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6.3.2.1 General
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A PC5 communication channel is used to carry the discovery message over PC5 and the discovery message over PC5 is differentiated from other PC5 messages by AS layer.
Both Model A and Model B discovery as defined in TS 23.303 [3] are supported:
- Model A uses a single discovery protocol message (Announcement).
- Model B uses two discovery protocol messages (Solicitation and Response).
Depicted in figure 6.3.2.1-1 is the procedure for 5G ProSe Direct Discovery with Model A.
Figure 6.3.2.1-1: 5G ProSe direct discovery with Model A
1. The Announcing UE sends an Announcement message. The Announcement message may include the Type of Discovery Message, ProSe Application Code or ProSe Restricted Code, security protection element, [metadata information]. The Application layer metadata information may be included as metadata in the Announcement message.
The Destination Layer-2 ID and Source Layer-2 ID used to send the Announcement message are specified in clause 5.8.1.2 and clause 5.8.1.3.
The Monitoring UE determines the Destination Layer-2 ID for signalling reception. The Destination Layer-2 ID is configured with the UE(s) as specified in clause 5.8.1.2.
Depicted in figure 6.3.2.1-2 is the procedure for 5G ProSe Direct Discovery with Model B.
Figure 6.3.2.1-2: 5G ProSe direct discovery with Model B
1. The Discoverer UE sends a Solicitation message. The Solicitation message may include Type of Discovery Message, ProSe Query Code, security protection element.
The Destination Layer-2 ID and Source Layer-2 ID used to send the Solicitation message are specified in clause 5.8.1.2 and clause 5.8.1.3.
How the Discoveree UE determines the Destination Layer-2 ID for signalling reception is specified in clause 5.8.1.2.
2. The Discoveree UE that matches the solicitation message responds to the Discoverer UE with the Response message. The Response message may include Type of Discovery Message, ProSe Response Code, security protection element, [metadata information]. The Application layer metadata information may be included as metadata in the Response message.
The Source Layer-2 ID used to send the Response message is specified in clause 5.8.1.3. The Destination Layer-2 ID is set to the Source Layer-2 ID of the received Solicitation message.
NOTE: Details of security protection element are specified in TS 33.503 [29].
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6.3.2.2 Group Member Discovery
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6.3.2.2.1 General
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Group Member Discovery is applicable to public safety use and commercial services. To perform Group Member Discovery, the UE is configured with the related information as described in clause 5.2.
Group Member Discovery is a form of restricted discovery in that only users that are affiliated with each other can discover each other (e.g. only users sharing the same Application Layer Group ID).
In the case of Public Safety use, the ProSe Restricted Code is not used for Group Member Discovery and pre-configured or provisioned information for the Discovery procedures as defined in clause 5.2 is used.
NOTE: The Group Member Discovery performed by Application Layer in coordination with Application Server is out of scope of this specification.
Both Model A and Model B discovery are supported:
- Model A uses a single discovery protocol message (Announcement).
- Model B uses two discovery protocol messages (Solicitation and Response).
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6.3.2.2.2 Procedure for Group Member Discovery with Model A
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Depicted in Figure 6.3.2.2.2-1 is the procedure for Group Member Discovery with Model A.
Figure 6.3.2.2.2-1: Group Member Discovery with Model A
1. The announcing UE sends a Group Member Discovery Announcement message. The Group Member Discovery Announcement message includes the Type of Discovery Message, Announcer Info and Application Layer Group ID (See clause 5.8.1).
The Destination Layer-2 ID and Source Layer-2 ID used to send the Group Member Discovery Announcement message are specified in clause 5.8.1.2 and clause 5.8.1.3.
The Monitoring UE determines the Destination Layer-2 ID for signalling reception as specified in clause 5.8.1.2.
NOTE: A UE may send multiple Group Member Discovery Announcement messages (Model A) if the UE belongs to more than one discovery group.
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6.3.2.2.3 Procedure for Group Member Discovery with Model B
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Depicted in Figure 6.3.2.2.3-1 is the procedure for Group Member Discovery with Model B.
Figure 6.3.2.2.3-1: Group Member Discovery with Model B
1. The discoverer UE sends a Group Member Discovery Solicitation message. The Group Member Discovery Solicitation message includes the Type of Discovery Message, Discoverer Info, Application Layer Group ID and optionally Target Info (see clause 5.8.1).
The Destination Layer-2 ID and Source Layer-2 ID used to send the Group Member Discovery Solicitation message are specified in clause 5.8.1.2 and clause 5.8.1.3.
How the Discoveree UE determines the Destination Layer-2 ID for signalling reception is specified in clause 5.8.1.2.
2. The discoveree UEs that match the values of the parameters (including Application Layer Group ID and Target Info) contained in the solicitation message, responds to the discoverer UE with a Group Member Discovery Response message. The Group Member Discovery Response message includes the Type of Discovery Message, Discoveree Info and Application Layer Group ID (see clause 5.8.1).
The Source Layer-2 ID used to send the Group Member Discovery Response message is specified in clause 5.8.1.3. The Destination Layer-2 ID is set to the Source Layer-2 ID of the received Group Member Discovery Solicitation message.
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6.3.2.3 5G ProSe UE-to-Network Relay Discovery
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6.3.2.3.1 General
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5G ProSe UE-to-Network Relay Discovery is applicable to both 5G ProSe Layer-3 and Layer-2 UE-to-Network relay discovery for public safety use and commercial services. To perform 5G ProSe UE-to-Network Relay Discovery, the 5G ProSe Remote UE and the 5G ProSe UE-to-Network Relay are pre-configured or provisioned with the related information as described in clause 5.1.
In 5G ProSe UE-to-Network Relay Discovery, the UEs use pre-configured or provisioned information for the relay discovery procedures as defined in clause 5.1.4.1.
The Relay Service Code (RSC) is used in the 5G ProSe UE-to-Network Relay discovery, to indicate the connectivity service the 5G ProSe UE-to-Network Relay provides to the 5G ProSe Remote UE. The RSCs (including the dedicated one(s) for emergency service) are configured on the 5G ProSe UE-to-Network Relay and the 5G ProSe Remote UE as defined in clause 5.1.4. The 5G ProSe UE-to-Network Relay and the 5G ProSe Remote UE are aware of whether a RSC is offering 5G ProSe Layer-2 or Layer-3 UE-to-Network Relay service and whether a RSC is for emergency service, based the policy as specified in clause 5.1.4. A 5G ProSe UE-to-Network Relay supporting multiple RSCs can advertise the RSCs using multiple discovery messages, with one RSC per discovery message.
NOTE: When the 5G ProSe UE-to-Network Relay can advertise the emergency RSC(s) is specified in clause 5.4.4.
Additional information not directly used for discovery can also be advertised using the PC5-D protocol stack in single or separate discovery messages of type "Relay Discovery Additional Information" as defined in clause 5.8.3.1.
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6.3.2.3.2 Procedure for 5G ProSe UE-to-Network Relay Discovery with Model A
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Depicted in Figure 6.3.2.3.2-1 is the procedure for 5G ProSe UE-to-Network Discovery with Model A.
Figure 6.3.2.3.2-1: 5G ProSe UE-to-Network Relay Discovery with Model A
1. The 5G ProSe UE-to-Network Relay sends a UE-to-Network Relay Discovery Announcement message. The UE-to-Network Relay Discovery Announcement message contains the Type of Discovery Message, Announcer Info and RSC and is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.3.
For 5G ProSe Layer-3 UE-to-Network Relay, the 5G ProSe Layer-3 UE-to-Network Relay shall only include a RSC in the UE-to-Network Relay Discovery Announcement when the S-NSSAI associated with that RSC belongs to the Allowed NSSAI of the UE-to-Network Relay.
The 5G ProSe Remote UE (1 to 3) determines the Destination Layer-2 ID for signalling reception. The Destination Layer-2 ID is configured with the UE(s) as specified in clause 5.1.4.1.
5G ProSe Remote UE (1 to 3) monitors announcement messages with the 5G ProSe UE-to-Network RSC corresponding to the desired services.
Optionally, the 5G ProSe UE-to-Network Relay may also send Relay Discovery Additional Information messages as defined in clause 6.5.1.3. The parameters contained in this message and the Source Layer-2 ID and Destination Layer-2 ID used for sending and receiving the message are described in clause 5.8.3.
The 5G ProSe Remote UE selects the 5G ProSe UE-to-Network Relay based on the information received in step 1.
NOTE: Access Stratum layer information used for 5G ProSe UE-to-Network Relay selection is specified in RAN specifications.
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6.3.2.3.3 Procedure for 5G ProSe UE-to-Network Relay Discovery with Model B
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Depicted in Figure 6.3.2.3.3-1 is the procedure for 5G ProSe UE-to-Network Relay Discovery with Model B.
Figure 6.3.2.3.3-1: 5G ProSe UE-to-Network Relay Discovery with Model B
1. The 5G ProSe Remote UE sends a 5G ProSe UE-to-Network Relay Discovery Solicitation message. The 5G ProSe UE-to-Network Discovery Solicitation message contains the Type of Discovery Message, Discoverer Info, RSC and optionally Target Info and is send using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.3. The 5G ProSe Remote UE discovering a 5G ProSe UE-to-Network Relay sends a solicitation message with the RSC which is associated to the desired connectivity service. The RSC is based on the Policy/Parameters specified in clause 5.1.4.1.
How the 5G ProSe UE-to-Network Relays (1 to 3) determine the Destination Layer-2 ID for signalling reception is specified in clause 5.8.3. The Destination Layer-2 ID is configured with the UE(s) as specified in clause 5.1.4.1.
2. If the RSC contained in the solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.4.1, of a 5G ProSe UE-to-Network Relay and the Target Info contained in the solicitation message, if any, matches the 5G ProSe UE-to-Network Relay, the 5G ProSe UE-to-Network Relays (e.g. 1 and 2) respond to the 5G ProSe Remote UE with a UE-to-Network Relay Discovery Response message. The 5G ProSe UE-to-Network Relay Discovery Response message contains the Type of Discovery Message, Discoveree Info and RSC and is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.3.
For 5G ProSe Layer-3 UE-to-Network Relay, the 5G ProSe UE-to-Network Relay shall only respond to a matching RSC in the UE-to-Network Relay Discovery Solicitation message when the S-NSSAI associated with that RSC belongs to the Allowed NSSAI of the 5G ProSe UE-to-Network Relay.
The 5G ProSe Remote UE selects the 5G ProSe UE-to-Network Relay based on the information received in step 2.
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6.3.2.4 5G ProSe UE-to-UE Relay Discovery
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6.3.2.4.1 General
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5G ProSe UE-to-UE Relay Discovery is applicable to both 5G ProSe Layer-3 and Layer-2 UE-to-UE Relay Discovery for public safety use and commercial services. To perform 5G ProSe UE-to-UE Relay Discovery, the 5G ProSe End UE and the 5G ProSe UE-to-UE Relay are pre-configured or provisioned with the related information as described in clause 5.1.
A Relay Service Code (RSC) is used in the 5G ProSe UE-to-UE Relay Discovery, to indicate the connectivity service the 5G ProSe UE-to-UE Relay provides to 5G ProSe End UEs. The RSCs are pre-configured or provisioned on the 5G ProSe UE-to-UE Relay and the 5G ProSe End UE as defined in clause 5.1. The 5G ProSe UE-to-UE Relay and the 5G ProSe End UE are aware of whether a RSC is offering 5G ProSe Layer-2 or Layer-3 UE-to-UE Relay service based on the UE-to-UE Relay Layer indicator as specified in clause 5.1. A 5G ProSe UE-to-UE Relay supporting multiple RSCs advertises the RSCs using multiple discovery messages, with one RSC per discovery message.
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6.3.2.4.2 Procedure for 5G ProSe UE-to-UE Relay Discovery with Model A
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Depicted in Figure 6.3.2.4.2-1 is the procedure for 5G ProSe UE-to-UE Discovery with Model A.
Figure 6.3.2.4.2-1: 5G ProSe UE-to-UE Relay Discovery with Model A
1. The 5G ProSe UE-to-UE Relay has discovered other UEs in proximity and obtains the Direct discovery set from other UEs in proximity per RSC. (e.g. via a previous 5G ProSe UE-to-UE Relay Discovery or via secure PC5 connection between 5G ProSe U2U Relay and 5G ProSe End UE (refer to TS 33.503 [29])).
2. The 5G ProSe UE-to-UE Relay sends a UE-to-UE Relay Discovery Announcement message. The UE-to-UE Relay Discovery Announcement message contains the Type of Discovery Message, User Info ID of the 5G ProSe UE-to-UE Relay, RSC and Direct discovery set including list of protected user info (i.e. Application Layer ID) received from the 5G ProSe End UEs supporting the RSC. The UE-to-UE Relay Discovery Announcement message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4.
The 5G ProSe UE-to-UE Relay shall only announce user info (i.e. Application Layer ID) of other UEs in proximity that did not include an Announce Prohibited Indication when they were previously discovered.
NOTE: 5G ProSe UE-to-UE Relay announces Direct discovery set from other UEs in proximity only if their PC5 signal strength measured by the 5G ProSe UE-to-UE Relay is above configured signal strength threshold as specified in TS 38.331 [16].
A 5G ProSe End UE monitors announcement messages from a 5G ProSe UE-to-UE Relay. The 5G ProSe End UEs determine the Destination Layer-2 ID for signalling reception as specified in clause 5.1.
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6.3.2.4.3 Procedure for 5G ProSe UE-to-UE Relay Discovery with Model B
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Depicted in Figure 6.3.2.4.3-1 is the procedure for 5G ProSe UE-to-UE Relay Discovery with Model B.
Figure 6.3.2.4.3-1: 5G ProSe UE-to-UE Relay Discovery with Model B
1. The discoverer 5G ProSe End UE (UE-1) sends a 5G ProSe UE-to-UE Relay Discovery Solicitation message. The 5G ProSe UE-to-UE Relay Discovery Solicitation message contains the Type of Discovery Message, RSC and the Direct Discovery set which includes the protected user info (i.e. Application Layer ID) of the discoverer 5G ProSe End UE (UE-1) and the discoveree 5G ProSe End UE (UE-2). The 5G ProSe UE-to-UE Relay Discovery Solicitation message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4.
A 5G ProSe UE-to-UE Relay determines the Destination Layer-2 ID for signalling reception as specified in clause 5.1.
The discoverer 5G ProSe End UE may include an Announce Prohibited Indication in the UE-to-UE Relay Discovery Solicitation message. If a 5G ProSe UE-to-UE Relay receives a Relay Discovery Solicitation message with an Announce Prohibited Indication it does not consider the 5G ProSe End UE as discovered during this procedure for inclusion in 5G ProSe UE-to-UE Relay Discovery with Model A, see clause 6.3.2.4.2, step 1.
2. If the RSC contained in the solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.5.1, of a 5G ProSe UE-to-UE Relay, the 5G ProSe UE-to-UE Relay sends a 5G ProSe UE-to-UE Relay Discovery Solicitation message. The 5G ProSe UE-to-UE Relay Discovery Solicitation message contains the Type of Discovery Message, the Direct Discovery set which includes the list of protected user info (i.e. Application Layer ID) of the discoverer 5G ProSe End UE (UE-1) and the discoveree 5G ProSe End UE (UE-2), User Info ID of UE-to-UE Relay, RSC. 5G ProSe UE-to-UE Relay Discovery Solicitation message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4.
A 5G ProSe End UE determines the Destination Layer-2 ID for signalling reception as specified in clause 5.1.
The 5G ProSe UE-to-UE Relay self-selects the Source Layer-2 ID as specified in clause 5.8.4.2.
3. If the RSC contained in the solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.5.1, of the discoveree 5G ProSe End UE (UE-2) and the discoveree 5G ProSe End UE (UE-2) matches the user info (i.e. Application Layer ID) of the discoveree 5G ProSe End UE (UE-2) contained in the solicitation message, then the discoveree 5G ProSe End UE (UE-2) responds to the 5G ProSe UE-to-UE Relay with a 5G ProSe UE-to-UE Relay Discovery Response message. The 5G ProSe UE-to-UE Relay Discovery Response message contains the Type of Discovery Message, RSC, the Direct Discovery set which includes the protected user info (i.e. Application Layer ID) of the discoverer 5G ProSe End UE (UE-1) and the discoveree 5G ProSe End UE (UE-2). The 5G ProSe UE-to-UE Relay Discovery Response message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4. If the discoveree 5G ProSe End UE (UE-2) receives multiple UE-to-UE Relay Discovery Solicitation messages from different 5G ProSe UE-to-UE Relays with the same RSC and the user info (i.e. Application Layer ID) of the discoveree 5G ProSe End UE (UE-2), it may choose to respond or not to a 5G ProSe UE-to-UE Relay (e.g. based on the PC5 signal strength of each message received).
The discoveree 5G ProSe End UE may include an Announce Prohibited Indication in the UE-to-UE Relay Discovery Response message. If a 5G ProSe UE-to-UE Relay receives a Relay Discovery Response message with an Announce Prohibited Indication it does not consider the 5G ProSe End UE as discovered during this procedure for inclusion in 5G ProSe UE-to-UE Relay Discovery with Model A, see clause 6.3.2.4.2, step 1.
4. The 5G ProSe UE-to-UE Relay sends a 5G ProSe UE-to-UE Relay Discovery Response message. The 5G ProSe UE-to-UE Relay Discovery Response message contains the Type of Discovery Message, User Info ID of UE-to-UE Relay, RSC, the Direct Discovery set which includes the list of protected user info (i.e. Application Layer ID) of the discoverer 5G ProSe End UE (UE-1) and the discoveree 5G ProSe End UE (UE-2). The 5G ProSe UE-to-UE Relay Discovery Response message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4.
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6.3.2.4.4 Candidate 5G ProSe UE-to-UE Relay Discovery
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This procedure for candidate 5G ProSe UE-to-UE Relay Discovery to support the negotiated Relay reselection as described in clause 6.7.4 when the discoverer End UE discovers a candidate 5G ProSe UE-to-UE Relay.
The procedure for 5G ProSe UE-to-UE Relay Discovery with Model B (see clause 6.3.2.4.3) is used with the following differences:
- Step 1: In the 5G ProSe UE-to-UE Relay Discovery Solicitation message the RSC and the User Info ID of a candidate 5G ProSe UE-to-UE Relay are included in the UE-to-UE Relay Discovery set and the Direct Discovery set is not included. If the 5G ProSe End UE receives the Layer-2 ID of the candidate 5G ProSe UE-to-UE Relay in a Link Modification Request message, it may set the Layer-2 ID of the candidate 5G ProSe UE-to-UE Relay as the Destination Layer-2 ID.
NOTE: The User Info ID of the candidate 5G ProSe UE-to-UE Relay and the user info (i.e. Application Layer ID) of the discoveree 5G ProSe End UE can be distinguished by the 5G ProSe UE-to-UE Relay as different IEs in the message.
- Step 2 and step 3 are skipped because Direct Discovery set is absent and the User Info ID of the candidate 5G ProSe UE-to-UE Relay in the received 5G ProSe UE-to-UE Relay Discovery Solicitation message matches that of the 5G ProSe UE-to-UE Relay.
- Step 4: If a 5G ProSe UE-to-UE Relay matches the User Info ID of a candidate 5G ProSe UE-to-UE Relay received in the 5G ProSe UE-to-UE Relay Discovery Solicitation then it sends the 5G ProSe UE-to-UE Relay Discovery Response (with the RSC received in step 1) and does not include the Direct Discovery set.
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6.3.2.4.5 Acquiring Direct discovery set by model A discovery
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The 5G ProSe UE-to-UE Relay may monitor Announcement messages from the 5G ProSe End UEs.
When receiving an Announcement message from a 5G ProSe End UE, the 5G ProSe UE-to-UE Relay may include the received protected user info (i.e. Application Layer ID) in the UE-to-UE Relay Discovery Announcement message as specified in clause 6.3.2.4.2.
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6.3.2.5 5G ProSe multi-hop UE-to-Network Relay Discovery
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6.3.2.5.1 General
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5G ProSe multi-hop UE-to-Network Relay Discovery is applicable to both 5G ProSe multi-hop Layer-3 and Layer-2 UE-to-Network relay discovery for public safety use and commercial services. To perform 5G ProSe multi-hop UE-to-Network Relay Discovery, the 5G ProSe Remote UE, the 5G ProSe Intermedidate UE-to-Network Relay and the 5G ProSe UE-to-Network Relay are (pre-)configured or provisioned with the related information as described in clause 5.1.4
The RSC is used in the 5G ProSe multi-hop UE-to-Network Relay discovery, to indicate the connectivity service the 5G ProSe Intermedidate UE-to-Network Relay and the 5G ProSe UE-to-Network Relay provide to the 5G ProSe Remote UE. The maximum number of hops is provisioned by the network to the 5G ProSe Remote UE, 5G ProSe Intermedidate UE-to-Network Relay and the 5G ProSe UE-to-Network Relay per RSC.
A 5G ProSe UE-to-Network Relay supporting multiple RSCs can advertise the RSCs using multiple discovery messages, with one RSC per discovery message.
Additional information not directly used for discovery can also be advertised using the PC5-D protocol stack in single or separate discovery messages of type "Relay Discovery Additional Information".
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6.3.2.5.2 Procedure for 5G ProSe multi-hop UE-to-Network Relay Discovery with Model A
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Figure 6.3.2.5.2-1 presents the procedures for 5G ProSe multi-hop UE-to-Network Relay Discovery using Model A discovery.
