or devices that perform address and/or port translation are located on the media path only. The IP address and/or port translation device can be a NAT or a NAPT as defined in IETF RFC 2663 [34]. Another type of translation is NA(P)T‑PT as specified in IETF RFC 2766 [33]. In the rest of this clause NAT will be used for all of the devices that perform one or more of NA(P)T and NA(P)T‑PT functions. Note that the procedures of this Annex shall only be applied when they are necessary. If the terminal and/or the access network provide a transparent way of NAT traversal or no IP address translation is needed between the IP‑CAN and the IMS domain on the media path then the function as defined in this Annex shall not be invoked. It is expected the NAT traversal methods of this Annex will co-exist. UE may support one or more of these methods. It shall be possible for an operator to use one or more of NAT traversal methods in its IMS domain. The selection of the method for a particular case shall depend on the UE's capabilities, the capabilities of the network and policies of the operator. Where possible, usage of these procedures shall not adversely impact usage of power saving modes in the UEs, i.e. when the NAT is integrated with the IMS Access Gate way which is under operator control, the reserved temporary addresses and port (binding) should be retained without requiring keep-alive messages from the UE. If the access type to IMS is GPRS, then the UE is not required to initiate any keep-alive messages, see clause E.6 for more information. NOTE: A solution to allow power saving modes when non-operator controlled NATs are used is not defined in this version of the specification. G.1.1 General requirements The following list contains requirements that a NAT Traversal solution should satisfy: - Support multiple UEs (on one or more devices) behind a single NAT; - Support both inbound and outbound requests to and from UEs through one or more NAT device(s); - Support the traversal of NATs between the UE and the IMS CN; - Support uni-directional and bi-directional media flows; - Minimize additional session setup delay. G.2 Reference models This clause describes various reference models which can be used for NAT traversal. G.2.1 IMS-ALG and IMS Access Gateway model Figure G.1 presents the general reference model for IMS access when both the signalling and media traverses NAT devices. Figure G.2 presents the general reference model when IP address translation is needed between the IP‑CAN and the IMS domain. The IMS network architecture is the same for both cases. The NAT integrated with the IMS Access Gateway is under operator control in this reference model. Figure G.1: Reference model for IMS access when both the signalling and media traverses NAT Figure G.2: Reference model for IMS access when NAT is needed between the IP‑CAN and the IMS domain G.2.2 ICE and Outbound reference model Figure G.2a presents the general reference model for IMS access when both the signalling and media traverses NAT devices. Functional elements with dashed lines represent optional functionality. The transport of the Gm signalling is also subject to the policy enforcement. Figure G.2a: Reference model for ICE and Outbound Methodology The STUN Function shown within the P‑CSCF is a limited STUN Server for supporting STUN keep-alive messages as described in clause G.5.3.2. For deployments where the IMS Access gateway (or other media manipulating functional entities, such as a MRFP, are used (see clause G.2.1), such functional entities shall be placed on the network side of the STUN server and STUN relay server (i.e. not between the UE and the STUN server or STUN relay server) as shown in figure G.2a. Otherwise they will prevent STUN messages from reaching the STUN Relay/Server outside of a session. G.3 Network elements for employing the IMS-ALG and IMS Access Gateway G.3.1 Required functions of the P‑CSCF When supporting IMS communication for a UE residing behind a NAT or when IP address translation is needed between the IP‑CAN and the IMS domain on the media path only, the P‑CSCF may include the IMS-ALG function that is defined in Annex I of this specification. The following functions shall be performed in the P‑CSCF: 1) The P‑CSCF shall be able to recognize that the UE is behind a NAT device or IP address translation is needed between the IP‑CAN and the IMS domain on the media path only. 2) The IMS-ALG function in the P‑CSCF shall control the IMS Access Gateway, e.g. request transport addresses (IP addresses and port numbers) from the IMS Access Gateway and shall perform the necessary changes of the SDP parameters. 3) The IMS-ALG function in the P‑CSCF shall perform the necessary changes of headers in SIP messages. 4) The IMS-ALG function in the P‑CSCF shall be able to support scenarios where IMS CN domain and IP‑CAN use the same IP version and where they use different IP versions. 5) The IMS-ALG function in the P-CSCF shall be able to request opening and closing of gates on the IMS Access Gateway. 6) The IMS-ALG function in the P-CSCF may configure the IMS Access Gateway to police the remote source address/port of the associated media flow(s). 7) The IMS-ALG function in the P-CSCF may configure the IMS Access Gateway to police the bandwidth/data rate of the associated media flow(s) (see TS 23.333 [73]). 8) The IMS-ALG may configure the IMS Access Gateway to set the differentiated service code point for egress packets to an explicit value or alternately to allow the differentiated service code point of the ingress packet to be copied into the corresponding egress packet. An IMS Access Gateway can also support differentiated service code point marking based on local configuration. 9) The IMS-ALG may request an IMS Access Gateway to detect and report inactive media flows. G.3.2 Required functions of the IMS Access Gateway The required functions of the IMS Access Gateway for NAT translation are the following: 1) It allocates and releases transport addresses according to the requests coming from the IMS-ALG function of the P‑CSCF. 2) It ensures proper forwarding of media packets coming from or going to the UE. 3) It shall support the scenarios where IMS CN domain and IP‑CAN use the same IP version and where they use different IP versions. 4) It shall support opening and closing of gates, under control of the IMS-ALG. 5) It shall support policing of the remote source address/port and bandwidth/data rate of media flows, as configured by the IMS-ALG. 6) It shall support the setting of the differentiated service code point for egress packets as configured by the IMS-ALG or else based on local configuration. 7) It may support detection and reporting of inactive media flows. 8) It shall support remote NAT traversal. G.3.3 Iq reference point The Iq reference point is between the P‑CSCF and the IMS Access Gateway. It conveys the information necessary for the IMS-ALG to activate the procedures defined in clause G.3.2. Those procedures are further detailed in TS 23.334 [74]. G.4 Procedures for employing the IMS-ALG and IMS Access Gateway G.4.1 General The procedures described in this clause are applied in addition to the procedures of the P‑CSCF described in the other clauses of this specification. G.4.2 NAT detection in P‑CSCF When supporting the IMS-ALG function, the P‑CSCF, based on information received in a SIP request message (e.g. a REGISTER request), shall detect if there is NAT between the UE and itself and shall make a decision if IMS-ALG function shall be invoked for the session of subscriber. In addition to when a NAT is detected between the UE and the P‑CSCF, the IMS-ALG function may be invoked for other reasons (e.g. UEs using IP address from a Private IP address range). G.4.3 Session establishment procedure This procedure is applied when P‑CSCF invokes the IMS-ALG function for a session. This can happen at terminating side if the called party is behind a NAT or at the originating side if the session initiator is behind a NAT. Both cases are handled in the P‑CSCF and the IMS Access Gateway as described in this clause. Figure G.3: Session establishment procedure with NAT traversal NOTE 1: In figure G.3 if UE_A belongs to the P‑CSCF (originating case) then there will be IMS elements, i.e. CSCFs, between the P‑CSCF and UE_B. If UE_B belongs to the P‑CSCF (terminating case) then there will be IMS elements, i.e. CSCFs, between the P‑CSCF and UE_A. NOTE 2: The Transport address refers to both the IP address and Ports (see definition in clause 3.1). 1) The P‑CSCF receives a SIP message with an SDP offer from UE_A and decides to invoke the IMS-ALG function for this session. The session can either an originating or a terminating session. The SDP offer contains the transport address(es) of UE_A where the media flow(s) should be sent. 2) The P‑CSCF requests a transport address for each media flow from the IMS Access Gateway. Each request contains sufficient information to determine the side of the IMS access gateway that the transport request is being requested for. (e.g. local or remote side with respect to UE_A). 3) The IMS Access Gateway reserves one of its transport addresses for the given side of the media flow and this transport address is sent back to the P‑CSCF. The IMS Access Gateway shall keep the reserved temporary transport address (binding) until the session is released. 4) The P‑CSCF changes the original transport address(es) of the SDP offer to the transport address(es) received from the IMS Access Gateway. 5) The P‑CSCF forwards the SIP message with the modified SDP offer according to the normal routing procedures. 6) UE_B sends back a SIP message with an SDP answer, which is forwarded to the P‑CSCF according to the normal SIP message routing procedures. 7) The P‑CSCF requests a transport address for each media flow in the routing domain of its own IMS network from the IMS Access Gateway. The request contains sufficient information to correlate to the transport address request performed in step 2. NOTE: If some of the offered media flows are rejected in the answer, then the P‑CSCF shall indicate this to the IMS Access Gateway. The IMS Access Gateway can release the resources (e.g. the transport address) reserved for that media flow. The P‑CSCF may indicate directly to release the resources. 8) The IMS Access Gateway reserves one of its transport addresses for the given side of the media flow and this transport address is sent back to the P‑CSCF. 9) The P‑CSCF changes the original transport address(es) of the SDP answer to the transport address(es) received from the IMS Access Gateway. 10) The P‑CSCF forwards the SIP message with the modified SDP answer according to the normal SIP message routing procedures. G.4.4 Session release procedure This procedure is applied when a session has to be released, for which the IMS-ALG function is invoked. Figure G.4: Session release procedure with NAT traversal 1) The P‑CSCF receives a trigger to release a session, for which the IMS-ALG function is invoked. 2) The P‑CSCF sends an indication to the IMS Access Gateway for each media flow of the session that the resources allocated during the session establishment procedures are to be released. 3) The IMS Access Gateway releases its resources allocated for the given media flows. G.4.5 Session modification A session modification can cause the creation and/or modification and/or release of media flows. When a new media flow is created the procedure used during session establishment shall be applied. When an existing media flow is released the procedure for session termination shall be applied for the particular media flow. When an existing media flow is modified, this may lead to a modification of the media flow directly, or to the establishment of a new media flow and release of the existing one. G.4.6 Media forwarding in the IMS Access Gateway This clause presents the media forwarding performed by the IMS Access Gateway. The behaviour presented in this clause is valid in both directions. Figure G.5: Packet forwarding in the IMS Access Gateway 1) UE_A sends a media packet to the transport address of the IMS Access Gateway that was received during the session establishment/modification. 2) After receiving the media packet the IMS Access Gateway recognizes the media flow based on the transport address where the packet arrived at. The IMS Access Gateway changes the source transport address to its own transport address that was given to the UE_B as the destination transport address during session establishment/modification and the destination transport address to the transport address of UE_B. The IMS Access Gateway can learn the transport addresses where the inbound (i.e. towards the UE) media packets shall be forwarded to in two ways, depending on whether there is a NAT device in the path or not. In absence of a NAT device in the path, it is the P‑CSCF that signals the destination transport address for the inbound media flows. In presence of NAT device in the path, it is the IMS Access Gateway that may, upon being informed that there is a NAT in the network, determine the destination transport address of the inbound media flow based on previously received media packets in the opposite direction. Beyond the changes of transport addresses the IMS Access Gateway shall perform the other necessary changes in the IP header as it is specified in the NAT related IETF specifications, IETF RFC 2766 [33] and IETF RFC 2663 [34]. NOTE 1: If the IMS Access Gateway does not know the transport address where a packet shall be forwarded, i.e. no packet of the other direction of the media flow has been received, then it can store or drop the packet. NOTE 2: If this is not the first packet then the IMS Access Gateway can check the source transport address. If it is not the same as the transport address previously used for this media flow in this direction then the media packet may be a fraud one and should be dropped. NOTE 3: This solution (i.e. when the IMS Access Gateway determine the destination transport address on its own) assumes that the UE supports "symmetric media" i.e. it supports receiving media packets at the same address and port as it uses for sending. 3) The IMS Access Gateway routes the media packet towards UE_B. G.5 Network elements for employing NAT Traversal for ICE and Outbound G.5.1 General requirements In addition to the general requirements outline in clause G.1.1, the following NAT traversal solution also addresses the following additional requirements: - Does not require the network to be aware of the presence of a NAT; - Avoid unnecessarily long media paths due to media pinning; - It shall be possible to establish communication towards a remote UE that does not support of the functionality listed in G.5; - Minimize the impacts on Policy and Charging Control functionality. G.5.2 ICE G.5.2.1 Overview The Interactive Connectivity Establishment (ICE) described in IETF RFC 5245 [45] defines a methodology for media traversal of NAT devices. However, ICE is not a complete solution in of itself as ICE only addresses address advertisement and NAT binding maintenance. ICE does not address RTP and RTCP port symmetry requirements or non-sequential RTP and RTCP port assignment. A complete UE managed NAT traversal solution shall take into account each of these issues. G.5.2.2 Required functions of the UE When supporting ICE, the UE is responsible for managing the overall NAT traversal process and for invoking the various protocol mechanisms to implement the NAT traversal approach. As such, the following functions shall be performed by the UE: - STUN relay server and STUN server discovery; NOTE: A configuration mechanism can be used to provision STUN server and STUN relay server addresses in the UE. - Transmission of media packets from the same port on which it expects to receive media packets; - RTCP port advertisement. - ICE functionality which includes: - Maintaining of NAT bindings to insure inbound media packets are allowed to traverse the NAT device. - Address advertisement, which consists of the following operations: - Gathering candidate addresses for media communications; - Advertising the candidate addresses in a special SDP attribute (a=candidate) along with the active transport address in the m/c lines of the SDP. - Perform connectivity checks on the candidate addresses in order to select a suitable address for communications. Depending on the results of the connectivity checks, one of the candidate addresses may be promoted to become the active transport address. Depending on the active transport address, provide additional information in the session description to insure that correct policy and charging functionality can be applied on relayed media packets. Given the desire to minimize session establishment delays during connectivity checks, the UE shall advertise its active address in the SDP offer or answer in the following order based on their availability: 1. STUN relay server assigned address; 2. STUN derived address; 3. Locally assigned address. G.5.2.3 Required functions of the STUN relay server The STUN relay server and associated signalling requirements are documented in IETF RFC 5766 [46] and its use is detailed in IETF RFC 5245 [45]. No additional requirements are placed on this server. NOTE: While it is not required that a STUN relay server be deployed in the network, a STUN Relay server would allow for media exchange in the presence of all NAT types. G.5.2.4 Required functions of the STUN server The STUN server and associated signalling requirements are documented in RFC 5389 [47] and its use is detailed in IETF RFC 5245 [45]. No additional requirements are placed on this server. NOTE: While it is not required that STUN servers be deployed in the network, a STUN server would allow for UEs to discover the WAN facing transport address of the NAT. Such discovery may minimize the need for STUN Relay server resources by allowing UEs to directly exchange media in the presence of the majority of NAT types. G.5.3 Outbound G.5.3.1 Overview RFC 5626 [48] "Managing Client-Initiated Connections in the Session Initiation Protocol" (Outbound) defines a methodology for signalling traversal of NAT devices. This methodology involves the establishment of flows to allow for the routing of inbound dialog initiating requests and the maintenance of the flow through keep-alive messages. Outbound does not however address inbound response routing or inbound mid-dialog requests. A complete UE managed NAT traversal solution shall take into account each of these issues. This clause is restricted to the use of Outbound in the context of SIP NAT traversal and not to the usage of Outbound for multiple registration support. NOTE: ICE and Outbound are not dependent on each other and can be deployed separately or together. The STUN keep-alive function, for SIP signalling, can also be implemented as a standalone function, without ICE or Outbound. G.5.3.2 Required functions of the P‑CSCF When supporting Outbound, the P‑CSCF's primary role in NAT traversal is to ensure that requests and responses occur across a flow for which there is an existing NAT binding. The P‑CSCF shall ensure that inbound dialog initiating requests can be forwarded to the UE on a flow for which there is an existing NAT binding. The P‑CSCF shall ensure that all responses to the UE including those from mid-dialog requests are sent to the same source IP address and port which the request was received from. The P‑CSCF shall also implement a limited STUN server functionality to support the STUN keep-alive usage as defined in RFC 5389 [47] which is used by the UE to maintain the NAT bindings. NOTE: The STUN server implementation on the P‑CSCF need only support the STUN functionality required for the STUN binding request operation. Additionally the P‑CSCF shall transmit signalling packets from the same port on which it expects to receive signalling packets. G.5.3.3 Required functions of the S‑CSCF When supporting Outbound, the S‑CSCF should be responsible for indicating to the UE that Outbound procedures are supported. G.5.3.4 Required functions of the UE When supporting Outbound, the UE is responsible for managing the overall NAT traversal process and for invoking the various protocol mechanisms to implement the NAT traversal approach. As such, the following functions shall be performed by the UE: - Maintaining of NAT bindings between the UE and the P‑CSCF through the use of a keep-alive mechanism to insure inbound signalling packets are allowed to traverse the NAT device. NOTE: Solutions to determine the frequency of the keep-alive are not defined in this version of the specification. A configuration mechanism can be used in place of a dynamic discovery process. - Transmission of signalling packets from the same port on which it expects to receive signalling packets; - Establishment of signalling flows to its assigned P‑CSCF(s) during registration. NOTE 1: The UE can determine that STUN based keep-alive can be used towards the P‑CSCF based on the presence of the STUN keep-alive parameter from the P‑CSCF SIP URI received during P‑CSCF discovery. NOTE 2: If a UE supports only STUN keep-alives, but not Outbound, it does not need to determine Outbound support and it does not need to register flows as defined by Outbound. It only sends STUN requests to the P‑CSCF to keep NAT bindings open. G.6 Procedures for employing ICE and Outbound The procedures described in the following clauses are applied in addition to the procedures of the UE and P‑CSCF described in other clauses of this specification. G.6.1 Flow establishment procedures This procedure is initiated by the UE at network registration time and allows for the establishment of a flow between a UE and its assigned P‑CSCF. This flow can then be used by the P‑CSCF to allow an initial inbound request to traverse the NAT. Figure G.7: Flow Establishment Procedures for Outbound 1. UE-A initiates network registration by sending a registration request to its assigned P‑CSCF. 2. Upon receipt of a registration request, the P‑CSCF stores received transport header. This includes information to identify the flow between P‑CSCF and UE. 3. The P‑CSCF then sends the registration request to the assigned S‑CSCF after adding information identifying the serving P‑CSCF to the registration request. 4. The S‑CSCF stores the information identifying the serving P‑CSCF and returns a registration response. 5. Upon receipt of the registration responses from the S‑CSCF, the P‑CSCF forwards the registration response to UE-A using the stored transport address information from the registration request. 6. UE-A sends a Keep-Alive request to its assigned P‑CSCF using the same transport address information (source and destination) which was used for the registration request. This Keep-Alive ensures that a NAT binding exists between UE-A and the P‑CSCF allowing for inbound session requests from the P‑CSCF to UE-A. 7. The P‑CSCF responds with a Keep-Alive response which also reflects the received source transport address information. Inclusion of such information allows UE-A to determine if the NAT has rebooted and assigned a new binding and take appropriate action. G.6.2 Session establishment procedures The following procedure illustrates the session establishment procedures when both UEs support the ICE methodology. These procedures apply to both the terminating and originating side of the session regardless of whether the UE is behind a NAT. In the following figure the STUN element represents both a STUN server and STUN Relay server as a single logical element. It would be equally valid if these functions we represented in separate logical elements. The procedures are unaffected by the grouping. Further, this call flow represents a simplified view to illustrate the NAT traversal procedures only. Other network elements not show may be involved in the session establishment process. Figure G.8: Session Establishment procedure for NAT Traversal using ICE and Outbound 1. UE-A begins candidate transport address collection by performing a request for a transport address for each media flow from the STUN server. 2. The STUN server reserves one of its transport addresses for each media flow and sends the reserved transport address information back to the UE. The STUN server also reflects the source transport address of the original request for a transport address. If the UE fails to identify STUN servers it concludes that ICE and Outbound procedures are not supported by the network and defaults to operation using the procedures described in clause G.4. 3-4. UE-A repeats the procedures for requesting a transport address for each RTCP flow. These steps may be executed in parallel with steps 1. – 2. or in series. 5. With its three candidates (locally assigned, server reflected and relay) UE-A forms an offer and forwards to its assigned P‑CSCF. The UE includes the SP cand-type, SP rel-addr and SP rel-port in the candidate attribute as defined in IETF RFC 5245 [45]. 6. To ensure subsequent responses to the offer are allowed through the NAT, the P‑CSCF stores the transport address information received in the transport header of the offer. 7. The P‑CSCF forwards the Offer to UE-B using one of the previously established flows. 8-11. UE-B performs the candidate gathering procedures as outlined in steps 1. – 4. above. 12. With its three candidates (locally assigned, server reflected and relay) UE-B forms an answer and forwards to its assigned P‑CSCF. 13. The P‑CSCF for UE-A forwards the Answer to UE-A based on the previously stored transport address information. Media can being to flow at this point using the default transport addresses (recommended to be the STUN Relay provided address). 14. Both UE-A and UE-B perform connectivity tests on each received transport address to determine which of the received transport addresses are actually reachable. 15. After the connectivity tests are concluded UE-A sends an updated SDP Offer indicating the agreed to transport address. 16. The P‑CSCF forwards the Offer according to normal routing procedures. 17. UE-B sends an Answer indicating the agreed to transport address. 18. The P‑CSCF forwards the Answer according to normal routing procedures. Media can begin flowing using the newly identified addresses. 19-21. STUN Relay allocated transport addresses are released by the UE once a more efficient address has been identified and the session updated. G.6.3 Session release procedures This procedure is applied to by the UE if the IMS-ALG function is not supported by the network, but the network does support ICE and Outbound procedures. Normal session release procedures are followed with the following exception. If a STUN Relay allocated transport address was used for the session, it shall be released by the UE for which the transport address was allocated. In the following figure the STUN element represents both a STUN server and STUN Relay server as a single logical element. It would be equally valid if these functions we represented in separate logical elements. The procedures are unaffected by the grouping. Figure G.9: Session Release Procedure with STUN Relay Resources 1. UE-A receives a trigger to release the session for which STUN Relay resources were allocated. 2. UE-A sends an indication to the STUN Relay server to release resources allowed for RTP. 3. The STUN Relay server releases the allocated resources and returns a response. 4. UE-A sends an indication to the STUN Relay server to release resources allowed for RTCP. 5. The STUN Relay server releases the allocated resources and returns a response. G.6.4 Session modification procedures A session modification can cause the creation and/or modification and/or release of media flows. This procedure is applied to by the UE if the IMS-ALG function is not supported by the network, but the network does support ICE and Outbound procedures. When a new media flow is created the procedure used during session establishment for updating the transport addresses (steps 15-17. of the session establishment procedures) shall be applied. When an existing media flow is released the procedure for session termination shall be applied for the particular media flow. When an existing media flow is modified, this may lead to a modification of the media flow directly, or to the establishment of a new media flow and release of the existing one. G.6.5 Policy and Charging Control procedures When PCC is to be employed for a session, the P‑CSCF is responsible for providing the PCRF/PCF with IMS media flow information related to the service. If the UE has indicated that the active transport address corresponds to a relayed address, the P‑CSCF shall be responsible for using the additional information provided by the UE to convert the media flows derived from the SDP into flow descriptions which will traverse the Policy and Charging Enforcement Point. The deployment of STUN relay servers requires that the UE be able to communicate with such servers prior to session establishment. The PCC for the IP‑CAN must be set up to allow communication with the STUN relay server prior to IMS session establishment. This may impact gating control in some IP‑CANs which do not support a default or best effort flow which can be used to communicate with the STUN relay server prior to session establishment. NOTE 1: Predefined PCC rules can be created to allow the UE to communicate with the STUN relay much in the same way the UE is allowed to communicate with the IMS network for session management. NOTE 2: Given that a STUN relay is a forwarding server under the direction of the UE, necessary precaution needs to be taken by the operator in how it chooses to craft these rules. It is recommended that such predefined rules only guarantee the minimal amount of bandwidth necessary to accomplish the necessary UE to STUN relay communication. Such an approach helps reduce the resources required to support NAT traversal mechanisms. Finally, such an approach allows the preconfigured rule to be over-ridden by dynamic rules which allow for the necessary bandwidth needed by the session. NOTE 3: The dynamic PCC rule will need to differentiate between different media traffic between UE and STUN relay (e.g. voice vs. video), which can be identified by the different ports assigned by the residential NAT. Session bindings need to take into account that the relevant Terminal IP address may be contained within the ICE candidates contained in the session description, rather than in the normal media description. G.6.6 Detection of NAT Traversal support The UE shall be able to determine whether the IMS CN supports the Outbound procedures by the capabilities indicated in the registration response to the UE. If the indication of the capability is present, the UE knows that the IMS CN supports Outbound and the associated procedures. NOTE: A configuration mechanism can be used to provision STUN server and STUN relay server addresses in the UE. G.6.7 Procedures at other IMS entities processing SDP IMS entities processing SDP, such as the P‑CSCF, IBCF or MRFs, may or may not be updated to understand the "candidate alternative addresses" that are part of the ICE procedures, IETF RFC 5245 [45]. IMS entities processing SDP that do not understand the ICE procedures will, in accordance with there compatibility procedures, ignore the "alternative addresses" and media entities, such as the IMS Access Gateway, PCEF, MRFP and TrGW, controlled by the IMS entities processing SDP will not pass connectivity check requests and media on those addresses. IMS entities processing SDP which behave as B2BUAs may or may not pass on the alternative address in accordance with their own compatibility procedures. Annex H (informative): Example HSS deployment This clause describes possible deployment scenarios for the HSS when it operates as an IMS only database. The following depicts the HSS functionality as described in TS 23.002 [1] repeated here for clarity; note that the functional description in TS 23.002 [1] shall always be considered as the most updated version, if it is different than the version shown here. 3GPP HSS contains functions also known as HLR and AuC, which are needed for 3GPP GPRS and CS domain access authentication and authorization and overall subscription handling as well as service data management. Figure H.1: HSS functional decomposition In cases where the HSS would operate as an IMS only entity, the functions and interfaces specific to IMS operations would be applicable. These include support of functionalities such as identification handling, service provisioning support, call/session establishment support, application services support, IMS access authentication and authorization provided by the interfaces Cx, Sh and Si (if applicable to interwork with CAMEL) and any additional subscription and configuration handling for IMS users. This type of configuration of the HSS would be used for access to the IMS as defined by, for example, TISPAN NGN. Annex I (normative): Border Control Functions I.1 General This annex describes a collection of functions that can be performed on interconnection boundaries between two IM CN subsystem networks or between an IM CN subsystem network and other SIP based multimedia network, based on operator configuration. I.2 Overall architecture Figure I.1 presents a high-level architecture diagram showing how Border Control Functions fit into the IMS architecture. Figure I.1: Border Control Functions The Mx reference point allows S‑CSCF/I‑CSCF/P‑CSCF/MSC Server enhanced for ICS or MSC Server enhanced for SRVCC to communicate with an IBCF in order to provide border control functions. The functionality of the reference point is specified in TS 24.229 [10a]. The Mm reference point allows IBCF to be the entry / exit point towards other IM Core Network Subsystems and provide border control functions. The Ici reference point allows IBCF to be the entry / exit point towards other SIP networks and provide border control functions. The functionality of the reference points are specified in TS 24.229 [10a]. The Ix reference point allows the IBCF to control the TrGW. The functionality of Ix is defined in TS 29.162 [75]. I.3 Border Control Functions I.3.1 IP version interworking The IP version interworking should not adversely affect IMS sessions that do not require IP version interworking. The network shall, at a minimum, support mechanisms that support IP version interworking for UEs, which comply with previous release of specifications. In addition, any impacts due to specific properties of the IP‑CAN shall be taken care of by the IP‑CAN itself without affecting the IMS. One possible architecture scenario can be based on the principle defined in TS 23.221 [7] using gateways. The IMS ALG provides the necessary application function for SIP/SDP protocol stack in order to establish communication between IPv6 and IPv4 SIP applications. The IMS ALG receives an incoming SIP message from CSCF nodes or from an external IPv4 SIP network. It then changes the appropriate SIP/SDP parameters, translating the IPv6 addresses to IPv4 addresses and vice versa. The IMS ALG needs to modify the SIP message bodies and headers that have IP address association indicated. The IMS ALG will request NA(P)T-PT to provide the bindings data between the different IP addresses (IPv6 to IPv4 and vice versa) upon session initiation and will release the bindings at session release. I.3.1.1 Originating Session Flows towards IPv4 SIP network The following example session flow shows a scenario where the S‑CSCF is responsible for inserting the IMS-ALG in the session path. No I‑CSCF node shown in this scenario, if configuration requires presence of an I‑CSCF then it would have been collocated with the IMS-ALG. Figure I.2: Originating IMS session towards an IPv4 end point 1. UE (A) initiates an IMS session towards User B, via the session path for IMS and the session is analysed at the S‑CSCF of UE (A). 2. S‑CSCF for user A determines via DNS (or other mechanism) that the User B's domain cannot be communicated via IPv6 but can be via IPv4. 2a. S‑CSCF forwards the request to IMS-ALG. 3. The IMS-ALG then acquires the necessary resources from the TrGW such as the IPv4 address and ports on behalf of user A so that User A can communicate with user B transparently. 4. The IMS-ALG continues IMS signalling towards User B network where User A's IPv6 address/port information is replaced by IPv4 information. 5. When User (B) responds to the session initiation requests, the IMS-ALG will replace the IPv4 address/port information of User (B) with its own IPv6 information for signalling and with TrGW IPv6 information for the media path as the contact information of User (B) and forward the request to S‑CSCF of UE (A). Session signalling path is then established between the UE and the S‑CSCF, the S‑CSCF and the IMS-ALG, the IMS-ALG and the external network for User B. 6. The media path is established between the UE (A) and the TrGW, via the IP‑CAN and then between the TrGW and user B. At session release, the IP address/Port information will be released for reuse by other sessions. I.3.1.2 Terminating Session Flows from IPv4 SIP network The following session flow shows an example of a terminating session from an IPv4 SIP client towards an IPv6 IMS client. In order for the IPv6 IMS client to be reachable by the IPv4 network, it is assumed that the IPv4 network discovers (via mechanism such as DNS query) the IMS-ALG as the entry point to the IPv6 IMS network. Figure I.3: Terminating IPv4 SIP session towards an IPv6 IMS user 1. In the IMS-ALG, a terminating session is received. IMS-ALG determines either via DNS query or via pre-configuration the appropriate I‑CSCF for the user (B) in the IMS network. 2. IMS-ALG also communicates with TrGW to get the mapping of IPv6 address and ports on behalf of user (A) and replaces the User (A) information in the incoming SIP message and forwards the message towards S‑CSCF. From S‑CSCF point of view, it continues setting up the IMS session like any other IMS sessions. 3. The incoming session arrives in the S‑CSCF for the user (B). 4. Session set up continues as usual in the IMS domain towards user (B). 5. When UE (B) responds to the session initiation requests, the IMS-ALG will replace the IPv6 address/port information of User (B) with its own IPv4 information for signalling and with TrGW IPv4 information for the media path as contact information of UE (B) and forward the request towards the network of User (A). Session signalling path is established between User (B) and S‑CSCF, S‑CSCF and I‑CSCF/IMS-ALG and IMS-ALG and the external User (A)'s network. 6. Media path is established between UE (B) and the TrGW, via the IP‑CAN and then between the TrGW and User (A). At session release, the IP address/Port information will be released for reuse by other sessions. I.3.2 Configuration independence between operator networks The THIG functionality may be used to hide the network topology from other operators. It shall be possible to restrict the following information from being passed outside of an operator's network: addresses of operator network entities. NOTE: The THIG functionality was not intended to be invoked in IMS roaming scenarios when the P‑CSCF and IBCF are both located in the visited network as information available in certain SIP headers may be used by the home network for further processing of signalling messages. The specific mechanism chosen needs to take into account the following separate aspects: Network management: In the case that network details (i.e. S‑CSCF addresses) are visible by other external network elements, any (temporary or permanent) changes to the network topology need to be propagated to network elements outside of the operator's network. This is highly undesirable from a network management perspective. Network scalability: Establishing security associations on a pair-wise basis among all CSCFs is likely to be unscalable. The security associations shall be independent of the number of network elements. Competitively aspects: The operational details of an operator's network are sensitive business information that operators are reluctant to share with their competitors. While there may be situations (partnerships or other business relations) where the sharing of such information is appropriate, the possibility should exist for an operator to determine whether or not the internals of its network need to be hidden. Security aspects: Network element hiding may help to reduce the vulnerability of the overall system to external attacks (e.g. denial of service attacks). Further work is needed in this area. NOTE: The encryption mechanism for implementing network configuration hiding is specified in TS 33.203 [19]. I.3.3 Transcoding Support for Interworking I.3.3.1 General The IBCF/TrGw provides the necessary function for codec transcoding, when required by interworking agreement and session information, in order to establish communication between end points belonging to different IMS domains. These transcoding procedures are applicable to both the originating and the terminating side of the session or (in inter-network scenarios) in a transit network Transcoding shall only be performed in the case where a common codec cannot be negotiated between the two UEs. Media transcoding services can be triggered proactively (before the session request is sent to the called UE) or reactively (after the session request has been sent to and rejected by, the called UE). The IBCF may allocate a TrGW before sending the SDP Offer to the terminating UE or it may allocate the TrGW upon receiving the SDP answer. The protocol solutions should ensure that the called party is not alerted until resources for transcoding are seized and user plane connection towards the calling party is established to avoid ghost ringing or voice clipping. NOTE: The proactive transcoding example flows illustrates only the allocation of the TrGW before sending the SDP offer. If the IBCF is configured per local policy to use proactive transcoding, the IBCF shall add codecs to the offer. When inserting additional codec(s), the network should be able to indicate the preferred codec order. If the IBCF is configured per local policy to use reactive transcoding, the IBCF shall first determine the codecs supported by the calling and called UEs so that insertion of the TrGW is performed when necessary, if not required for any other interconnect function. This means that the IBCF shall trigger a new offer/answer to the terminating UE, based on the initial offer from the originating UE but including additional codecs supported by the TrGW in the same manner as for the proactive support. I.3.3.2 Session Flows I.3.3.2.1 Proactive transcoding support The following example session flow shows a proactive transcoding support scenario where an IBCF acting as an exit point allocates a TrGW prior to signalling towards the entry point of the other operator's network. The IBCF inserts additional codecs in the SIP signalling. The calling UE capabilities are contained in the SDP offer. Based on the interworking agreement between IM CN subsystems, terminating IBCFs acting as the network entry points may also insert additional codecs in the SIP signalling. The IBCF and TrGW in Figure I.4 below may be located in the originating network (the IBCF acts as an exit point), or in the terminating network (the IBCF acts as an entry point). There can also be additional IBCF's and TrGW's (not shown) in the case of scenarios involving transit networks. Figure I.4: Proactive transcoding invocation 1. UE (A) initiates an IMS session towards User B, via the session path for IMS and the session is analysed at the IMS network of UE (A). 2. The IMS network of UE (A) determines that the User B's domain need be communicated via IBCF and forwards the request to the IBCF. 3. The IBCF checks the SIP message and decides whether additional codec(s) need be inserted into SIP message based on the session information (such as ICSI , SDP) and interworking agreement. When inserting additional codec(s), the network should be able to indicate the preferred codec order. A TrGW is allocated. 4. The IBCF generates a new SIP message towards User B network based on the received SIP message where additional codec(s) have been added and where the transport address and port information has been altered to indicate the addresses associated by the TrGW. 5. User (B) selects a codec from the offer modified by IBCF and responds with an SDP answer. 6. When receiving the SDP answer, if the IBCF invoked the TrGW in step 3, it now configures the TrGW with address and port towards UE (B). The IBCF checks if the agreed codec belongs to the original offer it received in step 3 or it is one of the codecs that was added by IBCF. If the agreed codec was added by the IBCF, the IBCF configures the TrGW to enable the transcoding functionality. Otherwise, the IBCF will not invoke the transcoding function. NOTE 1: If the IBCF forwards an SDP offer without allocating a TrGW and changing the connection information and the subsequent SDP answer indicates selection of a transcoding option associated with the TrGW, then the IBCF needs to allocate a TrGW and initiate another SDP offer/answer transaction to forward the TrGW connection information. If the IBCF forwards an SDP offer with connection information for its TrGW and the subsequent SDP answer indicates the use of an original codec (transcoding is not needed), then the IBCF can initiate another SDP offer/answer transaction to forward the original connection information and de-allocate the TrGW. The details are not shown. 7. The IBCF generates a new response message back to UE (A) based on the received response message where the codec received from peer side has been replaced with the selected codec. NOTE 2: On the new response message the selected codec will based on the SDP offer received by IBCF on step 3. 8. Session signalling path is established between User (A) and IBCF, IBCF and User (B). 9. The media path is established between the UE (A) and the TrGW and then between the TrGW and user B. At session release, the codec transcoding resource will be released. I.3.3.2.2 Reactive transcoding support The following example session flow shows a reactive transcoding scenario where IBCF located at the network exit point first determines if a session can be established without addition of transcoding options and, will insert additional codecs in the SIP signalling only after failure to establish a session due to lack of a common codec. Based on the interworking agreement between IM CN subsystems the terminating IBCF may also perform this function. NOTE 1: In the event a session is being forked in the terminating network, the reactive transcoding will only be performed if all UEs receiving the forked request initially reject the session for any reason, e.g. due to lack of support for the offered codecs. Figure I.5: Reactive transcoding invocation 1. UE (A) initiates an IMS session towards User B and the session is analysed at the IBCF. The SDP offer is forwarded toward User B without the proactive addition of transcoding options. 2. A subsequent entity in the signalling path determines that it does not support any codec in the SDP offer and answers with an appropriate error response. This response may include a list of supported codecs. NOTE 2: The subsequent entity in the signalling path can be a network entity in a transit network, in the terminating network, or UE (B). 3. Based on the response, the IBCF detects the need for reactive transcoding invocation. 4. The IBCF instructs the TrGW to allocate media processing resources for the session, allocate appropriate transcoding resources for the session and bridge the media flows between the calling and called party endpoints. 5. Based on the response from the TrGW, the IBCF creates a new SDP offer that contains the codec and transport address information received from the TrGW. If no information about supported codecs was available from the error response, the IBCF may offer all codecs supported by the transcoding device. The IBCF sends this SDP offer towards UE (B). 6. UE (B) selects a codec and acknowledges the SDP offer with an SDP answer. 7. Upon receipt of the SDP answer, the IBCF updates the TrGW with the information from the SDP answer. 8. The IBCF prepares an SDP answer to the SDP offer in step 1, including the selected codec and transport address information for the originating side of the TrGW. The session between the end-points is now established with the media flow traversing the transcoding device. At session release, the codec transcoding resource will be released. Annex J (informative): Dynamic User Allocation to the Application Servers J.1 General The complexity of operating a network increases with the number of supported subscribers and one contributor will be the management of allocating subscribers to the application servers for the same set of services, where there is a requirement for a user to be assigned to an application servers longer than the duration of one session. This would occur when there is data which is to be retained together with the processing resources longer than a single session. Possible solutions described below do not require impacts on the stage 3 specifications. J.2 Representative AS J.2.1 Concept of Representative AS The Representative AS is the application server which allocates the user to the application servers and keeps the user allocation information and relevant data for the service during the duration of a session or longer than that. The incoming call for the service is received and forwarded to the allocated application server by the Representative AS. The following points are considered as requirements for the dynamic user allocation procedures using the representative AS. - The representative AS for each service is the initial contact point for all signalling. This can include ISC; and for example, Ut; and others signalling that may or may not be defined in 3GPP. - For the ISC, the representative AS is included in every message which opens a new dialogue. It is not included after the initial transaction. - For example, when the AS is to be invoked by evaluating the iFC at the S‑CSCF, the address in the iFC is the address of the Representative AS. The following figure shows an example service deployment for three different services using the representative AS. Figure J.2.1: Dynamic User Allocation using Representative AS J.2.2 Procedures related to Representative AS Figure J.2.2: Bypassing Representative AS procedure Procedure is as follows: 1. The initial SIP INVITE request is sent to S‑CSCF to create a new dialogue. 2. The SIP INVITE request is forwarded to the Representative AS according to the service logic, e.g. iFC evaluation at the S‑CSCF. 3. The Representative AS retrieves the user allocation information and forwards the SIP INVITE request to the AS#1 according to the allocation information. If there is no allocated AS for the user, the Representative AS allocates one. 4. The SIP INVITE request is forwarded to the AS#1. Note that the Representative AS does not record-route itself. 5-7. The SIP INVITE request is processed and results in the 200 OK response. 8. The subsequent SIP INVITE request in the same dialog is sent to the S‑CSCF. 9. The SIP INVITE request is forwarded directly to the AS#1 according to the Route information in the request message. 10-11. The SIP INVITE request is processed and results in the 200 OK response. J.3 Dynamic assignment of AS by S‑CSCF caching J.3.1 Concept of Dynamic assignment of AS by S‑CSCF caching The proposed solution "Dynamic assignment of AS by S‑CSCF caching" is based on standard SIP session control combined with a new S‑CSCF caching functionality. This solution is re-using the DNS (IETF RFC 1035) mechanism and supports only the ISC interface. J.3.2 Procedures related to Dynamic assignment of AS by S‑CSCF caching Figure J.3.2.1 shows the procedure for allocating an AS by the first request of a service to an IMS registered user: Figure J.3.2.1: Assignment of AS via DNS query during first service request 1. After IMS registration a user sends an initial request to the S‑CSCF for requesting a service (served by an AS). 2. The S‑CSCF performs the DNS query on the server name and resolves one (or a prioritised list) of the IP address(es), which represents a physical or logical AS. 3. The S‑CSCF caches the IP address of the assigned AS and stores it during the IMS registration period of the user. 4. The S‑CSCF routes the request to the assigned AS. (Depending on the service the AS could read/write/store user data, e.g. using Sh interface). Figure J.3.2.2 shows how subsequent service requests are routed directly to the assigned AS during the registration period of the IMS user: Figure J.3.2.2: S‑CSCF has stored assigned AS for following service requests 5. The IMS user requests the service again and sends an initial request to the S‑CSCF. 6. The S‑CSCF has stored the IP Address (or a prioritised list) of the assigned AS. There is no longer need to perform a DNS query. 7. The S‑CSCF routes the request to the assigned AS. (Depending on the service the AS can reuse prior stored user data). The AS pre-assignment and storage could be also done after downloading the service profile during the user registration procedure. Annex K (normative): Inter-IMS Network to Network Interface between two IM CN subsystem networks K.1 General This annex describes the Inter-IMS Network to Network Interface which is used to interconnect two IM CN subsystem networks. K.2 Overall architecture Figure K.1 illustrates an high-level architecture diagram showing the Inter-IMS Network to Network Interface (II-NNI) between two IM CN subsystem networks. Figure K.1: Inter-IMS Network to Network Interface between two IM CN subsystem networks The protocols over the two reference points Ici and Izi make up the Inter-IMS Network to Network Interface. The Ici reference point allows IBCFs to communicate with each other in order to provide the communication and forwarding of SIP signalling messaging between IM CN subsystem networks. The Izi reference point allows TrGWs to forward media streams between IM CN subsystem networks. NOTE: Whenever the Inter-IMS Network to Network Interface is used to interconnect two IM CN subsystem networks belonging to different security domains security procedures applies as described in TS 33.210 [20]. Annex L (normative): Aspects for use of Common IMS in 3GPP2 systems L.1 General This clause describes the main concepts that are used when providing IMS services using 3GPP2 IP‑CAN as defined in 3GPP2 X.S0011 [60] or using 3GPP2 radio access with CDMA 1X as defined in 3GPP2 C.S0001-D [61] and/or HRPD as defined in 3GPP2 C.S0024-A [62] and/or UMB as defined in 3GPP2 C.S0084-000 [63] radio access. L.2 Definitions L.2.1 HSS For 3GPP2 systems, the term "HSS" is used to represent the Home AAA entity plus the Databases to which it interfaces. The HSS in 3GPP2 systems does not include the HLR functionality. Figure x shows the HSS in 3GPP2 systems. Figure L.1: HSS in 3GPP2 L.3 Mobility related concepts when using 3GPP2 Packet Data Subsystem L.3.1 General The Mobility related procedures for 3GPP2 systems are described in 3GPP2 X.S0011 [60] and the IP address management principles are described in 3GPP2 X.S0011 [60]. As specified by these procedures, the UE acquires the necessary IP address(es) to access IM CN system. The restriction on using a single IP address for IMS Local Breakout functionality as defined in clause 5.1.0 does not apply to 3GPP2 based systems. L.3.2 Procedures for P‑CSCF discovery This clause describes the P‑CSCF discovery procedures applicable for 3GPP2 systems. These procedures follow the generic mechanisms described in clause 5.1.1 with the following exception: - Discovery of P‑CSCF as part of establishment of connectivity towards the 3GPP2 IP‑CAN is not supported. L.4 QoS related concepts when using 3GPP2 Packet Data Subsystem The QoS procedures follow the generic requirements described in clause 4.2.5 with the following modification to bullet 6.e in clause 4.2.5: - The initiation of any required end-to-end QoS signalling, negotiation and resource allocation processes at different network segments may take place before or after the initiation and delivery of a session set-up request. L.5 IP version support in IMS when using 3GPP2 Packet Data Subsystem The UE shall support IPv4 only or both IPv4 and IPv6. L.6 Address and identity management concepts L.6.1 Deriving IMS identifiers ISIM is the primary source for IMS identity information. If an ISIM is not present, the UE shall use the IMS credentials stored in the IMC to access IMS. If no IMS credentials are stored in the IMC, then temporary credentials shall be derived as follows: - a Temporary Private User Identity shall be derived from the Mobile Station ID (IMSI, MIN or IRM), which allows for uniquely identifying the user within the operator's network; - a Temporary Public User Identity shall be derived from the MSID and shall be used in SIP registration procedures. The Temporary Public User Identity shall take the form of a SIP URI (as defined in RFC 3261 [12] and RFC 3986 [13]). It is strongly recommended that the Temporary Public User Identity is set to barred for SIP non-registration procedures. The following applies if the Temporary Public User Identity is barred: - A Temporary Public User Identity shall not be displayed to the user and shall not be used for public usage such as displaying on a business card. - The Temporary Public User Identity shall only be used during the SIP initial registration, re-registration and mobile initiated de-registration procedures. - The implicitly registered Public User Identities shall be used for session handling, in non-registration SIP messages and may be used at subsequent SIP registration procedures. - A Temporary Public User Identity shall only be available to the CSCF and HSS nodes. NOTE: If a Temporary Public Identity is used, the user can not initiate any sessions until the implicitly registered public identities are available in the UE. When a Temporary Public Identity has been used to register an IMS user, the implicit registration will ensure that the UE, P‑CSCF & S‑CSCF have Public User Identity(s) for all IMS procedures after the initial registration has been completed. L.7 Relationship to 3GPP Generic User Profile (GUP) 3GPP GUP is not applicable to 3GPP2 systems. Annex M (informative): IMS Local Breakout M.1 P‑CSCF located in visited network M.1.1 Description M.1.1.0 General The architectures and flows in this clause are only showing EPS and 5GS. The principles shown are also applicable for GPRS Core Network. For 5GS, there is no support for roaming interface between vPCF and hPCF in this Release of the specification. M.1.1.1 Architecture The architecture for this scenario is shown in figure M.1.1.1. Figure M.1.1.1: EPS/5GS architecture for IMS Local Breakout with P‑CSCF located in visited network Optionally IBCF and TrGW may be present in the HPLMN and VPLMN according to II‑NNI reference architecture (see Annex K) and thus there will be an Ici reference point between the IBCFs and an Izi reference point between the TrGWs. M.1.1.2 Flow for originating session The information flows for originating session for this scenario is illustrated in figure M.1.1.2. Figure M.1.1.2: Example scenario with P‑CSCF located in visited network and IBCF and TrGW in home network 1. The UE obtains an IP address from the EPS/5GS in the visited network according to the procedures specified by TS 23.401 [70] / TS 23.502 [94]. 2. The EPS/5GS obtains default PCC rules and associates it with this IP‑CAN. The V‑PCRF/vPCF and H‑PCRF (in the case of S9 in EPS) provides these rules according to TS 23.203 [54] / TS 23.503 [95]. 3. Using the IP address obtained in step 1, the UE performs IMS registration. This SIP message is routed by the EPS/5GS in the visited network through the P‑CSCF in the visited network, which was discovered according to the procedures in Annex E/Annex Y, to the S‑CSCF in the home network, via IBCFs also in the visited and home network if deployed. 4. Using the IP address obtained in step 1 in the SDP, the UE initiates a SIP session. The INVITE request is routed by the EPS/5GS in the visited network through the P‑CSCF to the IBCF in the home network. 5. If the IBCF decides to route media to home based on operator policy, it then allocates resources in TrGW and alters the offered SDP accordingly. NOTE 1: Per operator policy, the IBCF may have other reasons than only address translation to route media home. 6. IBCF sends the INVITE further to the S‑CSCF and S‑CSCF continues the session towards the far-end. 7 The 200 OK received from the far-end is sent by the S‑CSCF to the IBCF. If a TrGW was allocated in step 5, then IBCF changes the SDP answer accordingly. NOTE 2: Step 7a) If the IBCF decides to anchor the call when it has received SDP answer (e.g. because the MRFP needs to be involved in the user plane or because of other reasons), then step 5 in the procedure starts again and it re-INVITEs the far-end. 8. The 200 OK is sent further on to the P‑CSCF and via EPS/5GS in the visited network towards the UE. 9. The P‑CSCF in the visited network also provides the session information to the V‑PCRF/vPCF in the visited network. 10. The H‑PCRF in the home network provides PCC rules to the V‑PCRF in the visited network when S9 is supported. The V‑PCRF/vPCF in the visited network provisions PCC rules in the EPS/5GS in the visited network 11. Media exchanged between the UE and the far end is now routed either between the 5GS in the visited network and the far end, thus achieving local breakout mode of operation; or between the EPS/5GS in the visited network via the TrGW in the home network if IBCF was deployed. NOTE 3: Per operator policy, the IBCF can route media home due to other reasons than stated in this specification, thus also giving the possibility to get home routed mode of operation. M.2 P‑CSCF located in home network M.2.1 Description M.2.1.0 General The architectures and flows in this clause are only showing EPS and 5GS. The principles shown are also applicable for GPRS Core Network. This scenario assumes that both IMS signalling and IMS media traffic are anchored in EPS/5GS in the Visited network. UE performs a P‑CSCF discovery according to clause 5.1.1.0. M.2.1.1 Architecture The Local Breakout architecture for P‑CSCF at home is shown in figure M.2.1.1. Figure M.2.1.1-1: EPS/5GS architecture for IMS Local breakout with P‑CSCF located in home network M.2.1.2 Flow for originating session The information flows for originating session for this scenario is illustrated in figure M.2.1.2. Figure M.2.1.2: Example scenario with P‑CSCF located in home network 1 The UE obtains an IP address from the EPS/5GS in the visited network, according to the IP Connectivity Access Network procedures specified by TS 23.401 [70] /TS 23.502 [94]. 2 The serving EPS/5GS (in visited network) obtains default PCC rules and associates it with this IP‑CAN. The V‑PCRF/vPCF and H‑PCRF (in the case S9 in EPS is available) provides these rules according to TS 23.203 [54] / TS 23.503 [95]. 3 Using the IP address obtained in step 1, the UE performs IMS registration. This SIP message is IP-routed by the EPS/5GS, in the visited network, to the P‑CSCF in the home network, which was discovered according to the procedures in clause 5.1.1. When P‑CSCF receives the REGISTER message, it optionally interacts with H‑PCRF/vPCF to subscribe to signalling bearer state changes. 4 Using the IP address obtained in step 1 in the SDP, the UE initiates a SIP session. The INVITE request is routed from the EPS/5GS in the visited network, via the visited PDN to the P‑CSCF in the home network. 5 If the P‑CSCF decides to route media to home e.g. due to the need for address translation or due to other reasons, it then allocates resources in IMS AGW and alters the offered SDP accordingly. NOTE 1: Per operator policy, the P‑CSCF may have other reasons to route media to the home PLMN. 6. INVITE proceeds from P‑CSCF to S‑CSCF and onwards. 7. 200 OK is received from the far end by the P‑CSCF. If an IMS-AGW was allocated in step 5, the P‑CSCF changes the SDP answer accordingly. NOTE 2: In step 7a) if the P‑CSCF decides to route media home when it receives the SDP answer, then step 5 in the procedures starts again and it re-INVITEs the far end. 8. The P‑CSCF provides the session information to the H‑PCRF/hPCRF in the home network. 9. The 200 OK received from the far-end is sent by the P‑CSCF through the EPS/5GS in the visited network towards the UE. 10-11. Based on the IP address included in the session information, the H-PCRF in the home network provides the PCC rules to the V‑PCRF in the visited network when S9 is available. The V‑PCRF/vPCF in the visited network provisions PCC rules in the EPS/5GS in the visited network. 12. Media exchanged between the UE and the far end is now routed either between the EPS/5GS in the visited network and the far end, thus achieving local breakout mode of operation; or between the EPS/5GS in the visited network via the IMS AGW in the home network if step 5 or step 7a happened. NOTE 3: Per operator policy, the P‑CSCF may route media home due to other reasons than stated in this specification, thus also giving the possibility to get home routed mode of operation. M.2.2 Address assignment Home domain and visiting domains can not be managed to share the same private IPv4 address space and furthermore Rx and N5 do not support globally unique addresses (realm information is not supported) which would be needed to handle overlapping private IPv4 address spaces. Therefore, both the address assigned to the UE and the address of the P‑CSCF must be globally unique IP addresses. If the visited operator cannot assign a globally routable IPv4 address to an individual UE, then an IPv6 address will be assigned, if the UE supports IPv6. M.2.3 IPv4 - IPv6 interworking In a dual-stack IMS environment, an SDP offer to an UE with a single IP address may offer a media bearer over the IP version not supported by the UE. For such a call to succeed, a NAPT‑PT capable media relay is needed to be inserted in the media path. The alternatives for this are: to deploy either IMS‑AGWs either in home or visited network; or TURN servers in visited network. To use IMS‑AGWs in the home network is the way the home operator is able to control whether the IMS user plane traffic shall be routed home or not in this scenario. Thus, it is possible to do NAPT‑PT, but it will be done in the home network, which means all traffic that needs interworking will be home routed. To use TURN servers requires all IPv6 terminals to support TURN IPv4 - IPv6 interworking and that the visited network supports TURN IPv4 - IPv6 interworking. NOTE 1: Since IPv4 - IPv6 interworking must be done on IPv6 side, IPv6 originating sessions to IPv4 UEs may need an extra INVITE because first INVITE may fail. NOTE 2: An IP type PDU session for a 5GS UE will have either an IPv4 or an IPv6 address, see Annex Y. M.2.4 NAT traversal Although this scenario assumes globally routable IP addresses, there is still a possibility that end users may use residential NAT/firewalls before connecting to EPS. Annex G describes two methods how NAT/FW may be supported, if the UE accesses IMS using an IP address of a local private network. M.3 P-CSCF located in visited network and with VPLMN loopback possibility M.3.1 Description M.3.1.1 General The architecture and flows in this clause are assuming local breakout with P-CSCF in VPLMN, for further info about local breakout see clause M.1. M.3.1.2 Architecture The architecture for this scenario is shown in figure M.3.1.2. The Transit and Roaming Function and the related requirements are defined in clause 4.15a. Figure M.3.1.2: Overall architecture for IMS Local Breakout with P-CSCF located in visited network and with VPLMN loopback possibility M.3.1.3 Flow for originating session with VPLMN routing The information flows for originating session with VPLMN routing for this scenario is illustrated in figure M.3.1.3. Figure M.3.1.3: Example scenario with P‑CSCF located in visited network and with VPLMN routing 1. The roaming UE sends an INVITE request to the P-CSCF. 2. P-CSCF forwards the INVITE request to the visited IBCF. Based on operator policy, the P-CSCF adds a reference to the preferred Transit and Roaming Function. 3. This first IBCF in the VPLMN allocates a TrGW for the media and follows standard OMR procedures when forwarding the INVITE request to allow this TrGW to be bypassed if the INVITE request later returns to the VPLMN and no other intermediate nodes anchor the media before the request returns. 4-5. The intermediate network and the first IBCF in the HPLMN forward the INVITE request to the S-CSCF. Nodes in the intermediate network and the first IBCF in the HPLMN support OMR and allow their TrGWs to be bypassed. 6. The S-CSCF performs service invocation. 7. The S-CSCF performs routing decision and based on local policy and on the facts that the UE is roaming, a roaming agreement for VPLNM call routing is in place and home routing is not required, the S-CSCF decides to route back to the VPLMN for call routing. A loopback indicator is included in the INVITE request to inform the VPLMN that this request is being routed back to the VPLMN for call routing. The S-CSCF can also forward UE location information to the VPLMN. If a reference to the preferred Transit and Roaming Function is available in the request, the S-CSCF uses this information to route the session back to the VPLMN. If a reference to the preferred Transit and Roaming Function is not available, the S-CSCF uses a default derived address to the Transit and Roaming Function to route the session back to the VPLMN. If local policy requires access to BGCF routing data to make the loopback decision for a particular SIP request, then the loopback decision can be performed in the BGCF. 8-9. The IBCF in the HPLMN and the intermediate network forward the SIP request towards the indicated Transit and Roaming Function in the VPLMN. Functions in the intermediate network support OMR and allow their TrGWs (if any) to be bypassed. 10. The IBCF in the VPLMN receives the SIP request, notes that the SDP includes an alternative media address within the VPLMN that allows bypass of allocated TrGWs, applies OMR to remove any TrGWs allocated between the VPLMN and HPLMN and forwards the request to the indicated Transit and Roaming Function. 11. Based on the loopback indicator, the Transit and Roaming Function detects that this is a loopback request. The Transit and Roaming Function routes the request toward the destination network based on available SIP URI, ENUM lookup, or BGCF routing. The Transit and Roaming Function can use information such as originating UE location to select a nearby egress point for media anchoring. 12. If the called party is determined to be available in IMS, the call is routed towards the remote end through an IBCF. If the called party is determined to be available in CS, the call is broken out to CS through an MGCF. If the called party is determined to be available in VPLMN, the call is routed to the I-CSCF. The called party information is included in the Request URI when forwarding the request to the next hop. When forwarding to an IBCF, the Transit and Roaming Function ensures by means of signalling that media is anchored in the VPLMN. NOTE 1: If the called user is an IMS user of the VPLMN then the call will be routed directly to the terminating side, (i.e. I-CSCF of the VPLMN) without traversing an MGCF/IBCF. 13. The MGCF/IBCF performs normal call routing procedures to route towards the remote network/end. NOTE 2: The call will be anchored in the VPLMN (outgoing IBCF) and OMR is not provided towards the terminating side. 14. The session establishment is completed. NOTE 3: During subsequent session establishment signalling, OMR information passed back through the IBCFs and intermediate networks between the VPLMN and HPLMN cause them to release any allocated TrGWs. M.3.1.4 Flow for originating session with Home routing The information flows for originating session with the possibility for VPLMN routing, but where the HPLMN decides to perform home routing is illustrated in figure M.3.1.4. Figure M.3.1.4: Example scenario with P‑CSCF located in visited network and with home routing 1-6. These steps are done according to clause M.3.1.3. 7. The S-CSCF performs routing decision and based on the facts that the UE is roaming and home routing is required, the S-CSCF decides to route the INVITE request directly from the home network towards the terminating side. If local policy requires access to BGCF routing data to make the routing decision for a particular SIP request, then the routing decision can be performed in the BGCF. When forwarding, the S‑CSCF/BGCF ensures by means of signalling that media is anchored in the HPLMN. NOTE: The S-CSCF decides whether to perform home routing based on local policy or based on knowledge that the VPLMN does not support the loopback procedure. 8. The session establishment is completed. M.3.2 Interaction with SRVCC and ICS The IMS roaming with local breakout and possibility for loopback also applies for ICS and SRVCC as follows: - For an originating session for PS to CS SRVCC or vSRVCC that uses ATCF enhancements, the ATCF is in the signalling path between the P-CSCF and IBCF in the VPLMN (i.e. at step 2 in clause M.3.1.3). - For an originating sessions that uses CS media with MSC Server enhanced for ICS, the UE initiates a CS call setup towards the MSC Server enhanced for ICS and the MSC Server enhanced for ICS will initiate the call setup towards IMS analogous to the INVITE request from P-CSCF (i.e. at step 2 in clause M.3.1.3). As for the P-CSCF, the MSC Server enhanced for ICS may provide a reference to the preferred Transit and Roaming Function: Annex N (normative): Aspects for use of Common IMS in Fixed xDSL, Fiber and Ethernet based systems N.1 Origination procedures N.1.1 (FO#1) Fixed xDSL origination, home This origination procedure applies to users located in their home service area. As in clause 5.6.2, the UE is located in the home network, but is using an xDSL IP‑CAN to access the IM CN Subsystem. NOTE: The below flows are example flows. The detailed stage 2 description of the RACS information flows can be found in ETSI ES 282 003 [78]. Figure N.1.1: Fixed xDSL originating - home (example flow) Procedure F0#1 is as follows: 1. UE sends the SIP INVITE request, containing an initial SDP, to the P‑CSCF address determined with P‑CSCF discovery mechanism. The initial SDP may represent one or more media for a multi-media session. 2. A connection is reserved in the C‑BGF with optional NAT binding list retrieval. 3. P‑CSCF remembers (from the registration procedure) the next hop CSCF for this UE. In this case it forwards the INVITE to the S‑CSCF in the home network. 4. S‑CSCF validates the service profile and invokes any origination service logic required for this user. This includes authorization of the requested SDP based on the user's subscription for multi-media services. 5. S‑CSCF forwards the request, as specified by the S-S procedures. In addition, subject to operator policy, the S‑CSCF may insert in the request a reference location of the user, when network-provided location information is not already present. The reference location (e.g. line identification) is determined by the operator as part of the user profile and may be received from the HSS at registration. 6. The media stream capabilities of the destination are returned along the signalling path, per the S-S procedures. 7-9. S‑CSCF forwards the Offer Response message to the P‑CSCF which triggers RACS. RACS performs admission control based on the Offer and Answer parameters. RACS configures the connections in the C‑BGF based on the SDP answer and optionally requests a NAT binding list. 10. UE decides the offered set of media streams for this session, confirms receipt of the Offer Response and sends the Response Confirmation to P‑CSCF. The Response Confirmation may also contain SDP. This may be the same SDP as in the Offer Response received in step 9 or a subset. If new media are defined by this SDP, a new connection configuration shall be performed following step 2. The originating UE is free to continue to offer new media in this request or in subsequent requests using the Update method. Each offer/answer exchange will cause the P‑CSCF to repeat the RACS interactions again. 11. P‑CSCF forwards this message to S‑CSCF 12. S‑CSCF forwards this message to the terminating endpoint, as per the S-S procedure. 13. The terminating end point responds to the originating end with an acknowledgement. If Optional SDP is contained in the Response Confirmation, the Confirmation Acknowledge will also contain an SDP response. If the SDP has changed, the admission control and configure connection flows are repeated. 14-15. S‑CSCF and P‑CSCF forward the answered media towards the UE. 16-18. The destination UE may optionally perform alerting. If so, it signals this to the originating party by a provisional response indicating Ringing. This message is sent to S‑CSCF per the S-S procedure. It is sent from there toward the originating end along the signalling path. UE indicates to the originating user that the destination is ringing. 