Figure 6.3.2.5.2-1: 5G ProSe multi-hop UE-to-Network Relay discovery procedure with Model A
0. The 5G ProSe Remote UE, the 5G ProSe Intermedidate UE-to-Network Relay and the 5G ProSe UE-to-Network Relay are (pre-)configured or provisioned with the related information to support multi-hop UE-to-Network Relay discovery, as specified in clause 5.1.4. If the 5G ProSe Remote UE, 5G ProSe Intermedidate UE-to-Network Relay and 5G ProSe UE-to-Network Relay belong to different PLMNs, their HPLMNs ensure that consistent configuraitons are provided.
1. If a 5G ProSe UE-to-Network Relay is successfully registered and authorized by the 5GS and has the configurations to operate multi-hop UE-to-Network Relay in the current region, it can start the discovery procedure. Otherwise, it shall not perfrom the 5G ProSe multi-hop UE-to-Network Relay discovery, i.e. not sending any announcement message.
2. The 5G ProSe UE-to-Network Relay sends a 5G ProSe UE-to-Network Relay Discovery Announcement message. To support multi-hop UE-to-Network Relay discovery, the 5G ProSe UE-to-Network Relay sets the Hop-Count to 1, sets the Announcer Info to its own User Info ID and sets the RSC according to the configuration as in clause 5.1.4.
3. The 5G ProSe Intermedidate UE-to-Network Relay creates a corresponding discovery entry based on the received 5G ProSe UE-to-Network Relay Discovery Announcement message, if the discovery message meets the AS layer criteria and the Hop-Count is less than the (pre-)configured maximum number of hops for the associated RSC and the optional Hop-Limit in the message.
The discovery entry includes the following information: RSC, (optional) Root Relay Info, Announcer Info, Hop-Count, (optional) Accumulated QoS for PC5 link, (optional) NCGI, (optional) RRC Container, (optional) Hop-Limit.
The Announcer Info is set to the Announcer Info of the received message. The Root Relay Info is set to the Root Relay Info of the reived message. The Hop-count is set to the value of the received message. The Accumulated QoS for PC5 link, if present in the received discovery message, will be updated based on the QoS of the PC5 link between the 5G ProSe Intermedidate UE-to-Network Relay and the sender of the message (e.g. sum of delay of each hop).
If an discovery entry already exist, i.e. with the same RSC and (optional) Root Relay Info and if the Hop-Count of the received message is less than the Hop-Count stored in the discovery entry, the 5G ProSe Intermedidate UE-to-Network Relay updates the discovery entry accordingly. The Announcer Info and Hop-Count are set to the Annoncer Info and Hop-Count of the newly received discovery message.
NOTE: Based on implementation, a 5G ProSe Intermedidate UE-to-Network Relay may decide to update the discovery entry based on the Accumulated QoS for PC5 link instead of the Hop-Count, or a combination of the two information elements.
4a. 5G ProSe Intermedidate UE-to-Network Relay sends a 5G ProSe UE-to-Network Relay Discovery Announcement message, using the information from the stored discovery entry. The Hop-Count value will be incremented by 1 and the Announcer Info is set to the User Info of the 5G ProSe Intermedidate UE-to-Network Relay.
When received by the 5G ProSe Remote UE, the information in the 5G ProSe UE-to-Network Relay Discovery Announcement message will be used for relay (re)selection, if the Hop-Count is less or equal to the (pre-)configured maximum number of hops for the associated RSC and the optional Hop-Limit in the message. The 5G ProSe Remote UE can also take the Accumulated QoS for PC5 link into account. For relay reselection, the Root Relay Info may be used to prioritize a relay offering the connection to the same 5G ProSe UE-to-Network Relay.
4b. 5G ProSe Intermedidate UE-to-Network Relay sends a 5G ProSe UE-to-Network Relay Discovery Announcement message, using the information from the stored discovery entry. This message may reach another 5G ProSe Intermedidate UE-to-Network Relay.
5. The 5G ProSe Intermedidate UE-to-Network Relay drops the received message if the Hop-Count is not less than the (pre-)configured maximum number of hops for the associated RSC and the optional Hop-Limit in the message.
6. The 5G ProSe Intermedidate UE-to-Network Relay sets a locally configured timer for each of the discovery entry based on implementation. If the 5G ProSe Intermedidate UE-to-Network Relay does not have an active PC5 link with the relay identfied by the Announcer Info and it does not receive any new announcement message from that relay when the timer expires, the 5G ProSe Intermedidate UE-to-Network Relay removes the corresponding discovery entry and stops sending related 5G ProSe UE-to-Network Relay Discovery Announcement message.
The 5G ProSe Intermediate UE-to-Network Relay shall establish a Layer-2 link with the parent Intermediate UE-to-Network Relay or the 5G ProSe UE-to-Network Relay identified by the Announcer Info in the discovery entry before sending the 5G ProSe UE-to-Network Relay Discovery Announcement message.
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6.3.2.5.3 Procedure for Multi-hop 5G ProSe UE-to-Network Relay Discovery with Model B
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Figure 6.3.2.5.3-1: General Procedures for 5G ProSe Multi-hop UE-to-Network Relay Discovery with Model B
1. The 5G ProSe Remote UE determines the Hop-Limit for discovery based on policy configuration (i.e. a mapping between maximum number of hops and RSC) or QoS requirements.
If the Hop-Limit is determined based on configuration associated with the RSC, the 5G ProSe Remote UE does not include the Hop-Limit in the Solicitation message. Otherwise, the 5G ProSe Remote UE includes the Hop-Limit in the Solicitation message.
2a. The 5G ProSe Remote UE sends a 5G ProSe UE-to-Network Relay Discovery Solicitation message. The 5G ProSe UE-to-Network Relay Discovery Solicitation message additionally contains following IEs compared with that in clause 6.3.2.3.3: an indication that multi-hop relay is supported, Hop-Count and Hop-Limit (optional).
The Target Info may contain the User Info ID of the UE-to-Network Relay and Intermediate UE-to-Network Relay(s).
3a. If an indication that multi-hop relay is supported is contained in the received Solicitation message, the RSC contained in the Solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.4.1a, of a 5G ProSe Intermediate UE-to-Network Relay and the Target Info matches the User Info ID of the 5G ProSe Intermediate UE-to-Network Relay (if any), the 5G ProSe Intermediate UE-to-Network Relay may decide to send a 5G ProSe UE-to-Network Relay Discovery Solicitation message.
The 5G ProSe Intermediate UE-to-Network Relay shall drop the received Solicitation message if the hop count (corresponding to the number of Relays included in the message) has reached the Hop-Limit of the received Solicitation message or the (pre)configured maximum number of hops associated with the RSC.
The 5G ProSe Intermediate UE-to-Network Relay may send a Response message when it has already found or established PC5 link with 5G ProSe UE-to-Network Relay(s), without sending Solicitation message. i.e. steps 4a-7a are skipped and step 8a is performed directly. The response message additionally contains the User Info ID of UE-to-Network Relay, path information to the UE-to-Network Relay which is an (ordered) list of User Info ID of intermediate UE-to-Network Relay(s).
If the same information on User Info IDs of Remote UE and UE-to-Network Relay is received from different ProSe UEs, the 5G ProSe Intermediate UE-to-Network Relay may select a Solicitation message to be sent to the next hop based on various criteria (e.g. hop count, delay, channel quality of received messages, etc.).
4a. A 5G ProSe Intermediate UE-to-Network Relay sends the Solicitation message, it additionally includes its own User Info ID in the message. i.e. the message contains the path information which is an (ordered) list of User Info ID and Layer-2 ID of Relays in the path that has relayed the Solicitation message. The hop count is increased by 1. The solicitation message may include Accumulated QoS for PC5 link (e.g. sum of delay of each hop).
The Accumulated QoS for PC5 link, if present in the received solicitation message, will be updated to include the QoS of the PC5 link between the 5G ProSe Intermediate Relay and its child UE (Intermediate Relay or Remote UE).
2b.-5b. The Solicitation message from the same Remote UE goes through a different ordered list of 5G ProSe Intermediate UE-to-Network Relays.
6-7. If the RSC contained in the solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.4.1, of the 5G ProSe UE-to-Network Relay and the Target Info matches the User Info ID of the 5G ProSe UE-to-Network Relay (if any), then the 5G ProSe UE-to-Network Relay responds to the 5G ProSe Intermediate UE-to-Network Relay with a 5G ProSe UE-to-Network Relay Discovery Response message. The 5G ProSe UE-to- Network Relay Discovery Response message additionally contains the path information compared with that in clause 6.3.2.3.3. The response message may include the received Accumulated QoS for PC5 link.
The 5G ProSe UE-to-Network Relay may choose the path based on e.g. the PC5 signal strength of each message received, hops to the Remote UE, the path information, Accumulated QoS for PC5 link, etc.
NOTE 1: It is up to implementation how the 5G ProSe UE-to-Network Relay decides when to send the Relay Discovery Response message.
8-9. When a 5G ProSe UE-to-Network Relay Discovery Response message is received, if the User Info ID of the receiving 5G ProSe Intermediate UE-to-Network Relay is included in the path information, the 5G ProSe Intermediate UE-to-Network Relay forwards the 5G ProSe UE-to-Network Relay Discovery Response message. The Response message additionally contains the path information which is a list of User Info IDs of 5G ProSe Intermediate UE-to-Network Relay(s) and the remote UE in the order (starting with the remote UE and ending with the last 5G ProSe Intermediate UE-to-Network Relay) of position in the path. Based on the path information, the Relay Discovery Response message is forwarded along the path, where each 5G ProSe Intermediate UE-to-Network Relay determines the next hop information (e.g. User Info ID and Layer-2 ID) to forward the Relay Discovery Response message. The response message may include the received Accumulated QoS for PC5 link.
10. If the Remote UE receives multiple Discovery Response messages within a pre-configured time window, it may perform relay path selection based on e.g. path information, the PC5 signal strength between Remote UE and its neighbour Intermediate UE-to-Network Relay, Accumuled QoS for PC5 link and the number of hops to the 5G ProSe UE-to-Network Relay.
NOTE 2: If the 5G ProSe Remote UE does not receive any response after a pre-configured time, based on application requirement, it may increase the Hop-Limit and send the discovery message again.
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6.3.2.5.4 Additional parameters announcement procedure over 5G ProSe multi-hop UE-to-Network Relay
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Additional parameters announcement procedure outlined in figure 6.3.2.5.4-1 is used by a 5G ProSe Remote UE to request a 5G ProSe UE-to-Network Relay to announce additional parameters (using Model A). The Additional parameters announcement procedure specified in clause 6.5.1.3 is used with the following differences described in the procedure below.
Figure 6.3.2.5.4-1: Procedure for additional parameters announcement for multi-hop UE-to-Network relaying
1. 5G ProSe Remote UE has discovered a 5G ProSe UE-to-Network Relay for connectivity to the network as described in clause 6.3.2.5.2 and requires additional parameters.
2. The 5G ProSe Remote UE sends to the 5G ProSe Intermediate UE-to-Network Relay an Additional Parameters Announcement Request including the following additional information to obtain additional parameters.
- Relay Service Code: information about the connectivity service provided by the 5G ProSe UE-to-Network Relay.
- Root Relay Info: identify information (i.e. User Info ID) of the 5G ProSe UE-to-Network Relay.
3-4. The Additional Parameters Announcement Request is sent up to the 5G ProSe UE-to-Network Relay.
5. The 5G ProSe UE-to-Network Relay acknowledges receipt of the request in step 4 with an Additional Parameters Announcement Response (Additional_Parameters_Announcement_Request_Refresh Timer).
6-7. The Additional Parameters Announcement Response is sent to the 5G ProSe Remote UE, relayed via the 5G ProSe Intermediate UE-to-Network Relay.
8. The 5G ProSe UE-to-Network Relay reuses the Relay Discovery Additional Information message as defined in clause 5.8.3 with the following additional information:
- Hop-Count: the value is set to 1.
The Destination Layer-2 ID to send the Relay Discovery Additional Information message is selected based on the configuration as described in clause 5.1.4.1.
9. The 5G ProSe Intermediate UE-to-Network Relay forwards the Relay Discovery Additional Information message. The 5G ProSe Intermediate UE-to-Network Relay updates the Hop-Count as below and may include additional information, Announcer Info and NCGI of 5G ProSe Intermediate UE-to-Network Relay if its NCGI is available:
- Hop-Count: the value of the received Relay Discovery Additonal Information message is incremented by 1.
- Announcer Info of 5G ProSe Intermediate UE-to-Network Relay: identity information (i.e. User Info ID) of the 5G ProSe Intermediate UE-to-Network Relay transmitting this message.
- NCGI of 5G ProSe Intermediate UE-to-Network Relay: indicates the NCGI of the serving cell of the 5G ProSe Intermediate UE-to-Network Relay.
10. The 5G ProSe Intermediate UE-to-Network Relay forwards the Relay Discovery Additional Information message, with the Hop-Count incremented. The 5G ProSe Intermediate UE-to-Network Relay shall not forward the Relay Discovery Additional Information message if the Hop-Count is bigger than the configured maximum number of hops.
11. The 5G ProSe UE-to-Network Relay detects new or updated additional parameters.
12-14. Same as steps 8-10.
If the 5G ProSe Intermediate UE-to-Network Relay connected to 5G ProSe UE-to-Network Relay detects new or updated additional parameters (e.g. due to change of its serving cell, moving into network coverage), it may send a Relay Discovery Additional Information message including the new or updated additional parameters. In this case, the 5G ProSe Intermediate UE-to-Network Relay acts as the 5G ProSe UE-to-Network Relay in figure 6.3.2.5.4-1, i.e. to send Relay Discovery Additional Information message. The 5G ProSe Intermediate UE-to-Network Relay also keeps a record of the additional parameters from the 5G ProSe UE-to-Network Relay.
NOTE: The NCGI of the 5G ProSe Intermediate UE-to-Network Relay connected to 5G ProSe UE-to-Network Relay can be used as supplementary by the 5G ProSe Remote UE and not provided to the network side from the 5G ProSe Remote UE.
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6.3.2.6 5G ProSe Mulit-hop UE-to-UE Relay Discovery
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6.3.2.6.1 General
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The 5G ProSe Multi-hop UE-to-UE Relay discovery may use one of the two different types of discovery operations, i.e. discovery for IP PDU type and discovery for non-IP PDU type, depends on the RSC for the discovery.
5G ProSe Multi-hop UE-to-UE Relay discovery of IP PDU type only needs to discover the presence of the 5G ProSe Multi-hop UE-to-UE Relay. The discovery of the target 5G ProSe End UEs are performed via DNS queries after establshing a link with the 5G ProSe Multi-hop UE-to-UE Relay(s). This procedure is also used by Multi-hop UE-to-UE Relay(s) among themselves in order to join/create MANET network. The details of the procedure are defined in clause 6.3.2.6.2.
5G ProSe Multi-hop UE-to-UE Relay discovery of non-IP (Ethernet or Unstructured) PDU type is for the discovery of a target 5G ProSe End UE and the corresponding routes. The procedures for 5G ProSe Multi-hop UE-to-UE Relay discovery Model A/B for non-IP PDUs (e.g. Ethernet or Unstructured) are defined in clause 6.3.2.6.3.
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6.3.2.6.2 Procedure for 5G ProSe Multi-hop UE-to-UE Relay discovery of IP PDU type
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Depicted in figure 6.3.2.6.2-1 is the procedure for 5G ProSe Multi-hop UE-to-UE Relay discovery of IP PDU type, with Model A.
Figure 6.3.2.6.2-1: 5G ProSe Multi-hop UE-to-UE Relay Discovery of IP PDU type with Model A
1. The 5G ProSe Multi-hop UE-to-UE Relay is configured to operate IP PDU type of discovery based on the indication associated with the RSC, as defined in defined in clause 5.1.5.1.
2. The 5G ProSe Multi-hop UE-to-UE Relay sends a Multi-hp UE-to-UE Relay Discovery Announcement message. This message contains the Type of Discovery Message, User Info ID of the 5G ProSe Multi-hop UE-to-UE Relay and the RSC, as defined in clause 5.8.6.2.
The 5G ProSe Multi-hop UE-to-UE Relay self generates a Source Layer-2 ID and decides a Destiantion Layer-2 ID as defined in clause 5.8.6.2.
The 5G ProSe End UE(s) or other 5G ProSe Multi-hop UE-to-UE Relay(s) in proximity monitoring the same RSC may receive the announcement message and process it accordingly, e.g. initiates a Layer-2 Link establishment with the announcing 5G ProSe Multi-hop UE-to-UE Relay.
Depicted in figure 6.3.2.6.2-2 is the procedure for 5G ProSe Multi-hop UE-to-UE Relay discovery of IP PDU type, with Model B. A 5G ProSe Multi-hop UE-to-UE Relay may also use the procedure, i.e. send the Multi-hop UE-to-UE Relay Discovery Solicitation (taking the role of the 5G ProSe End UE (Discoverer)), if it needs to discover other 5G ProSe Multi-hop UE-to-UE Relays.
Figure 6.3.2.6.2-2: 5G ProSe Multi-hop UE-to-UE Relay Discovery of IP PDU type with Model B
1. The 5G ProSe End UE is configured to operate IP PDU type of discovery based on the indication associated with the RSC, as defined in defined in clause 5.1.5.1.
2. The 5G ProSe End UE sends a Multi-hop UE-to-UE Relay Discovery Solicitation message. This message contains the Type of Discovery Message, RSC and (optional) User Info ID of the 5G ProSe Multi-hop UE-to-UE Relay, as defined in clause 5.8.6.2.
The User Info ID of the 5G ProSe Multi-hop UE-to-UE Relay is only included if the 5G ProSe End UE wants to find a specific target relay.
The 5G ProSe End UE self generates a Source Layer-2 ID and decides a Destination Layer-2 ID as defined in clause 5.8.6.2.
3. The 5G ProSe Multi-hop UE-to-UE Relay-1 may send a Multi-hop UE-to-UE Relay Discovery Response message, if the RSC contained in the solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.5.1. If User Info ID is included in the solicitation message, 5G ProSe Multi-hop UE-to-UE Relay-1 only sends the response message when it matches its own User Info ID.
The 5G ProSe Multi-hop UE-to-UE Relay-1 in proximity may decide not to respond if the criteria are not met, or due to UE local configurations.
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6.3.2.6.3 Procedure for 5G ProSe Multi-hop UE-to-UE Relay discovery of non-IP PDU type
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6.3.2.6.3.1 Procedure for Multi-hop 5G ProSe UE-to-UE Relay Discovery of non-IP PDU type with Model A
Depicted in Figure 6.3.2.6.3.1-1 is the procedure for Multi-hop 5G ProSe UE-to-UE Relay Discovery of non-IP PDU type with Model A.
Figure 6.3.2.6.3.1-1: 5G ProSe multi-hop UE-to-UE Relay Discovery of non-IP PDU type with Model A
1. The 5G ProSe UE-to-UE Relay has discovered End UEs in proximity and obtains the Direct discovery set from End UEs in proximity per RSC. (e.g. via a previous 5G ProSe UE-to-UE Relay Discovery or via secure PC5 connection between 5G ProSe U2U Relay and 5G ProSe End UE (refer to TS 33.503 [29])). 5G ProSe UE-to-UE Relay may also get the Hop-Limit from End UEs.
2. The 5G ProSe UE-to-UE Relay sends a UE-to-UE Relay Discovery Announcement message. The UE-to-UE Relay Discovery Announcement message contains the User Info ID of itself, a list of protected user info of End UEs, a list of paths indicated by an (ordered) list of User Info ID of Relays (initially it only contains the User Info ID of UE-to-UE Relay1 in the figure), hop count (which is set to 1 initially) corresponding to each protected user info in the message and optionally Hop-Limit corresponding to each protected user info in the message. Each path corresponds to a user info in the Direct Discovery set.
The UE-to-UE Relay Discovery Announcement message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4.
3. After receiving UE-to-UE Relay Discovery Announcement message(s) from another 5G ProSe UE-to-UE relay, a 5G ProSe UE-to-UE Relay checks the information associated to the received protected User Info(s). For each protected user info in the received message, if the corresponding path does not include the User Info ID of the 5G ProSe UE-to-UE Relay and the hop count is less than the corresponding Hop-Limit, the relay will add the protected user info into its own list of protected user info to be sent (if it is not added before) and add its own User Info ID into the path(s) of the corresponding protected user info(s) and increase the hop count by 1. If the relay already has the protected user info in its own list of protected user info to be sent with the hop count less than or equal to the received one, then it is up to relay's implementation to determine if add the protected user info again.
NOTE: Based on implementation, Relay UEs can determine if two protected user infos are identical, e.g. by comparing the protected user info bit by bit if it is encrypted.
A 5G ProSe UE-to-UE Relay may associate the User Info ID and Layer-2 ID of neighbour UE-to-UE Relay(s) according to the Announcement message. The association may be used in the subsequent Link Management procedures.
4. A 5G ProSe End UE or a 5G ProSe UE-to-UE Relay monitors Announcement message from a 5G ProSe UE-to-UE Relay. The 5G ProSe End UEs and 5G ProSe UE-to-UE Relays determine the Destination Layer-2 ID for signalling reception as specified in clause 5.1.
6.3.2.6.3.2 Procedure for Multi-hop 5G ProSe UE-to-UE Relay Discovery of non-IP PDU type with Model B
Depicted in Figure 6.3.2.6.3.2-1 is the procedure for Multi-hop 5G ProSe UE-to-UE Relay Discovery of non-IP PDU type with Model B.
Figure 6.3.2.6.3.2-1: Multi-hop 5G ProSe UE-to-UE Relay Discovery of non-IP PDU type with Model B
1. The Source End UE determines the Hop-Limit for discovery based on policy configuration (i.e. a mapping between Hop-Limit and RSC) or QoS parameters.