19-20. When the destination party answers, the terminating endpoint sends a SIP 200-OK final response along the signalling path to the originating endpoint, as specified by the termination procedures and the S-S procedures. 21. P‑CSCF performs the approval of QoS Commit procedure which triggers the Open Gates procedures if required. 22. P‑CSCF passes the 200-OK response back to UE. 23. UE starts the media flow(s) for this session. 24-26. UE responds to the 200 OK with an ACK message which is sent to P‑CSCF and passed along the signalling path to the terminating endpoint. N.2 Termination procedures N.2.1 (FT#1) Fixed xDSL termination, home NOTE: The below flows are example flows. The detailed stage 2 description of the RACS information flows can be found in ETSI ES 282 003 [78]. This termination procedure applies to users located in their home service area. As in clause 5.7.2, the UE is located in the home network, but has registered to the IM CN Subsystem via an xDSL IP‑CAN. Figure N.2.1: Fixed xDSL terminating - home (example flow) Procedure FT#1 is as follows: 1. UE#1 sends the SIP INVITE request, containing an initial SDP, via one of the origination procedures and the S‑S procedures, to the S‑CSCF for the terminating UE. 2. S‑CSCF validates the service profile and invokes any termination service logic required. This includes authorization of the requested SDP based on the user's subscription for multi-media services. 3. S‑CSCF remembers (from the registration procedure) the P‑CSCF address for this UE. The S‑CSCF forwards the INVITE to the P‑CSCF, which in this case is located in the home network. 4. The P‑CSCF triggers RACS which reserves a connection in C‑BGF with optional NAT binding retrieval. 5. P‑CSCF remembers (from the registration procedure) the UE address and forwards the INVITE to the UE. 6. UE determines the subset of the media flows proposed by the originating endpoint that it is capable and willing to support and responds with an Offer Response message back to the originator. The SDP may represent one or more media for a multi-media session. This response is sent to the P‑CSCF. 7. P‑CSCF triggers RACS to perform admission control based on Offer and Answer parameters. RACS configures the connection in the C‑BGF based on SDP answer with optional NAT binding retrieval. 8. P‑CSCF forwards the Offer Response message to S‑CSCF. 9. S‑CSCF forwards the Offer Response message to the originator, per the S‑S procedure. 10-15. The originating endpoint sends a Response Confirmation via the S‑S procedure, to the terminating S‑CSCF. The Response Confirmation may also contain SDP. This may be the same SDP as in the Offer Response sent in step 19 or a subset. If new media are defined by this SDP, a new interaction with the RACS (as in steps 4‑8) will be done by the P‑CSCF. The originating UE is free to continue to offer new media in this request or in a subsequent request using the Update method. Each offer/answer exchange will cause the P‑CSCF to repeat the RACS interactions (steps 4-8) again. 16-18. UE may alert the user and wait for an indication from the user before completing the session. If so, it indicates this to the originating party by a provisional response indicating Ringing. This message is sent to P‑CSCF and along the signalling path to the originating endpoint. 19. When the destination party answers, UE sends a SIP 200 OK final response to P‑CSCF. 20. P‑CSCF indicates that the resources reserved for this session should now be committed. 21-22. P‑CSCF forwards the 200 OK to S‑CSCF, following the signalling path. 23-25. The session originator responds to the 200 OK by sending the ACK message to S‑CSCF via the S‑S procedure and it is forwarded to the terminating end along the signalling path. N.3 Geographical Identifier For fixed xDSL, Fiber or Ethernet access, Geographical Identifier may be used within the IMS as described in clause E.8. Annex P (informative): Transcoding Support involving the MRFC/MRFP P.1 General P.1.1 Scope This clause describes media transcoding services involving the MRFC/MRCP applicable in the following cases: - between two IMSs; - between an IMS and other SIP based multimedia network; and - internal to an IMS servicing media endpoints with different media encoding requirements. This can arise due to support of different access technologies (e.g. wireline-wireless interworking, or support of non-3GPP wireless technologies), or from divergence in supported or allowed media encoding formats (e.g. configuration of devices to only allow certain codecs). The MRFC and MRFP act as transcoding entity in an IMS solving media encoding mismatches due to codec selection between operator networks, as well as to deal with encoding formats in a converged service environment. P.1.2 Description Application Servers can invoke the MRFC for the purpose of media transcoding between UEs that have no supported codec in common. The MRFC controls functionality in the MRFP to perform media plane transcoding. The decision to perform media transcoding requires knowledge of the codecs supported by the calling and called UEs. Media transcoding services can be triggered proactively (before the session request is sent to the called UE) or reactively (after the session request has been sent to and rejected by, the called UE). Proactive transcoding invocation requires prior knowledge of the codecs supported by the UE at which the called party is registered. In the case of reactive transcoding the list of codecs supported by the called UE is carried in the SIP response message. NOTE: Calling and called UEs can be in an IMS or in a CS network. SIP requests are sent by either the called UE or a network entity acting on behalf of the calling UE. SIP requests are answered by either the called UE or a network entity acting on behalf of the called UE. P.1.3 Session flows P.1.3.1 General The following use cases illustrate session procedures involving the MRFC required to support transcoding between UEs due to error cases or incompatible terminal equipment. In addition, transcoding procedures are applicable to both the originating and the terminating side of the session or even (in inter-network scenarios) in a transit network and are subject to bilateral agreements and operator configuration. A media transcoding session refers to a SIP session between an entity in the IMS control plane (hereafter referred to as the "invoking function") and the MRFC/MRFP as actual transcoding device, setup for the purpose to mediate between calling and called UEs. The SIP session between the invoking function and the MRFC is used to reserve resources at the transcoding unit, in this case the MRFP and to exchange transport address and port information. The session flows described here have been simplified by abbreviating the message exchange, e.g. by eliminating 100 trying messages. Similar session flows are available in Annex B of TS 23.218 [71]. P.1.3.2 Proactive transcoding invocation As noted above, proactive transcoding invocation requires prior knowledge of the codecs supported by the UE at which the called party is registered. At session initiation the calling UE capabilities are contained in the SDP offer, while called UE capabilities can be either preconfigured or known by other means in the network (e.g. if the control plane entity responsible for detecting the need of transcoding previously learned the codecs supported by the UE that is now called by monitoring session requests initiated by it). The following session flow illustrates proactive media transcoding: Figure P.1.3.2-1: Proactive transcoding triggering logic 1. Calling UE sends a SIP request targeted at an address registered at the called UE, including an SDP offer containing codec(s) and the IP address and TCP or UDP port number at which the calling UE wishes to receive media. 2. The SIP request is received by an IMS control plane entity responsible for detecting the need of proactive transcoding invocation. If the SDP offer does not include any codec supported by the called UE, then the invoking function is triggered to set up a SIP session with the MRFC, providing codecs and transport parameters to initiate a transcoding session. NOTE 1: If the codec(s) supported by the called UE are not known, or the SDP includes one of the codec(s) supported by the called UE, the SIP request is forwarded to the called UE without manipulation. This step is not illustrated in the figure. 3. The invoking function instructs the MRFC to: - allocate media processing resources from an MRFP entity under the MRFC's control, configured with the address and port at which the calling UE wishes to receive media, using a codec (say, codec-A) previously included by the calling UE in the SDP offer and hence known to be supported; - allocate media processing resources from the same MRFP entity to the called UE, using a codec (say, codec-B) known to be supported by the called UE; and - cause the MRFP entity to bridge those two media flows, such that media received on one will be converted to the format of and transmitted on the other. The MRFC accepts the transcoding request and contacts an MRFP to allocate the requested resources. The MRFP responds with the IP address and port number associated with each requested codec. The MRFC returns this information to the invoking function. 4. The invoking function updates the SIP request received in step 1 by appending codec-B to the list of codecs in the SDP offer (after all codecs that were previously in the offer) and altering the transport address and port information to indicate the addresses associated by the MRFP with its resources of type codec-B. 5. Called UE acknowledges the SDP offer and makes a codec selection (codec-B), providing also its actual IP address/port number information in the SDP answer. 6. Upon receipt of the answer from the called UE, the invoking function updates the session with the MRFC (providing the codec selected and the address /port information from the SDP answer). The MRFC processes the received information to configure the transcoding unit with the codec, the destination address and port towards the called UE. 7. The invoking function modifies the SDP answer to reference codec-A and the transport address and port information to indicate the addresses associated by the MRFP with its resources of type codec-A. The invoking function forwards the SIP message containing the SDP answer to the calling UE. NOTE 2: If the invoking function determines that the called UE has selected a codec from the original SDP offer, it will inform the MRFC to release the transcoding resources allocated in step 3, send a new SIP request to the called UE to change the transport address and port information to those of the calling UE and forward the unmodified SDP answer to the calling UE. These steps are not illustrated in the figure. P.1.3.3 Reactive transcoding invocation Reactive invocation of media transcoding is useful in the case that the calling and called UE support no common codec and for whatever reason transcoding is not proactively invoked. In this case the SDP offer received by the called UE contains no codecs that the called UE supports. The called UE will answer with an appropriate SIP error response, which can include information about actually supported codecs. Transcoding invoked in response to receipt of such an error response is termed Reactive. The following example session flow describes reactive invocation of media transcoding: Figure P.1.3.3-1: Reactive transcoding triggering logic 1. Calling UE sends a SIP request, including an SDP offer containing codec(s) and the IP address and TCP or UDP port number at which calling UE wishes to receive media. For some reason, e.g. because proactive invocation of media transcoding is not supported in the terminating network, transcoding is not proactively invoked. 2. The called UE or a terminating network entity (such as MGCF) determines that it does not support any codec in the SDP offer and answers with an appropriate error response. This response can include a list of codecs that the called UE can support. 3. Based on the response from called UE indicating that it does not support the offered codecs, an IMS control plane entity responsible for detecting the need of reactive transcoding invocation triggers the invoking function to set up a SIP session with the MRFC, providing codecs and transport parameters to initiate a transcoding session. 4. The invoking function instructs the MRFC to: - allocate media processing resources from an MRFP entity under the MRFC's control, configured with the address and port at which the calling UE wishes to receive media, using a codec (say, codec-A) previously included by calling UE in the SDP offer hence known to be supported by calling UE; - allocate media processing resources from the same MRFP entity to called UE, using a codec (say, codec-B) known to be supported by called UE; and - cause the MRFP entity to bridge those two media flows, such that media received on one will be converted to the format of and transmitted on the other. The MRFC accepts the transcoding request and contacts an MRFP to allocate the requested resources. The MRFP responds with the IP address and port number associated with each requested codec. The MRFC returns this information to the invoking function. 5. Based on the information received from the MRFC, the invoking function creates a new SDP offer that contains the information provided by the MRFC (codec and transport addresses). If no information about supported codecs was available from the error response, the invoking function offers all codecs supported by the transcoding device. It sends this offer to the called UE. 6. Called UE acknowledges the SDP offer and makes a codec selection, providing in the SDP answer the IP address and TCP or UDP port at which it wants to receive media. 7. Upon receipt of the answer from the called UE, the invoking function updates the session with the MRFC (providing the codec selected and the address /port information from the SDP answer). The MRFC processes the received information to configure the transcoding unit with the codec, the destination address and port towards the called UE. 8. The invoking function modifies the SDP answer received from the called UE such that it refers to codec-A and the MRFP address and port number associated with it in step 4 and sends this message to the calling UE. The session between the end points is now established with the media flow traversing the transcoding device. Annex Q (normative): Optimal media routing Q.1 General The purpose of optimal media routing (OMR) is to identify and remove unnecessary media functions from the media path for each media stream associated with a session. The IP Multimedia Subsystem has the option to deploy media functions such as TrGWs on the media path associated with each media stream associated with a session. These media functions can perform only transport level functions such as firewall or NAT, or can also perform application level functions such as transcoding or conferencing. These media functions are typically allocated proactively during SDP offer/answer signalling within a session since it is unknown which of the functions are actually needed for a media stream until the SDP offer/answer signalling completes. For example, a transcoder can be allocated during session establishment but whether transcoding is needed is determined once the SDP offer reaches the far endpoint. In another example, the IBCFs at the boundary of a network allocate TrGWs to protect media functions within the network or to provide address translation to the private address space used within the network, however it might be determined later during session establishment that no media resources are needed within the network, thus making the TrGWs unnecessary. Any SIP signalling entity within the IMS network that allocates, to a session flow, a media function that might later be determined to be unnecessary may implement the procedures in this Annex to assist in the removal of unnecessary media functions. In particular, any entity with an IMS-ALG may implement the OMR algorithm. This includes the IBCF (see Annex I) and P-CSCF (see Annex G). Any AS performing as a B2BUA controlling media resources may also implement the OMR procedures. Annex Q shows every controlling OMR entity as an IMS-ALG and every controlled media resources as a TrGW, but other options are possible. An MGCF or AS performing as UA may also implement OMR procedures to assist in the removal of unnecessary media functions in some cases. MGCF and AS procedures can be derived from the procedures in this annex by collocating an IMS-ALG with the MGCF or AS. The OMR procedures identify and name the IP address realm used for each media path segment among UAs and TrGWs. The terms IP realm and realm are equivalent to the term IP address realm in this annex. An IP realm name is associated with each set of IP endpoints that are mutually reachable via IP routing and without address translation. Endpoints in different IP realms usually require allocation of a TrGW between those IP realms for connectivity and possibly for NAT. When endpoints in different IP realms are mutually reachable without allocation of a TrGW, then OMR procedures may use provisioned information about such connected IP realms to determine possible optimal media paths through these connected realms. NOTE: Connected IP realms are particularly useful when there are bilateral IP transport connections between operator networks, e.g. using IP tunnels via IP transport networks. In this case, each operator network can manage its own IP realm for inter-operator interconnection and provision the names of connected IP realms. Without the concept of connected IP realms, each bilateral connection (e.g. IP tunnel) in this example would need to be defined as its own IP realm. IMS-ALGs implementing OMR shall include information in forwarded SDP regarding IP realm, codec and IP connectivity information for TrGWs on the media path to assist in bypassing unnecessary TrGWs. A TrGW can be bypassed when it is not required to transcode, when it is unnecessary to protect a network resource and when a successive TrGW on the path is reachable by a previous TrGW on the path via a common IP realm. The OMR procedures have the following additional characteristics: - They build on the ALG NAT traversal model that is an alternative to the ICE NAT traversal model. - They usually complete within a single end-to-end SDP offer/answer transaction. Some transcoding scenarios require additional signalling to complete optimisation. - They apply independently to each media stream established by an SDP offer/answer transaction. - They apply to media streams established between any types of endpoints (e.g. UEs, media servers, media gateways). - They apply to media streams established using SIP 3pcc procedures. OMR applies to the endpoints of an SDP offer/answer transaction and not necessarily to the endpoints of a SIP dialog. - They apply separately to each dialog when forking occurs. An IMS-ALG shall delay the release of a TrGW for OMR until it is clear that no forked dialog needs the TrGW. - For early media negotiated with the same SDP as normal media, the OMR procedures have no direct impact on early media handling since path modifications are in place as soon as the SDP offer/answer transaction completes. An IMS-ALG can anchor in place any TrGW needed for blocking of unauthorized early media by removing OMR SDP extension attributes as necessary. For separate early-session disposition SDP the OMR algorithm shall not be applied. - They do not require endpoints to support new procedures, although some additional optimisations are possible in some special cases. Q.2 Procedures and flows Q.2.1 SDP extension Each OMR-capable entity on the signalling path of an SDP offer/answer transaction shall be able to manipulate an SDP offer to describe the following information about the IP realm associated with each known media path segment for each media line: - a unique name for the IP realm on the subsequent media path segment, - the position of the IP realm instance in the media path, - connection/port data for the corresponding media resource in the IP realm on the subsequent media path segment, - sufficient information to reconstruct the codec list for the previous media path segment if the codec list has changed (e.g. to offer transcoding options). Each instance of such information is called an IP realm instance. Each IP realm instance associated with a media line in an SDP offer is a visited realm instance. If a signalling entity on the path controls a media resource with connection to an alternate IP realm not already associated with a media line, the SDP may also include the same information about the alternate IP realm, called a secondary realm instance. An OMR-capable entity that forwards an SDP offer with OMR specific attributes for a media line shall ensure that the forwarded SDP offer includes a visited realm instance that matches the connection information for the media line in the forwarded SDP offer. This SDP offer shall also include information that makes it possible for a subsequent OMR-capable entity to detect if an intermediate entity has changed any codec information for the media line without also changing the connection and port information for the media line. To bypass one or more previous TrGWs for a media line, an IMS-ALG shall include an IP realm instance with valid connection information for the earliest acceptable IP realm in the forwarded SDP answer. It shall be possible to identify the visited or secondary realm instance from the SDP offer that corresponds to the IP realm instance in the SDP answer. Globally reachable IPv6 addresses shall be associated with a reserved realm name to assure that networks are not artificially isolated. Globally reachable IPv4 addresses shall be associated with another reserved realm name. Networks with private or restricted reachability shall have unique realm names. Q.2.2 General IMS-ALG procedures IMS-ALGs supporting OMR shall be able to support the call flows in clauses Q.2.4 and Q.2.5 according to local policy. These call flows describe the simplest scenarios and should be treated as examples. It shall be possible to support the addition of IMS-ALGs and TrGWs in any flow between any of the entities shown whenever such additions are reasonable. It shall be possible to support any interconnection of these flows whenever it is reasonable to do so. Additional information can be present in the forwarded SDP messages to support these more complex scenarios. The following high level procedures apply to all of the scenarios. Upon receiving an initial SDP offer, the IMS-ALG in the signalling path shall perform the following for each media line: - If the SDP offer includes realm instance information for the media line and the latest visited realm instance is not for the connection information in the incoming SDP offer, then the IMS-ALG shall remove all OMR specific SDP attributes from the SDP offer. NOTE: A non-OMR-capable IMS-ALG might have inserted a TrGW without removing unrecognized OMR specific SDP attributes. - If the SDP offer includes realm instance information that corresponds to the connection information in the incoming SDP offer, then the IMS-ALG shall attempt to verify that no intermediate entity has changed the codec information in the SDP offer since it was generated by the previous OMR-capable entity. If the IMS-ALG cannot verify that the codec information is unchanged, it shall remove all OMR specific SDP attributes from the SDP offer. - Determine according to local policy if a TrGW is required in the user plane path for a purpose unrelated to transcoding or NAT, e.g. lawful intercept. Visited realm and secondary realm instances for previous user plane segments shall be removed to prevent subsequent signalling entities from bypassing the media resource. - Based on the outgoing IP realm, IP realm accessibility from controlled TrGWs and information from visited realm and secondary realm instances in the received SDP offer, the IMS-ALG shall determine whether to allocate a TrGW and whether one or more previous TrGWs can be bypassed. If transcoding is also supported, the IMS-ALG may also consider whether to modify the codec set, move the transcoding point and which transcoding procedure to apply, if any. - Allocate a TrGW and transcoder as necessary. If the IMS-ALG allocates a transcoder, it shall include information about the transcoding options in the visited realm instance for the outgoing realm. - Optionally allocate one or more secondary TrGWs according to local policy. - Forward the SDP offer after modifying the connection, port, codec, visited realm instances and secondary realm instances as appropriate. If the IMS-ALG added a TrGW it shall: - Add a visited realm instance with the connection/port and IP realm on the the previous media path segment if no visited realm instances have been received and local policy allows potential bypass of the TrGW by subsequent entities. - Add a visited realm instance with the connection/port and IP realm on the the subsequent media path segment. Upon receiving an initial SDP answer, the IMS-ALG in the signalling path shall perform the following for each media line: - Based on the selected codec, connection information and IP realm instances in the SDP answer and information from the received SDP offer, the IMS-ALG shall determine whether to deallocate any TrGW(s) and whether a second SDP offer/answer transaction is needed to send updated connection information towards the SDP answerer. - Initiate and complete the second SDP offer/answer transaction if required. - Determine how to modify the forwarded SDP answer to signal the bypass of previous TrGWs/transcoders, if any. - Deallocate any unused TrGW/transcoder as necessary. - Forward the modified SDP answer to signal other TrGW bypass decisions. The end-to-end user plane path selected via the OMR procedures during the initial SDP offer-answer exchange should not be modified by subsequent SDP offer-answer exchanges, unless the new SDP offer-answer exchanges requires a new media path (e.g. transcoding, adding media, playing announcements). NOTE: If the media path is changed, there is a risk of speech gaps and/or media drops during the media path switch. Q.2.3 Common flows Q.2.3.1 IMS-ALG allocates a TrGW When an IMS-ALG allocates a TrGW during forwarding of an SDP offer without performing any media optimisations and is not bypassed during subsequent processing of the SDP answer, OMR has no impact on the standard call flow except for the addition of some SDP extension information to the SDP messages. If an IMS-ALG does not support OMR then it will treat all OMR extension attributes as unrecognized SDP information. If an IMS-ALG that does not support OMR inserts a TrGW in the media path and removes unrecognized OMR attributes from the SDP before forwarding, then the IMS-ALG will remove any OMR extension attributes from the forwarded SDP, thus effectively anchoring its TrGW in the media path and preventing further optimisation of the user plane segment prior to this point. If an IMS-ALG that does not support OMR inserts a TrGW in the path without removing unrecognized OMR attributes, then the subsequent OMR-capable entity in the signalling path shall remove OMR extension attributes from the SDP offer before handling. Q.2.3.2 IMS-ALG does not allocate a TrGW When an IMS-ALG does not allocate a TrGW during forwarding of an SDP offer and does not perform any media optimisations during processing of either the SDP offer or SDP answer, it transparently passes any SDP extensions for OMR in forwarded SDP messages. OMR has no impact on the standard call flow except for the addition of some SDP extension information to the SDP messages. If an IMS-ALG that does not support OMR and does not allocate a TrGW upon receipt of an SDP offer transparently forwards the SDP offer, including unrecognized SDP attributes related to OMR, then it is possible for other OMR-compliant IMS-ALGs to perform user plane optimisations. If an IMS-ALG that does not support OMR and does not allocate a TrGW upon receipt of an SDP offer removes unrecognized SDP attributes from the forwarded SDP offer, then further optimisation of the user plane segment prior to this point is not possible. Q.2.3.3 IMS-ALG bypasses its TrGW and one or more prior TrGWs Figure Q.1 applies when an IMS-ALG (IMS-ALG2) recognizes that it can avoid allocating a TrGW because an address for the outgoing IP realm is already available from a previous user plane segment. Thus it can bypass its own TrGW and one or more prior TrGWs. A common application of this scenario is when realm R1 is the internet and realm R2 is a private network isolated by the two IMS-ALGs. If no media resources are required within the network of realm R2 then there is no need to allocate TrGWs. IMS-ALG1 must initially allocate a TrGW since it does not know the ultimate destination of the SDP offer. NOTE: Realm instances shown in italics in this and subsequent figures indicate their optionality. For example, an SDP offer from a UE will contain no realm instances. Figure Q.1: IMS-ALG bypasses its TrGW and one or more prior TrGWs 1. IMS-ALG1 receives an SDP offer from realm R1. The SDP offer can include IP realm instances Rx associated with prior user plane segments and can include a visited realm instance for incoming realm R1. If realm instances are included in the received SDP offer, the IMS-ALG1 (and subsequent IMS-ALGs) verify that intermediate signalling entities have not modified the SDP. 2. IMS-ALG1 allocates TrGW1 to provide a NAT between R1 and R2. 3. IMS-ALG1 forwards connection information for TrGW1 in the SDP offer along with prior IP realm instance information Rx and visited realm instances for both the incoming and outgoing realms. IMS-ALG1 creates a new visited realm instance for the incoming realm if it was not present in the received SDP offer. 4. Since an IP address already exists within a visited realm instance for the outgoing realm R1, the IMS-ALG2 can avoid allocating a TrGW and can bypass a previous TrGW1. 5. IMS-ALG2 forwards connection information from the SDP offer in step 1 (IP1), which is valid in the outgoing realm R1. The forwarded SDP offer retains those IP realm instances that remain connected to the media path. 6. IMS-ALG2 receives an SDP answer with valid connection information (IP3) in realm R1. 7. IMS-ALG2 forwards the SDP answer to IMS-ALG1 after including an IP realm instance for the connection information from the SDP answer in step 6. The IP realm instance in the SDP answer identifies a corresponding realm instance from the SDP offer associated with the same IP realm, thus uniquely identifying the TrGWs to be bypassed. The connection information in the forwarded SDP answer cannot be used by the receiving IMS-ALG to establish this segment of the media path. 8. IMS-ALG1 de-allocates TrGW1 since there is no valid connection information available in the SDP answer for realm R2. 9. IMS-ALG1 forwards the SDP answer after modifying the connection information to correspond to the IP realm instance received in step 7. 10. A user plane connection is now established in realm R1 without the need to allocate any additional TrGWs. Q.2.3.4 IMS-ALG bypasses its TrGW using secondary realm from prior IMS-ALG Figure Q.2 applies when an IMS-ALG (IMS-ALG2) recognizes that it can avoid allocating a TrGW by using a secondary realm instance from a prior IMS-ALG. Figure Q.2: IMS-ALG bypasses its TrGW using secondary realm from prior IMS-ALG 1. IMS-ALG1 receives an SDP offer from realm R1. The SDP offer can include IP realm instances Rx associated with prior user plane segments and can include a visited realm instance for incoming realm R1. 2. IMS-ALG1 allocates TrGW1 to provide a NAT between R1 and R2. IMS-ALG1 also allocates TrGW2 to provide a NAT between R1 and alternate realm R3. 3. IMS-ALG1 forwards connection information for TrGW1 in the SDP offer along with prior IP realm instance information Rx, visited realm instances for both the incoming and outgoing realms R1 and R2 and a secondary realm instance for realm R3. 4. Since an IP address already exists within a secondary realm instance for the outgoing realm R3, the IMS-ALG2 can avoid allocating a TrGW. 5. IMS-ALG2 forwards the SDP offer with connection information from the secondary realm instance received in step 3 (IP3), which is valid in the outgoing realm R3. The forwarded SDP offer retains those IP realm instances that remain connected to the media path. 6. IMS-ALG2 receives an SDP answer with valid connection information (IP4) in realm R3. 7. IMS-ALG2 forwards the SDP answer to IMS-ALG1 after including an IP realm instance for the connection information from the SDP answer in step 6. The connection information in the forwarded SDP answer cannot be used by the receiving IMS-ALG to establish this segment of the media path. 8. IMS-ALG1 de-allocates TrGW1 since there is no valid connection information available in the SDP answer for realm R2. IMS-ALG1 retains TrGW2 to maintain the user plane connection via R3. 9. IMS-ALG1 forwards the SDP answer after modifying the connection information to correspond to the IP address of the TrGW2 in realm R1. 10. A user plane connection is now established with one segment in realm R1 and a second segment in realm R3, mediated by TrGW2. Q.2.3.5 IMS-ALG bypasses one or more prior TrGWs using a secondary realm Figure Q.3 applies when an IMS-ALG (IMS-ALG2) determines that it must allocate a TrGW under its control but can bypass previously allocated TrGWs by allocating a TrGW with access to an alternate realm (not the incoming one) associated with an earlier user plane segment. Figure Q.3: IMS-ALG bypasses one or more prior TrGWs using a secondary realm 1. IMS-ALG1 receives an SDP offer from realm R1. The SDP offer can include IP realm instances Rx associated with prior user plane segments and can include a visited realm instance for incoming realm R1. 2. IMS-ALG1 allocates TrGW1 to provide a NAT between R1 and R2. 3. IMS-ALG1 forwards connection information for TrGW1 in the SDP offer along with prior IP realm instance information Rx and visited realm instances for both the incoming and outgoing realms. 4. If IMS-ALG2 controls a TrGW (TrGW2) with access to realm R1, then IMS-ALG2 can use the visited realm instance for R1 to establish the incoming user plane segment, rather than using the connection information for TrGW1 from the received SDP offer in step 3. IMS-ALG2 allocates TrGW2 to provide a NAT between alternate realm R1 and realm R3. 5. IMS-ALG2 forwards the SDP offer with connection information for TrGW2 in realm R3 along with IP realm instances Rx and the visited realm instances for R1 and R3. 6. IMS-ALG2 receives an SDP answer with valid connection information (IP4) in realm R3. 7. IMS-ALG2 forwards the SDP answer to IMS-ALG1 after including an IP realm instance for the TrGW2 address in realm R1. The connection information in the forwarded SDP answer cannot be used by the receiving IMS-ALG to establish this segment of the media path. 8. IMS-ALG1 de-allocates TrGW1 since there is no valid connection information available in the SDP answer for realm R2. 9. IMS-ALG1 forwards the SDP answer after modifying the connection information to correspond to the IP address of the TrGW2 in realm R1. 10. A user plane connection is now established with one segment in realm R1 and a second segment in realm R3, mediated by TrGW2. Q.2.3.6 IMS-ALG bypasses TrGWs performing NAT traversal Figure Q.4 applies when an IMS-ALG (IMS-ALG2) that is performing NAT traversal for a terminating UA recognizes that the offering UA is in the same private realm behind a NAT, so that all TrGWs can be bypassed and a direct user plane connection established between the endpoints. Figure Q.4: IMS-ALG bypasses TrGWs performing NAT traversal 1. IMS-ALG1 receives an SDP offer from UA1 in private realm R1 behind a NAT. 2. IMS-ALG1 allocates TrGW1 to provide NAT traversal between private realm R1 and realm R2. TrGW1 can only be bypassed if the answering UA2 is in the same private realm R1. 3. IMS-ALG1 forwards connection information for TrGW1 in the SDP offer along with visited realm instances for the private realm R1 for UA1 and the outgoing realm R2. 4. Since an IP address already exists within the visited realm instance for the private realm R1 for UA2, the IMS-ALG2 can avoid allocating a TrGW and can bypass a previous TrGW1. 5. IMS-ALG2 forwards connection information from the SDP offer in step 1 (IP1), which is valid in the outgoing private realm R1 behind the NAT. 6. IMS-ALG2 receives an SDP answer with valid connection information (IP3) in realm R1. 7. IMS-ALG2 forwards the SDP answer to IMS-ALG1 after including an IP realm instance for the connection information from the SDP answer in step 6. The connection information in the forwarded SDP answer cannot be used by the receiving IMS-ALG to establish this segment of the media path. 8. IMS-ALG1 de-allocates TrGW1 since there is no valid connection information available in the SDP answer for realm R2. 9. IMS-ALG1 forwards the SDP answer after modifying the connection information to correspond to the IP realm instance received in step 7. 10. A user plane connection is now established in realm R1 without the need to allocate any TrGWs. Q.2.5 Flows with transcoding Q.2.5.1 Proactive transcoding where transcoding is required When an IMS-ALG supporting OMR allocates a TrGW during forwarding of the SDP offer for proactive transcoding with resource reservation, if subsequent IMS-ALGs do not replace the transcoder and the answering side signals in the SDP answer that transcoding is required, then the IMS-ALG retains the TrGW for transcoding and anchors it in the user plane path. The call flow is the same as the usual call flow for TrGW insertion except for the addition of some SDP extension information to the SDP messages. Q.2.5.2 Proactive transcoding where transcoding not required Figure Q.5 applies when IMS-ALG1 allocates a TrGW during forwarding of the SDP offer for proactive transcoding with resource reservation, IMS-ALG1 is the last signalling entity on the path before UA2 and UA2 signals in the SDP answer that transcoding is not required. UA2 ignores unrecognized OMR extension attributes. A second SDP offer/answer transaction is required to remove the transcoder from the path. As an alternative to the procedure shown, the IMS-ALG1 may forward connection information for a prior user plane segment without transcoding options while including an IP realm instance for the transcoding TrGW. This alternative avoids a second SDP offer/answer transaction if transcoding is not required, but does include a second SDP offer/answer transaction if transcoding is required. NOTE: Realm instances shown in bold in this and subsequent figures include codec change information. Figure Q.5: Proactive transcoding where transcoding not required 1. IMS-ALG1 receives an SDP offer from realm R1. The SDP offer can include IP realm instances Rx associated with prior user plane segments and can include a visited realm instance for incoming realm R1. The realm instances in this and other messages in the figure are shown in italics to indicate their optionality. For example, an SDP offer from a UE will contain no realm instances. If realm instances are included in the received SDP offer, the IMS-ALG1 (and subsequent IMS-ALGs) verify that intermediate signalling entities have not modified the SDP. 2. IMS-ALG1 allocates TrGW1 to offer transcoding options to UA2. 3. IMS-ALG1 forwards connection information for TrGW1 in the SDP offer along with prior IP realm instance information Rx and visited realm instances for both its incoming and outgoing user plane segments. IMS-ALG1 creates a new visited realm instance for the incoming realm if it was not present in the received SDP offer. The visited realm instance for the outgoing side includes information about the codec changes associated with TrGW1. 4. UA2 selects one of the original codecs, i.e. transcoding is not needed. In response to the SDP offer, UA2 sends an SDP answer to IMS-ALG1 with connection information for its address in realm R1. 5. IMS-ALG1 determines that the transcoder is not needed and forwards a second SDP offer to UA2 with connection information from a prior realm. This SDP offer includes those IP realm instances that remain options without transcoding. 6. UA2 updates its remote connection information and responds with a new SDP answer. 7. IMS-ALG1 de-allocates TrGW1. 8. IMS-ALG1 forwards the SDP answer with connection information for UA2 in realm R1. 9. A user plane connection is now established in realm R1 without use of any TrGWs. Q.2.5.3 IMS-ALG bypasses prior unrequired proactive transcoder Figure Q.6 applies when IMS-ALG1 allocates a TrGW during forwarding of the SDP offer for proactive transcoding with resource reservation, another IMS-ALG (IMS-ALG2) is the last signalling entity on the path before UA2, IMS-ALG2 must allocate a TrGW to provide NAT and UA2 signals in the SDP answer that transcoding is not required. There may be additional IMS-ALGs between IMS-ALG1 and IMS-ALG2. This scenario avoids the need for a second SDP offer/answer transaction as required in clause Q.2.5.3 and clause Q.2.5.5. IMS-ALG2 signals to IMS-ALG1 in the SDP answer to bypass the transcoder. Figure Q.6: IMS-ALG bypasses prior unrequired proactive transcoder 1. IMS-ALG1 receives an SDP offer from realm R1. The SDP offer can include IP realm instances Rx associated with prior user plane segments and can include a visited realm instance for incoming realm R1. 2. IMS-ALG1 allocates TrGW1 to offer transcoding options to UA2. 3. IMS-ALG1 forwards connection information for TrGW1 in the SDP offer along with prior IP realm instance information Rx and visited realm instances for both its incoming and outgoing user plane segments. The visited realm instance for the outgoing side includes information about the codec changes associated with TrGW1. 4. IMS-ALG2 allocates TrGW2 to provide a NAT between R1 and R2. 5. IMS-ALG2 forwards the SDP offer with connection information for TrGW2 in realm R2 along with IP realm instances for prior user plane segments. 6. UA2 selects one of the original codecs, i.e. transcoding is not needed. In response to the SDP offer, UA2 sends an SDP answer to IMS-ALG2 with connection information for its address in realm R2. 7. IMS-ALG2 determines that transcoding is not necessary. 8. IMS-ALG2 forwards the SDP answer to IMS-ALG1 after including an IP realm instance for the TrGW2 address in realm R1. The connection information in the forwarded SDP answer cannot be used by the receiving IMS-ALG to establish this segment of the media path. 9. IMS-ALG1 de-allocates transcoder TrGW1 since there is no valid connection information available in the SDP answer. 10. IMS-ALG1 forwards the SDP answer after modifying the connection information to correspond to the IP address of the TrGW2 in realm R1. 11. A user plane connection is now established with one segment in realm R1 and a second segment in realm R2, mediated by TrGW2. Q.2.5.4 IMS-ALG bypasses its TrGW and prior unrequired proactive transcoder Figure Q.7 applies when IMS-ALG1 allocates a TrGW during forwarding of the SDP offer for proactive transcoding with resource reservation, another IMS-ALG (IMS-ALG2) is the last signalling entity on the path before UA2, IMS-ALG2 does not need to allocate a TrGW to provide NAT and UA2 signals in the SDP answer that transcoding is not required. There may be additional IMS-ALGs between IMS-ALG1 and IMS-ALG2. A second SDP offer/answer transaction is required to remove the transcoder from the path. The scenario allows IMS-ALG2 to initiate the second SDP offer/answer transaction rather than requiring IMS-ALG1 to do this, thus saving some messaging. As an alternative to the procedure shown, the IMS-ALG1 may forward connection information for a prior user plane segment without transcoding options while including an IP realm instance for the transcoding TrGW. This alternative avoids a second SDP offer/answer transaction if transcoding is not required, but does include a second SDP offer/answer transaction if transcoding is required. Figure Q.7: IMS-ALG bypasses its TrGW and prior unrequired proactive transcoder 1. IMS-ALG1 receives an SDP offer from realm R1. The SDP offer can include IP realm instances Rx associated with prior user plane segments and can include a visited realm instance for incoming realm R1. 2. IMS-ALG1 allocates TrGW1 to offer transcoding options to UA2. 3. IMS-ALG1 forwards connection information for TrGW1 in the SDP offer along with prior IP realm instance information Rx and visited realm instances for both its incoming and outgoing user plane segments. The visited realm instance for the outgoing side includes information about the codec changes associated with TrGW1. 4. IMS-ALG2 does not allocate a TrGW since its incoming and outgoing realms are compatible. 5. IMS-ALG2 forwards the SDP offer with no changes. 6. UA2 selects one of the original codecs, i.e. transcoding is not needed. In response to the SDP offer, UA2 sends an SDP answer to IMS-ALG2 with connection information for its address in realm R1. 7. IMS-ALG2 determines that transcoding is not necessary and sends a second SDP offer with the connection information from the visited realm instance for a prior user plane segment. This SDP offer includes those IP realm instances that remain options without transcoding. 8. UA2 updates its remote connection information and responds with a new SDP answer. 9. IMS-ALG2 determines that the prior transcoder is to be bypassed. 10. IMS-ALG2 forwards the SDP answer to IMS-ALG1 after including an IP realm instance for the UA2 address in realm R1. The connection information in the forwarded SDP answer cannot be used by the receiving IMS-ALG to establish this segment of the media path. 11. IMS-ALG1 de-allocates transcoder TrGW1 since there is no valid connection information available in the SDP answer. 12. IMS-ALG1 forwards the SDP answer after modifying the connection information to correspond to the IP address of UA2 in realm R1. 13. A user plane connection is now established in realm R1. Q.2.5.5 IMS-ALG replaces prior proactive transcoder Figure Q.8 applies when IMS-ALG1 allocates a TrGW during forwarding of the SDP offer for proactive transcoding with resource reservation and a later IMS-ALG (IMS-ALG2) chooses to bypass the transcoding offered by IMS-ALG1 and optionally offer its own transcoding options. There may be additional IMS-ALGs between IMS-ALG1 and IMS-ALG2. The flow assumes that TrGW2 must remain to providing transcoding or NAT. The call flow variant if TrGW2 is not needed can be derived by combining this flow with one of the other transcoding flows. An IMS-ALG may remove codec options, or re-instate codec options removed by a previous IMS-ALG by bypassing that IMS-ALG's TrGW if allocated. The call flow continues to apply except that TrGW allocation is optional. Figure Q.8: IMS-ALG replaces prior proactive transcoder 1. IMS-ALG1 receives an SDP offer from realm R1. The SDP offer can include IP realm instances Rx associated with prior user plane segments and can include a visited realm instance for incoming realm R1. 2. IMS-ALG1 allocates TrGW1 to offer transcoding options to UA2. 3. IMS-ALG1 forwards connection information for TrGW1 in the SDP offer along with prior IP realm instance information Rx and visited realm instances for both its incoming and outgoing user plane segments. The visited realm instance for the outgoing side includes information about the codec changes associated with TrGW1. 4. IMS-ALG2 bypasses the prior transcoder and allocates TrGW2 to provide alternate transcoding options to UA2. 5. IMS-ALG2 forwards the SDP offer with connection information for TrGW2 in realm R2 along with IP realm instances associated with all user plane segments. The forwarded SDP offer includes information about all potential transcoders so that a subsequent entity has the option to choose the earlier one if appropriate. 6. IMS-ALG2 receives an SDP answer with connection information for a valid address in realm R2. 7. IMS-ALG2 forwards the SDP answer to IMS-ALG1 after including an IP realm instance for the TrGW2 address in realm R1. The connection information in the forwarded SDP answer cannot be used by the receiving IMS-ALG to establish this segment of the media path. 8. IMS-ALG1 de-allocates transcoder TrGW1 since there is no valid connection information available in the SDP answer. 9. IMS-ALG1 forwards the SDP answer after modifying the connection information to correspond to the IP address of the TrGW2 in realm R1. 10. A user plane connection is now established with one segment in realm R1 and a second segment in realm R2, mediated by TrGW2. Q.2.5.6 Proactive transcoding without resource reservation An IMS-ALG performing proactive transcoding without resource reservation provides an indication in the forwarded SDP that an address is unavailable if transcoding is selected. Subsequent IMS-ALGs can replace this transcoder when forwarding the SDP offer according to the procedure in clause Q.2.5.6, but cannot insert a transcoding TrGW on behalf of the IMS-ALG performing proactive transcoding if needed. Thus the procedures in clause Q.2.5.4 and clause Q.2.5.5 do not apply. If transcoding is required, the IMS-ALG performs a procedure very similar to clause Q.2.5.3 to allocate the transcoding TrGW and signal its address to the answering side. Q.2.5.7 Reactive transcoding An IMS-ALG performing reactive transcoding follows all OMR procedures when forwarding the initial SDP offer but does not allocate a transcoder. If the initial SDP offer is rejected due to lack of support for an offered codec, the IMS-ALG performing reactive transcoding will restart the OMR procedure with the answering side after allocating and anchoring a TrGW with transcoding. The IMS-ALG removes all prior visited realm and secondary realm instances from the SDP offer before forwarding. Q.3 Charging Charging records shall include sufficient information to capture the allocation and/or bypass of TrGWs in the media path of an IMS session. If required by local configuration, charging records shall indicate whether the resulting user plane connection on either the incoming or outgoing leg of the IMS session traverses an IP realm different from its default IP realm (the IP realm traversed without OMR). If required by local configuration, charging records shall indicate whether a transcoder is inserted by the IMS-ALG. Annex R (informative): Distribution of Network Provided Location Information within IMS R.1 General This annex describes how the user location and/or UE Time Zone information can be further distributed to IMS entities once it has been retrieved by either P-CSCF or an IMS AS. The exact mechanism for how the user location and/or UE Time Zone information are obtained is not described in this annex. Information related to the location of the user provided by the access network may be required in IMS in order to comply with regulatory requirements (e.g. data retention, lawful interception) and/or in order to enable certain types of added value services based on the user's location. To simplify the information flows, the IMS AS shown in the figures can represent several AS's. The CSCF represents the I-CSCF and/or the S-CSCF. For the P-CSCF case in the originating side, the P-CSCF can, depending on operator policy, retrieve the user location and/or UE Time Zone information either before sending the INVITE towards the terminating side or upon reception of the SDP answer from the terminating side. The transfer of the user location and/or UE Time Zone information within IMS signalling does not affect the transfer of any UE provided user location information. User location and/or UE Time Zone information provided in the signalling by the network will be distinguished from user location information provided by the UE. R.2 Session Establishment/Modification at Mobile Origination - Location Info in Request This information flow shows the procedure when operator policy requires the the user location and/or UE Time Zone information to be included within IMS session establishment/modification signalling before sending the INVITE towards the terminating side. Figure R.2 -1: Mobile origination (user location and/or UE Time Zone information included within INVITE) 1. The UE sends a SIP INVITE request. It can contain user location information provided by the UE. 2. The P-CSCF obtains the user location and/or UE Time Zone information from the access network. 3. The P-CSCF includes the user location and/or UE Time Zone information obtained from the access network and sends the INVITE towards the next hop together with the user location information provided by the UE. 4. If an AS is to be invoked for this session, the S-CSCF (or I-CSCF) sends the INVITE towards the AS, including the user location and/or UE Time Zone information (assuming the AS is in the same trust domain). 5. The AS sends the INVITE towards the S-CSCF, still containing the user location and/or UE Time Zone information. 6. The S-CSCF routes the INVITE towards the terminating side. The user location and/or UE Time Zone information may be removed or modified (e.g. to change location granularity to just indicate the serving PLMN) before routing outside the trust domain. R.3 Session Establishment/Modification at Mobile Origination - Location Info in Response Figure R.3-1: Mobile origination (user location and/or UE Time Zone information included within Response Confirmation) 1. The UE sends a SIP INVITE request. It can contain user location information provided by the UE. 2a. Optionally, the P-CSCF may start procedures to obtain the user location and/or UE Time Zone information from the access network at reception of SDP Offer in parallel with steps 2b to 7. 2b. The P-CSCF sends the INVITE towards the next hop. 3. If an AS is to be invoked for this session the S-CSCF (or I-CSCF) sends the INVITE towards the AS. 4. The AS sends the INVITE towards the S-CSCF. 5. The S-CSCF routes the INVITE towards the terminating side. 6a. The P-CSCF receives an SDP answer sent by the terminating side. 6b. If the P-CSCF did not initiate procedures to obtain the user location and/or UE Time Zone information from the access network at step 2a, it will initiate them. This step will be executed together with Authorization of QoS resources. 6c. The P-CSCF forwards the SDP answer to the UE. 7. The UE provides a response confirmation towards the P-CSCF. 8. The P-CSCF inserts the user location and/or UE Time Zone information provided by the access network in the response confirmation and this is routed towards the terminating side in steps 9 - 11. The user location and/or UE Time Zone information may be removed or modified (e.g. to change location granularity to just indicate the serving PLMN) before routing outside the trust domain. R.4 Session Establishment/Modification at Mobile Termination This information flow shows the procedure when operator policy requires the user location and/or UE Time Zone information from the access network to be included within IMS session establishment/modification signalling before sending the response towards the originating side. Figure R.4-1: Mobile termination 1. The CSCF receives an incoming INVITE. 2. The CSCF send the INVITE to the P-CSCF. 3. The P-CSCF sends the INVITE to the UE. 4. The UE sends a response to the INVITE (the response can be either a provisional or final response). This can contain user location information provided by the UE. 5. The P-CSCF invokes procedures to obtain user location and/or UE Time Zone information from the access network. This step will be executed together with Authorization of QoS resources. In some scenarios, it might be possible to obtain or at least initiate the fetching of user location and/or UE Time Zone information already at step 3. 6. The P-CSCF adds the user location and/or UE Time Zone information obtained from the access network and sends the response towards the next CSCF, together with the user location information provided by the UE (if available). 7-9. The response is routed towards the originating party. The user location and/or UE Time Zone information may be removed or modified (e.g. to change location granularity to just indicate the serving PLMN) before routing outside the trust domain. R.5 Session Establishment/Modification - Location Information Distributed by IMS AS The call flow in this clause describes the procedures to distribute user location and/or UE Time Zone information provided by the network within IMS session establishment/modification signalling when the retrieval of user location and/or UE Time Zone information is performed by an IMS AS. Figure R.5-1: User location and/or UE Time Zone information Distribution by an IMS AS Terminating Side: 1. A SIP INVITE request is received bv an AS. 2. The INVITE is processed by the AS and returned to the S-CSCF. NOTE 1: If the AS requires user location and/or UE Time Zone information for the service execution as such, the user location and/or UE Time Zone information can be fetched prior sending the INVITE to the next hop. 3. The SDP Answer is received by the AS. 4. The AS retrieves user location and/or UE Time Zone information from the access network via the HSS. The HSS retrieves the requested information from the Access Network The HSS/UDM may not be aware whether the UE is currently camping on 3GPP or Non 3GPP access and may need to request Location Information from the AMF, the MME, the SGSN and from the TWAN (via the AAA server in this last case). The HSS provides the AS with the requested information. When the HSS has received multiple user location (from multiple access: 3GPP and non 3GPP), the HSS provides the AS with the most recent user location. 5. The AS includes the user location and/or UE Time Zone information obtained from the access network via the HSS and sends the SDP answer towards the S-CSCF. NOTE 2: The S-CSCF may further distribute user location and/or UE Time Zone information to other ASs within the trust domain. Originating Side: 6. A SIP INVITE request is received by an AS. 7. The AS retrieves user location and/or UE Time Zone information from the access network via the HSS. The same procedures as described in steps 4a and 4b above apply. 8. The AS includes the user location and/or UE Time Zone information obtained from the access network via the HSS and sends the INVITE towards the S-CSCF. NOTE 3: The S-CSCF can further distribute user location and/or UE Time Zone information to other ASs within the trust domain. The S-CSCF does not distribute the user location and/or UE Time Zone information to the P-CSCF. R.6 Session Release The call flows in this clause present the mobile or network initiated IMS session release for both the Mobile Originating (MO) side and the Mobile Terminating (MT) side valid when either P-CSCF or an IMS AS retrieve user location and/or UE Time Zone information from the access network. Figure R.6-1: IMS Session Release Terminating Side: 1. A session release message which terminates the dialog, e.g. BYE, is received by the P-CSCF/IMS AS. 2. The P-CSCF/IMS AS invokes procedures to obtain the user location and/or UE Time Zone information from the access network. In the P-CSCF, this step will be executed together with the procedure to release corresponding QoS resources in the IP-CAN. 3. The P-CSCF/IMS AS forwards the BYE message to the UE or the S-CSCF respectively. 4. The UE/S-CSCF provides a response to the P-CSCF/IMS AS. 5. The P-CSCF/IMS AS inserts the user location and/or UE Time Zone information in the response confirmation and this is routed towards IMS Core. Originating Side: 6. A session release message which terminates the dialog, e.g. BYE, is received by the P-CSCF/IMS AS. 7. The P-CSCF/IMS AS invokes procedures to obtain the user location and/or UE Time Zone information from the access network. In the P-CSCF, this step will be executed together with the procedure to release corresponding QoS resources in the IP-CAN. 8. The P-CSCF/IMS AS forwards the BYE message within IMS Core containing the user location and/or UE Time Zone information together with the user location information provided by the UE. The user location and/or UE Time Zone information may be removed or modified (e.g. to change location granularity to just indicate the serving PLMN) if routing outside the trust domain is needed. 9-10. The Session Release procedure is completed. Annex S (normative): Business Trunking S.1 General This annex describes the IMS architecture and procedures for support of IP‑PBX business trunking. Two different modes of operation are supported - Registration mode, or - Static mode. In both modes, the IP‑PBX can be provisioned as a subscriber in the HSS. In registration mode, the IP‑PBX registers to and receives service from the IMS network as specified in TS 24.525 [81]. The architecture and procedures for an IP- PBX using static mode is described in clause S.2. S.2 IP‑PBXs using static mode Business Trunking S.2.1 High level architecture The support for business trunking in static mode is provided by either an IBCF or a P‑CSCF. The architecture for support of IP‑PBX in static mode of operation is shown in Figure S.2-1. NOTE: The IP‑PBX can not register when using the static mode. Figure S.2-1: High level Static mode business trunking Architecture The IP‑PBX identity assertion and the routing of terminating sessions are performed by Application Server(s), which may or may not also host a business trunking application. The architecture for support of IP‑PBX in static mode of operation shown in Figure S.2-1 allows for two different deployment alternatives. - The Application Server(s) hosting these functionalities are invoked by the S-CSCF based on Initial Filter Criteria contained in the unregister part of the IP‑PBX's subscriber profile, retrieved from the HSS. - As according to clause 4.15 and TS 24.525 [81], this deployment relies on the Transit function with Application Server(s) hosting these functionalities are invoked by the Transit Function based on transit invocation criteria, which need to be provisioned in the Transit Function. In both cases, the AS performing the routing of terminating sessions needs to be the last AS invoked for terminating sessions. Both deployment options can simultaneously be used in in an IMS Network, although it requires that the enterprise user identities allocated in the different deployments are not overlapping. S.2.2 High level Flows S.2.2.1 General Before any originating or terminating procedures can take place between the IP‑PBX and the P‑CSCF or between the IP‑PBX and the IBCF of the IMS network, security and authentication between the IP‑PBX and IMS is done using the TLS procedures according to TS 33.310 [5], using certificates. The certificates are provided by a trusted root. The P‑CSCF or the IBCF is provisioned with its own certificate and will receive the IP‑PBX certificate during the TLS handshake. In configurations where there is a NAT between the IP‑PBX and the IMS, the TLS connection needs to be initiated and maintained by the IP‑PBX. If the network between the PBX and the IBCF complies with the peering based interconnect procedures according to TS 24.525 [81], the IBCF may deploy the Gq' interface. The Gq' interface and its interactions are not depicted in these flows. S.2.2.2 Originating procedures S.2.2.2.1 Originating procedures using the S-CSCF This clause depicts originating procedures for IP‑PBXs using static mode business trunking when the IP‑PBX is provisioned as a subscriber in HSS and served via the S‑CSCF. Figure S.2-1: Originating procedures for IP‑PBXs using static mode business trunking and served by the S‑CSCF The following steps are performed: 1. An enterprise user within the IP‑PBX tries to establish a call. The IP‑PBX sends an INVITE towards IMS via the P‑CSCF or via the IBCF (contact point for the IP‑PBX). If no security association exists between the P‑CSCF/IBCF and the IP‑PBX, TLS will be initiated as a result of trying to send the INVITE. Once the TLS session is setup (using the certificates), the INVITE will be sent over the secure connection. The INVITE is assumed to include a calling party identity. 2. The P‑CSCF/IBCF may apply general screening rules to the request and adds a P-Served-User-Identity to the INVITE with the identity of the PBX (SIP URI identifying the domain of the PBX retrieved from the certificate). Additionally, the P‑CSCF/IBCF adds the orig parameter to the INVITE to indicate that this is an origination request. The P‑CSCF/IBCF forwards the INVITE to the I‑CSCF. 3. The I‑CSCF performs the normal (originating request) user location request towards HSS to find an S‑CSCF to serve the IP‑PBX. If there is no subscription in the HSS, the I‑CSCF forwards the request to a Transit Function (and routing may continue as described in step 4 of clause S.2.2.2.2); otherwise, the following steps are performed. 4. The I-CSCF forwards the request to the S‑CSCF. 5. When the S‑CSCF does not have the IP‑PBX's subscriber profile, the S‑CSCF contacts HSS to download the subscriber information for the unregistered IP‑PBX. NOTE: The load on the Cx interface due to the downloading of unregistered IP‑PBXs subscriber profiles is dependent on the timer in the S-CSCF defining the duration the profile is kept for unregistered users. By increasing this timer, this load can be lowered. 6. The S‑CSCF performs normal (unregistered) originating service invocation for the incoming request. 7. The S‑CSCF forwards the request to the AS hosting the IP‑PBX identity assertion. Based on the P-Served-User-Identity, this AS identifies the IP‑PBX and inserts a P-Asserted-Identity identifying the enterprise user. Other Application Servers may be triggered based on iFC and may, based on the P-Asserted-Identity, perform any enterprise specific actions if required. 8. Each of the triggered ASs may optionally query HSS for any subscriber information if required using the Sh interface. 9. The INVITE is forwarded to S‑CSCF for further onward routing towards the remote side. 10. The S‑CSCF performs onward routing towards the remote side. 11. The session setup is completed. S.2.2.2.2 Originating procedures using the Transit Function This clause depicts the originating procedures for IP‑PBXs using static mode business trunking as described in TS 24.525 [81] when the IP‑PBX is not provisioned as a subscriber in HSS and served via the Transit Function. Figure S.2-2: Originating procedures for IP‑PBXs using static mode business trunking and served by the Transit Function The following steps are performed: 1. An enterprise user within the IP‑PBX tries to establish a call. The IP‑PBX sends an INVITE towards IMS via the IBCF (contact point for the IP‑PBX). If no security association exists between the IBCF and IP‑PBX, TLS will be initiated as a result of trying to send the INVITE. Once the TLS session is setup (using the certificates), the INVITE will be sent over the secure connection. The INVITE is assumed to include a calling party identity. 2a. The IBCF may apply general screening rules to the request and adds a P-Served-User-Identity to the INVITE with the identity of the IP‑PBX (SIP URI identifying the domain of the IP‑PBX retrieved from the certificate). Additionally, the IBCF adds the orig parameter to the INVITE to indicate that this is an origination request. The IBCF sends the INVITE to the I‑CSCF). 2b. The IBCF performs the same actions as in step 2a. but sends the INVITE directly to the Transit Function instead of the I‑CSCF. (The next step is step 5). 3. The I‑CSCF performs the normal (originating request) user location request towards HSS to find the served user, but as it is not provisioned in HSS, "user not found" is returned. 4. The I‑CSCF sends the INVITE to the Transit Function. 5. The Transit Function is configured with a set of Transit invocation criteria that are triggered to find a correct AS to route to. As this is an origination case (as indicated by the orig parameter), the P-Served-User-Identity is used to identify the IP‑PBX. 6. The Transit Function forwards the request to the AS hosting the IP‑PBX identity assertion. Based on the P-Served-User-Identity, this AS identifies the IP‑PBX, verifies that this IP‑PBX is a valid user and inserts a P-Asserted-Identity identifying the enterprise user. Other ASs may be triggered based on iFC and may, based on the P-Asserted-Identity, apply any enterprise specific actions if required. 7. The INVITE is forwarded for further onward routing towards the remote side. 8. Transit Function performs onward routing towards the remote side. 9. The session setup is completed. S.2.2.3 Terminating Procedures S.2.2.3.1 Terminating procedures using the S‑CSCF This clause depicts terminating procedures for IP‑PBXs using static mode business trunking when the IP‑PBX is provisioned as a subscriber in HSS and served via the S‑CSCF. Figure S.2-3: Terminating procedures for IP‑PBXs using static mode business trunking and served by the S‑CSCF The following steps are performed: 1. An INVITE is sent from the remote side towards the I‑CSCF with a Request-URI which belongs to a particular enterprise user of a served IP‑PBX. 2. The I‑CSCF performs the normal user location request towards HSS to find an S‑CSCF to serve the IP‑PBX. 3. The I‑CSCF forwards the request to the S‑CSCF. 4. When the S-CSCF does not have the IP‑PBX's subscriber profile, the S‑CSCF contacts HSS to download the subscriber information for the unregistered IP‑PBX. NOTE 1: The load on the Cx interface due to the downloading of unregistered IP‑PBXs subscriber profiles is dependent on the timer in the S‑CSCF defining the duration the profile is kept for unregistered users. By increasing this timer, this load can be lowered. 5. The S‑CSCF performs normal (unregistered) terminating service invocation for the incoming request. 6. The S‑CSCF forwards the request to the ASs to be triggered per iFC. Each of these ASs may identify the IP‑PBX the enterprise user belongs to and perform any enterprise specific actions if required. 7. Each of the triggered ASs may optionally query HSS for any subscriber information if required using the Sh interface. 8. The IP‑PBX routing functionality (hosted by the last AS in the iFC chain) identifies the particular IP‑PBX the enterprise user belongs to and also the P‑CSCF(s) or the IBCF(s) serving the IP‑PBX and forwards the INVITE toward the IP‑PBX (by creating a route to the IP‑PBX, adding the S‑CSCF, the P‑CSCF/IBCF and the IP‑PBX in the Route header fields). NOTE 2: Inserting the route to the IP‑PBX in Route header fields will not allow to trigger any AS after the IP‑PBX routing functionality. Similar to the T-ADS functionality, the IP‑PBX routing functionality has to be last in the chain of iFCs. 9. The INVITE is forwarded using the route information to the P‑CSCF or the IBCF. 10. The P‑CSCF/IBCF will forward the INVITE to the IP‑PBX using the route information provided by the IP‑PBX routing functionality. If no security association exist between the P‑CSCF/IBCF and the IP‑PBX (and TLS is used), TLS will be initiated as a result of trying to send the INVITE. Once the TLS session is setup (using the certificates) the INVITE will be sent over the secure connection. 11. The session setup is completed. S.2.2.3.2 Terminating procedures using the Transit Function This clause depicts the terminating procedures for IP‑PBXs using static mode business trunking as described in TS 24.525 [81] when the IP‑PBX is not provisioned as a subscriber in HSS and served via the Transit Function. Figure S.2-4: Terminating procedures for IP‑PBXs using static mode business trunking and served by the Transit Function The following steps are performed: 1. An INVITE is sent from the remote side via an incoming IBCF towards the Transit Function with a Request-URI targeting an enterprise user allocated to a particular IP‑PBX. NOTE: The INVITE from the IBCF can be sent via an I‑CSCF before it ends up in the Transit Function. In such case, the I‑CSCF will detect that this is not a provisioned user and therefore decide to route to the Transit Function. 2. The Transit Function will based on the Request-URI determine that the served user is belonging to an IP‑PBX and corresponding transit invocation criteria that are used to identify the ASs to be triggered, including the AS hosting the IP‑PBX routing functionality, which is the last AS to be triggered. 3. The Transit Function forwards the request to the required ASs. Each of these ASs may identify the IP‑PBX the enterprise user belongs to and perform any enterprise specific actions if required. 4. The IP‑PBX routing functionality (hosted by the last AS in the chain) identifies the particular IP‑PBX the enterprise user belongs to and optionally also the IBCF(s) serving the IP‑PBX and forwards the INVITE toward the IP‑PBX by creating a route to the IP‑PBX, adding the Transit Function, the IBCF and the IP‑PBX in the Route header fields. 5. The INVITE is forwarded using the route information to the IBCF. 6. The IBCF will forward the INVITE to the IP‑PBX using the route information provided by the AS. If no security association exist between the IBCF and the IP‑PBX (and TLS is used), TLS will be initiated as a result of trying to send the INVITE. Once the TLS session is setup (using the certificates) the INVITE will be sent over the secure connection. 7. The session setup is completed. Annex T (normative): IP-Connectivity Access Network specific concepts when using Trusted WLAN (TWAN) to access IMS T.0 General This clause describes the main IP-Connectivity Access Network specific concepts that are used for the provisioning of IMS services over a Trusted WLAN (TWAN) access to EPC. As IMS is accessed over EPC, most of the features defined in clause E for the case of EPC (and PDN connections/EPS bearers) apply in the case of a TWAN access, e.g. a P‑GW is used as an IP anchor point and IP-Connectivity Access Network bearers are provided by PDN connections and bearers. Following specific considerations apply to the case of a TWAN access: - The Mobility related procedures for EPS and TWAN access are described in TS 23.402 [82] - TWAG/TWAP (refer to clause 16 of TS 23.402 [82]) are used to interface the access network and to control relevant PDN connectivity (over S2a) towards a P-GW. - For a TWAN access, the way the notification of the loss of IP-CAN session for an UE is triggered within a TWAN is out of scope of 3GPP specifications. T.1 Retrieval of Network Provided Location Information in TWAN access For a TWAN access, Access Network Information may be reported to the IMS as described in clause E.7 for the case of a GPRS/EPS access, with following exceptions: - The Access Network Information being reported to the P-CSCF is defined in clause 16 of TS 23.402 [82]. A Geographical Identifier may be generated by the P-CSCF or an IMS AS based on the retrieved Access Network Information, as specified in clause E.8. Information related to the location of the user provided by the access network may be required in IMS in order to comply with regulatory requirements for SMS over IP. The P-CSCF applies the above mechanisms upon reception of a MESSAGE including the distribution of received information to other IMS entities. Annex U (normative): WebRTC access to IMS - network-based architecture U.1 Overview U.1.0 General Web Real-Time Communication (WebRTC) is specified in IETF RFC 8825 [84] and WebRTC 1.0 [85]. This Annex specifies a network-based architecture for the support of WebRTC client's access to IMS. Any requirements for specific audio and video codecs from IETF RFC 8825 [84] (directly and indirectly referenced) do not apply for WebRTC access to IMS; the codecs that shall be supported for WebRTC access to IMS are described in TS 26.114 [76]. NOTE: The UE can also perform WebRTC access to IMS by implementation specific means in the UE in which it exposes a standard Gm interface towards IMS. U.1.1 Assumptions - This Release specifies an option to use a signalling interface from the UE to the network based on SIP over WebSocket (RFC 7118 [89]), which is used as the information model which may be used by other options. Options other than SIP over WebSocket, such as XMPP or other application protocols over WebSocket, a RESTful based interface, etc. are allowed but not described. Alternative message body formats such as JSON and alternative transport protocols are also not precluded. Any enhancements required to accommodate an unspecified signalling interface are considered compliant to the Release as long as other defined interfaces in the architecture are not impacted. - SDP offer/answer exchange is the mechanism used for media plane feature negotiation. - The architecture does not support media multiplexing that is defined for WebRTC clients. A WebRTC IMS Client (WIC) accessing IMS services should not allow usage of media multiplexing in the browser. - If an SDP offer with media multiplexing is sent to the network the part of the SDP offer associated with media multiplexing shall be removed at the entry of the IMS network. - WebRTC specific media plane extensions will be handled at the access edge and will not be propagated to other IMS functions. - For network based interworking between WebRTC and IMS, in the case of 3GPP and EPC access from a WebRTC client: - Use of available techniques to select preferred access technologies and APNs/DNNs and to provide IP address continuity, are allowed but not described. - When the WebRTC client is served by an IP-CAN that supports PCC, it is possible to request QoS within the IP-CAN for WebRTC media. NOTE: To ensure full end to end QoS support, proper IP forwarding policies can be set in the path between the P‑GW and the Functions supporting media interworking to the IMS. - QoS can be provided in configurations where the IMS can identify the transport (TCP-UDP/IP) addresses handled by the PCEF and where based on this information PCC functions can identify the UE media flows to prioritize. - The eP-CSCF is located in the Home IMS domain of the IMS Public User Identity being registered via the eP-CSCF. - The WIC may have no way to access the content of an ISIM/USIM on the UE U.1.2 Architecture and reference model Figure U.1.2-1 shows the WebRTC IMS architecture. The WWSF (WebRTC Web Server Function) is located either within the operator network or within a third party network and is the web server contacted by the user agent (generally after clicking on a link or entering a URL into the browser). The P-CSCF enhanced for WebRTC (eP‑CSCF) is the endpoint for the signalling connection from the client and is located in the operator network. NOTE 1: The presence of dashed elements in the figure depends on the configuration. PCC functional elements are present only for EPC access with QoS. The corresponding PCC elements for fixed access are also optionally supported but not shown. The NAT in figure U.1.2-1 is meant for non-cellular access to IMS. Figure U.1.2-1: WebRTC IMS architecture and reference model NOTE 2: W3 corresponds to the output of the IETF RTCWEB discussions. NOTE 3: The enhanced network entities, such as the eP-CSCF, might be decomposed into multiple network elements (e.g. P-CSCF and WebRTC Signalling Function) in future Releases to address additional use cases and configurations. NOTE 4: The W5 reference point is an optional signalling interface between the WAF and the eP-CSCF. The W5 reference point is not specified and is implementation specific. U.1.3 Functional entities U.1.3.1 WIC (WebRTC IMS Client) A WebRTC IMS Client (WIC) is an application using the WebRTC extensions specified in WebRTC 1.0 [85] except for those extensions specifically exempted by 3GPP specifications (e.g. TS 26.114 [76]) and providing access to IMS by interoperating with the WebRTC IMS access architecture defined in this Annex. Any IP access network with access to the internet may be used by a WIC; nevertheless WebRTC traffic is subject to the QoS and reachability limitations of this access network. U.1.3.2 WWSF (WebRTC Web Server Function) The WebRTC Web Server Function (WWSF) is the initial point of contact in the Web that controls access to the IMS communications services for the user. The WWSF has the following characteristics and functions: - The WWSF is located either in the operator network or a third party network - The WWSF provides the Web page presenting the user interface to the user for IMS access. - The WWSF provides the JS WIC application for downloading to the browser on the UE. - The WWSF manages the allocation of authorized IMS identities to WICs. The JS application downloaded from the WWSF controls which authentication method applies. NOTE 1: The WWSF represents a collection of functions that might be further split across servers or networks, so long as they behave in the aggregate as described in this Annex U. NOTE 2: The WWSF can include WAF functionality in the case WWSF and WAF are in the same domain. U.1.3.3 eP-CSCF (P-CSCF enhanced for WebRTC) The P-CSCF enhanced for WebRTC (eP-CSCF) is a P-CSCF including the IMS-ALG functionality and with the following additional functions: - The eP-CSCF shall support at least one WebRTC IMS client-to-network signalling protocol, e.g. SIP over WebSocket, REST/HTTP based interface, XMPP over WebSocket, etc. NOTE 1: Other application protocols, alternative message body formats such as JSON and alternatives to WebSocket transport are also not precluded. - The eP-CSCF provides interworking between W2 and Mw. - The eP-CSCF verifies that the UE is executing a WIC from an authorized WWSF. - In the case of WIC registration of individual Public User Identity using IMS Authentication, the eP-CSCF shall relay the IMS authentication and registration information between W2 and Mw. - Otherwise, i.e. for users authorized by the WWSF or WAF: - The eP-CSCF shall verify any UE authorization information received from the WIC; - The eP-CSCF shall verify that the WWSF is authorized to allocate IMS identities; NOTE 2: For this purpose the eP-CSCF can identify an existing trust relationship between the eP-CSCF and the WWSF or WAF. - The eP-CSCF shall perform Trusted Node Authentication (TNA) in IMS, as defined in TS 33.203 [19]. - The eP-CSCF shall control the media plane interworking functions provided by the eIMS-AGW, including those additional media plane functions specific to WebRTC. - The eP-CSCF shall ensure via signalling that RTP streams are not multiplexed ("bundled") onto the same port. - The eP-CSCF shall negotiate via signalling whether RTP and RTCP flows of an RTP stream are multiplexed onto the same port and shall configure the eIMS-AGW to (de)multiplex such flows if entities anchoring the session media path in the IMS domain do not support that capability. - The eP-CSCF is located in the domain of the operator that provides the WWSF or with which the WWSF has a service level agreement. U.1.3.4 eIMS-AGW (IMS Access GateWay enhanced for WebRTC) The IMS-AGW enhanced for WebRTC (eIMS-AGW) is a standard IMS-AGW with the following additional mandatory characteristics and functions: - The eIMS-AGW shall support the media plane interworking extensions as needed for WICs. - The eIMS-AGW shall reside in the same network as the eP-CSCF. - The eIMS-AGW shall support media security of type "e2ae" (as specified in TS 33.328 [83]) for media protocols specific to WebRTC, including media consent and DTLS-SRTP as key exchange mechanism for media components using SRTP. - The eIMS-AGW shall provide NAT traversal support including ICE - The eIMS-AGW may be used to perform any transcoding needed for audio and video codecs supported by the browser. - When GTT service is required, the eIMS-AGW shall perform transport level interworking between T.140 [87] over Data Channels and other T.140 transport options supported by IMS. - When MSRP is transported over the data channel, the eIMS-AGW shall act as an MSRP B2BUA between MSRP over Data Channels and the other MSRP transport options supported by IMS. NOTE: If CEMA extensions for transport-level interworking for MSRP are supported in IMS, the eIMS-AGW will also support this option. - When BFCP service is required for conference floor control and BFCP is transported over Data Channels, the eIMS-AGW shall perform transport level interworking between BFCP over Data Channels and other BFCP transport options supported by IMS. - The eIMS-AGW shall support the media plane optimization for WICs. - The eIMS-AGW shall support that RTP and RTCP flows of an RTP stream between WIC and eIMS-AGW are multiplexed onto the same port and shall support de-multiplexing such RTP and RTCP flows toward the core network. U.1.3.5 WAF (WebRTC Authorisation Function) The WebRTC Authorisation Function (WAF) has the following characteristics and functions: - The WAF shall issue the authorisation token to WWSF. - The WAF may either authenticate the user itself as part of the token issuance process, or it trusts the user identity provided by the WWSF. - The WAF may either reside in the operator domain or the third party domain. The WAF is not used in the case of IMS registration scenario using IMS Authentication, described in clause U.2.1.1. NOTE: The WWSF can include WAF functionality in the case WWSF and WAF are in the same domain. U.1.4 Reference points U.1.4.1 W1 (UE to WWSF) The W1 reference point is between the UE and the WWSF. The HTTPS protocol is normally used to access the web page providing the User Interface for the WIC and to download the WIC JS application to the browser. U.1.4.2 W2 (UE to eP-CSCF) The W2 reference point is the signalling interface between the UE and the eP-CSCF. SIP over secure WebSocket is a non-mandatory option for W2 in Release 12, where the SIP/SDP procedures are based on Gm with enhancements to support extensions defined for WIC and secure WebSocket is the supported transport protocol. Other protocols are allowed on W2 for WebRTC access but are not described in this document. U.1.4.3 Iq (eP-CSCF to eIMS-AGW) The Iq reference point is between the eP-CSCF and eIMS-AGW and is enhanced to control the additional bearer plane functions specific to WIC. U.1.4.4 W3 (UE to eIMS-AGW) The W3 reference point is between the UE and eIMS-AGW. W3 carries the user plane between the UE and the network (see clause U.1.5). U.1.4.5 W4 (WWSF to WAF) The W4 reference point is the signalling interface between the WWSF and the WAF. The WWSF obtains an authorisation token from the WAF from which the user's identities, identities of WWSF and WAF and a lifetime may be derived in the case of IMS registration scenarios based on web authentication and assignment from a pool of user identities. U.1.5 Media plane protocol architecture U.1.5.0 General The IMS AGW enhanced for WebRTC (eIMS-AGW) is the media plane interworking element with the functions described in clause U.1.3.4. NOTE: In this clause, the figures describe the end to end scenario where "the peer" corresponds to a remote IMS terminal. In this case, when e2ae security is needed, TS 33.328 [83] shall govern the interaction between "the peer" and the IMS-AGW that serves it. Other scenarios with other kind of peers (e.g. the peer is another webRTC terminal) are possible but not represented. U.1.5.1 Protocol architecture for MSRP Figure U.1.5.1-1 shows the protocol architecture for support of MSRP, when transported over the data channel, from a WebRTC IMS client (WIC). When MSRP is transported over the data channel, the eIMS-AGW shall provide either a transport relay function from Data Channel to TCP or an MSRP B2BUA to allow interoperation with existing MSRP peer endpoints. UDP transport of DTLS shall be supported and TCP transport of DTLS may be supported to enable traversal of UDP-blocking NATs/firewalls. Figure U.1.5.1-1: Protocol architecture for MSRP Figure U.1.5.1-2: Protocol architecture for MSRP acting as transport relay function U.1.5.2 Protocol architecture for BFCP Figure U.1.5.2-1 shows the protocol architecture for support of BFCP, when transported over the data channel for conference floor control, from a WebRTC IMS client (WIC). When BFCP service is required for conference floor control and BFCP is transported over Data Channels, the eIMS-AGW shall provide a transport relay function from Data Channel to TCP to allow interoperation with existing BFCP peer endpoints. UDP transport of DTLS shall be supported and TCP transport of DTLS may be supported to enable traversal of UDP-blocking NATs/firewalls. Figure U.1.5.2-1: Protocol architecture for BFCP U.1.5.3 Protocol architecture for T.140 Figure U.1.5.3-1 shows the protocol architecture for support of T.140 from a WebRTC IMS client (WIC). The eIMS-AGW shall provide a transport relay function from Data Channel to RTP to allow interoperation with existing T.140 peer endpoints. UDP transport of DTLS shall be supported and TCP transport of DTLS may be supported to enable traversal of UDP-blocking NATs/firewalls. Figure U.1.5.3-1: Protocol architecture for T.140 U.1.5.4 Protocol architecture for Voice and Video Figure U.1.5.4-1 shows the protocol architecture for support of Voice and Video from a WebRTC IMS client (WIC). Transcoding (i.e. allowing codec1 to be different from codec2) is optional. SRTP between the UE and the eIMS-AGW relies on keying material negotiated via DTLS. NOTE 1: Transcoding at the eIMS-AGW may apply to none, one or both of the voice and video components Figure U.1.5.4-1: Protocol architecture for Voice and Video NOTE 2: RFC 4571 [90] framing is used for RTP streams transferred over TCP. RTP over TCP may be used when NATs/Firewalls perform UDP blocking. U.2 Procedures U.2.0 WWSF discovery The URI to a WWSF for WebRTC access to IMS may be configured in the UICC. Prior to performing registration, a UE may use the following mechanism to determine the URI of the WWSF: - If the UICC contains a URI to a WWSF for WebRTC access to IMS, then the UE uses this URI for registration. - Otherwise, the UE derives the URI to WWSF from the home domain name as specified in TS 23.003 [24]. Alternatively, the URI to a WWSF may be obtained by means outside the 3GPP scope. U.2.1 Registration U.2.1.1 Introduction The WebRTC IMS architecture supports the following different IMS registration scenarios that may differ in the authentication method and ownership of the WWSF (i.e. operator network or third party): - "WIC registration of individual Public User Identity using IMS authentication": The user has a subscription with an individual Public User Identity and an IMS authentication mechanism as specified in TS 33.203 [19] is used to authenticate with IMS. Clause U.2.1.2 provides detailed procedures for this scenario. - "WIC registration of individual Public User Identity based on web authentication": The user has an IMS subscription. The WWSF or WAF authenticates the user using a web identity and authentication scheme. The WWSF determines IMS identities for the user (e.g. based on the user's web identity via database lookup or other translation means). An individual registration is handled by the S-CSCF per WIC registration. Clause U.2.1.3 provides detailed procedures for this scenario. - "WIC registration of individual Public User Identity from a pool of Public User Identities": The WWSF is typically located in a third party network and has a business arrangement with the IMS operator. The WWSF or WAF authenticates the user using a web identity and authentication scheme, or authorizes the WIC without authenticating the user. The WWSF assigns IMS identities to the user from within a pool allocated by the operator. An individual registration is handled by the S-CSCF per WIC registration. Clause U.2.1.4 provides detailed procedures for this scenario. U.2.1.2 WIC registration of individual Public User Identity using IMS authentication The WIC obtains information needed for IMS registration (e.g. Private User Identity and Public User Identity) via unspecified means. For example, some of this information might be stored in cookies or local browser storage after visiting a secure web site provided by the IMS operator. Figure U.2.1.2-1 shows a registration call flow where IMS authentication is used to register the WIC. Figure U.2.1.2-1: WIC registration of individual Public User Identity using IMS authentication 1. The WIC initiates an HTTPS connection to the WWSF. The TLS connection provides one-way authentication of the server based on the server certificate. The browser downloads and initializes the WIC from the WWSF. 2. The WIC opens a WSS (secure WebSocket) connection using cross-origin mechanism to the eP-CSCF. Standard cross-origin resource sharing procedures are used to ensure that the WIC originated from a WWSF authorized to access this eP-CSCF. 3-6. The WIC initiates a registration transaction with IMS via the eP-CSCF by sending a REGISTER request to the eP-CSCF via the WSS (secure Web Socket) connection. The REGISTER request includes IMS Authentication parameters, Private User Identity, Public User Identity and other information as needed for proper IMS registration. This request is translated into an IMS registration process by the eP‑CSCF. This process leverages user credentials in HSS. U.2.1.3 WIC registration of individual Public User Identity based on web authentication Figure U.2.1.3-1 shows a registration call flow where the WIC registers with IMS based on web authentication with the WWSF. Figure U.2.1.3-1: WIC registration of individual Public User Identity based on web authentication 1. The WIC initiates an HTTPS connection to the WWSF. The TLS connection provides one-way authentication of the server based on the server certificate. The browser downloads and initializes the WIC from the WWSF. The WWSF or WAF authenticates the user using a common web authentication procedure. The WWSF determines the Private User Identity and Public User Identity for the WIC and returns the security token which is issued by the WAF to the WIC. The IMS identities may be provided to the WIC in addition to the security token. 2. The WIC opens a WSS (secure WebSocket) connection using cross-origin mechanism to the eP-CSCF. Standard cross-origin resource sharing procedures are used to ensure that the WIC originated from a WWSF authorized to access this eP-CSCF. 3. The WIC sends a REGISTER request to the eP-CSCF via the WSS (secure Web Socket) connection. The request includes the security token received from the WWSF. If the WIC received the IMS identities in step 1, the request shall include the IMS identities. 4. The eP-CSCF validates the contents of the security token and obtains the IMS identities being registered. The eP-CSCF then forwards the authorized REGISTER request to IMS to initiate authentication-less IMS registration using TNA (see TS 33.203 [19], Annex U) procedures, with an indication that the authentication has already been carried out. 5. The S-CSCF responds with a 200 OK message are accepted. 6. The eP-CSCF sends the OK response back to the WIC. As the security token may be associated with a lifetime, the WIC may need to periodically refresh its registration. This registration refresh process entails all steps above with following exceptions: - For Step 1, the opening of the TLS connection, the downloading of the WIC and the web authentication of the user using the WIC may not be needed. - Step 2 may not be needed. U.2.1.4 WIC registration of individual Public User Identity from a pool of Public User Identities The WWSF is provided with a pool of IMS subscriptions, each associated to a single Private User Identity and one or more Public User Identities as specified in clause 4.3.3.4. The WWSF can assign individual Public and Private User Identities from this pool. The WWSF may be located in a third party network and have a business arrangement with the IMS operator. For pool management, the IMS operator may also provide the WWSF with an unbounded number of Private User Identities/Public User Identities associations to be allocated to WIC users, where each user may use multiple WICs sharing the same Public User Identity and each WIC being assigned a different Private User Identity. NOTE: How the HSS handles and manages the unbounded users is implementation specific. The registration call flow for a WIC being assigned an individual Public User Identity from a pool of Public User Identities assigned to the WWSF is the same registration call flow defined in Figure U.2.1.3-1 with following differences: - In step 1, the WWSF or WAF may decide not to authenticate the user. Unauthenticated users are anonymous to the third party but may still be authorized for IMS service. - The lifetime of the security should be coordinated between the IMS provider and the WWSF provider; otherwise, the WWSF cannot know when a Public User Identity Private User Identity association from its pool can be re-assigned to another user. - Alternatively, as an implementation specific option, eP-CSCF may indicate to the WWSF when a certain Public User Identity can be re-assigned. U.2.2 Session management related procedures Origination and termination and Session release procedures for WebRTC IMS clients follow standard IMS procedures in the core network (see clauses 5.6 and 5.7 and 5.10) with the exception that routing of all messages between the WIC and S-CSCF traverse the eP-CSCF (rather than P-CSCF) and that parameters of Iq procedures take into account the WebRTC-specific extensions used by the WIC to send and receive media. U.2.3 De-Registration procedures De-registration procedure for WebRTC IMS clients follows standard IMS procedures in the core network (see clause 5.3) with the exception that routing of all messages between the WIC and S-CSCF traverse the eP-CSCF (rather than P-CSCF). U.2.4 Media plane Optimization The IMS operator is able to convey the audio and chat session without bearer level protocol conversion when session is between WebRTC clients. When both ends are WebRTC client, the eIMS-AGWs remain allocated but media plane interworking is disabled, except when LI is needed. When media plane optimization is enabled, the eIMS-AGW forwards all protocol layers either including DTLS, or on top of DTLS transparently (see clause U.1.5). NOTE: Terminating the DTLS protocol layer for all calls can improve the transparency of LI. When LI is performed, media plane interworking is performed according to TS 33.328 [83]. Figure U.2.4-1 shows a call flow diagram establishing the e2ae communication between WebRTC clients through the IMS network. I/S-CSCFs are not shown for brevity. Figure U.2.4-1: Media plane Optimization 1. WebRTC client (WIC-1) initiates a call, creating a Session Description Protocol (SDP) offer and sends it to the originating side eP-CSCF. The SDP offer may contain SRTP, ICE and Data Channel information. The WIC-1 IP address is IP1. 2. The eP-CSCF-1 receives the SDP offer from WIC-1. The eP-CSCF-1 allocates eIMS-AGW1 and configures it to terminate ICE procedures and provide interworking (e.g. transcoding, or transport interworking between a Data Channel and transport outside a Data Channel). eIMS-AGW1 allocates address IP2. It also requests the media gateway to provide a transport port suitable for a transparent forwarding of the media. IMS-AGW1 allocates port P2t for that purpose. Depending on configuration, it either configures the IMS-AGW1to terminate or to transparently forward the DTLS layer for transparent media. The eP-CSCF-1 shall not apply OMR procedures according to Annex Q. 3. The eP-CSCF-1 describes the new media2 that result from the interworking and inserts the address IP2 at the eIMS-AGW1 in the SDP offer connection line it sends. Within the SDP offer, the eP-CSCF-1 also indicates that the media1 targeted for transparent forwarding (those media are called "transparent media" in what follows) can be selected instead and also encapsulates in SDP attribute(s) information about those transparent media (SDP attributes, SDP media line including transport protocol and port P2t, Data Channel related information, but no ICE related information. A DTLS fingerprint is included and depending on configuration, it either contains the fingerprint received from the WIC-1 or a fingerprint allocated by eIMS-AGW1). To enable the check in step 6 wether intermediates which do not support switching to the encapsulated media are inserted into the media path, the eP-CSCF-1 also encapsulates the address IP2. 4. A possible intermediate (e.g. IBCF with attached TrGW or MTFC with attached MRFP) may also insert a media gateway into the user plane. Such an intermediate may optionally also support switching to the transparent media; this is required to allow the transparent media to be selected when its media gateway is present in the media path. Intermediates which do not support switching to the transparent media will be detected and will cause media 2 to be selected in step 6. The possible intermediate can also apply OMR procedures according to Annex Q to offer that its media gateway is bypassed by an optimised media path. 5 The intermediate replaces the transport address within the connection line in the SDP offer with the address IP3 allocated at its media gateway. If the intermediate supports switching to the transparent media, it also modifies the transparent media information encapsulated in SDP attribute(s) by replacing the encapsulated transport address with IP3 and the port information with P3t. 6. eP-CSCF-2 allocates eIMS-AGW2. It compares the transport address in the SDP connection line with the transport address in the transparent media information encapsulated in SDP attribute(s). Because both addresses match, the eP-CSCF-2 takes the transparent media information into consideration. Otherwise it shall ignore the transparent media information. The eP-CSCF-2 shall not apply OMR procedures according to Annex Q and shall discard any received OMR related information. Because eP-CSCF2 knows that the served WIC-2 is a WIC, it decides that the transparent media information is appropriate and configures the eIMS-AGW2 to transparently forward those media; depending on configuration, eP-CSCF2 either configures the eIMS-AGW2 either transparently forward the DTLS layer or to terminate it and it either forwards the fingerprint received as part of the transparent media information or a fingerprint allocated by eIMS-AGW2. 7. The eP-CSCF-2 forwards SDP offer with the transparent media1 and the transport address IP4 allocated at eIMS-AGW2 to WIC-2. 8. WIC2 selects media3 from the offered media1 and sends the selected media3 in the SDP answer to the eP-CSCF-2. 9. The eP-CSCF-2 forwards the SDP answer including connection information for eIMS-AGW2 and the unmodified media3 and includes an indication that the transparent media have been selected. Depending on configuration, it either forwards the fingerprint received from WIC2 or a fingerprint allocated by eIMS-AGW2. 10. The possible intermediate reconfigures its MGW to transparently pass media3. 11. The intermediate forwards the SDP answer with unmodified media3 and indication that the transparent media have been selected and includes address information IP7 of the controlled MGW. 12. According to received SDP answer, the eP-CSCF-1 knows that there is no bearer level protocol conversion. So eP-CSCF-1 deactivates media plane interworking in eIMS-AGW1. 13. The eP-CSCF-1 forwards the SDP answer to WIC-1. Depending on configuration, it either forwards the fingerprint received in step 12 or a fingerprint allocated by eIMS-AGW1. Annex V (normative): IP-Connectivity Access Network specific concepts when using Untrusted WLAN to access IMS V.1 General This clause describes the main IP-Connectivity Access Network specific concepts that are used for the provisioning of IMS services over untrusted WLAN access to EPC. Following specific considerations apply to the case of untrusted WLAN access: - The Mobility related procedures for untrusted WLAN access to EPC are described in TS 23.402 [82]. - For untrusted WLAN access, ePDG is used to interface the access network and to control relevant PDN connectivity (over S2b) towards a P-GW. - For untrusted WLAN access, the way the notification of the loss of IP-CAN session for a UE is triggered within an untrusted WLAN is out of scope of 3GPP specifications. - For untrusted WLAN access, the Reporting of User location information (i.e. UE local IP address and Network Provided WLAN Location Information) in the EPS is defined in clauses 4.5.7.2.8, 7.4.3.1, 7.9.2, 7.10 and 7.11.14 of TS 23.402 [82] and the related PCC Access Network Information reporting procedure is defined in clause H.4 of TS 23.203 [54]. Information flows on how user location information can be further distributed within IMS can be found in Annex R. - In order to fulfil regulatory requirements, IMS requires in addition to the UE local IP address, the identity of the ePDG to which the UE is connected and the UE source port (TCP port or UDP port) used by the UE to establish the IKEv2 tunnel with the ePDG. NOTE 1: The identity of the ePDG is the IP address used in IKEv2 tunnel. NOTE 2: The P-CSCF has to subscribe to the IP-CAN type changes with PCRF to be notified when IP-CAN type changes to non 3GPP and the ePDG IP address (and other information) is than provided to the P-CSCF. V.2 UE Provided Access Information in Untrusted WLAN access A UE accessing IMS via untrusted WLAN shall support the following: - If available, provide the identity of the WLAN AP the UE is currently associated with and used for IMS signalling at IMS registration, IMS emergency registration, IMS session initiation, SMS over IP and in any procedure defined in TS 24.229 [10a], where access network information is provided. - If available, provide geographical location coordinates during IMS emergency session setup. - Provide the cell information (cell-ID) for the most recent seen cell at IMS registration, IMS emergency registration, IMS emergency session initiation and in any procedure defined in TS 24.229 [10a] where access network information is provided. The cell-ID access information shall include additional information describing when the information about the cell-ID was collected and that can be used to calculate the "age" of the information. The information about the cell-ID shall be included in an appropriate field of the SIP request that is distinguished from the information about the access network currently used to transport SIP signalling (i.e. Untrusted WLAN). NOTE: Operator specific local control policies may be applied and which can result in a registration being accepted, rejected and/or may also result in additional implementation specific actions. Any node that participates in the registration process (e.g. P-CSCF, HSS) may apply these local control policies. Annex W (normative): Support of IMS Services for roaming users in deployments without IMS-level roaming interfaces W.1 General This clause describes the functions that are used to support IMS services for roaming users in deployments without IMS-level roaming interfaces. This annex is applicable to UEs connected to EPS and 5GS. In this roaming model the mobility anchor (i.e. PGW or UPF) is located in the home PLMN and therefore UE IMS signalling and user plane traffic are routed to home PLMN. It is assumed that confidentiality protection is not used in HPLMN and VPLMN for IMS media plane traffic. For the LBO roaming model where P-CSCF is in VPLMN, see Annex M. W.2 Architecture W.2.1 EPS The architecture to support IMS services for roaming users, including Voice over IMS, in deployments without IMS-level roaming interfaces is shown in figure W.2-1 The following architecture requirements apply: - P-CSCF (at HPLMN) identifies the serving network (VPLMN) where the UE is located using the procedure defined in clause W.3. Figure W.2-1: architecture IMS architecture W.2.2 5GS See clause Y.9.2. W.3 Void W.4 Procedures related to PLMN ID change W.4.1 Subscription to changes of PLMN ID at IMS Initial Registration In deployments without IMS-level roaming interfaces, the home network determines the serving PLMN of the UE using procedure defined in TS 23.203 [54], TS 23.503 [95] or TS 29.214 [11], where the P-CSCF requests the PCRF/PCF to report the PLMN identifier where the UE is currently located. The received PLMN ID information is then forwarded in the SIP REGISTER request. This procedure shall be applied by the P-CSCF at initial UE IMS registration. The below procedure relates to EPS, the corresponding procedure for 5GS is defined in Annex Y. Figure W.4.1-1: Subscription by P-CSCF to changes in PLMN ID during initial IMS Registration 1. The UE sends a SIP REGISTER request to the P-CSCF. 2. If this is the initial IMS registration then the P-CSCF subscribes to the PCRF/PCF to be notified of the PLMN ID where the UE is currently attached. The subscription to PLMN changes is active as long as the UE is IMS registered. 3. The PCRF/PCF forwards the PLMN ID to the P-CSCF. The P-CSCF stores the PLMN ID. 4. The P-CSCF includes the received PLMN ID in the SIP REGISTER request before forwarding the request to the I-CSCF. 5. Normal IMS registration procedure is then completed. W.4.2 UE is not active in an IMS voice session The following procedure shall be applied by IMS at reception of PLMN change when the UE is not active in an IMS voice call and when the PDN connection/PDU session is kept at PLMN change. NOTE 1: This clause assumes that the UE has not established an IMS session for other services. Additional functionality covering non-voice IMS sessions is up to future enhancements. Figure W.4.2-1: Procedure for PLMN change 1. EPC/5GC detects PLMN change. 2. H-PCRF/PCF notifies P-CSCF that PLMN change has occurred and indicates the new PLMN ID. 3. P-CSCF sends SIP MESSAGE with new PLMN ID to S-CSCF. 4. Based on regulatory requirements (see NOTE 2), S-CSCF sends SIP NOTIFY with re-authentication request to the UE. NOTE 2: Regulatory requirements in the country of the new PLMN could require the possibility to get access to IMS signalling information. If the source PLMN uses encryption for IMS signalling, the Re-Registration procedure can trigger the HPLMN to change encryption to use null encryption which would enable the new PLMN to get access to future IMS signalling information. Also, the Re-registration can trigger to turn on encryption in the new PLMN if the HPLMN requires it. 5. UE initiates re-registration procedure. During the re-registration procedure, the P-CSCF may update the SIP signalling encryption depending on roaming agreements, e.g. moving from HPLMN to VPLMN can result in turning off IMS encryption while retaining integrity protection of IMS signalling. W.4.3 UE is active in an IMS voice session The following procedure shall be applied by IMS at reception of PLMN change when the UE is active in an IMS voice call and when the PDN connection/PDU session is kept at PLMN change. Figure W.4.3-1: PLMN change detected by EPC/5GC 0. UE is active in an IMS voice call. 1. EPC/5GC detects PLMN change. 2. H-PCRF/PCF notifies the P-CSCF that PLMN change has occurred and indicates the new PLMN ID. 3. P-CSCF sends SIP MESSAGE with the new PLMN ID to the S-CSCF. 3a. P-CSCF sends SIP MESSAGE with new PLMN ID to the TAS so that the TAS may update any charging records with the new PLMN ID. 4. Based on regulatory requirements (see NOTE 1), S-CSCF sends SIP NOTIFY with re-authentication request to the UE. 5. UE initiates re-registration procedure. During the re-registration procedure, the P-CSCF may update the SIP signalling encryption depending on roaming agreements, e.g. moving from HPLMN to VPLMN can result in turning off IMS encryption while retaining integrity protection of IMS signalling. 6. Once the re-registration procedure is completed and based on regulatory requirements (see NOTE), the P-CSCF may send a SIP MESSAGE to the TAS indicating that TAS should send a re-INVITE request to the UE. 7. TAS sends SIP Re-INVITE to UE including, subject to the privacy settings associated with the original call, call related information (e.g. calling and called party information, indication whether UE was calling party or called party in the call, redirecting party information (if present), media endpoints and used codecs). Codec endpoints are translated in the P-CSCF if needed. The UE should not reveal this information to the user. 8. UE sends SIP 200 OK to TAS. NOTE: Whether the P-CSCF executes step 4 and/or step 6 depends on regulatory requirements of the new PLMN. Regulatory requirements in the country of the new PLMN could require the possibility to get access to IMS signalling information. If the source PLMN uses encryption for IMS signalling, the IMS Re-Registration procedure can trigger the HPLMN to change encryption to use null encryption which would enable the new PLMN to get access to future IMS signalling information. Also, the IMS Re-registration can trigger to turn on encryption in the new PLMN if required by the HPLMN. Sending SIP Re-Invite request to the UE enables the new PLMN to get access to call related information. Annex X (normative): IMS 3GPP PS Data Off Service Accessibility X.1 General 3GPP PS Data Off is an optional feature. When activated by the user and when the network supports the feature, this feature allows control of the IMS services and more broadly SIP based services using the IMS framework that the user is allowed to access, for both originating and terminating sessions. The list of 3GPP PS Data Off Exempted Services is configured by the HPLMN in the UE and in the network for enforcement. The list of SIP based service can include any one or any combination of the following services: - MMTel Voice; - SMS over IMS; - MMTel Video; - USSI; - Services over IMS Data Channel; - Particular IMS Services not defined by 3GPP, where each such IMS service is identified by an IMS communication service identifier. NOTE: "Services over IMS Data Channel" is configured as a whole service in the list of 3GPP PS Data Off Exempt Services. X.2 UE Behaviour X.2.1 UE 3GPP PS Data Off Status Reporting The UE shall include an indication that depicts the 3GPP PS Data Off status (active/inactive) at initial IMS registration and subsequent to that, any time the end user changes the 3GPP PS Data Off status in a (re-)REGISTER request. In all these registration requests the UE shall register the SIP based services that are configured in the UE. NOTE: When the 3GPP PS Data Off status is reported, the configured SIP based services in UE are registered as defined in clause B.3.1.0 of TS 24.229 [10a]. The UE and the network shall ensure that the proper services are enforced in accordance with the 3GPP PS Data Off status. X.2.2 UE Provisioning The UE may be provisoned by HPLMN with up to two enumerated lists of SIP-based services that are 3GPP PS Data Off exempted either via Device Management or in the UICC, one list is valid for the UEs camping in the home PLMN and the other list is valid for any VPLMN the UE is roaming in. When the UE is configured only with a single list, without an indication to which PLMNs the list is applicable, then this list is valid for the home PLMN and any PLMN the UE is roaming in. A UE provisioned with an updated list shall enforce the updated list immediately. X.2.3 UE Enforcement of 3GPP SIP-Based 3GPP PS Data Off Exempt Services When the UE changes its 3GPP PS Data Off status from inactive to active, the UE shall ensure that only the 3GPP PS Data Off Exempted Services in the provisioned list are allowed to be transported and the corresponding IP uplink packets shall be sent accordingly as follows: - The UE shall prevent sending of UE-originating SIP requests which are for services other than the 3GPP PS Data Off Exempted Services configured in the UE via device management or in the UICC. - The UE shall prevent sending of SDP offers and SDP answers with media streams for the media types other than those related to the 3GPP PS Data Off Exempted Services configured via device management or in the UICC. - A UE shall immediately stop sending any media packets and shall terminate all ongoing sessions for all SIP-based services that are not 3GPP PS Data Off Exempt. Specifically, when Services over IMS Data Channel is not in the list of 3GPP PS Data Off Exempt services: - If the ongoing session is an IMS DC session including MMTel media (audio/video/messaging) and the MMTel media is exempted, the UE shall remove all the IMS Data Channels as specified in clause AC.7.6. - If the ongoing session is a standalone IMS DC session, the UE shall terminate the standalone IMS DC session. - A UE provisioned with an updated list shall enforce the updated list immediately. To that effect, the UE shall immediately stop sending any media packets and terminate all ongoing SIP-based sessions handling the 3GPP PS Data Off Exempt Service(s) removed from the list. X.3 Network Behaviour X.3.1 Network Update to 3GPP PS Data Off Exempted Services The HPLMN network shall provision in the UE either via Device Management or in the UICC the lists of 3GPP PS Data Off Exempt Services. Up to two lists are provisioned in the UE for that purpose: one list is used when the UE is at home, while the second list is used when the UE is roaming in any visited PLMN. The information shall be provisioned in the UE prior to enabling the 3GPP PS Data Off Service. Any change to either one or both lists shall immediately be sent to the UE for enforcement. X.3.2 Network Enforcement of SIP-Based 3GPP PS Data Off Exempted Services Application Servers implementing the SIP-based services shall enforce the SIP based 3GPP PS Data Off Exempted services for all UEs. Each Application Server shall be configured with up to two lists of 3GPP PS Data Off Exempt Services, one list for non-roaming users and the other list for users roaming in the various VPLMNs with whom roaming agreements exist. The AS shall become aware of the UE 3GPP Data Off status (active/inactive) at IMS (re-)Registration through third party registration. If the UE has changed its 3GPP PS Data Off status from inactive to active, the AS shall ensure that only SIP-based services which are part of the SIP-based 3GPP PS Data Off Exempt Services are permitted. In the context of IMS Data Channel, the AS may further notify the DCSF about the UE's 3GPP PS Data Off status during IMS session establishment and subsequently notifies the DCSF about any changes to the UE's 3GPP PS Data Off status during the IMS session. If the UE has changed its 3GPP PS Data Off status from active to inactive, the AS shall also let through the terminating requests to the UE for services that were not Data Off exempt. NOTE 1: The AS could be implemented in an existing AS e.g. SCC AS or distributed across other AS's. NOTE 2: The operator needs to ensure coordinated lists of 3GPP Data Off Exempt services provisioned in the UE and configured the network. NOTE 3: The notification about the UE 3GPP PS Data Off status to the DCSF can be used by operators for further control, which is out of scope. Annex Y (normative): IP-Connectivity Access Network specific concepts when using 5GS to access IMS Y.0 General This clause describes the main IP-Connectivity Access Network specific concepts that are used for the provisioning of IMS services over 5GS. HSS is used to store IMS related subscription and context as shown in the Figure 4.0 "Reference Architecture" specified in clause 4.0. For 5GS, HSS functionality for IMS shall continue to be as standalone regardless if it is co-located or implemented as part of the UDM. When the HSS and UDM are deployed as separate network functions, their interaction is defined by TS 23.632 [97] and TS 29.563 [98], or it may be implementation specific. A single IMS subscription profile is used regardless of UE accessing IMS via different IP-CANs. Figure Y.0-1: UDM and HSS collocated or HSS as part of UDM NOTE: The HSS shown in Figure Y.0-1 is only considering the functionality required for IMS. From IMS perspective, either the N5 interface as specified in TS 23.503 [95] or the Rx interface as specified in TS 23.203 [54] are used between the P‑CSCF and the Policy Control Function (PCF). NOTE: In PLMNs where both Rx and N5 are used it is implementation specific how the P-CSCF determins the applicable interface/protocol used for a particular interaction with the PCF/PCRF - e.g. Separate P-CSCF's used for Rx and N5, local routing configuration in the P-CSCF. In 5G System the Gm reference point defined in clause 4.0 and clause 4.4 is supported for the communication between UE and IMS, e.g. related to registration and session control. Therefore, the same interface is used, i.e. Gm, from P-CSCF perspective towards the UE, when UE is in 5G System or any other IP-CAN. Y.1 Mobility related concepts Y.1.0 General To support IMS, the UE shall establish a PDU session with PDU session type set to IP for the corresponding DNN (see TS 23.501 [93], clause 5.6.1) and acquire an IP address according to TS 23.501 [93], clause 5.8.2.2. If IMS Multimedia Telephony Service as specified in TS 22.173 [53] is to be used within the PDU session, SSC mode 1 shall be set for the PDU session. In this release of the specification, it is assumed that single PDU session with multiple PDU session anchors defined in TS 23.501 [93] clause 5.6.4 is not applicable for PDU sessions dedicated to IMS. NOTE 1: In the case of Dual Registration as defined in TS 23.501 [93], the UE will register (and if needed re-register) in IMS with the IP address of the IMS PDU session when the IMS PDU session is transferred between 5GS and EPS. If the UE changes its IP address due to changes triggered by the 5GS procedures or due to, for example, PLMN change, then the UE shall re- register in the IMS. If the UE acquires an additional IP address, then the UE may perform an IMS registration using this additional IP address as the contact address. If IMS registration is performed, this IMS registration may co-exist with the previous IMS registration from this UE and the UE shall be notified that this IMS registration results in multiple simultaneous registrations. NOTE 2: In this Release of the specification, the UE can acquire an additional IP address that can be used for registration to the IMS only outside of the 5G System. In Dual Connectivity with 5GC case, the UE shall use the access network information based on the primary cell of the Master RAN node that is serving the UE for network location information when the UE interacts with IMS, regardless whether the IMS traffic is routed via the Master RAN node or the Secondary RAN node or both. Y.1.1 Procedures for P‑CSCF discovery All the procedures described in clause 5.1.1 apply with the following additions: - For the option where P-CSCF discovery is part of the IP-CAN connectivity establishment the following applies: - P‑CSCF discovery shall take place during the PDU session establishment procedure see TS 23.502 [94], clause 4.3.2. In addition to the procedures in clause 5.1.1, the SMF may determine the P-CSCF using service-based discovery methods (using the NRF), as described in TS 23.501 [93] clause 5.16.3. Y.2 QoS related concepts Y.2.1 Application Level Signalling for IMS Y.2.1.0 General When the UE uses 5GS-access for IMS services, it shall be possible to establish at least one QoS flow identified by a QFI for IMS signalling. Y.2.1.1 QoS Requirements for Application Level Signalling It shall be possible to request prioritised handling over the 5GS system for IMS signalling by applying the appropriate 5QI for the established QoS flow for the IMS signalling, see TS 23.501 [93], clause 5.7. Y.2.1.2 Void Y.2.2 The QoS requirements for an IMS session Y.2.2.0 General The selection, deployment, initiation and termination of QoS signalling and resource allocation shall consider: - The general requirements described in clause 4.2.5. - The QoS handling is described in TS 23.501 [93], TS 23.502 [94] and TS 23.203 [54] and TS 23.503 [95]. Y.2.2.1 Relation of IMS media components and 5GS QoS flows carrying IMS media All associated media flows (such as e.g. RTP / RTCP flows) used by the UE to support a single media component are assumed to be carried within the same 5GS QoS flow. Y.2.3 Interaction between 5GS QoS and session signalling Y.2.3.0 General The generic mechanisms for interaction between QoS and session signalling are described in clause 5.4.7. The mechanisms described there and the related procedures througout the present specification are applicable to 5GS-accesses as well with the following clarifications: - An IP-CAN bearer in this specification shall be interpreted as a 5GS QoS flow. - An IP-CAN session in this specification shall be interpreted as a 5GS PDU session of type IP. - The negotiation of the bearer establishment mode does not apply for the 5GS. - The PCEF corresponds to the combination of SMF and UPF. Y.2.3.1 Resource Reservation with PCF The UE or 5GC can initiate the resource reservation request for the media parameters negotiated over SDP using PDU session modification procedure, see TS 23.502 [94], clause 4.3.3. However, for IMS. the network shall initiate the establishment, modification and termination of 5GS QoS flows triggered by negotiated SDP. Y.2.4 Network initiated session release - P-CSCF initiated Y.2.4.0 General In the event of loss of coverage for 5GS radio access, TS 23.502 [94], clause 4.2.6, defines the N2 release procedure. This procedure releases the QoS flows. This is indicated to the P‑CSCF as shown in figure Y.3. Y.2.4.1 Network initiated session release - P-CSCF initiated Covers radio coverage loss and that GFBR cannot be maintained by the radio access. Figure Y.3: Network initiated session release - P‑CSCF initiated after loss of radio coverage 1. In the case of loss of radio coverage or that GFBR cannot be retained in NG-RAN, the 5GC may release the related GBR QoS flow and PCF and P-CSCF are notified appropriately. 2. The P‑CSCF decides on the termination of the IMS session. In the event of the notification that the signalling transport to the UE is no longer possible, the P‑CSCF shall terminate any ongoing IMS session with that specific UE. If the P‑CSCF decides to terminate the IMS session, it indicates this to PCF, which removes the authorization for resources that had previously been issued for this endpoint for this session. (see TS 23.503 [95]). The following steps are only performed in the case the P‑CSCF has decided to terminate the session. 3. The P‑CSCF generates a Release (Bye message in SIP) to the S‑CSCF of the releasing party. 4. The S‑CSCF invokes whatever service logic procedures are appropriate for this ending session. The S‑CSCF of the releasing party forwards the Release to the S‑CSCF of the other party. 5. The S‑CSCF invokes whatever service logic procedures are appropriate for this ending session. The S‑CSCF of the other party forwards the Release on to the P‑CSCF. 6. The P‑CSCF of the other party removes the authorization for resources if they have previously been issued for this endpoint for this session. The P‑CSCF forwards the Release to the UE. 7. The UE of the other party responds with a SIP OK to the P‑CSCF 8. Depending on the Bearer Control Mode selected for the IP‑CAN session, the release of previously reserved resources shall be initiated either by the UE or by the IP‑CAN itself. The SIP OK message is sent to the S‑CSCF of the other party. 9. The S‑CSCF of the other party forwards the OK to the S‑CSCF of the releasing party. 10. The S‑CSCF of the releasing party forwards the OK to the P‑CSCF of the releasing party. Y.3 Address and identity management concepts Y.3.1 Deriving IMS identifiers from the USIM If the UICC does not contain an ISIM application and the permanent user identity is IMSI then clause E.3.1 applies. Y.4 IP version interworking in IMS A PDU session is associated with either an IPv4 or an IPv6 address. For communication with the IMS, the UE shall acquire an IP address according to TS 23.501 [93], clause 5.8.1.1 for the PDU session. The IP address will be either an IPv4 address or and IPv6 address. Hence, a UE will register to the IMS with either an IPv4 or an IPv6 address. Here the P-CSCF and IMS-AGW may support both IP versions and/or may do interworking depending IP version used within the IMS. If the P-CSCF and IMS-AGW do not support both versions, then network design is expected to ensure that IP address incompatibility does not occur. Y.5 Usage of NAT in 5GS There should be no NAT (or its existence should be kept transparent towards the UE) located between the UPF and the P‑CSCF, which is possible as they are either located within the same private network and share same address space, or both the UE and the P‑CSCF are assigned globally unique IP addresses (see Annex M). NOTE: If the UE discover a NAT between the UE and the P‑CSCF, the UE might send frequent keep-alive messages and that may drain the UE battery. Y.6 Retrieval of Network Provided Location Information in 5GS Information related to the location of the user provided by the access network may be required in IMS in order to comply with regulatory requirements (e.g. data retention, lawful interception) and/or in order to enable certain types of added value services based on the user's location. Depending on usage scenario, the following mechanisms are defined and can be used to retrieve the user location and/or UE Time Zone information from the access network when using 5GS to access IMS: - The P‑CSCF can retrieve the user location and/or UE Time Zone information using PCC mechanisms as specified in TS 23.203 [54] / TS 23.503 [95] and in TS 29.214 [11]. Operator policy determines whether to provide the user location and/or UE Time Zone information from the access network in the INVITE request, a MESSAGE request, or within a subsequent message of the dialog. - When the user location and/or UE Time Zone information is required from the access network but not already available (e.g. when required in an INVITE request, when it is needed prior to session delivery, or when call is broken out to a MGCF), an IMS AS can trigger the retrieval of the user location and/or UE Time Zone information from the AMF via the HSS/UDM as specified in TS 29.328 [79] and as described in clause 4.2.4a. Information flows on how user location and/or UE Time Zone information can be further distributed within IMS depending on the alternative mechanism used can be found in, Annex R, where the terms HSS and HSS/UDM shall be understood as in clause Y.0. The level of granularity of user location information may be changed at network/trust boundaries. Thus, the level of user location information granularity that can be retrieved by an IMS AS via the HSS/UDM-based procedures in roaming scenarios depends on inter-operator agreement and needs to be aligned with policies in the P-CSCF. Information related to the location of the user provided by the access network may be required in IMS in order to comply with regulatory requirements for SMS over IP. The P-CSCF applies the above mechanisms upon reception of a MESSAGE including the distribution of received information to other IMS entities. Y.7 Geographical Identifier A network which requires the Geographical Identifier to be generated in the IMS may implement a mapping table between a NG-RAN cell identifier received as part of Access Network Information and a Geographical Identifier. The P-CSCF or an IMS AS may then, based on operator policy, use this mapping table to convert the user location into a Geographical Identifier and insert the Geographical Identifier in the SIP signalling, thus enabling routing decision in downstream IMS entities or interconnected network. In the case that a given cell belongs to more than one area identified by a Geographical Identifier, based on operator policy, the P-CSCF or an IMS AS may use the UE mobility analytics provided by NWDAF as specified in TS 23.288 [103]. Y.8 Support for Paging policy differentiation for IMS services P-CSCF may support Paging Policy Differentiation (as defined in TS 23.501 [93]) for a specific IMS service by marking packet(s) to be send towards the UE related to that IMS service. For such an IMS service, a specific DSCP (IPv4) value and/or a specific Traffic Class (IPv6) value are assigned by local configuration in the P-CSCF. NOTE 1: The packet marking used for Paging Policy Differentiation can also be used for determination of the Paging Cause, for the Multi-USIM UE support, by the relevant 5GS node. When Paging Policy Differentiation is deployed in a PLMN, all P-CSCF entities of that PLMN shall homogeneously support it and shall be configured with the same policy for setting the specific DSCP (IPv4) and/or Traffic Class (IPv6) values used by P-CSCF for that feature. NOTE 2: It is assumed that the DSCP / Traffic Class header is not rewritten by intermediate routers between the P-CSCF and the UPF. Y.9 Support of IMS Services for roaming users Y.9.1 General This clause describes support for IMS services for roaming users using IMS level roaming interfaces or without IMS level roaming interfaces. Y.9.2 Architecture without IMS-level roaming interfaces This clause describes the functions that are used to support IMS services for roaming users in deployments without IMS-level roaming interfaces. In this roaming model the UPF holding the UE's IP point of presence is located in the home PLMN and therefore UE IMS signalling and user plane are routed to home PLMN. The architecture to support IMS services for roaming users, including Voice over IMS in deployments without IMS-level roaming interfaces is shown in figure Y.9.2-1. The following architecture requirements apply: - P-CSCF (in HPLMN) identifies the serving network (VPLMN) where the UE is located using the procedure defined in clause Y.9.3. Figure Y.9.2-1: IMS traffic home routed Y.9.3 Architecture with IMS-level roaming interfaces For IMS services with roaming level interfaces the P-CSCF and UPF are located in VPLMN (local breakout), see clauses 4.2.3 and M.1. For roaming architecture for voice over IMS with local breakout see clause 4.15a. For information on how to apply the loopback possibility in clause 4.15a, see clause M.3. Y.9.4 Subscription to changes in PLMN ID at IMS Initial Registration In IMS local breakout where P-CSCF is located in VPLMN (see Annex M.1 and Annex M.3), the home network determines the serving PLMN of the UE from the location of the P-CSCF during initial IMS Registration, using the P‑CSCF network identifier. In deployments without IMS-level roaming interfaces, the home network determines the serving PLMN of the UE using procedure defined in TS 23.503 [95], where P-CSCF requests the PCF to report the PLMN identifier where the UE is currently located. The received PLMN ID information is then forwarded in the SIP REGISTER request. This procedure shall be applied by the P-CSCF at initial UE IMS registration. Figure Y.9.4-1: Subscription by P-CSCF to changes in PLMN ID during initial IMS Registration 1. The UE sends a SIP REGISTER request to the P-CSCF. 2. If this is initial IMS registration then the P-CSCF subscribes to the PCF to be notified of the PLMN ID where the UE is currently attached. The subscription to PLMN changes is active as long as the UE is IMS registered. NOTE: P-CSCF cancels the subscription to PLMN changes at the PCF when the UE is IMS de-registered. 3. The PCF forwards the PLMN ID to the P-CSCF. The P-CSCF stores the PLMN ID. 4. The P-CSCF includes the received PLMN ID in the SIP REGISTER request before forwarding the request to the I-CSCF. 5. Normal IMS registration procedure is then completed. Y.10 Support of RAN Assisted Codec Adaptation RAN assisted codec adaptation is supported as described in clause E.10 with the addition that RAN assisted codec adaptation needs to be supported on NR RAT as specified in TS 38.300 [101] and TS 38.321 [102], in addition to E-UTRA RAT. Y.11 Void Y.12 P-CSCF Registration in NRF In order to support service based SMF discovery of the P-CSCF using the NRF (as described in TS 23.501 [93] clause 5.16.3) the P-CSCF's in a network will need to register with an applicable NRF. When a network uses other P-CSCF discovery methods (as described in clause 5.1.1) the P-CSCF does not need to register with the NRF. Local configuration of the P-CSCF is used to determine if the P-CSCF shall perform registration with the NRF. When the P-CSCF is configured to support SMF discovery of the P-CSCF, P-CSCF shall register in NRF their capabilities using the Nnrf_NFManagement_NFRegister Request message. The NF profile of the P-CSCF registered in NRF shall include the IP address and may include an FQDN if available. The same applies to the Nnrf_NFManagement_NFUpdate Request. Based on the same configuration, a P-CSCF taken out of service will deregister itself using the Nnrf_NFManagement_NFDeregister Request. Y.13 Subscription to EPS Fallback Event Based on local configuration in the case of an originating or a terminating session, the P-CSCF may subscribe to the PCF for notification for the EPS Fallback event using existing procedures defined in TS 23.503 [95]. If the PCF reports that an EPS fallback occurred, based on local configuration, the P-CSCF may include this information in outgoing SIP messages towards other IMS nodes. Annex Z (normative): Support of IMS-based Restricted Local Operator Services (RLOS) Z.1 General This clause describes the required functions to support IMS-based restricted local operator services (RLOS). RLOS services are operator owned services that are offered to the following categories of subscribers: - Roaming users who are subscribers of other operators with whom the local operator has no roaming agreement, or the local operator cannot communicate with their network. - Roaming users who are subscribers of other operators with whom the local operator has roaming agreements for IMS services and for Restricted Operator Local Services. - Operator own subscribers who roamed in cells with restricted services. These subscribers may or may not have been successfully authenticated prior to roaming in cells with restricted services. NOTE: Operator restricted services can also be offered to the local operator own subscribers roaming in unrestricted areas, however this is out of scope. RLOS is used only for originating services. In this version of the specification, RLOS is only defined for users connected to IMS over EPS (see TS 23.401 [70]); Z.2 Architecture Support for RLOS requires additional functionalities in the P-CSCF, I- CSCF and S-CSCF as will be depicted below. The additional functionality can be built on the existing functionality to support RLOS and non-RLOS IMS services. Optionally, dedicated IMS nodes (P/I/S-CSCFs) supporting only RLOS can be deployed. NOTE: Architecture for roaming scenarios without IMS-level roaming agreement (as defined in Annex W) does not apply to RLOS users accessing IMS. Z.3 IMS Registration to access RLOS Z.3.1 RLOS IMS Registration for Roaming users (no roaming Agreements with home network) Figure Z.3.1-1: RLOS IMS Registration procedures for roaming users without roaming agreements with their home network 1. After the UE has obtained IP connectivity (as defined in TS 23.401 [70] for RLOS users), it performs regular IMS registration and includes an indication that this is an RLOS related IMS registration in the Register information. 2. The P‑CSCF is a P-CSCF that supports RLOS and upon receipt of the Register information, optionally and based on operator policy performs the security checks in clause Z.3.3. Based on the subscriber being a roaming user without roaming agreement with his home network and the RLOS indication in the Register information, the P-CSCF shall send the Register information to the S-CSCF configured in the P-CSCF to handle RLOS users. NOTE: The P-CSCF ID for handling RLOS would have been sent to the UE during the Attach procedure which included an explicit indication to access RLOS. Steps 3-8 apply if the S-CSCF has responded with 420 response. 3. Upon receipt of the Register information, the S-CSCF, based on the RLOS indication and the subscriber being a roaming user without roaming agreement with his home network and depending on the network configuration and if the network supports GIBA, sends back a 420 response with sec-agree value listed in the unsupported header field. 4. The P-CSCF forwards the 420 response to the UE. 5. The UE initiates a new Register request and does not include the Authorization header field. 6. The P-CSCF optionally performs the RLOS APN verification in clause Z.3.3, then sends the Register information to the S-CSCF allocated to the UE. 7. Upon receipt of the Register information, the S-CSCF shall accept the Registration, creates a temporary record for the unauthenticated UE with a default service profile and responds with a 200 OK. 8. The P-CSCF sends the 200 OK to the UE. Steps 9-10 apply if the S-CSCF has responded with 403 response. 9. Upon receipt of the Register information, the S-CSCF, based on the RLOS indication and the subscriber being a roaming user without roaming agreement with his home network and depending on the network configuration as well as operator configuration (no support for GIBA), responds with a 403 response. The S-CSCF creates a temporary registration record for the unauthenticated UEs with a default service profile. 10. The P-CSCF sends the 403 response to the UE. The P-CSCF creates a temporary registration record for the unauthenticated UE given that the subscriber is a roaming user without roaming agreement with his home network. The UE is allowed to initiate an IMS session. Z.3.2 RLOS IMS Registration for Operator own subscribers and Roaming users with roaming agreements with their home network Operator own subscribers and/or roaming users with IMS services and Restricted Local Operator Services roaming agreement with their home network, shall perform a new IMS registration, as specified below, to access IMS-based Restricted Local Operator Services upon roaming in cells with restricted services. The UE shall also delete any valid IMS registration performed by the UE prior to roaming in cells with restricted services. Z.3.2.1 Unsuccessful IMS Registration Figure Z.3.2.1-1: Unsuccessful RLOS IMS Registration procedure 1. After the UE has obtained IP connectivity (as defined in TS 23.401 [70] for RLOS users), it performs regular IMS registration and includes an indication that this is an RLOS IMS related registration in the Register information. 2. The P-CSCF is a P-CSCF that supports RLOS and upon receipt of the Register information optionally and based on operator policy, performs the RLOS APN verification in clause Z.3.3. The P-CSCF based on the RLOS indication and the subscriber being its own subscriber sends the Register information to the I-CSCF. NOTE 1: The P-CSCF ID for handling RLOS would have been sent to the UE during the Attach procedure which included an explicit indication to access RLOS. 3. The I-CSCF queries HSS for the subscriber S-CSCF. If the I-CSCF determines based on configuration that the received S-CSCF does not support RLOS and since this is an RLOS related registration, the I-CSCF queries HSS again for required S-CSCF capabilities in the user profile. The I-CSCF shall use the returned S-CSCF capability information and in addition configured information about S-CSCF support for RLOS to select a S-CSCF. NOTE 2: The S-CSCF allocated to a subscriber may be from an old registration that did not expire and is not deleted, or for an RLOS related registration. The S-CSCF support of RLOS is preconfigured in the I-CSCF rather than a capability stored in the user profile within the HSS as otherwise RLOS support would be a requirement for the S-CSCF selection even if the registration is not for RLOS. 4. The I-CSCF sends the Register information to the selected S-CSCF. 5. The S-CSCF fetches the authentication information from HSS. 6. The S-CSCF challenges the UE by sending a 401 response. 7. The I-CSCF forwards the 401 response to the P-CSCF. 8. The P-CSCF forwards the 401 response to the UE. 9. The UE sends a new Register request to the P-CSCF including the authentication information. 10. The P-CSCF optionally and based on operator policy, performs the RLOS APN verification in clause Z.3.3, then sends the Register information to the I-CSCF. 11. The I-CSCF queries HSS for the subscriber S-CSCF and receives the S-CSCF name allocated to the UE. If the I-CSCF determines based on configuration that the received S-CSCF does not support RLOS and since this is an RLOS related registration, the I-CSCF queries HSS again for required S-CSCF capabilities in the user profile. The I-CSCF shall use the returned S-CSCF capability information and in addition configured information about S-CSCF support for RLOS to select a S-CFCF. 12. The I-CSCF sends the Register information to the selected S-CSCF. 13. The S-CSCF validates the UE received authentication information but failed to successfully authenticate the UE. Since this is an RLOS related IMS registration, the S-CSCF creates a temporary "unauthenticated subscriber" registration record for the UE with a default service profile and responds with a 403 response. 