If the Hop-Limit is determined based on RSC, the Source End UE may not include the Hop-Limit in the Solicitation message. Otherwise, the Source End UE includes the Hop-Limit in the Solicitation message.
2a. The Source End UE sends a 5G ProSe UE-to-UE Relay Discovery Solicitation message. The 5G ProSe UE-to-UE Relay Discovery Solicitation message contains the information as described in clause 5.8.6.3.
3a. If the RSC contained in the solicitation message matches any of the (pre)configured RSC(s) of a 5G ProSe UE-to-UE Relay, the 5G ProSe UE-to-UE Relay may decide to send a 5G ProSe UE-to-UE Relay Discovery Solicitation message.
The 5G ProSe UE-to-UE Relay should drop the received Solicitation message when its own User Info ID is contained in the Path information of received Solicitation message, or if the hop count (i.e. the number of Relays included in the message) has reached the Hop-Limit of the received Solicitation message. The Hop-Limit may be obtained from the Solicitation message or may be decided based on RSC if it is not obtained from the message.
If the same Direct Discovery Set is received from different 5G ProSe-enabled UEs, the 5G ProSe UE-to-UE Relay may select a Solicitation message to be sent to the next hop based on various criteria (e.g. hop count, delay, channel quality of received messages, etc.).
NOTE 1: If the Source End UE does not receive any response after a timeout, based on application requirement, it may increase the Hop-Limit and send the discovery message again.
NOTE 2: Based on implementation, Relay UEs can decide to send the discovery message with the same direct discovery set at most once in order to control the total number of discovery messages transferred among Relays. To determine the identical direct discovery set, the Relay UE can compare the direct discovery set bit by bit if it is encrypted, or check the source End UE and target End UE User info if the direct discovery set is not encrypted.
4a. A 5G ProSe UE-to-UE Relay sends a Solicitation message, it additionally includes its own User Info ID in the message. i.e. the message contains the path information which is an (ordered) list of User Info ID of Relays in the path that has sent the Solicitation message. The hop count is increased by 1.
2b.-5b. (Optional) Another transmission path of the Solicitation message.
6-7a. If the RSC contained in the solicitation message matches any of the (pre)configured RSC(s) of the Target 5G ProSe End UE and the Target 5G ProSe End UE matches the user info (i.e. Application Layer ID) of the discoveree 5G ProSe End UE contained in the solicitation message, then the Target 5G ProSe End UE responds to the 5G ProSe UE-to-UE Relay with a 5G ProSe UE-to-UE Relay Discovery Response message. The 5G ProSe UE-to-UE Relay Discovery Response message contains the information as described in clause 5.8.6.3. The 5G ProSe UE-to-UE Relay decides the information (e.g. User Info ID, Layer-2 ID) to unicast the Relay Discovery Response message based on its own User Info ID and the path information contained in the received message.
The Target 5G ProSe End UE may choose a path and sends Response message to 5G ProSe UE-to-UE Relay(s) based on e.g. the PC5 signal strength of each solicitation message received, the number of hops to the Source End UE, the path information, order in which solicitation message were received, etc.
8a. A 5G ProSe UE-to-UE Relay sends a 5G ProSe UE-to-UE Relay Discovery Response message. A 5G ProSe UE-to-UE Relay may associate the User Info ID and Layer-2 ID of neighbour UE-to-UE Relay(s) according to the Response message. The association may be used in the subsequent Link Management procedures.
7b.-9b. (Optional) Transmission of another Response message corresponding to another path.
10. The Source End UE may perform the UE-to-UE Relay(s)/path selection for subsequent Link Management procedures based on e.g. the PC5 signal strength of the received Response messages, the number of hops to Target 5G ProSe End UE.
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6.4 5G ProSe Direct Communication
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6.4.1 Broadcast mode 5G ProSe Direct Communication
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To perform 5G ProSe direct communication over PC5 reference point in broadcast mode operation, the UE is configured with the related information as described in clause 5.1.3.
Figure 6.4.1-1 shows the procedure for broadcast mode of 5G ProSe direct communication over PC5 reference point.
Figure 6.4.1-1: Procedure for Broadcast mode of 5G ProSe direct communication over PC5 reference point
1. The ProSe layer of receiving UE(s) determines the following for the broadcast mode communication reception:
- the destination Layer-2 ID for broadcast reception as specified in clause 5.8.2.2;
- the PC5 QoS parameters for this broadcast ProSe service as specified in clause 5.6.1; and
- the NR Tx Profile based on the configuration as specified in clause 5.1.3.1.
The destination Layer-2 ID, the NR Tx Profile and the PC5 QoS parameters are passed down to the AS layer of receiving UE(s) for the reception.
The AS layer of receiving UE(s) determines the PC5 DRX parameter values as specified in clause 5.13.
2. The transmitting UE ProSe application layer provides data unit and may provide ProSe Application Requirements specified in clause 5.6.1 to ProSe layer.
3. The ProSe layer of transmitting UE determines the following for the broadcast mode communication transmission:
- the destination Layer-2 ID for broadcast as specified in clause 5.8.2.2;
- the PC5 QoS parameters for this broadcast ProSe service as specified in clauses 5.6.1; and
- the NR Tx Profile based on the configuration as specified in clause 5.1.3.1.
The transmitting UE self-assigns the source Layer-2 ID as specified in clause 5.8.2.2.
The source Layer-2 ID, the destination Layer-2 ID, the NR Tx Profile and the PC5 QoS parameters are passed down to the AS layer of transmitting UE for the transmission.
The AS layer of transmitting UE determines the PC5 DRX parameter values as specified in clause 5.13.
4. The transmitting UE sends the ProSe data using the source Layer-2 ID and the destination Layer-2 ID.
NOTE: In step 4, there is only one broadcast message from the transmitting UE.
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6.4.2 Groupcast mode 5G ProSe Direct Communication
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Figure 6.4.2-1 shows the procedure for groupcast mode of 5G ProSe Direct Communication.
Figure 6.4.2-1: Procedure for groupcast mode 5G ProSe Direct communication
Steps 1 to 3 are optional, e.g. applicable for Application Layer managed group. Groupcast mode ProSe Direct communication can be performed without steps 1 to 3 based on the provisioned parameters as defined in clause 5.1.3.1.
1. ProSe Group management is carried out at ProSe application layer. This may be performed in coordination with ProSe Application Server.
Group Member Discovery parameters as specified in clause 5.1.2.1 can be provisioned in ME from PCF or configured in UICC or provided from ProSe Application Server to the UE.
2. Each UE may perform a ProSe group member discovery (similar to the procedures in clause 6.3.2.2) that is restricted only to users sharing the same Application Layer Group ID obtained in step 1.
The Application layer discovery messages including the Application Layer Group ID for Application Layer managed group may be exchanged between UEs to discover each other sharing the same Application Layer Group ID. When the group is formed, the Application layer discovery message including group size and member ID may be provided by one UE to all other UEs. The Application layer discovery messages may be included as metadata in a PC5 direct discovery message.
3. The ProSe Application layer may provide group identifier information (i.e. the Application Layer Group ID discovered based on discovery messages exchanged in step 2) as specified in clause 5.8.2.3.
The ProSe application layer may also provide ProSe Application Requirements for this communication.
If the ProSe application layer does not provide ProSe Application Requirements, the ProSe layer determines the PC5 QoS parameters based on the mapping of ProSe service to PC5 QoS parameters as specified in clause 5.1.3.1.
The ProSe application layer may provide a group size and a member ID (optionally based on discovery messages exchanged in step 2) as specified in clause 5.3.3 for Application Layer managed group.
4. The ProSe layer of transmitting UE self-assigns a source Layer-2 ID and determines the following for the groupcast mode communication transmission:
- a destination Layer-2 ID as specified in clauses 5.8.2.1 and 5.8.2.3.
- The PC5 QoS parameters for this groupcast mode communication as specified in clause 5.6.1.
- the NR Tx Profile based on the configuration as specified in clause 5.1.3.1.
The source Layer-2 ID, destination Layer-2 ID, the NR Tx Profile and the PC5 QoS parameters are passed down to the AS layer of transmitting UE for the groupcast mode communication transmission.
The ProSe layer of receiving UE(s) determines the following for the groupcast mode communication reception:
- destination Layer-2 ID as specified in clauses 5.8.2.1 and 5.8.2.3;
- the PC5 QoS parameters for this groupcast mode communication as specified in clause 5.6.1; and
- the NR Tx Profile based on the configuration as specified in clause 5.1.3.1.
The destination Layer-2 ID, the NR Tx Profile and the PC5 QoS parameters are passed down to the AS layer of receiving UE(s) for the reception.
If the group size and the member ID for Application Layer managed group are provided by the ProSe application layer, the ProSe layer passes them to the AS layer as described in clause 5.3.3.
The AS layer of transmitting UE and the AS layer of receiving UE(s) determine the PC5 DRX parameter values as specified in clause 5.13.
5. Transmitting UE sends the ProSe data using the source Layer-2 ID and the destination Layer-2 ID.
NOTE: In step 5, there is only one groupcast message from the transmitting UE. That is, all receiving UEs can receive the groupcast message directly from the transmitting UE.
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6.4.3 Unicast mode 5G ProSe Direct Communication
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6.4.3.1 Layer-2 link establishment over PC5 reference point
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To perform unicast mode of ProSe Direct communication over PC5 reference point, the UE is configured with the related information as described in clause 5.1.3.
Figure 6.4.3.1-1 shows the layer-2 link establishment procedure for the unicast mode of ProSe Direct communication over PC5 reference point.
Figure 6.4.3.1-1: Layer-2 link establishment procedure
1. The UE(s) determine the destination Layer-2 ID for signalling reception for PC5 unicast link establishment as specified in clause 5.8.2.4.
2. The ProSe application layer in UE-1 provides application information for PC5 unicast communication. The application information includes the ProSe Service Info, UE's Application Layer ID. The target UE's Application Layer ID may be included in the application information.
The ProSe application layer in UE-1 may provide ProSe Application Requirements for this unicast communication. UE-1 determines the PC5 QoS parameters and PFI as specified in clause 5.6.1.
If UE-1 decides to reuse the existing PC5 unicast link as specified in clause 5.3.4, the UE triggers the Layer-2 link modification procedure as specified in clause 6.4.3.4.
3. UE-1 sends a Direct Communication Request message to initiate the unicast layer-2 link establishment procedure. The Direct Communication Request message includes:
- Source User Info: the initiating UE's Application Layer ID (i.e. UE-1's Application Layer ID).
- If the ProSe application layer provided the target UE's Application Layer ID in step 2, the following information is included:
- Target User Info: the target UE's Application Layer ID (i.e. UE-2's Application Layer ID).
- ProSe Service Info: the information about the ProSe identifier(s) requesting Layer-2 link establishment.
- Security Information: the information for the establishment of security.
NOTE 1: The Security Information and the necessary protection of the Source User Info and Target User Info are defined in TS 33.503 [29].
The source Layer-2 ID and destination Layer-2 ID used to send the Direct Communication Request message are determined as specified in clauses 5.8.2.1 and 5.8.2.4. The destination Layer-2 ID may be broadcast or unicast Layer-2 ID. When unicast Layer-2 ID is used, the Target User Info shall be included in the Direct Communication Request message.
UE-1 sends the Direct Communication Request message via PC5 broadcast or unicast using the source Layer-2 ID and the destination Layer-2 ID.
A default PC5 DRX configuration may be used for transmitting and receiving of this message (see TS 38.300 [12]).
4. Security with UE-1 is established as below:
4a. If the Target User Info is included in the Direct Communication Request message, the target UE, i.e. UE-2, responds by establishing the security with UE-1.
4b. If the Target User Info is not included in the Direct Communication Request message, the UEs that are interested in using the announced ProSe Service(s) over a PC5 unicast link with UE-1 responds by establishing the security with UE-1.
NOTE 2: The signalling for the Security Procedure is defined in TS 33.503 [29].
When the security protection is enabled, UE-1 sends the following information to the target UE:
- If IP communication is used:
- IP Address Configuration: For IP communication, IP address configuration is required for this link and indicates one of the following values:
- "DHCPv4 server" if only IPv4 address allocation mechanism is supported by the initiating UE, i.e. acting as a DHCPv4 server; or
- "IPv6 Router" if only IPv6 address allocation mechanism is supported by the initiating UE, i.e. acting as an IPv6 Router; or
- "DHCPv4 server & IPv6 Router" if both IPv4 and IPv6 address allocation mechanism are supported by the initiating UE; or
- "address allocation not supported" if neither IPv4 nor IPv6 address allocation mechanism is supported by the initiating UE.
- Link-Local IPv6 Address: a link-local IPv6 address formed locally based on RFC 4862 [17] if UE-1 does not support the IPv6 IP address allocation mechanism, i.e. the IP Address Configuration indicates" address allocation not supported".
- QoS Info: the information about PC5 QoS Flow(s). For each PC5 QoS Flow, the PFI and the corresponding PC5 QoS parameters (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifier(s).
- Optional PC5 QoS Rule(s).
The source Layer-2 ID used for the security establishment procedure is determined as specified in clauses 5.8.2.1 and 5.8.2.4. The destination Layer-2 ID is set to the source Layer-2 ID of the received Direct Communication Request message.
Upon receiving the security establishment procedure messages, UE-1 obtains the peer UE's Layer-2 ID for future communication, for signalling and data traffic for this unicast link.
5. A Direct Communication Accept message is sent to UE-1 by the target UE(s) that has successfully established security with UE-1:
5a. (UE oriented Layer-2 link establishment) If the Target User Info is included in the Direct Communication Request message, the target UE, i.e. UE-2 responds with a Direct Communication Accept message if the Application Layer ID for UE-2 matches.
5b. (ProSe Service oriented Layer-2 link establishment) If the Target User Info is not included in the Direct Communication Request message, the UEs that are interested in using the announced ProSe Service(s) respond to the request by sending a Direct Communication Accept message (UE-2 and UE-4 in Figure 6.4.3.1-1).
The Direct Communication Accept message includes:
- Source User Info: Application Layer ID of the UE sending the Direct Communication Accept message.
- QoS Info: the information about PC5 QoS Flow(s). For each PC5 QoS Flow, the PFI and the corresponding PC5 QoS parameters requested by UE-1 (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifiers(s).
- Optional PC5 QoS Rule(s).
- If IP communication is used:
- IP Address Configuration: For IP communication, IP address configuration is required for this link and indicates one of the following values:
- " DHCPv4 server " if only IPv4 address allocation mechanism is supported by the target UE, i.e. acting as a DHCPv4 server; or
- "IPv6 Router" if only IPv6 address allocation mechanism is supported by the target UE, i.e. acting as an IPv6 Router; or
- "DHCPv4 server & IPv6 Router" if both IPv4 and IPv6 address allocation mechanism are supported by the target UE; or
- "address allocation not supported" if neither IPv4 nor IPv6 address allocation mechanism is supported by the target UE.
- Link-Local IPv6 Address: a link-local IPv6 address formed locally based on RFC 4862 [17] if the target UE does not support the IPv6 IP address allocation mechanism, i.e. the IP Address Configuration indicates "address allocation not supported" and UE-1 included a link-local IPv6 address in the security establishment in step 4. The target UE shall include a non-conflicting link-local IPv6 address.
If both UEs (i.e. the initiating UE and the target UE) are selected to use link-local IPv6 address, they shall disable the duplicate address detection defined in RFC 4862 [17].
NOTE 3: When either the initiating UE or the target UE indicates the support of IPv6 routing, the corresponding address configuration procedure would be carried out after the establishment of the layer 2 link and the link-local IPv6 addresses are ignored.
The ProSe layer of the UE that established PC5 unicast link passes the PC5 Link Identifier assigned for the unicast link and the PC5 unicast link related information down to the AS layer. The PC5 unicast link related information includes Layer-2 ID information (i.e. source Layer-2 ID and destination Layer-2 ID). This enables the AS layer to maintain the PC5 Link Identifier together with the PC5 unicast link related information.
Two UEs may negotiate the PC5 DRX configuration in the AS layer and the PC5 DRX parameter values can be configured per pair of source and destination Layer-2 IDs in the AS layer.
6. ProSe data is transmitted over the established unicast link as below:
The PC5 Link Identifier and PFI are provided to the AS layer, together with the ProSe data.
Optionally in addition, the Layer-2 ID information (i.e. source Layer-2 ID and destination Layer-2 ID) is provided to the AS layer.
NOTE 4: It is up to UE implementation to provide the Layer-2 ID information to the AS layer.
UE-1 sends the ProSe data using the source Layer-2 ID (i.e. UE-1's Layer-2 ID for this unicast link) and the destination Layer-2 ID (i.e. the peer UE's Layer-2 ID for this unicast link).
NOTE 5: PC5 unicast link is bi-directional, therefore the peer UE of UE-1 can send the ProSe data to UE-1 over the unicast link with UE-1.
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6.4.3.2 Link identifier update for a unicast link
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Figure 6.4.3.2-1 shows the link identifier update procedure for a unicast link. When privacy requirements are configured for a ProSe Identifier associated with the unicast link, identifiers used for the unicast mode of 5G ProSe communication over PC5 reference point (e.g. Application Layer ID, Source Layer-2 ID and IP address/prefix) shall be changed over time as specified in clauses 5.8.2.1 and 5.8.2.4. A UE may decide to change the identifiers for other reasons, e.g. application layer requirement. This procedure is used to update and exchange new identifiers between the source and the peer UEs for a unicast link before using the new identifiers, to prevent service interruptions. When there are privacy requirements as indicated above, this procedure is executed over a security protected unicast link.
If a UE has multiple unicast links using the same Application Layer IDs or Layer-2 IDs, the UE needs to perform the link identifier update procedure over each of the unicast links.
Figure 6.4.3.2-1: Link identifier update procedure
0. UE-1 and UE-2 have a unicast link established as described in clause 6.4.3.1.
1. UE-1 decides to change its identifier(s), e.g. due to the Application Layer ID change or upon expiry of a timer. UE-1 generates its new Layer-2 ID and sends a Link Identifier Update Request message to UE-2 using the old identifiers.
The Link Identifier Update Request message includes the new identifier(s) to use (including the new Layer-2 ID, Security Information, optionally the new Application Layer ID and optionally new IP address/prefix if IP communication is used). The new identifier(s) shall be cyphered to protect privacy if security is configured for the unicast link. After sending the Link Identifier Update Request message, if the UE-1 has data to send, UE-1 keeps sending data traffic to UE-2 with the old identifiers until UE-1 sends the Link Identifier Update Ack message to UE-2.
NOTE 1: The timer is running on per Source Layer-2 ID.
NOTE 2: When one of the two UEs acts as IPv6 router as described in clause 5.5.1.1 and the IP address/prefix also needs to be changed, the corresponding address configuration procedure would be carried out after the Link Identifier update procedure.
2. Upon reception of the Link Identifier Update Request message, UE-2 changes its identifier(s). UE-2 responds with a Link Identifier Update Response message which includes the new identifier(s) to use (including the new Layer-2 ID, Security Information, optionally the new Application Layer ID and optionally a new IP address/prefix if IP communication is used). The new identifier(s) shall be cyphered to protect privacy if security is configured for the unicast link. The Link Identifier Update Response message is sent using the old identifiers. UE-2 continues to receive traffic with the old Layer-2 ID from UE-1 until UE-2 receives traffic with the new Layer-2 ID from UE-1. After sending the Link Identifier Update Response message, UE-2 keeps sending data traffic to UE-1 with the old identifier, if UE-2 has data to send, until UE-2 receives the Link Identifier Update Ack message from UE-1.
3. Upon reception of the Link Identifier Update Response message, UE-1 responds with a Link Identifier Update Ack message. The Link Identifier Update Ack message includes the new identifier(s) from UE-2, as received on the Link Identifier Update Response message. The Link Identifier Update Ack message is sent using the old identifiers. UE-1 continues to receive traffic with the old Layer-2 ID from UE-2 until UE-1 receives traffic with the new Layer-2 ID from UE‑2.
4. The ProSe layer of UE-1 passes the PC5 Link Identifier for the unicast link and the updated Layer-2 IDs (i.e. new Layer-2 ID for UE-1 for the source and new Layer-2 ID of UE-2 for the destination) down to the AS layer. This enables the AS layer to update the provided Layer-2 IDs for the unicast link.
UE-1 starts using its new identifiers and UE-2's new identifiers for this unicast link.
5. Upon reception of the Link Identifier Update Ack message, the ProSe layer of UE-2 passes the PC5 Link Identifier for the unicast link and the updated Layer-2 IDs (i.e. new Layer-2 ID of UE-2 for the source and new Layer-2 ID for UE-1 for the destination) down to the AS layer. This enables the AS layer to update the provided Layer-2 IDs for the unicast link.
UE-2 starts using its new identifiers and UE-1's new identifiers for this unicast link.
NOTE 3: The Security Information in the above messages also needs to be updated at the same time as the Layer-2 IDs. This is defined in TS 33.503 [29].
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6.4.3.3 Layer-2 link release over PC5 reference point
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Figure 6.4.3.3-1 shows the layer-2 link release procedure over PC5 reference point.
Figure 6.4.3.3-1: Layer-2 link release procedure
0. UE-1 and UE-2 have a unicast link established as described in clause 6.4.3.1.
1. UE-1 sends a Disconnect Request message to UE-2 in order to release the layer-2 link and deletes all context data associated with the layer-2 link. The Disconnect Request message includes Security Information.
2. Upon reception of the Disconnect Request message, UE-2 shall respond with a Disconnect Response message and deletes all context data associated with the layer-2 link. The Disconnect Response message includes Security Information.