14. The I-CSCF sends the 403 response to the P-CSCF. 15. The P-CSCF sends the 403 response to the UE and creates a temporary "unauthenticated subscriber" registration record for the UE. Z.3.2.2 Successful IMS Registration A successful IMS registration is identical to the failed one with following exceptions: - The S-CSCF successfully authenticates the UE in step 12. - The S-CSCF tags the UE registration record as being successfully RLOS registered. - The S-CSCF updates HSS with the S-CSCF name being allocated to the UE, downloads the UE profile from HSS and stores it. This step is not performed in the previous case. - The P-CSCF tags the UE registration record as being successfully RLOS registered. Z.3.3 RLOS APN Verification The P-CSCF may be configured with a range of IP addresses dedicated to UEs requesting access to RLOS. These addresses, if configured, shall be checked against the contact information received by the P-CSCF Register information at IMS registration. Furthermore, the P-CSCF shall validate that an incoming IMS registration did indeed use the APN dedicated to RLOS by the access network. To that effect, the P-CSCF shall indicate to the PCRF that the UE requests access to RLOS. The PCRF shall then validate whether the UE uses the APN dedicated to RLOS and otherwise reject the related Rx session with the indication that the UE is not using the APN dedicated to RLOS. Upon reception of such an indication from the PCRF, the P-CSCF shall reject the IMS registration. Z.4 IMS-based RLOS Session Initiation Clause 5.6.2 applies with the following additional requirements: - The UE shall include an RLOS indication in all originating sessions. The P-CSCF shall reject an originating session without such an indication. - The S-CSCF shall include the RLOS indication in its charging data related to an IMS session. - The S-CSCF shall forward the session initiation request to the Telephony Application Server. The Telephony Application Server shall bypass originating services for all successfully authenticated UEs. The Telephony Application Server, based on operator policy, may be configured with different policies (e.g. set of destinations) for all of the above registration cases. The Telephony Application Server shall enforce these policies. - The S-CSCF shall include the RLOS indication in its charging data related to an IMS session. - The registered identity shall be used as the asserted identity. Annex AA (normative): Support of SBA in IMS AA.1 General AA.1.0 Overview This Annex AA describes support for SBA for IMS nodes. This Annex is intended to be used in conjunction with 5GC. AA.1.1 Architectural Support Figure AA.1.1-1 shows the architecture to support SBA interactions between IMS entities. Figure AA.1.1-1: System Architecture to support SBA in IMS NOTE 1: The DCSF and MRF supports NF registration and discovery, but they do not provide services in this release of the specification. NOTE 2: Nimsas services are defined in the context of IMS Data Channel, see clause AA.2.4. Figure AA.1.1-2 shows the architecture using the reference point representation. Figure AA.1.1-2: System Architecture to support SBA in IMS in reference point representation NOTE 3: In this Release of the specification the SBI capable IMS AS supporting data channel services is collocated with the TAS. AA.1.2 Reference point to support SBA in IMS Following reference points are realized by service-based interfaces in IMS: N5: Reference point between the PCF and an AF. NOTE: P-CSCF acts as an AF from PCF point of view. N5 Reference point is defined in TS 23.501 [93]. N70: Reference point between an SBI capable I/S-CSCF and an SBI capable HSS. N71: Reference point between an SBI capable IMS AS and an SBI capable HSS. DC1: Reference point between an SBI capable IMS AS and DCSF. DC2: Reference point between an SBI capable IMS AS and MF. N72: Reference point between DCSF and an SBI capable HSS. AA.1.3 Service based interface to support SBA in IMS Npcf: Service-based interface exhibited by PCF. Nhss: Service-based interface exhibited by an SBI capable HSS. These SBI services provide equivalent functionality to the Diameter Rx and Cx/Sh reference points. Nimsas: Service-based interface exhibited by an SBI capable IMS AS. Nmf: Service-based interface exhibited by MF. These SBI services provide functionality to support data channel management and media handling in IMS network. To support co-existence of IMS nodes supporting SBA services and IMS nodes not supporting SBA services SBI enabled IMS nodes may support both SBI and non-SBI interfaces. NOTE: Nnrf may assist other IMS nodes to use NRF to perform registration, discovery, or selection, as described in clause AA.4. AA.2 IMS SBA Services AA.2.1 HSS Services AA.2.1.1 General The following table shows the services exposed by an SBI capable HSS. Table AA.2.1.1-1: IMS Services provided by an SBI capable HSS Service Service Operations Operation Semantics Example Consumer(s) ImsSubscriber Data Get Request/Response S-CSCF, I-CSCF, AS, DCSF Management (_ImsSDM) Subscribe Subscribe/Notify S-CSCF, AS Unsubscribe Subscribe/Notify S-CSCF, AS Notification Subscribe/Notify S-CSCF, AS Update Request/Response AS, DCSF Ims UE Context Registration Request/Response S-CSCF, IMS AS Management DeregistrationNotification Subscribe/Notify S-CSCF (_ImsUECM) Deregistration Request/Response S-CSCF, IMS AS Authorize Request/Response I-CSCF Update Request/Response S-CSCF RestorationInfoGet Request/Response S-CSCF RestorationInfoUpdate Request/Response S-CSCF ImsUE Authentication AsInfoGet Request/Response NEF (_ImsUEAU) Get Request/Response S-CSCF ImsEventExposure Subscribe Subscribe/Notify NEF, Trusted AF (_ImsEE) Unsubscribe NEF, Trusted AF AA.2.1.2 Nhss_ImsUEContextManagement (ImsUECM) service AA.2.1.2.1 Nhss_ImsUECM_Registration service operation Service operation name: Nhss_ImsUECM_Registration Description: If S-CSCF is the consumer, this service operation registers the serving S-CSCF assigned to an IMS User. If authentication is not to be performed, this operation also sets the registration state. The S-CSCF is implicitly subscribed to be notified when it is deregistered in HSS. This notification is done by means of Nhss_ImsUECM_DeregistrationNotification operation. If IMS AS is the consumer, this service operation registers the IMS AS instance assigned to an IMS user. Inputs, Required: Public Identity, S-CSCF name if the S-CSCSF is the consumer, IMS AS instance Id if the IMS AS is the consumer, Registration Type (e.g. Initial Registration, Unregistered). Inputs, Optional: Private Identity. Outputs, Required: Result indication. Outputs, Optional: List of registered Private Identities sharing the same Public Identity which is being registered, S-CSCF Restoration indication. AA.2.1.2.2 Nhss_ImsUECM_Deregistration service operation Service operation name: Nhss_ImsUECM_Deregistration Description: This service operation deregisters the S-CSCF allocated to a public identity if the consumer is S-CSCF and deregisters the IMS AS instance assigned to the public identity if the consumer is IMS AS. Inputs, Required: S-CSCF name if the S-CSCSF is the consumer, IMS AS instance ID if the IMS AS is the consumer, Deregistration Type. Inputs, Optional: User Identity (Private Identity and/or Public Identity), P-CSCF Restoration indication, Session Priority. Outputs, Required: Result indication. Outputs, Optional: None. AA.2.1.2.3 Nhss_ImsUECM_DeregistrationNotification service operation Service operation name: Nhss_ImsUECM_DeregistrationNotification Description: This service operation enables HSS to inform a S-CSCF which has previously registered in HSS of a Public Identity deregistration. This notification corresponds to an implicit subscription. Inputs, Required: Private Identity, Reason for Deregistration. Inputs, Optional: Public Identity, Associated Private Identities. Outputs, Required: Result indication. Outputs, Optional: Associated Private Identities, Identities with Emergency Registration. AA.2.1.2.4 Nhss_ImsUECM_Authorize service operation Service operation name: Nhss_ImsUECM_Authorize Description: This service operation is used by the I-CSCF to request authorization from HSS for: - The registration of a Public Identity by a UE in a P‑CSCF network identifier according to the IMS User's subscription and operator limitations/restrictions. - The reception of a terminating request based on the user state and IMS user's subscription (e.g. IMS User's barring status). If the IMS User is authorized, the HSS may provide the address of the S-CSCF assigned to the Public Identity if any. Additionally, this service operation is used to authorize in HSS a S-CSCF reselection (e.g. after I-CSCF detection if a S-CSCF failure). Inputs, Required: Public Identity, Authorization Type. Inputs, Optional: Private User Identity, P‑CSCF network identifier. Outputs, Required: Result indication. Outputs, Optional: S-CSCF name. AA.2.1.2.5 Nhss_ImsUECM_Update service operation Service operation name: Nhss_ImsUECM_Update Description: This service operation updates the registration state of a Public Identity or Private Identity in HSS i.e. to update the registration state from Not Registered or Unregistered to Registered state. NOTE: This operation is used by S-CSCF after successful authentication to set the registration state (if not already set). Inputs, Required: Public Identity, S-CSCF name. Inputs, Optional: Private Identity. Outputs, Required: Result indication. Outputs, Optional: None. AA.2.1.2.6 Nhss_ImsUECM_RestorationInfoGet service operation Service operation name: Nhss_ImsUECM_RestorationInfoGet Description: This service operation is used between the S-CSCF and the HSS to retrieve information from HSS to support the S-CSCF procedures. Inputs, Required: Public Identity. Inputs, Optional: Private Identity. Outputs, Required: Result Indication. Outputs, Optional: Restoration data. AA.2.1.2.7 Nhss_ImsUECM_RestorationInfoUpdate service operation Service operation name: Nhss_ImsUECM_RestorationInfoUpdate Description: This service operation is used between the S-CSCF and the HSS to update information in HSS to support the S-CSCF Restoration procedures. Inputs, Required: Private Identity, Public Identity, Restoration data. Inputs, Optional: None. Outputs, Required: Result indication. Outputs, Optional: None. AA.2.1.2.8 Nhss_ImsUECM_AsInfoGet service operation Service operation name: Nhss_ImsUECM_AsInfoGet Description: This service operation is used by the service consumer NF, e.g. the NEF, to retrieve the information of the IMS AS served the specific subscriber from the HSS, e.g. the address. Inputs, Required: Public Identity. Inputs, Optional: None. Outputs, Required: Result indication. Outputs, Optional: IMS AS instance. AA.2.1.3 Nhss_ImsSubscriberDataManagement (ImsSDM) service AA.2.1.3.1 General IMS Subscriber data types used in the Nhss_ImsSDM Service are defined in Table AA.2.1.3.1-1 below. NOTE: IMS Subscriber data is terminology only used in Annex AA. It includes IMS subscription data and other data related to the subscriber, e.g. network functionality entity address, location information or T-ADS information. Table AA.2.1.3.1-1: IMS Subscriber data types IMS Subscriber data Description Service Profile Data This may include e.g. service parameters, the S-CSCF allocated to a public identity or the list of S-CSCFs and their capabilities, Application Server address, triggers, information on subscribed media, profile parameters (e.g. barring indicator, etc.) as defined in TS 29.228 [30]. Service Profile Data is consumed by CSCF. Repository Data Data that is understood syntactically but not semantically by the HSS (unstructured Data). It is data that an AS or DCSF may store in the HSS to support its service logic. One example is data that an AS or DCSF stores in the HSS, using it as a repository. Service Indication identifies the set of service related transparent data associated to a Public Identity. Repository Data is consumed by IMS-AS and DCSF. Non-Transparent Data Data that is understood both syntactically and semantically by the HSS e.g. location information. Non-Transparent Data is structured using data references as defined in TS 29.328 [79]. Non-Transparent Data is consumed by IMS-AS. At least a mandatory key is required for each IMS Subscriber Data Type to identify the corresponding data as defined in Table AA.2.1.3.1-2 below. Table AA.2.1.3.1-2: IMS Subscriber data types keys IMS Subscriber Data Types Data Key Data Sub Key Service Profile Data Public Identity Repository Data Public Identity Service Indication Non-Transparent Data See NOTE 1 NOTE 1: TS 29.328 [79] defines the data keys/subkeys required by each data reference. AA.2.1.3.2 Nhss_ImsSDM_Get service operation Service operation name: Nhss_ImsSDM_Get Description: This service operation enables the NF consumer to fetch the service profile data, repository data and non-transparent data references for an IMS User. The HSS shall check that the requested NF consumer is authorized to fetch the requested data. In the case that the requested data is Repository data, the HSS may also authorize based on service indication. Inputs, Required: NF Type, IMS Subscriber data type(s), Key for each IMS Subscriber data type(s). Inputs, Optional: Application Service Identity. Outputs, Required: Result indication. Outputs, Optional: Requested Data. AA.2.1.3.3 Nhss_ImsSDM_Subscribe service operation Service operation name: Nhss_ImsSDM_Subscribe Description: The NF consumer subscribes for updates to requested data. HSS shall check that the requested NF consumer is authorized to subscribe to requested updates. Inputs, Required: NF Type, IMS Subscriber data type(s), Key for each IMS Subscriber data type(s). Inputs, Optional: Application Server Identity. Outputs, Required: When the subscription is accepted: Subscription Correlation ID. Outputs, Optional: None. AA.2.1.3.4 Nhss_ImsSDM_Unsubscribe service operation Service operation name: Nhss_ImsSDM_Unsubscribe Description: The NF consumer unsubscribes for updates to Requested data. Inputs, Required: Subscription Correlation ID. Inputs, Optional: None. Outputs, Required: Result. Outputs, Optional: None. AA.2.1.3.5 Nhss_ImsSDM_Notification service operation Service operation name: Nhss_ImsSDM_Notification Description: This service operation enables HSS to notify a NF of any changes to what the NF subscribed to. Inputs, Required: IMS Subscriber data type(s), Key for each IMS Subscriber data type(s). Inputs, Optional: None. Outputs, Required: Result indication. Outputs, Optional: None. AA.2.1.3.6 Nhss_ImsSDM_Update service operation Service operation name: Nhss_ImsSDM_Update Description: The NF consumer updates HSS subscription data if authorized to do so. Inputs, Required: NF Type, IMS Subscriber data type(s), Key for each IMS Subscriber data type(s). Inputs, Optional: Application Service Identity. Outputs, Required: Result. Outputs, Optional: None. AA.2.1.4 Nhss_ImsUEAuthentication service AA.2.1.4.1 Nhss_ImsUEAuthenticate_Get service operation Service operation name: Nhss_ImsUEAuthenticate_Get Description: This service operation is used between the S-CSCF and the HSS to exchange information to support the authentication between the end user and the home IMS network. Inputs, Required: Private User Identity, Public User Identity, Authentication Data (Authentication Scheme). Inputs, Optional: Authentication Data (Authentication Context, Authorization Information). Outputs, Required: Result Indication. Outputs, Optional: User Identity, Authentication Data (e.g. AV). AA.2.1.5 Nhss_ImsEventExposure (ImsEE) service AA.2.1.5.1 Nhss_ImsEE_Subscribe service operation Service operation name: Nhss_ImsEE_Subscribe Description: The NF consumer subscribes for a specific subscriber related IMS event. Inputs, Required: IMS Public Subscriber identity, Event-ID(s) representing the event of interest, Notification Target address, Event Reporting Information as defined in Table 4.15.1-1 of TS 23.502 [94]. Event-ID represents one or multiple events as defined in clauses AD.2.4 and AD.2.5. Inputs, Optional: Notification Correlation ID, Expiry time, Event Filters, Subscription Correlation ID (in the case of modification of the event subscription). Outputs, Required: When the subscription is accepted: Subscription Correlation ID, Expiry time (required if the subscription can expire based on the operator's policy). Outputs, Optional: First corresponding event report is included, if available (see clause 4.15.1 of TS 23.502 [94]). AA.2.1.5.2 Nhss_ImsEE_Unsubscribe service operation Service operation name: Nhss_ImsEE_Unsubscribe Description: The NF consumer unsubscribes for notifications to requested IMS event. Inputs, Required: Subscription Correlation ID. Inputs, Optional: None. Outputs, Required: Result. Outputs, Optional: None. AA.2.2 Mapping of Cx and Sh operations and terminology to HSS SBI services AA.2.2.1 General This clause gives mappings from Cx and Sh operations to HSS SBI services and service operations. AA.2.2.2 Mapping of Cx messages to HSS SBI services The following table defines the mapping between stage 2 Cx messages and HSS SBI services and service operations: Table AA.2.2.2-1: Cx messages to HSS SBI services and service operations mapping Cx message Source Destination HSS SBI service operation name Cx-Query I-CSCF HSS Nhss_ImsUECM_Authorize Cx-Select-Pull I-CSCF HSS Nhss_ImsSDM_Get (see NOTE 1) Cx-Put S-CSCF HSS Nhss_ImsUECM_Registration (see NOTE 2) Nhss_ImsUECM_Deregistration (see NOTE 3) Nhss_ImsUECM_Update (see NOTE 4) Nhss_ImsUECM_RestorationInfoUpdate (see NOTE 5) Cx-Pull S-CSCF HSS Nhss_ImsSDM_Get (see NOTE 6) Nhss_ImsSDM_Subscribe (see NOTE 6) Nhss_ImsSDM_Unsubscribe Nhss_ImsUECM_RestorationInfoGet (see NOTE 7) Cx-Location-Query I-CSCF HSS Nhss_ImsUECM_Authorize Nhss_ImsSDM_Get (see NOTE 8) Cx-AuthDataReq S-CSCF HSS Nhss_ImsUECM_Registration (see NOTE 9) Nhss_ImsUEAuthenticate_Get Cx-Deregister HSS S-CSCF Nhss_ImsUECM_DeregistrationNotification Cx-Update_Subscr_Data HSS S-CSCF Nhss_ImsSDM_Notification NOTE 1: Corresponds to Cx-Select-Pull for the requests of S-CSCF capabilities from I-CSCF to the HSS. NOTE 2: Corresponds to Cx-Put for Registration of S-CSCF in HSS during Registration/Re-registration and Unregistered cases. NOTE 3: Corresponds to Cx-Put for de-registration of S-CSCF in HSS. NOTE 4: Corresponds to Cx-Put message for updating the registration state of Public Identity in HSS. NOTE 5: Corresponds to Cx-Put message for storing S-CSCF Restoration data during IMS registration procedures. NOTE 6: Corresponds to Cx-Pull when S-CSCF needs to fetch and subscribe to notification of changes in IMS User's Service Profile Data. NOTE 7: Corresponds to Cx-Pull for retrieval of S-CSCF Restoration data from HSS. NOTE 8: Corresponds to Cx-Location-Query for the requests of S-CSCF capabilities from I-CSCF to the HSS. NOTE 9: Corresponds to Cx-Put for the assignment of a S-CSCF during execution of the authentication of the IMS User. AA.2.2.3 Mapping of Sh messages to HSS SBI services The following table defines the mapping between stage 2 Sh messages and HSS SBI services and service operations: Table AA.2.2.3-1: Sh messages to HSS SBI services and service operations mapping Sh message Source Destination HSS SBI service operation name Sh-Pull AS HSS Nhss_ImsSDM_Get Sh-Update AS HSS Nhss_ImsSDM_Update Sh-Subs-Notif AS HSS Nhss_ImsSDM_Subscribe Nhss_ImsSDM_Unsubscribe Nhss_ImsSDM_Get Sh-Notif HSS AS Nhss_ImsSDM_Notification NOTE: The mapping of Sh messages to HSS or IMS AS SBI services is defined in TS 29.328 [79] AA.2.3 Void AA.2.4 IMS AS Services AA.2.4.1 General The following table shows the IMS AS Services and IMS AS Service Operations. Table AA.2.4.1-1: NF services provided by the IMS AS Service Name Service Operations Operation Semantics Example Consumer(s) Nimsas_SessionEventControl Subscribe Subscribe/Notify DCSF Notify Subscribe/Notify DCSF Nimsas_MediaControl MediaInstruction Request/Response DCSF Nimsas_ImsSessionManagement Create Request/Response NEF, Trusted AF Update Request/Response NEF, Trusted AF Delete Request/Response NEF, Trusted AF Notify Subscribe/Notify NEF, Trusted AF Nimsas_ImsEventExposure (ImsEE) Subscribe Subscribe/Notify NEF, HSS, Trusted AF Unsubscribe Subscribe/Notify NEF, HSS, Trusted AF Notify Subscribe/Notify NEF, Trusted AF Nimsas_ImsParameterProvision (ImsPP) Create Request/Response NEF, Trusted AF Update Request/Response NEF, Trusted AF Delete Request/Response NEF, Trusted AF NOTE 1: In this Release the IMS AS services is introduced to support Data Channel services in IMS further described in Annex AC. NOTE 2: There shall be no overlap between events supported in Nimsas_ImsEventExposure service vs events implicitly supported in Nimsas_SessionEventControl service. AA.2.4.2 Nimsas_SessionEventControl AA.2.4.2.1 General Service description: This service enables the consumer to be notified about session events when served IMS subscribers take part in IMS sessions. The following operations are available for this service: - Explicit subscription to receive session events. This is not specified in this Release. - Notifying IMS session control events of a specific IMS subscriber to NFs, e.g. DCSF, based on local configuration in the IMS AS. IMS AS processing of the session event is paused until the consumer acknowledges reception of the session event notification. The consumer is given the possibility to apply session media control and policies by invoking the Nimsas_MediaControl service before giving IMS AS a session event notification acknowledgement. If the consumer does not apply media control/policies to a session event, IMS AS continues processing and forwards the event as is (including the media state) to calling/called party. The AS may notify the DCSF about the UE's 3GPP PS Data Off status during IMS session establishment and subsequently notifies the DCSF about any changes to the UE's 3GPP PS Data Off status during the session based on implicit subscription to the PSDataOffStatusChangeEvent. AA.2.4.2.2 Nimsas_SessionEventControl_Notify service operation Service operation name: Nimsas_SessionEventControl_Notify Description: This service operation enables IMS AS to notify consumers of session events related to a specific served IMS subscriber that has IMS data channel subscription. Inputs, Required: Session ID, Event ID, Session ID is the identity of the IMS session for which the event relates to. Event ID is the event triggered within the IMS session. Inputs, Optional: Calling ID, Called ID, Session case, Event initiator, 3GPP PS Data Off Status, Media info list, Media information set. Calling ID is the public identity of the calling IMS subscriber. Called ID is the public identity of the called IMS Subscriber. Session case indicates if this is an originating, terminating IMS session or external initiated session. Event initiator indicates initiator of the event, i.e. 'served IMS subscriber', 'remote IMS subscriber' or 'third party'. 3GPP PS Data Off Status is the active/inactive of 3GPP PS Data Off of the UE the network is serving. Media info list includes for each media corresponding to a m line in the SDP offer or answer in the list: - media ID: uniquely identifies this media item within the list. The identity is allocated by IMS AS. - media specification(s): This depends on media type including relevant media attributes of interest to the consumer. If the media type is data channel and multiple data channels are multiplexed in the same m line in the SDP offer or answer, multiple media specifications for all multiplexed data channels are included, each of which represents a data channel being multiplexed in the media item. Each media specification includes the following media description attributes: - Media Type: DC, Audio, or Video. When the media type is "DC", the elements below are derived from the SDP received by the IMS AS in an SIP INVITE or a re-INVITE related to an IMS Data Channel and the corresponding DTLS connection. - Data Channel Mapping and Configuration Information: This attribute is applicable to Data Channel and includes relevant configuration Information, including the stream ID and application binding information of the Data Channel as specified in TS 26.114 [76]. - Maximum Message Size: This attribute defines the maximum size to be expected. - Data Channel Port: This attribute identifies the port for the Data Channel. - Data Channel SCTP Port: This attribute identifies the SCTP port for the Data Channel. - Security Setup: This attribute identifies the security set up of the DTLS connection. - Security Certificate Fingerprint: This attribute identifies the security certificate fingerprint. - Security Transport Identity: This attribute identifies transport layer identity. Media information set is included only for the following events: - For Event ID "ExternalSessionCreateEvent", the media information set is described in clause AA.2.4.4.2. - For Event ID "ExternalSessionUpdateEvent", the media information set is described in clause AA.2.4.4.2. Outputs, Required: Result indication. Outputs, Optional: None. The table below presents supported EventIDs and related parameters. Table AA.2.4.2.2-1: List of events and Related Optional parameters EventID Parameters SessionEstablishmentRequestEvent Calling ID, Called ID, Session case, Event initiator, Media info list, 3GPP PS Data Off Status SessionEstablishmentProgressEvent Media info list SessionEstablishmentAlertingEvent Media info list SessionEstablishmentSuccessEvent Media info list SessionEstablishmentFailureEvent MediaChangeRequestEvent. Event initiator, Media info list, Calling ID, Called ID, Session case MediaChangeSuccessEvent Media info list MediaChangeFailureEvent Media info list SessionTerminationEvent Session case ExternalSessionUpdateEvent Media information set ExternalSessionCreateEvent Calling ID, Called ID, Session case, Event initiator, Media information set PSDataOffStatusChangeEvent 3GPP PS Data Off Status AA.2.4.3 Nimsas_MediaControl Service AA.2.4.3.1 General Service description: This service enables the consumer to control IMS AS handling of media flow within an IMS session. The service can be used by the consumer after receiving and before responding to a Nimsas_SessionEventControl_Notify request. AA.2.4.3.2 Nimsas_MediaControl_MediaInstruction service operation Service operation name: Nimsas_MediaControl_MediaInstruction Description: This operation provides instructions to the IMS AS for all media flows a consumer wants to control based on its policies for the received IMS session event and that may require resource reservation in media resource e.g. MF. For the case when a specific media flow needs to be terminated in MF media resource (i.e. termination of a Data Channel media descriptor offered by one of the IMS subscribers) or originated by the MF (i.e. origination of a data channel media descriptor to be offered towards one of the IMS subscribers), the consumer must provide a complete MF media specification including information required by MF to know how to terminate or originate the media flow. Inputs, Required: Session ID, Media instruction set Session ID specifies the IMS session for which the MediaInstruction operation applies. Media instruction set includes a set of instructions for each media flow to control. Each instruction includes: - media ID: used by the producer (IMS AS) and the consumer for referencing purposes. The consumer reuses the media ID it received from the IMS AS for referencing the same media or, if this media is originally a data channel multiplexing media and is instructed to be de-multiplexed, one of the de-multiplexed media component. This field shall be null for instructions related to originating new media or for data channel media components de-multiplexed from a data channel multiplexing media which do not reuse the media ID of that data channel multiplexing media. NOTE 1: When a data channel multiplexing media is de-multiplexed to multiple data channel media components, which data channel media component reuses the original media ID of the data channel multiplexing media is decided by the consumer by implementation. - associated Media ID: This parameter only exists when a multiplexed media is de-multiplexed to multiple media and is used to associate different media streams which are de-multiplexed from a multiplexed media component. This parameter is set to the value of the media ID of the original multiplexed media. - Media resource capability: Identify the Media Resource capabilities the Media instruction is intended for (e.g. DC, AR). - Media instruction: includes instructions to the producer (IMS AS) for handling the media. The following instructions are supported: - "TerminateMedia": Terminate the offered media descriptor of the UE in the mediaResource, i.e. this media descriptor will not be exposed to the other UE. - "OriginateMedia": Originate and offer a media descriptor from the mediaResource to the UE. The media ID representing the new media flow will be provided by the IMS AS in the response. - "TerminateAndOriginateMedia": Terminate the offered media flow in the mediaResource from the UE and originate the same media flow from the mediaResource to the other UE, i.e. the offered media descriptor of the originating UE will be replaced by the mediaResource provided media descriptor, which is sent towards the other UE. - "UpdateMedia": Update a media flow of the mediaResource previously allocated by the instructions "TerminateMedia", "OriginateMedia" and "TerminateAndOriginateMedia" - "DeleteMedia": Delete a media flow of the mediaResource previously allocated by the instructions "TerminateMedia", "OriginateMedia" and "TerminateAndOriginateMedia". - "RejectMedia": Remove an offered media flow, i.e. the offered media descriptor will be removed both from the offer sent to the remote UE and from the answer returned to the initiator of the offer. - DC Media Specification(s): Description of additional media specification information needed for data channel media stream from application layer. If multiple application data channels are multiplexed in the same m line in the SDP, multiple DC media specifications for all multiplexed data channels are included. Each media specification includes: - Media proxy configuration (HTTP or UDP) applicable to the media flow. - MDC1/MDC2 media endpoint address of the application layer. - Replacement HTTP URL per stream ID allocated by the application layer representing the application list (e.g. graphical user interface) provided to the IMS subscriber via the MDC1 interface. - Data Channel Mapping and Configuration information when originating/terminating data channel media flows on the Mb interface. - Data Channel Port. - Data Channel SCTP Port. - AR Media Specification: Description of additional media specification information needed for AR communication services from application layer, which includes: - Media Processing Specification: It specifies how the media stream should be processed. - Avatar Media Specification: Description of additional media specification information needed for avatar communication services from application layer, which includes: - Resource URL: URL that allocated by DC AS for MF to retrieve the avatar representation. - Rendering mode: identifies the mode of rendering avatar media, i.e. UE centric, network centric with MF rendering, network centric with DC AS rendering. - Media Processing Specification: It specifies how the media stream should be processed. NOTE 2: DC Media Specification and AR Media Specification are optional depending on the scenario and media type. Inputs, Conditional: None. Inputs, Optional: None. Outputs, Required: operation result indication. Outputs, Optional: media resource information set: This set includes entries corresponding to each instruction in the received media instruction set. Each entry in the set includes the media ID (same as received or new for new or de-multiplexed media) and includes the media type according to SDP. Each entry may optionally contain Avatar Media Specification, DC Media Specification and/or AR Media Specification. The DC Media Specification shall exist only with media type "DC" and contains additional media resource information, e.g. allocated media address for MDC2 interface when an offer must be provided to Data Channel Application Server. The AR Media Specification contains media processing instruction for MF on how to process the media. The Avatar Media Specification contains media processing instruction for MF on how to perform network rendering for avatar communication. AA.2.4.4 Nimsas_ImsSessionManagement Service AA.2.4.4.1 General Service description: This service enables the consumer to request IMS AS to create and release an IMS session and modify the media in a specific IMS session. NOTE: In this release only session management of IMS data channel is specified. AA.2.4.4.2 Nimsas_ImsSessionManagement_Create service operation Service operation name: Nimsas_ImsSessionManagement_Create Description: This service enables the consumer NF to create an IMS session with the requested media (e.g. standalone data channel media). NOTE 1: Only data channel media is supported in this Release. Inputs, Required: Calling ID, Called ID, Media Information set. Calling ID: It is the public identity of calling IMS Subscriber or the identity of the consumer NF, e.g. DC AS. Called ID: It is the public identity of called IMS Subscriber. Media Information set: Includes a set of media information indicating how the media used in the created session. Each media information contains: - Media Correlation ID: It identifies the media component to be created. It is allocated by the consumer NF. - Media Type: It indicates the media type used in the created session, e.g. Data Channel. - Media Parameter set: It indicates the related media parameters. For different media, it contains different parameters. - When the Media Type is Data Channel, it includes: - DC Type: indicates the Data Channel Type (ADC or BDC); - When DC Type is ADC: - ADC Type: the ADC type (P2A, P2P, P2A2P); - Application Binding Information; and - Target ID(s): the public identity(ies) of the IMS Subscriber the DC is targeted; NOTE 2: For P2P ADC, the Calling ID and Called ID of the session are used as the Target IDs. - If P2A or P2A2P is selected, the MDC2 media endpoint address(es) of the application layer is included. - When DC Type is BDC: - Target ID: the public identity of the IMS Subscriber the DC is targeted; - the MDC1 media endpoint address. Inputs, Optional: Notification Target Address and Notification Correlation ID. If the request includes a Notification Target Address, the request creates an implicit subscription to be notified for the events in Table AA.2.4.4.5-1. Outputs, Required: Result indication. Outputs, Optional: Session ID allocated by IMS AS. AA.2.4.4.3 Nimsas_ImsSessionManagement_Update service operation Service operation name: Nimsas_ImsSessionManagement_Update Description: This service operation enables the consumer NF to modify the media in a specific IMS session, such as adding or removing bootstrap data channel(s) or application data channel(s), modify media parameters for the targeted data channel(s). Inputs, Required: Session ID, Media operation set. Session ID: It is the identity of session that this request targeted to. Media operation set: Includes a set of media operations commands indicating how to modify the media used in the specific session. Each media operation command contains: - Media Correlation ID: It identifies the media component to be created. - Operation Type: It indicates adding, updating or removing the corresponding media. - Media Type: It indicates the type of operated media (e.g. Data Channel). - Media Parameter set: It indicates the related media parameters. For different media, it contains different parameters. - When the Media Type is Data Channel, it includes: - DC Type: indicates the Data Channel Type (ADC or BDC); - When DC Type is ADC: - ADC Type: the ADC type (P2A, P2P, P2A2P); - Application Binding Information; and - Target ID: the public identity of the IMS Subscriber the DC is targeted; - If P2A or P2A2P is selected, if the Operation Type indicates adding or updating the media, the MDC2 media endpoint address(es) of the application layer is included. - When DC Type is BDC: - Target ID: the public identity of the IMS Subscriber the DC is targeted; - if the Operation Type indicates adding or updating the media, the MDC1 media endpoint address. Inputs, Optional: Notification Target Address and Notification Correlation ID. If the request includes a Notification Target Address, the request creates an implicit subscription to be notified for the events in Table AA.2.4.4.5-1. Outputs, Required: Result indication. Outputs, Optional: None. AA.2.4.4.4 Nimsas_ImsSessionManagement_Delete service operation Service operation name: Nimsas_ImsSessionManagement_Delete Description: This service operation enables the consumer NF to release the specific IMS session. Inputs, Required: Session ID. Inputs, Optional: None. Outputs, Required: Result indication. Outputs, Optional: None. AA.2.4.4.5 Nimsas_ImsSessionManagement_Notify service operation Service operation name: Nimsas_ImsSessionManagement_Notify Description: Provides the subscribed event information to the NF Consumer. Inputs, Required: Event ID, Notification Correlation ID. Inputs, Optional: Session ID, Media resource information. Media resource information set includes entries corresponding to each media. Each entry in the set includes the Media correlation ID and DC Media Specification. The DC Media Specification shall exist only with media type "DC" and contains additional media resource information, e.g. remote media address for MDC2 interface. Outputs, Required: Result indication. Outputs, Optional: None. The table below presents supported Event IDs and related parameters. Table AA.2.4.4.5-1: List of events and related optional parameters EventID Parameters SessionEstablishmentSuccessEvent Session ID SessionEstablishmentFailureEvent Calling or Called party ID, reason of the failure MediaChangeSuccessEvent Calling or Called party ID MediaChangeFailureEvent Calling or Called party ID, reason of the failure SessionTerminationEvent Calling or Called party ID AA.2.4.5 Nimsas_ImsEventExposure (ImsEE) service AA.2.4.5.1 Nimsas_ImsEE_Subscribe service operation Service operation name: Nimsas_ImsEE_Subscribe Description: The NF consumer subscribes for a specific subscriber related IMS Event. Inputs, Required: Event-ID(s) representing the event of interest,, Notification Target address, Event Reporting Information as defined in Table 4.15.1-1 of TS 23.502 [94]. Event-ID represent one or multiple events as defined in clauses AD.2.4 and AD.2.5. Inputs, Optional: IMS Public Subscriber identity if the subscribe request is for a subscriber specific event, Notification Correlation ID, Expiry time, Event Filters, Subscription Correlation ID (in the case of modification of the event subscription). Outputs, Required: When the subscription is accepted: Subscription Correlation ID, Expiry time (required if the subscription can expire based on the operator's policy). Outputs, Optional: First corresponding event report is included, if available (see clause 4.15.1 of TS 23.502 [94]). AA.2.4.5.2 Nimsas_ImsEE_Unsubscribe service operation Service operation name: Nhss_ImsEE_Unsubscribe Description: The NF consumer unsubscribes for updates to Requested event. Inputs, Required: Subscription Correlation ID. Inputs, Optional: None. Outputs, Required: Result. Outputs, Optional: None. AA.2.4.5.3 Nimsas_ImsEE_Notify service operation Service operation name: Nimsas_ImsEE_Notify Description: This service operation is used by the IMS AS to report the information associated with a subscribed Event. Inputs, Required: Event ID, Event Reporting information. The Event ID parameter defines the event for which the notification applies. Inputs, Optional: Notification Correlation Information, Event information (defined on a per Event ID basis). Outputs, Required: Operation execution result indication. AA.2.4.6 Nimsas_ImsParameterProvision (ImsPP) service AA.2.4.6.1 Nimsas_ImsPP_Create service operation Service operation name: Nimsas_ImsPP_Create Description: This service operation is used by the AF/NEF to create the IMS user related information (e.g. RCD URL, RCD server address or RCD information) for the target IMPU. Inputs, Required: AF Identifier, Transaction Reference ID(s). Inputs, Optional: Public User Identity, RCD properties as defined in clause AF.2.2.1. Outputs, Required: Result Indication. Outputs, Optional: None. AA.2.4.6.2 Nimsas_ImsPP_Update service operation Service operation name: Nimsas_ImsPP_Update Description: This service operation is used by the AF/NEF to update the information which can be used for an IMS user in the IMS (e.g. RCD URL, RCD server address or RCD information) for the target IMPU. Inputs, Required: AF Identifier, Transaction Reference ID(s). Inputs, Optional: Updated RCD properties as defined in clause AF.2.2.1. Outputs, Required: Result Indication. Outputs, Optional: None. AA.2.4.6.3 Nimsas_ImsPP_Delete service operation Service operation name: Nimsas_ImsPP_Delete Description: This service operation is used by the AF/NEF to delete the IMS user related information (e.g. RCD URL, RCD server address or RCD information) for the target IMPU. Inputs, Required: AF Identifier, Transaction Reference ID(s). Inputs, Optional: None. Outputs, Required: Result Indication. Outputs, Optional: None. AA.2.5 MF Services AA.2.5.1 General The following table illustrates the MF Services and Service Operations. Table AA.2.5.1-1: NF services provided by the MF NF service Service Operations Operation Semantics Example Consumer(s) Nmf_MediaResourceManagement (MRM) Create Request/Response IMS AS Update Request/Response IMS AS Delete Request/Response IMS AS AA.2.5.2 Nmf_MediaResourceManagement (MRM) service AA.2.5.2.1 General Service description: This service enables the consumer to create, update and delete media resources related to IMS Data Channel. The media resource represents a media context including one or multiple media terminations. A media termination includes media resources for one or multiple media streams on the Mb interface. Each media resource context is identified by a Media Resource Context ID. Each media termination is identified by a Termination ID. Each media stream is identified by a Media ID and specified by a media descriptor. NOTE: Termination is a concept widely used in media protocols like H.248. When a media stream, e.g. application data channel, pass through the MF, there is one termination for the input stream and one termination for the output stream. In this case, the two terminations can use the same media ID. Figure AA.2.5.2.1-1illustrates the above. The Figure shows a media Context whose ID is AX and two media terminations whose IDs are AB and XY. Media Termination AB anchors two media streams; 1 and 3. Media termination XY anchors media streams 2 and 3. Figure AA.2.5.2.1-1: Media Context Resource Example If the MF support data channel multiplexing as specified in clause AC.7.10, the MF correlates the multiplexed media streams between terminations as follows: - If the multiplexed media streams are kept unchanged between terminations in the MF, the MF correlates the media streams in different terminations associated with the same Media ID for data forwarding. - If the media streams are multiplexed in one termination and demultiplexed in the other termination, the MF correlates the media streams in different terminations via the same associated Media ID as specified in clause AA.2.5.2.2 for data forwarding. AA.2.5.2.2 Nmf_MRM_Create service operation Service operation name: Nmf_MRM_Create Description: The consumer NF requests the MF to create a media context including one or multiple media terminations and reserve media resources for anchoring one or multiple media streams of Mb interface in each termination. The consumer NF may also include media application function specification information requested by the application layer, e.g. DCSF, to be applied on the media stream by the MF. Inputs, Required: List of Media Termination Descriptors. Each Media Termination Descriptor of the list includes: - Termination ID: A unique identity of the termination within the media context resource. The identity is allocated by the producer and must be set to value 'null' by the consumer when adding a termination to a context. - List of Media Stream Descriptors belonging to the Termination. Each Media Stream Descriptor of the list includes: - Media ID: A unique identity of the media stream within the media context instance. The Media ID value is set by the consumer. - associated Media ID: This parameter only exists when a multiplexed media is de-multiplexed to multiple media and is used to associate different media streams which are de-multiplexed from a multiplexed media component. This parameter is set to the value of the media ID of the original multiplexed media. NOTE 1: Different Termination IDs associated with the same Media ID or associated media ID corresponding to the same Media ID represent the media stream flow for data forwarding. - Remote Mb Specification: Media Specification specifying SDP parameters of a remote media endpoint e.g. media stream IP address and ports allocated at the remote UE. NOTE 2: In the case of reserving termination media resource before receiving media negotiation information from the UE, Remote Mb Specification should be set to Null. - Media Function Specifications: Specification of the media function to be applied to the media stream as requested by the application layer, which includes: - Media Function Type: The value is set based on the type of the media function required, e.g. "DC media function type or AR media function type. - Media Function Description: Application specific media function description specifying how the media function shall handle and process the media stream. Data content depends on type of media function. If the Media Function Type is "DC Media Function", then the Media Function Description incudes: - Media proxy configuration (HTTP or UDP) applicable to the media flow. - Remote MDC1/MDC2 media endpoint address. - Replacement HTTP URL per Stream ID allocated by the application layer representing the application list (e.g. graphical user interface) provided to the IMS subscriber via the MDC1 interface. - Data Channel Mapping and Configuration information when originating/terminating data channel media flows on the Mb interface. - Maximum Message Size: This attribute defines the maximum size to be expected. - Data Channel Port: This attribute identifies the port for the Data Channel. - Data Channel SCTP Port: This attribute identifies the SCTP port for the Data Channel. - Security Setup: This attribute identifies the security setup of the DTLS connection. - Security Certificate Fingerprint: This attribute identifies the security certificate fingerprint. - Security Transport Identity: This attribute identifies transport layer identity NOTE 3: Some of the above attributes are optional depending on the scenario and proxy configuration. If the Media Function Type is "AR Media Function", then the Media Function Description includes: - AR Media Specification: Description of additional media specification information needed for AR communication services from application layer, which includes: - Media Processing Specification: It specifies the how the media stream should be processed. NOTE 4: The detail of Media Processing Specification is defined by SA4 and needs to be further aligned. - Avatar Media Specification: Description of additional media specification information needed for avatar communication services from application layer, which includes: - Resource URL: URL that allocated by DC AS for MF to retrieve the avatar representation. - Rendering mode: identifies the mode of rendering avatar media, i.e. UE centric, network centric with MF rendering, network centric with DC AS rendering. - Media Processing Specification: It specifies how the media stream should be processed. NOTE 5: Avatar Media Specification are optional depending on the scenario. Inputs, Optional: None. Outputs, Required: Result indication for the entire list, Media Resource Context ID, List of allocated Media Termination Descriptor Resource information. For each Media Termination Descriptor; the Termination ID and the list of media stream descriptors corresponding to the input list of media stream descriptor: Media Resource Context ID uniquely identifies the media resources created by the MF. This identity shall be used as reference when updating or deleting the created media resource. List of allocated Media Termination Descriptor Resource information includes one or multiple Media Termination Descriptor Resources allocated. The list will include same number of terminations, in the same order as provided in the request. Each Media Termination Descriptor Resource includes: - Termination ID: Unique identity allocated by the consumer. The identity shall be used when updating/deleting the Media Termination. - List of Media Stream Descriptor Resource information elements allocated within the media termination. The list will include same number of media streams, in the same order as provided in the request. Media Stream Descriptor Resource information includes: - Media ID: Unique identity of the media stream within the media context instance allocated by the consumer. This is identical to the Media ID used in the input. - associated Media ID: identical to the associated Media ID received from the consumer. - Local Mb Specification: Media specification specifying SDP parameters representing the media endpoint of the provider e.g. media stream IP address and port. - Media Application Function Output Description: Optional media application function description including information required by the application layer. The Media Application Function Output Description shall be relayed to the DCSF by the consumer NF. Data content depends on type of media function. If the Media type is "DC media function", the Media Application Function Output Description includes: - MDC1/MDC2 media point information (IP address/port number, etc.) which shall be relayed to the DCSF by the consumer NF. Outputs, Optional: None. AA.2.5.2.3 Nmf_MRM_Update service operation Service operation name: Nmf_MRM_Update Description: The consumer NF requests the MF to update one or multiple media resources within a specific media resource context. Terminations and/or Media Streams can be added, modified, or deleted within an Update request. Inputs, Required: Media Resource Context ID, List of Media Termination Descriptors to be updated. Media Resource Context ID specifies the media context resource to be updated. List of Media Termination Descriptors includes one or multiple media terminations impacted by the update request. Each Media Termination Descriptor includes: - Termination ID: A unique identity of the termination within the media context resource. The identity is allocated by the consumer and must be set to value 'null' when adding a termination to a context. - List of Media Stream Descriptors belonging to the Termination. The complete set of Media Stream Descriptors of a Media Termination must be specified in case a Media Termination is either added or modified. The consumer NF can remove media streams from a Media Termination by omitting the media stream from the list. The list will be set to 'null' when deleting a Media Termination. The detail of this list is identical to the input information in the Nmf_MRM_Create service. Inputs, Optional: None. Outputs, Required: Result indication, List of Media Termination Descriptor Resource information. List of Media Termination Descriptor Resource information includes one or multiple Media Stream Termination Descriptor Resources allocated. The list will include same number of terminations, in the same order as provided in the request. Each Media Termination Descriptor Resource information includes: - Termination ID: A unique identity of the termination within the media context resource. The identity is allocated by the consumer. - List of Media Stream Descriptor Resource information elements allocated/updated within the media termination. The list will include same number of media streams, in the same order as provided in the request. The list will be set to 'null' when deleting a Media Termination. The detail of this list is identical to the output information in the Nmf_MRM_Create service. Outputs, Optional: None. AA.2.5.2.4 Nmf_MRM_Delete service operation Service operation name: Nmf_MRM_Delete Description: The consumer NF requests the MF to delete a specific media context resource including all existing terminations and media streams. Inputs, Required: Media Context Resource ID. Media Context Resource ID specifies the media context resource to be deleted. Inputs, Optional: None. Outputs, Required: Result indication. Outputs, Optional: None. AA.3 SBI Capable HSS Discovery and Selection AA.3.1 General An SBI capable IMS entity (e.g. I-CSCF, S-CSCF, IMS AS or DCSF) performs HSS discovery to discover an HSS that manages the user subscriptions. The SBI capable IMS entity shall utilize the NRF to discover the SBI capable HSS instance(s) unless the information about SBI capable HSS instances is available by other means, e.g. locally configured on the SBI capable IMS entity. The HSS selection function in SBI capable IMS entities selects an SBI capable HSS instance based on the available SBI capable HSS instances (obtained from the NRF or locally configured). An SBI capable IMS entity always selects an HSS within its own PLMN. The HSS selection should consider one of the following factors when available to the SBI capable IMS entity: 1. HSS Group ID of the IMS identity (IMPI or IMPU, or PSI). 2. IMS private identity (IMPI); e.g. the SBI capable IMS entity selects an SBI capable HSS instance based on the IMPI set the UE's IMPI belongs to, configured locally or based on the results of a discovery procedure with NRF using the UE's IMPI as input for HSS discovery. 3. IMS public identity (IMPU); e.g. the SBI capable IMS entity selects an SBI capable HSS instance based on the IMPU set the UE's IMPU belongs to, configured locally or based on the results of a discovery procedure with NRF using the UE's IMPU as input for HSS discovery. 4. Public Service Identity (PSI); e.g. the SBI capable IMS entity selects an SBI capable HSS instance based on the PSI set the received PSI belongs to, configured locally or based on the results of a discovery procedure with NRF using the received PSI as input for HSS discovery. 5. MSISDN; e.g. the SBI capable IMS entity selects an SBI capable HSS instance based on the MSISDN set the UE's MSISDN belongs to, configured locally or based on the results of a discovery procedure with NRF using the MSISDN as input for HSS discovery. Unless the information about the interface type to be used towards HSS is locally configured on the SBI capable IMS entity, an SBI capable IMS entity can also use the NRF to decide the type of interface (SBI vs diameter) to be used towards HSS. The following clause describes the procedure for HSS registration in NRF, SBI capable HSS discovery and interface type selection via NRF. AA.3.2 HSS Registration in NRF An SBI capable HSS registers in the NRF using the Nnrf_NFManagement_NFRegister Request message as defined in TS 23.502 [94]. The NF profile of the HSS registered in NRF includes necessary information for an SBI capable IMS entity to send SBI service requests to the selected SBI capable HSS service instance. Different SBI capable HSS instances managing different sets of IMPIs/IMPUs may be deployed in a given PLMN. In this case, the SBI capable HSS instances register in NRF using either different ranges of IMPIs/IMPUs and/or HSS Group IDs. NOTE: In deployments where simple IMPU and IMPI ranges are not suitable to describe the IMPU/IMPI sets served by HSS instances, it is expected the HSS instances only register HSS Group IDs. AA.3.3 HSS Discovery and Selection via NRF AA.3.3.1 General During the IMS procedure, an SBI capable IMS entity sends a Nnrf_NFDiscovery_Request to NRF as defined in TS 23.502 [94] to discover SBI capable HSS instances within a given PLMN. The SBI capable IMS entity may store all returned SBI capable HSS instances and their NF profiles for subsequent use, including, if applicable, supported IMPIs/IMPUs ranges and/or HSS Group IDs. If no SBI capable HSS instance is available in the PLMN, then the NRF replies to the SBI capable IMS entity with no information. In this case, the SBI capable IMS may then attempt to communicate with the HSS using non-SBA protocols. NOTE: The SBI enabled IMS entity can also perform HSS discovery prior to receiving an IMS request without any public identity information. When an SBI capable IMS entity receives an NRF response that HSS supports SBI and stores the information received from the HSS, it shall make use of Nnrf_NFStatusSubscribe/Unsubscribe service operations with NRF as defined in TS 23.502 [94] to receive Nnrf_NFStatusNotify service operation for updates to the NF profiles of SBI capable HSS instances registered in NRF. AA.3.3.2 HSS Discovery The call flow in Figure AA.3.3.2-1 illustrates the steps to locate the HSS instance for an IMS public identity. Figure AA.3.3.2-1: HSS discovery and selection Steps 1 - 2 may be performed, any time after power up, e.g. in the scenario where only a single HSS instance or HSS group is deployed and in the scenario where an operator has IMPI/IMPU ranges that are registered in NRF as described in clause AA.3.2. In this case there is no need for any IMPU to perform the 2 steps. 1. An SBI capable IMS entity may discover the SBI capable HSS instances available in the PLMN via Nnrf_NFDiscovery_Request. 2. The NRF provides the SBI capable IMS entity with the HSS instances and/or any HSS Group IDs registered in the PLMN. If no SBI capable HSS instance and/or any HSS Group ID is available in the PLMN, then the NRF will reply to the SBI capable IMS entity with no information about available SBI capable HSS instances. 3. The SBI capable IMS entity receives an IMS procedure related to a given IMS user (IMPI or IMPU depending on the procedure). Steps 4 - 6 may be performed, e.g. if the SBI capable IMS entity did not retrieve and store information about HSS instances and/or HSS Group IDs registered in the PLMN at an earlier stage (performed steps 1-2). 4. An SBI capable IMS entity may discover the SBI capable HSS instances available in the PLMN via Nnrf_NFDiscovery_Request. 5. The NRF provides the SBI capable IMS entity with the HSS instances and/or any HSS Group IDs registered in the PLMN. If no SBI capable HSS instance and/or any HSS Group ID is available in the PLMN, then the NRF will reply to the SBI capable IMS entity with no information about available SBI capable HSS instances. 6. The SBI capable IMS entity stores the result of the NRF discovery, if any is received. The IMS capable entity may store the received response for future use, otherwise the IMS entity must perform the query in response to each IMS request it receives. If the SBI capable IMS entity received no results at all, the procedure is exited and the SBI capable IMS entity may use Diameter interfaces to interact with an HSS. NOTE 1: The SBI capable IMS entity can request the NRF to be notified of updates in the SBI capable HSS instances/ HSS Group IDs registered in NRF by using a Nnrf_NFManagement_NFStatusSubscribe service operation. Steps 7 - 10 are performed only if the SBI capable IMS entity cannot locate an HSS instance corresponding to the IMS public identity based on stored information. 7. The SBI capable IMS entity sends to NRF an Nnrf_NFDiscovery_Request with the IMS public identity received in step 3. 8. NRF may query the UDR, via the Nudr_GroupIDmap service, for the HSS Group ID corresponding to the IMS public identity. 9. If requested the UDR returns the HSS-IMS Group ID to NRF. 10. NRF locates HSS instance(s) corresponding to the HSS Group ID. NRF returns and provides and them to the SBI capable IMS entity the HSS instance(s) profile which includes the HSS Group ID. NOTE: In indirect communication with delegated discovery as specified in TS 23.501 [93], the SBI capable IMS entity does not interact directly with the NRF. In this case, the SBI capable IMS entity is not informed about the HSS Group ID the IMS identity belongs to. 11. The SBI capable IMS entity selects the HSS instance. 12. The SBI capable IMS entity can then start interaction with the selected HSS instance. AA.3.3.3 Handling of HSS Group ID in IMS Procedures The HSS group ID may be transported in SIP signalling related to the following procedures: - Initial IMS Registration procedure. - IMS Terminating session establishment procedure. - IMS Originating session establishment procedure. An SBI enabled I-CSCF receiving an HSS Group ID during the NRF-based HSS discovery procedure should include the HSS Group ID for transportation to the next hop in subsequent SIP signalling related to the above procedures. In addition, every IMS node receiving an HSS Group ID in SIP signalling (e.g. S-CSCF and IMS AS) should store it as part of the UE information and should use the received HSS Group ID to select an SBI capable HSS. Additionally, an IMS node receiving an HSS Group ID in SIP signalling should include it in subsequent SIP signalling related to the above procedures. The HSS Group ID in SIP signalling is specific to the UE served by this IMS and shall not be sent to any other party involved in the session/communication (e.g. to the terminating side and/or outside the HPLMN). AA.4 NRF based Discovery and Selection for other IMS nodes AA.4.1 Service Based MRF Discovery and Selection AA.4.1.1 General While no SBI procedures are defined for MRF (and hence MRFC and MRFP), it is possible to utilize NRF to discover and select the MRF. In networks where MRFC and MRFP are co-located it is only necessary to indicate that the service function is MRF, in networks where separated MRFC and MRFP are deployed the network function discovering the MRF (or MRFC) may not know the network topology and thus the service function descriptor is always set to MRF (even when registering/discovering an MRFC). The MRFP service descriptor is only used by the MRFC when separate MRFC and MRFP are deployed and the MRFC is configured to use the NRF to discover a suitable of MRFP. NOTE: In many implementations where the MRFC and MRFP are separate entities the MRFP resource is directly linked to the MRFC and thus SBI discovery mechanisms are not necessary. When an SBI capable IMS entity selects a MRF it shall use the IMS media service list to ensure that the selected MRF supports the required media capabilities for the application. The SBI capable IMS entity may utilize other available information to assist in selecting the MRF based on implementation criteria (e.g. proximity of the UE to MRF to minimize transmission delays). A SBI capable IMS entity always selects an MRF (or MRFC within its own PLMN. AA.4.1.2 MRF Registration If an MRF has been configured to support NRF based discovery or selection it shall register with the NRF using the Nnrf_NFManagement_NFRegister Request message as defined in TS 23.502 [94]. The NF profile for the MRF includes all common information for SBI capable IMS entities plus a text-based list of IMS media services offered by the MRF (e.g. "video transcoding", "data channel services", "voice conferencing", "in-call announcements"). NOTE: The list of media services is implementation specific, with each potential service in the list defined and configured by the IMS service provider (and thus not specified by 3GPP). Individual entries in the list need to be configured to exactly correspond to the discovery requests made by the AS or other SBA entities. The MRF registration may include other optional information pertaining to the implementation (e.g.NF location to support routing media to the nearest MRF). In the case when the MRFC and MRFP are separate entities, the MRFC identifies itself using the MRF service descriptor during SBA interactions. In cases where the MRFP is a separate entity to the MRFC, it may be necessary for the MRFP to perform registration with the NRF (unless local configuration is used). In such cases the MRFP registers with the NRF using a NF profile that also includes a similar list of media services and uses the NF identifier "MRFP". AA.4.1.3 MRF Discovery and Selection During the IMS procedure, an SBI capable IMS entity sends a Nnrf_NFDiscovery_Request to NRF as defined in TS 23.502 [94] to discover applicable MRF instances within a given PLMN. The SBI capable entity may include a list of the service or services it is requesting to use, in which case the NRF will respond with the MRF (s) that support all the services listed. When separate MRFC and MRFP (or a mix of MRF, MRFC, MRFP) are deployed in a network - the entity performing discovery of the MRFC may not know the network topology and thus the discovery request sent by the SBI entity uses the MRF service descriptor, even if the resulting node is an MRFC. If necessary when there is no direct linkage between an MRFC and MRFP, then discovery and selection of the MRFP may be needed after the MRFC discovery; in such a case the MRFC may perform SBI discovery of the MRFP using the NRF, in such a case the requested service descriptor is MRFP. Only an MRFC may discover the MRFP in this manner. Annex AB (informative): Support of IMS in SNPN AB.1 IMS in SNPN AB.1.0 General Annex AB describes deployment options for SNPNs to enable access to IMS services for SNPN subscribers. Two potential deployment options are described below. For the purpose of this Annex, an IMS Subscription Holder (ISH) identifies the administrative domain holding the IMS subscription for a UE subscribed to receive IMS services. The ISH can be the same or independent from the SNPN domain which deploys the 5GS. In the case the ISH is different from the administrative domain of the SNPN, the UE needs to have two separate subscriptions, one for accessing the 5GS of the SNPN (provided by the SNPN or Credentials Holder (CH) as defined in TS 23.501 [93]) and one for accessing IMS services provided by the ISH. The UE needs to be successfully authenticated in each domain, using the appropriate subscription, before able to receive IMS services. AB.1.1 SNPN deployed IMS In this option, the SNPN deploys its own IMS used by subscribers with a SNPN 5GS subscription. The SNPN and the ISH belong to the same administrative domain. In this deployment scenario, either USIM/ISIM or IMC is used to authenticate and authorize a UE for accessing IMS services. AB.1.2 IMS services provided by independent IMS provider AB.1.2.1 General This option is applicable to SNPNs not providing own IMS services. It enables the SNPN to use IMS services from an independent IMS provider, e.g. PLMN or another entity, which is the ISH, providing IMS services for SNPN subscribers. It is assumed that the SNPN has an agreement with the ISH. This agreement describes e.g. P-CSCF address provisioning and security aspects for all standardized reference points that are implemented between both administrative domains. In this deployment option either IMC or USIM/ISIM credentials are used to authenticate and authorize a UE for IMS services. NOTE 1: The provisioning of IMC is out of scope of 3GPP. The UE holds an association between an SNPN subscription and the corresponding IMS subscription to ensure proper credentials are used to access SNPN and IMS services in this deployment option. The mechanism how this association is stored in the UE is out of scope of 3GPP. A potential architecture for this deployment option is depicted in Figure AB.1.2-1. NOTE 2: Potential usage of reference points as shown in Figure AB.1.2-1, e.g. NU1, is up to deployment. NOTE 3: It is assumed that there is no NAT device located between the UPF and the P‑CSCF. This can be enabled e.g. by deploying the N6 reference point in a private IP network where both the UPF on the SNPN side and the P-CSCF and IMS-AGW on the ISH side share the same address space. Subject to the agreement between SNPN and ISH, in some deployments the P-CSCF and IMS-AGW of the ISH can also be deployed on the SNPN premises. NOTE 4: SEPPs are not shown in the figure. Figure AB.1.2.1-1: Potential deployment architecture for IMS services in SNPN provided by independent IMS provider AB.1.2.2 Support for Emergency Services Support for Emergency Services requires that the SNPN, based on an agreement with the ISH, broadcasts IMS Emergency Services support as described in TS 23.501 [93]. AB.1.2.3 SNPN Support for Multiple Independent IMS Providers In order for an SNPN to enable IMS services to be provided via multiple independent ISH, it is required that for every SNPN subscriber, the IMS DNN stored in UDM of the SNPN contains the information, which is used to identify the corresponding ISH, e.g. ISH domain name is encoded as part of IMS DNN. At PDU session setup, the SMF selects the P-CSCF of the ISH based on clause 5.16.3.11 and clause 5.16.3.4 of TS 23.501 [93]. The CH and SNPN need to agree that the AMF in SNPN that receives the subscription information that includes the IMS DNN and contains information to identify the corresponding ISH, is able to determine the ISH and therefore derive correctly the IMS voice over PS Session Supported Indication as defined in clause 5.16.3.2 of TS 23.501 [93]. Annex AC (normative): Support of Data Channel services in IMS AC.1 General This annex describes IMS architecture enhancements to support data channel services. Service based interfaces applicable to data channel services are specified in clauses AA.2.4 and AA.2.5. The architecture in this annex supports separation of signalling function and media function supporting data channel services. A network function for data channel management signalling, Data Channel Signalling Function (DCSF), is specified. The network function to handle data channel media can be provided by introducing a new network function called Media Function (MF), which interacts with the IMS AS via the service-based interface DC2. MF provides media capabilities in support of IMS DC and Augmented Reality. NOTE: In this Release of the specification the IMS AS supporting data channel services is collocated with the TAS. The IMS architecture supporting data channel services also supports exposure of IMS DC. The architecture and procedures of IMS DC event exposure are specified in Annex AD. The architecture and procedures of IMS DC capability exposure are specified in Annex AG. In this Release of the specification IMS Data Channel is supported in the case of non-roaming and home routed roaming scenarios. Multiplexing of multiple IMS Data Channel streams with different endpoints onto a single SCTP association is not supported in this Release of the specification. AC.2 Architecture and functions AC.2.1 Architecture Figure AC.2.1-1 shows the data channel architecture when using the service-based DC media function. Figure AC.2.1-1: Architecture option of IMS supporting DC usage with MF NOTE 1: MDC2 may connect different IMS security domains. NOTE 2: DC5 reference point is not specified in 3GPP. NOTE 3: MDC1, MDC2 and MDC3 reference points are not specified in 3GPP. NOTE 4: DC3 and DC4 reference points are not specified in this Release. NOTE 5: The reference points related to exposure of IMS DC events and capabilities are specified in Annex AD and Annex AG. AC.2.2 Functional entities AC.2.2.1 Data Channel Signalling Function (DCSF) The DCSF is the signalling control function that provides data channel control logic. The DCSF is not involved in SIP signalling. The DCSF supports the following functionalities: - The DCSF receives event reports from the IMS AS and decides whether data channel service is allowed to be provided during the IMS session. - The DCSF manages bootstrap data channel and (if applicable) application data channel resources at the MF via the IMS AS. - The DCSF manages interworking between application data channel media and audio/video media when applied and instructs to the MF via the IMS AS; NOTE 1: Interworking between application data channel and voice/video refers to the change of transporting protocols which is specified in SA WG4. - The DCSF supports HTTP web server functionality to download data channel applications (bootstrapping) via MF to the UE based on UE subscription. - The DCSF downloads data channel applications from the Data Channel Application Repository. NOTE 2: The detailed procedures to download data channel applications to the UE are out of scope of this specification. - The DCSF interacts with NEF for data channel capability exposure via DC3. NOTE 3: Interaction with NEF is not specified in this release of the specification. - The DCSF interacts with the DC Application Server for DC resource control via DC4/DC3/N33 and for traffic forwarding via MDC3. NOTE 4: Interaction with the DC Application Server for resource control is not specified in this release of the specification. - The DCSF interacts with HSS for retrieving and storing DCSF service specific data via N72/Sc. AC.2.2.2 Data Channel Application Repository (DCAR) The Data Channel Application Repository stores the verified data channel applications which are retrieved by the DCSF when required. AC.2.2.3 Data Channel Media Function (MF) The MF provides the media resource management and forwarding of data channel media traffic. The MF provides the following functionalities: - The MF manages the data channel media resources (bootstrap and application data channel resources, if applicable) under the control of the IMS AS. - The MF terminates the bootstrap data channel from the UE and forward HTTP traffic between the UE and DCSF via MDC1. - The MF may anchor the application data channel in P2P scenarios, if required and forward application data traffic from/to the UEs. - The MF relay traffic on the A2P/P2A application data channels between the UE and the DC Application Server via MDC2. - The MF handles transcoding of data channel media following the media instructions from the DCSF. AC.2.2.4 IMS AS The IMS AS is enhanced to support the following functionalities: - The IMS AS interacts with the DCSF via DC1 for event notifications. - The IMS AS interacts with the NEF for event subscription and notification. - The IMS AS receives the data channel control instructions from the DCSF and accordingly interacts with the MF via DC2 for data channel media resource management. - The IMS AS interacts with HSS for retrieving and storing DC enhanced IMS AS service specific data via N71/Sh. - The IMS AS receives data channel control request from NEF/DC AS for establishment, update or release of bootstrap data channel and/or application data channel. - The IMS AS may register in NRF the events it supports. - The IMS AS interacts with HSS to register its NF instance for event subscription. - The IMS AS supports IMS DC events exposure as specified in Annex AD. - The IMS AS supports IMS DC capability exposure as specified in Annex AG. AC.2.2.5 S-CSCF In addition to the functions defined in clause 4.6.3, the S-CSCF is enhanced to support the following functionalities: - The S-CSCF includes a Feature-Caps header field indicating its data channel capability in the 200 OK response to the initial and any subsequent REGISTER request from UE. AC.2.2.6 HSS In order to support data channel service, the HSS is additionally enhanced with the following functionalities: - The HSS stores IMS Data Channel subscription data as transparent data. - The HSS interacts with DCSF during service data retrieval by DCSF via N72/Sc. - The HSS interacts with IMS AS during service data retrieval by IMS AS via N71/Sh. - The HSS interacts with IMS AS to subscribe to event notifications on behalf of other NF, e.g. NEF or DC application server. - The HSS supports IMS DC event subscription as specified in Annex AD. AC.2.2.7 NEF The NEF supports exposure of IMS DC events and IMS DC capability: - The IMS AS supports exposure of IMS DC events as specified in Annex AD; - The IMS AS supports exposure of IMS DC capabilities as specified in Annex AG. AC.2.3 Reference points The following reference points are defined to support data channel service in IMS: - DC1: Reference point between the DCSF and the IMS AS. - DC2: Reference point between the IMS AS and MF. - DC3: Reference point between the DCSF and NEF. - DC4: Reference point between the DCSF and DC Application Server. - DC5: Reference point between the DCSF and DCAR. - N72/Sc: Reference point between the DCSF and HSS. The following reference points are updated to support data channel signalling control in IMS: - N70/Cx/Dx: Reference point between the CSCF and HSS. - N71/Sh: Reference point between the IMS AS and HSS. The following reference points are defined for data channel media handling: - MDC1: Reference point for transport of data channel media between data channel media function MF and DCSF. - MDC2: Reference point for transport of data channel media between data channel media function MF and DC Application Server, between BAR and DC Application Server and between MF and BAR. - MDC3: Reference point for transport of data channel media between DCSF and DC Application Server. AC.3 IMS Data Channel Service Subscription Service subscription for IMS Data Channel shall be an extension to the MMTEL related service profile in HSS. The Data Channel subscription data shall be used by the IMS AS and S-CSCF during IMS registration, session initiation or update to authorize subscribers to use the DC service. IMS AS Service specific data is enhanced with DC specific service data, optionally stored in HSS (e.g. as repository data) and retrieved by IMS AS using N71/Sh interface. DCSF service specific data used by DCSF for data channel management, may be stored (e.g. as repository data) and retrieved from HSS using the N72/Sc interface. DCSF service specific data are out of scope of 3GPP. AC.4 IMS DC Channel Setup The following principles apply when an IMS Data Channel is established: - - UE can establish an IMS Data Channel simultaneously while establishing an IMS audio/video session or upgrade an ongoing IMS audio/video session through a re-INVITE to an IMS Data Channel session. NOTE: An IMS Data Channel established simultaneously with an IMS audio/video session can have impact to the IMS session setup time. - The UE may be configured by the HPLMN either via Device Management or in the UICC whether and when to initiate a DC establishment request. If the UE is not configured by the HPLMN, it is left for UE implementation whether and when to initiate the DC establishment request. The UE shall not initiate a DC establishment request if the network has not indicated support for IMS DC service during IMS registration or if the UE is configured to not establish an IMS Data Channel. - If a UE that has not subscribed to IMS Data Channel establishes an IMS Data Channel simultaneously with an IMS audio/video IMS session, the IMS AS shall discard the Data Channel request and proceed with the audio/video IMS session establishment. - The DCSF provides stream ID and a corresponding URL to the MF via the IMS AS during data channel media resource reservation for the bootstrap data channel that enables downloading a subscriber specific graphical user interface to the UE via the bootstrap data channel. The stream ID is optional. Once the MF, acting as HTTP proxy, receive a HTTP GET Request containing the root ("/") URL through the bootstrap data channel, the MF replaces the root ("/") URL in the HTTP GET Request with the subscriber specific URL corresponding to the stream ID (if available) of the bootstrap data channel and forward the request to the DCSF for downloading the subscriber specific graphical user interface to the UE. The MF retrieves the stream ID of the bootstrap data channel from the transport layer of the data channel connection. The UE shall maintain the HTTP session state when interacting with the MF. AC.5 Binding of DC Application with the related DC Information for the binding of DC Application with the related DC is required to support multiple, simultaneous DC applications in a UE. The binding information is maintained by the HPLMN or retrieved from DC application provider when a DC Application is uploaded to DCSF. DCSF may be configured with a DC application profile associated with the binding information, which indicates the DC control policy (e.g. whether the Application DC establishment follows the P2P, P2A/A2P or P2A2P procedure). The UE receives the binding information of a DC application via the Bootstrap DC, e.g. when the DC application is downloaded to the UE. When the UE is establishing an IMS Application DC as defined in clause AC.7.2, the binding information is provided by the UE in the attribute of the SDP offer as specified in clause 6.2.13 of TS 26.114 [76]. The IMS AS provides the binding information to the DCSF. The DCSF may use the binding information for controlling the Application DC setup. AC.6 Data Channel Media Setup MF provides media anchoring when needed for the IMS Bootstrap Data Channel and the IMS Application Data Channel. To that effect, they support the following capabilities: - HTTP Proxy: In this configuration, MF supports terminating DTLS with HTTP traffic being transparent to MF. When acting as HTTP Proxy, MF reserves media resources on both the UE side and on the MDC1/MDC2 side allowing to send HTTP traffic to the DC Application Server. This mode is deployed both for Bootstrap Data Channel and HTTP Application Data Channels. Figure AC.6-1 illustrates the protocol stack for the HTTP proxy configuration mode for the Bootstrap Data Channel case. When used with HTTP Application Data Channel, the downloaded Data Channel application will in this case communicate with the DC Application Server, using basic HTTP, within the same bootstrap SCTP association as in which this application was downloaded. UDP, TCP and SCTP should be supported as the transport layer protocols for MDC2. Figure AC.6-1: MF acting as "HTTP Proxy" - UDP Proxy: In this configuration, MF transparently proxies HTTP traffic to its target. When acting as UDP Proxy, the media resources reserved by MF contain MF connection information (e.g. IP addresses and port numbers). This mode is deployed only for Application Data Channels. Figure AC.6-2 illustrates the protocol stack for the UDP proxy configuration mode for the Application Data Channel case, providing a Person2Application/Application2Person/Person2Person Data Channel Application. Figure AC.6-2: MF acting as "UDP Proxy" - DC Application Proxy: In this configuration, MF transparently proxies DC application traffic between two DCMTSI UEs. When acting as DC Application Proxy, the MF terminates UDP/DTLS/SCTP towards both peer UEs. This mode is deployed only for network initiated P2P Application Data Channels. Figure AC.6-3 illustrates the protocol stack for the DC Application proxy configuration mode for the P2P Application Data Channel case, Figure AC.6-3: MF acting as "DC Application Proxy" AC.7 Data Channel Procedures AC.7.0 IMS DC capability negotiation The IMS network and the UE need to mutually negotiate the capability of supporting IMS data channel when a UE supporting IMS data channel registers to IMS network. IMS data channel capability negotiation includes two aspects: - The network discovers the data channel capability of the UE. - The UE discovers the data channel capability of the network. When the UE supporting IMS data channel registers on the IMS network and the UE is allowed to use IMS data channel as specified in clause AC.4, it includes the media feature tag as specified in TS 26.114 [76] in the Contact header field of the initial REGISTER request and any subsequent REGISTER request to allow the home IMS network to discover its IMS data channel capability. If the IMS network supports IMS data channel, the S-CSCF includes a Feature-Caps header field indicating its data channel capability in the 200 OK response to the initial and any subsequent REGISTER request as specified in clause 9.2 of TS 24.186 [105], which is used by the UE to discover the IMS data channel capability of its home IMS network. The UE may receive a Feature-Caps header field indicating its data channel capability in the 200 OK response to a subsequent REGISTER request when the network starts supporting IMS data channel after successful initial registration of the UE. When the UE supporting IMS data channel initiates an IMS session and if the UE is allowed to use IMS data channel as specified in clause AC.4, it includes the media feature tag as specified in TS 26.114 [76] in the Contact header field of the initial INVITE or any re-INVITE request message, regardless of data channel media being part of the SDP or not. The UE shall not include the media feature tag as specified in TS 26.114 [76] in the Contact header field and data channel media description in the SDP offer of the initial INVITE request or any subsequent re-INVITE request message, if the S-CSCF has not included the data channel capability indication in the Feature-Caps header field in the 200 OK response either to the initial REGISTER or a subsequent REGISTER request message. If the UE is not configured whether to use IMS data channel, it is up to UE implementation whether or not to include the media feature tag in the Contact header field. AC.7.1 Bootstrap Data Channel Setup Signalling procedure Figure AC.7.1-1depicts a signalling flow diagram for establishing a bootstrap data channel in a person-to-person use case. The MF anchors the bootstrap data channel and the originating network is offering a bootstrap data channel to the remote peer as well for application download. NOTE 1: Some SIP signalling not relevant for the procedure, is not shown in the call flow below. Figure AC.7.1-1: Bootstrap Data Channel set up Signalling Procedure The steps in the call flow are as follows: 1. UE#1 sends the SIP INVITE request with an initial SDP to the IMS AS, through P-CSCF and S-CSCF in the originating network. The initial SDP contains offers for the bootstrap data channel establishment request with bootstrap DC stream ID. In this example procedure, the SDP contains both bootstrap data channel offers for originating side and terminating side. NOTE 2: This SIP INVITE can also be a SIP re-INVITE performed after the initial IMS audio session is setup. The SIP re-INVITE can be initiated either from UE#1 or UE#2. 