The ProSe layer of each UE informs the AS layer that the unicast link has been released. The ProSe layer uses PC5 Link Identifier to indicate the released unicast link. This enables the AS layer to delete the context related to the released unicast link.
NOTE: The Security Information in the above messages is defined in TS 33.503 [29].
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6.4.3.4 Layer-2 link modification for a unicast link
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Figure 6.4.3.4-1 shows the layer-2 link modification procedure for a unicast link. This procedure is used to:
- add new PC5 QoS Flow(s) in the existing PC5 unicast link.
- This covers the case for adding new PC5 QoS Flow(s) to the existing ProSe service(s) as well as the case for adding new PC5 QoS Flow(s) to new ProSe service(s).
- modify existing PC5 QoS Flow(s) in the existing PC5 unicast link.
- This covers the case for modifying the PC5 QoS parameters for existing PC5 QoS Flow(s).
- This also covers the case for removing the associated ProSe service(s) from existing PC5 QoS Flow(s) as well as the case for associating new ProSe service(s) with existing PC5 QoS Flow(s).
- remove existing PC5 QoS Flow(s) in the existing PC5 unicast link.
Figure 6.4.3.4-1: Layer-2 link modification procedure
0. UE-1 and UE-2 have a unicast link established as described in clause 6.4.3.1.
1. The ProSe application layer in UE-1 provides application information for PC5 unicast communication. The application information includes the ProSe Service Info and the initiating UE's Application Layer ID. The target UE's Application Layer ID may be included in the application information. If UE-1 decides to reuse the existing PC5 unicast link as specified in clause 5.3.4, so decides to modify the unicast link established with UE-2, UE-1 sends a Link Modification Request to UE-2.
The Link Modification Request message includes:
a) To add new PC5 QoS Flow(s) in the existing PC5 unicast link:
- QoS Info: the information about PC5 QoS Flow(s) to be added. For each PC5 QoS Flow, the PFI, the corresponding PC5 QoS parameters (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifier(s).
- Optional PC5 QoS Rule(s).
b) To modify PC5 QoS Flow(s) in the existing PC5 unicast link:
- QoS Info: the information about PC5 QoS Flow(s) to be modified. For each PC5 QoS Flow, the PFI, the corresponding PC5 QoS parameters (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifier(s).
- Optional PC5 QoS Rule(s).
c) To remove PC5 QoS Flow(s) in the existing PC5 unicast link:
- PFIs.
2. UE-2 responds with a Link Modification Accept message.
The Link Modification Accept message includes:
- For case a) and case b) described in step 1:
- QoS Info: the information about PC5 QoS Flow(s) requested by UE-1. For each PC5 QoS Flow, the PFI, the corresponding PC5 QoS parameters (i.e. PQI and conditionally other parameters such as MFBR/GFBR, etc.) and optionally the associated ProSe identifier(s).
- Optional PC5 QoS Rule(s).
The ProSe layer of each UE provides information about the unicast link modification to the AS layer. This enables the AS layer to update the context related to the modified unicast link.
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6.4.3.5 Layer-2 link maintenance over PC5 reference point
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The PC5 Signalling Protocol shall support keep-alive functionality that is used to detect if a particular PC5 unicast link is still valid. Either side of the PC5 unicast link can initiate the layer-2 link maintenance procedure (i.e. keep-alive procedure), based on for example triggers from the AS layer or internal timers. The UEs shall minimize the keep-alive signalling, e.g. cancel the procedure if data are successfully received over the PC5 unicast link.
Figure 6.4.3.5-1: Layer-2 link maintenance procedure
0. UE-1 and UE-2 have a unicast link established as described in clause 6.4.3.1.
1. Based on trigger conditions, UE-1 sends a Keep-alive message to UE-2 in order to determine the status of the PC5 unicast link.
NOTE 1: It is left to Stage 3 to determine the exact triggers for the keep-alive messages. For example, the trigger can be based on a timer associated with the Layer-2 link. The timer can be reset with a successful reception event defined by TS 38.300 [12].
2. Upon reception of the Keep-alive message, UE-2 responds with a Keep-alive Ack message.
The UE initiating the keep-alive procedure shall determine the follow-up actions based on the result of the signalling, e.g. proceed with implicit layer-2 link release.
NOTE 2: It is left to Stage 3 to determine the follow-up actions. For example, a successful reception event can also cancel the layer-2 link release if received in time.
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6.4.3.6 Layer-2 link management over PC5 reference point for 5G ProSe UE-to-Network Relay
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The Layer-2 link procedures over PC5 reference point for unicast mode 5G ProSe Direct Communication as depicted from clause 6.4.3.1 to clause 6.4.3.5 can be used for the PC5 reference point between 5G ProSe Remote UE and 5G ProSe UE-to-Network Relay, with the following differences and clarifications:
- The Layer-2 link modification procedure is applicable to ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay, other procedures are applicable to both ProSe Communication via 5G ProSe Layer-2 UE-to-Network Relay and ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay.
- The UE oriented Layer-2 link establishment is used with UE-1 representing the 5G ProSe Remote UE and UE-2 representing the 5G ProSe UE-to-Network Relay. For other procedures either UE-1 represents the 5G ProSe Remote UE and UE-2 represents the 5G ProSe UE-to-Network Relay, or UE-1 represents the 5G ProSe UE-to-Network Relay and UE-2 represents the 5G ProSe Remote UE. I.e. the Layer-2 link establishment is initiated by the 5G ProSe Remote UE, while other procedures may be initiated either by the 5G ProSe Remote UE or by the 5G ProSe UE-to-Network Relay.
For the UE oriented Layer-2 link establishment as described in the clause 6.4.3.1,
- In step 1, the 5G ProSe Remote UE determines the destination Layer-2 ID for PC5 unicast link establishment based on the unicast source Layer-2 ID of the selected 5G ProSe UE-to-Network Relay (as specified in clause 5.8.3) during UE-to-Network Relay discovery as specified in clause 6.3.2.3.
- In step 2, 5G ProSe Remote UE (UE-1) determines the Relay Service Code to be used. The Relay Service Code to be used is selected from the received Relay Service Code(s) during UE-to-Network Relay discovery as specified in clause 6.3.2.3.
- In step 3, 5G ProSe Remote UE (UE-1) sends a unicast Direct Communication Request message to the selected 5G ProSe UE-to-Network Relay. The destination Layer-2 ID used to send the Direct Communication Request message shall be unicast Layer-2 ID as determined in step 1. The Direct Communication Request message includes:
- Source User Info: the identity of the Remote UE requesting relay operation (i.e. User Info ID).
NOTE 1: The details of which additional identity/identities of the Remote UE to be included during Layer-2 link establishment are specified in TS 33.503 [29].
- Target User Info: the identity of the UE-to-Network Relay provided to the 5G ProSe Remote UE during UE-to-Network Relay Discovery procedure (i.e. User Info ID).
- Relay Service Code: indicates the connectivity service (which may be non-emergency or emergency) provided by the 5G ProSe UE-to-Network Relay as requested by the 5G ProSe Remote UE.
- Security Information: the information for the establishment of security.
NOTE 2: PC5 link for emergency RSC can be established with or without PC5 security; how to establish PC5 security link for emergency service is specified in TS 33.503 [29].
- In step 4 and step 5, step 4a and step 5a are performed if the 5G ProSe UE-to-Network Relay's identity matches the Target User Info and the Relay Service Code is one of the Relay Service Codes included during UE-to-Network Relay discovery as specified in clause 6.3.2.3. The Source User Info in the Direct Communication Accept message is the identity of the UE-to-Network Relay (i.e. User Info ID). In the case of 5G ProSe Layer-2 UE-to-Network Relay, the Remote UE does not send the IP Address Configuration, Link-Local IPv6 Address and QoS Info to the 5G ProSe Layer-2 UE-to-Network Relay and the Direct Communication Accept message does not include IP Address Configuration, Link-Local IPv6 Address and QoS Info. In the case of 5G ProSe Layer-3 UE-to-Network Relay, the Direct Communication Accept message does not include the IP Address Configuration indicating the value "address allocation not supported".
- In the case of 5G ProSe Layer-2 UE-to-Network Relay, step 6 is not performed.
For the link identifier update as described in the clause 6.4.3.2,
- Application Layer ID is replaced by User Info ID.
- In the case of 5G ProSe Layer-2 UE-to-Network Relay, the changed identifiers do not include IP address/prefix.
For the Layer-2 link release as described in the clause 6.4.3.3,
- In step1, if the Layer-2 link release procedure is initiated by the 5G ProSe UE-to-Network Relay, the Disconnect Request message may indicate the 5G ProSe UE-to-Network Relay is temporarily not available as described in clause 5.12.
NOTE 3: The form of the temporarily not available indication will be determined by stage 3.
- If the service authorization for acting as a 5G ProSe Remote UE or as a 5G ProSe UE-to-Network Relay is revoked, the 5G ProSe Remote UE or the 5G ProSe UE-to-Network Relay should initiate the release of the layer-2 link that the revoked authorization affects.
- A 5G ProSe Layer-2 Remote UE or a 5G ProSe Layer-2 UE-to-Network Relay initiates the release of the layer-2 link upon receiving an indication from its AS layer to trigger PC5 unicast link release as specified in TS 38.331 [16].
NOTE 4: The timing to initiates layer-2 link release is up to UE implementation.
A 5G ProSe Remote UE and a 5G ProSe UE-to-Network Relay shall set up a separate PC5 unicast links if an existing unicast link(s) was established with a different Relay Service Code or without a Relay Service Code.
NOTE 5: A single PC5 unicast link is established between a 5G ProSe Layer-2 UE-to-Network Relay and a 5G ProSe Layer-2 Remote UE, as specified in TS 38.300 [12], for supporting PDU sessions of the 5G ProSe Layer-2 Remote UE.
Each PC5 unicast link for 5G ProSe UE-to-Network Relay is associated with a Unicast Link Profile, which includes:
- User Info ID and Layer-2 ID of 5G ProSe Remote UE; and
- User Info ID and Layer-2 ID of 5G ProSe UE-to-Network Relay; and
- Relay Service Code; and
- In the case of 5G ProSe Layer-3 UE-to-Network Relay, the network layer protocol and the information about PC5 QoS Flow(s).
The Unicast Link Profile shall be updated accordingly after a Layer-2 link modification or Layer-2 link identifier update.
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6.4.3.7 Layer-2 link management over PC5 reference point for 5G ProSe UE-to-UE Relay
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6.4.3.7.1 Common part for Layer-2 link management over PC5 reference point for 5G ProSe UE-to-UE Relay
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For the 5G ProSe Communication via 5G ProSe UE-to-UE Relay as described in clause 6.7.1 and clause 6.7.2:
- The Direct Communication Request message over the first hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of source 5G ProSe End UE: the identity of the source 5G ProSe End UE requesting relay operation.
- User Info ID of 5G ProSe UE-to-UE Relay: the identity of the UE-to-UE Relay provided to the source 5G ProSe End UE during 5G ProSe UE-to-UE Relay Discovery procedure.
- user info (i.e. Application Layer ID) of target 5G ProSe End UE: the identity of the target 5G ProSe End UE provided to the source 5G ProSe End UE during UE-to-UE Relay Discovery procedure.
- (optional) Destination Layer-2 ID of target 5G ProSe End UE: the unicast destination Layer-2 ID of the target 5G ProSe End UE determined by the source 5G ProSe End UE as specified in clause 5.8.2.4.
- ProSe Service Info: the information about the ProSe identifier(s) requesting Layer-2 link establishment.
- RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
- Security Information: the information for the establishment of security for the first hop PC5 link establishment (see TS 33.503 [29]).
The Direct Communication Request message over the second hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of source 5G ProSe End UE.
- user info (i.e. Application Layer ID) of target 5G ProSe End UE.
- User Info ID of 5G ProSe UE-to-UE Relay.
- ProSe Service Info: the information about the ProSe identifier(s).
- RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
- Security Information: the information for the establishment of security for the second hop PC5 link establishment (see TS 33.503 [29]).
The Direct Communication Accept message over the second hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of target 5G ProSe End UE.
The Direct Communication Accept message over the first hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of target 5G ProSe End UE.
- User Info ID of 5G ProSe UE-to-UE Relay.
The Link Modification Request message over the first hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of target 5G ProSe End UE: the identity of the target 5G ProSe End UE provided to the source 5G ProSe End UE during UE-to-UE Relay Discovery procedure.
- (optional) Destination Layer-2 ID of target 5G ProSe End UE: the unicast destination Layer-2 ID of the target 5G ProSe End UE determined by the source 5G ProSe End UE as specified in clause 5.8.2.4.
The Link Modification Request message over the second hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of source 5G ProSe End UE.
- user info (i.e. Application Layer ID) of target 5G ProSe End UE.
The Link Modification Accept message over the second hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of target 5G ProSe End UE.
The Link Modification Accept message over the first hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of target 5G ProSe End UE.
Each end-to-end unicast link for 5G Layer-2 ProSe UE-to-UE Relay is associated with a Unicast Link Profile, which includes:
- user info (i.e. Application Layer ID) and Layer-2 ID of source 5G ProSe End UE; and
- user info (i.e. Application Layer ID) and Layer-2 ID of target 5G ProSe End UE; and
- Relay Service Code; and
- information about PC5 QoS Flow(s).
Each PC5 unicast link for 5G Layer-3 ProSe UE-to-UE Relay over the first hop is associated with a Unicast Link Profile, which includes:
- user info (i.e. Application Layer ID) and Layer-2 ID of the 5G ProSe End UE; and
- User Info ID and Layer-2 ID of 5G ProSe UE-to-UE Relay; and
- Relay Service Code; and
- the network layer protocol and the information about PC5 QoS Flow(s).
Each PC5 unicast link for 5G Layer-3 ProSe UE-to-UE Relay over the second hop is associated with a Unicast Link Profile, which includes:
- User Info ID and Layer-2 ID of 5G ProSe UE-to-UE Relay; and
- user info (i.e. Application Layer ID) and Layer-2 ID of the 5G ProSe End UE; and
- Relay Service Code; and
- the network layer protocol and the information about PC5 QoS Flow(s).
The Unicast Link Profile shall be updated accordingly after a Layer-2 link modification or Layer-2 link identifier update.
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6.4.3.7.2 Layer-2 link management over PC5 reference point for 5G ProSe Layer-2 UE-to-UE Relay
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For the 5G ProSe Communication via 5G ProSe Layer-2 UE-to-UE Relay as described in clause 6.7.2, the description in clause 6.4.3.7.1 applies. In the case of ProSe communication via 5G ProSe Layer-2 UE-to-UE Relay, an end-to-end Direct Communication Request message between the source 5G ProSe End UE and the target 5G ProSe End UE is transmitted after the per-hop connections have been established. The information from end-to-end unicast link profile in clause 6.4.3.7.1 is used for mapping of the destination Layer-2 ID as specified in TS 38.300 [12] and TS 38.331 [16].
The message contents over PC5 reference point for unicast mode 5G ProSe Direct Communication as depicted from clause 6.4.3.1 to clause 6.4.3.5 are same for the end-to-end connection between peer 5G ProSe End UEs.
When the 5G ProSe End UEs initiate End-to-End PC5-S signalling to release an end-to-end ProSe link via 5G ProSe Layer 2 UE-to-UE relay, the 5G ProSe End UE which has initiated the PC5-S release procedure triggers Layer-2 link modification or a Layer-2 link release procedure as described in clause 6.4.3.7 towards 5G ProSe Layer-2 UE-to-UE relay.
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6.4.3.7.3 Layer-2 link management over PC5 reference point for 5G ProSe Layer-3 UE-to-UE Relay
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For the 5G ProSe Communication via 5G ProSe Layer-3 UE-to-UE Relay as described in clause 6.7.1, the description in clause 6.4.3.7.1 applies with following differences and clarifications:
- In the Security Procedure of the first hop PC5 reference point, the source 5G ProSe Layer-3 End UE provides the IP Address Configuration or Link-Local IPv6 Address and QoS Info of the end-to-end QoS to the 5G ProSe Layer-3 UE-to-UE Relay. If the PC5 link is used for transferring Ethernet traffic, the source 5G ProSe Layer-3 End UE provides its Ethernet MAC address instead of IP related information.
- In the Security Procedure of the second hop PC5 reference point, the 5G ProSe Layer-3 UE-to-UE Relay provides the IP Address Configuration or Link-Local IPv6 Address and QoS Info of the second hop QoS to the target 5G ProSe End UE. If the PC5 link is used for transferring Ethernet traffic, the 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the source 5G ProSe Layer-3 End UE instead of IP related information.
- The Direct Communication Accept message over the second hop PC5 reference point additionally includes IP Address Configuration or Link-Local IPv6 Address and QoS Info of the second hop QoS. If the PC5 link is used for transferring Ethernet traffic, the target 5G ProSe Layer-3 End UE provides its Ethernet MAC address instead of IP related information.
- The 5G ProSe Layer-3 UE-to-UE Relay decides the QoS Info of the first hop QoS with considering the received second hop QoS, the Direct Communication Accept message over the first hop PC5 reference point additionally includes IP Address Configuration or Link-Local IPv6 Address, QoS Info of the first hop QoS and may include IP address of the target 5G ProSe End UE. If the PC5 link is used for transferring Ethernet traffic, 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the target 5G ProSe Layer-3 End UE instead of IP related information.
- For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, in the Link Modification Request message over the first hop PC5 reference point, the source 5G ProSe End UE additionally includes QoS Info of the end-to-end QoS as described in the clause 6.4.3.4. For removing end-to-end QoS flows(s), in the Link Modification Request message over the first hop PC5 reference point, the source 5G ProSe End UE includes PFI(s) of the QoS flow(s) of the first hop as described in the clause 6.4.3.4. If the PC5 link is used for transferring Ethernet traffic, the source 5G ProSe Layer-3 End UE may provide its Ethernet MAC address.
- For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, in the Link Modification Request message over the second hop PC5 reference point, the 5G ProSe Layer-3 UE-to-UE Relay additionally includes QoS Info of the second hop QoS to the target 5G ProSe End UE. For removing end-to-end QoS flow(s), in the Link Modification Request message over the second hop PC5 reference point, the 5G ProSe Layer-3 UE-to-UE Relay includes PFI(s) of the QoS flow(s) of the second hop. If the PC5 link is used for transferring Ethernet traffic, the 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the source 5G ProSe Layer-3 End UE.
- For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, the Link Modification Accept message over the second hop PC5 reference point additionally includes QoS Info of the second hop QoS. If the PC5 link is used for transferring Ethernet traffic, the target 5G ProSe Layer-3 End UE may provide its Ethernet MAC address.
- For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, the 5G ProSe Layer-3 UE-to-UE Relay decides the QoS Info of the first hop QoS with considering the received second hop QoS, the Link Modification Accept message over the first hop PC5 reference point additionally includes QoS Info of the first hop QoS and may include IP address of the target 5G ProSe End UE. If the PC5 link is used for transferring Ethernet traffic, 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the target 5G ProSe Layer-3 End UE instead of IP related information.
When the PC5 link between a 5G ProSe Layer-3 End UE and the 5G ProSe Layer-3 UE-to-UE Relay is released, the 5G ProSe Layer-3 UE-to-UE Relay may initiate the PC5 link release to the peer 5G ProSe Layer-3 End UE(s) or notify the peer 5G ProSe Layer-3 End UE(s) the peer PC5 link is released.
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6.4.3.7.4 Layer-2 link management over PC5 reference point for 5G ProSe UE-to-UE Relay Communication with integrated Discovery
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This clause is for the 5G ProSe UE-to-UE Relay Communication with integrated Discovery procedure as described in clause 6.7.3.
The Direct Communication Request message over the first hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of source 5G ProSe End UE.
- (optional) user info (i.e. Application Layer ID) of target 5G ProSe End UE: the identity of the target 5G ProSe End UE if provided from the ProSe application layer.
- (optional) Destination Layer-2 ID of target 5G ProSe End UE: the unicast destination Layer-2 ID of the target 5G ProSe End UE determined by the source 5G ProSe End UE as specified in clause 5.8.2.4.
- ProSe Service Info: the information about the ProSe identifier(s) requesting Layer-2 link establishment.
- RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
- Relay_indication: indicates whether a 5G ProSe UE-to-UE Relay can send a Direct Communication Request message based on the received Direct Communication Request message which contains the relay_indication.
- Security Information: the information for the establishment of security for the first hop PC5 link establishment (see TS 33.503 [29]).
The Direct Communication Request message over the second hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of source 5G ProSe End UE.
- User Info ID of 5G ProSe UE-to-UE Relay.
- (optional) user info of target 5G ProSe End UE.
- ProSe Service Info: the information about the ProSe identifier(s).
- RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
- Security Information: the information for the establishment of security for the second hop PC5 link establishment (see TS 33.503 [29]).
The Direct Communication Accept message over the second hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of target 5G ProSe End UE.
The Direct Communication Accept message over the first hop PC5 reference point includes:
- user info (i.e. Application Layer ID) of target 5G ProSe End UE.
- User Info ID of 5G ProSe UE-to-UE Relay.
For the 5G ProSe Communication via 5G ProSe Layer-3 UE-to-UE Relay, additional clarifications are as following:
- In the Security Procedure of the second hop PC5 reference point, the 5G ProSe Layer-3 UE-to-UE Relay provides the IP Address Configuration or Link-Local IPv6 Address to the target 5G ProSe End UE.
- The Direct Communication Accept message over the second hop PC5 reference point additionally includes IP Address Configuration or Link-Local IPv6 Address (if IP communication is used), Ethernet MAC address of target 5G ProSe End UE (if Ethernet communication is used). QoS Info is not included in the Security Procedure or Direct Communication Accept message of the second hop PC5 reference point.
- In the Security Procedure of the first hop PC5 reference point, the source 5G ProSe End UE provides the IP Address Configuration, Link-Local IPv6 Address and QoS Info of the end-to-end QoS to the 5G ProSe Layer-3 UE-to-UE Relay.
- The 5G ProSe Layer-3 UE-to-UE Relay provides the QoS info of the second hop QoS to the target 5G ProSe End UE using the Layer-2 link modification as described in the clause 6.4.3.4.
- The 5G ProSe Layer-3 UE-to-UE Relay decides the QoS Info of the first hop QoS with considering the received second hop QoS from the target 5G ProSe End UE, the Direct Communication Accept message over the first hop PC5 reference point additionally includes IP Address Configuration or Link-Local IPv6 Address, QoS Info of the first hop QoS and may include IP address of the target 5G ProSe End UE (if IP communication is used) or Ethernet MAC address of target 5G ProSe End UE (if Ethernet communication is used).
For the 5G ProSe Communication via 5G ProSe Layer-2 UE-to-UE Relay, the message contents over PC5 reference point for unicast mode 5G ProSe Direct Communication as depicted from clause 6.4.3.1 to clause 6.4.3.5 are same for the end-to-end connection between peer 5G ProSe End UEs.
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6.4.3.8 Layer-2 link management over PC5 reference point for 5G ProSe multi-hop UE-to-Network Relay (based on Model A discovery)
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6.4.3.8.1 Layer-2 Link establishment and management
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Each of the 5G ProSe Intermediate UE-to-Network Relay shall establish a Layer-2 Link with its parent Intermediate UE-to-Network Relay or the 5G ProSe UE-to-Network Relay, before it can serve the 5G ProSe Remote UE, or a child Intermediate UE-to-Network Relay. The 5G ProSe Intermediate UE-to-Network Relay shall establish the Layer-2 Link with a parent relay before sending the 5G ProSe UE-to-Network Relay Discovery Announcement message.
Layer-2 link management procedures as defined in clause 6.4.3.6 for 5G ProSe UE-to-Network Relay operation are used. When establishing the Layer-2 link with its parent relay (either a 5G ProSe UE-to-Network Relay or another 5G ProSe Intermediate UE-to-Network Relay), the 5G ProSe Intermediate UE-to-Network Relay takes the role of the 5G ProSe Remote UE and its parent relay takes the role of 5G ProSe UE-to-Network Relay. The Layer-2 link is established per RSC.
The 5G ProSe Remote UE uses the procedure defined in clause 6.4.5.6 to establish a Layer-2 Link with the selected 5G ProSe Intermediate UE-to-Network Relay. The Intermediate UE-to-Network Relay takes the role of of 5G ProSe UE-to-Network Relay in the procedure.
NOTE: In the case of Layer-3 UE-to-Network Relay operation, only the root 5G ProSe UE-to-Network Relay needs to establish the PDU session with the network.
When an Intermediate UE-to-Network Relay has a child Intermediate UE-to-Network Relay or a 5G ProSe Remote UE connected, it updates the Layer-2 link with its parent relay, using the procedure defined in clause 6.4.3.4, with the following enhancements:
- The link modification procedure is enhanced to inform the parent relay, e.g. another 5G ProSe Intermediate UE-to-Network Relay or the 5G ProSe UE-to-Network Relay, of the User Info of the child relay(s) or the Remote UE(s). The Link Modification Request message contains a list of 5G ProSe Remote UE (Remote User ID, Remote UE Info, hop-count) and the corresponding PC5 QoS Flow associated with each 5G ProSe Remote UE. The Remote User ID and Remote UE Info are as defined in clause 6.5.1.1. The hop-count corresponds to the PC5 hops of the Remote UE from the network.
The Remote UE triggers the link modification procedure to its parent relay after obtaining the IP address/prefix from the 5G ProSe UE-to-Network Relay.
An Intermediate UE-to-Network Relay triggers a link modification procedure towards its parent relay if a new Remote User ID is received from its child relay during the link modification procedure.
The 5G ProSe UE-to-Network Relay's Remote UE reporting procedure includes all the Remote UE information reported by its child relays.
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6.4.3.8.2 IP address/prefix management for 5G ProSe Layer-3 Multi-hop UE-to-Network Relay
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When IP based PDU session types are used by the 5G ProSe UE-to-Network Relay, the Intermediate UE-to-Network Relay needs to act as an IP Router.
The IP address allocation for Remote UE and Intermediate UE-to-Network Relay is performed by the 5G ProSe UE-to-Network Relay.
To support DHCP based IP address configuration, the 5G ProSe Intermediate UE-to-Network Relay acts as a DHCP client towards the UE-to-Network Relay or the parent Intermediate UE-to-Network Relay and as a DHCP server towards the Remote UE or the child Intermediate UE-to-Network Relay. To support IPv6 Stateless Address auto-configuration, the 5G ProSe Intermediate UE-to-Network Relay relays the Router Solicitation and Router Advertisement messages between the 5G ProSe Remote UE and the 5G ProSe UE-to-Network Relay.
The 5G ProSe Intermediate UE-to-Network Relay builds its local IP routing table based on the Remote UE info from the link modification procedures as described in clause 6.4.3.8.1. The local IP routing table is per RSC and used based on RSC of the link the packet is received.
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6.4.3.8.3 Relay reselection and mobility support
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There are two types of situations for parent relay reselection, i.e. for a single 5G ProSe Remote UE and for a 5G ProSe Intermediate UE-to-Network Relay with multiple child relays or 5G ProSe Remote UEs.
For a single 5G ProSe Remote UE, when the connection with an old parent relay (either a 5G ProSe Intermediate UE-to-Network Relay or a 5G ProSe UE-to-Network Relay) is lost or the link quality drops below a configured threshold, the 5G ProSe Remote UE triggers the reselection of the relays that offers the same service, identified by the same RSC. The path failure (connection lost or link quality drop) may be detected by a lower layer (e.g. PC5-RRC layer). The lower layer (e.g. PC5-RRC layer) indicates to an upper layer (e.g. PC5-S signalling layer) about the detected failure, together with the information on the detected failure/event, and the PC5 Link Identifier for the unicast link (which can be used to retrieve the corresponding UE ID(s) from the link context).
Figure 6.4.3.8.3-1: Relay reselection for 5G ProSe Remote UE with 5G ProSe Multi-hop UE-to-Network Relays without Root Relay change
Figure 6.4.3.8.3-1 depicts the Relay reselection operation for this situation. When the 5G ProSe Remote UE has lost the connection or has an imminent connection loss/deteriorated connection with the 5G ProSe Intermediate UE-to-Network Relay-1, the 5G ProSe Remote UE performs relay reselection by using the relay discovery procedure in clause 6.3.2.5. The 5G ProSe Remote UE discovered the 5G ProSe Intermediate UE-to-Network Relay-2 that offers the same RSC. In case there are multiple 5G ProSe Intermediate UE-to-Network Relays discovered, the 5G ProSe Intermediate UE-to-Network Relay that offers connection to the same 5G ProSe UE-to-Network Relay is prioritized.
5G ProSe Remote UE establishes the Layer-2 link with the 5G ProSe Intermediate UE-to-Network Relay-2 as specified in clause 6.4.3.8.1. After the connection establishment, the Intermediate UE-to-Network Relay-2 uses the Layer-2 Link Modification procedure to update the 5G ProSe UE-to-Network Relay regarding the 5G ProSe Remote UE. If the same 5G ProSe UE-to-Network Relay is used, it switches the connection/routing context for the 5G ProSe Remote UE from the Layer-2 link with the 5G Intermediate UE-to-Network Relay-1 to that of the Layer-2 link with the 5G ProSe Intermediate UE-to-Network Relay-2.
The 5G ProSe Remote UE tears down the link with the 5G ProSe Intermediate UE-to-Network Relay-1 (or the link failure is detected), which will trigger the 5G ProSe Intermediate UE-to-Network Relay-1 to update the 5G ProSe UE-to-Network Relay to remove its association with 5G ProSe Remote UE.
If the same 5G ProSe UE-to-Network Relay is selected after the relay reselection, the 5G ProSe Remote UE can keep its IP address/prefix (in case of Layer-3 UE-to-Network relay).
If a new 5G ProSe UE-to-Network Relay is used after the relay reselection, the procedures as that described in clause 6.4.3.8.1 will be executed. In this case, IP address/prefix changes may happen (in case of Layer-3 UE-to-Network relay).
The relay reselection procedure can be used by a 5G ProSe Intermediate UE-to-Network Relay, taking the role of the 5G ProSe Remote UE in the procedure, when its connection with a parent Relay (either a 5G ProSe Intermediate UE-to-Network Relay or a 5G ProSe UE-to-Network Relay) is lost or the link quality drops below a configured threshold.
If the 5G ProSe Intermediate UE-to-Network Relay can not complete the reselection, e.g. it is not able to discover the 5G ProSe UE-to-Network Relay, or the 5G ProSe Intermediate UE-to-Network Relay determines to not perform the reselection procedure, it may send re-selection indication and optionally with a cause value to 5G ProSe Remote UE via the established multi-hop relay path. After receving the re-selection indication the 5G ProSe Remote UE may trigger the reselection of the relays as described above.
During the transmition of re-selection indication to 5G ProSe Remote UE, after receving the re-selection indication a 5G ProSe Intermediate UE-to-Network Relay in the path based on configuration may determine to relay the re-selection indication to 5G ProSe Remote UE, or perform relay reselection by itself as described above.
Figure 6.4.3.8.3-2: Relay reselection for 5G ProSe Remote UE with 5G ProSe Multi-hop UE-to-Network Relays with Root Relay change
When the 5G ProSe Intermediate Relay-1 has lost the connection or has an imminent connection loss/deteriorated connection with its parent 5G ProSe Intermediate Relay or the 5G ProSe UE-to-Network Relay, the 5G ProSe Intermediate Relay-1 performs relay reselection by using the relay discovery procedure in clasue 6.3.2.5. For Layer-3 UE-to-Network relay, if the 5G ProSe Intermediate Relay-1 decides a new 5G ProSe UE-to-Network Relay is used after the relay reselection, IP address/prefix changes may happen. In this case, the Intermediate UE-to-Network Relay-1 notifies its child relay(s) and/or Remote UE(s) about the change of Root 5G ProSe UE-to-Network Relay before sending Remote User ID and Remote UE Info to its parent Relay. The 5G ProSe Intermediate Relay-1 sends Link Modification Request message to its child relay(s) and Remote UE(s) including an indication that the Root UE-to-Network Relay is changed. The nofitication triggers the Remote UE to request for a new IP address/prefix from the new Root 5G ProSe UE-to-Network Relay.
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6.4.3.9 Layer-2 link management over PC5 reference point for Multi-hop 5G ProSe UE-to-Network Relay (based on Model B Discovery)
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6.4.3.9.1 Layer-2 Link establishment and management
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The Layer-2 link procedures over PC5 reference point for unicast mode 5G ProSe Direct Communication as depicted from clause 6.4.3.6 is used for the PC5 reference point among the 5G ProSe Remote UE, the 5G ProSe Intermediate UE-to-Network Relay and the UE-to-Network Relay after Model B Discovery, with the following differences and clarifications:
For the UE oriented Layer-2 link establishment as described in the clause 6.4.3.1,
- The 5G ProSe Remote UE determines the destination Layer-2 ID for PC5 unicast link establishment based on the unicast source Layer-2 ID of the selected (neighbour) 5G ProSe Intermediate Relay (as specified in clause 5.8.3) during UE-to-Network Relay discovery as specified in clause 6.3.2.5.3.
- The 5G ProSe Intermediate UE-to-Network Relay determines the destination Layer-2 ID for PC5 unicast link establishment based on the unicast source Layer-2 ID of the selected 5G ProSe Intermediate Relay or UE-to-Network Relay (as specified in clause 5.8.3) during UE-to-Network Relay discovery as specified in clause 6.3.2.5.3.
NOTE 1: How long the Intermediate UE-to-Network Relay keeps the Layer-2 ID information of other Relays obtained in the discovery procedures is based on implementation, the Intermediate UE-to-Network Relay can take the Hop-Limit into account.
NOTE 2: It is up to implementation how long the 5G ProSe Intermediate UE-to-Network Relay keeps the Layer-2 ID information of other realys/Remote UE obtained in the discovery procedures, e.g. until it receives the a certain number of Response message(s) towards the Remote UE or based on an implementation timer.
- 5G ProSe Remote UE sends a unicast Direct Communication Request message to the selected (neighbour) 5G ProSe Intermediate UE-to-Network Relay. The Direct Communication Request message additionally includes:
- Path information: an (ordered) list of User Info ID of 5G ProSe Intermediate Relays and the UE-to-Network Relay selected by the 5G ProSe Remote UE based on the path information provided to the 5G ProSe Remote UE during 5G ProSe UE-to-Network Relay Discovery procedure.
- QoS Info: indicates the End to End QoS Info.
- 5G ProSe Intermediate UE-to-Network Relay sends a unicast Direct Communication Request message to the next 5G ProSe Intermediate UE-to-Network Relay or the UE-to-Network Relay according to the path information in the received Direct Communication Request message. The Direct Communication Request message additionally includes:
- Path information: an (ordered) list of User Info ID of 5G ProSe Intermediate UE-to-Network Relays and the UE-to-Network Relay selected by the 5G ProSe Remote UE based on the path information provided to the 5G ProSe Remote UE during 5G ProSe UE-to-Network Relay Discovery procedure.
- QoS Info: End to End QoS Info and the remaining QoS Info of hops from the Intermediate UE-to-Network Relay to the network as specified in clause 5.6.2.
- In step 4 and step 5, step 4a and step 5a are performed if the 5G ProSe Intermediate/UE-to-Network Relay's identity matches the Target Info (if any) and the Relay Service Code is one of the Relay Service Codes included during UE-to-Network Relay discovery as specified in clause 6.3.2.5.3.
For the Layer-2 link release as described in the clause 6.4.3.3,
- If the Layer-2 link release procedure is initiated by the 5G ProSe Intermediate UE-to-Network Relay, the Disconnect Request message may indicate the 5G ProSe UE-to-Network Relay is temporarily not available as described in clause 5.12.
- If the service authorization for acting as a 5G ProSe Intermediate UE-to-Network Relay is revoked, the 5G ProSe Intermediate UE-to-Network Relay should initiate the release of the Layer-2 link that the revoked authorization affects.
Each PC5 unicast link for 5G ProSe UE-to-Network Relay is associated with a Unicast Link Profile, which additionally includes:
- Path Information: which contains the User Info ID of Intermediate UE-to-Network Relay at the next hop to the Remote UE.
Each PC5 unicast link for 5G ProSe Intermediate UE-to-Network Relay is associated with a Unicast Link Profile, which additionally includes:
- Path Information: which contains the User Info ID of Intermediate UE-to-Network Relay or UE-to-Network Relay at the adjancent hop.
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6.4.3.9.2 IP address/prefix management for 5G ProSe Layer-3 Multi-hop UE-to-Network Relay
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When IP based PDU session types are used by the 5G ProSe UE-to-Network Relay, the Intermediate UE-to-Network Relay acts as an IP Router.
The IP address allocation is performed by the 5G ProSe UE-to-Network Relay, as defined in clause 6.5.1.
DHCP based IP address configuration and IPv6 routing advertisement is performed as described in clause 6.4.3.8.2.
After IP address assignment, the Remote UE may initiate a Link Modification Procedure which includes the Remote UE ID and the Remote UE information. The 5G ProSe Intermediate UE-to-Network Relays builds their local IP routing table based on the Remote UE info and the received multihop path info for UE-to-Network Relay during link establishment procedure for unicast PC5 connection (step 4 in clause 6.5.1.4 or step 3 in clause 6.5.1.5).
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6.4.3.9.3 Relay reselection
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After being connected to the 5G ProSe UE-to-Network Relay, the 5G ProSe Remote UE and 5G ProSe Intermediate UE-to-Network Relay keep performing the measurement of the signal strength of PC5 unicast link with its parent Relay (Intermediate Relay or U2N relay) for relay reselection.
When a 5G ProSe Intermediate UE-to-Network Relay detects the link failure or link quality degradation, the 5G ProSe Intermediate UE-to-Network Relay sends to the 5G ProSe Remote UE a Relay re-selection indication with the cause (e.g. the link failure or link quality degradation of the PC5 link) so that the 5G ProSe Remote UE may initiate multihop UE-to-Network Relay reselection procedure.
The 5G ProSe Remote UE may perform the 5G ProSe UE-to-Network Relay discovery procedures defined in clause 6.3.2.3 to discover available 5G ProSe UE-to-Network Relays or 5G ProSe multi-hop UE-to-Network Relay Discovery procedures defined in clause 6.3.2.5.3 to discover available multihop paths to the 5G ProSe UE-to-Network Relays for 5G ProSe (multihop) UE-to-Network Relay reselection and select a new path for 5G ProSe (multi-hop) UE-to-Network relay. Additionally, the 5G ProSe Remote UE may initiate link establishment procedure for unicast PC5 connection by sending a DCR or a LMR with the newly selected path info to the next hop 5G ProSe Intermediate UE-to-Network Relay at the newly selected path.
After the 5G ProSe multihop UE-to-Network relay reselection procedure, if the same 5G ProSe UE-to-Network Relay is used for connection with a 5G ProSe Remote UE, the existing IP address of the 5G ProSe Remote UE is reused. The IP address of the Remote UE may be included by the 5G ProSe UE-to-Network Relay and Intermediate UE-to-Network Relays in the DCA/LMA message.
After a preconfigured duration, the Relay that detected the need for reselection releases the link with the previous and next relays if applicable, unless it is reselected by the Remote UE. This will trigger them to perform the same procedure until the complete path has been released. Then, the 5G ProSe UE-to-Network Relay removes its association with the 5G ProSe Remote UE including the allocated IP address.
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6.4.3.10 Layer-2 link management for 5G ProSe Layer-3 Multi-hop UE-to-UE Relay
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6.4.3.10.1 Layer-2 Link establishment and management for IP PDU type
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For the 5G ProSe Communication via 5G ProSe UE-to-UE Relay as described in clause 6.7.5.2:
- The Direct Communication Request message over the PC5 reference point (between a 5G ProSe End UE and 5G ProSe Multi-hop UE-to-UE Relay, or between 5G ProSe Multi-hop UE-to-UE Relays) includes:
- User info (i.e. Application Layer ID) of source 5G ProSe End UE or User Info ID of 5G ProSe Multi-hop UE-to-UE Relay: the identity of the source 5G ProSe End UE or 5G ProSe Multi-hop UE-to-UE Relay requesting the connection establishment.
- User Info ID of 5G ProSe Multi-hop UE-to-UE Relay: the identity of the target 5G ProSe Multi-hop UE-to-UE Relay provided during the 5G ProSe Multi-hop UE-to-UE Relay Discovery procedure.
- (optional)ProSe Service Info: the information about the ProSe identifier(s) requesting Layer-2 link establishment.
- RSC: the connectivity service provided by the 5G ProSe Multi-hop UE-to-UE Relay as requested.
- Security Information: the information for the establishment of security for the PC5 link establishment (see TS 33.503 [29]).
- (Optional) Hop-Limit: the 5G ProSe End UE may include a hop-limit value smaller than the configured "maximum number of hops per RSC", if it desires to reduce the number of hops the other End UE can communicate with it via the relays.
The Direct Communication Accept message over the PC5 reference point (between a 5G ProSe End UE and 5G ProSe Multi-hop UE-to-UE Relay, or between 5G ProSe Multi-hop UE-to-UE Relays) includes:
- User Info ID of 5G ProSe UE-to-UE Relay: the identity of the 5G Prose Multi-hop UE-to-UE Relay sending the Accept message.
Other link management procedures as defined in clause 6.4.3 (i.e. Link identifier update in 6.4.3.2, Layer-2 link release in clause 6.4.3.3, Layer-2 link modification in clause 6.4.3.4, Layer-2 link maintenance in 6.4.3.5) can be used for the layer-2 link without enhancements.
When a new layer-2 link is established, or an existing layer-2 link is released, the 5G ProSe Multi-hop UE-to-UE Relay need to inform the status change internally to the MANET router stack.
Each of the established layer-2 link with another 5G ProSe UE-to-UE Relay is treated as a MANET interface as defined in RFC 6130 [36]. The layer-2 links of the same 5G ProSe UE-to-UE Relay may share the same IP address, as they are isolated, i.e. each of the layer-2 link only allows communication with one peer 5G ProSe UE-to-UE Relay.
The 5G ProSe UE-to-UE Relay may based on local configuration use a large value for HELLO_INTERVAL, VALIDITY_TIME and REFRESH_INTERVAL as defined in RFC 6130 [36] to reduce the frequency of periodic HELLO messages. The 5G ProSe UE-to-UE Relay can use the information from 5G ProSe link management procedures defined in clause 6.4.3 for maintaining the information in Neighbor Information Base.
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6.4.3.10.2 Layer-2 link establishement and management over PC5 reference point for non-IP PDU type
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For the 5G ProSe Communication via Multi-hop 5G ProSe Layer-3 UE-to-UE Relay as described in clause 6.7.1a, the description in clause 6.4.3.7.1 applies with following differences and clarifications:
- The Direct Communication Request message over the PC5 reference point between source End UE and the first hop UE-to-UE Relay additionally includes:
- Path Information: an (ordered) list of User Info ID of 5G ProSe UE-to-UE Relays selected by the source 5G ProSe End UE based on the path information provided to the source 5G ProSe End UE during 5G ProSe UE-to-UE Relay Discovery procedure.