2. IMS AS validates user subscription data to determine whether the session establishment event should be notified to DCSF. If the IMS AS determined, based on the user profile, that the session establishment event needs to be notified to DCSF, the IMS AS selects a DCSF for this user based on local configuration or discovery and selection of a DCSF instance via NRF. If the IMS AS determined, based on the user profile, that the session establishment event need not to be notified to DCSF, or DCSF decides that DC request is not allowed, the IMS AS proceeds with normal IMS procedures to setup the MMTel session without performing Data Channel bootstrapping, by deleting DC related media information and sending the updated SIP INVITE to the originating S-CSCF. 3. IMS AS notifies the DCSF of the session establishment event by sending Nimsas_SessionEventControl_Notify (SessionEstablishmentRequestEvent, Session ID, Calling ID, Called ID, Session Case, Event initiator, Media InfoList, DC Stream ID) request to the DCSF. 4. After receiving the DC control request, the DCSF determines the policy about how to process the bootstrap data channel establishment request based on the related parameters in the Data Channel control request (e.g. CallingID, CalledID, DC Stream ID) and/or DCSF service specific policy. 5. Since the SessionEstablishmentRequestEvent indicates that served user is offered local bootstrap media, DCSF, based on its policies reserves originating side MDC1 media information, as well as the terminating side MDC1 remote bootstrap media (targeting remote UE), which are used to receive UE request for application downloading from MF. 6. DCSF invokes the Nimsas_MediaControl_MediaInstruction (Session ID, Media Instruction Set) operation based on its policies instructing the IMS AS how to set up bootstrap data channel with MF both for originating and terminating side. The MediaInstructionSet provided by the DSCF, includes its MDC1 media endpoint addresses created in step 5, DC Stream ID and the replacement HTTP URL representing the application list offered via the MDC1 interface. In this scenario, the DCSF instructs the IMS AS to terminate bootstrap data channel establishment request on originating MF and initiate remote bootstrap data channel establishment request(targeting remote UE) as well as forwarding remote bootstrap data channel establishment request of served user (targeting remote DCSF) towards terminating network. 7. The IMS AS selects a MF based on local configuration or discovers and selects a MF instance supporting DC media function via NRF. 8. IMS AS invokes Nmf_MRM_Create(List of Media Termination Descriptors) service operation to instruct MF to allocate required data channel media resources. IMS AS request creation of two different Media Terminations, one representing the local bootstrap media to be terminated and the other representing the remote bootstrap media to be offered to remote UE. Each Media Termination includes information required to allocate resources in both Mb and the MDC1 interfaces. The MF responds with the negotiated data channel media resource information to IMS AS. NOTE 3: The MF media resource allocation in step 8 could be done with one or multiple service invocations. 9. IMS AS responds to the MediaInstruction request received in step 6. The response may include the atomic success result of operation and also includes negotiated data channel media resource information for MDC1. 10. The DCSF stores the media resource information and responds to the Notify Request received in step 3. 11-13. IMS AS sends the INVITE which includes the updated SDP offer adding media information of MF via the originating S-CSCF to remote network side and UE#2. In this scenario, the SDP offer for bootstrap data channel to UE#2 is included. Step 2-10 applies to the IMS AS and DCSF in terminating network, i.e. the IMS AS determines to notify the DCSF based on DC subscription and UE DC capability and the DCSF instructs the IMS AS and MF to establish the resource for the required data channels provided to terminating UE. 14. UE#2 and terminating network returns an 18X response with the SDP answer to bootstrap data channel to originating network. According to the received SDP answer, IMS AS may notify the DCSF using Nimsas_SessionEventControl_Notify and then instruct MF to update data channel media resource information for UE#2. 15-16: UE#2 and terminating network returns a 200 OK response. 17. The IMS AS notifies the successful session establishment event, Nimsas_SessionEventControl Notify (SessionEstablishmentSuccessEvent, Session ID, Media Info List) to DCSF. 18. The DCSF responds to the Nimsas notification request. 19. 200 OK forwarded to UE#1 which indicates the bootstrap data channel has been established. 20. The originating network P-CSCF executes QoS procedure for bootstrap data channel as specified in TS 23.203 [54] and TS 23.503 [95]. 21-24: The bootstrap data channels have been established between originating MF and UE#1/UE#2. The UEs send application request messages to MF to request a data channel application or an application list if multiple DC applications are available, via the established bootstrap data channel with its data channel capabilities. The MF replaces the root URL with the replacement URL received in steps 8 and forwards the message to received media point of DCSF. The DCSF provides the application list and proper data channel applications further to UE#1 and UE#2 based on their data channel capabilities and their choices through MF. The bootstrap data channels have also been established between terminating MF and UE#1/UE#2. The data channel application is requested and downloaded to UE#1 and UE#2 from terminating DCSF. Either UE in the IMS session may attempt to select an application from either its local or remote DCSF. Depending on a local policy in DCSF, the DCSF may decline the application selection from the remote UE, unless the application has been selected by the peer UE first. NOTE 4: How the DCSF declines the application selection is out of scope of 3GPP. NOTE 5: It is assumed that user of the remote UE is informed about the chosen application of the peer user together with a choice to accept or reject that request. Steps 20-24 may be executed after step 14, if the SDP answer in 200 OK to the PRACK and UPDATE messages contain the information required to establish bootstrap data channels. NOTE 6: IMS-AGW needs to allow the establishment of bootstrap data channels based on the information in the 200 OK to PRACK and UPDATE messages. 25. Subsequent procedures continue. NOTE 7: In the DC application list, the DCSF may provide DC applications supported by both UEs, or only supported by the UE who sends the application request message. The details of how to provide the application list to the UE and how to use it by the UE are not defined in this specification. AC.7.2 Application Data Channel Setup Signalling Procedure AC.7.2.1 Person to Person (P2P) Application Data Channel Setup Figure AC.7.2.1-1 depicts a signalling flow diagram for establishing an application data channel in a person-to-person use case. In this scenario, the MF is not used to anchor the Application data channel. In the call flow the UEs have already established an IMS audio session and the originating UE is updating the IMS audio/video session to an IMS data channel session. Figure AC.7.2.1-1: Person-to-Person Application Data Channel set up Signalling Procedure The steps in the call flow are as follows: 0. IMS session and bootstrap data channel have been established as described in Figure AC.7.1-1. Each UE (UE#1 and UE#2) may have bootstrap data channels established with both originating MF and terminating MF. Selected data channel application has been downloaded to UE#1 and possibly UE#2. 1. UE#1 initiates a Person-to-Person Application Data Channel for the selected application. The UE#1 sends the SIP reINVITE request with an updated SDP to IMS AS, through originating network P-CSCF and S-CSCF. The updated SDP contains the bootstrap data channel information, as well as the requested application data channel and the associated DC application binding information, according to clause AC.5 and TS 26.114 [76]. NOTE 1: The SIP re-INVITE can be initiated either from UE#1 or UE#2. 2. The IMS AS validates user subscription data to determine whether the media change request event should be notified to the DCSF. 3. The IMS AS notifies the DCSF, via Nimsas_SessionEventControl_Notify (MediaChangeRequest Event, Calling ID, Called ID, Session ID, Event Direction, Media Info List) of the media change request event. 4. After receiving the session event notification, the DCSF determines the policy about how to process the application data channel establishment request based on the related parameters (i.e. associated DC application binding information) in the notification and/or DCSF service specific policy. 5. The DCSF determines that the added application data channel media descriptor of the SDP offer takes UE#2 as target endpoint and does not require anchoring on the local MF. NOTE 2: If MF needs to anchor application data channel, DCSF would have used the Nimsas_MediaControl service operation to instruct IMS AS to allocate data channel media resources of the MF. 6. DCSF responds to the notification received in step 3. 7-8. IMS AS sends the re-INVITE to the originating S-CSCF and then to the terminating network side and UE#2. 9-11. UE#2 and terminating network returns a 200 OK response with SDP answer for application data channel to originating network. UE#2 may need to download the corresponding DC Application signalled in the SDP offer, if not done already and associate it with the requested application DC. NOTE 3: It is assumed that the data channel application is downloaded to the UE#2 via the established bootstrap data channel between UE#2 and the MF/DCSF when UE#1 has downloaded the application from DCSF. In a case the UE#2 does not have it available when UE#2 receives the SDP offer for the application DC, the UE#2 can attempt to download it again. NOTE 4: The UE at the terminating side is capable to determine if to use the DC application based on the received DC application binding information. 12. IMS AS notifies the DCSF of the successful data channel modification. 13. DCSF responds to the notification received in step 12. 14-15. The IMS AS sends 200 OK response to the originating S-CSCF and P-CSCF. 16. The originating network P-CSCF executes QoS procedure for application data channel media based on the SDP answer information from the 200 OK response. 17. P-CSCF returns the 200 OK response to UE#1. 18. UE#1 sends ACK to the terminating network. 19. The application data channel between UE#1 and UE#2 is established. In this example, it is not anchored in MF. If the DCSF receives a notification for a media change request event for an application request that is initiated from the remote UE, if the local policy does not allow the remote UE to use an application, the DCSF may use the Nimsas_MediaControl_MediaInstruction service operation to instruct IMS AS to reject the offered media. NOTE 5: It is possible that the remote UE has cached the application during a previous IMS DC session. AC.7.2.2 Person-to-Application (P2A) Application Data Channel Setup Figure AC.7.2.2-1 depicts a signalling flow diagram for establishing an Application Data Channel in a person to application use case. Figure AC.7.2.2-1: Person-to-Application (P2A) Application Data Channel set up Signalling Procedure The steps in the call flow are as follows: 0-3. Steps 0-3 of clause AC.7.2.1 applies. NOTE 1: The SIP re-INVITE can be initiated either from UE#1 or UE#2. 4. After receiving the session event notification, the DCSF determines the policy about how to process the application data channel establishment request based on the related parameters (i.e. associated DC application binding information) in the notification and/or DCSF service specific policy. 5. The DCSF determines that the added Application Data Channel media of the offer takes DC Application Server as target endpoint and requires to anchor in the MF. 6. The DCSF invokes Nimsas_MediaControl service operation to instruct IMS AS to terminate the media flow of the originating UE to MF. The instruction also includes information to be consumed by the MF that the data channel media shall be relayed via the MDC2 interface. 7. The IMS AS invokes Nmf_MRM_Create(List of Media Termination Descriptors) service operation to instruct MF on application data channel establishment and data channel media resource reservation based on the DC media information received from DCSF. 8. The IMS AS notifies the MediaControl instruction control response to DCSF. 9. The DCSF stores the media resource information and sends a P2A application data channel establishment request (including the MDC2 media resource received from MF) to the DC Application Server via DC3/DC4. 10. DC Application Server accepts the P2A application data channel establishment request, returning an MDC2 reserved media resource as answer and is prepared for UE#1 traffic through MDC2. NOTE 2: Details on how DCSF communicates with the DC Application Server is out of scope of this Release. 11. DCSF requests IMS AS to update the MF resource with MDC2 media endpoint information of DC Application Server. 12. IMS AS updates the MF resource. 13. IMS AS notifies the MediaControl instruction control response to DCSF. 14. DCSF replies to the notification received in step 13. 15-16. IMS AS sends the re-INVITE to remote network side and UE#2, via the originating S-CSCF, which does not include application data channel request in the SDP for the application data channel. 17-19: UE#2 and terminating network returns a 200 OK response with SDP answer for audio/video. 20. IMS AS notifies the DCSF about the successful result of the MediaChangeRequest event. 21. DCSF replies to the notification. 22-23. The IMS AS includes SDP answer for application data channels to UE#1 in 200 OK response and sends 200 OK response to S-CSCF and P-CSCF. 24. The originating network P-CSCF executes QoS procedure for application data channel media based on the SDP answer information from the 200 OK response. 25. CSCF returns the 200 OK response to UE#1. 26. UE#1 send ACK to the terminating network. 27. The application data channel between UE#1 and DC Application Server is established via MF. MF forwards data channel traffic between UE#1 and DC Application Server based on MDC2 media point information received in step 9 and 12. AC.7.2.3 Person-to-Application and Application-to-Person (P2A2P) Procedure This procedure enables originating and terminating UE to establish application data channels for the same application to communicate with the same Data Channel Application Server. The P2A2P procedure requires the establishment of application data channels from UE#1 to MF and from UE#2 to MF. The two application data channels are associated with the same application. This enables UE#1 and UE#2 to interact with the same DC Application Server simultaneously and the DC Application Server to correlate the data exchanged with both UEs. The P2A procedures as described in clause AC.7.2 are used to establish one application data channel between UE#1 and MF and, for A2P scenario, one application data channel between UE#2 and MF. In case of two involved UEs, this enables independent communication between UE#1 and UE#2 with the DC Application Server. Figure AC.7.2.3-1: Symmetric Application Data Channel Establishment 0. IMS session and bootstrap data channels are established as described in Figure AC.7.1-1. Each UE (UE#1 and UE#2) may have bootstrap data channels established with both originating MF and terminating MF. Selected data channel application is downloaded to UE#1 and possibly UE#2. 1. UE#1 initiates a Person-to-Application Application Data Channel for the selected application. The UE#1 sends SIP re-INVITE request with an updated SDP to IMS AS. The updated SDP contains the bootstrap data channel, the application data channel information and associated DC application binding information, according to clause AC.5 and TS 26.114 [76]. NOTE 1: The SIP re-INVITE can be initiated either from UE#1 or UE#2. 2. IMS AS validates the data channel media description information and/or user subscription data to determine whether the DCSF needs to be notified. 3. IMS AS selects and notifies the DCSF about the call event and data channel establishment request. 4. The DCSF determines how to process the application data channel establishment request based on the parameters (i.e. associated DC application binding information) in the notification from IMS AS and/or DCSF service specific policy. 5. DCSF determines that the added application data channel media in the SDP offer requires the DC Application Server is the endpoint for both originating and terminating UE and that the application DC must be anchored at the MF. DCSF communicates with the DC Application Server for DC resource control. Once the application data channel is established, the DC Application Server will send/receive traffic to/from UE#1 through the MDC2 interface. NOTE 2: Details on how the DCSF communicates with the DC Application Server are out of scope of this release. 6. DCSF invokes Nimsas_MediaControl service to send data channel control request to IMS AS, including information how to relay data channel media via the MDC2 interface. 7. IMS AS reserves data channel media resources at the MF via DC2 based on the DC media information received from DCSF. These requests by the IMS AS, are used to create two associated resources (one for the originating UE and one for the terminating UE) in the MF. 8. IMS AS notifies the DCSF about MediaControl instruction control response. 9. DCSF communicates with the DC Application Server for DC resource control and provides information on data channel media resources reserved at the MF. 10. The DCSF stores the media resource information and replies to the Nimsas notification request. 11-12. IMS AS sends re-INVITE which include the SDP offer from MF for the application data channel to the originating S-CSCF and then to the remote network and UE#2. 13-16. UE#2 and terminating network return 200 OK with SDP answer for audio/video and for the application data channel. The terminating network P-CSCF executes QoS procedure for application data channel media based on the SDP in the 200 OK. The UE#2 may need to download the corresponding DC Application signalled in the SDP offer, if not done already and associate it with the requested application DC. NOTE 3: It is assumed that the data channel application is downloaded to the UE#2 via the established bootstrap data channel between UE#2 and the MF/DCSF when UE#1 has downloaded the application from DCSF. In the case that the UE#2 does not have it available when UE#2 receives the SDP offer for the application DC, the UE#2 can attempt to download it again. NOTE 4: The UE at the terminating side is capable to determine if to use the DC application based on the received DC application binding information. 17. IMS AS notifies the DCSF about the successful result of the MediaChangeRequest event. 18. DCSF updates media resources in the MF via IMS AS. 19. DCSF replies to the notification received in step 17. 20-21. The IMS AS includes SDP answer for application data channel to UE#1 in 200 OK and sends 200 OK to S-CSCF and P-CSCF. 22. The originating network P-CSCF executes QoS procedure for application data channel media based on the SDP in the 200 OK. 23. P-CSCF returns the 200 OK to UE#1. 24. UE#1 sends ACK to the terminating network. 25. The application data channel between UE#1 and DC Application Server is established via MF. MF forwards data channel traffic between UE#1 and DC Application Server via MDC2. 26. The application data channel between UE#2 and DC Application Server is established via MF. MF forwards data channel traffic between UE#2 and DC Application Server via MDC2. If the DCSF receives a notification for a media change request event for an application request that is initiated from the remote UE, if the local policy does not allow the remote UE to use an application, the DCSF may use the Nimsas_MediaControl_MediaInstruction service operation to instruct IMS AS to reject the offered media. NOTE 5: It is possible that the remote UE has cached the application during a previous IMS DC session. AC.7.3 Void AC.7.4 NF service registration and discovery If the NRF is used for NF registration and discovery, the DCSF and the MF shall register their services at the NRF before providing services to consumers and existing NRF based mechanism needs to be extended with DC specific profiles. according to clause 4.17.1 of TS 23.502 [94]. AC.7.4.1 DCSF Registration and Discovery The DCSF profile includes NF type=DCSF and may include IMPU ranges for calling identities or called identities of users it serves. The DCSF can update and deregister in the NRF after registration and the procedures are specified in clauses 4.17.2 and 4.17.3 of TS 23.502 [94]. After registration in the NRF, the DCSF can be discovered by other consumer NFs as specified in clauses 4.17.4 and 4.17.5 of TS 23.502 [94]. AC.7.4.2 MF Registration and Discovery The MF profile includes NF type=MF and may include MF location information to select a local MF to minimize transmission delays in the media path. NOTE: The MF location information is operator specific. The MF can update and deregister in the NRF after registration and the procedures are specified in clauses 4.17.2 and 4.17.3 of TS 23.502 [94]. After registration in the NRF, the MF and its services can be discovered by other consumer NFs as specified in clauses 4.17.4 and 4.17.5 of TS 23.502 [94]. AC.7.5 Providing subscriber specific graphical user interface to the UE According to clause 6.2.10.1 of TS 26.114 [76], the UE can send a HTTP GET Request for the root ("/") URL through the bootstrap data channel which is replied with a data channel application describing the graphical user interface and the logic needed to handle any further data channel usage beyond the bootstrap data channel itself. The graphical user interface can e.g. contain a menu of applications, from which the user can choose one or several. The graphical user interface should be subscriber specific and contain only applications for which the user has subscribed to and is authorized to use. To provide the graphical user interface containing subscriber specific data channel applications via the bootstrap data channel to the UE, the DCSF, when receiving a call event notification including subscriber specific information and optionally stream ID from the IMS AS, creates the URL identifying the graphical user interface corresponding to the stream ID (if available) for this subscriber. NOTE: How the DCSF creates the URL is implementation specific. AC.7.6 Termination of IMS Data Channel When a bootstrap data channel is established successfully, the bootstrap data channel shall be kept available during the IMS MMTel session and it shall be terminated along with the release of the call. The application data channel shall be terminated along with the release of the call or be terminated by closing this application separately. In the latter case, the UE triggers a SDP negotiation to release the application data channel. The termination of application data channel shall not have any impact on the audio or video within the IMS sessions. AC.7.7 QoS requirement of IMS Data Channel The appropriate 5QI/QCI for the QoS flows of the IMS data channel media, as defined in TS 26.114 [76], shall be applied over the 5GS system or EPS system for IMS data channel. AC.7.8 Void AC.7.9 IMS data channel setup Signalling Procedure for interworking with MTSI UE Editor's note: The impact on services in clause AA.2.4.1 is FFS. Editor's note: The completion of the clauses under clause AC.7.9 are FFS. AC.7.9.0 General defined in TS 26.114 [76]. When the originating DCMTSI UE initiates an IMS DC session to the terminating MTSI UE, a bootstrap data channel is set up between the originating DCMTSI UE and the originating network (i.e. DCSF and MF) and an MMTEL session for the other media (e.g. audio, video, the MMTEL media other than data channel) may be set up with the terminating side based on the SDP response from the terminating MTSI UE. This is described in clause AC.7.9.1. The originating DCMTSI UE may initiate an application data channel setup which is associated with the MMTEL session between the DCMTSI UE and the MTSI UE (e.g. for real-time screen sharing). The data channel media sent from the originating DCMTSI UE is transcoded to MMTEL media and transcoded to the terminating MTSI UE via the associated RTP stream and the MMTEL media sent from the terminating MTSI UE is transcoded to data channel media and transferred to the originating DCMTSI UE via the associated application data channel stream. This is described in clause AC.7.9.2. The DCMTSI UE may initiate application data channel setup with the DC AS for the data channel applications which is configured to support interworking with MTSI UE. The DC AS subscribes to the IMS AS to be notified any application data channel for the data channel applications that require interworking with an MTSI UE is set up. It is described in clause AC.7.9.3. The DC AS may initiate data channel between the serving network of the DCMTSI UE and the DCMTSI UE when it requires interworking with MTSI UE. The DC AS subscribes the event to the IMS AS to be notified about the IMS session is established with the DCMTSI UE as the callee which is configured as an interworking provider (e.g. customer service centre). This is described in clause AC.7.9.4. AC.7.9.1 Bootstrap Data Channel Setup Signalling Procedure Figure AC.7.9.1-1 depicts a signalling flow diagram for establishing a bootstrap data channel when the originating DCMTSI UE initiates an IMS DC session to the terminating MTSI UE. In Figure AC.7.9.1-1, the procedure starts with the INVITE including SDP offer. The SDP offer includes for audio and data channel media and represent the minimum SDP offer to start this procedure, but it is not limited only for that media (e.g. the video offer may be included). Figure AC.7.9.1-1: Bootstrap Data Channel set up Signalling Procedure for IMS data channel interworking with MTSI UE 1. UE#1 sends the SIP INVITE request with an initial SDP to the IMS AS, through P-CSCF and S-CSCF in the originating network. The initial SDP contains SDP offers for audio and the bootstrap data channel with bootstrap DC stream ID. 2. Data channel management procedure in originating network is executed as per step2~10 in Figure AC.7.1-1. 3-4. IMS AS sends the INVITE request to remote network with SDP containing data channel media for terminating network and UE #2. 5-7. UE#2 and terminating network returns bootstrap DC negotiation result to originating network. The port number of bootstrap data channel in the SDP answer is set to zero. implying that the terminating UE #2 does not support IMD DC or is not accepting the establishment of bootstrap data channel 8. IMS AS requests MF to update the local DC media resources accordingly. 9-11. When IMS AS sends the bootstrap DC negotiation result to DCSF, since the port of bootstrap data channel for UE #2 is set to zero, the DCSF knows that the terminating network or UE #2 does not support IMS DC or does not want to use IMS data channel in this session. 12-18. These procedures are same as step14~20 in Figure AC.7.1-1. 19. The bootstrap data channels have been established only between originating MF and UE#1. 20. The subsequent procedure applies. AC.7.9.2 Signalling Procedure of Application Data Channel Interworking via MF Figure AC.7.9.2-1 depicts a signalling flow diagram for establishing the application data channel when the originating DCMTSI UE initiates an IMS DC session to the terminating MTSI UE, providing interworking of application data channel to MTSI UE via MF. This signalling flow takes the data channel application which enables the transcode between the data channel media and the MMTEL media such as audio and video, e.g. Real-time Screen Sharing. Figure AC.7.9.2-1: Application Data Channel set up signalling procedure for IMS data channel interworking with MTSI UE via MF 1-3. UE#1 initiates a re-INVITE request to establish an application data channel in which the application data channel and data channel application information (for instance, application ID) is included. The IMS AS validates user subscription data to determine whether this request should be notified to the DCSF as stated in clause AC.7.2. 4. After receiving the notification, the DCSF determines the policy about how to process the application data channel establishment request based on the related parameters (i.e. associated DC application binding information as application ID) in the notification and/or DCSF service specific policy. 5-7. Since the DCSF is aware that the terminating network or UE #2 does not support or does not want to use IMS data channel in this session, the DCSF determines that interworking of the application data channel media to MTSI UE is needed and possible, based on the application information, i.e. application id. The DCSF invokes Nimsas_MediaControl_MediaInstruction to the IMS AS and instructs the IMS AS to create resources and association for the application data channels on originating side and video media on terminating side. The DCSF also includes the instruction on how to transcode data channel media to video media. The IMS AS invokes Nmf_MediaResourceManagement to the MF to allocate resource and transcode data channel media to video media according to DCSF's instruction. NOTE: The media instruction enables the MF to perform transport protocol translation from DC protocol (UDP/DTLS/SCTP) on one side and video media (RTP/AVPF) on the other. 8-9. IMS AS responds to the MediaInstruction request received in step 6. The response may include the atomic success result of operation and also includes negotiated data channel media resource information for MDC1. The DCSF stores the media resource information and responds to the request received in step 3. 10-11. After the media resource reservation, the IMS AS sends a re-INVITE request with the SDP offer for anchoring the video media of UE#2 to the MF. 12-14. After terminating network side negotiation, UE#2 and terminating network returns 200 OK for the re-INVITE. 15-16. DCSF is notified about the terminating network media negotiation result. 17-21. The IMS AS sends 200 OK for re-INVITE initiated by UE#1 and UE#1 returns ACK. 22. UE#1 initiates SCTP association and DTLS connection establishment procedures and establishes the application data channels with the MF. 23-24. The IMS AS reports media negotiation result to the DCSF and reports that anchoring video stream is successful. The DCSF sends a Call Control Request to the MMTel AS indicating it to continue the call process. 25. The IMS AS sends a Media Resource Management Request to the MF to associate application data channel stream between UE#1 and the MF with the allocated video streams between UE#2 and the MF. The application data channels between the MF and UE#1 are associated with the RTP video streams between the MF and UE#2. The RTP stream of UE#1's (e.g. screenshare sequence) is received by UE#2 from video streams. AC.7.9.3 Signalling Procedure of Application Data Channel Interworking via DC AS Figure AC.7.9.3-1 depicts a signalling flow diagram for establishing an application data channel from DCMTSI UE to DC application server, providing interworking of application data channel to MTSI UE via DC application server. The originating DCMTSI UE sends the data channel application media to the DC AS, which performs the necessary interworking actions on the application media for the terminating MTSI UE. Figure AC.7.9.3-1: Application Data Channel set up signalling procedure for IMS data channel interworking with MTSI UE via DC application server The steps in the call flow are as follows: 1. DC AS subscribes via the NEF to be notified when any application DC for a DC application that requires interworking is established. 1a. The DC AS subscribes to the NEF by using Nnef_ImsEE_Subscribe Request (event ID: DC Interworking Required, DC Interworking Information). The DC Interworking Information includes the application ID(s) of the DC application which requires interworking with MTSI UE. 1b. The NEF responses to DC AS by using Nnef_ImsEE_Subscribe Response. 1c. The NEF locates the IMS AS(s) via NRF. 1d. The NEF subscribes to the IMS AS as requested by DC AS in step 1a, by using Nimsas_ImsEE_Subscribe Request. 1e. The IMS AS responses to NEF by using Nimsas_ImsEE_Subscribe Reponse. 2. IMS session and bootstrap data channel have been established. Selected DC application(s) have been downloaded to UE#1. The DCSF knows the UE#2 or terminating network does not support IMS DC based on procedure in clause AC.7.9.1. Hence, the bootstrap data channel is established only between the UE#1 and the originating network. 3-5. The UE#1 initiates a P2P application DC. Steps 1-2 of clause AC.7.2.1 applies. 6. After receiving the session event notification from the IMS AS, the DCSF determines that IMS DC interworking for the requested DC application is to be performed based on the application information, i.e. application id. the remote network or UE#2 not supporting IMS DC, or not willing to use IMS DC. The DCSF changes P2P application DC to P2A application DC. 6a. The DCSF informs to the IMS AS that IMS DC interworking action is required for the requested DC application and the UE#2 side Information. The UE#2 side Information may include the SIP URI of the UE#2 or Called ID. 6b. The IMS AS notifies to the NEF that the DC Interworking Required event is detected with the UE#2 side Information by using Nimsas_ImsEE_Notify Request. 6c. The NEF responses to the IMS AS by using Nimsas_ImsEE_Notify Response. 6d. The NEF notifes to the DC AS that the DC Interworking Required event is detected with the UE#2 side Information by using Nnef_ImsEE_Notify Request. 6e. The DC AS responses to the NEF by using Nnef_ImsEE_Notify Response. 7. The DCSF instructs the MF via the IMS AS to establish the media resource of the P2A application DC and the DC connection is established between UE and the DC AS. During P2A connection establishment, the DC AS takes into account the information received in step 6d. Steps 5-14 of clause AC.7.2.2 applies. 8-9. IMS AS sends the re-INVITE to remote network side and UE#2,which does not include bootstrap data channel information and application data channel media components in the SDP. 10. Steps 17-26 of clause AC.7.2.2 applies. 11. UE#1 uses the established application data channel to provide DC application specific information e.g. sends the file (e.g. a photo) to the DC AS, which will be sent to UE#2 from DC AS. 12. DC AS performs interworking actions based on the notification received in step 6d and the data received in step 11. NOTE: How the DC AS performs interworking actions to provide DC application specific information to the MTSI UE is out of scope of this specification. The DC AS can for example generate a hyperlink associated with the file received in step 11 and sends the hyperlink to UE#2 through a SMS, where the user of UE#2 can download the file using the hyperlink if he/she wants. AC.7.9.4 Signalling Procedure of Application Data Channel Interworking via DC AS for originating MTSI UE Figure AC.7.9.4-1 depicts a signalling flow diagram for establishing an application data channel from DC application server to DCMTSI UE, providing interworking of application data channel to MTSI UE via DC application server. The DC AS initiates the procedure of application data channel setup between the serving network of the DCMTSI UE and the DCMTSI UE (terminating side) and the terminating DCMTSI UE sends the data channel application media to the DC AS. The DC AS performs the necessary interworking actions on the application media for the originating MTSI UE. Figure AC.7.9.4-1: Application Data Channel set up signalling procedure for IMS data channel interworking with originating MTSI UE via DC application server The steps in the call flow are as follows: 1. DC AS subscribes via the NEF to be notified when any application DC for a DC application that requires interworking is established. 1a. The DC AS subscribes to the NEF by using Nnef_ImsEE_Subscribe Request (event ID: DC Interworking Required, DC Interworking Information). The DC Interworking Information includes the UE#2 side Information which is configured as an interworking provider e.g. the service number of the customer service centre. 1b. The NEF responses to DC AS by using Nnef_ImsEE_Subscribe Response. 1c. The NEF locates the IMS AS(s) via NRF. 1d. The NEF subscribes to the IMS AS as requested by DC AS in step 1a, by using Nimsas_ImsEE_Subscribe Request. 1e. The IMS AS responses to NEF by using Nimsas_ImsEE_Subscribe Reponse. 2. The UE#1 initiates an IMS session with the UE#2. 3. The IMS AS determines that IMS DC interworking for the DC application served by the DC AS is to be performed based on the SDP offer received in step 2, e.g. the Called ID that matches with the service number included in the UE#2 side Information. 3a. The IMS AS notifies to the NEF that the DC Interworking Required event is detected with the UE#1 side Information by using Nimsas_ImsEE_Notify Request. The UE#1 side Information may include the SIP URI of the UE#1 or Calling ID. 3b. The NEF responses to the IMS AS by using Nimsas_ImsEE_Notify Response. 3c. The NEF notifies to the DC AS that the DC Interworking Required event is detected with the UE#1 side Information by using Nnef_ImsEE_Notify Request. 3d. The DC AS responses to the NEF by using Nnef_ImsEE_Notify Response. 4. The IMS AS sends the INVITE to remote network side and UE#2 and the IMS session establishment procedure is continued. 5. After IMS session establishment, the IMS AS notifies via the NEF that the IMS Session is established for the UEs that IMS DC interworking to be performed. 5a. The IMS AS notifies to the NEF that the IMS Session is established with the UE#1 side Information by using Nimsas_ImsEE_Notify Request. The notification of IMS Session establishment is implicitly subscribed in step 3b. 5b. The NEF responses to the IMS AS by using Nimsas_ImsEE_Notify Response. 5c. The NEF notifies to the DC AS that the IMS Session is established with the UE#1 side Information by using Nnef_ImsEE_Notify Request. The notification of IMS Session establishment is implicitly subscribed in step 3d. 5d. The DC AS responses to the NEF by using Nnef_ImsEE_Notify Response. 6. DC AS requests to the serving network of the UE#2 (terminating network) to add a local data channel for the UE#2, based on the procedure of Adding Data Channel to an Existing IMS Session as described in clause AG.2.1. The IMS AS of the serving network of the UE#2 does not send the INVITE to the UE#1. 7. P2A Application Data Channel is set up between the serving network and the UE#2 based on the procedure described in the clause AC.7.2.2. During P2A connection establishment, the DC AS takes into account the information received in step 3c. 8. UE#2 uses the established application data channel to provide DC application specific information (e.g. customer service menu) to the DC AS, which will be sent to UE#1 from DC AS. 9. DC AS performs interworking actions based on the notification received in step 3c and the data received in step 8. NOTE: How the DC AS performs interworking actions to provide DC application specific information to the MTSI UE is out of scope of this specification. The DC AS can for example generate a hyperlink associated with the file received in step 8 and sends the hyperlink to UE#1 through a SMS, where the user of UE#1 can download the file using the hyperlink if he/she wants. AC.7.10 Multiplexing multiple DC streams over single SCTP connection AC.7.10.1 General When multiple data channels are used in an IMS session, the UE and IMS network may support SDP negotiation to multiplex multiple data channel streams into a single data channel SDP media description m line and transport streams of multiple applications in the same SCTP connection, to save the number of m lines used by the UE and to improve the efficient usage of media resources. The UE and IMS network also need to support data channel de-multiplexing when supporting data channel multiplexing. If the UE receives streams targeting to different applications over a single SCTP connection, it identifies the applications and delivers the data of the streams to corresponding applications. If the IMS network receives multiplexed streams which have different remote endpoints, e.g. a local bootstrap data channel and a remote bootstrap data channel of a UE, the MF terminates the multiplexing and sends different streams to corresponding endpoints based on instructions of DCSF. The following multiplexing scenarios are supported in this Release: - Multiplexing local bootstrap data channel and remote bootstrap data channel between the UE and its home IMS network using a single SDP m line media description if both support data channel multiplexing capability; - Multiplexing different application data channels for applications with compatible QoS requirements between the UE and its IMS network using a single SDP m line media description if both support multiplexing capability; - Multiplexing different application data channels for applications with compatible QoS requirements between the originating IMS network and terminating IMS network using a single SDP m line media description if both support DC multiplexing capability. Multiplexing the data channels using the same stream ID are not supported. The following de-multiplexing scenarios are supported in this Release: - The supporting IMS network de-multiplexes local bootstrap data channel and remote bootstrap data channel from a SDP media description towards a UE that does not support multiplexing; - The supporting IMS network de-multiplexes application data channels from a SDP media description, if the data channels have different endpoints e.g. a P2P application and a P2A application or towards a UE that does not support multiplexing; - The supporting originating IMS network de-multiplex data channels towards remote network if the remote network or remote UE does not support DC multiplexing. If the UE decides to use data channel multiplexing, when the UE generates SDP offer in INVITE or re-INVITE request, the DC stream IDs associated with the data channels to be multiplexed and the binding information combined with the data channels are included in the SDP offer for a single m line. NOTE: How the application id and the DC stream IDs are included in the SDP is specified in SA WG4. The IMS AS notifies the event of data channel multiplexing along with the data channel media information and binding information to the DCSF if data channel multiplexing is allowed for the subscriber. The DCSF determines whether and how the data channels are multiplexed or de-multiplexed. When the DCSF determines that some data channels are allowed to be multiplexed, it instructs the IMS AS to multiplex the specific data channel streams to the same m line on the MF. The IMS AS further instructs MF to reserve a single media termination for the streams to be multiplexed. If the DCSF determines that a data channel needs to be de-multiplexed from a SCTP connection, it instructs the IMS AS to de-multiplex the specific data channel stream on the MF. Based on the instruction of the DCSF, the IMS AS further indicates the MF to reserve separate media termination for the de-multiplexed stream in stead of using the same media termination with other multiplexed streams. If the IMS AS is instructed by DCSF to use data channel multiplexing, when IMS AS generates SDP offer in INVITE or re-INVITE request to remote network or serving UE, the DC stream IDs associated with the data channels to be multiplexed and the binding information combined with the data channels are included in the SDP offer for a single m line. AC.7.10.2 Capability negotiation AC.7.10.2.1 Capability negotiation between UE and IMS network The UE and IMS network may support DC multiplexing capability negotiation as follows: - The UE and the IMS network mutually negotiate their capabilities of data channel multiplexing during registration procedure. - If the UE supports data channel multiplexing, when the UE registers on the IMS network, the UE shall include a media feature tag in the Contact header field indicating its capability of supporting data channel multiplexing in the initial and any subsequent REGISTER request. - If the UE supports data channel multiplexing, when the UE initiates a IMS session using data channel multiplexing, the UE shall include the media feature tag in the Contact header field indicating its capability of supporting data channel multiplexing in the INVITE request. - If the P-CSCF supports data channel multiplexing, when the P-CSCF receives the REGISTER request from the UE, the P-CSCF shall include a Feature-Caps header field indicating its capability of supporting data channel multiplexing in the initial and any subsequent REGISTER request. NOTE: The P-CSCF and IMS-AGW need to understand the multiplexed SDP to avoid gating the multiplexed media streams. - If the home IMS network supports this feature, the S-CSCF includes a Feature-Caps header field indicating its capability of supporting data channel multiplexing in the 200 OK response to the initial and any subsequent REGISTER request. - If the IMS network supports this feature, the S-CSCF includes a Feature-Caps header field indicating its capability of supporting data channel multiplexing in the SIP request messages to the remote network. AC.7.10.2.2 Capability negotiation between originating and terminating network The DCSF in originating IMS network shall determine whether the terminating IMS network supports data channel multiplexing by local configuration or based on the SDP answer received from remote network setting port of multiplexed DC media to zero. NOTE 1: The DCSF can be configured to only allow multiplexing data channels between the UE and the IMS network, i.e. on UNI interface. If the DCSF in originating IMS network receives session establishment failure 488 response to INVITE request from IMS AS and if the IMS session is a standalone IMS DC session, based on operator policy, the DCSF may assume the session failure is due to terminating network not supporting data channel multiplexing and instruct the IMS AS to de-multiplex all data channel media and resend INVITE request with de-multiplexed SDP offer as described in clause AC.7.10.3.1. NOTE 2: If the IMS session rejected by 488 includes other media components, e.g. voice, it means the session is not rejected because of not supporting data channel multiplexing. Thus re-sending INVITE request with de-multiplexed SDP is not needed. AC.7.10.3 Determination and handling of multiplexing and de-multiplexing AC.7.10.3.1 Determination of multiplexing and de-multiplexing When the IMS AS receives the INVITE request with data channel multiplexing, if data channel multiplexing is supported, it reports the event to the DCSF for data channel management. The DCSF determines whether the data channel multiplexing is allowed and whether serving network needs to de-multiplex the data channel traffic based on subscription data, binding information, the endpoints of data channels and capability of terminating network. When the IMS AS receives a response that rejects the multiplexed data channel media, e.g. a 18X with SDP answer setting port of multiplexed data channel media to zero, or a 488 response to the INVITE request of a standalone IMS DC session with multiplexed SDP offer, the IMS AS shall firstly report the session establishment failure event to the DCSF and follows the instructions from DCSF. The DCSF determines whether to release the session or retry the session establishment with normal SDP offer as specified in clause AC.7.10.2.2. If the DCSF determines to retry the session establishment, it instructs the IMS AS to modify the media resource of multiplexed data channels in the MF and further re-send INVITE request with de-multiplexing SDP offer after the media resource modification is successful. AC.7.10.3.2 Handling multiplexing and de-multiplexing at the originating network The IMS AS and DCSF in the originating network follows the following principles to handle data channel multiplexing and de-multiplexing: - If the data channels are kept multiplexed, the DCSF instructs originating IMS AS accordingly. The originating IMS AS further instructs the MF to reserve the same media termination for multiplexed data channels. This attempt may succeed and IMS session establishment may be successful. - If the data channels are kept multiplexed, the DCSF instructs originating IMS AS accordingly. The originating IMS AS further instructs the MF to reserve the same media termination for multiplexed data channels. If the terminating network rejects the SDP offer because the terminating network does not support multiplexing, then originating IMS AS and originating DCSF needs to revert to a new demultiplexed SDP offer towards the target network as described in next bullet. - If the originating network determines to de-multiplex the data channels, the DCSF in the originating network instructs originating IMS AS accordingly. The originating IMS AS further instructs the MF to reserve separate media terminations for the de-multiplexed streams. When the originating IMS AS sends the SDP offer to terminating IMS network, the data channels are not multiplexed in the SDP offer. IMS session establishment continues. AC.7.10.3.3 Handling at the terminating network. The IMS AS and DCSF in the terminating network follows the following principles to handle data channel multiplexing and de-multiplexing: - If the data channels are kept multiplexed, the terminating DCSF instructs terminating IMS AS accordingly. The terminating IMS AS further instructs the MF to reserve the same media termination for multiplexed data channels; - If the data channels is determined to be de-multiplexed, the terminating DCSF instructs terminating IMS AS accordingly. The terminating IMS AS further instructs the MF to reserve separate media terminations for the de-multiplexed streams. When the terminating IMS AS sends the SDP offer to terminating UE, the data channels are not multiplexed in the SDP offer. AC.7.10.4 Procedures AC.7.10.4.1 Bootstrap data channel establishment AC.7.10.4.1.1 Bootstrap data channels multiplexing in originating network Figure AC.7.10.4.1.1-1 shows the procedure when the local bootstrap data channel and remote bootstrap data channel is multiplexed by the originating UE. The originating UE initiates an IMS session with multiplexed SDP for the two bootstrap data channels. The originating IMS network de-multiplexes the bootstrap data channel due to the two data channels have different endpoints. Figure AC.7.10.4.1.1-1: Multiplexing bootstrap data channels in originating network 1. When the UE wants to multiplex its bootstrap data channels, i.e. local bootstrap data channel and remote bootstrap data channel, the UE includes multiplexed SDP media description in initial INVITE request. The media feature tag in the Contact header field indicating its capability of supporting data channel multiplexing is included in reINVITE request. 2-3. The IMS AS selects and report event to DCSF. 4. The DCSF determines based on stream id in the SDP that local bootstrap and remote bootstrap data channels need to be de-multiplexed. 5. The DCSF generates data channel media information for originating side and terminating side. 6. The DCSF instructs the IMS AS to reserve resources on MF. 7. The IMS AS selects MF supporting data channel multiplexing. 8. The IMS AS instructs MF to reserve media resources for multiplexed data channel streams and other media resources based on instructions from DCSF. 9-12. The session continues after the media resource is reserved successfully. The SDP offer in the INVITE request may also be multiplexed if needed. 13-16. The terminating network responds and the session is established successfully. The streams of local data channel and remote data channel are transported in the same SCTP connection between UE#1 and MF and are routed to DCSF and remote network correspondingly. AC.7.10.4.1.2 Bootstrap data channel multiplexing in terminating network Figure AC.7.10.4.1.2-1 shows the procedure when the terminating IMS network multiplexes the received remote data channel and the local bootstrap data channel towards the terminating UE. In this procedure, when the terminating IMS network receives the SDP offer of remote bootstrap DC for terminating UE, it multiplexes this bootstrap data channel with the local bootstrap data channel for terminating UE. When the terminating UE receives the multiplexed SDP offer, it replies with the multiplexed SDP answer to allow multiplexing of the two bootstrap data channels between terminating UE and terminating IMS network. Figure AC.7.10.4.1.2-1: Multiplexing bootstrap data channels in terminating network 1. The originating network sends initial INVITE request with SDP offer for remote bootstrap data channel to UE#2. 2-3. The IMS AS selects and reports event to DCSF. 4. The DCSF determines that local bootstrap and remote bootstrap data channels to UE#2 need to be multiplexed. 5. The DCSF generates data channel media information for originating side and terminating side. 6. The DCSF instructs the IMS AS to reserve resources on MF. 7. The IMS AS selects MF supporting data channel multiplexing. 8. The IMS AS instructs MF to reserve media resources for multiplexed data channel streams and other media resources based on instructions from DCSF. 9-12. The session continues after the media resource is reserved successfully. 13-16. The UE#2 responds and the session is established successfully. The streams of local data channel and remote data channel are transported in the same SCTP connection to UE#2. AC.7.10.4.2 Application data channel establishment AC.7.10.4.2.1 Application data channel multiplexing when both originating and terminating networks support data channel multiplexing Figure AC.7.10.4.2.1-1 shows the procedure of multiplexing application data channels when both originating and terminating networks support data channel multiplexing. In this example procedure, the originating UE initiates a IMS session with audio and DC media components. The UE multiplexes 3 applications all with different endpoints. The originating IMS network and terminating IMS network eventually de-multiplexes the applications based on the different endpoints. Since the originating network and terminating network both support data channel multiplexing, application data channels are multiplexed between originating network and terminating network. Figure AC.7.10.4.2.1-1: Application data channel multiplexing when both originating and terminating networks support data channel multiplexing 1. When the UE#1 wants to multiplex its application data channels for app#1, #2 and #3, the UE includes multiplexed SDP media description when sending reINVITE request. The endpoints of the applications are different, that of app#1 is DC AS in originating network, that of app#2 is DC AS in terminating network and that of app#3 is terminating UE. The media feature tag in the Contact header field indicating its capability of supporting data channel multiplexing is included in reINVITE request. 2. The IMS AS report event to DCSF. 3. The DCSF determines that data channel for app#1 needs to be de-multiplexed because its target endpoint is local DC AS. The DCSF also determine that the multiplexing for app#2 and #3 is kept unchanged towards their target terminating network as described in clause AC.7.10.3. NOTE 1: If UE#2 has established application data channels in the IMS session with the local DC AS in the originating network before step 1, the DCSF can determine to multiplex data channels for app#2 and #3 with them between originating and terminating MFs. 4. The DCSF generates data channel media information for originating side and terminating side. 5. The DCSF instructs the IMS AS to reserve resources on MF. 6. The IMS AS instructs MF to reserve media resources for multiplexed data channel streams and other media resources based on instructions from DCSF. 7-8. The session continues after the media resource is reserved successfully. 9-10. The IMS AS generates reINVITE request to terminating network. The reINVITE request includes capability of supporting data channel multiplexing and the SDP offer for multiplexed data channels of app#2 and #3. 11. The terminating network supports data channel multiplexing. The IMS AS in terminating network reports event to DCSF. 12. The DCSF in terminating network determines that data channel for app#2 and #3 needs to be de-multiplexed as described in clause AC.7.10.3 because they have different endpoints, NOTE 2: If UE#2 has already established application data channels in the IMS session with the local DC AS in the terminating network before step 1, the DCSF can determine to multiplex data channel for app#3 with them between UE#2 and terminating MF. 13. The DCSF generates data channel media information for originating side and terminating side. 14. The DCSF instructs the IMS AS to reserve resources on MF. 15. The IMS AS instructs MF to reserve media resources for multiplexed data channel streams and other media resources based on instructions from DCSF. 16-17. The session continues after the media resource is reserved successfully. 18-19. The IMS AS generates reINVITE request to UE#2. 20-21. The UE#2 replies 18X response with SDP answer for app#3. 22-23. The IMS AS replies 18X response with capability indication of supporting data channel multiplexing and SDP answer for multiplexed data channels for app#2 and #3 to originating network. 24. The IMS AS replies 18X response with SDP answer for multiplexed data channels for app#1, #2 and #3 to UE#1. 25-26. The IMS AS reports event to DCSF. 27. The session is established successfully. The streams of app#1, #2 and #3 are transported in the same SCTP connection between UE#1 and originating MF. The stream of app#1 is routed to DC AS and streams of app#2 and #3 are transported in the same SCTP connection between MFs of originating and terminating network and are routed to DC AS and UE#2 accordingly. AC.7.10.4.2.2 Void AC.7.10.4.2.2a Application data channel multiplexing when terminating network rejects multiplexed data channel media Figure AC.7.10.4.2.2a-1 shows the procedure of multiplexing application data channels when terminating network does not support data channel multiplexing and rejects the multiplexed data channel media. In this example procedure, the originating UE initiates a IMS session with audio and DC media components. The UE multiplexes 3 applications all with different endpoints. The originating network de-multiplexes app#1 because app#1 is terminated in originating network. The originating network further de-multiplexes app#2 and app#3 because the terminating network does not support data channel multiplexing and rejects the multiplexed SDP offer, by updating the session towards terminating network with normal SDP offer. Figure AC.7.10.4.2.2a-1: Application data channel multiplexing when terminating network does not support data channel multiplexing 1. When the UE#1 wants to multiplex its application data channels for app#1, #2 and #3, the UE includes multiplexed SDP media description when sending reINVITE request. The endpoints of the applications are different, that of app#1 is DC AS in originating network, that of app#2 is DC AS in terminating network and that of app#3 is terminating UE. The media feature tag in the Contact header field indicating its capability of supporting data channel multiplexing is included in reINVITE request. 2. The IMS AS report event to DCSF. 3. The DCSF determines that data channel for app#1 needs to be de-multiplexed because its target endpoint is local DC AS. The DCSF also determine that the multiplexing for app#2 and #3 is kept unchanged towards their target terminating network as described in clause AC.7.10.3. NOTE: The DCSF can determines that terminating network does not support data channel multiplexing based on local configuration, In this case, the DCSF will determine to de-multiplex app#2 and app#3 and instruct IMS AS to send normal SDP offer to terminating network without the following steps. 4. The DCSF generates data channel media information for originating side and terminating side. In this example, media stream of data channel for app#1 reuses the originating media ID of multiplexed media in the SDP, media stream of data channels for app#2 and #3 5. The DCSF instructs the IMS AS to reserve resources on MF. 6. The IMS AS instructs MF to reserve media resources for multiplexed data channel streams and other media resources based on instructions from DCSF. 7-8. The session continues after the media resource is reserved successfully. 9-10. The IMS AS generates reINVITE request to terminating network. The reINVITE request includes capability of supporting data channel multiplexing and the SDP offer for multiplexed data channels of app#2 and #3. 11-12. The terminating network does not support data channel multiplexing. The terminating network replies 18X with the port of media component for multiplexed data channels set to zero in SDP answer and no capability indication of supporting data channel multiplexing is included. 13. The IMS AS reports the event of terminating network not supporting data channel multiplexing to the DCSF along with the media information of SDP answer. 14. The DCSF instructs the IMS AS and the IMS AS further requests the MF to modify media resources for streams of app#2 and #3. 15-16. The IMS AS determines that the terminating network does not support data channel multiplexing. It sends UPDATE request with normal SDP offer for app#2 and #3 to re-negotiate SDP with terminating network. 17-18. The terminating network replies 200 OK (UPDATE) with SDP answer for app#2 and #3. 19. The IMS AS replies 18X response with SDP answer for multiplexed data channels for app#1, #2 and #3 to UE#1. 20. The session is established successfully. The streams of app#1, #2 and #3 are transported in the same SCTP connection between UE#1 and originating MF. The stream of app#1 is routed to DC AS and streams of app#2 and #3 are transported to terminating network and are routed to DC AS and UE#2 accordingly. AC.7.10.4.2.3 Application data channel multiplexing when terminating network rejects standalone IMS DC session Figure AC.7.10.4.2.3-1 shows the procedure of multiplexing application data channels when terminating network rejects the session. In this example procedure, the originating UE initiates a standalone IMS DC session. The UE multiplexes 2 applications. The originating network sends INVITE request with only multiplexed SDP offer towards terminating network. The terminating network returns 488 response due to not supporting data channel multiplexing. The IMS AS in originating network reports the session establishment failure event to the DCSF in originating network. The DCSF decides to retry the session establishment with normal SDP offer since the session is a standalone IMS DC session and instructs the IMS AS to modify the media resource of multiplexed data channels in the MF and further send INVITE request with de-multiplexing SDP offer after the media resource modification is successful. The session is established successfully after the retry in this example procedure. Figure AC.7.10.4.2.3-1: Application data channel multiplexing when terminating network rejects standalone IMS DC session 1. When the UE#1 initiates a standalone IMS DC session which multiplex the data channels for application #1 and #2, the UE includes multiplexed SDP media description when sending the INVITE request. The endpoints of the applications are terminating network. The media feature tag in the Contact header field indicating its capability of supporting data channel multiplexing is included in INVITE request. 2. The IMS AS report event to DCSF. 3. The DCSF determines that data channels for app#1 and app#2 are kept multiplexed towards terminating network. 4. The DCSF generates data channel media information for originating side and terminating side. 5. The DCSF instructs the IMS AS to reserve resources on MF. 6. The IMS AS instructs MF to reserve media resources for multiplexed data channel streams and other media resources based on instructions from DCSF. 7-8. The session continues after the media resource is reserved successfully. 9-10. The IMS AS generates an INVITE request to terminating network. The INVITE request includes capability of supporting data channel multiplexing and the SDP offer for multiplexed data channels of app#1 and #2. 11-12. The terminating network does not support data channel multiplexing. Since the multiplexed SDP offer is not supported, the terminating network rejects the session with 488 response and no capability indication of supporting data channel multiplexing is included. 13. The IMS AS determines that the terminating network does not support data channel multiplexing and the session is a standalone IMS DC session. It reports the session establishment failure event to the DCSF with the indication that the terminating network does not support data channel multiplexing. 14. The DCSF determines to retry session establishment to use SDP offer with separate data channels for app#1 and #2 since the session is a standalone IMS DC session. 15-17. The DCSF instructs the IMS AS and the IMS AS further requests the MF to modify media resources of streams of app#2 and #3 from multiplexed data channels to separate data channels. 18. The DCSF responds the session establishment failure event notification and indicates to the IMS AS to retry the session establishment. 19-20. The IMS AS sends INVITE request to terminating network again with updated SDP offer with separate data channels for app#1 and #2. 21-26. The session is established successfully. The streams of app#1 and #2 are transported in same SCTP connection between UE#1 and originating MF and in separate SCTP connections between originating MF and terminating network. AC.8 Void AC.9 Support of AR Communication AC.9.1 General This clause describes the enhancements to the IMS architecture supporting data channel services to additionally support AR services. Two modes for AR services are supported: UE centric and network centric. AC.9.2 Architecture Figure AC.9.2-1: Architecture to support AR communication To support AR communication, the data channel architecture is enhanced as follows: NOTE 1: The term "AR communication" includes many different combinations of use cases, device capabilities and AR media content for which network assisted functions can be provided. AR Application Server (AR AS): - The AR Application Server is responsible for AR service control related to AR communication, including AR session media control, AR media capability negotiation with the UE. NOTE 2: The AR Application Server is a specific DC Application Server and is out of scope of 3GPP. MF: - The MF supports AR media processing. It receives and stores AR service media handling logic from the AR AS and provides Augmented Reality MF capability based on the AR data received from UE. NOTE 3: AR data includes AR metadata and AR related media, e.g. audio, video, etc. IMS AS: - The IMS AS receives the media control instructions from the DCSF and accordingly interacts with the UE for connecting the UE's audio/video media termination to the MF. The following reference points are used for network assisted IMS AR related signalling. - DC4: Reference point between the AR Application Server and the DCSF for AR service handling and AR session media control. This is out of scope of this Release. - DC2: Service based reference point between the IMS AS and the MF for AR media resource management. The following reference points are used for IMS AR related media. - MDC2: Reference point between the AR Application Server and the MF for transmission of application data channel traffic. NOTE 4: The MDC2 reference point is not specified in 3GPP. - Mb: Reference point used for IMS media transport and AR media transmission. AC.9.2.1 UE Centric AR Communication For the UE centric case, AR traffic is transparent to the IMS network and is exchanged between the two peer UEs via the deployed media functions (e.g. IMS AGW/TrGW). NOTE: The UE can download the AR metadata from AR AS through application data channel. AC.9.2.2 Network Centric AR Communication Multiple realization alternatives for network assisted AR are available depending on device capability and what requirements the AR application has on the media transport protocol used between the UE and the network assisted AR function. AR services can be delivered via the following mechanisms: - The AR application server provides network assisted rendering by having all AR media being transported using an established application data channel between the UE and the AR application server. This scenario represents a standard P2A/A2P data channel application as per clause AC.7.2 and consequently not requiring any further description. - An IMS Media Function (MF) having the Augmented Reality media function capability, provides required network assisted AR media processing. AC.9.3 Procedures AC.9.3.1 UE Centric Procedure Figure AC.9.3.1-1: Establishment of UE Centric AR communication session Figure AC.9.3.1-1 depicts a typical call flow procedure to establish a UE centric AR IMS session from UE-A perspective. The main steps in the call flow are as follows: 1. UE-A initiates an IMS communication with UE-B, including establishment of bootstrap data channel. 2. The user of UE-A upgrades the IMS session with AR experience. UE-A initiates a re-INVITE adding media descriptors required by the AR application to be established E2E, e.g. RTP and/or application data channels. Application data channel may be anchored in the MF. In this scenario, the UE performs AR media rendering based on the AR data from its local application. NOTE: In other scenarios, the UE may acquire AR data from other sources, e.g. the peer UE, the AR AS etc. 3. UE-A captures the AR data, performs AR media rendering locally and then encodes AR media e.g. audio/video media stream. 4. UE-A sends the AR media to UE-B through the established media connection(s). 5. UE-A receives the AR media from UE-B through established media connection(s). 6. UE-A decodes the AR media and performs AR media rendering locally and displays it on its screen. AC.9.3.2 Network Centric Procedure Figure AC.9.3.2-1 depicts an example for a call flow procedure to establish a network centric AR IMS session from UE-A perspective with rendering in the network for one of the UEs (UE-A) involved in AR communication. The main steps in the call flow are as follows: Figure AC.9.3.2-1: Establishment of Network Centric AR communication session 1. The UE-A initiates an IMS session and establishes audio and video session connections with the UE-B. The bootstrap data channel(s) are established at the same time for both the UE-A and UE-B. AR Media Rendering Negotiation Procedure: 2. The UE-A decides to request network media rendering based on its status such as power, signal, computing power, internal storage, etc. 3. The UE-A finishes AR media rendering negotiation with the AR AS. NOTE 1: The media negotiation for split rendering between the UE and the network is out of scope of this Release. NOTE 2: The negotiation procedure in steps 2, 3 and 4 is specified in TS 26.264 [104]. 4. If the negotiation result is successful in step 3, the UE-A initiates new P2A application data channels, which are used for AR data transmission between the UE-A and the network. During the P2A application data channel establishment procedure, the DCSF will instruct the MF via IMS AS how to establish the data channel and corresponding media processing specification. 5(Optional). IMS AS initiates a Media re-Negotiation request with UE-A, to connect UE-A's audio/video media stream to MF. 6. IMS initiates a Media re-Negotiation request with UE-B, to connect UE-B's audio/video media stream to MF. The UE-A can request to change the network rendering content if the status changed in the UE-A, such as low power, low computing power, etc. Networking Centric Procedure: 7. The UE-A captures AR data and sends AR data to MF for network assisted rendering. 8. Based on the AR data received from the UE-A and/or instructions received from the AR AS, the MF performs AR media rendering according to the negotiation result in step 3. 9. The MF sends the rendered audio/video media stream to the UE-B. AC.10 Standalone IMS Data Channel Sessions AC.10.1 General A standalone IMS data channel session is applied to establish data channels without MMTel media (e.g. audio, video, messaging). A standalone IMS data channel session with bootstrap data channels is used for downloading application list and applications from the DCSF. Application data channels between two UEs may be initiated with bootstrap data channels simultaneously or not during the standalone IMS data channel session establishment. NOTE 1: The remote UE can reject the IMS data channel session without downloading the application. There are two types of standalone IMS data channel session: a) IMS session with only bootstrap data channel towards PSI, which cannot add MMTel media. b) IMS session with only bootstrap and application data channels towards peer UE. In the case of b), the terminating UE sends 180 Ringing only when the terminating UE successfully downloaded the DC application indicated by the originating UE. The IMS data channel session is able to be answered by the terminating UE after the DC application for communication is allowed to run on the terminating UE. It is assumed early media is used during the process. NOTE 2: The alert on terminating UE for an incoming standalone IMS data channel session may occur at proper time for user concern on, e.g. incoming standalone IMS data channel session, application downloading and/or application running, etc. The terminating UE may be able to be configured by the user to automatically allow some specific performance, e.g. application downloading. The alert may be a ringtone accompanied with additional display of the information from application, e.g. the human readable application name, the brief introduction of the application, the required permissions of the application, etc. The detail of information shown to the user is out of scope of this specification. NOTE 3: The time between alerting the terminating user and the download of the application needs to conform to SIP Session timers. The standalone IMS data channel session towards peer UE can be updated by adding MMTel media to the session. All MMTel media can be removed from an IMS data channel session towards peer UE if standalone IMS data channel session is supported. When standalone IMS data channel session is supported, based on operator policy, additional subscription information for standalone IMS data channel service may be required to be included in service subscription. The additional subscription information is used by the IMS AS to determine whether to accept or reject a standalone IMS data channel session. When subscription for a standalone IMS data channel session is needed and if a UE that has not subscribed for standalone IMS data channel session, the IMS AS rejectS the request of standalone IMS data channel session establishment. Standalone IMS data channel sessions use SIP session timer as per RFC 4028 [106] to avoid hanging resources in the UE and the network. Usage of SIP session timer in IMS is specified in TS 24.229 [10a]. Establishment of standalone IMS data channel sessions does not require SIP precondition. The standalone IMS data channel session is terminated by the existing session release procedure specified in clause AC.7.6. The session release may be triggered by the expiry of the session timer or by sending a SIP BYE request. AC.10.2 Procedures AC.10.2.1 Originating Standalone Bootstrap DC Setup using PSI The originating standalone Bootstrap DC setup using PSI is triggered by a UE for downloading application list and/or applications from DCSF. In this procedure, a PSI is configured in the UE for that purpose. After the standalone bootstrap DC is established, the UE downloads the application list and/or applications via the bootstrap DC. The list of application information is used for selection, downloading and/or initiating standalone application DC in a subsequent IMS data channel session. The UE terminates the standalone IMS data channel session when the session timer expires. Whether and when to initiate the standalone Bootstrap DC setup using PSI is up to UE implementation. Figure AC.10.2.1-1depicts a signalling flow diagram for originating standalone bootstrap data channel setup using PSI. AC.10.2.1-1: Originating Standalone Bootstrap DC Setup using PSI 1. UE#1 sends the SIP INVITE request with an initial SDP offer to the IMS AS, through P-CSCF and S-CSCF in the originating network. The Request URI of the SIP INVITE message is a specific target URI, i.e. a specific PSI indicating standalone bootstrap DC. The initial SDP offer includes only the bootstrap data channel establishment request with bootstrap DC stream ID(s). The SIP precondition is not needed. NOTE 1: The PSI is pre-configured in the UE#1. How and when the PSI is pre-configured is left to implementation. NOTE 2: UE#1 can perform step 1 at any time before initiating a standalone application data channel, such as, immediately after completing the SIP registration procedure for downloading the list of application information and applications in order to save the duration of consequence (standalone) IMS DC session establishment. 