- QoS Info: indicates the End to End QoS Info from the source End UE to the target End UE.
The Direct Communication Request message over the PC5 reference point between two UE-to-UE Relays includes:
- User Info of source 5G ProSe End UE.
- User Info of target 5G ProSe End UE.
- Path information.
- ProSe Service Info: the information about the ProSe identifier(s).
- RSC: the connectivity service provided by the 5G ProSe UE-to-UE Relay as requested by the source 5G ProSe End UE.
- Security Information: the information for the establishment of security for the PC5 link establishment between two UE-to-UE Relays or between target End UE and UE-to-UE Relay (see TS 33.503 [29]).
- QoS Info: indicates the rest QoS Info from the UE-to-UE Relay to the target End UE.
The Direct Communication Request message over the PC5 reference point between between the target End UE and UE-to-UE Relay additionally includes:
- Path information.
- QoS Info: indicates the rest QoS Info from the UE-to-UE Relay to the target End UE.
The Direct Communication Accept message over the PC5 reference point between target End UE and UE-to-UE Relay additionally includes:
- QoS Info which is the accepted QoS Info of the hop between target End UE and the last UE-to-UE Relay.
The Direct Communication Accept message over the PC5 reference point between two UE-to-UE Relays includes:
- User Info of target 5G ProSe End UE.
- Path information.
- QoS Info which is the accepted QoS Info of the hop between two UE-to-UE Relays and the accumulated QoS Info of hops from the receiver UE-to-UE Relay to the target End UE.
The Direct Communication Accept message over the PC5 reference point between the source End UE and UE-to-UE Relay additionally includes:
- Path information.
- QoS Info which is the accepted QoS Info of the hop between two UE-to-UE Relays and the accumulated QoS Info of hops from the source End UE to the target End UE.
The Link Modification Request message over the PC5 reference point between source End UE and the first hop UE-to-UE Relay additionally includes:
- Path Information: an (ordered) list of User Info ID of 5G ProSe UE-to-UE Relays provided to the source 5G ProSe End UE during 5G ProSe UE-to-UE Relay Discovery procedure.
- QoS Info: indicates the End-to-End QoS Info from the source End UE to the target End UE.
The Link Modification Request message over the PC5 reference point between two UE-to-UE Relays includes:
- User Info of source 5G ProSe End UE.
- Path Information.
- User Info of target 5G ProSe End UE.
- QoS Info: indicates the rest QoS Info from the UE-to-UE Relay to the target End UE.
The Link Modification Request message over the PC5 reference point between the target End UE and UE-to-UE Relay additionally includes:
- Path Information.
- QoS Info: indicates the rest QoS Info from the UE-to-UE Relay to the target End UE.
The Link Modification Accept message over the PC5 reference point between the target End UE and UE-to-UE Relay additionally includes:
- Path information.
- QoS Info which is the accepted QoS Info of the hop between target End UE and UE-to-UE Relay.
The Link Modification Accept message over the PC5 reference point between two UE-to-UE Relays includes:
- Path information.
- QoS Info which is the accepted QoS Info of the hop between two UE-to-UE Relays and the accumulated QoS Info of hops from the UE-to-UE Relay to the target End UE.
The Link Modification Accept message over the PC5 reference point between source End UE and the first UE-to-UE Relay additionally includes:
- Path information.
- QoS Info which is the accepted QoS Info of the hop between source End UE and the first UE-to-UE Relay and the accumulated QoS Info of hops from the UE-to-UE Relay to the target End UE.
NOTE: The path information in DCR/LMR/DCA/LMA message is used for multi-hop 5G ProSe UE-to-UE Relay Discovery only. A 5G ProSe UE-to-UE Relay Discovery that only supports single-hop UE-to-UE Relay will ignore the messages that contains path information.
In the Security Procedure of the PC5 reference point between source End UE and UE-to-UE Relay, the source 5G ProSe Layer-3 End UE provides the QoS Info of the end-to-end QoS to the 5G ProSe Layer-3 UE-to-UE Relay. If the PC5 link is used for transferring Ethernet traffic, the source 5G ProSe Layer-3 End UE provides its Ethernet MAC address. The 5G ProSe Layer-3 UE-to-UE Relay may provide the Ethernet MAC address of the target 5G ProSe Layer-3 End UE in the DCA/LMA message.
In the Security Procedure of the PC5 reference point between two UE-to-UE Relays, a 5G ProSe Layer-3 UE-to-UE Relay provides the QoS Info from itself to the target 5G ProSe Layer-3 UE-to-UE Relay. If the PC5 link is used for transferring Ethernet traffic, the 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the source 5G ProSe Layer-3 End UE. The 5G ProSe Layer-3 UE-to-UE Relay may provide the Ethernet MAC address of the target 5G ProSe Layer-3 End UE in the DCA/LMA message
In the Security Procedure of the PC5 reference point between target End UE and a UE-to-UE Relay, the 5G ProSe Layer-3 UE-to-UE Relay provides the QoS Info of the last hop QoS to the target 5G ProSe End UE. If the PC5 link is used for transferring Ethernet traffic, the 5G ProSe Layer-3 UE-to-UE Relay provides the Ethernet MAC address of the source 5G ProSe Layer-3 End UE. The target 5G End UE may provide its Ethernet MAC address in the DCA/LMA message
The 5G ProSe Layer-3 UE-to-UE Relay decides the QoS Info of the next hop to source End UE with considering the accumulated QoS Info of the hop(s) to the target End UE which is received in the Direct Communication Accept message.
For adding new end-to-end QoS flow or modifying existing end-to-end QoS flow, the Link Modification Accept message over each PC5 reference point additionally includes QoS Info of that hop. If the PC5 link is used for transferring Ethernet traffic, the target 5G ProSe Layer-3 End UE may provide its Ethernet MAC address. For a path between a specific pair of End UEs, if at least one of the PC5 link is released, the 5G ProSe Layer-3 UE-to-UE Relay(s) in the path may release other PC5 link(s) in the path.
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6.5 5G ProSe UE-to-Network Relay Communication
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6.5.1 5G ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay
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6.5.1.0 General
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5G ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay may be performed with or without involving N3IWF for non-emergency service and for emergency service as specified in clause 5.4.4.
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6.5.1.1 5G ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay without N3IWF
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A 5G ProSe Layer-3 UE-to-Network Relay registers to the network (if not already registered). 5G ProSe Layer-3 UE-to-Network Relay establishes a PDU Session(s) or modifies an existing PDU Session(s) in order to provide relay traffic towards 5G ProSe Layer-3 Remote UE(s). PDU Session(s) supporting 5G ProSe Layer-3 UE-to-Network Relay shall only be used for 5G ProSe Layer-3 Remote UE(s) relay traffic.
The PLMN serving the 5G ProSe Layer-3 UE-to-Network Relay and the PLMN to which the 5G ProSe Layer-3 Remote UE registers can be the same PLMN or two different PLMNs.
Figure 6.5.1.1-1: 5G ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay without N3IWF
1. Service authorization and provisioning are performed for the 5G ProSe Layer-3 UE-to-Network Relay (step 1a) and 5G ProSe Layer-3 Remote UE (step 1b) as described in clause 6.2.
2. The 5G ProSe Layer-3 UE-to-Network Relay may establish a PDU Session for relaying. In the case of IPv6, the 5G ProSe Layer-3 UE-to-Network Relay obtains the IPv6 prefix via prefix delegation function from the network as defined in TS 23.501 [4].
NOTE 1: 5G ProSe Layer-3 UE-to-Network Relay can establish a PDU Session for any Relay Service Code it supports before the connection is established with the 5G ProSe Layer-3 Remote UE.
3. The 5G ProSe Layer-3 Remote UE performs discovery of a 5G ProSe Layer-3 UE-to-Network Relay as described in clause 6.3.2.3. As part of the discovery procedure the 5G ProSe Layer-3 Remote UE learns about the connectivity service the 5G ProSe Layer-3 UE-to-Network Relay provides.
4. The 5G ProSe Layer-3 Remote UE selects a 5G ProSe Layer-3 UE-to-Network Relay and establishes a connection for unicast mode communication as described in clause 6.4.3.6. If there is no PDU Session associated with the Relay Service Code or a new PDU Session for relaying is needed, the 5G ProSe Layer-3 UE-to-Network Relay initiates a new PDU Session establishment procedure for relaying before completing the PC5 connection establishment.
When the 5G ProSe Layer-3 Remote UE sends the Direct Communication Request message including the dedicated emergency RSC, the 5G ProSe Layer-3 UE-to-Network Relay sets up an emergency PDU session for relaying the emergency service if there is not an emergency PDU Session established in step 2.
NOTE 2: If the 5G ProSe Layer-3 UE-to-Network Relay has its own emergency service ongoing, how to handle the conflict case is specified in clause 5.4.4.3.
The network decides that the PDU Session to be established is for relay traffic and then generates the QoS rules and QoS Flow level QoS parameters to 5G ProSe Layer-3 UE-to-Network Relay with relay consideration and can initiate the setup of QoS flows as specified in clause 5.6.2.1. The Remote UE can also initiate the setup of QoS flows by providing PC5 QoS info and (optionally) PC5 QoS rule(s) to the 5G ProSe Layer-3 UE-to-Network Relay during connection setup, according to the procedure as specified in clause 5.6.2.1.
The 5G ProSe Layer-3 UE-to-Network Relay determines the PDU Session type for relaying as specified in clause 5.4.1.1.
According to the PDU Session Type for relaying, the 5G ProSe Layer-3 UE-to-Network Relay performs relaying function at the corresponding layer as follows:
- When the IP type PDU Session is used for IP traffic over PC5 reference point, the 5G ProSe Layer-3 UE-to-Network Relay acts as an IP router. For IPv4, the 5G ProSe Layer-3 UE-to-Network Relay performs IPv4 NAT between IPv4 addresses assigned to the 5G ProSe Layer-3 Remote UE and the IPv4 address assigned to the PDU Session used for the relay traffic.
- When the Ethernet type PDU Session is used for Ethernet traffic over PC5 reference point, the 5G ProSe Layer-3 UE-to-Network Relay acts as an Ethernet switch.
- When the Unstructured type PDU Session is used for Unstructured traffic over PC5 reference point, the 5G ProSe Layer-3 UE-to-Network Relay performs traffic relaying based on a mapping between the PC5 Link Identifier and the PDU Session ID and a mapping between PFI for PC5 Layer-2 link and the QFI for the PDU Session. These mappings are created when the Unstructured type PDU Session is established for the 5G ProSe Layer-3 Remote UE.
- When the IP type PDU Session is used for Ethernet or Unstructured traffic over PC5 reference point, the 5G ProSe Layer-3 UE-to-Network Relay uses IP tunneling. For this IP tunnelling, the 5G ProSe Layer-3 UE-to-Network Relay locally assigns an IP address/prefix for the 5G ProSe Layer-3 Remote UE and uses it on the Uu reference point to encapsulate and decapsulate the uplink and downlink traffic for the 5G ProSe Layer-3 Remote UE. The tunnelled traffic over Uu reference point is transported over the PC5 reference point as Ethernet or Unstructured traffic.
5. For IP PDU Session Type and IP traffic over PC5 reference point, IPv6 prefix or IPv4 address (including NAT case) is allocated for the 5G ProSe Layer-3 Remote UE as defined in clause 5.5.1.3.
6. The 5G ProSe Layer-3 Remote UE may provide PC5 QoS Info and PC5 QoS rule(s) to the 5G ProSe Layer-3 UE-to-Network Relay using Layer-2 link modification procedure as specified in clause 6.4.3.4. The 5G ProSe Layer-3 UE-to-Network Relay generates the Packet Filters used over Uu interface based on the received PC5 QoS Info and QoS Rule(s) as described in clause 5.6.2.1 and may perform the UE requested PDU Session Modification as defined in TS 23.502 [5] clause 4.3.3 to setup a new QoS Flow or bind the traffic to an existing QoS Flow.
From this point the uplink and downlink relaying can start. For downlink traffic forwarding, the PC5 QoS Rule is used to map the downlink packet to the PC5 QoS Flow. For uplink traffic forwarding, the 5G QoS Rule is used to map the uplink packet to the Uu QoS Flow.
7. The 5G ProSe Layer-3 UE-to-Network Relay shall send a Remote UE Report (Remote User ID, Remote UE info) message to the SMF for the PDU Session associated with the relay. The Remote User ID, as defined in TS 33.503 [29], is an identity of the 5G ProSe Layer-3 Remote UE user that was successfully connected in step 4. The Remote UE info is used to assist identifying the 5G ProSe Layer-3 Remote UE in the 5GC. For IP PDU Session Type, the Remote UE info is Remote UE IP info. For Ethernet PDU Session Type, the Remote UE info is Remote UE MAC address which is detected by the 5G ProSe Layer-3 UE-to-Network Relay. For Unstructured PDU Session Type, the Remote UE info is not included. The SMF stores the Remote User IDs and the related Remote UE info in the 5G ProSe Layer-3 UE-to-Network Relay's SM context for this PDU Session associated with the relay.
The Remote UE Report is N1 SM NAS message sent with the PDU Session ID to the AMF, in turn delivered to the SMF.
NOTE 3: The privacy protection for Remote User ID is specified in TS 33.503 [29].
For IP info the following principles apply:
- for IPv4, the 5G ProSe Layer-3 UE-to-Network Relay shall report TCP/UDP port ranges assigned to individual 5G ProSe Layer-3 Remote UE(s) (along with the Remote User ID);
- for IPv6, the 5G ProSe Layer-3 UE-to-Network Relay shall report IPv6 prefix(es) assigned to individual 5G ProSe Layer-3 Remote UE(s) (along with the Remote User ID).
If the PDU Session for relaying is released by the UE-to-Network Relay or the network as described in clause 4.3.4 of TS 23.502 [5], the UE-to-Network Relay should initiate the release of the layer-2 links associated with the released PDU Session using the procedure defined in clause 6.4.3.3.
The PDU Session(s) used for relaying should be released as described in clause 4.3.4 of TS 23.502 [5] (e.g. by 5G ProSe Layer-3 UE-to-Network Relay), if the service authorization for acting as a 5G ProSe Layer-3 UE-to-Network Relay in the serving PLMN is revoked.
The 5G ProSe Layer-3 UE-to-Network Relay shall send the Remote UE Report message when the 5G ProSe Layer-3 Remote UE disconnects from the 5G ProSe Layer-3 UE-to-Network Relay (e.g. upon explicit layer-2 link release or based on the absence of keep alive messages over PC5) to inform the SMF that the 5G ProSe Layer-3 Remote UE(s) have left.
NOTE 4: In order for the SMF to have the 5G ProSe Layer-3 Remote UE(s) information, the HPLMN and the VPLMN where the 5G ProSe Layer-3 UE-to-Network Relay is authorised to operate, needs to support the transfer of the 5G ProSe Layer-3 Remote UE related parameters if the SMF is in the HPLMN.
It is up to 5G ProSe Layer-3 UE-to-Network Relay implementation how PDU Session(s) used for relaying are released or QoS Flow(s) used for relaying are removed by the 5G ProSe Layer-3 UE-to-Network Relay when 5G ProSe Layer-3 Remote UE(s) disconnect from the 5G ProSe Layer-3 UE-to-Network Relay.
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6.5.1.2 5G ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support
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6.5.1.2.1 Connection management via 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support
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In order to relay 5G ProSe Layer-3 Remote UE's traffic via N3IWF (see clause 6.5.1.2.2 for N3IWF selection), the 5G ProSe Layer-3 UE-to-Network Relay needs suitable ProSe Policies configured for establishing a PDU Session associated with a UPF that conveys the traffic towards the N3IWF. A 5G ProSe Layer-3 UE-to-Network Relay registers to the network as specified in clause 6.5.1.1. Based on configuration and authorization, the 5G ProSe Layer-3 UE-to-Network Relay is provisioned with PDU Session parameters in the ProSe Policy allowing the access to the N3IWF. When the corresponding PDU Session is established, the 5GS, e.g. SMF, based on the parameters (i.e. DNN, S-NSSAI) selects the UPF that ensures the connection to the N3IWF. The UPF for the 5G ProSe UE-to-Network Relay and the N3IWF may be collocated.
A 5G ProSe Layer-3 UE-to-Network Relay with a PDU Session providing access via N3IWF may also have other PDU Sessions for supporting access from the 5G ProSe Layer-3 Remote UE without going through a N3IWF.
NOTE 1: Whether a different PDU Sessions need to be established to serve traffics for Layer-3 Remote UE with or without going through a N3IWF is determined by Layer-3 Relay UE per TS 23.503 [9].
Figure 6.5.1.2.1-1: Connection establishment over 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support
1. 5G ProSe Layer-3 UE-to-Network Relay performs Registration procedures and obtains the ProSe Policy that corresponds to the operation supporting the access to N3IWF. The ProSe Policy includes the RSC and PDU Session parameters allowing the access to the N3IWF.
The 5G ProSe Layer-3 Remote UE is configured with the corresponding ProSe Policy and URSP rules. The URSP policy indicates if a particular service needs to be accessed within a PDU Session and thus should use a 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support as described in clause 6.5.4.
2-4. A 5G ProSe Layer-3 UE-to-Network Relay and 5G ProSe Layer-3 Remote UE follow the procedures described in steps 3-5 in clause 6.5.1.1 using the RSC configured for making the 5G ProSe Layer-3 Remote UE access to 5GC via N3IWF.
NOTE 2: The services requiring the access via N3IWF can be configured with the RSC(s) that can be served by the same 5G ProSe UE-to-Network Relay.
5. The 5G ProSe Layer-3 Remote UE that connects to a 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support selects an N3IWF and determines the N3IWF IP address. The 5G ProSe Layer-3 Remote UE follows the N3IWF selection procedure as described in clause 6.5.1.2.2.
6. The 5G ProSe Layer-3 Remote UE establishes a signalling IPsec tunnel using IKE procedures with a N3IWF and performs NAS Registration as shown in Figure 4.12.2.2-1 of TS 23.502 [5]. After the IPSec tunnel is established, the 5G ProSe Layer-3 Remote UE can perform any of the NAS procedures (incl. PDU Session establishment for the 5G ProSe Layer-3 UE-to-Network Relay PDU Sessions) as specified in clause 4.12 of TS 23.502 [5].
7. After the PDU session(s) and associated QoS Flows are established in the 5G ProSe Layer-3 Remote UE's 5GC, the N3IWF determines the number of IPsec Child SA(s) that is needed and initiates the creation of the Child SA(s) as specified in clause 4.12.5 of TS 23.502 [5]. Once the Child SA(s) has been created the 5G ProSe Layer‑3 Remote UE will have the mapping between the DSCP markings for the IPsec Child SA(s), the corresponding QoS and N3IWF IP address(es) and provides this information, if needed, to the 5G ProSe Layer-3 UE-to-Network Relay as specified in clause 5.6.2.2. If needed, the 5G ProSe Layer-3 UE-to-Network Relay performs the PDU Session Modification procedure to request QoS flow(s) configuration that maps to the 5G ProSe Layer-3 Remote UE's Child SA(s).
IKE keep alive(s) between the 5G ProSe Layer-3 Remote UE and the N3IWF are used for detecting possible path failure. The 5G ProSe Layer-3 Remote UE may change 5G ProSe Layer-3 UE-to-Network Relay(s) while maintain the session with the N3IWF when the 5G ProSe Layer-3 Remote UE and the N3IWF support MOBIKE. This is negotiated between the 5G ProSe Layer-3 Remote UE and the N3IWF as specified in TS 23.502 [5], clause 4.12.2.2). When IKE keep alive(s) are used, the 5G ProSe Layer-3 Remote UE needs to keep the PC5 connection and 5G ProSe Layer-3 UE-to-Network Relay keeps the PDU Session.
When 5G ProSe Remote UE is in CM-CONNECTED state, the 5G ProSe Remote UE keeps the PC5 link. When the 5G ProSe Remote UE is in CM-IDLE state, it may either release the PC5 link for relaying or not.
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6.5.1.2.2 N3IWF selection for 5G ProSe Layer-3 Remote UE procedure
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When the 5G ProSe Layer-3 Remote UE relays traffic over 5G ProSe Layer-3 UE-to-Network Relay that supports N3IWF, the 5G ProSe Layer-3 Remote UE selects the N3IWF using the N3IWF selection procedure that is specified in clause 6.3.6.2 of TS 23.501 [4] for untrusted non-3GPP access with the following differences.
To support the N3IWF selection for 5G ProSe Layer-3 Remote UE, a 5G ProSe Layer-3 Remote UE is configured by HPLMN with N3IWF identifier configuration for 5G ProSe Layer-3 Remote UE and 5G ProSe Layer-3 UE-to-Network Relay access node selection information as described in clause 5.1.4.1.
When the 5G ProSe Layer-3 Remote UE decides to select an N3IWF in the HPLMN, the 5G ProSe Layer-3 Remote UE uses the N3IWF identifier configuration for 5G ProSe Layer-3 Remote UE, if configured, to find the IP address of the N3IWF in the HPLMN. Otherwise, 5G ProSe Layer-3 Remote UE constructs N3IWF FQDN based on either the Tracking Area Identity FQDN or on Operator Identifier FQDN of the 5G ProSe Layer-3 UE-to-Network Relay node selection information.
To assist the 5G ProSe Layer-3 Remote UE with N3IWF selection, the 5G ProSe Layer-3 UE-to-Network Relay supporting N3IWF access advertises the 5GS TAI corresponding to the serving cell, as defined in clause 5.8.3.2, in the 5G ProSe UE-to-Network Relay Discovery procedure as defined in clause 6.3.2.3.
A 5G ProSe Layer-3 Remote UE constructs the FQDN using either Tracking Area Identity FQDN or on Operator Identifier FQDN and selects the N3IWF using the procedures of N3IWF selection in clause 6.3.6.2 of TS 23.501 [4].
When the 5G ProSe Layer-3 Remote UE relays traffic over 5G ProSe Layer-3 UE-to-Network Relay using N3IWF for emergency services, the 5G ProSe Layer-3 Remote UE selects the N3IWF using the N3IWF selection procedure that is specified in clause 6.3.6.4.2 of TS 23.501 [4].
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6.5.1.2.3 Mobility of 5G ProSe Layer-3 Remote UE between Direct and Indirect Network communication path
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When 5G ProSe Layer-3 Remote UE changes from Direct Network Communication to Indirect Network Communication path, TS 23.502 [5] clause 4.9.2.2 applies after the 5G ProSe Layer-3 Remote UE establishes PC5 connection to the 5G Layer-3 UE-to-Network Relay.
When 5G ProSe Layer-3 Remote UE changes from Indirect Network Communication path to Direct Network Communication, the 5G ProSe Layer-3 Remote UE follows TS 23.502 [5] clause 4.9.2.1.
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6.5.1.3 Additional parameters announcement procedure
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Additional parameters announcement procedure outlined in figure 6.5.1.3-1 is used by a 5G ProSe Remote UE to request a 5G ProSe UE-to-Network Relay to announce additional parameters (using Model A) as defined in clause 5.8.3.
Figure 6.5.1.3-1: Additional parameters announcement procedure
1. 5G ProSe Remote UE has discovered a 5G ProSe UE-to-Network Relay and requires additional parameters.
2. The 5G ProSe Remote UE sends to the 5G ProSe UE-to-Network Relay an Additional Parameters Announcement Request to obtain additional parameters.
3. The 5G ProSe UE-to-Network Relay acknowledges receipt of the request in step 2 with an Additional Parameters Announcement Response (Additional_Parameters_Announcement_Request_Refresh Timer). The Additional_Parameters_Announcement_Request_Refresh Timer (configurable in the 5G ProSe UE-to-Network Relay), is provided to the 5G ProSe Remote UE so that when this timer expires the 5G ProSe Remote UE repeats the Additional Parameters Announcement Request procedure if it still needs to obtain the additional parameters. If the 5G ProSe Remote UE does not initiate new Additional Parameters Announcement Request procedure when this Additional_Parameters_Announcement_Request_Refresh Timer expires and no other UE request additional parameters announcement before the Additional_Parameters_Announcement_Request_Refresh timer expires in the 5G ProSe UE-to-Network Relay, then the relay shall stop announcing the addtional parameters.
4. The 5G ProSe UE-to-Network Relay announces the additional parameters by sending Relay Discovery Additional Information message as defined in clause 5.8.3. This is repeated periodically with a configurable frequency (normally higher than the one related to the Additional_Parameters_Announcement_Request_Refresh Timer) until there is no UE requesting to announce the additional parameters as determined by the Additional_Parameters_Announcement_Request_Refresh Timer running in the 5G ProSe UE-to-Network Relay.
NOTE: Based on UE implementation, the 5G ProSe UE-to-Network Relay can send the Relay Discovery Additional Information message several times consecutively in step 4 if there are other 5G ProSe Remote UE(s) that have connected to the 5G ProSe UE-to-Network Relay but not yet requested any additional parameters. This ensures the other 5G ProSe Remote UE(s) obtain such additional parameters without invoking any new request(s).
5. The 5G ProSe UE-to-Network Relay detects new or updated additional parameters.
6. Detection of new or updated additional parameters in step 5 triggers the 5G ProSe UE-to-Network Relay to announce the additional parameters by sending a Relay Discovery Additional Information Message immediately and to repeat it periodically with a configurable frequency as in step 4 until there are no UEs requesting to announce the additional parameters, i.e. until the Additional_Parameters_Announcement_Request_Refresh Timer expires in the 5G ProSe UE-to-Network Relay.
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6.5.1.4 5G ProSe Communication via Multi-hop 5G ProSe Layer-3 UE-to-Network Relay without N3IWF (based on Model B Discovery)
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Figure 6.5.1.4-1: Connection establishment via Multi-hop 5G ProSe Layer-3 UE-to-Network Relay without N3IWF support
Connection establishment via Multi-hop 5G ProSe Layer-3 UE-to-Network Relay without N3IWF support as described in clause 6.5.1.1 is used for multi-hop UE-to-Network Relay after Model B Discovery with the following differences and clarifications:
1. Service authorization and provisioning are performed for the 5G ProSe Layer-3 UE-to-Network Relay, Intermediate Relay(s) and 5G ProSe Layer-3 Remote UE.
2. The 5G ProSe Layer-3 UE-to-Network Relay may establish a PDU Session for relaying.
3. The 5G ProSe Layer-3 Remote UE performs Model B discovery of a 5G ProSe Layer-3 UE-to-Network Relay. The Remote UE obtains the path information to the UE-to-Network Relay(s) from the discovery procedure.
4. The 5G ProSe Layer-3 Remote UE selects a path and establishes a connection for unicast mode communication as described in clause 6.4.3.9.
5. For IP PDU Session Type and IP traffic over PC5 reference point, the UE-to-Network Relay assigns IPv6 prefix or IPv4 address to Intermediate Relay(s) and the Remote UE as defined in clause 6.4.3.9.2.
6. The 5G ProSe Layer-3 Remote UE may provide PC5 QoS Info and PC5 QoS rule(s) to the 5G ProSe Layer-3 UE-to-Network Relay using Layer-2 link modification procedure via Intermediate Relay(s). Intermediate Relays may split the PC5 QoS hop-by-hop as described in clause 5.6.2.
Editor's note: It is FFS how to handle QoS.
7. For the Remote UE Report, the Remote User ID is an identity of the 5G ProSe Layer-3 Remote UE.
For IP PDU Session Type, the Remote UE info is IP info related to Remote UE.
- for IPv4, the 5G ProSe Layer-3 UE-to-Network Relay shall report IP address and TCP/UDP port ranges that are assigned to 5G ProSe Layer-3 Remote UE(s) by the UE-to-Network Relay;
- for IPv6, the 5G ProSe Layer-3 UE-to-Network Relay shall report IPv6 prefix(es) assigned to individual 5G ProSe Layer-3 Remote UE(s).
For Ethernet PDU Session Type, the Remote UE info is Remote UE MAC address which is detected by the 5G ProSe Layer-3 UE-to-Network Relay.
NOTE: For IP type of PDU Sessions, the Intermediate Relays forward the Downlink packet to the correct PC5 links based on destination IP address of the packet. For Ethernet type of PDU Sessions, the Intermediate Relay forwards the Downlink packets according to the destination Ethernet MAC address.
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6.5.1.5 5G ProSe Communication via Multi-hop 5G ProSe Layer-3 UE-to-Network Relay with N3IWF after Model B Discovery
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5G ProSe Communication via 5G ProSe Layer-3 UE-to-Network Relay with N3IWF as described in clause 6.5.1.2 is used for multi-hop UE-to-Network Relay after Model B Discovery with the following differences and clarifications:
Figure 6.5.1.5-1: 5G ProSe Communication via Multi-hop 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support
1. 5G ProSe Layer-3 UE-to-Network Relay performs Registration procedures and obtains the ProSe Policy that corresponds to the operation supporting the access to N3IWF. The 5G ProSe Layer-3 Remote UE is configured with the corresponding ProSe Policy and URSP rules.
Supporting of the RSC configured for making the 5G ProSe Layer-3 Remote UE access to 5GC via N3IWF is preconfigured or provisioned to the Intermediate Relay by the ProSe Policy.
2-4. A 5G ProSe Layer-3 UE-to-Network Relay, 5G ProSe Intermediate Relay(s) and 5G ProSe Layer-3 Remote UE perform multi-hop discovery using the RSC configured for making the 5G ProSe Layer-3 Remote UE access to 5GC via N3IWF. The Remote UE obtains the path information to the UE-to-Network Relay(s) from the discovery procedure. Details of discovery procedure and path establishement procedure are described in clause 6.3.2.5.3 and clause 6.4.3.9, respectively.
5. The 5G ProSe Layer-3 Remote UE that connects to a 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support selects an N3IWF and determines the N3IWF IP address.
6. The 5G ProSe Layer-3 Remote UE establishes a signalling IPsec tunnel using IKE procedures with an N3IWF via Intermediate Relays and UE-to-Network Relay performs NAS Registration as described in clause 4.12.2.2 of TS 23.502 [5].
7. Based on Additional QoS Information received from the N3IWF, the 5G ProSe Layer-3 Remote UE determines whether it is necessary to request for QoS session modification for the dedicated QoS Flows toward the 5G ProSe Layer-3 UE-to-Network Relay as described in clause 5.6.2.2, taking the number of hops into account.
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6.5.2 5G ProSe Communication via 5G ProSe Layer-2 UE-to-Network Relay
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6.5.2.1 Registration and Connection Management
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6.5.2.1.1 Registration Management
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Registration Management for the 5G ProSe Layer-2 Remote UE and the 5G ProSe Layer-2 UE-to-Network Relay follows the principles and procedures defined in TS 23.501 [4] and TS 23.502 [5]. The 5G ProSe Layer-2 Remote UE and the 5G ProSe Layer-2 UE-to-Network Relay may be served by the same AMF or different AMFs.
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6.5.2.1.2 Connection Management
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Connection Management for the 5G ProSe Layer-2 Remote UE and the 5G ProSe Layer-2 UE-to-Network Relay follows the principles and procedures defined in TS 23.501 [4] and TS 23.502 [5] with the following modifications.
The 5G ProSe Layer-2 UE-to-Network Relay may only relay data/signalling for the 5G ProSe Layer-2 Remote UE(s) when the 5G ProSe Layer-2 UE-to-Network Relay is in CM-CONNECTED state. If the 5G ProSe Layer-2 UE-to-Network Relay is in CM_IDLE state and receives a connection request from the 5G ProSe Layer-2 Remote UE for relaying, the 5G ProSe Layer-2 UE-to-Network Relay shall trigger Service Request procedure to enter CM_CONNECTED state before relaying the 5G ProSe Layer-2 Remote UEs traffic. If the 5G ProSe Layer-2 UE-to-Network Relay in RRC_IDLE receives a connection request from the 5G ProSe Layer-2 Remote UE using emergency RSC, then 5G ProSe Layer-2 UE-to-Network Relay sets the establishment cause to "emergency".
The state of 5G ProSe UE-to-Network Relay is controlled by NG-RAN with the following:
- If any 5G ProSe Layer-2 Remote UE connected to the 5G ProSe Layer-2 UE-to-Network Relay is in CM-CONNECTED with RRC Connected state, the 5G ProSe Layer-2 UE-to-Network Relay shall remain CM-CONNECTED state with RRC Connected state unless the network needs to release the connection.
- If all 5G ProSe Layer-2 Remote UEs connected to the 5G ProSe Layer-2 UE-to-Network Relay enter CM-IDLE or CM-CONNECTED with RRC Inactive state, the 5G ProSe Layer-2 UE-to-Network Relay may enter CM-IDLE state or CM-CONNECTED with RRC Inactive state, or may remain CM-CONNECTED with RRC Connected state.
When 5G ProSe Layer-2 Remote UE is in CM-CONNECTED state, the 5G ProSe Layer-2 UE-to-Network Relay and 5G ProSe Layer-2 Remote UE keep the PC5 link. When the 5G ProSe Remote UE is in CM-IDLE state, it may either release the PC5 link for relaying or not.
For paging a 5G ProSe Layer-2 Remote UE, it follows the principles and procedures defined in TS 23.501 [4] and TS 23.502 [5] and the paging message delivery from NG-RAN to 5G ProSe Layer-2 Remote UE is specified in TS 38.300 [12].
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6.5.2.2 Connection establishment
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Figure 6.5.2.2-1: Connection Establishment for 5G ProSe Layer-2 UE-to-Network Relay
0. If in coverage, the 5G ProSe Layer-2 Remote UE and 5G ProSe Layer-2 UE-to-Network Relay may independently perform the initial registration to the network according to registration procedures in TS 23.502 [5].
1. If in coverage, the 5G ProSe Layer-2 Remote UE and 5G ProSe Layer-2 UE-to-Network Relay independently get the service authorization for 5G ProSe Layer-2 UE-to-Network Relay operation from the network. Service authorization and parameters provisioning for 5G ProSe Layer-2 UE-to-Network Relay operation are performed for the 5G ProSe Layer-2 UE-to-Network Relay and 5G ProSe Layer-2 Remote UE as specified in clause 5.1.4.
If the 5G ProSe Layer-2 Remote UE is "not served by NG-RAN", the pre-configured parameters are used and the service authorization and parameters may be updated after step 6.
If the 5G ProSe Layer-2 Remote UE has not performed Initial Registration, the 5G ProSe Layer-2 Remote UE may perform the Initial Registration in step 6.
2. The 5G ProSe Layer-2 Remote UE and 5G ProSe Layer-2 UE-to-Network Relay perform 5G ProSe UE-to-Network Relay Discovery and selection, as specified in clause 6.3.2.3.
3. The 5G ProSe Layer-2 Remote UE initiates a one-to-one communication connection with the selected 5G ProSe Layer-2 UE-to-Network Relay over PC5 using the procedure as described in clause 6.4.3.
4. The 5G ProSe Layer-2 Remote UE establishes an RRC Connection with the same NG-RAN serving the selected 5G ProSe Layer-2 UE-to-Network Relay, specified in TS 38.300 [12]. The 5G ProSe Layer-2 Remote UE sets the RRC Establishment Cause as defined in TS 38.331 [16].
5. During step 4, if the 5G ProSe Layer-2 UE-to-Network Relay is in CM_IDLE state and receives a trigger from the AS layer to enter CM-CONNECTED state due to Remote UE's AS layer connection set up with the NG-RAN, the 5G ProSe Layer-2 UE-to-Network Relay performs Service Request procedure in the clause 4.2.3.2 of TS 23.502 [5].
6. The 5G ProSe Layer-2 Remote UE sends a NAS message to the serving AMF. The NAS message is encapsulated in an Uu RRC message that is sent over PC5 to the 5G ProSe Layer-2 UE-to-Network Relay and the 5G ProSe Layer-2 UE-to-Network Relay forwards the Uu RRC message to the NG-RAN specified in TS 38.300 [12]. NG-RAN selects the 5G ProSe Layer-2 Remote UE's serving AMF and forwards the NAS message to this AMF.
If 5G ProSe Layer-2 Remote UE has not performed the initial registration, the NAS message is an initial Registration message. Otherwise, the NAS message is either a service request message, or a mobility or periodic Registration message taking into account the TAI in the RRC container received from the 5G ProSe Layer-2 UE-to-Network Relay during Relay Discovery (see clause 5.8.3.3) or PC5-RRC message, as specified in TS 38.300 [12].
7. The 5G ProSe Layer-2 Remote UE may trigger the PDU Session Establishment procedure as defined in clause 4.3.2.2 of TS 23.502 [5].
8. The data is transferred between the 5G ProSe Layer-2 Remote UE and UPF via the 5G ProSe Layer-2 UE-to-Network Relay and NG-RAN. The 5G ProSe Layer-2 UE-to-Network Relay forwards all the data messages between the 5G ProSe Layer-2 Remote UE and NG-RAN, as specified in TS 38.300 [12].
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6.5.2.3 Path switching between direct network communication path and indirect network communication path via 5G ProSe Layer-2 UE-to-Network Relay
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Procedure on indirect-to-direct path switching for 5G ProSe Layer-2 Remote UE in CM-CONNECTED with RRC_CONNECTED state is specified in TS 38.300 [12]. Xn based (as defined in clause 4.9.1.2 of TS 23.502 [5]) and N2 based (as defined in clause 4.9.1.3 of TS 23.502 [5]) Handover procedure is used for inter-gNB indirect-to-direct path switching for 5G ProSe Layer-2 Remote UE in CM-CONNECTED with RRC_CONNECTED state.
Procedure on direct-to-indirect path switching for 5G ProSe Layer-2 Remote UE in CM-CONNECTED with RRC_CONNECTED state is specified in TS 38.300 [12]. Xn based (as defined in clause 4.9.1.2 of TS 23.502 [5]) and N2 based (as defined in clause 4.9.1.3 of TS 23.502 [5]) Handover procedure is used for inter-gNB direct-to-indirect path switching for 5G ProSe Layer-2 Remote UE in CM-CONNECTED with RRC_CONNECTED state with following modification:
- the Source to Target transparent container is modified as specified in clause 9.3.1.29 of TS 38.413 [34].
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6.5.3 5G ProSe UE-to-Network Relay reselection
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After being connected to the 5G ProSe UE-to-Network Relay, the 5G ProSe Remote UE keeps performing the measurement of the signal strength of PC5 unicast link with the 5G ProSe UE-to-Network Relay for relay reselection.
The 5G ProSe UE-to-Network Relay discovery procedures defined in clause 6.3.2.3 are used to discover available 5G ProSe UE-to-Network Relays for 5G ProSe UE-to-Network Relay reselection.
For 5G ProSe Multi-hop UE-to-Network Relay, relay reselection is triggered if a 5G ProSe UE-to-Network Relay or Intermediate UE-to-Network Relay is no longer available, if a connection with the previous or next relay is lost, or if the link quality drops below a configured threshold. The path failure (connection lost or link quality drop) may be detected by a lower layer (e.g. PC5-RRC layer). The lower layer (e.g. PC5-RRC layer) indicates to an upper layer (e.g. PC5-S signalling layer) about the detected failure, together with the information on the detected failure/event and the PC5 Link Identifier for the unicast link (which can be used to retrieve the corresponding UE ID(s) and path information from the link context).
For 5G ProSe Multi-hop UE-to-Network Relay reselection is performed as described in clause 6.4.3.8.3 for model A discovery and clause 6.4.3.9.3 for model B discovery.
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6.5.4 5G ProSe Remote UE traffic handling for 5G ProSe UE-to-Network Relay support
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For the 5G ProSe Remote UE to access the service via 5G ProSe UE-to-Network Relay, the following apply:
- The application traffic on the 5G ProSe Remote UE is managed by URSP rules (with consideration of local configurations), following the procedure defined in clauses 6.1.2.2.1 and 6.6.2.3 of TS 23.503 [9]. The URSP rules defined in clause 6.6.2.1 of TS 23.503 [9] applies for the 5G ProSe Remote UE, with RSD enhanced to include:
- a "ProSe Layer-3 UE-to-Network Relay Offload indication"; or
- a "ProSe Multi-path Preference".
- If an application or application traffic matches a URSP rule, corresponding RSDs shall be used to evaluate the existing PDU sessions, or establish a new PDU session, or determine to offload outside of a PDU session, or multi-path communication via 5G ProSe Layer-3 UE-to-Network Relay outside of a PDU session and a PDU Session over Uu reference point.
- If the selected RSD contains "ProSe Layer-3 UE-to-Network Relay Offload indication":
- The 5G ProSe Remote UE will route the traffic to the 5G ProSe Layer-3 UE-to-Network Relay connection without establishing a PDU session, when such connection is available.
This may trigger the 5G ProSe Remote UE to start 5G ProSe UE-to-Network Relay discovery if it is not yet started. The discovery and establishment of the connection with the 5G ProSe Layer-3 UE-to-Network Relay is controlled by the ProSe Policy (pre-) configured on the 5G ProSe Remote UE.
- If the matched URSP rule contains both a RSD with ''Non-Seamless Offload indication" and a RSD with "ProSe Layer-3 UE-to-Network Relay Offload indication", whether to offload the traffic to non-3GPP access or the 5G ProSe Layer-3 UE-to-Network Relay connection depends on the priority of the RSDs and the availability of the connections, as specified in the clause 6.6.2.3 of TS 23.503 [9].
- If the selected RSD does not contain the "ProSe Layer-3 UE-to-Network Relay Offload indication" or, "Non-Seamless Offload indication", the 5G ProSe Remote UE shall use a PDU session to route the corresponding application traffic.
If configured in the ProSe Policy, the 5G ProSe Remote UE may attempt the discovery of a Relay Service Code corresponding to a 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support in the discovery procedure, when the non-3GPP access type is preferred in the selected RSD. The 5G ProSe Remote UE may attempt the discovery of a Relay Service Code corresponding to a 5G ProSe Layer-2 UE-to-Network Relay in the discovery procedure, when the 3GPP access type is preferred in the selected RSD.
- If the selected RSD contains "ProSe Multi-path Preference":
- The 5G ProSe Remote UE is preferred to route the traffic over a PC5 connection with a 5G ProSe Layer-3 UE-to-Network Relay and a PDU Session matched to other components (e.g. Network Slice Selection) in the selected RSD. If either connection is not available then the traffic may be routed via a PC5 connection with a 5G ProSe Layer-3 UE-to-Network Relay or a PDU Session matched to other components.
- If the PC5 connection with 5G ProSe Layer-3 UE-to-Network Relay associated with the desired RSC is not available, this may trigger the 5G ProSe Remote UE to start 5G ProSe UE-to-Network Relay discovery and connection establishment, controlled by the ProSe Policy configured on the 5G ProSe Remote UE. If the PC5 connection with 5G ProSe Layer-3 UE-to-Network Relay associated with the desired RSC is available, this may trigger Layer-2 link modification to associate the corresponding ProSe service into the PC5 connection. Determination on the desired RSC is based on the Policy/Parameters specified in clause 5.1.4.1.
- If the PDU Session matched to other components in the selected RSD is not available, this may trigger the establishment of a new PDU Session over Uu reference point using the values specified by the selected RSD.