2-4. Steps 2-4 of clause AC.7.1 apply with the following difference: - The IMS AS rejects a session initiated by a UE not subscribed for a standalone IMS data channel session. 5. Since the SessionEstablishmentRequestEvent indicates that served user is offered only a local bootstrap media, the DCSF, based on the value of the Called ID (i.e. the specific PSI) and the content of the initial SDP offer, determines that the UE#1 requests to establish a standalone bootstrap DC and reserves only originating side MDC1 media information, which is used to receive the UE request for application downloading from the MF. 6. The DCSF invokes the Nimsas_MediaControl_MediaInstruction (Session ID, Media Instruction Set) service operation based on its policies instructing the IMS AS how to set up bootstrap data channel with the MF for originating side. The MediaInstructionSet provided by the DSCF, includes its MDC1 media endpoint addresses created in step 5, DC Stream ID and the replacement HTTP URL representing the application list offered via the MDC1 interface. 7. Step 7 of clause AC.7.1 applies. 8. The IMS AS invokes Nmf_MRM_Create (List of Media Termination Descriptors) service operation to instruct the MF to allocate required data channel media resources for originating side only. The IMS AS requests creation of only one Media Termination which representing the local bootstrap media to be terminated. 9-10. Steps 9-10 of clause AC.7.1 apply. 11. The IMS AS does not forward the SIP INVITE request based on the specific Request URI (i.e. PSI) and sends the SIP 18X response with the SDP answer through S-CSCF and P-CSCF to UE#1. 12-13. The standalone IMS data channel session with only bootstrap data channel is answered and bootstrap data channel between the originating MF and UE#1 is established. 14. The UE#1 sends application request messages to the MF to request a data channel application or an application list if multiple DC applications are available, via the established bootstrap data channel. The MF forwards the message to the received media point of DCSF. The DCSF provides the application list and proper data channel applications further to the UE#1 based on their data channel capabilities and their choices through MF. 15-16. If the established bootstrap DC is not used for a period of time (expiry of the session timer), UE#1 sends SIP BYE to release the bootstrap DC. AC.10.2.2 Originating Standalone IMS DC Session if Application not Available in Originating UE When an originating UE initiates a standalone IMS data channel session and the DC application is not available in the originating UE, the originating UE initiates standalone bootstrap DC setup. After successful establishment of bootstrap DC with the DCSF, the originating UE downloads the DC application via the bootstrap DC and updates the IMS session to add application DC. If the DC application is not downloaded yet by the terminating UE, the terminating UE does not accept the addition until the DC application is downloaded via the bootstrap DC. If the terminating UE did not successfully download the DC Application, the terminating UE, as an example, does not alert the user at all and tear down the entire IMS session. Figure AC.10.2.2-1 depicts a signalling flow diagram for originating standalone IMS DC Session if application is not available in the originating UE with the assumption that application list is available in the originating UE. Figure AC.10.2.2-1: Originating Standalone IMS DC Session if Application not Available in Originating UE The steps in the call flow are as follows: 1. The UE#1 sends an initial SIP INVITE request with an initial SDP offer including media component for bootstrap data channel for originating side and optional for terminating side. The SIP precondition is not needed. The originating P-CSCF may include the P-Early-Media header field indicating support of early media authorization in the initial SIP INVITE request if not exists. 2-13. Steps 2-13 of clause AC.7.1 apply. In this scenario, the SDP offer for bootstrap data channel to UE#2 are included. 14. The UE#2 returns a SIP 18X response with an SDP answer for bootstrap data channel. The IMS AS includes the P-Early-Media header field indicating early media allowed in the SIP 18X response based on the SDP answer not indicating any application data channel. Simultaneously, the UE#2 may alert the terminating user the incoming session is a standalone IMS data channel session that DC application will be indicated later. 15. Step 21 of clause AC.7.1 applies, except that the UE#1 may download the application list. 16. The UE#1 sends a SIP PRACK request towards the terminating side before or during performing step 15 and the UE#2 returns a SIP 200 OK response for the PRACK. After the DC application has been downloaded, the UE#1 initiates the SIP UPDATE request to update the IMS session for adding the application DC and to inform the UE#2 the associated DC application binding information. The IMS AS, the DCSF and the MF repeat steps 3-10 with the media information of bootstrap data channel and application data channel, optionally including allocation of MDC2 resources for originating and terminating side. The IMS AS sends the SIP UPDATE request with the modified SDP offer including media component for bootstrap data channel and application data channel towards the terminating network and the UE#2. The IMS AS includes the P-Early-Media header field indicating early media allowed in the SIP UPDATE request based on the previously received SDP answer not indicating any application data channel. 17. The bootstrap data channels have been established between the originating MF and the UE#2. If the DC application is not available in the UE#2, the UE#2 may alert the terminating user for DC application downloading. The UE#2 sends application request messages to the MF to request downloading the DC application and application list if needed. 18-23. When the DC application is available in the UE#2, steps 15-20 of clause AC.7.1 apply with the difference that bootstrap data channel and application data channel established is indicated. The IMS AS may include the P-Early-Media header field indicating early media allowed in the SIP 200 response for the UPDATE forwarded to the originating side. 24. The UE#2 alerts the terminating user for running the DC application. The UE#2 returns a SIP 180 response to indicate the UE#2 is ringing. 25. Subsequent procedures continue. When the terminating user accepts to run the DC application for communication, the UE#2 answers the IMS session. AC.10.2.3 Originating Standalone IMS DC Session if Application Available in Originating UE When an originating UE initiates a standalone IMS data channel session and the user selected DC application is available in the originating UE, the originating UE may initiate combined bootstrap DC and application DC. If the selected DC application is not downloaded yet by the terminating UE, the terminating UE will not establish the application DC and indicate the originating UE the DC application is desired to be downloaded. The originating UE further updates the standalone IMS data channel session to add the selected application DC. If the terminating UE did not successfully download the DC Application, the terminating UE, as an example, does not alert the user and tear down the entire IMS session. Figure AC.10.2.3-1 depicts a signalling flow diagram for originating standalone IMS DC Session if application is available in the originating UE. Figure AC.10.2.3-1: Originating Standalone IMS DC Session if Application Available in Originating UE The steps in the call flow are as follows: 1. The UE#1 sends the initial SIP INVITE request with an initial SDP offer including the media information of the bootstrap DC and application DC, as well as the associated DC application binding information. The SIP precondition is not needed. The originating P-CSCF may include the P-Early-Media header field indicating support of early media authorization in the initial SIP INVITE request if not exists. 2. The IMS AS determines whether the IMS session is a standalone IMS data channel session and determines if the session is allowed to be established based on local configuration or subscription data. If standalone IMS data channel session is not allowed, the IMS AS rejects the request, otherwise the IMS AS selects a DCSF for this user based on local configuration or discovery and selection of a DCSF instance via NRF. 3-10. Steps 3-10 of clause AC.7.1 apply with the media information of bootstrap data channel and application data channel, optionally including allocation of MDC2 resources for originating and terminating side. 11-13. Steps 11-13 of clause AC.7.1 apply. In this scenario, the SDP offer for bootstrap data channel, application data channel and the associated DC application binding information to UE#2 are included. 14. The UE#2 returns a SIP 18X response with the SDP answer for bootstrap data channel and application data channel. If the DC application is not available in the UE#2, the UE#2 may alert the terminating user for DC application downloading. The UE#2 indicates the DC application is not available but desired to be downloaded in the SDP answer if needed. Editor's note: How to indicate DC application is not available but desired to be downloaded is FFS. 15. The bootstrap data channels have been established between originating MF and the UE#1. 16. The bootstrap data channels have been established between originating MF and the UE#2. 17. The UE#1 sends a SIP PRACK request towards the terminating side before or during performing step 15. If the indication that DC application is desired to be downloaded is received, the UE#1 will consequently send a SIP UPDATE request to update the IMS session for adding the selected application data channel. The IMS AS includes the P-Early-Media header field indicating early media allowed in the SIP UPDATE request forwarded to the terminating side based on the indication. 18. The UE#2 sends application request messages to MF to request downloading the DC application and application list if needed. 19-24. If the DC application does not need to be downloaded in the UE#2, the UE#2 returns a 200 response for the PRACK. Otherwise, after the DC application successfully downloaded, steps 15-20 of clause AC.7.1 apply with the difference that bootstrap data channel and application data channel established is indicated. The IMS AS may include the P-Early-Media header field indicating early media allowed in the SIP 200 response for the UPDATE forwarded to the originating side. 25. The UE#2 alerts the terminating user for running the DC application. The UE#2 returns a SIP 180 response to indicate the UE#2 is ringing. 27. Subsequent procedures continue. When the terminating user accepts to run the DC application for communication, the UE#2 answers the IMS session. NOTE: This procedure covers only the scenario of UE#1 selects a DC application to communicated with UE#2. The bootstrap DC is established only with DCSF of UE#1. If the UE#2 wants to add another DC application of UE#2, another bootstrap DC with DCSF of UE#2 may also be established by UE#2 by sending SIP reINVITE message. AC.10.2.4 Adding MMTel Media to Standalone IMS Data Channel Session When a standalone IMS data channel session between two UEs is ongoing, any of the UE may add some MMTel media (e.g. audio/video/messaging) into the IMS session, which turns the standalone IMS data channel session to IMS data channel session. Figure AC.10.2.4-1depicts a signalling flow diagram for adding MMTel media (e.g. audio/video/messaging0 to standalone IMS data channel session between two UEs. Figure AC.10.2.4-1: Adding MMTel Media to standalone IMS data channel session 1. A standalone IMS DC session has been established between the UE-A and the UE-B, which does not include MMTel media. 2. The UE-A sends SIP re-INVITE request which includes an SDP offer containing the media description of both application data channel and MMTel media description. 3. The IMS AS, the DCSF and the UE-B handles the SIP re-INVITE request as specified in steps 2-9 of clause AC.7.2.1. 4. If the UE-B accepts the session update, the UE-B sends 200 OK response to the UE-A through the IMS AS, as specified in steps 10-18 of clause AC.7.2.1, indicating the MMTel media has been added. AC.10.2.5 Removing All MMTel Media from IMS Data Channel Session When a IMS data channel session between two UEs is ongoing, any of the UE may remove all MMTel media (e.g. audio/video/messaging) from the IMS session, which turns the IMS data channel session to standalone IMS data channel session. Figure AC.10.2.5-1depicts a signalling flow diagram for removing all MMTel media (e.g. audio/video/messaging) from IMS data channel session between two UEs. Figure AC.10.2.5-1: Removing all MMTel Media from IMS data channel session 1. An IMS DC session has been established between the UE-A and the UE-B, which includes MMTel and application DC media. 2. The UE-A sends SIP re-INVITE request with an SDP offer containing media information for MMTel media and application data channel, which sets the port number of MMTel media stream to zero, as specified in RFC 3264 [72]. 3. The IMS AS, the DCSF and the UE-B handles the SIP re-INVITE request as specified in steps 2-9 of clause AC.7.2.1. 4. If the UE-B accepts the session update, the UE-B sends 200 OK response to the UE-A through the IMS AS, as specified in steps 10-18 of clause AC.7.2.1, indicating the MMTel media has been removed. AC.11 Support of Avatar Communication AC.11.1 General This clause describes the enhancements to the IMS architecture supporting data channel services to additionally support Avatar communication services. For Avatar communication over IMS data channel, the list of Avatar ID(s) and/or Avatar Representations is downloaded to the UE by following options: - Pre-configured in the UE: The Avatar ID List and/or Avatar Representations is provisioned or downloaded to the UE before a data channel for avatar call is setup. The UE and the BAR may interact by means out of the scope of 3GPP. - Through bootstrap data channel: The Avatar ID List is fetched by the DC AS from the BAR when the associated Avatar communication application is downloaded and transferred from the DC AS to the DCSF and downloaded to UE through bootstrap data channel. - Through application data channel: The Avatar ID List is fetched by the DC AS from the BAR and downloaded to the UE through application data channel. Avatar ID List contains the list of Avatar IDs and/or the associated information. Editor's note: The reference to stage 3 details of parameters and associated information included in the Avatar ID List is FFS. When the Avatar ID List is downloaded through bootstrap data channel along with the associated Avatar communication application, a DC AS URL is used by DCSF to connect the corresponding DC AS serving the Avatar communication application to fetch the Avatar ID List. There may be multiple DC AS URLs targeting to different DC AS in operator network serving different types of applications. The DC AS URL(s) may be pre-configured in the DCSF, or stored as part of DCSF service specific data in HSS that can be fetched by DCSF. When the downloading of Avatar ID List is requested through bootstrap data channel, the DCSF requests DC AS to fetch the Avatar ID List from the BAR for the authorized user of the UE. NOTE: If there are multiple DC AS associated with the same DC app, how the DCSF selects the correct DC AS URL is implementation specific and out of scope of 3GPP. The BAR and/or the DC AS may be deployed either in the trusted domain or untrusted domain of operator's network. The Avatar Representation is identified by Avatar ID and is stored in the BAR. It is downloaded via application data channel for the avatar communication application. After selection of Avatar ID to use in the avatar call from the Avatar ID List by the user of the UE, the Avatar Representation identified with the selected Avatar ID is provided from the BAR to MF directly or through the DC AS, using the resource URL as defined in clause AA.2.4.3.2. The Avatar Representation may be transferred to the local UE (if not locally available) and/or to the remote UE according to the UE cenrtic rendering mode via application data channel if needed. The avatar media is rendered by processing the Avatar Representation with the animation data. - The avatar media rendering process may be performed by the sending UE, the receiving UE, or the network according to the rendering mode. - The animation data may be generated by the sending UE, the receiving UE, or the network (e.g. from audio, video and/or metadata such as UE sensors collected data). AC.11.2 Architecture Figure AC.11.2-1: Architecture to support Avatar communication To support Avatar communication, the data channel architecture and functions described in clause AC.2 is enhanced as below: Base Avatar Repository (BAR): - The BAR stores Avatar Representation, its Avatar ID and the associated information as described in clause AC.11.1. One or more Avatar Representation(s), is stored for a user and each Avatar Representation is identified with Avatar ID. - The BAR may provide Avatar ID List to the DC Application Server and the DC Application Server may further provide to DCSF. - The BAR may provide Avatar Representation and the associated information to the DC AS directly or to the MF directly after URL redirection from the DC AS. DCSF: - If the Avatar ID List is downloaded through bootstrap data channel, the DCSF may fetch the Avatar ID List from the DC AS and send to MF via MDC1. MF: - The MF enables downloading the Avatar ID List and associated information through bootstrap data channel or application data channel to the UE. The MF supports the UE downloading the Avatar Representation through application data channel. - The MF may retrieve the Avatar Representation and the associated information from BAR directly via MDC2 when redirected by the DC AS. Optionally, the MF may retrieve the Avatar Representation and the associated information from BAR indirectly via the DC AS. - The MF may support Avatar media processing and transcoding (e.g. ASR/TTS). DC AS: - The DC AS may provide the DC AS URL(s) to DCSF via DC3/N33 or DC4 for downloading of Avatar ID List through bootstrap data channel. - The DC AS retrieves the Avatar ID List from BAR(s) via MDC2. - The DC AS sends the Avatar ID List either to DCSF via MDC3 for downloading through bootstrap data channel, or to MF via MDC2 for downloading through application data channel. - The DC AS may retrieve the Avatar Representation and the associated information from BAR and sends them to MF via MDC2, or redirect the MF to retrieve the Avatar Representation and the associated information from BAR directly, via a URL. - The DC AS supports Avatar media negotiation and provides the instruction for Avatar media processing. AC.11.3 Procedure Editor's note: Which network entity will authenticate the UE will be decided by SA WG3 and the procedure will be aligned with SA WG3 decision. Editor's note: Whether and which user identity(ies) should be used by the user of the sending UE (UE#1) and/or the receiving UE (UE#2) for downloading of the Avatar Representations in receiving UE rendering mode will be decided by SA WG3 and the procedure will be aligned with SA WG3 decision. AC.11.3.1 Avatar ID List Download through Bootstrap Data Channel Figure AC.11.3.1-1: Procedures of Avatar ID List Download through Bootstrap Data Channel Figure AC.11.3.1-1 depicts a typical call flow procedure of avatar ID list download procedure through bootstrap data channel. The main steps in the call flow are as follows: NOTE: The avatar ID list can be downloaded via application data channel or pre-configured in the UE locally as described in clause AC.11.1. 1. IMS session and bootstrap data channel have been established. 2. The UE1 downloads application list through established bootstrap data channel. 3. The UE1 selects and downloads avatar communication application through established bootstrap data channel. 4. The DCSF checks the requested DC application is avatar communication application and select the corresponding DC AS associated with the requested DC application. The DCSF gets DC AS URL of the selected DC AS by local configuration or retrieves it from DCSF service specific data stored in HSS. 5-6. The DCSF downloads avatar communication from DCAR. 7. The DCSF requests DC AS to get UE1's avatar ID list using DC AS URL. 8. The DC AS get UE1's avatar ID list from BAR. 9-10. The BAR returns UE1's avatar ID list to the DC AS, the DC AS returns it to the DCSF. 11. The DCSF sends the avatar ID list together with the avatar application to the UE1. AC.11.3.2 UE centric procedure The UE centric mode includes two scenarios: - Sending UE centric: When the UE initiates an avatar communication with the peer UE, the UE that owns the avatar representation should download the avatar representation from BAR, if the Avatar representation is not locally available. The sending UE performs avatar animation and sends the animated video stream to the peer UE. - Receiving UE centric: When the UE initiates an avatar communication with the peer UE, the UE that owns the avatar representation should sends the avatar ID to the peer UE. The peer UE downloads the avatar representation from BAR based on the received avatar ID, performs the avatar animation and displays the animated video stream. NOTE 1: It is assumed that both UEs support IMS data channel and at least one UE support avatar animation capability among the two UEs in an avatar communication session. NOTE 2: UEs could transmit additional data using application data channel and/or audio/video to each other to support the UE centric rendering. The usage of those data is out of scope of this specification. AC.11.3.2.1 Sending UE centric procedure Figure AC.11.3.2.1-1: Procedures of Sending UE centric IMS Avatar communication Figure AC.11.3.2.1-1 depicts a typical call flow procedure of sending UE centric IMS Avatar communication. The main steps in the call flow are as follows: 1. IMS audio/video session and bootstrap data channel have been established. UE1 downloads avatar communication application. The avatar ID list is downloaded as described in clause AC.11.1. Then UE1 chooses an avatar ID and runs the avatar communication application. If the avatar representation is locally available in UE1, steps 2-6 are skipped. 2. P2A application data channel(s) are established for avatar representation transmission. The rendering mode is set to 'UE centric' by the DC AS. The DCSF instructs the MF to establish MDC2 connection either to the BAR or the DC AS. NOTE 1: In this step, the UE fetches the associated URL associated with the requested Avatar ID. 3. UE1 requests downloading Avatar representation from BAR via MF using the associated URL and UE1's identity (. i.e. MSISDN) through the established application data channel. The MF, based on the instruction received in step 2 fetches the Avatar representation from the BAR or DC AS using the resource URL for that purpose. 4-5. The BAR authorizes the request of downloading Avatar representation and responses with avatar representation data to the MF. NOTE 2: The MF downloads UE1's avatar representation from BAR directly or indirectly via DC AS based on the MDC2 connection established in step 2. and6. The MF sends the avatar representation data to UE1. 7. UE1 performs avatar animation with the selected Avatar representation. 8. UE1 transmits the animated video stream over RTP to UE2. AC.11.3.2.2 Receiving UE centric procedure Figure AC.11.3.2.2-1: Procedures of Receiving UE centric IMS Avatar communication Figure AC.11.3.2.2-1 depicts a typical call flow procedure of receiving UE centric IMS Avatar communication. The main steps in the call flow are as follows: 1. IMS session and bootstrap data channel have been established. UE1 downloads avatar communication application. The avatar ID list is downloaded as described in clause AC.11.1. Then UE1 chooses an avatar ID and runs the avatar communication application. 2. P2A2P application data channel(s) are established between UE1/UE2 and DC AS. The rendering mode is set to 'UE centric' by the DC AS. The DCSF instructs the MF to establish MDC2 connection either to the BAR or the DC AS. NOTE 1: In this step, the UE fetches the associated URL associated with the requested Avatar ID. 3. UE1 decides to request peer UE to perform avatar animation based on its status such as power, signal, computing power, internal storage, etc. 4. UE1 performs avatar animation negotiation with the DC AS and UE2. The negotiation includes usage of the UE1's avatar ID and the animation data types (e.g. text and/or facial expression) supported by UE1. Editor's note: The negotiation procedure needs to be further defined in SA WG4 and cooperation with SA WG4 is needed. 5. UE2 requests downloading avatar representation from BAR via MF using the associated URL received from UE1 through the established application data channel in step 2. The MF, based on the instruction received in step 2 fetches the Avatar representation from the BAR or DC AS using the Resource URL for that purpose. 6-7. The BAR authenticates and authorizes the request of downloading avatar representation using UE1's avatar ID and responds with UE1's avatar representation data. The DC AS should authorize the UE2 download request based on the negotiation result from step 4. NOTE 2: The MF downloads UE1's avatar representation from BAR directly or indirectly via DC AS based on MDC2 connection established in step 2. 8. The MF sends UE1's Avatar representation data to UE2. and9. Based on the avatar animation negotiation result in step 4, UE1 may send metadata (e.g. facial expression) to UE2 through the established application data channel or audio/video through RTP channel between UE1 and UE2. 10. UE2 performs avatar animation with the UE1's avatar representation based on the received metadata or audio/video from UE1. AC.11.3.3 Network centric procedure Figure AC.11.3.3-1: Procedures of network centric IMS Avatar communication Figure AC.11.3.3-1 depicts a typical call flow procedure of network centric IMS avatar communication. The main steps in the call flow are as follows: 1. IMS session and bootstrap data channel have been established. UE1 downloads avatar communication application. The avatar ID list is downloaded as described in clause AC.11.1. Then UE1 chooses an avatar ID and runs the avatar communication application. 2. UE1 decides to request network to perform avatar animation based on its status such as power, signal, computing power, internal storage, etc. 3. UE1 initiates application data channel establishment procedure. Application data channel(s) are established between UE1 and DC AS and UE2 and DC AS. 4. The avatar animation negotiation is finished between the DC AS and UE1 via the application data channel established in step 3. Editor's note: The avatar animation negotiation procedure and parameters need to be further defined in SA WG4 and cooperation with SA WG4 is needed. 5. If the negotiation result in step 4 is that the network will perform the rendering, the UE1 initiates new P2A2P or P2P application data channels, which are specifically used for avatar rendering-related data transmission between the UE1/UE2 and the network. NOTE 1: The data channel application and DC AS decides what type of application data channel would be needed for network centric procedure. and6-7. During the application data channel establishment procedure, the IMS AS notifies the DCSF via Nimsas_SessionEventControl_Notify of the media change request event. The DCSF checks that the app id in the ADC establishment request belongs to Avatar communication DC app, subsequently, then the DCSF fetches DC AS URL from DCSF service specific data or configured locally in DCSF. 8-9. The DCSF retrieves the avatar media specification data from DC AS using DC AS URL. The DCSF also receives additional instruction on what type of application data channel should be used and what type of rendering mode (e.g. network centric with MF rendering, network centric with DC AS rendering) applies for network-centric rendering initiated in step 5. NOTE 2: The Service operation of step 8-9 is not specified in this Release. 10-11. The DCSF instructs the MF via IMS AS how to establish the data channel and corresponding avatar media processing specification, via Nimsas_MediaControl_MediaInstruction with the parameters set according to the decisions in step 8-9. If the rendering mode is network centric with MF rendering, IMS AS selects a MF that support network centric with MF rendering based on local configuration or via NRF. 12. The IMS AS sends the MediaControl Instruction response to the DCSF. 13-18. Steps 11-23 of clause AC.7.2.3, or steps 7-17 of clause AC.7.2.1 applies, depends on type of application data channel decided in step 5. 19. The application data channel(s) are established. In the network centric with MF rendering mode, the application data channel terminated at MF. In the network centric with DC AS rendering mode, the MF proxies the media transparently to the DC AS. 20. The IMS AS initiates the media re-negotiation between UE1, UE2 and MF, which anchors UE1 and UE2's audio/video to MF. The procedure in subsequent steps only depicts the scenario which MF performs the rendering, although Figure AC.11.3.3-1 captures both. 21. The MF downloads UE1's avatar representation using the Resource URL in the avatar media specification data sent from DCSF in step 10. 22. Based on the type of network rendering mode decided in step 9, either option 1 or option 2 is performed in steps 22-26. The UE1 sends avatar metadata (e.g. facial expression) through the ADC established in step 19 and/or audio/video through RTP channels established in step 20. 23. Optionally, the UE2 may send avatar metadata (e.g. facial expression) through the ADC established in step 19 and/or audio/video through RTP channels established in step 20. 24. MF performs avatar animation based on the avatar metadata received from application data channel and/or audio/video. MF should support different media processing according the avatar type, e.g. animation with no rendering for 2D avatar, animation and rendering for 3D avatar. 25-26. MF sends the animated video stream to UE2 and sends the animated video stream to UE1 if required. The above procedures also apply for the transition from audio/video communication between two users to avatar communication. In an ongoing audio/video communication, one of UEs decides to switch the communication to avatar mode, it will interact with the IMS Core and peer UE to establish application data channel for the avatar communication. Then two UEs will exchange avatar media; and the original video media between two UEs may be stopped. Annex AD (normative): Subscribe/Notify Framework for Event Monitoring in IMS AD.1 General This annex describes the Subscribe/Notify framework to support event monitoring in the IMS architecture. The framework enables third party AF and network functions to subscribe to IMS DC events. IMS event exposure for event monitoring allows a consumer (e.g. a DC AS) to subscribe to and being notified about subscriber specific and non-subscriber specific IMS events and to invoke IMS services exposed by the IMS network via the NEF. A subscriber specific event monitoring request includes the targeted subscribers. The targeted subscribers can be either one distinct subscriber or multiple subscribers indicated by their IMS public user identities. The events in the subscriber specific event monitoring request are common to all targeted subscribers. The NEF sends one event subscription request per targeted subscriber to the HSS serving the given subscriber. The NEF may determine the serving HSS based on configuration or based on HSS discovery as depicted in clause AA.3.3. A non-subscriber specific event monitoring request does not contain any target subscriber. Non-subscriber specific event monitoring requests are sent by the NEF directly to all IMS AS instances which support monitoring of the requested IMS event. The NEF may be configured with available IMS AS instances, or the NEF can discover IMS AS instances via NRF. Once an IMS subscriber successfully registers in IMS and one of the IMS AS is assigned to the subscriber, the IMS AS which supports monitoring of IMS events registers its address in the HSS. For subscriber specific event monitoring requests received from the AF (e.g. DC AS), the NEF uses Nhss_ImsEE service to manage the subscription requests (e.g. subscribe/unsubscribe) via HSS. HSS uses Nimsas_ImsEE service to manage the subscriber specific subscription requests with the IMS AS assigned to the subscriber. AD.2 Architecture and functions AD.2.1 Architecture Figure AD.2.1-1 depicts the Subscribe/Notify framework for event monitoring in IMS. The framework supports trusted and untrusted AFs. Figure AD.2.1-1: Subscribe/Notify Framework for event monitoring in IMS NOTE 1: Trusted AFs can use N33 or, based on operator policy, can use Nhss and Nimsas services. NOTE 2: An untrusted AF can only use N33. AD.2.2 Reference points The following service-based reference points support the IMS subscribe/notify framework: - N33: Reference point between AF and NEF. - N91: Reference point between NEF and HSS. - N92: Reference point between IMS AS and NEF. - N71/Sh: Reference point between IMS AS and HSS. AD.2.3 Functional Entities AD.2.3.1 NEF The NEF, in addition to its role as defined TS 23.502 [94], is the entry point for subscriptions to notifications for monitoring of IMS related events, via N33 reference point using the Nnef_ImsEE_Subscribe service operation. An incoming subscription request to the NEF for a subscriber specific event may include a single IMS subscriber or a list of IMS subscribers. The NEF initiates an individual subscription request to the HSS instance corresponding to each IMS subscriber included in the incoming subscribe request from the AF. NEF initiates a subscription request for subscriber specific events towards HSS via N91 reference point using the Nhss_ImsEE_Subscribe service operation. NEF initiates a subscription request for non-subscriber specific events towards applicable IMS AS instances via N92 reference point using the Nimsas_ImsEE service. NEF receives notifications corresponding to subscribed IMS events from the applicable IMS AS instances via N92 reference point using the Nimsas_ImsEE_Notify service operation. NEF sends the received notifications to the requesting AFs via N33 reference point using the Nnef_ImsEE_Notify service operation. AD.2.3.2 HSS HSS handles subscriptions to IMS DC events related to registered and unregistered IMS subscribers and ensures that a subscription is persistent when UE registers, deregisters and re-registers in IMS. HSS receives subscription requests for subscriber specific events from NEF via N91 reference point using the Nhss_ImsEE_Subscribe service operation. HSS stores the incoming subscription request and sends the subscription request to the IMS AS instance supporting the requested event and assigned to the IMS subscriber via N71 reference point, using the Nimsas_ImsEE_Subscribe service operation, or via Sh reference point. The IMS AS assigned to an IMS subscriber is registered in HSS via N71 reference point using the Nhss_ImsUECM_Registration service operation, or via Sh reference point. If the IMS subscriber in the incoming subscription request is not registered, HSS ensures that when the IMS subscriber registers, any pending subscription request is sent to the applicable IMS AS instance assigned to the IMS subscriber. IMS AS rejects subscriptions to IMS DC events for a subscriber that is not subscribed to IMS DC service. HSS ensures that corresponding notifications are directly sent to the NEF as subscribing entity and not via HSS. AD.2.2.3 IMS AS Once an IMS subscriber successfully registers in IMS, any DC supporting IMS AS allocated to the subscriber that supports monitoring of IMS events shall register in HSS its IMS AS instance via N71 reference point using the Nhss_ImsUECM_Registration service operation, or via Sh reference point. The IMS AS receives subscription requests from HSS related to supported subscriber specific IMS DC events via the N71 reference point using the Nimsas_ImsEE_Subscribe service operation, or via the Sh reference point. IMS AS also receives subscription requests from NEF related to non-subscriber specific events via the N92 reference point using the Nimsas_ImsEE service operation. IMS AS sends notification events directly to the NEF as subscribing entity included in the subscription request via N92 reference point using the Nimsas_ImsEE_Notify service operation. AD.2.4 Determination of IMS Events supported by an IMS AS The NF profile registered in NRF of an IMS AS that supports monitoring of IMS events may include support for the Nimsas_ImsEE service and related service operations. Additionally, the NF profile of the IMS AS may include the list of IMS events the IMS AS instance supports. NF consumers of the Nimsas_ImsEE service (i.e. HSS and NEF) can make use of this information in the NF profile of the IMS AS to determine the IMS AS instances that support monitoring of a given IMS event. As an optimization option, a subscriber can subscribe to a number of events in a single subscription. In this case, event filters are applied to each event independently for event detection. Additionally, notification to detected events are handled individually. AD.2.5 Exposure Events AD.2.5.1 General Subscription requests for the notification of an IMS event type may include event filter information, e.g. condition for notifying the event. The event filter depends on the event type. The IMS events and corresponding event filters are only meaningful for the AF and the IMS AS. The involved NF consumer of the IMS AS (e.g. HSS/NEF) determines which IMS AS supports a given IMS event type by matching the IMS event ID requested by the AF with the list of supported IMS event types included in the NF profile of IMS AS registered in the NRF or by implementation means. NOTE 1: The actual value of IMS event types and corresponding event filters are transparent for the NRF, HSS and NEF. This allows that additional standardized as well as non-standardized event types can be supported without the need to upgrade the NRF, HSS or NEF. Subscription requests for the notification of an IMS event shall include Event Reporting information. The Event Reporting information defines the type of reporting requested (e.g. event reporting mode, number of reports, maximum duration of reporting). The contents of the Event Reporting Information along with the presence requirement of each information element is described in Table 4.15.1-1 of TS 23.502 [94]. NOTE 2: Not all of the Event Reporting Information is applicable to the Exposure Events in IMS. AD.2.5.2 Event Monitoring Table AD.2.5.3-1 enumerates the IMS DC exposure events and their detection criteria: Table AD.2.5.3-1 List of events for monitoring capability Event Description and Detection criteria Which NF detects the event Bootstrap Data Channel established Detected when a Bootstrap data channel is established. Network detects that a Bootstrap data channel is established when the SDP for an established IMS DC includes the media for a Bootstrap data channel with the corresponding Bootstrap DC stream ID according to TS 26.114 [76]. IMS AS Bootstrap Data Channel Release Detected when an established Bootstrap data channel is released. Network detects that a Bootstrap data channel is released when an IMS DC that includes an SDP with the media for a Bootstrap data channel with the corresponding Bootstrap DC stream ID according to TS 26.114 [76] is released, or an IMS DC is updated to remove the media for a Bootstrap data channel with the corresponding Bootstrap DC stream ID according to TS 26.114 [76]. IMS AS Application Data Channel established Detected when an Application Data Channel is established. Network detects that an Application data channel is established when the SDP for an established IMS DC includes the media for an Application data channel with the corresponding Application DC stream ID according to TS 26.114 [76]. The Application DC stream ID can be explicit or any stream ID. IMS AS Application Data Channel Release Detected when an Application data channel is released. Network detects that an Application data channel is released when an IMS DC that includes an SDP with the media for an Application data channel with the corresponding Application DC stream ID according to TS 26.114 [76] is released, or an IMS DC is updated to remove the media for an Application data channel with the corresponding Application DC stream ID according to TS 26.114 [76]. IMS AS Application Data Channel requires interworking is established Detected when an Application Data Channel requires interworking is in the process of establishment. Network detects that an P2A Application data channel is in process of establishment and the MDC2 resources are assigned for the Application data channel. IMS AS Event Filters are used to specify the conditions to match for notifying the events (i.e. "List of Parameter values to match"). If there are no conditions to match for a specific Event ID, then the Event Filter is not provided. The following list provides an example how the conditions to match for event reporting can be specified for various Event IDs for IMS DC exposure events: - Calling ID: Identifies the public identity of calling subscriber in the targeted IMS session if present. - Called ID: Identifies the public identity of called subscriber in the targeted IMS session if present. - Media Information Set: If present, includes a set of media information indicating how the media used in the created targeted session for the selected event. Each media information contains: - Media Type: It indicates the media type used in the created session, e.g. Data Channel. - Media Parameter: It indicates the related media parameters. Different media, includes different parameters. - When the Media Type is Data Channel, it indicates the Data Channel Type (ADC or BDC). - When the Data Channel Type is BDC, it indicates local or remote, for local UE or for remote UE. - When the media type is ADC, Data Channel application binding information is included. - Session ID: Indicates the targeted Session ID if present. AD.3 Subscribe/Notify Procedures for Event Monitoring in IMS AD.3.1 IMS AS instance Registration in HSS Figure AD.3.1-1depicts a signalling flow diagram for an IMS AS registering in HSS the IMS AS instance assigned to a registering UE. Figure AD.3.1-1: IMS AS Instance Registration in HSS 1. UE performs initial IMS Registration (see clause 5.2). 2. S-CSCF performs third party Registration with the IMS AS instance assigned to the registering UE. 3. IMS AS assigned to the UE/IMPU registers in HSS using Nhss_ImsUECM_Registration service operation or using Sh interface. NOTE: Figure AD.3.1-1 shows only SBA services. Corresponding Sh procedure is not included in the Figure. AD.3.2 Subscribe/Notify Procedure for subscriber specific IMS events Figure AD.3.2-1depicts a signalling flow diagram for establishing a subscription for notification of a subscriber specific IMS event. Figure AD.3.2-1: SUBSCRIBE/NOTIFY Procedure for Subscriber specific IMS events The steps in the call flow are as follows: 1. UE performs initial IMS Registration as per clause AD.3.1. 2. AF subscribes to NEF initiating the Nnef_imsEE_Subscribe Request for a subscriber specific IMS event. The AF may include one or more IMS subscriber IDs in the subscription request. 3. NEF initiates for each IMS subscriber in the incoming subscription request a separate subscription request towards HSS for the requested event via the Nhss_ImsEE_Subscribe Request service operation. The NEF creates a Notification Target address and Notification Correlation ID and includes it to the Nhss_ImsEE_Subscribe Request. 4. NEF returns to AF the Nnef_ImsEE_Subscribe Response. 5. HSS locates the IMS AS instance serving the UE based on the IMS AS registration in HSS executed in step 1. The HSS determines if the IMS AS instance for the IMS subscriber (IMPU) supports the requested IMS event based on the NF profile of the registered IMS AS instances stored in NRF. If the UE is not IMS registered in HSS, steps 6 and 7 are skipped. NOTE 1: If the UE is not IMS registered as in step 1, then the HSS will store the event subscription request per IMPU. 6. HSS subscribes to the IMS AS instance serving the UE and supporting the requested IMS event, using Nimsas_ImsEE_Subscribe Request for the requested IMS event including the IMPU and the NEF address as notification endpoint. Alternatively, HSS can use Sh interface to send the requested IMS event to the IMS AS instance assigned to the UE. 7. IMS AS returns to HSS with the Nimsas_ImsEE_Subscribe Response or returns to HSS via Sh interface. 8. HSS returns to NEF the Nhss_ImsEE_Subscribe Response. 9. At some point, the requested event for the UE is detected by the IMS AS. 10. The IMS AS sends an Nimsas_ImsEE_Notify Request to NEF. 11. NEF sends to IMS AS Nimsas_ImsEE Notify Response to the IMS AS. 12. The NEF maps the Notification Correlation ID to the subscription in the NEF. NEF sends Nnef_ImsEE_Notify Request to AF using the Notification Target Address and Notification Correlation ID received in step 2. 13. The AF sends an Nnef_ImsEE_Notify Response to the NEF. NOTE 2: Figure AD.3.2-1 shows only the SBA services. Corresponding Sh procedure is not included in the Figure. AD.3.3 Subscribe/Notify Procedure for Non-subscriber specific IMS events Figure AD.3.3.1-1 depicts a signalling flow diagram for establishing a subscription for notification of a non-subscriber specific IMS event. Figure AD.3.3-1: SUBSCRIBE/NOTIFY Procedure for non-subscriber specific IMS events The steps in the call flow are as follows: 1. AF subscribes to NEF initiating the Nnef_imsEE_Subscribe Request for non-subscriber specific IMS event. 2. NEF returns to AF the Nnef_ImsEE_Subscribe Response. 3. NEF locates the IMS AS instances that support the requested IMS event via NRF or by local configuration. 4. For each IMS AS instance that supports the requested IMS event, NEF subscribes to the IMS AS using Nimsas_ImsEE_Subscribe Request for the requested IMS event. 5. IMS AS returns to NEF the Nnef_ImsEE_Subscribe Response. 6. At some point, the requested event for the UE is detected by the IMS AS. 7. The IMS AS sends an Nimsas_ImsEE_Notify Request to NEF. 8. NEF sends to IMS AS Nimsas_ImsEE Notify Response. 9. NEF sends Nnef_ImsEE_Notify Request to AF. 10. The AF sends an Nnef_ImsEE_Notify Response to the NEF. NOTE: Figure AD.3.3-1 shows only the SBA services. Corresponding Sh procedure is not included in the Figure. Annex AE (normative): Support of UE-Satellite-UE communication in IMS AE.1 General This annex describes IMS architecture enhancements to support UE-Satellite-UE communication in IMS, i.e. optimized media routing via IMS user plane on-board satellite. In this Release of the specification, this feature is supported only for IMS voice/video service and for UEs belonging to the same PLMN and in the non-roaming scenario. The term and the 5GS architecture for UE-Satellite-UE communication is defined in TS 23.501 [93]. The optimized media routing described in this annex refers to a routing of media between UEs under the coverage of the same or of different serving satellites, using the 5GS network as the IP-CAN and with the media not transiting through any network elements on the ground. The ground fallback routing refers to the case with the media transiting through the ground segment. The P-CSCFs serving the MO UE and the MT UE negotiate with each other to determine whether or not to activate UE-satellite-UE communication, that is, whether it is possible to apply media routing that only relies on IMS user plane on-board satellite. AE.2 Architecture and functional entities AE.2.1 Architecture AE.2.1.1 Support of IMS satellite media plane optimization with IMS-AGW deployed on satellite(s) To support IMS satellite media plane optimization, as depicted in Figure AE.2.1.1-1, the IMS-AGW may be deployed on the satellite(s) that host the gNB and UPF (UL CL/BP and L-PSA) of the 5GC. NOTE 1: It is assumed that the satellite(s) can always connect to the ground with IP transport networks. Figure AE.2.1.1-1: Reference architecture of IMS satellite media plane optimization NOTE 2: Iq interface is over satellite transport layer links (feeder link and optionally inter-satellite links), where the lower layer protocol is out of 3GPP scope. NOTE 3: For clarity, the connections within 5GC and IMS core are not fully depicted in the architecture diagrams. For more information on 5GC architectures refer to clause 4.2.3 of TS 23.501 [93]. The above figure depicts a reference architecture for IMS satellite media plane optimization with following assumption: - For the IMS related PDU Session, the IP address allocated to the UE corresponds to a PSA UPF located on the ground. Thus, the IP address of the UE is not changed when serving satellite is changed. - UE(s) register onto IMS with this IP address and don't need to reregister when there is change of serving satellite. - The architecture deployment assumes, ISL(s) can be set-up within the same satellite constellation or across different constellations depending on satellite operator's deployments (SLA). The set of ISL(s) builds up an IP network which is out of 3GPP scope. - The routing between Onboard AGWs across satellite via ISL is assumed to be based on IP routing and the Onboard AGWs in satellite need to have non-conflicting IP address during resource allocation. It is up to the deployment to manage IP routing across ISL links and is out of 3GPP scope. AE.2.2 Functional entities AE.2.2.1 P-CSCF The P-CSCF used for this feature is enhanced to support the following functionalities: - the P-CSCF determines the activation of optimized media routing and interacts with 5GS, as described in clause AE.3. - the P-CSCF interacts with IMS AGW, as described in clause AE.4. - the P-CSCF requests IMS AS used for this feature to initiate SIP re-INVITE to complete IMS AGW relocation, as described in clause AE.4. AE.2.2.2 IMS AS The IMS AS used for this feature is enhanced to support the following functionalities: - the IMS AS, requested by P-CSCF used for this feature, initiates SIP re-INVITE to complete IMS AGW relocation, as described in clause AE.4. AE.3 Optimized media routing activation AE.3.1 General If UE-Satellite-UE communication in IMS is supported and if enabled subject to operator policy, the following behaviour described in clause AE.3 applies. AE.3.2 At call setup The P-CSCF receives from the PCF the satellite identifier of the satellite serving the UE and receives from the P-CSCF serving the remote UE the satellite identifier of the satellite serving the remote UE according to clause AE.5.1 and clause AE.5.3. Subject to operator policy, the P-CSCF uses this information to determine whether or not activate optimized media routing. With the lack of the satellite identifier of the satellite either serving the local UE or the remote UE, the P-CSCF determines not to activate optimized media routing. NOTE: In this Release of the specification, how the P-CSCF uses the satellite identifier to derive whether optimized media routing is possible is not specified. If P-CSCF determines the activation of optimized media routing, the P-CSCF instructs the PCF to authorize the necessary resources according to clause AE.5.1 and clause AE.5.3, so that the PCF proceeds to establish a 5GS user plane path for optimized media routing. AE.3.3 At change of satellite The P-CSCF is notified of the identifier of the target satellite from the PCF when the serving satellite of the UE changes according to clause AE.5.2.1. The P-CSCF determines whether optimized media routing continues to be possible between the target satellite and the satellite serving the remote UE based on the identifiers of those satellites. If there is no target satellite identifier in the notification, the P-CSCF determines that optimized media routing is no longer possible. NOTE: In this Release of the specification, how the P-CSCF uses the satellite identifier to derive whether optimized media routing can continue is not specified. If the P-CSCF determines that optimized media routing can continue at change of satellite, the P-CSCF invokes Npcf_PolicyAuthorization_Update service operation to the PCF as defined in clause 4.3.6.3 of TS 23.502 [94] and according to clause AE.5.2.1 to establish a path through the target satellite for optimized media routing. If the P-CSCF determines that optimized media routing is no longer possible e.g. due to a change of satellite, the P-CSCF executes the ground fallback procedure as per clause AE.5.2.2 to route the media via the ground. AE.4 Interaction with IMS AGW AE.4.1 General If UE-Satellite-UE communication in IMS is supported and if enabled subject to operator policy, the following behaviour described in clause AE.4 applies. AE.4.2 At call setup The P-CSCF serving the MO UE selects an IMS AGW on ground at call setup according to TS 23.334 [74], clause AE.5.1 and clause AE.5.3. The P-CSCFs serving the MO UE and MT UE proceed with the determination of whether UE-Satellite-UE communication is possible as described in clause AE.3.2. If the P-CSCF determines the activation of optimized media routing is possible, after deciding to use the optimized media routing (e.g. with consideration of whether early media is in progress or not), the P-CSCF releases the IMS AGW on ground if allocated and select instead an IMS AGW on satellite according to TS 23.334 [74]], clause AE.5.1 and clause AE.5.3. If early media is in progress during call setup, the P-CSCF serving the MO UE does not release the IMS-AGW on ground until the IMS session is answered, then selects the IMS-AGW on satellite according to clause AE.5.3 for using the optimized media routing. AE.4.3 At change of satellite When P-CSCF is informed that the satellite serving UE changes as defined in clause 4.3.6.3 of TS 23.502 [94] and according to clause AE.5.2, the P-CSCF selects an IMS AGW on the target satellite according to clause AE.5.2.1 or on ground according to clause AE.5.2.2, while keeping the IMS AGW on the source satellite, depending on whether optimized media routing continues to be possible or not. After configuring and reserving resources in the IMS AGW on the target satellite or on ground, the P-CSCF requests the IMS AS to initiate SIP re-INVITE to inform the remote network and then the local UE to use the new IMS AGW(s) according to clauses AE.5.2.1 and AE.5.2.2. AE.5 Procedures for optimizing media routing AE.5.1 At call setup When the originating P-CSCF receives the initial INVITE request from the originating UE using regenerative NR satellite access, it selects the IMS-AGW on ground and triggers media negotiation by sending SDP offer to the terminating side indicating that satellite access is used on the originating side. If the terminating P-CSCF activates UE-satellite-UE communication, the originating P-CSCF re-selects an IMS-AGW on satellite. See Figure AE.5.1-1 that describes the procedure. In the procedure, UE A and P-CSCF A represent originating side function or entity, UE B and P-CSCF B represent terminating side function or entity. NOTE 1: To support the UE-satellite-UE communication, P-CSCFs (AF) need to support N5 interface for AF influence on traffic routing and user plane management event subscription/notification. Figure AE.5.1-1: Session establishment procedure with activation of optimizing media routing 1. UE A sends a SIP INVITE request, containing an initial SDP offer, to P‑CSCF A. The access information in the SIP INVITE request indicates that the UE is accessing from NR satellites access as defined in TS 24.229 [10a]. 2. After receiving the SIP INVITE request indicating NR satellite access, if UE A is not roaming and the P-CSCF A supports UE-Satellite-UE communication, the P-CSCF requests Access Network Information, which includes an indication for requesting satellite identifier information, for UE A from the PCF as described in TS 23.503 [95] via Npcf_PolicyAuthorisation_Create service operation. The PCF requests Access Network Information, which includes the identifier of UE A's serving satellite, from the SMF via Npcf_SMPolicyControl_UpdateNotify service operation. Then the PCF receives the Access Network Information via Npcf_SMPolicyControl_Update service operation as described in TS 23.502 [94] and TS 23.503 [95]. This satellite identifier is subsequently conveyed to the P-CSCF in the Access Network Information Notification via Npcf_PolicyAuthorization_Notify service operation. 3. The P-CSCF A allocates an IMS-AGWon the ground as default. P-CSCF A interacts with IMS-AGW on the ground to allocate transport resources based on the mechanism defined in TS 23.334 [74]. Steps 4-20 are performed if the UE-Satellite-UE communication is possible based on step 2 (i.e. UE A is using NR regenerative payload satellite access and is not roaming). Otherwise, procedures for IMS user plane traffic routing with IMS-AGW on ground are performed (details have been omitted from the diagram). 4. P-CSCF A updates the SIP INVITE request inserting the identifier of the satellite serving UE A and updates SDP offer with the IMS-AGW transport addresses allocated in step 3. P-CSCF A forwards the updated SIP INVITE request to the terminating side via IMS core (details have been omitted from the diagram). 5. After receiving the SIP INVITE request which contains a satellite identifier indicating that UE A is using regenerative satellite access, if UE B is not roaming and the P-CSCF B supports UE-Satellite-UE communication, the P-CSCF B requests Access Network Information, which includes an indication for requesting satellite identifier information, for UE B from PCF as described in TS 23.503 [95] via Npcf_PolicyAuthorization_Create service operation.. The PCF obtains Access Network Information, which may include an identifier of the satellite serving UE B, from the SMF via Npcf_SMPolicyControl_UpdateNotify and Npcf_SMPolicyControl_Update service operations as described in TS 23.502 [94] and TS 23.503 [95]. This satellite identifier, if received, is subsequently conveyed to the P-CSCF in the Access Network Information Notification via Npcf_PolicyAuthorization_Notify service operation. NOTE 2: P-CSCF B can decide to include an indication for requesting satellite identifier information based on e.g. access information in the SIP REGISTER request (or other SIP messages) which indicates that UE B is accessing from NR satellites access as defined in TS 24.229 [10a]. 6. Based on the Access Network Information received at step 5, if UE B is using regenerative payload satellite access and if the two satellites identified in step 4 and 5 are the same or connected with ISL(s), P-CSCF B determines to activate the UE-Satellite-UE communication in IMS. and If UE-Satellite-UE communications in IMS is not activated, P-CSCF B selects an IMS-AGW on ground for UE B; otherwise, P-CSCF B selects an IMS-AGW on satellite for UE B. NOTE 3: How the terminating P-CSCF uses the satellite identifiers to derive whether the two satellites are connected with ISL(s) and are equipped with UPF and IMS-AGW is based on implementation or operators' policy e.g. by querying transport network system or based on node level information reported by the IMS-AGW deployed on the satellites. 6a-6b. Based on the decision in step 6, P-CSCF B interacts with IMS-AGW onboard the satellite or IMS-AGW on ground to allocate transport resources based on the mechanism defined in TS 23.334 [74]. Steps 7-20 are performed if the UE-Satellite-UE communication is activated. Otherwise, SIP message routing procedures with IMS-AGW on the ground should be performed after P-CSCF B selecting a ground IMS-AGW for usage (details have been omitted from the diagram). 7-9. P-CSCF B forwards the updated SIP INVITE request to UE B. UE B returns an 18X response with SDP Answer as normal SIP message routing procedures. 9a-9b. After receiving the SDP Answer, P-CSCF B interacts with the IMS-AGW onboard the satellite to allocate transport resources based on the mechanism defined in TS 23.334 [74]. 10. P-CSCF B instructs the PCF to authorize the resources necessary to establish a QoS flow for media via Npcf_PolicyAuthorization_Update service operation. To indicate the SMF to insert a UL CL/BP and L-PSA UPF for IMS PDU session to enable UE-Satellite-UE communication, the P-CSCF B should send following parameters via the request to PCF based on Application Function influence on traffic routing mechanism described in clause 5.6.7 of TS 23.501 [93] and clause 4.3.6 of TS 23.502 [94]: - A flow description information which contains the IP address of the IMS-AGW onboard the satellite; - A DNAI associated with the IMS-AGW onboard the satellite and optionally corresponding N6 traffic routing information. NOTE 4: DNAI value can be derived from the satellite identifier as per operator policy and implementation. 10a. To be notified of satellite change and perform IMS-AGW relocation at change of satellite as described in clause AE.5.2, P-CSCF B subscribes to notification of User Plane management events (i.e. UP path change) via Npcf_PolicyAuthorization_Update service operation to the PCF, which in turn subscribes to the events from SMF via Npcf_SMPolicyControl_UpdateNotify service operation and receives the event notifications from the SMF via Nsmf_EventExposure_Notify service operation as specified in clause 4.3.6 of TS 23.502 [94]. The P-CSCF B inserts the following parameters in its subscription request (i.e. Npcf_PolicyAuthorization_Update service operation) as specified in clause 5.2.5.3.3 of TS 23.502 [94]: - Early and late notifications about UP path management events. NOTE 5: If Rx is used by P-CSCF, implicit subscription is assumed as part of PCC rules setting. 11. P-CSCF B updates the 18X response to carry the identifier of the satellite serving UE B to indicate that UE-Satellite-UE communication is activated. Then, P-CSCF B returns the updated 18X response to originating side via IMS core (details have been omitted from the diagram). 12. Based on the identifier of the satellite serving UE B in step 11, P-CSCF A determines to perform UE-satellite-UE communication and select an IMS-AGW onboard the satellite. 12a-12c. P-CSCF A interacts with IMS-AGW onboard the satellite to allocate transport resources for both IMS access and IMS Core network sides. P-CSCF A also releases the IMS-AGW on ground. 13. P-CSCF A instructs the PCF to authorize the resources necessary to establish a QoS flow for media via Npcf_PolicyAuthorization_Update service operation. To indicate to the SMF to insert a UL CL/BP and L-PSA UPF for the IMS PDU session to enable UE-Satellite-UE communication in IMS, P-CSCF B should send following parameters via the request to PCF based on Application Function influence on traffic routing mechanism described in clause 5.6.7 of TS 23.501 [93] and clause 4.3.6 of TS 23.502 [94]: - A flow description information which contains the IP address of the IMS-AGW onboard satellite; - A DNAI associated with the IMS-AGW onboard satellite and optionally corresponding N6 traffic routing information. NOTE 6: DNAI value can be derived from the satellite identifier as per operator policy and implementation. 13a. To be notified of satellite change and perform IMS-AGW relocation at change of satellite as described in clause AE.5.2, P-CSCF A subscribes to notification of user plane management events (i.e. UP path change) via Npcf_PolicyAuthorization_Update service operation to the PCF, which in turn subscribes to the events from SMF via Npcf_SMPolicyControl_UpdateNotify service operation and receives the event notifications from the SMF via Nsmf_EventExposure_Notify service operation as specified in clause 4.3.6 of TS 23.502 [94]. The P-CSCF A inserts the following parameters in its subscription request (i.e. Npcf_PolicyAuthorization_Update service operation) as specified in clause 5.2.5.3.3 of TS 23.502 [94]: - Early and late notifications about UP path management events. NOTE 7: If Rx is used by P-CSCF, implicit subscription is assumed as part of PCC rules setting. 14. P-CSCF A updates the SDP answer in the 18X response with the IMS-AGW transport addresses allocated in step 12 and forwards the updated 18X response to UE A. 15. UE A acknowledges the 18X Response and sends the Response Confirmation to P-CSCF A. 16-17. P-CSCF A forwards the Response Confirmation to P-CSCF B. The Response Confirmation includes SDP offer modified/generated by P-CSCF A which contains the IMS-AGW transport address obtained in step 12. Upon receiving the SDP offer, P-CSCF B updates the allocated IMS-AGW on the satellite for UE B with the transport address in the SDP offer. 18. P-CSCF B sends the Response Confirmation to UE B. 19. Procedure continues to setup the call as defined in clauses 5.6 and 5.7. AE.5.2 IMS AGW relocation and media routing path change due to change of satellites AE.5.2.1 Continued optimized media routing procedure Figure AE.5.2.1-1 depicts a signalling flow diagram for continuation of optimized media routing after change of satellites that serve a UE. The procedure is written in such a way that change of satellite occurs in the originating network for the purpose of the explanation, while change of satellite can occur in the terminating network as well. NOTE 1: IMS entities not relevant for the procedure are omitted below for brevity of the description. NOTE 2: In this Release of the specification, the originating network and the terminating network are the same PLMN. Use of the N5 interface between IMS and 5GC is assumed. Based on the procedure described in clause AE.5.1, P-CSCF is expected to subscribe from 5GC for the early and the late notification of the satellite user plane management events associated with UE-Satellite-UE communication media traffic as specified in clause 5.6.7 of TS 23.501 [93] and clause 4.3.6.3 of TS 23.502 [94]. Figure AE.5.2.1-1: Continued optimized media routing procedure The steps in the call flow are as follows: 1. A media path in both directions is established between UEs. IMS AGWs on satellite forward voice/video media via ULCL and L-PSA on satellite between the UEs. 2. P-CSCF receives the early notification of the satellite user plane management events associated with UE-Satellite-UE communication media traffic from PCF as defined in clause 4.3.6.3 of TS 23.502 [94]. This early notification contains satellite ID of a target satellite that has gNB to which the UE gets connected and an indication being set "EARLY", indicating that 5GC is prepared to change the user plane path for optimized media routing to the one through this target satellite. 3. P-CSCF determines that optimized media routing continues to be possible based on the satellite ID received in step 2 for the originating network and the satellite ID stored for the terminating network. P-CSCF determines to continue activating optimized media routing. NOTE 3: How P-CSCF uses the satellite IDs to determine whether the two satellites are connected and whether optimized media routing is possible is up to implementation. If P-CSCF determines that optimized media routing cannot continue, P-CSCF follows the ground fallback procedure as defined in clause AE.5.2.2 for subsequent steps. 4. P-CSCF requests IMS AGW on the target satellite to configure the IP address allocated in UE, which P-CSCF has stored, to be used by the IMS AGW on the target satellite as the destination of media traffic towards the UE and to reserve an IP address in the IMS AGW on the target satellite to be used by the UE as the destination of media traffic. In addition, the P-CSCF requests the IMS AGW on the target satellite to configure context information other than IP addresses of the connection point towards the UE based on the corresponding context in the IMS AGW on the source satellite. This step 4 is performed according to clause 8.2 of TS 23.334 [74]. 5. P-CSCF requests IMS AGW on the target satellite to configure the IP address allocated in IMS AGW on the remote satellite in the terminating network, which P-CSCF has stored, to be used by the IMS AGW on the target satellite as the destination of media traffic towards the terminating network and to reserve an IP address in the IMS AGW on the target satellite to be used by the IMS AGW on the remote satellite in the terminating network as the destination of media traffic towards the originating network. In addition, the P-CSCF requests the IMS AGW on the target satellite to configure context information other than IP addresses of the connection point towards the terminating network based on the corresponding context in the IMS AGW on the source satellite. This step 5 is performed according to clause 8.2 of TS 23.334 [74]. NOTE 4: It is assumed in general that the newly selected IMS AGW (i.e. IMS AGW on the target satellite) allows voice/video media to flow immediately after the reservation and configuration are completed (e.g. without waiting for the response from the remote end if the reservation and configuration are made triggered by SIP re-INVITE). 6. P-CSCF replies to PCF by invoking Npcf_PolicyAuthorization_Update service operation as defined in clause 4.3.6.3 of TS 23.502 [94] to the early notification received in step 2. The Npcf_PolicyAuthorization_Update request is a positive response indicating that the change of the user plane paths for optimized media routing to the one through the target satellite should be performed. This request also includes the IP address allocated in IMS AGW on the target satellite to be used by UE as the destination of media traffic and optional N6 traffic routing information associated with target DNAI. SMF in 5GC establishes UL CL/BP and L-PSA on the target satellite, with the UL CL/BP configured with traffic filters containing this IP address to route the IMS media towards the L-PSA, according to clause 4.3.5.7 of TS 23.502 [94]. If N6 traffic routing information associated with target DNAI is received, SMF also configures the N6 traffic routing information on the L-PSA. 7. P-CSCF updates via PCF the packet filter list of the QoS rule in UE for media traffic to additionally contain the IP address allocated in IMS AGW on the target satellite to be used by UE as the destination of media traffic according to clause 4.3.3.2 of TS 23.502 [94]. 8. P-CSCF receives the late notification of the satellite user plane management events associated with UE-Satellite-UE communication media traffic from PCF as defined in clause 4.3.6.3 of TS 23.502 [94]. This late notification contains an indication being set "LATE" that indicates that 5GC has established the user plane path for optimized media routing through the target satellite. NOTE 5: The UL CL/BP and L-PSA on the source satellite are retained as long as active traffic exists over the N9 forwarding tunnel as described in clause 4.3.5.7 of TS 23.502 [94]. 9. P-CSCF sends a SIP MESSAGE to IMS AS to request it to send SIP re-INVITE to the terminating network (i.e. Step 10) and then towards the UE in the originating network after receiving the SDP answer from the terminating network (i.e. Step 16). This SIP message contains the IP address allocated in IMS AGW on the target satellite to be used by the terminating network as the destination of media traffic. This SIP message also contains the satellite ID of the target satellite. 10. IMS AS sends SIP re-INVITE to the terminating network. This SIP re-INVITE contains an SDP offer that has the IP address allocated in IMS AGW on the target satellite to be used by the terminating network as the destination of media traffic. This SIP re-INVITE also contains a SIP header for conveying the satellite ID of the target satellite. The following steps 11-15 are performed in the terminating network. 11. P-CSCF requests IMS AGW on satellite to configure the IP address received in step 10 to be used by the IMS AGW on satellite as the destination of media traffic towards the originating network. This step 11 is performed so far according to clause 8.4 of TS 23.334 [74]. In addition, P-CSCF stores the satellite ID of the target satellite in the originating network for future use. NOTE 6: RTP/RTCP is not symmetric between step 11 and step 17. 12. The media path from the originating network to the terminating network remains the same. The media path from the terminating network to the originating network is via UL CL/BP, L-PSA and IMS AGW on the remote satellite in the terminating network and further via IMS AGW, L-PSA and UL CL/BP on the target satellite in the originating network. 13. P-CSCF sends SIP re-INVITE containing an SDP offer to UE. 14. UE sends SIP 200 OK containing an SDP answer to P-CSCF. 15. P-CSCF sends SIP 200 OK to the originating network. This SIP 200 OK also contains a SIP header for conveying the satellite ID of the satellite in the terminating network and an SDP answer. The satellite ID is the same as the one sent before the satellite change in the originating network. The following steps 16-22 are performed in the originating network. 16. IMS AS sends SIP re-INVITE to P-CSCF. This SIP re-INVITE also contains a SIP header for conveying the satellite ID of the satellite in the terminating network and an SDP offer. 17. P-CSCF sends SIP re-INVITE to UE. This SIP re-INVITE contains an SDP offer that has the IP address allocated in IMS AGW on the target satellite to be used by UE as the destination of media traffic. 18. The media path in both directions is via ULCL, L-PSA and IMS AGW on the target satellite in the originating network and UL CL/BP, L-PSA and IMS AGW on the remote satellite in the terminating network. 19. UE sends SIP 200 OK containing an SDP answer to P-CSCF. 20. P-CSCF sends SIP 200 OK containing an SDP answer to IMS AS. 21. SMF in 5GC releases UL CL/BP and L-PSA on the source satellite according to steps 11 and 12 in clause 4.3.5.7 of TS 23.502 [94]. NOTE 7: The SMF releases the UL CL/BP and L-PSA on satellite after detecting no active traffic over the N9 forwarding tunnel as described in step 10 of clause 4.3.5.7 of TS 23.502 [94]. 22. P-CSCF releases IMS AGW on the source satellite sometime after receiving SIP 200 OK in step 19. This step 22 is performed according to clause 8.5 of TS 23.334 [74]. AE.5.2.2 Ground fallback procedure Figure AE.5.2.2-1 depicts a signalling flow diagram for the case that optimized media routing is abandoned and the routing with the media transiting through the ground segment is selected after change of satellites that serve a UE. The procedure is written in such a way that change of satellite occurs in the originating network for the purpose of the explanation, while change of satellite can occur in the terminating network as well. NOTE 1: IMS entities not relevant for the procedure are omitted below for brevity of the description. NOTE 2: In this Release of the specification, the originating network and the terminating network are the same PLMN. Use of the N5 interface between IMS and 5GC is assumed. Based on the procedure described in clause AE.5.1, P-CSCF is expected to subscribe from 5GC for the early and the late notification of the satellite user plane management events associated with UE-Satellite-UE communication media traffic as specified in clause 5.6.7 of TS 23.501 [93] and clause 4.3.6.3 of TS 23.502 [94]. Figure AE.5.2.2-1: Ground fallback procedure The steps in the call flow are as follows: 1. Step 1 of clause AE.5.2.1 applies. 2. P-CSCF receives the early notification of the satellite user plane management events associated with UE-Satellite-UE communication media traffic from PCF as defined in clause 4.3.6.3 of TS 23.502 [94]. This early notification contains an indication being set "EARLY". This early notification may contain satellite ID of a target satellite that has gNB to which the UE gets connected, which indicates that 5GC is prepared to change the user plane path for optimized media routing to the one through this target satellite. 3. P-CSCF determines that optimized media routing cannot continue if there is no target satellite ID included in the early notification as received in step 2, or the two satellites identified by the satellite ID received in step 2 for the originating network and the satellite ID stored for the terminating network have no ISLs. The P-CSCF determines to activate ground fallback routing. NOTE 3: How P-CSCF uses the satellite IDs to determine whether the two satellites are connected and whether optimized media routing is possible is up to implementation. 4. P-CSCF requests IMS AGW on ground to configure the IP address allocated in UE, which the P-CSCF has stored, to be used by the IMS AGW on ground as the destination of media traffic towards the UE and to reserve an IP address in the IMS AGW on ground to be used by the UE as the destination of media traffic. In addition, the P-CSCF requests the IMS AGW on ground to configure context information other than IP addresses of the connection point towards the UE based on the corresponding context in the IMS AGW on satellite. This step 4 is performed according to clause 8.2 of TS 23.334 [74]. 5. P-CSCF requests IMS AGW on ground to reserve an IP address in the IMS AGW on ground to be used by the terminating network as the destination of media traffic towards the originating network. In addition, the P-CSCF requests the IMS AGW on ground to configure context information other than IP addresses of the connection point towards the terminating network based on the corresponding context in the IMS AGW on satellite. This step 5 is performed according to clause 8.2 of TS 23.334 [74]. 6. P-CSCF replies to PCF by invoking Npcf_PolicyAuthorization_Update service operation as defined in clause 4.3.6.3 of TS 23.502 [94] to the early notification received in step 2. The Npcf_PolicyAuthorization_Update request indicates that the change of the user plane paths for the continuation of optimized media routing should not be performed. P-CSCF also sends to PCF the IP address allocated in IMS AGW on ground to be used by UE as the destination of media traffic, so that 5GC updates the packet filter list of the QoS rule in the UE for media traffic to additionally contain this IP address according to clause 4.3.3.2 of TS 23.502 [94]. 7. P-CSCF sends a SIP MESSAGE to IMS AS to request it to send SIP re-INVITE to the terminating network (i.e. Step 8) and then towards the UE in the originating network after receiving the SDP answer from the terminating network (i.e. Step 18). This SIP message contains the IP address allocated in IMS AGW on ground to be used by the terminating network as the destination of media traffic. This SIP message does not contain any satellite ID. 8. IMS AS sends SIP re-INVITE to the terminating network. This SIP re-INVITE contains an SDP offer that has the IP address allocated in IMS AGW on ground to be used by the terminating network as the destination of media traffic. This SIP re-INVITE does not contain any satellite ID. The following steps 9-16 are performed in the terminating network. 9. P-CSCF receives the SIP re-INVITE. 10. P-CSCF requests IMS AGW on ground to configure the IP address allocated in UE, which the P-CSCF has stored, to be used by the IMS AGW on ground as the destination of media traffic towards the UE and to reserve an IP address in the IMS AGW on ground to be used by the UE as the destination of media traffic. In addition, the P-CSCF requests the IMS AGW on ground to configure context information other than IP addresses of the connection point towards the UE based on the corresponding context in the IMS AGW on satellite. This step 10 is performed according to clause 8.2 of TS 23.334 [74]. 11. P-CSCF requests IMS AGW on ground to configure the IP address received in step 9 to be used by the IMS AGW on ground as the destination of media traffic towards the originating network and to reserve an IP address in the IMS AGW on ground to be used by the originating network as the destination of media traffic towards the terminating network. In addition, the P-CSCF requests the IMS AGW on ground to configure context information other than IP addresses of the connection point towards the originating network based on the corresponding context in the IMS AGW on satellite. This step 11 is performed according to clause 8.2 of TS 23.334 [74]. NOTE 4: It is assumed in general that the newly selected IMS AGW (i.e. IMS AGW on ground) allows voice/video media to flow immediately after the reservation and configuration are completed (e.g. without waiting for the response from the remote end if the reservation and configuration are made triggered by SIP re-INVITE). 12. P-CSCF sends to PCF the IP address allocated in IMS AGW on ground to be used by UE as the destination of media traffic, so that 5GC updates the packet filter list of the QoS rule in UE for media traffic to additionally contain this IP address according to clause 4.3.3.2 of TS 23.502 [94]. 13. P-CSCF sends SIP re-INVITE to UE. This SIP re-INVITE contains an SDP offer that has the IP address allocated in IMS AGW on ground to be used by UE as the destination of media traffic. NOTE 5: RTP/RTCP is not symmetric between step 13 and step 20. 14. The media path from the originating network to the terminating network remains the same. The media path from the terminating network to the originating network is via UL CL on satellite, PSA on ground, IMS AGW on ground in the terminating network and further via IMS AGW on ground, PSA on ground and UL CL on satellite in the originating network. 15. UE sends SIP 200 OK containing an SDP answer to P-CSCF. P-CSCF sets an implementation-specific timer for releasing IMS AGW on satellite that expires sometime after UE in the originating network receives SIP re-INVITE in step 20. 16. P-CSCF sends SIP 200 OK to the originating network. This SIP 200 OK contains an SDP answer that has the IP address allocated in IMS AGW on ground to be used by the originating network as the destination of media traffic towards the terminating network. This SIP 200 OK does not contain any satellite ID. The following steps 17-23 are performed in the originating network. 17. IMS AS receives the SIP 200 OK. 18. IMS AS sends SIP re-INVITE to P-CSCF. This SIP re-INVITE contains an SDP offer that has the IP address allocated in IMS AGW on ground in the terminating network to be used by the originating network as the destination of media traffic towards the terminating network. This SIP re-INVITE does not contain any satellite ID. 19. P-CSCF requests IMS AGW on ground to configure the IP address received in step 18 to be used by the IMS AGW on ground as the destination of media traffic towards the terminating network. This step 19 is performed according to clause 8.4 of TS 23.334 [74]. 20. P-CSCF sends SIP re-INVITE to UE. This SIP re-INVITE contains an SDP offer that has the IP address allocated in IMS AGW on ground in the originating network to be used by UE as the destination of media traffic. 21. The media path in both directions is via UL CLs on satellite, PSAs on ground and IMS AGWs on ground. 22. UE sends SIP 200 OK containing an SDP answer to P-CSCF. 23. P-CSCF sends SIP 200 OK containing an SDP answer to IMS AS. This SIP 200 OK does not contain any satellite ID. 24. Both in the originating network and in the terminating network, SMF in 5GC releases UL CL and L-PSA on satellite according to steps 11 and 12 in clause 4.3.5.7 of TS 23.502 [94]. NOTE 6: The SMF releases the UL CL and L-PSA on satellite after detecting no active traffic over the N9 forwarding tunnel as described in step 10 of clause 4.3.5.7 of TS 23.502 [94]. 25. P-CSCF in the originating network releases IMS AGW on satellite in the originating network sometime after receiving SIP 200 OK in step 22. P-CSCF in the terminating network releases IMS AGW on satellite in the terminating network after the timer being set in step 15 expires. This step 25 is performed according to clause 8.5 of TS 23.334 [74]. 26. The media path in both directions is via PSAs on ground and IMS AGWs on ground. AE.5.3 At call setup with early media During the call setup with both originating and terminating UEs using regenerative NR satellite access, the originating P-CSCF uses the IMS-AGW on ground to transfer early media then, after the IMS session is answered, releases the IMS-AGW on ground and selects the IMS-AGW on satellite to transfer regular media. See Figure AE.5.3-1 that describes the procedure. In this procedure, the IMS AS for early media uses existing method for providing early media and updating the IMS session when answered. Figure AE.5.3-1: IMS session establishment procedure with early media 1-11. Steps 1-11 of clause AE.5.1 apply with the difference that the IMS AS serving early media allocates early media resources with MRF, as well as includes the P-Early-Media header field and a modified SDP answer for early media in the 18X response. The IMS AS may instruct the MRF to play early media any time before step 12. 12. Based on the identification of the satellite serving UE B and the P-Early-Media header field in step 11, P-CSCF A determines to perform UE-satellite-UE communication with early media. P-CSCF A selects an IMS-AGW A on satellite but does not release the IMS-AGW A on ground in order to use it for early media. 12a-12b. P-CSCF A interacts with IMS-AGW A on ground for early media to allocate and configure transport resources for IMS access side as well as configure transport resources for IMS core network side. 13.` step 13 of clause AE.5.1 applies. The early media is able to be sent to the UE A via the IMS AGW A on ground, the UPF A on ground and the UPF A on satellite. 14. Step 14 of clause AE.5.1 applies with the difference that P-CSCF A includes in the SIP 18X response an SDP answer containing the transport address of IMS-AGW A on ground obtained in step 12. 15-16. Steps 15-16 of clause AE.5.1 apply with difference that P-CSCF A does not generate/modify SDP offer in step 16. Step 17 of clause AE.5.1 is not performed because no SDP offer for regular media is received. 17-18. Steps 18-19 of clause AE.5.1 apply and UE B is ringing. 19. The UE B answers the IMS session and sends SIP 200 response for the INVITE. 20. The IMS AS serving early media instructs the MRF to stop playing early media. UE A may play local ring tone when early media is stopped. 21. The IMS AS serving early media triggers the SDP re-negotiation procedure between UE A and UE B using existing mechanism, e.g. sending SIP ACK and SIP reINVITE without SDP information towards UE B. NOTE: In order to reduce the latency, P-CSCF B can delegate UE B and/or, P-CSCF A can delegate UE A to perform the SDP re-negotiation procedure, i.e. does not interact with UE. 22. During the SDP re-negotiation procedure, P-CSCF A releases the IMS AGW A on ground and interacts with the IMS-AGW A on satellite selected in step 12 for regular media to allocate and configure transport resources for both IMS access side and IMS core network side. 23. The SDP re-negotiation procedure continues. After receiving the SIP 200 response for the INVITE, the UE A is able to send regular media and is ready to receive regular media. The regular media uses UE-satellite-UE communication path. 24. During the SDP re-negotiation procedure, P-CSCF B updates the allocated IMS-AGW on the satellite for UE B with the transport address in the received SDP information for regular media to configure transport resources for IMS core network side. 25. P-CSCF B forwards the SIP ACK towards UE B. After receiving the SIP ACK, the UE B is able to send regular media. Annex AF (normative): Support for authorization, signing and verification of third party user identity information in IMS AF.1 General This annex describes support for authorization, signing and verification of third-party user identity information in IMS. A third party user in this context is a user belonging to a third party network which can be e.g. an Enterprise or private network. The format of third-party user identity information used in IMS follows the definitions in draft-ietf-sipcore-callinfo-rcd-12 [107]. This allows to associate third party user identity information in IMS with Rich Call Data (RCD) information. An RCD server in the third-party network or optionally the HSS may store third party user identity information. The IMS network can retrieve the third-party user identity information from the RCD server during IMS session establishment and include this information in the outgoing SIP INVITE request. Based on operator policies, third party user identity information can be signed by the originating IMS network and verified by the terminating IMS network. The process of signing and verifying third party user identity information follows draft-ietf-stir-passport-rcd-26 [108]. The AS for signing and the AS for verification need to be able to sign and verify following information elements: RCD information and RCD URL. AF.2 Architecture and functions AF.2.1 Architecture Figure AF.2.1-1 shows the overall system architecture to support authorization, authentication and verification of third party user identity information in IMS. Figure AF.2.1-1: System architecture to support authorization, signing and verification of third party user identity information in IMS Following interfaces are added to the interfaces defined in the main clause of this document - an interface between IMS entities (e.g. IMS AS) and the AS for signing; this interface is defined in draft-ietf-stir-passport-rcd-26 [108]; - an interface between IMS entities (e.g. IMS AS) and the AS for verification; this interface is defined in draft-ietf-stir-passport-rcd-26 [108] and TS 24.229 [10a]; - an interface between the IMS AS or the UE and the RCD server; this interface is out of scope of 3GPP. An RCD server may be operated either by the IMS network operator or by a third party. AF.2.2 Functional entities AF.2.2.1 HSS HSS stores either one RCD server address or one RCD URL per IMPU or wildcarded IMPU, or it may store a limited set of RCD properties (e.g. caller name, company name, job title and Email address), whose format shall be compliant with draft-ietf-sipcore-callinfo-rcd-12 [107], in the HSS repository data. Optionally, the RCD information, the RCD server address or the RCD URL may be provisioned per IMPU or wildcarded IMPU in the HSS repository data. NOTE: RCD information, RCD server address and RCD URL are stored as part of the IMS AS repository data (e.g. in the MMTel repository data). Table AF.2.2.1-1 RCD properties RCD properties Description RCD Server Address It refers to a server in a third party network storing IMS subscriber specific RCD information. This can be an IP address or a FQDN. RCD URL It refers to the URL from where RCD information of a specific IMS subscriber stored at an RCD server can be retrieved from. RCD Information It refers to a collection of properties associated with an IMS subscriber. Such properties can be caller name, company name, Email address, telephone number, job title. AF.2.2.2 IMS AS Based on the received RCD properties from NEF, IMS AS validates the RCD information and stores the RCD information in HSS repository data by using the existing Nhss_ImsSDM_update service operation. Originating IMS AS retrieves the RCD URL, RCD address or RCD information from the HSS. IMS AS can use the RCD server address or RCD URL to fetch the RCD information from the RCD server. Based on operator policies, IMS AS can invoke signing of the RCD information or the RCD URL. NOTE: The interface between IMS AS and RCD server is out of scope of 3GPP. Terminating IMS AS forwards the RCD URL or RCD information to the terminating UE after successful signature verification. AF.2.2.3 UE and IP-PBX Based on agreements and trust relationship between the third-party network and the IMS network, the originating IP-PBX in the third party network can provide RCD information or RCD URL in outgoing initial SIP INVITE requests to the IMS network. The IMS network, based on operator policy, may sign the provided RCD information or RCD URL. NOTE 1: Based on operator policies and implementation means, the IMS network (i.e. S-CSCF or IMS AS) can authorize the IP-PBX to use third party user identity information in the outgoing initial SIP INVITE request towards the IMS network. NOTE 2: The IMS network can remove, add or replace third party user identity information provided by the IP-PBX in the SIP INVITE request based on implementation and operator policies. The terminating UE may present third party user identity information of the calling-party to the called party, either received from RCD information in the SIP INVITE request or fetched from the RCD server based on the received RCD URL. AF.2.2.4 IBCF The IBCF, based on operator policies, can invoke signing and verification of the RCD information or the RCD URL received in SIP signalling. AF.2.2.5 S-CSCF For calls inside an IMS network and based on operator policies, the S-CSCF can invoke signing and verification of the RCD information or the RCD URL received in SIP signalling. AF.2.2.6 NEF The NEF, in addition to its role as defined TS 23.502 [94], is the entry point for provisioning of RCD properties by the AF via N33 reference point using the Nnef_ImsPP service operation. NOTE: NEF services used by AF for RCD properties provisioning are defined in TS 23.502 [94]. An incoming provisioning request from the AF to the NEF may include RCD properties for a single IMPU or wildcarded IMPU. The NEF initiates Parameter Provisioning request to the IMS AS instance for the RCD server address, RCD URL or RCD information using the Nimsas_ImsPP service operation. The NEF may be configured with available IMS AS instances, or the NEF can discover IMS AS instances via NRF. AF.3 Procedure for signing and verification of third party user identity information in IMS Figure AF.3-1 depicts the procedure for signing and verification of third party user identity information in IMS. Figure AF.3-1: Procedure for signing and verification of third party user identity information in IMS and1-2. The UE / IP-PBX sends an initial SIP INVITE request. The originating IMS network authorizes the use of received third party user identity information. NOTE 1: If the third party user identity information is provided to the IMS network in the incoming initial SIP INVITE request, the originating IMS network can determine to skip steps 3-5 based on local policies and SLA between the third party network and the originating IMS network. NOTE 2: UE provided third party user identity information is not supported in this Release of the specification. 3. The originating IMS AS may retrieve RCD server address, RCD URL, or RCD information from the HSS, based on the originating IMPU or wildcarded IMPU. 4. The originating IMS AS may receive RCD server address, RCD URL, or RCD information from the HSS. 5. If the IMS AS has retrieved an RCD URL, the IMS AS, based on configuration, may retrieve the RCD information from the RCD server using the RCD URL. The IMS AS includes either the RCD URL or, if retrieved from the RCD server, the RCD information in the outgoing SIP INVITE request. If the IMS AS has retrieved an RCD server address, the IMS AS provides the originating IMPU or wildcarded IMPU to the RCD server, to retrieve the RCD information. The IMS AS includes the retrieved RCD information in the outgoing SIP INVITE request. NOTE 3: How RCD URL or RCD information are carried in SIP signalling is defined in TS 24.229 [10a]. 6-8. The originating IMS network (S-CSCF, IMS AS or IBCF) invokes signing of the RCD information or RCD URL included in the outgoing SIP INVITE request with a signing AS. NOTE 4: Based on operator policies, either the S-CSCF, IMS AS or IBCF in the originating network invoke signing of the RCD information or RCD URL. 9-10. Based on operator policies, the S-CSCF, IMS AS or IBCF in the terminating IMS network invokes signature verification of the RCD information or RCD URL included in the incoming SIP INVITE request with a verification AS. The S-CSCF, IMS AS or IBCF in the terminating IMS network may reject the call when the signature verification is unsuccessful. 11-12. The terminating UE may present third party user identity information of the calling-party to the called party either retrieved from RCD information, if present, in the SIP INVITE request or fetched from the RCD server based on the received RCD URL. AF.4 Provisioning of IMS user specific properties Support for provisioning of information which can be used for an IMS user in the IMS subsystem (e.g. RCD server address, RCD URL or RCD information for a single IMPU or wildcard IMPU as described in clause AF.2.2.6) is depicted below. Figure AF.4-1: IMS user specific properties provisioning procedure 1. The AF (e.g. located in a third party network) provides information which can be used for an IMS user in the IMS subsystem, e.g. RCD server address, RCD URL or RCD information for a single IMPU or wildcard IMPU using Nnef_ImsPP_Create service operation as described in clause 5.2.6 of TS 23.502 [55]. 2. NEF after receiving the provisioning information can locate an IMS instance as described in clause AF.2.2.6 and provisions the received parameters to IMS AS using Nimsas_ImsPP_Create service operation. 3. IMS AS validates the retrieved information from NEF (e.g. check the syntax and semantics of the information). 4. IMS AS stores the IMS user information in the HSS repository data using existing Nhss_ImsSDM_Update service operation. Annex AG (normative): IMS Capability Exposure Framework in IMS AG.1 Description The following scenarios utilizing IMS data channel capability exposure services are depicted in clause AG.2: - Adding, removing or updating the data channel to an existing IMS session, for which Nimsas_ImsSessionManagement_Update is used. - Creating a standalone data channel session, for which Nimsas_ImsSessionManagement_Create is used. - Terminating a standalone data channel session, for which Nimsas_ImsSessionManagement_Delete is used. The procedures can be triggered via the NEF on the originating or terminating side. Editor's note: References to SA WG3 specification documenting the Privacy and security aspects regarding adding, removing, updating data channels by the network is FFS. AG.2 IMS Data Channel capability exposure procedures AG.2.1 Updating an existing IMS session AG.2.1.0 General This clause describes the procedure for adding, removing or updating bootstrap data channel(s) and application data channel(s) to an existing IMS session via dedicated NEF services. The DC AS sends a request to the NEF via Nnef_ImsSessionManagement_Update to update an existing IMS session with a specific session ID with a data channel. The procedures of adding A2P, P2P and P2A2P application data channel(s) to an existing IMS session are provided below. For removing or updating application data channel(s) in an existing IMS session, as well as for adding, removing, or updating bootstrap data channel(s) in an existing IMS session, the same principle applies. AG.2.1.1 Adding A2P Application Data Channel to an existing IMS session Figure AG.2.1.1-1 depicts the call flow of adding A2P application data channel(s) to an existing IMS session. In this scenario, the MF-2 is used to anchor the application data channel between the UE B and the DC AS. Figure AG.2.1.1-1: Procedure of adding A2P application data channel(s) to an existing IMS session An IMS session between UE A and UE B has been established, a bootstrap DC has also been established and the DC AS has received the IMS session ID. 0. DC AS determines to add A2P application data channel(s) to an existing IMS session, e.g. based on the event notification of the related IMS session to which the DC AS subscribed to. 1. The DC AS sends a Nnef_ImsSessionManagement_Update request to the NEF requiring to add A2P application data channel(s) to the existing IMS session. The AF request contains the DC AS identifier as AF ID. The DC AS includes the session ID of the existing IMS session to be updated, the operation type as Adding, media operation set including the parameters for the media type set as A2P ADC, the UE B as the target of the A2P ADC, the application binding information and the MDC2 media endpoint address (e.g. FQDN or IP address and port number) in Nnef_ImsSessionManagement_Update request. The DC AS may include a Notification Target Address and Correlation ID to the Nnef_ImsSessionManagement_Update request to be notified of the session update progress. NOTE 1: To be able to initiate data sending to the UE via MF, the DC AS needs to be informed of the reserved media resources. and the DC AS needs to subscribe to the progress of the session update. 2. The NEF uses the Nhss_ImsUECM_AsInfoGet service operation to retrieve the IMS AS instance serving UE B. 3. The NEF sends a Nimsas_ImsSessionManagement_Update request to the IMS AS-2 requiring to add A2P application data channel(s) to the specific IMS session. The received session ID of the existing IMS session, the operation type as Adding, the media type as A2P ADC, the UE B as the target of the A2P ADC, the application binding information and the MDC2 media endpoint address shall be included in the request. The NEF may include a Notification Target Address and Correlation ID to the Nimsas_ImsSessionManagement_Update request to be notified of the session update progress. 4. The IMS AS-2 validates the user subscription data and checks the IMS DC capability of UE B and determines whether the data channel request should be notified to DCSF-2. If UE B does not have subscription of IMS data channel or does not have the IMS DC capability, then the request shall be rejected with appropriate cause and subsequent steps are skipped. If the IMS AS-2 allows the request to proceed, it returns a successful Nimsas_ImsSessionManagement_Update response to the NEF. If the same IMS data channel is already established and if there are no other operations included in the request, then the request shall be rejected with an appropriate cause and the following steps are skipped. 5. The NEF returns a successful Nnef_ImsSessionManagement_Update response to the DC AS. 6. The IMS AS-2 sends a Nimsas_SessionEventControl_Notify request to the DCSF-2 with event set to ExternalSessionUpdateEvent. The notification includes the necessary parameters based on the information extracted from media operation set parameters received in step 3 and other stored parameters in the IMS AS-2 if applicable. 7. After receiving the session event control notification, the DCSF-2 determines the policy how to process the application data channel establishment request based on the related parameters in the notification and/or DCSF-2 service specific policy. 8. The DCSF-2 determines that the added application data channel media requires the DC to be anchored in MF-2. 9. The DCSF-2 instructs the IMS AS-2 to set up the A2P application data channel(s) by sending a Nimsas_MediaControl_MediaInstruction request. 10. Based on the instruction from DCSF-2, the IMS AS-2 interacts with the MF-2 to allocate data channel media resource towards UE B and MDC2 media resource towards DC AS. The IMS AS-2 also requests MF-2 to update DC AS side MDC2 media resource information using the received MDC2 media endpoint address in step 3. 11. The IMS AS-2 may respond to Nimsas_MediaControl_MediaInstruction request. 12. The DCSF-2 may respond to Nimsas_SessionEventControl_Notify. 13. The IMS AS-2 generates a re-INVITE request(s) in which the SDP offer contains the media information of the data channel required by the DC AS, application binding information, the existing IMS session ID, together with the other existing media descriptions. The IMS AS-2 sends the re-INVITE request(s) to the target UE B. 14. The UE B may download the corresponding DC application signalled in the SDP offer, if not done already and associate it with the requested application DC. 15. The DC media negotiation is completed and corresponding data channel(s) are established. The UE B returns a 200 OK response with SDP answer for the application data channel(s). 16. The IMS AS-2 requests MF-2 to update UE B side media resource information based on the received SDP answer for the application data channel from the UE B. 17. The IMS AS-2 sends ACK to the UE-B. NOTE 2: When the session update is successfully concluded, the IMS AS-2 notifies the DCSF-2 about the IMS session events with the Nimsas_SessionEventControl_Notify service operation as described in clause AC.7 with the event set to MediaChangeSuccessEvent. This is not depicted in the Figure. 18. If the DC AS included a Notification Target Address in the Nnef_ImsSessionManagement_Update request in step 1, the IMS AS-2 notifies the NEF on the progress of the session update with the Nimsas_ImsSessionManagement_Notify request. The MF-2 side MDC2 media information is included in the request. 19. The NEF notifies the DC AS on the progress of the session update with the Nnef_ImsSessionManagement_Notify request, including the MF-2 side MDC2 media information. 20. The DC AS updates its MF-2 side MDC2 media information and returns with Nnef_ImsSessionManagement_Notify response to the NEF. 21. The NEF returns a Nimsas_ImsSessionManagement_Notify response to the IMS AS-2. AG.2.1.2 Adding P2P Application Data Channel to an existing IMS session Figure AG.2.1.2-1 depicts the call flow of adding P2P application data channel(s) to an existing IMS session. In this scenario, the MF-2 is used to anchor the application data channel between the UE B and UE A. Figure AG.2.1.2-1: Procedure of adding P2P data channel(s) to an existing IMS session An IMS session between UE A and UE B has been established, the bootstrap DCs have also been established and the DC AS has received the IMS session ID. 0. DC AS may determine to add P2P application data channel(s) to an existing IMS session based on the event notification of the related IMS Session for which DC AS subscribed to. 1. The DC AS sends a Nnef_ImsSessionManagement_Update request to the NEF requiring to add P2P application data channel(s) in the existing IMS session. The AF request contains the DC AS identifier as AF ID. The DC AS shall include session ID of the existing session, the operation type as Adding, the media type as P2P ADC and the application binding information in Nnef_ImsSessionManagement_Update request. The DC AS includes the media operation set parameters and may include UE B and UE A as the targets of the P2P ADC as well as a Notification Target Address and Correlation ID to the Nnef_ImsSessionManagement_Update request to be notified for the progress of the session update. NOTE 1: To be able to initiate data sending to the UE via MF, the DC AS needs to be informed of the reserved media resources. and the DC AS needs to subscribe to the progress of the session update. 2. The NEF uses the Nhss_ImsUECM_AsInfoGet service operation to retrieve the IMS AS instance serving the UE B. 3. The NEF sends a Nimsas_ImsSessionManagement_Update request to the IMS AS-2 requiring to add P2P application data channel(s) in the specific session. The received IMS session ID of the existing session, the operation type as Adding, the media type as P2P ADC and the application binding information are included in the request. The NEF may include UE B and UE A as the targets of the P2P ADC, as well as a Notification Target Address and Correlation ID to the Nimsas_ImsSessionManagement_Update request to be notified on the progress of the session update. 4. The IMS AS-2 validates the user subscription data and checks the IMS DC capability of UE B and determines whether the data channel request should be notified to DCSF-2. If the UE B does not have subscription for IMS data channel or does not have the IMS DC capability, then the request shall be rejected with an appropriate cause and the subsequent steps are skipped. If the IMS AS-2 allows the request to proceed, it returns a successful Nimsas_ImsSessionManagement_Update response to the NEF. If the same IMS data channel is already established and if there are no other operations included in the request, then the request shall be rejected with an appropriate cause and the subsequent steps are skipped. 5. The NEF returns a successful Nnef_ImsSessionManagement_Update response to the DC AS. 6. The IMS AS-2 sends a Nimsas_SessionEventControl_Notify request to the DCSF-2 with event set to ExternalSessionUpdateEvent. The notification includes the necessary parameters based on the information extracted from media operation set parameters received in step 3 and other stored parameters in the IMS AS-2 if applicable. 7. After receiving the session event control notification, the DCSF-2 determines the policy how to process the application data channel establishment request based on the related parameters in the notification and/or DCSF-2 service specific policy.The DCSF-2 determines that the added application data channel requires the DC to be anchored in the MF-2. 8. The DCSF-2 instructs the IMS AS-2 to set up the P2P application data channel(s) by sending a Nimsas_MediaControl_MediaInstruction request. 9. Based on the instruction from DCSF-2, the IMS AS-2 interacts with the MF-2 to allocate data channel media resources towards UE B and UE A. 10. The IMS AS-2 may respond to Nimsas_MediaControl_MediaInstruction request. 11. The DCSF-2 may respond to Nimsas_SessionEventControl_Notify. 12. The IMS AS-2 generates a re-INVITE request(s) in which the SDP offer contains the media information of the data channel, application binding information, the existing IMS session ID, together with the other existing media descriptions. The IMS AS-2 sends the re-INVITE request(s) to the target UE B. 13. The UE B may need to download the corresponding DC Application signalled in the SDP offer, if not done already and associate it with the requested application DC. 14. The DC media negotiation is completed. The UE B returns a 200 OK response with SDP answer for the application data channel. 15. The IMS AS-2 generates a re-INVITE request(s) in which the SDP offer contains the media information of the data channel, application binding information, the existing IMS session ID, together with the other existing media descriptions. The IMS AS-2 sends the re-INVITE request(s) to the target UE A. 16. The UE A may need to download the corresponding DC Application signalled in the SDP offer, if not done already and associate it with the requested application DC. 17. The DC media negotiation is completed. UE A returns a 200 OK response with SDP answer for the application data channel. NOTE 2: Steps 12-14 and steps 15-17 can be processed in parallel. 18. The IMS AS-2 requests MF-2 to update UE B side and UE A side media resource information based on the received SDP answer for the application data channel from UE B and UE A. 19. The IMS AS-2 sends ACK to the UE-B and UE A. NOTE 3: After the session is successfully updated, the IMS AS-2 notifies the DCSF-2 about the IMS session event with the Nimsas_SessionEventControl_Notify service operation as described in clause AC.7 with the event set to MediaChangeSuccessEvent. This is not depicted in the Figure. 20. If the DC AS included a Notification Target Address in the Nnef_ImsSessionManagement_Update request in step 1, the IMS AS-2 notifies the NEF for the progress of the session update with the Nimsas_ImsSessionManagement_Notify request. 21. The NEF notifies the DC AS for the progress of the session update with the Nnef_ImsSessionManagement_Notify request. 22. The DC AS may return a Nnef_ImsSessionManagement_Notify response to the NEF. 23. The NEF may return a Nimsas_ImsSessionManagement_Notify response to the IMS AS-2. AG.2.1.3 Adding P2A2P Application Data Channel to an existing IMS session Figure AG.2.1.3-1 depicts the call flow of adding P2A2P application data channel(s) to an existing IMS session. In this scenario, the MF-2 is used to anchor the application data channel between the UE B, the UE A and the DC AS. Figure AG.2.1.3-1: Procedure of adding P2A2P data channel(s) to an existing IMS session An IMS session between UE A and UE B has been established, bootstrap DCs have also been established and the DC AS has received the IMS session ID. 0. DC AS determines to add P2A2P application data channel(s) to an existing IMS session, e.g. based on the event notification of the related IMS Session to which DC AS subscribed to. 1. The DC AS sends a Nnef_ImsSessionManagement_Update request to the NEF requiring adding P2A2P application data channel(s) in the existing IMS session. The DC AS shall include session ID of the existing session, the operation type as Adding, the media type as P2A2P ADC, the application binding information and the MDC2 media endpoint address (e.g. FQDN or IP address and port number) in Nnef_ImsSessionManagement_Update request. The DC AS includes the media operation set parameters and may include UE B and UE A as the targets of the P2A2P ADC, as well as a Notification Target Address and Correlation ID to the Nnef_ImsSessionManagement_Update request to be notified on the progress of the session update. The AF request contains the DC AS identifier as AF ID. NOTE 1: To be able to initiate data sending to the UE via MF, the DC AS needs to be informed of the reserved media resources. and the DC AS needs to subscribe to the progress of the session update. 2. The NEF uses the Nhss_ImsUECM_AsInfoGet service operation to retrieve the IMS AS instance serving the UE B. 3. The NEF sends a Nimsas_ImsSessionManagement_Update request to the IMS AS-2 requiring to add P2A2P application data channel(s) in the specific session. The received session ID of the existing session, the operation type as Adding, the media type as P2A2P ADC, the application binding information and the MDC2 media endpoint address shall be included in the request. The NEF may include UE B and UE A as the targets of the P2A2P ADC, as well as a Notification Target Address and Correlation ID to the Nimsas_ImsSessionManagement_Update request to be notified for the progress of the session update. 4. The IMS AS-2 validates the user subscription data and checks the IMS DC capability of UE B and determines whether the data channel request should be notified to DCSF-2. If the UE B does not have subscription of IMS data channel or does not have the IMS DC capability, then the request shall be rejected with appropriate cause and the subsequent steps are skipped. If the IMS AS-2 allows the request to proceed, it returns a successful Nimsas_ImsSessionManagement_Update response to the NEF. If the same IMS data channel is already established and if there are no other operations included in the request, then the request shall be rejected with an appropriate cause and the subsequent steps are skipped. 5. The NEF returns a successful Nnef_ImsSessionManagement_Update response to the DC AS. 6. The IMS AS-2 sends a Nimsas_SessionEventControl_Notify request to the DCSF-2 with event set to ExternalSessionUpdateEvent. The notification includes necessary parameters based on the information extracted from Media operation set parameters received in step 3 and other stored parameters in the IMS AS-2 if applicable. 7. After receiving the session event notification, the DCSF-2 determines the policy how to process the application data channel establishment request based on the related parameters in the notification and/or DCSF-2 service specific policy. The DCSF-2 determines that the added application data requires to anchor the DC in the MF-2. 8. The DCSF-2 instructs the IMS AS-2 to set up the P2A2P application data channel(s) by sending a Nimsas_MediaControl_MediaInstruction request. 9. Based on the instruction from DCSF-2, the IMS AS-2 interacts with the MF-2 to allocate data channel media resource towards UE B and UE A and the originating and terminating MDC2 media resource towards DC AS.The IMS AS-2 requests MF-2 to update DC AS side MDC2 media resource information using the received MDC2 media endpoint address (e.g. FQDN or IP address and port number) in step 3. 10. The IMS AS-2 may respond to Nimsas_MediaControl_MediaInstruction request. 11. The DCSF-2 may respond to Nimsas_SessionEventControl_Notify. 12. The IMS AS-2 generates a re-INVITE request(s) in which the SDP offer contains the media information of the data channel, application binding information, the existing session ID, together with the existing media descriptions. The IMS AS-2 sends the re-INVITE request(s) to the target UE B. 13 The UE B may need to download the corresponding DC Application signalled in the SDP offer, if not done already and associate it with the requested application DC. 14. The DC media negotiation is completed. The UE B returns a 200 OK response with SDP answer for the application data channel. 15. The IMS AS-2 generates a re-INVITE request(s) in which the SDP offer contains the media information of the data channel, application binding information, the existing session ID with the existing media descriptions. The IMS AS-2 sends the re-INVITE request(s) to the target UE A. 16. The UE A may need to download the corresponding DC Application signalled in the SDP offer, if not done already and associate it with the requested application DC. 17. The DC media negotiation is completed. The UE A returns a 200 OK respond with SDP answer for the application data channel. 18. The IMS AS-2 requests MF-2 to update UE B side and UE A side media resource information based on the received SDP answer for the application data channel from UE B and UE A. 19. The IMS AS-2 sends ACK to the UE-B and UE A. NOTE 2: After the session is successfully updated, the IMS AS-2 notifies the DCSF-2 about the IMS session event with the Nimsas_SessionEventControl_Notify service operation as described in clause AC.7 with the event set to MediaChangeSuccessEvent. This is not depicted in the Figure. NOTE 3: The details on how the DC AS updates its MF-2 side MDC2 media information are out of scope of 3GPP. 20. If the DC AS included a Notification Target Address in the Nnef_ImsSessionManagement_Update request in step, the IMS AS-2 notifies the NEF for the progress of the session update with the Nimsas_ImsSessionManagement_Notify request. The MF-2 side originating and terminating MDC2 media information is included in the request. 21. The NEF notifies the DC AS for the progress of the session update with the Nnef_ImsSessionManagement_Notify request, including the MF-2 side originating and terminating MDC2 media information. 22. The DC AS updates its MF-2 side originating and terminating MDC2 media information, returns a Nnef_ImsSessionManagement_Notify response to the NEF. 23. The NEF returns a Nimsas_ImsSessionManagement_Notify response to the IMS AS-2. AG.2.1.4 DC AS initiated adding bootstrap data channel to an existing IMS session Figure AG.2.1.4-1 depicts the call flow of adding bootstrap data channel towards UE B to an existing IMS session. In this scenario, the MF-2 is used to anchor the bootstrap data channel between the UE B and the DCSF2. Figure AG.2.1.4-1: Procedure of adding bootstrap data channel to an existing IMS session An IMS voice session between UE A and UE B has been established. 0. DC AS decides to add a bootstrap DC to the existing IMS session, which is notified based on the event notification of the related IMS session to which the DC AS subscribed to. 1. The DC AS sends a Nnef_ImsSessionManagement_Update request to the NEF requiring to add a bootstrap data channel to the existing IMS session. The DC AS includes the session ID of the existing IMS session to be updated, the operation type as Adding, media operation set including the parameters for the media type set as BDC, the UE B as the target of the BDC, in Nnef_ImsSessionManagement_Update request. The DC AS may include a Notification Target Address and Correlation ID to the Nnef_ImsSessionManagement_Update request to be notified of the session update progress. 2. The NEF uses the Nhss_ImsUECM_AsInfoGet service operation to retrieve the IMS AS instance serving UE B. 3. If the NEF authorizes the request, the NEF sends a Nimsas_ImsSessionManagement_Update request to the IMS AS-2 requiring to add A2P application data channel(s) to the specific IMS session. The received session ID of the existing IMS session, the operation type as Adding, the media type as A2P ADC, the UE B as the target of the A2P ADC, the application binding information, and the MDC2 media endpoint address shall be included in the request. The NEF may include a Notification Target Address and Correlation ID to the Nimsas_ImsSessionManagement_Update request to be notified of the session update progress. 4. The IMS AS-2 determines whether the data channel request should be notified to DCSF-2 based on subscription information and DC capability of UE B. If UE B does not have subscription of IMS data channel or does not have the IMS DC capability, or then the request shall be rejected with appropriate cause and subsequent steps are skipped. If the IMS AS-2 allows the request to proceed, it returns a successful Nimsas_ImsSessionManagement_Update response to the NEF. If the bootstrap DC is already established, the request shall be rejected with an appropriate cause and the following steps are skipped. 5. The NEF returns a successful Nnef_ImsSessionManagement_Update response to the DC AS. 6. The IMS AS-2 sends a Nimsas_SessionEventControl_Notify request to the DCSF-2 with event set to ExternalSessionUpdateEvent. The notification includes the necessary parameters based on the information extracted from media operation set parameters received in step 3 and other stored parameters in the IMS AS-2 if applicable.. 7. Steps 7 to 10 in clause AC.7.1 applies. 8. The IMS AS-2 generates a re-INVITE request in which the SDP offer contains the media information of the bootstrap data channel and existing voice media and sends the request to UE B. 9. UE B responds 200 OK with SDP answer. 10. Steps 17 to 18 in clause AC.7.1 applies. 11. IMS AS sends ACK to UE B to complete the IMS session modification procedure. 12. If the NEF included a Notification Target Address in the Nimsas_ImsSessionManagement_Update request in step 3, the IMS AS-2 notifies the NEF MediaChangeSuccess event with the Nimsas_ImsSessionManagement_Notify request. 13. If the DC AS included a Notification Target Address in the Nnef_ImsSessionManagement_Update request in step 3, the NEF notifies the DS AS MediaChangeSuccess event with the Nnef_ImsSessionManagement_Notify request. 14-15. The DC AS and NEF return responses. AG.2.2 Establishing IMS session with standalone Data Channel AG.2.2.0 General This clause describes the procedures of establishing an IMS session with standalone bootstrap data channel(s) and standalone A2P application data channel(s) via dedicated NEF services. The DC AS sends a Nnef_ImsSessionManagement_Create request to the NEF to establish an IMS session with standalone data channel(s). AG.2.2.1 Establishing an IMS session with a standalone bootstrap data channel Figure AG.2.2.1-1 shows the establishment procedure of a standalone data channel session. Figure AG.2.2.1-1: Establishment procedure of a standalone BDC session 0. The DC AS decides to establish a standalone data channel session between UE A and UE B. A standalone data channel can be a standalone bootstrap or standalone application data channel. This call flow describes the case of a standalone bootstrap data channel. 1. The DC AS sends a Nnef_ImsSessionManagement_Create request to the NEF to create a standalone DC session with UE A. The request includes calling ID (UE A), called ID (UE B), media information set including the instructions for the BDC, associated with the standalone IMS DC session and the DC AS identifier as AF ID. The DC AS may include a Notification Target Address and Correlation ID to the Nnef_ImsSessionManagement_Create request to be notified for the progress of the session update. 2. The NEF queries the HSS for the address of the IMS AS serving the UE B if needed. If the UE B is unregistered, that is, the HSS fails to return the address of IMS AS, the NEF shall reject the Nnef_ImsSessionManagement_Create request from the DC AS with an error response and the subsequent steps are skipped. 3. The NEF sends a Nimsas_ImsSessionManagement_Create request to the IMS AS-2 requiring to create a standalone DC session. 4. The IMS AS-2 validates the user subscription data and checks the IMS DC capability of UE to determine whether the data channel request should be notified to DCSF-2. If the user B does not have subscription for IMS data channel, then the request shall be rejected with appropriate cause. If the IMS AS-2 allows the request to proceed, it returns a successful Nimsas_ImsSessionManagement_Create response to the NEF including a Session ID. 5. The NEF returns a successful Nnef_ImsSessionManagement_Create response to the DC AS. 6. The IMS AS-2 sends a Nimsas_ImsSessionEventControl_Notify request to the DCSF-2 with event set to ExternalSessionCreateEvent. The notification includes the necessary parameters based on the information extracted from parameters received in step 3. The DCSF-2 instructs the IMS AS-2 to set up the data channel by sending a Nimsas_MediaControl_MediaInstruction request. The IMS AS-2 interacts with the MF-2 to allocate data channel resource. The procedures in clause AC.7 are reused to interact with MF. The Nimsas_MediaControl_MediaInstruction request instructs the IMS AS to originate the indicated data channel(s) from the MF-2 using the MDC1 and/or MDC2 media endpoint address(es) as included in the Nimsas_ImsSessionManagement_Create request. NOTE: The type of data channel established is dependent on the instruction given by DCSF. 7. The IMS AS-2 generates INVITE request(s) in which the SDP offer contains the media information of the data channel(s) required by the DC AS. The IMS AS uses the calling and called parties as indicated in the Nimsas_SessionManagement_Create request in step 3 as targets when sending the INVITE requests. The IMS AS-2 sends the INVITE request(s) according to the IMS DC session establishment procedures described in clauses AC.7.1 and AC.7.2 to UE A and UE B with the SIP header "display-name" indicating that IMS AS-2 sends the INVITE request on behalf of the callee. 8. The DC media negotiation is completed and corresponding data channel are established. 9. The IMS AS notifies the DCSF for the IMS session events with the Nimsas_SessionEventControl_Notify service operation as described in clause AC.7. If the DC AS included a Notification Target Address to the Nnef_ImsSessionManagement_Create request in step 1, the IMS AS notifies the NEF for the progress of the session creation with the Nimsas_ImsSessionManagement_Notify service operation. 10. The NEF notifies the DC AS for the progress of the session creation with the Nnef_ImsSessionManagement_Notify service operation. AG.2.2.2 DC AS initiated IMS session establishment with a standalone A2P application data channel Figure AG.2.2.2-1 depicts the call flow of establishing an IMS session with a standalone A2P application data channel between the DC AS and UE A. Figure AG.2.2.2-1: Establishment procedure of an IMS session with a standalone A2P application data channel 0. The DC AS decides to establish an IMS session with a standalone A2P application data channel with UE A. 1. The DC AS sends a Nnef_ImsSessionManagement_Create request to the NEF requiring to create an IMS session with a standalone A2P application DC with UE A. The DC AS sends the media operation set including the parameters for the media type set as A2P ADC and the UE A as the target of the ADC to NEF. The DC AS may include a Notification Target Address and Correlation ID to the Nnef_ImsSessionManagement_Create request to be notified for the progress of the session creation. 2. If the NEF authorizes the request, the NEF queries the HSS with Nhss_ImsUECM_AsInfoGet service operation to retrieve the IMS AS instance serving UE A. 3. The NEF sends a Nimsas_ImsSessionManagement_Create request to the IMS AS-1 requiring to create an IMS session with a standalone A2P application DC. The media operation set includes the parameters for the media type set as A2P ADC and the UE A as the target of the A2P ADC. The NEF may include a Notification Target Address and Correlation ID to the Nimsas_ImsSessionManagement_Create request to be notified of the session create progress. 4. The IMS AS-1 validates the user subscription data and checks the IMS DC capability of UE A to determine whether the data channel request should be notified to DCSF-1. If UE A does not have subscription of IMS data channel or does not have the IMS DC capability, then the request shall be rejected with appropriate cause and the subsequent steps are skipped. If the IMS AS-1 allows the request to proceed, it returns a successful Nimsas_ImsSessionManagement_Create response to the NEF. 5. The NEF returns a successful Nnef_ImsSessionManagement_Create response with the session ID generated by the IMS AS-1 to the DC AS. 6. The IMS AS-1 sends a Nimsas_SessionEventControl_Notify request to the DCSF-1 with event set to 3rdPartySessionCreate. The notification includes the necessary parameters based on the information extracted from the media operation set received in step 3 and other stored parameters in the IMS AS-1 if applicable. 7. After receiving the session event control notification, the DCSF-1 determines the policy how to process the bootstrap data channel establishment request based on the related parameters in the notification and/or DCSF-1 service specific policy. 8. The DCSF-1 determines that the standalone A2P application data channel media requires the DC to be anchored in MF-1 and creates the originating side MDC1 media information required by MF-1. 9. The DCSF-1 instructs the IMS AS-1 to set up the standalone A2P application data channel by sending a Nimsas_MediaControl_MediaInstruction request. 10. Based on the instruction from DCSF-1, the IMS AS-1 interacts with the MF-1 to allocate data channel media resource towards UE A and MDC1 media resource towards the DCSF. 11. The IMS AS-1 returns the Nimsas_MediaControl_MediaInstruction response to the DCSF-1. 12. The DCSF-1 returns the Nimsas_SessionEventControl_Notify response to the IMS AS-1. 13. The IMS AS-1 generates an INVITE request in which the SDP offer contains the media information of the standalone A2P application data channel required by the DC AS, binding information and the session ID. The IMS AS-1 sends the INVITE request to UE A. If UE A does not store the DC application specified in binding information locally, then the request shall be rejected with appropriate cause and the subsequent steps are skipped. 14. DC media negotiation may be completed through 18X/PRACK/200 OK(PRACK)/200 OK(INVITE)/ACK procedure. 15. The IMS AS-1 requests MF-1 to update DC AS side media resource information. 16. UE A runs the DC application specified in binding information and establish the standalone A2P application data channel with the DC AS. 17. If the DC AS included a Notification Target Address in the Nnef_ImsSessionManagement_Create request in step 1, the IMS AS-1 notifies the NEF for the progress of the session creation with the Nimsas_ImsSessionManagement_Notify request. 18. The NEF notifies the DC AS for the progress of the session creation with the Nnef_ImsSessionManagement_Notify request. 19. The DC AS returns a Nnef_ImsSessionManagement_Notify response to the NEF. 20. The NEF returns a Nimsas_ImsSessionMangement_Notify response to the IMS AS-1. AG.2.3 Terminating standalone Data Channel session Figure AG.2.3-1 shows the terminating procedure of a standalone data channel session. A standalone data channel can be a standalone bootstrap or standalone application data channel. Figure AG.2.3-1: Terminating of a standalone data channel Session 1. The DC AS sends a Nnef_ImsSessionManagement_Delete request to the NEF requiring terminating a standalone DC session with UE A. The request includes the Session ID to be terminated. 2. The NEF queries the HSS for the address of the IMS AS-2 serving the specific UE if needed. 3. The NEF sends a Nimsas_ImsSessionManagement_Delete request to the IMS AS-2 requiring to terminate the standalone data channel session identified by the Session ID. 4. The IMS AS-2 returns a successful Nimsas_ImsSessionManagement_Delete response to the NEF. 5. The NEF returns a successful Nnef_ImsSessionManagement_Delete response to the DC AS. 6. The IMS AS-2 releases DC resources in the MF-2 and sends the BYE request according to existing IMS procedures to terminate the data channel session. 7. The IMS AS-2 sends a Nimsas_SessionEventControl_Notify request including the event SessionTerminationEvent to notify DCSF-2 that a session is terminated. 8. If the DC AS included a Notification Target Address to the Nnef_ImsSessionManagement_Create or Nnef_ImsSessionManagement_Update request, the IMS AS notifies the NEF for the progress of the session deletion with the Nimsas_SessionManagement_Notify service operation, based on Table AA.2.4.4.5-1. 9. The NEF notifies the DC AS for the progress of the session deletion with the Nnef_SessionManagement_Notify service operation. Annex AH (informative): Change history Change history Date Meeting TDoc CR Rev Cat Subject/Comment New version 2014-09 SA#65 SP-140430 1073 3 B Paging Policy Differentiation over LTE for IMS Voice 13.0.0 2014-09 SA#65 SP-140431 1084 2 B Sharing Resources For Sessions on Hold 13.0.0 2014-12 SA#66 SP-140690 1092 1 B Media components of a session put on hold 13.1.0 2014-12 SA#66 SP-140690 1093 2 B P-CSCF Information Reporting Shared resources 13.1.0 2014-12 SA#66 SP-140686 1095 1 A Interface between IM-SSF and HSS 13.1.0 2014-12 SA#66 SP-140676 1097 1 A Support for flexible BFCP 13.1.0 2014-12 SA#66 SP-140688 1098 1 F Configuration for paging policy differentiation 13.1.0 2014-12 SA#66 SP-140693 1099 - B Insertion of GI by an AS 13.1.0 2015-03 SA#67 SP-150109 1101 1 A T-ADS for UEs supporting access to IMS via WLAN connected to EPC using S2b or S2a 13.2.0 2015-03 SA#67 SP-150022 1103 1 A MSRP Clarification 13.2.0 2015-03 SA#67 SP-150022 1105 - A BFCP Clarification 13.2.0 2015-06 SA#68 SP-150223 1110 - A AS allowing non-international format Request-URI when RAVEL is used 13.3.0 2015-06 SA#68 SP-150225 1116 1 A Codecs for WebRTC 13.3.0 2015-06 SA#68 SP-150222 1120 - A Removal of long expired reference to draft-kaplan-enum-sip-routing 13.3.0 2015-06 SA#68 SP-150222 1126 2 A OMR handling of SDP offer-answer exchanges after media path has been selected 13.3.0 2015-06 SA#68 SP-150230 1129 2 A Stage 2 cleanup regarding the WIC registration with a security token 13.3.0 2015-06 SA#68 SP-150232 1134 3 B Supporting Class of Users 13.3.0 2015-09 SA#69 SP-150494 1135 1 D Clarifying IMPU/IMPI relationship for WIC registration from a pool of Identities 13.4.0 2015-09 SA#69 SP-150503 1136 3 B Support for providing and distinguishing multiple UE provided access information over untusted WLAN access 13.4.0 2015-09 SA#69 SP-150500 1139 2 F Clarifications on indication of resource sharing 13.4.0 2015-09 SA#69 SP-150526 1138 2 B Support Minimizing bearer level protocol conversion 13.4.0 2016-03 SA#71 SP-160155 1144 2 A Replacing Incorrect Reference for business trunking Specification TS 13.5.0 2016-06 SA#72 SP-160298 1142 7 C Priority sharing for concurrent sessions, IMS 13.6.0 2016-06 SA#72 SP-160297 1147 2 F NPLI for untrusted WLAN access in IMS 13.6.0 2016-06 SA#72 SP-160304 1146 6 B Support for Acquisition and subscription to changes in PLMN id by P-CSCF 14.0.0 2016-09 SA#73 SP-160660 1148 3 B Support for P-CSCF sending a response to UE or IMS network when receiving Bearer Setup Request Rejection for QCI=1 14.1.0 2016-09 SA#73 SP-160664 1151 2 A NPLI for untrusted WLAN access in IMS for LI purposes 14.1.0 2016-09 SA#73 SP-160651 1152 2 C Handling of Local Number Translation for roaming users in deployments without IMS-level roaming interfaces 14.1.0 2016-09 SA#73 SP-160658 1153 3 B TCP transport for data channels towards the WIC. 14.1.0 2016-09 SA#73 SP-160658 1154 3 B WebRTC Media plane optimization with DTLS termination. 14.1.0 2016-09 SA#73 SP-160651 1155 1 F Inter-PLMN Mobility support clarification for V8 14.1.0 2016-09 SA#73 SP-160658 1156 3 B Support of RTP/RTCP multiplexing for WebRTC 14.1.0 2016-09 SA#73 SP-160651 1157 - B MCC Implementation correction for text in clause 4.15b 14.1.0 2016-09 SA#73 SP-160658 1159 1 F Reference point clarification between IMS entities for IMS session and dialog 14.1.0 2016-09 SA#73 SP-160658 1160 3 B Control parameter for predictable pre-emption of media flows 14.1.0 2016-12 SA#74 SP-160809 1163 1 A Editorial change reflecting IMS being access agnostic 14.2.0 2016-12 SA#74 SP-160809 1164 1 A Editorial changes and inclusion of Mp Reference Point and missing reference point P-CSCF - I-CSCF 14.2.0 2016-12 SA#74 SP-160826 1166 5 B Support for 3GPP PS Data off for SIP-Based Service 14.2.0 2017-03 SA#75 SP-170051 1169 1 F 3GPP Data Off IMS Status Reporting Correction 14.3.0 2017-03 SA#75 SP-170052 1170 2 F Alignment with CT WG3 for support for subscription to changes to IP-CAN by P-CSCF at IMS session setup. 14.3.0 2017-06 SA#76 SP-170372 1172 2 F Adding SIP AS as the entity to determines when resource sharing is to be performed 14.4.0 2017-09 SA#77 SP-170716 1176 2 F Support for Enhanced Coverage for data centric UEs 14.5.0 2017-09 SA#77 SP-170732 1173 1 B WebRTC Web Server Function discovery 15.0.0 2017-09 SA#77 SP-170727 1174 4 B new annex to 23.228 for 5GS support 15.0.0 2017-09 SA#77 SP-170727 1175 2 B Adaptation to TS 23.228 due to 5GS 15.0.0 2017-09 SA#77 SP-170729 1177 2 C IMS support to 3GPP PS Data Off Phase 2 15.0.0 2017-12 SA#78 SP-170919 1179 1 F Improvements to TS 23.228 Annex M to reflect 5GS 15.1.0 2017-12 SA#78 SP-170919 1180 1 F Improvements to TS 23.228 Annex Y 15.1.0 2017-12 SA#78 SP-170921 1183 - C Clarification on UE behavior when receiving single list of Exempt Services - TS 23.228 15.1.0 2017-12 SA#78 SP-170924 1184 2 B Support for identity attestation and verification 15.1.0 2017-12 SA#78 SP-170915 1186 2 A Modification on PS Data Off support in IMS Client - TS 23.228 15.1.0 2018-03 SA#79 SP-180094 1187 1 F Clarification on additional IP address 15.2.0 2018-03 SA#79 SP-180090 1188 2 F IMS registration procedures for UE in Dual Registration mode 15.2.0 2018-09 SA#81 SP-180712 1191 1 F Clarification on access network information during IMS call in 5G dual connectivity scenario 15.3.0 2019-03 SA#83 SP-190156 1196 1 F Clause W.2 on "Architecture without IMS-level roaming interfaces" to refer to clause Y.9.2 that defines it for the 5GS case. 15.4.0 2019-03 SA#83 SP-190163 1193 4 B Support for RLOS in IMS 16.0.0 2019-03 SA#83 SP-190175 1194 1 B Support for RAN Assisted Codec Adaptation 16.0.0 2019-06 SA#84 SP-190419 1199 1 B eIMS P-CSCF use of NRF 16.1.0 2019-06 SA#84 SP-190419 1200 3 B SBA HSS Services for IMS 16.1.0 2019-06 SA#84 SP-190419 1201 3 B HSS Discovery and Interface Type Selection 16.1.0 2019-06 SA#84 SP-190419 1202 1 B Allowing SMF to perform P-CSCF Discovery using NRF 16.1.0 2019-06 SA#84 SP-190419 1203 3 B Allowing IMS to use N5 interface to interact with PCF 16.1.0 2019-06 SA#84 SP-190419 1204 - B Additional corrections for allowing IMS to use N5 interface to interact with PCF 16.1.0 2019-06 SA#84 SP-190419 1205 2 F Bearer establishment mode negotiation not applicable in 5GC 16.1.0 2019-06 SA#84 SP-190426 1206 1 B Introduction of UDICOM 16.1.0 2019-06 SA#84 SP-190406 1208 2 F Correction to Support for RAN Assisted Codec Adaptation 16.1.0 2019-09 SA#85 SP-190611 1211 5 F Update of SBA HSS Services for IMS 16.2.0 2019-09 SA#85 SP-190611 1212 3 F Clarification for HSS Discovery and Interface Type Selection 16.2.0 2019-09 SA#85 SP-190611 1218 - F Resolve EN on networks with both Rx and N5 support 16.2.0 2019-09 SA#85 SP-190611 1219 2 F Update P-CSCF Registration with NRF 16.2.0 2019-12 SA#86 SP-191087 1222 1 F Fixing incorrectly implemented 23.228 CR1193 16.3.0 2019-12 SA#86 SP-191078 1223 1 F HSS Service Name correction 16.3.0 2019-12 SA#86 SP-191078 1225 2 F Correction on HSS service Nhss_imsSubscriberDataManagement 16.3.0 2019-12 SA#86 SP-191078 1226 - F UDR service for mapping IMS Public Identity to HSS Group ID for HSS selection 16.3.0 2019-12 SA#86 SP-191087 1228 - F Corrections to S-CSCF discovery during RLOS IMS registration 16.3.0 2020-03 SA#87E SP-200080 1231 2 F EPS Fallback event transporting within IMS 16.4.0 2020-09 SA#89E SP-200678 1234 1 F HSS Selection Update 16.5.0 2020-09 SA#89E SP-200678 1235 - F Error correction for imsSubscriber Data Management Service and acquistion of an 5GS IP address for 16.5.0 2020-12 SA#90E SP-200956 1236 - F Correction to HSS Discovery and Selection via NRF 16.6.0 2020-12 SA#90E SP-200959 1237 1 C Providing User Location during IP Messaging 16.6.0 2021-03 SA#91E SP-210085 1238 1 B Upgrade IMS non-MPS session to an IMS MPS session. 17.0.0 2021-03 SA#91E SP-210088 1240 - C IMS signalling optimization with HSS GID 17.0.0 2021-03 SA#91E SP-210088 1241 - B Support for Attestation for IMS priority sessions 17.0.0 2021-03 SA#91E SP-210086 1242 1 B Use of Paging Policy Differentiation for setting the Paging Cause 17.0.0 2021-06 SA#92E SP-210353 1239 2 B KI#3: Support for IMC for SNPN 17.1.0 2021-06 SA#92E SP-210353 1243 3 F KI#3: IMS Support for SNPN 17.1.0 2021-09 SA#93E SP-210923 1245 1 F SNPN support for 1 to N independent IMS Providers 17.2.0 2021-09 SA#93E SP-210923 1246 1 F IMS Support for SNPN 17.2.0 2021-12 SA#94E SP-211305 1248 1 F Correction in HSSGID procedures 17.3.0 2021-12 SA#94E SP-211576 1255 - A Update IETF reference 17.3.0 2022-12 SA#98E SP-221094 1257 6 C IMS cross border mobility with Home routed IMS calls 18.0.0 2023-03 SA#99 SP-230060 1258 B Support of PSAP resolution with NWDAF 18.1.0 2023-03 SA#99 SP-230071 1263 9 B Architecture of IMS supporting data channel 18.1.0 2023-03 SA#99 SP-230071 1264 3 B IMS SBA Services 18.1.0 2023-03 SA#99 SP-230071 1266 2 B Binding information of DC Application with DC - 23.228 18.1.0 2023-03 SA#99 SP-230071 1267 03 B DCMF services 18.1.0 2023-03 SA#99 SP-230071 1268 02 B IMS DC capability discovery 18.1.0 2023-03 SA#99 SP-230071 1275 2 B Introduce Data Channel Related Definitions 18.1.0 2023-06 SA#100 SP-230482 1265 2 B KI#4 Describe option to support MRF registration and discovery using NRF 18.2.0 2023-06 SA#100 SP-230482 1278 4 C Clarification on IMS Data Channel Service 18.2.0 2023-06 SA#100 SP-230482 1281 - C Update to IMS AS SBA Services 18.2.0 2023-06 SA#100 SP-230482 1284 6 B Supporting UE centric AR Telephony Communication 18.2.0 2023-06 SA#100 SP-230482 1286 4 C UE trigger for IMS Data Channel setup 18.2.0 2023-06 SA#100 SP-230482 1287 1 C Establishing data channel before 200 OK 18.2.0 2023-06 SA#100 SP-230482 1294 1 B Provide application list based on UE DC capabilities 18.2.0 2023-06 SA#100 SP-230721 1295 6 C Update on the usage of DC App-ID and P2A2P procedures 18.2.0 2023-06 SA#100 SP-230482 1301 5 B Update of Bootstrap and application data channel setup procedures 18.2.0 2023-06 SA#100 SP-230482 1302 3 C Procedures on Data Channel termination and QoS requirement 18.2.0 2023-06 SA#100 SP-230482 1303 4 B Update of DCMF service to support media processing 18.2.0 2023-06 SA#100 SP-230482 1305 1 B Reference point between HSS and DCSF 18.2.0 2023-06 SA#100 SP-230482 1307 1 C DCMF service registration and discovery 18.2.0 2023-06 SA#100 SP-230482 1320 2 Usage of Mr/Cr with IMS DC 18.2.0 2023-06 SA#100 SP-230482 1325 - F Clarification on Interfaces and Reference Points Used for DC 18.2.0 2023-06 SA#100 SP-230482 1326 1 C Roaming support for IMS Data Channel service 18.2.0 2023-06 SA#100 SP-230482 1328 3 C Update on IMS AS service to support AR communication 18.2.0 2023-09 SA#101 SP-230852 1331 2 F Update to MF services 18.3.0 2023-09 SA#101 SP-230852 1333 2 F Architecture alignment to replace DCMF with MF 18.3.0 2023-09 SA#101 SP-230852 1337 2 F Update on Nimsas_SessionEventControl_Notify Service Operation Parameters 18.3.0 2023-09 SA#101 SP-230852 1338 - F Modification of Bootstrap Data Channel Setup Signalling Procedure 18.3.0 2023-09 SA#101 SP-230852 1342 - F Update of Nimsas_SessionEventControl_Notify for binding information 18.3.0 2023-09 SA#101 SP-230852 1347 2 F Update general description of HSS service for data channel 18.3.0 2023-09 SA#101 SP-230852 1354 1 F Update to data channel setup procedures 18.3.0 2023-09 SA#101 SP-230852 1355 - F Change media type value to DC 18.3.0 2023-09 SA#101 SP-230852 1356 - F Remove editor's note in clause AA.1.1 18.3.0 2023-09 SA#101 SP-230852 1357 2 F DCM selection based on IP address and location 18.3.0 2023-12 SA#102 SP-231266 1339 3 F Update on IMS Data Channel Service Subscription 18.4.0 2023-12 SA#102 SP-231266 1362 - F Correction on Figure AC.7.1-1: Bootstrap Data Channel set up Signalling Procedure 18.4.0 2023-12 SA#102 SP-231266 1363 2 F KI#2_ Update AR communicate procedure 18.4.0 2023-12 SA#102 SP-231266 1366 3 F Clarification on Function Description in AC.2.2 18.4.0 2023-12 SA#102 SP-231266 1368 1 F Correction of description in the Figure of the P2A2P procedure 18.4.0 2023-12 SA#102 SP-231266 1371 4 F Clarification on how to handle IMS DC capability indications 18.4.0 2023-12 SA#102 SP-231266 1372 2 F Correction on IMS DC event notification 18.4.0 2023-12 SA#102 SP-231266 1374 2 F Update of P2A and P2A2P procedures 18.4.0 2023-12 SA#102 SP-231266 1375 2 F IMS Data Channel establishment 18.4.0 2023-12 SA#102 SP-231266 1376 1 F 23.228 Editorial change for the DC call flow 18.4.0 2024-03 SA#103 SP-240105 1361 1 Clause Number Correction 18.5.0 2024-03 SA#103 SP-240105 1382 - F Update on IMS DC Capability Negotiation 18.5.0 2024-03 SA#103 SP-240105 1383 1 F Clarification on Bootstrap Data Channel Setup Signalling procedure 18.5.0 2024-03 SA#103 SP-240105 1386 - F 23.228 Editorial change for the DC procedure 18.5.0 2024-03 SA#103 SP-240105 1388 1 F Clarification on terminating UE initiated data channel 18.5.0 2024-06 SA#104 SP-240599 1384 3 F Update on UE Centric AR communication Procedure 18.6.0 2024-06 SA#104 SP-240599 1389 2 F Clarifications regarding DCMF 18.6.0 2024-06 SA#104 SP-240599 1391 1 F Clarification on DC QoS Handling in Application Data Channel Setup Procedures 18.6.0 2024-06 SA#104 SP-240599 1395 2 F Some correction and clarification to Annex AC 18.6.0 2024-06 SA#104 SP-240599 1397 1 F Mapping of DC binding information with SDP attribute 18.6.0 2024-09 SA#105 SP-241248 1393 3 F Updates on IMS AS service Nimsas_SessionEventControl 18.7.0 2024-09 SA#105 SP-241248 1443 1 F Editorial Change to Correct the Wording 18.7.0 2024-09 SA#105 SP-241248 1444 2 F Multiplexing of IMS data channels 18.7.0 2024-09 SA#105 SP-241248 1448 1 F Remove MRF from IMS data channel architecture 18.7.0 2024-09 SA#105 SP-241267 1418 3 B Support of IMS data channel interworking between DCMTSI UE and MTSI UE 19.0.0 2024-09 SA#105 SP-241266 1419 3 B Support of MPS priority for IMS Immediate Messaging and IMS Session-based Messaging 19.0.0 2024-09 SA#105 SP-241267 1422 3 B KI#6: Support of Standalone IMS Data Channel feature 19.0.0 2024-09 SA#105 SP-241267 1425 3 B Supporting of network initiated IMS Data Channel 19.0.0 2024-12 SA#106 SP-241491 1409 15 B KI#1: IMS Subscribe/Notify Framework Architecture 19.1.0 2024-12 SA#106 SP-241484 1416 5 B Terminating local BDC establishment without BDC media component in SDP of incoming INVITE request 19.1.0 2024-12 SA#106 SP-241491 1421 3 B KI#5: Support of Data off feature for data channel 19.1.0 2024-12 SA#106 SP-241485 1427 6 B Architecture for UE-satellite-UE communicaitons 19.1.0 2024-12 SA#106 SP-241485 1428 9 B Support of UE-Satellite-UE communication in IMS - Functionality 19.1.0 2024-12 SA#106 SP-241491 1462 1 F Resolve configuration EN for Standalone IMS DC feature 19.1.0 2024-12 SA#106 SP-241491 1478 11 B Support of third party user identity information in IMS 19.1.0 2024-12 SA#106 SP-241491 1479 8 B KI#3: DC interworking with MTSI UE 19.1.0 2024-12 SA#106 SP-241491 1480 11 B KI#8: Architecture for avatar communications 19.1.0 2024-12 SA#106 SP-241491 1483 8 B Address ENs in IMS AS Session Management Service 19.1.0 2024-12 SA#106 SP-241491 1489 10 B Network Capability Exposure Procedure 19.1.0 2024-12 SA#106 SP-241485 1492 3 B Call setup of UE-Satellite-UE communication in IMS with IMS-AGW on board 19.1.0 2024-12 SA#106 SP-241477 1496 1 A Correction of BDC Establishment Procedure 19.1.0 2024-12 SA#106 SP-241491 1498 2 B DCSF instructing the IMS AS to terminate the session at the IMS AS 19.1.0 2024-12 SA#106 SP-241490 1507 1 F Support of MPS priority for Messaging in IMS procedures 19.1.0 2024-12 SA#106 SP-241491 1509 2 B Alignment of DC exposure and standalone DC with IMS DC architecture 19.1.0 2024-12 SA#106 SP-241491 1511 2 B Support of multiplexing multiple DC applications over single SCTP connection 19.1.0 2024-12 SA#106 SP-241491 1518 3 F KI#6: Modification on standalone IMS DC session 19.1.0 2024-12 SA#106 SP-241491 1524 3 B Procedure for supporting of third party user identity information in IMS 19.1.0 2024-12 SA#106 SP-241491 1525 3 B Supporting Avatar Communication 19.1.0 2025-03 SA#107 SP-250048 1501 3 A Correlating the application DC with the bootstrap DC 19.2.0 2025-03 SA#107 SP-250048 1560 1 A Clarification on ADC Setup Procedure 19.2.0 2025-03 SA#107 SP-250040 1520 4 B Call setup of UE-Satellite-UE communication with early media in IMS 19.2.0 2025-03 SA#107 SP-250040 1521 11 B Mobility procedure for UE-Satellite-UE communication in IMS - continuation of optimized media routing 19.2.0 2025-03 SA#107 SP-250040 1522 11 B Mobility procedure for UE-Satellite-UE communication in IMS - ground fallback 19.2.0 2025-03 SA#107 SP-250056 1531 4 C Resolving ENs on Avatar communication 19.2.0 2025-03 SA#107 SP-250056 1533 1 F Clarification on PS Data Off status change reporting to DCSF 19.2.0 2025-03 SA#107 SP-250037 1535 1 F Priority IMS Registration 19.2.0 2025-03 SA#107 SP-250056 1537 3 F KI#8: Update to Architecture for avatar communications 19.2.0 2025-03 SA#107 SP-250056 1541 5 C KI#2: Update to Network Capability Exposure Procedures 19.2.0 2025-03 SA#107 SP-250056 1550 1 B Updates to Nimsas_ImsSessionManagement Service 19.2.0 2025-03 SA#107 SP-250056 1552 5 B Updates to support multiplexing multiple DC applications over single SCTP connection 19.2.0 2025-03 SA#107 SP-250048 1560 1 A Clarification on ADC Setup Procedure 19.2.0 2025-03 SA#107 SP-250040 1561 4 B Addition of mobility functionality for Support of UE-Satellite-UE communication in IMS 19.2.0 2025-03 SA#107 SP-250040 1562 4 B Clean-up of functionality at call setup for Support of UE-Satellite-UE communication in IMS 19.2.0 2025-03 SA#107 SP-250056 1563 1 B Clarification on how DCSF fetch DC AS URL if not pre-configured 19.2.0 2025-03 SA#107 SP-250040 1564 5 B Call setup update for UE-Satellite-UE communication in IMS with IMS-AGW on board 19.2.0 2025-03 SA#107 SP-250056 1567 4 C Update network-centric procedure of Avatar Communication 19.2.0 2025-03 SA#107 SP-250056 1579 5 F KI#4: Update of procedure description 19.2.0 2025-03 SA#107 SP-250056 1581 5 F KI#2: Update of procedures 19.2.0 2025-03 SA#107 SP-250037 1582 2 F MPS-subscribed UE definition correction 19.2.0 2025-03 SA#107 SP-250056 1583 2 F Update on multiplexing handling 19.2.0 2025-03 SA#107 SP-250056 1586 2 B Service updates to support multiplexing multiple DC applications over single SCTP connection 19.2.0 2025-03 SA#107 SP-250056 1587 2 B Updates on downloading Avatar representation in UE centric rendering mode 19.2.0 2025-03 SA#107 SP-250056 1589 2 B KI#2: Procedure of adding bootstrap DC to existing IMS session 19.2.0 2025-03 SA#107 SP-250056 1593 2 C Resolving ENs on Avatar ID List 19.2.0 2025-03 SA#107 SP-250056 1594 3 C Address EN on Avatar Representation Downloading 19.2.0 2025-03 SA#107 SP-250056 1596 3 C Update Network Capability Exposure Procedure 19.2.0
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1 Scope
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The present document specifies architectural enhancements to the 5G system using NR to support multicast and broadcast communication services, complying to the requirements in TS 22.146 [2], TS 22.246 [3] and TS 22.261 [4]. This document encompasses support for functions such as how to deliver multicast and broadcast communications including support within certain location areas, mobility, MBS session management, policy control and QoS, and support for features e.g. group message delivery.
The present document also covers interworking with E-UTRAN and EPC based eMBMS for Public Safety (e.g. MCX services).
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2 References
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The following documents contain provisions which, through reference in this text, constitute provisions of the present document.
- References are either specific (identified by date of publication, edition number, version number, etc.) or non‑specific.
- For a specific reference, subsequent revisions do not apply.
- For a non-specific reference, the latest version applies. In the case of a reference to a 3GPP document (including a GSM document), a non-specific reference implicitly refers to the latest version of that document in the same Release as the present document.
[1] 3GPP TR 21.905: "Vocabulary for 3GPP Specifications".
[2] 3GPP TS 22.146: "Multimedia Broadcast/Multicast Service (MBMS); Stage 1".
[3] 3GPP TS 22.246: "Multimedia Broadcast/Multicast Service (MBMS) user services; Stage 1".
[4] 3GPP TS 22.261: "Service requirements for the 5G system".
[5] 3GPP TS 23.501: "System architecture for the 5G System (5GS)".
[6] 3GPP TS 23.502: "Procedures for the 5G System; Stage 2".
[7] 3GPP TS 23.503: "Policy and charging control framework for the 5G System (5GS); Stage 2".
[8] 3GPP TS 23.246: "Multimedia Broadcast/Multicast Service (MBMS); Architecture and functional description".
[9] 3GPP TS 38.300: "NR; Overall description; Stage-2".
[10] 3GPP TS 23.468: "Group Communication System Enablers for LTE (GCSE_LTE)".
[11] 3GPP TS 26.348: "Northbound Application Programming Interface (API) for Multimedia Broadcast/Multicast Service (MBMS) at the xMB reference point".
[12] 3GPP TS 23.003: "Numbering, Addressing and Identification".
[13] Void.
[14] Void.
[15] 3GPP TS 38.413: "NG Application Protocol (NGAP)".
[16] 3GPP TS 38.401: "NG-RAN; Architecture description".
[17] 3GPP TS 29.244: "Interface between the Control Plane and the User Plane Nodes; Stage 3".
[18] 3GPP TS 26.502: "5G Multicast-Broadcast User Service Architecture".
[19] 3GPP TS 29.510: "Network Function Repository Services; Stage 3".
[20] 3GPP TS 33.501: "Security architecture and procedures for 5G system".
[21] 3GPP TS 23.289: "Mission Critical services over 5G System; Stage 2".
[22] 3GPP TS 26.517: "5G Multicast-Broadcast User Services; Protocols and Formats".
[23] 3GPP TS 29.281: "General Packet Radio System (GPRS) Tunnelling Protocol; User Plane (GTPv1-U)".
[24] 3GPP TS 38.423: "NG-RAN; Xn Application Protocol (XnAP)".
[25] 3GPP TS 24.501: "Non-Access-Stratum (NAS) protocol for 5G System (5GS); Stage 3".
[26] 3GPP TS 24.575: "5G System; Multicast/Broadcast UE pre-configuration; Management Object (MO)".
[27] 3GPP TS 23.379: "Functional architecture and information flows to support Mission Critical Push To Talk (MCPTT); Stage 2".
[28] 3GPP TS 38.331: "NR; Radio Resource Control (RRC); Protocol specification".
[29] 3GPP TS 32.255: "5G data connectivity domain charging; Stage 2".
[30] 3GPP TS 32.279: "5G Multicast-broadcast Services charging".
[31] 3GPP TS 32.240: "Charging management; Charging architecture and principles".
[32] 3GPP TS 23.527: "5G System; Restoration Procedures".
[33] 3GPP TS 29.571: "5G System; Common Data Types for Service Based Interfaces".
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3 Definitions of terms and abbreviations
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3.1 Terms
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For the purposes of the present document, the terms and definitions defined in TR 21.905 [1] and the following apply:
5GC Individual MBS traffic delivery: 5G CN receives a single copy of MBS data packets and delivers separate copies of those MBS data packets to individual UEs via per-UE PDU sessions, hence for each such UE one PDU session is required to be associated with a Multicast MBS Session.
5GC Shared MBS traffic delivery: 5G CN receives a single copy of MBS data packets and delivers a single copy of those MBS data packets to a RAN node.
Area Session Identifier: A unique identifier within an MBS Session used for an MBS session with location dependent content. When present, the Area Session ID, together with the TMGI, is used to uniquely identify the data flow of an MBS Session in a specific MBS service area.
Associated PDU Session: A PDU Session associated to a multicast MBS session that is used for 5GC Individual MBS traffic delivery method and for signalling related to a user's participation in a multicast MBS session such as join and leave requests.
Associated QoS Flow: A unicast QoS Flow that belongs to the associated PDU Session and is used for 5GC Individual MBS traffic delivery method. The associated QoS Flow is mapped from a multicast QoS Flow in a multicast MBS session.
Broadcast communication service: A 5GS communication service in which the same service and the same specific content data are provided simultaneously to all UEs in a geographical area (i.e. all UEs in the broadcast coverage area are authorized to receive the data).
NOTE 1: For the broadcast communication service, the content provider and network may not be aware whether the authorized UEs are actually receiving the data being delivered.
Broadcast MBS session: An MBS session to deliver the broadcast communication service. A broadcast MBS session is characterised by the content to send and the geographical area where to distribute it.
Broadcast service area: The area within which data of one or multiple Broadcast MBS session(s) are sent.
MBS QoS Flow: The finest granularity for QoS forwarding treatment for MBS data. Providing different QoS forwarding treatment requires separate MBS QoS Flows in 5GS supporting MBS.
MBS Service Announcement: Mechanism to allow users to be informed about the available MBS services.
MBS session: A multicast MBS session or a broadcast MBS session.
MBS service area: The area within which data of one Multicast or Broadcast MBS session may be sent. For location dependent MBS, for each MBS service area, an Area Session ID, which is unique per MBS Session ID, is allocated and the same location dependent content data for an MBS session is delivered to the UE(s) within an MBS service area.
MB-SMF service area: The area toward which MBS data received by any of the MB-UPF(s) controlled by the MB-SMF can be delivered. For MBS supporting NG-RAN node(s) within MB-SMF service area, MBS data are delivered via 5GC Shared MBS traffic delivery. For MBS non-supporting NG-RAN node(s) within MB-SMF service area, Multicast MBS session data are delivered via 5GC Individual MBS traffic delivery, while Broadcast MBS session data are not delivered.
NOTE 2: Within the 5GC, an MBS service area is described by a list of Cell ID(s) or a list of TAI (s). When a list of Cell ID(s) is used, the pertaining TAIs are also provided as to discover and select an AMF that serves NG-RAN nodes supporting the corresponding cells, as defined in TS 29.571 [33].
Multicast communication service: A 5GS communication service in which the same service and the same specific content data are provided simultaneously to a dedicated set of UEs (i.e. not all UEs in the coverage of the MBS service area are authorized to receive the data).
NOTE 3: For multicast communication service, the content provider and network can be aware whether the authorized UEs are actually receiving the data being delivered.
Multicast MBS session: An MBS session to deliver the multicast communication service. A multicast MBS session is characterised by the content to send, by the list of UEs that may receive the service and optionally by a geographical area where to distribute it.
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3.2 Abbreviations
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For the purposes of the present document, the abbreviations given in TR 21.905 [1], TS 23.501 [5] and the following apply. An abbreviation defined in the present document takes precedence over the definition of the same abbreviation, if any, in TR 21.905 [1].
AL FEC Application Level FEC
CDN Content Delivery Network
FEC Forward Error Correction
FSA Frequency Selection Area
LL SSM Lower Layer SSM
MBMS Multimedia Broadcast/Multicast Service
MBS Multicast/Broadcast Service.
MBSF Multicast/Broadcast Service Function.
MBSTF Multicast/Broadcast Service Transport Function.
MB-SMF Multicast/Broadcast Session Management Function.
MB-UPF Multicast/Broadcast User Plane Function
MSK MBS Service Key
MTK MBS Traffic Key
PTM Point To Multipoint
PTP Point To Point
PTW Paging Transmission Window
SSM Source Specific IP Multicast address.
TMGI Temporary Mobile Group Identity
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4 General Concept
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4.1 Overview of multicast and broadcast communication
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Multicast and Broadcast Service (MBS) is a point-to-multipoint service in which data is transmitted from a single source entity to multiple recipients, either to all users in a Broadcast service area, or to users in a multicast group as defined in TS 22.146 [2]. The corresponding types of MBS session are:
- Broadcast MBS session
- Multicast MBS session.
The MBS architecture defined in clause 5 follows the 5G System architectural principles as defined in TS 23.501 [5], enabling distribution of the MBS data from the 5GS ingress to NG-RAN node(s) and then to the UE. The MBS architecture provides:
- Efficient usage of RAN and CN resources, with an emphasis on radio interface efficiency;
- Efficient transport for a variety of multicast and broadcast services.
Multicast/Broadcast Service for roaming is not supported in this release.
Interaction between Multicast/Broadcast Service and support of deployments topologies with specific SMF Service Areas is not specified in this Release.
NOTE 1: For broadcast service over multiple MB-SMF Service Areas, mechanism of location dependent broadcast MBS Sessions is assumed to be applied.
The collection and reporting of MBS specific charging information are specified in TS 32.255 [29] for PDU session charging and TS 32.279 [30] for MBS session charging.
Transmission of Broadcast MBS Session is supported over NR non-terrestrial networks (NTN) as specified in TS 38.300 [9].
The restoration procedures to detect and handle failures affecting network functions and interfaces involved in the delivery of broadcast and/or multicast service are specified in TS 23.527 [32].
The MBS also provides functionalities such as local MBS service and location dependent MBS service, authorization of multicast MBS and QoS differentiation. Refer to clause 6 for more details.
MBS traffic is delivered from a single data source (e.g. Application Service Provider) to multiple UEs. Depending on many factors, there are several delivery methods which may be used to deliver the MBS traffic in the 5GS.
NOTE 2: For clarity, delivery methods are not referred to as unicast/multicast/broadcast but as described below. The term "unicast delivery" refers to a mechanism by which application data and signalling between the UE and the application server are delivered using PDU Session within the 3GPP network and using individual UE and application server addresses (e.g. IP addresses) between the 3GPP network and the application server. It is not equivalent to 5GC Individual MBS traffic delivery method defined in this clause.
Between 5GC and NG-RAN, there are two possible delivery methods to transmit the MBS data:
- 5GC Individual MBS traffic delivery method: This method is only applied for multicast MBS sessions. 5GC receives a single copy of MBS data packets and delivers separate copies of those MBS data packets to individual UEs via per-UE PDU sessions, hence for each such UE one PDU session is required to be associated with a Multicast MBS session.
- 5GC Shared MBS traffic delivery method: This method is applied for both broadcast and multicast MBS sessions. 5GC receives a single copy of MBS data packets and delivers a single copy of those MBS packets to an NG-RAN node, which then delivers the packets to one or multiple UEs.
The 5GC Shared MBS traffic delivery method is required in all MBS deployments. The 5GC Individual MBS traffic delivery method is required to enable mobility when there is an NG-RAN deployment with non-homogeneous support of MBS.
For the Multicast MBS session, a single copy of MBS data packets received by the CN may be delivered via 5GC Individual MBS traffic delivery method for some UE(s) and via 5GC Shared MBS traffic delivery method for other UEs.
Between the NG-RAN and the UE, two delivery methods are available for the transmission of MBS data packets over radio interface:
- Point-to-Point (PTP) delivery method: NG-RAN delivers separate copies of MBS data packets over radio interface to individual UE(s).
- Point-to-Multipoint (PTM) delivery method: NG-RAN delivers a single copy of MBS data packets over radio interface to multiple UEs.
NG-RAN may use a combination of PTP/PTM to deliver an MBS data packets to UEs.
NOTE 3: The PTP and PTM delivery methods are defined in RAN WGs.
As depicted in the following figure, 5GC Shared MBS traffic delivery method (with PTP or PTM delivery) and 5GC Individual MBS traffic delivery method may be used at the same time for a multicast MBS session.
Figure 4.1‑1: Delivery methods
For MBS broadcast communication, only 5GC Shared MBS traffic delivery method with PTM delivery is applicable.
For MBS multicast communication, if the NG-RAN node supports MBS, the network shall use the 5GC Shared MBS traffic delivery method for MBS data transmission.
NOTE 4: The exception is when the UE moves between NG-RAN node not supporting MBS (with 5GC Individual MBS traffic delivery method) and NG-RAN node supporting MBS, there is temporary co-existence between 5GC Shared MBS traffic delivery method and 5GC Individual MBS traffic delivery method. Refer to clause 6.3 for details.
For MBS multicast communication, the switching between 5GC Shared MBS traffic delivery method and 5GC Individual MBS traffic delivery method is supported. The UE mobility between RAN nodes both supporting MBS, and between a RAN node supporting MBS and a RAN node not supporting MBS is supported, for details see clause 6.3.
For MBS multicast communication, the switching between PTP and PTM delivery methods for 5GC Shared MBS traffic delivery shall be supported. NG-RAN is the decision point for switching between PTP and PTM delivery methods.
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4.2 MB service provisioning
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4.2.1 Multicast data provisioning
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An example for the sequence of phases for multicast data provisioning is described in the figure below:
Figure 4.2.1-1: Phases of Multicast data provisioning example
The following phases are performed for a specific UE:
- UE Session Join: UE Session Join is the process by which a UE joins an MBS Session, i.e. the UE indicates to 5GC that such UE wants to receive Multicast data identified by a specific MBS Session ID.
- UE Session Leave: UE Session Leave is the process by which a UE leaves a MBS Session, i.e. the UE no longer wants to receive Multicast data identified by a specific MBS Session ID.
The following phases are performed for a specific service:
- MBS Session Creation: It is the phase that the information of Multicast MBS session is created as described in clause 4.3. This step is optional.
- Service announcement: Service announcement is used to distribute information toward UEs about the service required for service reception (e.g. IP multicast address(es)) and possibly other service related parameters (e.g. service start time). This step is optional.
- Session Establishment: It is the phase that Multicast MBS session is established as described in clause 4.3.
- No data receiving: It is the phase when no multicast data is received by 5GC. This step is optional.
- Data transfer: It is the phase when Multicast data are transferred to the UEs.
- Session Release: It is the phase that the resources for Multicast MBS session is released as described in clause 4.3.
- Session Deletion: It is the phase that Multicast MBS session is deleted as described in clause 4.3.
NOTE: After session establishment, Multicast MBS session state could be switched between Active and Inactive several times, triggered by AF or User Plane event, see clause 7.2.5. 5GC further updates Multicast MBS session state towards NG-RAN nodes after Session Establishment.
The phase of Multicast data provisioning is illustrated with the following example of timeline:
Figure 4.2.1-2: Multicast service timeline example
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4.2.2 Broadcast data provisioning
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An example for the phases of broadcast data provisioning is described in the figure below:
Figure 4.2.2-1: Phases of Broadcast data provisioning
The following phases are performed for a specific service:
- MBS Session Creation and establishment: MBS Session Creation is used by the AF to create the MBS Session towards 5GC. MBS session creation can occur in several steps (e.g. TMGI allocation, provisioning information about MBS session, request to activate the MBS session). The last step of the MBS session creation triggers resource establishment for transmitting the DL Broadcast data between 5GC and NG-RAN.
NOTE: For broadcast communication, after MBS Session Creation and Session Establishment, the established resources are not only between 5GC and NG-RAN, but also between the AF to 5GC.
- Service announcement: Service announcement is used to distribute information towards UEs about the service required for service reception (e.g. IP multicast address(es)) and possibly other service related parameters (e.g. service start time). This step can occur in parallel or after the MBS session configuration. However, TMGI allocation is required before. The information of the service announcement, is defined in clause 6.11.
- Data transfer: It is the phase when broadcast data are transferred in the air interface.
- Session Release and Deletion: It is the point at which there will be no more need to transmit Broadcast data. At Session Release, the resources in 5GS are released and the broadcast MBS session is deleted.
The phase of Broadcast data provisioning is illustrated with the following example of timeline:
Figure 4.2.2-2: Broadcast service timeline
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4.3 Multicast session state model
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The following illustrate the states for the Multicast MBS session:
- Configured state: Information about the Multicast MBS session (e.g. QoS information) is available in 5GC NFs (e.g. MB-SMF) serving the Multicast MBS session, but no User Plane resources towards NG-RAN are reserved and no MBS data can be transmitted. Only resources at MB-SMF, NEF and MB-UPF are reserved and no multicast data are transmitted. A TMGI can be allocated for the Multicast MBS session. UEs may be allowed to join (subject to authorization check and configuration), but the first accepted UE join request will trigger the Multicast MBS session establishment towards the NG-RAN and the UE, see clause 7.2.1.
NOTE 1: The SMF is not involved in the Multicast MBS session while the Multicast MBS session is in configured state.
NOTE 2: There may be several interim states in the configured state, e.g. TMGI requested, or information about the Multicast MBS session provided, but these interim states will not be specified in this release.
- Active state: Multicast MBS session is established and MBS data can be transmitted to the UEs that have joined the Multicast MBS session. Radio resources for the Multicast MBS session are established. To receive multicast MBS session data, UEs that joined the Multicast MBS session shall be in CM-CONNECTED state for receiving data of the Multicast MBS session. UEs are allowed to join the Multicast MBS session (subject to authorization check). 5GC resources and radio resources for the Multicast MBS session are reserved for UEs that joined the Multicast MBS session.
NOTE 3: When receiving the data of the Multicast MBS session, the joined UEs can be in CM-CONNECTED with RRC_INACTIVE state as defined in clause 6.17.
- Inactive state: Multicast MBS session is established but no MBS data is transmitted to the UEs that have joined the Multicast MBS session. Radio resources for the Multicast MBS session are released, and the UEs that joined the Multicast MBS session may be in CM-CONNECTED or CM-IDLE state. UEs are allowed to join the Multicast MBS session (subject to authorization check).
The following procedures are defined which result in transition of the Multicast MBS session state:
Multicast Session Creation: The AF provides information about the Multicast MBS session and optionally requests the allocation of a TMGI, see clause 7.1.1.2 and 7.1.1.3. Alternatively, the information about the Multicast MBS session can be pre-configured in the network. The creation may indicate whether the Multicast MBS session may be established in active or inactive state and when a Multicast MBS session can become active. The AF may perform creation in several steps, e.g. to first request TMGI and then provide full information about the Multicast MBS session and allow it to be established, or to update the information whether the Multicast MBS session is to be in Active or Inactive state after establishment. Multicast MBS session state transitions from "Start (NULL)" to Configured state.
NOTE 4: A Multicast MBS session can also be created by the operator via OAM configuration or be established without prior creation.
- Multicast Session Establishment: When the join request of the first UE for the Multicast MBS session is accepted, the Multicast MBS session is established towards the NG-RAN node and the UE, see clause 7.2.1. Multicast session state transitions from "Start (NULL)" or Configured state to either Inactive or Active state.
- Multicast Session Activation: See clause 7.2.5.2, Triggered by the 5GC, the radio resources for the Multicast MBS session are established and Multicast MBS session data starts to be transmitted to the UE. UEs in CM-IDLE state and CM-CONNECTED with RRC Inactive state that joined the Multicast MBS session are notified. Activation can be triggered by AF request or data notification from the MB-UPF. Multicast session state transitions from Inactive state to Active state.
NOTE 5: The AF could not be aware, and the NEF will not be aware, whether a session is in created or established state. An AF may therefore update the session state to request the activation of a session prior to the establishment of the session, and this will determine that the session is subsequently established in Active state when the first UE joins, but will not trigger the Multicast Session Activation state transition.
- Multicast Session Deactivation: See clause 7.2.5.3. Triggered by the 5GC, the radio resources for the Multicast MBS session are released and Multicast MBS session data stops to be transmitted to the UE. Deactivation can be triggered by AF request or no reception of multicast data by the MB-UPF. Multicast session state transitions from Active to Inactive state.
- Multicast Session Release: Triggered by the last UE leaving the Multicast MBS session (see clause 7.2.2.2), or Multicast Session Deletion procedure (7.1.1.4 or 7.1.1.5), the resources for the Multicast MBS session are released in both 5GC nodes and RAN nodes, see clause 7.2.2. Multicast session state transitions from Active or Inactive state to Configured.
- Multicast Session Deletion: All information about the Multicast MBS session is removed from the 5GC, and the TMGI for the Multicast MBS session (if allocated during Multicast Session Configuration) is deallocated, see clause 7.1.1.4 or 7.1.1.5. The deletion may be triggered by an AF request. Multicast session state transitions from Configured, Active or Inactive state to "End (NULL)".
Figure 4.3-1: Multicast session states and state transitions
Figure 4.3-2: Multicast session states and state transitions in MB-SMF
Figure 4.3-3: Multicast session states and state transitions in NG-RAN
NOTE 6: Multicast session states and state transitions in NG-RAN is for illustration purpose, normative procedures are provided by RAN WGs.
Figure 4.3-4: Multicast session states and state transitions in SMF
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5 Architecture model
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5.1 General architecture
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Figure 5.1-1 depicts the MBS reference architecture. Service-based interfaces are used within the Control Plane. Support for interworking at reference points xMB and MB2 is described in Annex C.
Figure 5.1-1: 5G System architecture for Multicast and Broadcast Service.
NOTE 1: The MBSF is optional and may be collocated with the NEF or AF/AS, and the MBSTF is an optional network function.
NOTE 2: The existing service-based interfaces of Nnrf, Nudm, and Nsmf are reused to support MBS. Services for the service-based interfaces of Namf, Nmbsmf, Npcf and Nnef to support MBS are specified in clause 9. Services for the Nmbsf and Nmbstf service-based interfaces to support MBS are defined in TS 26.502 [18].
NOTE 3: An MBS-enabled AF uses either Nmbsf or Nnef to interact with the MBSF.
Figure 5.1-2 depicts the 5G system architecture for MBS using the reference point representation.
Figure 5.1-2: 5G System architecture for Multicast and Broadcast Service in reference point representation.
NOTE 4: The existing reference points of N1, N2, N4, N5, N10, N11, N30 and N33 are enhanced to support MBS.
NOTE 5: Regarding the functionalities, Nmb13, N29mb and Nmb1 are identical, Nmb5 and Nmb10 are identical, Nmb9 and N6mb are identical.
NOTE 6: Charging architecture is described in TS 32.240 [31].
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5.2 General architecture for interworking with EPS
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Interworking between MBS and eMBMS at service layer functionality applies in cases where the same Multicast/Broadcast service is provided via eMBMS and MBS. Figure 5.2-1 depicts the system architecture for interworking between E-UTRAN/EPC eMBMS and MBS at service layer, with collocated BM-SC and MBSF/MBSTF functionalities.
Figure 5.2-1: MBS-eMBMS interworking system architecture at service layer
The BM-SC+MBSF/MBSTF exposes common Nmb5/Nmb10/xMB-C/MB2-C and Nmb8/xMB-U/MB2-U reference points to the NEF and/or AF/AS. A common TMGI is used towards the AF/AS. The TMGI is also used as identifier for transport over E-UTRAN/EPC. The MBSTF distributes the received data to the MB-UPF at reference point Nmb9 and/or the MBMS-GW at reference point SGi-mb, when supported by operator network configuration.
NOTE 1: MB2-C/U and xMB-C/U are legacy reference points.
NOTE 2: In the case of MBSTF providing MB2-C/U, it may be used for the GCS/AS only supporting GC1 and MB2 interfaces, as defined TS 23.468 [10].
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5.3 Service-based interfaces, Reference point and functional entities
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5.3.0 Service-based interfaces
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The 5G System Architecture for MBS contains the following service-based interfaces:
Nmbsmf: Service-based interface exhibited by MB-SMF. Further details are described in clause 9.1.
Npcf: Service-based interface exhibited by PCF. Further details are described in clause 9.2.
Namf: Service-based interface exhibited by AMF. Further details are described in clause 9.3.
Nnef: Service-based interface exhibited by NEF. Further details are described in clause 9.4.
Nmbsf: Service-based interface exhibited by MBSF. Further details are described in clause 9.5.
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5.3.1 Reference point
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The 5G System Architecture for MBS contains the following new reference points:
N3mb: Reference point between the RAN and the MB-UPF.
N4mb: Reference point between the MB-SMF and the MB-UPF.
N6mb: Reference point between the MB-UPF and the AF/AS.
N7mb: Reference point between the MB-SMF and the PCF.
N11mb: Reference point between the AMF and the MB-SMF.
N16mb: Reference point between the SMF and the MB-SMF.
N19mb: Reference Point between the UPF and the MB-UPF.
N29mb: Reference point between the MB-SMF and the NEF.
Nmb1: Reference point between the MB-SMF and the MBSF.
Nmb2: Reference point between the MBSF and the MBSTF.
Nmb5: Reference point between the MBSF and the NEF.
Nmb8: Reference point between the MBSTF and the AF/AS.
Nmb9: Reference point between the MB-UPF and the MBSTF.
Nmb10: Reference point between the MBSF and the AF/AS.
Nmb12: Reference point between the MBSF and the PCF.
Nmb13: Reference point between the MB-SMF and the AF/AS.
Nmb14: Reference point between the NEF and the MBSTF.
N101: Reference point between the MB-SMF and the CHF.
5G System Architecture for MBS reuses the existing reference points of N1, N2, N4, N5, N10, N11, N30, N33 and N40 with enhancement to support MBS.
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5.3.2 Functional entities
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5.3.2.1 PCF
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In addition to the functions defined in TS 23.501 [5], the PCF performs the following functions to support MBS if dynamic PCC for MBS is needed:
- Supporting QoS handling for MBS Session.
- Providing policy information regarding the MBS Session to MB-SMF for authorizing the related QoS profiles.
- Interacting with UDR for QoS information retrieval.
- The PCF can receive MBS information from AF, NEF or MBSF, e.g. based on the different configuration options in Annex A.
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5.3.2.2 MB-SMF
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The MB-SMF performs the following functions to support MBS:
- General for Multicast and Broadcast MBS sessions:
- Supporting MBS session management (including QoS control).
- Configuring the MB-UPF for multicast and broadcast data transport, based on the policy rules for multicast and broadcast services from PCF or local policy.
- Allocating and de-allocating TMGIs.
- Specific for Broadcast MBS sessions:
- Interacting with RAN (via AMF) to control data transport using 5GC Shared MBS traffic delivery method.
- Specific for Multicast MBS sessions:
- Interacting with SMF to provide the SMF with MBS Session Context information.
- Interacting with RAN (via AMF) to establish data transmission resources between MB-UPF and RAN nodes for 5GC Shared MBS traffic delivery method.
- Controlling the MB-UPF for multicast data transport using 5GC Individual MBS traffic delivery method.
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5.3.2.3 SMF
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In addition to the functions defined in TS 23.501 [5], the SMF performs the following functions to support MBS:
- Discovering MB-SMF for a Multicast MBS session.
- Authorizing Multicast MBS session join operation for served UEs if needed.
- Interacting with MB-SMF to obtain multicast Session Context information used as input to modify the PDU Session associated with MBS session.
- Interacting with RAN to provide information about a Multicast MBS session that a UE is participating in.
- Interacting with RAN and UPF for multicast data transport using 5GC Individual MBS traffic delivery method.
- Interacting with RAN to provide MBS Assistance Information for the MBS session.
NOTE: SMF and MB-SMF may be co-located or deployed separately.
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5.3.2.4 MB-UPF
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The MB-UPF performs the following functions to support MBS:
- General for Multicast and Broadcast MBS sessions:
- Packet processing of incoming downlink packets for multicast and broadcast flows.
- QoS enforcement (MFBR) based on existing means.
- Interaction with MB-SMF for receiving multicast and broadcast data.
- Delivery of multicast and broadcast data to RAN nodes for 5GC Shared MBS traffic delivery method.
- Specific for Multicast MBS sessions:
- Delivery of multicast data to UPF for 5GC Individual MBS traffic delivery method.
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5.3.2.5 UPF
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In addition to the functions defined in TS 23.501 [5], the UPF performs the following functions to support MBS:
- Interacting with SMF for receiving multicast data from MB-UPF for 5GC Individual MBS traffic delivery method.
- Delivering multicast data to UEs via PDU Session for 5GC Individual MBS traffic delivery method.
NOTE: UPF and MB-UPF may be co-located or deployed separately.
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5.3.2.6 AMF
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In addition to the functions defined in TS 23.501 [5], the AMF performs the following functions to support MBS:
- Signalling with NG-RAN and MB-SMF for MBS Session management.
- Selection of NG-RANs for notification of multicast session activation toward UEs in CM-IDLE state.
- Selection of NG-RANs for broadcast traffic distribution.
Additionally, AMF being aware of NG-RAN MBS capability.
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5.3.2.7 NG-RAN
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In addition to the functions defined in TS 23.501 [5], the NG-RAN performs the following functions to support MBS:
- Management of MBS QoS flows via N2.
- Delivery of MBS data packets for multiple UEs over radio using PTM or PTP.
- Configuration of UE for MBS QoS flow reception at AS layer.
- Control switching between PTM and PTP delivery per UE.
- Support for multicast session service continuity during Xn Handover and N2 Handover.
- Support group paging at multicast session activation over radio toward UEs in CM-IDLE state and CM-CONNECTED with RRC_INACTIVE state.
- Reception of MBS data packets from 5GC via shared MBS traffic delivery.
- Support for efficient radio resource utilization for multiple broadcast MBS Sessions via multiple CNs to deliver the same broadcast content in the case of network sharing.
- If supported, determine to move UE(s) receiving multicast MBS data from RRC_CONNECTED state to CM-CONNECTED with RRC_INACTIVE state if the UE(s) are capable of receiving MBS data in RRC_INACTIVE state.
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5.3.2.8 UE
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In addition to the functions defined in TS 23.501 [5], the UE may perform the following functions to support MBS:
- Reception of multicast data using PTM/PTP in RRC_CONNECTED state.
- If supported, reception of multicast data using PTM in RRC_INACTIVE state.
- Reception of broadcast data using PTM.
- Handling of incoming MBS QoS flows.
- Support of signalling for joining and leaving a Multicast MBS session.
- MBS resource management support at AS layer.
- Reception of notification in CM-IDLE state and CM-CONNECTED with RRC _INACTIVE state for multicast data transmission.
- Support of the aforementioned functions for UE using power saving functions.
NOTE : UE functionality for MBS security is provided in TS 33.501 [20].
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5.3.2.9 AF
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The AF performs the following functions to support MBS:
- Requesting multicast or broadcast service from the 5GC by providing service information including QoS requirement to 5GC.
- Instructing MBS session operation towards 5GC if needed.
- Interacting with NEF for MBS related service exposure.
- Interacting with NEF for group message delivery to the UE(s).
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5.3.2.10 NEF
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In addition to the functions defined in TS 23.501 [5], the NEF performs the following functions to support MBS:
- Providing an interface to AFs for MBS procedures including service provisioning, MBS session and QoS management.
- Interacting with AF and NFs in 5GC, e.g. MB-SMF for MBS session operations, determination of transport parameters.
- Selection of MB-SMF to serve an MBS Session.
- Support of provisioning the optional MBS Session Assistance Information related to the reception of multicast MBS data in RRC_INACTIVE state.
- Interacting with AF and MBSF/MBSTF for group message delivery.
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5.3.2.11 MBSF
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The MBSF performs the following functions to support MBS:
- Service level functionality to support MBS, and interworking with LTE MBMS
- Interacting with AF and MB-SMF for MBS session operations, determination of transport parameters, and session transport.
- Selection of MB-SMF to serve an MBS Session.
- Controlling MBSTF if the MBSTF is used.
- Determination of destination IP multicast address for the MBS session if IP multicast address is sourced by MBSTF.
NOTE 1: MBSF functionality related to service and MBS data handling (e.g. encoding) is specified in TS 26.502 [18].
NOTE 2: MBSF functionality for MBS security is provided in TS 33.501 [20].
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5.3.2.12 MBSTF
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The MBSTF performs the following functions to support MBS if deployed:
- Media anchor for MBS data traffic if needed.
- Sourcing of IP Multicast if needed.
- Generic packet transport functionalities available to any IP multicast enabled application such as framing, multiple flows, packet FEC (encoding).
- Multicast/broadcast delivery of input files as objects or object flows.
NOTE 1: MBSTF functionality related to MBS data handling (e.g. encoding) is specified in TS 26.502 [18].
NOTE 2: MBSTF functionality for MBS security is provided in TS 33.501 [20].
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5.3.2.13 UDM
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In addition to the functions defined in TS 23.501 [5], the UDM performs the following functions to support MBS:
- Support management of subscription for authorization for multicast MBS sessions.
- Support management of subscription MBS Assistance Information related to the reception of multicast MBS data in RRC_INACTIVE state.
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5.3.2.14 UDR
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In addition to the functions defined in TS 23.501 [5], the UDR performs the following functions to support MBS if deployed:
- Support storage or retrieval of MBS subscription data by the UDM for UE authorization information for multicast MBS sessions and MBS Assistance Information.
- Support storage and retrieval of policy data by the PCF for Multicast or Broadcast MBS sessions.
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5.3.2.15 NRF
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5.3.2.15.1 General
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In addition to the functions defined in TS 23.501 [5], the NRF performs the following functions to support MBS:
- Support of new NF types MB-SMF and MBSF and their corresponding NF profiles.
- For both multicast and broadcast MBS sessions, support of MB-SMF discovery based on parameters such as DNN, S-NSSAI and MBS service area, at MBS Session creation.
- For multicast MBS sessions, support of MB-SMF discovery based on MBS Session ID by SMF serving the multicast Session at UE join.
NOTE: For broadcast MBS Session, AMF discovery by MB-SMF for an MBS service area is based on tracking area IDs related to that service area, as registered in the AMF profile according to TS 23.501 [5].
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5.3.2.15.2 Extensions to NF profile at NRF
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In addition to the NF profile contents defined in clause 6.2.6.2 of TS 23.501 [5], the NF profile in the NRF contains the following content:
- For MB-SMF, the NF profile may include MB-SMF service area, MBS Session ID(s), Area Session ID(s) and corresponding MBS service area(s) if available.
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6 Functionalities and features
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6.1 Authorization to MBS service
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6.1.1 AF authorization to the service for multicast and broadcast
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The AF should be authorized by the 5GC for delivering MBS data to the 5GC and/or interacting with the 5GC. For signalling exchange with the 5GC, the NEF perform authorization to the external AF for determination of whether the interaction with the 5GC is allowed or not.
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6.1.2 UE authorization to the service for multicast
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The following authorizations are defined:
a) Whether the UE is authorized to use the Multicast service in the PLMN.
b) The authorization for a UE of receiving the content of a specific multicast MBS session.
A Multicast MBS session may be "open to any UEs".
NOTE 1: UE authorization for a specific Multicast MBS session can be implicitly performed when UE is configured for a specific Multicast MBS session, e.g. via Service Announcement for public safety use case.
NOTE 2: The authorization mentioned by a) is required even if an authorization according to b) is available. If the UE is not authorized to use the Multicast service by the PLMN, the UE is not authorized to join any multicast MBS Session even if the Multicast MBS session is "open to any UEs".
For a Multicast MBS session, it is required that the 5GC authorizes the UE based on the MBS subscription data and whether the Multicast MBS session is "open to any UEs", which are preconfigured, or provided by the AF (see clause 7.2.9).
The procedure for UE authorization is a part of UE join procedure and is described in clause 7.2.1.3.
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6.2 Local MBS service and Location dependent MBS service
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6.2.1 General
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A Local MBS service is an MBS service provided in one MBS service area. A location dependent MBS service is an MBS service provided in several MBS service area(s). An MBS service area is identified by a cell list or a tracking area list; for MBS broadcast over NR NTN see also clause 6.21. The MBS service area could be geographical area information or civic address information, and NEF/MBSF translates the location information to Cell ID list or TAI list as MBS service area, see clause 7.1.1.2.
The MBS service area may be updated by the AF for both multicast MBS sessions and broadcast MBS sessions as specified in clause 7.1.1.6.
For more details, refer to clause 7.2.4 for multicast MBS session and refer to clause 7.3.4 for broadcast MBS session.
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6.2.2 Local MBS service
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For a local MBS service, only UEs within the MBS service area may receive content data, while UEs outside the MBS service area are not allowed to receive location specific content. For multicast MBS service, UEs outside the MBS service area are not allowed to join the MBS service, and the network shall not deliver location specific content anymore to the UEs moved out of the MBS service area. Depending on policy, for the multicast MBS service the network may remove UEs outside the MBS service area of the MBS session from the MBS Session Context after a grace period. The SMF may subscribe at the AMF to notifications about "UE moving in or out of a subscribed "Area Of Interest"" event.
For multicast communication, local MBS may be supported via 5GC Individual MBS traffic delivery towards RAN nodes not supporting MBS. If the SMF obtains a notification that the UE is no longer in the MBS service area, the SMF terminates the 5GC Individual MBS traffic delivery towards the UE.
The UE shall be able to obtain service area information of the local multicast service via MBS service announcement or via NAS signalling (UE Session Join Accept/Reject including Cell ID list or TAI list). If the UE Session Join procedure fails due to the UE being outside the MBS service area, the UE does not attempt to join the Multicast MBS session again until the UE moves inside the MBS service area. When the UE Session Join succeeds and if the Multicast MBS session is inactive, the UE does not perform monitoring the session activation notification and any other information related to the Multicast MBS session identified by an MBS Session ID over the radio if outside the MBS service area.
NOTE 1: Broadcast communication service is the service provided simultaneously to all UEs in a geographical area, therefore for broadcast it is naturally a local MBS service. If the MBS Service Area consists of areas belonging to multiple MB-SMF Service Areas, the procedure for location dependent MBS Session can be used but the content is the same in all the MB-SMF service areas.
NOTE 2: In this Release, deployments topologies with specific SMF Service Areas are not supported, as a result, local MBS service over multiple SMF Service Areas (corresponding to multiple MB-SMF Service Areas) using multicast communication is not supported.
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6.2.3 Location dependent MBS service
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A location dependent MBS is identified by MBS Session ID, and provided in several MBS service areas. The location dependent MBS service enables distribution of different content data to different MBS service areas. The same MBS Session ID is used but a different Area Session ID is used for each MBS service area. The Area Session ID is used, in combination with MBS Session ID, to uniquely identify the service area specific part of the content data of the MBS service within 5GS. The network supports the location dependent content distribution for the location dependent MBS services, while UEs are only aware of the MBS Session ID (i.e. UEs are not required to be aware of the Area Session IDs). When UE moves to a new MBS service area, content data from the new MBS service area shall be delivered to the UE, and the network ceases to deliver the content data from the old MBS service areas to the UE. For multicast MBS service, UEs outside all MBS service areas of the location dependent MBS session are not allowed to join the MBS service. When UE moves out of an MBS service area and there is no other MBS service area for the MBS session, the network ceases to deliver the content data to the UE. Depending on policy, for the multicast MBS service the network may remove UEs outside all MBS service areas of the location dependent MBS Session from the multicast MBS Session Context after a grace period The SMF may subscribe at the AMF to notifications about UE moving in or out of all MBS service areas of the location dependent MBS session.
For multicast communication towards an NG-RAN supporting MBS, the NG-RAN node handles mobility of UEs within the MBS session between MBS service areas served by the same NG-RAN without interaction with SMF.
For multicast communication, location dependent MBS services may be supported via 5GC Individual MBS traffic delivery towards RAN nodes not supporting MBS. If the SMF determines that the UE is in another MBS service area of the Multicast MBS session, the SMF configures the UPF to send multicast data relating to the new MBS service area towards the UE.
Information about different MBS service areas for a location dependent MBS service may be provided by one or several AFs or may be configured. The MBS Service Information provided is specified in clause 6.14. Different ingress points for location dependent points for the MBS session are supported for different MBS service area dependent content of the MBS session; different MB-UPF may be assigned for different MBS service areas within the same MB-SMF Service Area for an MBS session.
For broadcast communication, if MBS service areas covering different MB-SMF Service Areas are required, different MB-SMFs should be assigned for different MB-SMF service areas for an MBS session, and in this case the MB-SMF involved in the MBS Session should be able to accept TMGI value allocated by other MB-SMF(s).
The Area Session ID is allocated by MB-SMF in MBS Session creation procedure. MB-SMF allocates Area Session ID for each MBS services area which is unique within the MBS session. MB-SMF needs to further ensure there is no MBS service area overlapping with other MBS service areas that share the same MBS Session ID.
The same QoS applies to all MBS service areas of a location dependent MBS Session.
NOTE 1: In this Release, deployments topologies with specific SMF Service Areas are not supported, as a result, location dependent service using multicast communication is not supported when a UE moves outside its SMF service area.
NOTE 2: For location dependent service provided in different MBS service areas within the same SMF service area, it is assumed that one MB-SMF is used for an MBS Session.
NOTE 3: An example of Location dependent MBS is a nationwide weather forecast service with local weather reports.
NOTE 4: Area Session ID is equivalent to Flow ID as specified in TS 23.246 [8].
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6.2.5 Void
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6.3 Mobility support of MBS service
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6.3.1 Mobility of Multicast MBS session
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The mobility of multicast MBS service is supported when:
- The UE moves from a NG-RAN node that supports MBS to a target NG-RAN node that supports MBS; or
- The UE moves from a NG-RAN node that supports MBS to a target NG-RAN node that does not support MBS and vice versa.
During the mobility from a NG-RAN node that supports MBS to a target NG-RAN node that supports MBS, or between a NG-RAN node that supports MBS and a target NG-RAN node that does not support MBS, minimization of data loss should be supported, see clause 7.2.3.5 for details.
To support Handover from NG-RAN node that supports MBS to a target NG-RAN node that supports MBS:
- If the shared delivery for the MBS session has not been established towards target NG-RAN, the target NG-RAN establishes the shared delivery for the MBS Session with MB-SMF and MB-UPF.
To support Handover from NG-RAN node that supports MBS to a target NG-RAN node that does not support MBS:
- mapping information about unicast QoS flows for multicast data transmission and the information of associated multicast QoS flows are provided to the NG-RAN node. This is already performed during the PDU session modification procedure for the PDU session associated with the MBS session when the UE joins the MBS Session;
- during the handover procedure, the delivery method is switched from 5GC Shared MBS traffic delivery method to 5GC Individual MBS traffic delivery method, i.e. the N3 tunnel of the PDU Session for 5GC Individual MBS traffic delivery needs to be established towards the target NG-RAN node. The SMF realizes that the target NG-RAN node does not support MBS.
- the SMF and the MB-SMF shall activate the GTP tunnel between the UPF and the MB-UPF for 5GC Individual MBS traffic delivery method, if needed.
To support Handover from a NG-RAN node that does not support MBS to a target NG-RAN node that supports MBS:
- The PDU sessions, including the one associated with the MBS session and used for 5GC Individual MBS traffic delivery, are handed over to the target NG-RAN node.
- SMF triggers mode switch, i.e. from 5GC Individual MBS traffic delivery method to 5GC shared MBS traffic delivery method.
- When the MBS Session Context is given to the target NG-RAN node by the SMF, if the shared delivery for the MBS session has not been established towards target NG-RAN, the target NG-RAN establishes the shared delivery for the MBS Session with MB-SMF and MB-UPF.
- The 5GC terminates the 5GC Individual MBS traffic delivery and changes to the 5GC shared MBS traffic delivery.
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6.3.2 Mobility of Broadcast MBS session
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The UE receives the same Broadcast MBS service in the target NG-RAN if the same MBS session is established with 5GC Shared MBS traffic delivery method in the target NG-RAN node.
NOTE: When the UE moves into NG-RAN node not supporting MBS within the Broadcast MBS service area, how the UE get the same content via application level is out scope of this specification.
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6.4 Subscription to multicast services
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6.4.1 General
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The UDM stores the MBS subscription information. The MBS subscription data for a UE is included within the UE subscription data.
At any time, the operator may change the subscription for multicast services in the UDM.
The MBS subscription data in UE subscription data contains the following information:
- MBS authorization information that gives the user permission to use multicast services
- Whether the UE is authorized to use the multicast MBS service.
- Optionally, MBS Session ID(s) of the Multicast MBS session(s) that the UE is allowed to join.
NOTE: The MBS Session ID applies only for MBS session which is not "open to any UEs".
- Optionally, MBS assistance information indicating that a UE is preferred to be kept connected when the related MBS Session the UE joined is active, which contains the following information:
- MBS Session ID(s).
The MBS subscription data is provided by the UDM to the SMF during or after the establishment procedure of PDU Session associated with Multicast MBS session(s) using Nudm_SDM service for subscription data type "MBS subscription data" as defined in clause 7.2.1.2.
During multicast session join procedure, the SMF retrieves MBS Session information from the MB-SMF, and authorizes the MBS Session join request for the UE based on MBS subscription data of the UE received from UDM and the Any UE indication (i.e. whether the Multicast MBS session is "open to any UEs") received from MB-SMF as described in clause 7.2.1.3.
The UDR stores the MBS data, which may be updated by the UDM or the AF/NEF as specified in clause 4.15.6.2 of TS 23.502 [6], i.e. AF may provision Multicast MBS Session Authorization information for the MBS as described in clause 7.2.9.
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6.4.2 MBS subscription data in UDM
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The information stored in the UDM as defined in clause 5.2.3.3.1 of TS 23.502 [6] is extended as follows:
- MBS subscription data for a UE as part of UE subscription data, as defined in Table 6.4.2-1, with keys defined in Table 6.4.2-2.
Table 6.4.2-1: MBS subscription data type
Subscription data type
Field
Description
MBS allowed
Indicates whether the UE is authorized to use the multicast MBS service.
MBS subscription data
Allowed MBS Session ID(s)
Identifies the MBS Session(s) that the UE are allowed to join.
MBS assistance information
Indicates that the UE is preferred to be kept connected when the related MBS session the UE joined is active, which contains the related MBS Session ID(s)
Table 6.4.2-2: MBS subscription data type keys
Subscription Data Types
Data Key
Data Sub Key
MBS Subscription data
SUPI
-
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6.4.3 MBS information in UDR
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The MBS information may be stored in the UDR by the UDM as part of the subscription data, as defined in clause 5.2.12.2.1 of TS 23.502 [6].
1. MBS data as defined in Tables 6.4.2-1, with keys defined in Table 6.4.3-1.
Table 6.4.3-1: MBS data type keys
Data Set
Data Subset
Data Key
Data Sub Key
Subscription Data
MBS subscription data
SUPI
-
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6.5 Identifiers
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6.5.1 MBS Session ID
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The MBS session ID is used to identify a Multicast/Broadcast MBS Session by the 5G system on external interface towards AF and between AF and UE, and towards the UE.
MBS Session ID may have the following types:
- TMGI (for broadcast and multicast MBS sessions);
- source specific IP multicast address (for multicast MBS sessions).
If a multicast MBS session is provided within an SNPN, the multicast MBS session can still be identified by a (globally unique) source specific IP multicast address or TMGI. In 5GS internal signalling the PLMN ID, included in TMGI, is complemented with the NID to identify an SNPN.
Source specific IP multicast address or TMGI may be used as MBS Session ID in NAS messages exchange between a UE and a CN when the UE requests to join/leave a Multicast MBS session. For multicast MBS sessions that the UE joined with a source specific IP multicast address, a TMGI is also allocated by 5GC and is sent to the UE and used in other signalling messages between RAN, CN and UE. Details see clause 7.2.1.3.
The UE shall be able to obtain at least one MBS Session ID via MBS service announcement.
For multicast MBS sessions, a source specific IP multicast address can be assigned by external AFs.
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6.5.2 Temporary Mobile Group Identity
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TMGI (Temporary Mobile Group Identity) is defined in TS 23.003 [12] and is used to be able to identify a broadcast MBS Session or a multicast MBS session.
In SNPN (Stand-alone Non-Public Network), TMGI is used together with NID (Network Identifier) defined in TS 23.003 [12] to identify an MBS Session.
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6.5.3 Source Specific IP Multicast Address
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The source specific IP multicast address is used to identify an Multicast MBS session and consists of two IP addresses, one is an IP unicast address used as source address in IP packets for identifying the source of the multicast service (e.g. AF/AS), the other is an IP multicast address used as destination address in related IP packets for identifying a multicast communication service associated with the source.
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6.5.4 MBS Frequency Selection Area ID
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The MBS Frequency Selection Area (FSA) ID is used for broadcast MBS session to guide the frequency selection of the UE.
MBS FSA ID identifies a preconfigured area within, and in proximity to, which the cell(s) announces the MBS FSA ID and the associating frequency (details see TS 38.300 [9]). MBS FSA ID and their mapping to frequencies are provided to RAN nodes via OAM.
Based on this configuration, RAN nodes announce in SIBs over the radio interface information about the MBS FSA IDs and frequencies.
When a broadcast MBS session is created, the AF may provide MBS FSA ID(s) based on the business agreement. If the AF does not provide MBS FSA ID(s), the MB-SMF determines MBS FSA ID(s) based on configured mapping from MBS service area and/or broadcast MBS session information (e.g. application ID) to MBS FSA ID(s) and sends the determined MBS FSA ID(s), to the AF (optionally via NEF).
NOTE: The same MBS FSA ID(s) can be assigned to multiple Broadcast MBS sessions.
The MBS FSA ID(s) of a broadcast MBS session are communicated in the service announcement towards the UE. The UE compares those MBS FSA IDs(s) with the MBS FSA ID(s) in SIBs for frequency selection.
During MBS Session Start for Broadcast in clause 7.3.1 and MBS Session Update for Broadcast in clause 7.3.3, the MB-SMF may include the MBS FSA ID(s) for the MBS session and send them to the NG-RAN nodes via the AMF. The NG-RAN nodes may then use those MBS FSA ID(s) to determine cells/frequencies within the MBS service area to broadcast MBS session data. For details, see TS 38.300 [9] and TS 38.413 [15].
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6.5.5 Associated Session ID
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In the case of network sharing, an Associated Session ID may be used as specified in clause 6.18. When the AF creates multiple broadcast MBS Sessions via different CNs to deliver the same content, it may provide the Associated Session ID which enables the NG-RAN to identify the multiple MBS Sessions delivering the same content.
Source Specific IP Multicast Address specified in clause 6.5.3 may be used as Associated Session ID.
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6.6 QoS Handling for Multicast and Broadcast services
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For MBS services, the network shall support QoS control per MBS session.
The 5G QoS model and parameters as defined in TS 23.501 [5] clause 5.7 also apply to multicast/broadcast communication services with the following differences:
- Reflective QoS is not applicable;
- Wireline access network specific 5G QoS parameters do not apply to MBS services;
- Alternative QoS Profile is not applicable;
- QoS Notification Control is not applicable;
- UE-AMBR is not applicable;
NOTE 1: For multicast communication service, the UE-AMBR applies for associated PDU Session.
- Session-AMBR if provided is enforced at MB-UPF but not communicated to NG-RAN.
NOTE 2: Whether Session-AMBR is required in addition to the MBS service data flow bit rate is determined by operator policy and/or agreement with the service provider.
- For broadcast MBS session, the QoS rule and QoS Flow level QoS parameters are not provided to UE.
NOTE 3: For broadcast MBS session, the associated QoS Flow(s) are not applicable.
- For multicast MBS sessions, the QoS rule and QoS Flow level QoS parameters of MBS QoS Flow are not provided to UE.
- For multicast MBS sessions, the handling of QoS rule and QoS Flow level QoS parameters of the associated QoS Flow(s) is the same as for other QoS Flow without UL in a PDU Session.
NOTE 4: The UE does not need to know a QoS Flow within the PDU session is mapped from MBS QoS Flow.
The network shall support one or multiple QoS flows, which can be either GBR or non-GBR, for an MBS session.
If 5GC Individual MBS traffic delivery method is used to deliver multicast data packets, the network may use dedicated QoS Flows for multicast data packets in a PDU session. For the associated QoS Flow in the PDU session, the SMF uses the same QoS parameters (e.g. 5QI) provided by MB-SMF. These dedicated QoS Flows shall be kept separate from QoS Flows unrelated to multicast even if the same 5QI and other QoS parameters are assigned.
NOTE 5: When there is a need to apply 5GC Individual MBS traffic delivery, the Session-AMBR of the associated PDU Session can be configured with a sufficiently high value to cater for MBS Session-AMBR.
The MB-SMF may obtain QoS information for multicast and broadcast MBS session in different ways depending on the deployment and use cases.
If dynamic PCC is not deployed:
- When an MBS session is started, the MB-SMF is provided with service requirements including QoS information. If MBSF is not used, the service requirement is provided to the MB-SMF by the AF (directly or via the NEF). If the MBSF is used, the MBSF receives request from the AF (or via the NEF) and decides the related QoS requirements (e.g. considering support for FEC) and provides them to the MB-SMF. The MB-SMF determines the QoS profiles and QoS for N4 rules for the MBS session with QoS parameters of the MBS QoS flows, and provides related information to the RAN and the MB-UPF respectively.
NOTE 6: What information is included in the request from AF to MBSF requires collaboration with SA WG4.
If dynamic PCC is deployed:
- It is the PCF that generates policy rules for MBS Session based on the received service requirement and provides the policy rules to the MB-SMF. The MB-SMF, based on the policy rules from the PCF, determines to create, and/or modify MBS QoS Flow(s) including providing QoS information to NG-RAN and MB-UPF, and providing packet detection and forwarding information to MB-UPF.
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6.7 User plane management
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The MB-UPF acts as the MBS Session Anchor of an MBS session, and if the MBSTF is involved in the MBS session, then the MBSTF acts as the media anchor of the MBS traffic. The MB-UPF receives only one copy of MBS data packets from AF or MBSTF.
The user plane between MB-UPF and AF, may use either multicast transport or a unicast tunnel for the MBS session (depending on application and capabilities of control interface). If the transport network does not support multicast transport, the user plane uses a unicast tunnel for the MBS Session. The user plane between MBSTF and AF may use a unicast tunnel, multicast transport or other means (e.g. HTTP download from external CDN). The user plane between MBSTF and MB-UPF uses a unicast tunnel for the MBS session. If a unicast tunnel is used for the MBS Session between MB-UPF and AF or MBSTF, after receiving the downlink MBS data, the MB-UPF forwards the downlink MBS data without the received outer IP header and tunnel header information.
NOTE 1: For location dependent MBS Session, the user plane towards the MB-UPF can only use unicast tunnel and content to be delivered to different areas are sent to MB-UPF via different tunnels.
NOTE 2: If the user plane towards the MB-UPF uses a unicast tunnel, all the service data flows for the MBS Session or for an Area Session for a location-dependent MBS session are sent in the same tunnel.
The user plane from the MB-UPF to NG-RAN(s) (for 5GC Shared MBS traffic delivery) and the user plane from the MB-UPF to UPFs (for 5GC Individual MBS traffic delivery) may use multicast transport via a common GTP-U tunnel per MBS session, or use unicast transport via separate GTP-U tunnels at NG-RAN or at UPF per MBS session in the following way
- For 5GC Shared MBS traffic delivery (i.e. MB-UPF delivers user plane data to NG-RAN supporting MBS), if the transport network supports IP multicast, the NG-RAN node uses multicast transport via a common GTP-U tunnel per MBS session, otherwise unicast transport via separate GTP-U tunnel per MBS session per NG-RAN node is used.
- For 5GC Individual MBS traffic delivery (i.e. MB-UPF delivers user plane data to UPF), if the transport network supports IP multicast and the UPF supports reception of multicast data over N19mb, UPF use multicast transport via a common GTP-U tunnel per MBS session, otherwise unicast transport via separate GTP-U tunnel per MBS session per UPF is used.
If the user plane uses unicast transport, the transport layer destination is the IP address of the NG-RAN or UPF, each NG-RAN or UPF allocates the tunnel separately and multiple GTP-U tunnels are used for the MBS Session. If the user plane uses multicast transport, a common GTP-U tunnel is used for both RAN and UPF nodes. The GTP-U tunnel is identified by a common tunnel ID and an IP multicast address as the transport layer destination, both assigned by 5GC.
The above is depicted in Figure 6.7‑1. There could be more than one NG-RANs or UPFs that are involved in the MBS traffic delivery.
Figure 6.7‑1: Schematic showing user plane data transmission
The MB-SMF instructs the MB-UPF to receive packets related to an MBS session.
MB-UPF transmits the MBS data with the sequence number for each MBS QoS Flow as defined in TS 29.281 [23].
For shared delivery, if unicast transport over N3mb applies, the MB-SMF instructs MB-UPF to replicate the received MBS packets and forward them towards multiple RAN nodes via separate GTP tunnel. For shared delivery, if multicast transport over N3mb applies, the MB-SMF instructs the MB-UPF to replicate the received MBS data and forwards the data via a single GTP tunnel.
For individual delivery, the MBS data received by the MB-UPF is replicated towards the UPF(s) where individual delivery is performed in the following way:
- The MB-SMF configures the MB-UPF to receive packets related to an MBS session, to replicate those packets and forward them towards multiple UPFs via GTP tunnels if unicast transport over N19mb is applied, or via a single GTP tunnel if multicast transport over N19mb is applied.
- The SMF(s) instructs the UPF to receive packets related to a Multicast MBS session from an MB-UPF over N19mb, to replicate those packets and to forward them in multiple PDU sessions.
For the MB-SMF and MB-UPF, packet detection, replication and forwarding for an MBS session is realized by using for each MBS session one PDR that detects the incoming MBS packets and points to one FAR that describes the forwarding of the data towards multiple destinations (UPFs or RAN nodes):
- A PFCP session is created when the MBS Session is started, regardless of multicast or unicast transport over N3mb and N19mb.
- For Multicast transport over N3mb and N19mb, the destination in the FAR contains the MB-UPF IP Multicast Distribution Info.
- For unicast transport over N3mb and N19mb, the FAR in the PFCP session may contain multiple destinations represented by the NG-RAN N3mb Tunnel Info and UPF N19mb Tunnel Info (if applicable).
For the SMF and the UPF (for 5GC individual delivery), packet detection, replication and forwarding for an MBS session is realized by PDR and FAR of the PDU session in which the UE has joined the MBS session:
- The SMF instructs the UPF to associate the PFCP session of the PDU session with an MBS session.
- A new PDR with Source Interface "Core" is used to detect MBS data from N19mb.
NOTE 3: This PDR is also containing the MBS Session ID to enable a single detection of the incoming MBS data for multiple PDU sessions at the UPF.
- For unicast transport over N19mb, the SMF requests UPF to allocate N19mb Tunnel Info if not allocated.
- For multicast transport over N19mb, the SMF includes the low layer source specific multicast address information and C-TEID to UPF.
- If the SMF wants to maintain the MBS data reception over N19mb but suspends the delivery of the data to the UE's PDU session, the Action of FAR set to "drop" (e.g. when the UE is switching from 5GC Individual delivery to 5GC Shared delivery due to the UE moving from MBS non-supporting NG-RAN to MBS supporting NG-RAN). Otherwise the SMF remove the related PDR and FAR.
See TS 29.244 [17] for the details of user plane handling.
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6.8 Interworking with MBMS over E-UTRAN for public safety services
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In order to minimize the interruption of services, upon mobility for MBS service from NR/5GC to E-UTRAN/EPC and vice versa, the following applies:
- If the same MBS service is provided via eMBMS in E-UTRAN and MBS, interworking is supported at service layer.
- The UE is always configured with a common TMGI regardless of whether the UE is discovering the MBMS/MBS service via E-UTRAN or NR, for both multicast and broadcast MBS services.
- When the UE camps on NR and uses a multicast MBS service, the UE joins a multicast MBS session and uses procedures as defined in clause 7.2 for MBS reception for the TMGI. When the UE camps on E-UTRAN, the UE uses procedures as defined in TS 23.246 [8] for MBMS reception for the TMGI.
- The session context for multicast MBS service transferring is not handed over to E-UTRAN during mobility from 5GS to EPS.
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6.9 MBS Session Context
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6.9.1 MBS Session Context
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The MBS Session Context contains all information describing a particular MBS session in the 5GS and is created in each node involved in the delivery of the MBS data.
The content of the Multicast MBS Session Context is described in Table 6.9.1-1.
Table 6.9.1-1: Multicast MBS Session Context
Parameter
Description
NG-RAN
AMF
SMF
MB-SMF
State
State of MBS session ('Active' or 'Inactive' or 'Configured')
X
(note 2)
X
(note 2)
X
SSM (source specific IP multicast address)
IP multicast address identifying the MBS session.
X
(note 1)
X
(note 1)
TMGI
Temporary Mobile Group Identity allocated to the MBS Session.
X
X
x
X
Area Session Identifier
Used for MBS session with location dependent content. When present, the Area Session Identifier together with the TMGI uniquely identify the MBS Session in a specific MBS service area.
X
(note 1)
X
X
(note 1)
X
(note 1)
MB-SMF
The MB-SMF that handles the MBS session.
X
X
QoS information
QoS information of the MBS session.
X
X
X
MBS Service Area
Area over which the MBS session data is distributed (i.e. Cell ID list or TAI list).
X
(note 1)
X
(note 1)
X
(note 1)
NG-RAN Node ID(s)
NG-RAN nodes which are involved in the Multicast MBS session
X
X
(note 1, note 4)
AMF
The AMF(s) which are selected for the MBS session
X
X
IP multicast and source address for data distribution
IP addresses identifying the SSM user plane transport for shared delivery from MB-UPF to NG-RAN and for individual delivery from MB-UPF to UPF when the IP multicast transport is used.
X (note 1)
X
(note 1)
X
(note 1)
TEID for IP multicast distribution
Tunnel ID allocated by MB-UPF used for receiving the multicast data for shared delivery by NG-RAN and for individual delivery by UPF when the IP multicast transport is used.
X
X
X
(note 1)
SMF
The SMF(s) that manages the associated PDU session.
X
UE ID
ID identifying the UE that successfully join the Multicast MBS session. For NG-RAN it is NGAP UE ID and for SMF it is SUPI.
X
(note 3)
X
(note 3)
NG-RAN IP unicast distribution
The IP addresses and TEID of NG-RAN used for the user plane between NG-RAN and MB-UPF and between MB-UPF and UPF when Point to Point tunnel is used.
X (note 1)
X
(note 1)
X
(note 1, note 4)
PCF
The MB-PCF that provides policy control for the MBS session.
X (note 1)
NOTE 1: It is an optional parameter.
NOTE 2: The value 'Configured' is not applicable for NG-RAN and SMF.
NOTE 3: the UE ID is available within the UE Context which contains the MBS information.
NOTE 4: The Parameter needs to be stored in deployments with shared NG-U termination(s) if unicast transport is used.
In Broadcast MBS session, an MBS Session Context is created in the NG-RAN, AMF, MB-SMF and MBSF as a result of the MBS Session Start procedure.
The content of the Broadcast MBS Session Context is described in Table 6.9.1-2.
Table 6.9.1-2: Broadcast MBS Session context
Parameter
Description
NG-RAN
AMF
MB-SMF
TMGI
Temporary Mobile Group Identity allocated to the MBS Session.
X
X
X
Area Session Identifier
Used for MBS session with location dependent content. When present, the Area Session Identifier together with the TMGI uniquely identify the MBS Session in a specific MBS service area.
X
(note 1)
X
(note 1)
X
(note 1)
AMF
The AMF(s) which are selected for the MBS session
X
X
MB-SMF
The MB-SMF that handles the MBS session.
X
QoS information
QoS information for the MBS Session, including the QoS parameters of QoS flows.
X
X
MBS Service Area
Area over which the MBS session data is distributed (i.e. Cell ID list or TAI list, optionally as defined in clause 6.21 with additional NR NTN Intended Service Area) (NOTE 3).
X
X
X
NG-RAN Node ID(s)
NG-RAN nodes which are selected for the Broadcast MBS session
X
X
(note 1, note 2)
IP multicast address for data distribution
IP addresses identifying the SSM user plane transport used for shared delivery from MB-UPF to NG-RAN when the IP multicast transport is used.
X
(note 1)
X
(note 1)
TEID for IP multicast distribution
Tunnel ID allocated by MB-UPF used for receiving the broadcast data for shared delivery by NG-RAN when the IP multicast transport is used.
X
X
(note 1)
NG-RAN IP unicast distribution
IP address and TEID of NG-RAN used for the user plane from NG-RAN to MB-UPF when Point to Point tunnel is used.
X
(note 1)
X
(note 1, note 2)
PCF
The PCF that provides policy control for the MBS session.
X
(note 1)
MBS FSA ID
MBS Frequency Selection Area (FSA) ID is used for broadcast MBS sessions to guide the frequency selection of the UE.
X
X
Associated Session ID
Associated Session ID is used by NG-RAN in network sharing to identify MBS sessions via different CNs transmitting the same content.
X
(note 1)
X
(note 1)
NOTE 1: It is an optional parameter.
NOTE 2: The Parameter needs to be stored in deployments with shared NG-U termination(s) if unicast transport is used.
NOTE 3: An additional NR NTN Intended Service Area in the MBS service area only applies to NR NTN, see clause 6.21.
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6.10 Policy control for Multicast and Broadcast services
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6.10.1 General
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The policy and charging control framework as defined in TS 23.503 [7] applies to Multicast and Broadcast services in the following aspects:
- MBS Session binding: MBS Session binding is the association of an AF Session information to one and only one MBS Session or a location dependent MBS Session in an MBS Service Area. The PCF shall perform the session binding based on the MBS Session ID, i.e. TMGI or source specific IP multicast address. For location dependent MBS Session, Area Session Policy ID is used together with MBS Session ID to associate the AF Session information with the location dependent MBS Session in a specific MBS service area.
- QoS Flow binding: For an MBS Session, QoS Flow binding is the association of a PCC rule to a QoS Flow within an MBS Session. The MB-SMF performs QoS Flow binding for an MBS Session in the same way as the SMF for a PDU Session.
- The PCF should provision the same MBS policy information for all MBS service areas of a location dependent MBS Session.
- MBS policy information consists of:
- PCC rules for MBS Session are used to provide policy for QoS flows: The following PCC rule parameters defined in Table 6.3.1 of TS 23.503 [7] are applicable for MBS:
- Rule identifier.
- Service data flow detection: Precedence, Service data flow template (only for IP PDU traffic).
NOTE: If a unicast tunnel is used over the N6mb/Nmb9 interface to transport MBS data towards the MB-UPF (see Figure 8.2-1), the Service data flow template relates to the inner IP layer within the unicast tunnel.
- Policy Control: 5G QoS Identifier (5QI), DL-maximum bitrate, DL-guaranteed bitrate, ARP, Priority Level, Averaging Window, Maximum Data Burst Volume.
- Charging: Charging key (to indicate a rating group), metering method.
- Policy information can also be applicable for an entire MBS session. The following parameters defined for a PDU session in Table 6.4-1 of TS 23.503 [7] are applicable for an entire MBS session:
- Authorized Session-AMBR.
- Explicitly signalled QoS Characteristics.
- Policy Control Request Triggers for MBS Session are used to define the conditions when the MB-SMF shall interact again with the PCF to request an update of the policy information for the MBS session by providing information on the condition(s) that have been met. The following Policy Control Request Triggers are defined for MBS:
- MBS Session Update.
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6.10.2 MBS Session policy control data in UDR
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The policy control profile information may optionally be provided by the UDR at MBS Session establishment, using Nudr service for Data Set "Policy Data" and Data Subset "MBS Session policy control data", with the source specific multicast address used as MBS session ID or with AF Application identifier as data key is described in Table 6.10.2-1.
Table 6.10.2-1: MBS Session policy control information
Information element name
Description
Category
5QI(s)
Allowed 5QI(s) for a PCC rule of an MBS session (NOTE 1)
Optional
ARP
Highest ARP for any PCC rule of an MBS session (NOTE 1)
Optional
Session-AMBR
Maximum Session-AMBR for all Non-GBR QoS Flows of an MBS session (NOTE 1)
Optional
GBR
Maximum aggregated bitrate that can be provided across all GBR QoS Flows for an MBS session (NOTE 1)
Optional
NOTE 1: This information element may be used to decide whether to authorize received MBS Service Information.
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