- If the 5G ProSe Remote UE has an indirect connection via a 5G ProSe Layer-2 UE-to-Network Relay connection available, it will be treated as the "3GPP" access type. If the 5G ProSe Remote UE has an indirect connection via a 5G ProSe Layer-3 UE-to-Network Relay with N3IWF support available, it will be treated as the "non-3GPP" access type. The URSP handling as defined in TS 23.503 [9] applies.
For the 5G ProSe Layer-3 UE-to-Network Relay and 5G ProSe Layer-2 UE-to-Network Relay, the URSP handling does not apply to the relayed traffic from the 5G ProSe Remote UE.
For the 5G ProSe Layer-3 UE-to-Network Relay, the PDU session established for relaying the 5G ProSe Remote UE's traffic is controlled by the ProSe Policy.
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6.5.5 Procedures for Communication Path Switching between Two UE-to-Network Relays
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6.5.5.1 General
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The communication path switching between two UE-to-Network Relays includes the following scenarios:
- Layer-3 UE-to-Network Relay with N3IWF switching from/to Layer-3 UE-to-Network Relay with N3IWF.
- Layer-3 UE-to-Network Relay without N3IWF switching from/to Layer-3 UE-to-Network Relay without N3IWF.
- Layer-3 UE-to-Network Relay without N3IWF switching from/to Layer-3 UE-to-Network Relay with N3IWF.
- Layer-2 UE-to-Network Relay switching from/to Layer-2 UE-to-Network Relay.
- Layer-2 UE-to-Network Relay switching from/to Layer-3 UE-to-Network Relay without N3IWF.
- Layer-2 UE-to-Network Relay switching from/to Layer-3 UE-to-Network Relay with N3IWF.
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6.5.5.2 Procedures for Communication Path Switching between UE-to-Network Relays
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This clause specifies the communication path switching procedures between two UE-to-Network Relays.
When performing the path switching between two 5G ProSe Layer-3 UE-to-Network Relay without N3IWF, or between 5G ProSe Layer-3 UE-to-Network Relay without N3IWF and 5G ProSe Layer-2 UE-to-Network Relay, or between 5G ProSe Layer-3 UE-to-Network Relay without N3IWF and 5G ProSe Layer-3 UE-to-Network Relay with N3IWF, the application layer procedures are used for service continuity support which is out of scope of this specification.
Path switching between two 5G ProSe Layer-3 UE-to-Network Relay with N3IWF is performed using the mechanism specified for Local mobility anchor within untrusted non-3GPP access networks using MOBIKE in clause 6.2.9 of TS 23.501 [4].
When a 5G ProSe-enabled UE as a 5G ProSe Layer-2 Remote UE in CM-CONNECTED state switches the communication path to Layer-3 UE-to-Network Relay with N3IWF, 5G ProSe-enabled UE's PDU session(s) can handover to the indirect path via Layer-3 UE-to-Network Relay with N3IWF by reusing the procedures specified in clause 4.9.2 of TS 23.502 [5].
When a 5G ProSe-enabled UE as a 5G ProSe Layer-3 Remote UE switches the communication path from Layer-3 UE-to-Network Relay with N3IWF to an indirect path via Layer-2 UE-to-Network Relay, 5G ProSe-enabled UE's PDU session(s) can handover to the indirect path via Layer-2 UE-to-Network Relay by reusing the procedures specified in clause 4.9.2 of TS 23.502 [5].
Procedure on Path switching between two 5G ProSe Layer-2 UE-to-Network Relays is specified in TS 38.300 [12]. Xn based (as defined in clause 4.9.1.2 of TS 23.502 [5]) and N2 based (as defined in clause 4.9.1.3 of TS 23.502 [5]) Handover procedure is used for inter-gNB indirect-to-indirect path switching for 5G ProSe Layer-2 Remote UE in CM-CONNECTED with RRC_CONNECTED state with following modification:
- the Source to Target transparent container is modified as specified in clause 9.3.1.29 of TS 38.413 [34].
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6.6 Procedures for Service Authorization to NG-RAN
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6.6.1 General
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In order to support PC5 radio resource control in NG-RAN, ProSe service Authorisation information and PC5 QoS parameters for ProSe need to be made available in NG-RAN. This clause describes the corresponding procedures and aspects.
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6.6.2 Registration procedure
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The Registration procedure for UE is performed as defined in TS 23.502 [5] clause 4.2.2.2 with the following additions:
- The UE includes the 5G ProSe Capability as part of the "5GMM capability" in the Registration Request message. The AMF stores the 5G ProSe Capability for 5G ProSe operation.
- The 5G ProSe Capability indicates whether the UE supports one or more of the following ProSe capabilities:
- 5G ProSe Direct Discovery;
- 5G ProSe Direct Communication;
- 5G ProSe Layer-2 UE-to-Network Relay;
- 5G ProSe Layer-3 UE-to-Network Relay;
- 5G ProSe Layer-2 Remote UE;
- 5G ProSe Layer-3 Remote UE;
- 5G ProSe Layer-2 UE-to-UE Relay;
- 5G ProSe Layer-3 UE-to-UE Relay;
- 5G ProSe Layer-2 End UE;
- 5G ProSe Layer-3 End UE;
- 5G ProSe Layer-3 UE-to-Network Relay supporting 5G ProSe Layer-3 multi-hop UE-to-Network Relay;
- 5G ProSe Layer-3 Remote UE supporting 5G ProSe Layer-3 multi-hop UE-to-Network Relay;
- 5G ProSe Layer-3 Intermediate UE-to-Network Relay;
- 5G ProSe Layer-2 UE-to-Network Relay supporting 5G ProSe Layer-2 multi-hop UE-to-Network Relay;
- 5G ProSe Layer-2 Remote UE supporting 5G ProSe Layer-2 multi-hop UE-to-Network Relay;
- 5G ProSe Layer-2 Intermediate UE-to-Network Relay;
- 5G ProSe Layer-3 UE-to-UE Relay supporting 5G ProSe Layer-3 multi-hop UE-to-UE Relay;
- 5G ProSe Layer-3 End UE supporting 5G ProSe Layer-3 multi-hop UE-to-UE Relay.
NOTE 1: Encoding of these capabilities is defined in TS 24.501 [38].
- The AMF obtains the 5G ProSe subscription data as part of the user subscription data from UDM during UE Registration procedure using Nudm_SDM service as defined in clause 4.2.2.2.2 of TS 23.502 [5].
- The AMF determines whether the UE is authorised to use 5G ProSe services based on UE's 5G ProSe Capability and the ProSe Service Authorisation included in the subscription data received from UDM as specified in clause 5.7. ProSe NR UE-PC5-AMBR is also provided to the AMF as part of the subscription data for 5G ProSe services. The AMF stores the authorized 5G ProSe Capability.
- The AMF sends the authorized 5G ProSe Capability for 5G ProSe operation to PCF. Based on the received 5G ProSe Capability from the AMF, the PCF provides the PC5 QoS parameters for 5G ProSe to AMF. The AMF stores such information as part of the UE context.
- If the UE is authorised to use 5G ProSe services, then the AMF shall include in a NGAP message sent to NG-RAN:
- "5G ProSe authorised" information, including one or more of the following:
- whether the UE is authorized to use 5G ProSe Direct Discovery;
- whether the UE is authorized to use 5G ProSe Direct Communication;
- whether the UE is authorized to act as a 5G ProSe Layer-2 UE-to-Network Relay;
- whether the UE is authorized to act as a 5G ProSe Layer-3 UE-to-Network Relay;
- whether the UE is authorized to act as a 5G ProSe Layer-2 Remote UE;
- whether the UE is authorized to use multi-path communication via direct Uu path and via 5G ProSe Layer-2 UE-to-Network Relay as a 5G ProSe Layer-2 Remote UE;
- whether the UE is authorized to act as a 5G ProSe Layer-2 UE-to-UE Relay;
- whether the UE is authorized to act as a 5G ProSe Layer-2 End UE;
- whether the UE is authorized to act as a 5G ProSe Layer-3 UE-to-Network Relay supporting 5G ProSe Layer-3 multi-hop UE-to-Network Relay;
- whether the UE is authorized to act as a 5G ProSe Layer-2 UE-to-Network Relay supporting 5G ProSe Layer-2 multi-hop UE-to-Network Relay;
- whether the UE is authorized to act as a 5G ProSe Layer-2 Intermediate UE-to-Network Relay;
- whether the UE is authorized to act as a 5G ProSe Layer-2 Remote UE supporting 5G ProSe Layer-2 multi-hop UE-to-Network Relay.
NOTE 2: The authorization for "5G ProSe Direct discovery" and "5G ProSe Direct communication" can be used for 5G ProSe Layer-3 UE-to-UE Relay, 5G ProSe Layer-3 End UE, 5G ProSe Layer-3 UE-to-UE Relay supporting 5G ProSe Layer-3 multi-hop UE-to-UE Relay and 5G ProSe Layer-3 End UE supporting 5G ProSe Layer-3 multi-hop UE-to-UE Relay.
- ProSe NR UE-PC5-AMBR, used by NG-RAN for the resource management of UE's PC5 transmission for 5G ProSe services in network scheduled mode.
- the PC5 QoS parameters for 5G ProSe used by the NG-RAN for the resource management of UE's PC5 transmission for ProSe services in network scheduled mode.
- If the UE is authorised to use 5G ProSe services, then the AMF should not initiate the release of the signalling connection after the completion of the Registration procedure. The release of the signalling connection relies on the decision of NG-RAN, as specified in TS 23.502 [5].
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6.6.3 Service Request procedure
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The Service Request procedures for UE in CM-IDLE state are performed as defined in TS 23.502 [5] clause 4.2.3.2 and clause 4.2.3.3 with the following additions:
- If the UE is authorised to use ProSe services, then the AMF shall include "ProSe authorised" information in the NGAP message, indicating which of the ProSe services the UE is authorised to use as described in clause 6.6.2.
- The AMF includes the ProSe NR UE-PC5-AMBR in the NGAP message to the NG-RAN as part of the UE context and NG-RAN may use in resource management of UE's PC5 transmission for ProSe services in network scheduled mode.
- The AMF sends the PC5 QoS parameters for ProSe to NG-RAN via N2 signalling. The PC5 QoS parameters for ProSe may be stored in the UE context after the registration procedure. If the UE is authorised to use ProSe services but AMF does not have PC5 QoS parameters for ProSe available, the AMF fetches the PC5 QoS parameters for ProSe from the PCF.
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6.6.4 N2 Handover procedure
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The N2 based handover procedures for UE are performed as defined in TS 23.502 [5] clause 4.9.1.3 with the following additions:
- If the UE is authorised to use ProSe services, then the target AMF shall send the "ProSe authorised" information, ProSe NR UE-PC5-AMBR and PC5 QoS parameters for ProSe to the target NG-RAN in the NGAP Handover Request message.
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6.6.5 Xn Handover procedure
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The Xn based handover procedures for UE are performed as defined in TS 23.502 [5] clause 4.9.1.2 with the following additions:
- If the "ProSe authorised" information is included in the UE context, then the source NG-RAN shall include a "ProSe authorised" information, ProSe NR UE-PC5-AMBR and PC5 QoS parameters for ProSe in the XnAP Handover Request message to the target NG-RAN.
- If the "ProSe authorised" information is included in the UE context, then the AMF shall send the "ProSe authorised" information, the ProSe NR UE-PC5-AMBR and PC5 QoS parameters for ProSe to the target NG-RAN in the Path Switch Request Acknowledge message.
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6.6.6 Subscriber Data Update Notification to AMF
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The procedure of Subscriber Data Update Notification to AMF is performed as defined in TS 23.502 [5] clause 4.5.1 with the following additions:
- The Nudm_SDM_Notification service operation may contain the ProSe Service Authorisation or the ProSe NR UE-PC5-AMBR or any combination.
- The AMF updates the UE Context with the above new ProSe subscription data.
- When the AMF updates UE context stored at NG-RAN, the UE context contains the ProSe subscription data.
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6.6.7 Delivery of PC5 QoS parameters for ProSe to NG-RAN
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The UE Policy Association Establishment procedure and UE Policy Association Modification procedure, as defined in TS 23.502 [5], is used to provide the AMF with PC5 QoS parameters used by NG-RAN. When receiving the 5G ProSe Capability in Npcf_UEPolicyControl_Create Request from the AMF or when receiving the updated subscription data from UDR, the PCF generates the PC5 QoS parameters used by NG-RAN corresponding to a UE as defined in clause 5.4.2 of TS 23.287 [2].
The (V-)PCF provides the information to the AMF as follows:
- In the roaming case, the H-PCF includes the PC5 QoS parameters used by NG-RAN in the Npcf_UEPolicyControl_Create Response message or Npcf_UEPolicyControl UpdateNotify Request message sent to V-PCF in an N2 PC5 policy container and V-PCF relays this N2 PC5 policy container as the N2 container in the Namf_Communication_N1N2MessageTransfer message sent to AMF.
- In the non-roaming case, the PCF includes the PC5 QoS parameters used by NG-RAN in an N2 container in Namf_Communication_N1N2MessageTransfer message sent to AMF.
When the AMF receives the N2 PC5 policy container from (V-)PCF, the AMF stores such information as part of the UE context.
In the UE Configuration Update procedure triggered by UE Policy Association Establishment or UE Policy Association Modification:
- The AMF forwards the PC5 QoS parameters in the NGAP message to the NG-RAN if a N2 PC5 policy container is received in the Namf_Communication_N1N2MessageTransfer message.
NOTE 1: If the PC5 QoS parameters are provided to both NG-RAN and UE, both the N2 PC5 Policy Container and the UE Policy Container are included in the Namf_Communication_N1N2MessageTransfer message.
NOTE 2: Non-UE specific PC5 QoS parameters, e.g. default PC5 QoS parameters, can also be locally configured in NG-RAN. How such configuration is performed is out of scope of this specification.
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6.7 5G ProSe UE-to-UE Relay Communication
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6.7.1 5G ProSe Communication via 5G ProSe Layer-3 UE-to-UE Relay
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6.7.1.1 Layer-2 link establishment for PC5 communication via 5G ProSe Layer-3 UE-to-UE Relay
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Figure 6.7.1.1-1 shows the procedure for Layer-2 link establishment via 5G ProSe Layer-3 UE-to-UE Relay.
Figure 6.7.1.1-1: Layer-2 link establishment via 5G ProSe Layer-3 UE-to-UE Relay
1. Service authorization and provisioning are performed for source 5G ProSe Layer-3 End UE, target 5G ProSe Layer-3 End UE and 5G ProSe Layer-3 UE-to-UE Relay as described in clause 6.2.
2. The source 5G ProSe Layer-3 End UE performs discovery of a 5G ProSe Layer-3 UE-to-UE Relay as described in clause 6.3.2.4.
3. The source 5G ProSe Layer-3 End UE sends a Direct Communication Request message to initiate the unicast Layer-2 link establishment procedure with the 5G ProSe Layer-3 UE-to-UE Relay. The parameters included in the Direct Communication Request message are described in clause 6.4.3.7.
The Source Layer-2 ID of the Direct Communication Request message is self-assigned by the source 5G ProSe Layer-3 End UE and the Destination Layer-2 ID is set to the Source Layer-2 ID of the discovery message of the 5G ProSe Layer-3 UE-to-UE Relay.
The source 5G ProSe Layer-3 End UE gets application information and optional ProSe Application Requirements from ProSe application layer and determines the end-to-end QoS parameters as described in clause 5.6.3.1.
4. If the User Info ID of 5G ProSe Layer-3 UE-to-UE Relay in the Direct Communication Request message matches the 5G ProSe UE-to-UE Relay's User Info ID and the RSC in the Direct Communication Request matches one RSC that the relay is (pre)configured with, as specified in clause 5.1.5.1, the 5G ProSe Layer-3 UE-to-UE Relay responds by establishing the security with the source 5G ProSe Layer-3 End UE. When the security protection is enabled, the source 5G ProSe Layer-3 End UE sends the parameters as described in clause 6.4.3.7 to the 5G ProSe Layer-3 UE-to-UE Relay.
If the Ethernet MAC address of source 5G ProSe Layer-3 End UE is already used by another 5G ProSe Layer-3 End UE, then the 5G ProSe Layer-3 UE-to-UE Relay rejects the direct link establishment indicating that the MAC address is not unique.
The Source Layer-2 ID used for the security establishment procedure is self-assigned by the 5G ProSe Layer-3 UE-to-UE Relay and the Destination Layer-2 ID is set to the Source Layer-2 ID of the received Direct Communication Request message.
The 5G ProSe Layer-3 UE-to-UE Relay shall choose different Source Layer-2 IDs for PC5 links of different types of traffic, i.e. IP traffic, Ethernet traffic and Unstructured traffic.
If the PC5 link is used for transferring Unstructured traffic, the 5G ProSe Layer-3 UE-to-UE Relay shall choose different Source Layer-2 IDs for different pair of source and target 5G ProSe Layer-3 End UEs.
Upon receiving the security establishment procedure messages, the source 5G ProSe Layer-3 End UE obtains the 5G ProSe Layer-3 UE-to-UE Relay's Layer-2 ID for future communication, for signalling and data traffic for this unicast link.
5. After the Security Establishment procedure in step 4 is completed, the 5G ProSe Layer-3 UE-to-UE Relay decides whether to use an existing unicast Layer-2 link between itself and the target 5G ProSe End UE for the required service. If there is no existing unicast Layer-2 link of the required RSC with the target 5G ProSe Layer-3 End UE, the 5G ProSe Layer-3 UE-to-UE Relay sends a Direct Communication Request message to initiate the unicast Layer-2 link establishment procedure with the target 5G ProSe Layer-3 End UE. The parameters included in the Direct Communication Request message are described in clause 6.4.3.7.
The Source Layer-2 ID of the Direct Communication Request message is self-assigned by the 5G ProSe Layer-3 UE-to-UE Relay and the Destination Layer-2 ID may be broadcast or unicast Layer-2 ID. Unicast Layer-2 ID is used only if the Layer-2 ID of the target 5G ProSe Layer-3 End UE associated with the user info (i.e. Application Layer ID) is known to the 5G ProSe Layer-3 UE-to-UE Relay.
The 5G ProSe Layer-3 UE-to-UE Relay shall choose different Source Layer-2 IDs for PC5 links of different types of traffic, i.e. IP traffic, Ethernet traffic and Unstructured traffic.
If the PC5 link is used for transferring Unstructured traffic, the 5G ProSe Layer-3 UE-to-UE Relay shall choose different Source Layer-2 IDs for different pair of source and target 5G ProSe Layer-3 End UEs.
6. If the RSC included in the Direct Communication Request matches the target UE's RSC that the target UE is (pre)configured with as specified in clause 5.1.5.1 and if the user info included in the Direct Communication Request matches the target UE's user info, the target 5G ProSe Layer-3 End UE responds by establishing the security with the 5G ProSe Layer-3 UE-to-UE Relay. When the security protection is enabled, the 5G ProSe Layer-3 UE-to-UE Relay sends the parameters as described in clause 6.4.3.7 to the target 5G ProSe Layer-3 End UE.
The Source Layer-2 ID used for the security establishment procedure is self-assigned by the target 5G ProSe Layer-3 End UE and the Destination Layer-2 ID is set to the Source Layer-2 ID of the received Direct Communication Request message.
Upon receiving the security establishment procedure messages, the 5G ProSe Layer-3 UE-to-UE Relay obtains the target 5G ProSe Layer-3 End UE's Layer-2 ID for future communication, for signalling and data traffic for this unicast link.
7. The target 5G ProSe Layer-3 End UE sends a Direct Communication Accept message to the 5G ProSe Layer-3 UE-to-UE Relay that has successfully established security with. The parameters included in the Direct Communication Accept message are described in clause 6.4.3.7.
NOTE: The 5G ProSe Layer-3 UE-to-UE Relay can detect that the Ethernet MAC address of target 5G ProSe Layer-3 End UE is already used by another 5G ProSe Layer-3 End UE when it receives the Direct Communication Accept message.
8. For IP traffic, IPv6 prefix or IPv4 address is allocated for the target 5G ProSe Layer-3 End UE as defined in clause 5.5.1.4.
9. After receiving the Direct Communication Accept message from the target 5G ProSe Layer-3 End UE, the 5G ProSe Layer-3 UE-to-UE Relay sends a Direct Communication Accept message to the source 5G ProSe Layer-3 End UE that has successfully established security with. The parameters included in the Direct Communication Accept message are described in clause 6.4.3.7.
10. For IP traffic, IPv6 prefix or IPv4 address is allocated for the source 5G ProSe Layer-3 End UE as defined in clause 5.5.1.4.
11. For IP communication, the 5G ProSe Layer-3 UE-to-UE Relay may store an association of user info (i.e. Application Layer ID) and the IP address of target 5G ProSe Layer-3 End UE into its DNS entries and the 5G ProSe Layer-3 UE-to-UE Relay may act as a DNS server to other UEs. The source 5G ProSe Layer-3 End UE may send a DNS query to the 5G ProSe Layer-3 UE-to-UE Relay to request IP address of target 5G ProSe Layer-3 End UE after step 10 if the IP address of target 5G ProSe Layer-3 End UE is not received in step 9 and the 5G ProSe Layer-3 UE-to-UE Relay returns the IP address of the target 5G ProSe Layer-3 End UE to the source 5G ProSe Layer-3 End UE.
When handling DNS query, the 5G ProSe Layer-3 UE-to-UE Relay should only use the DNS entry associated to the related RSC, i.e. the UE-to-UE Relay determines the RSC based on local information (e.g. link profile including RSC, Layer-2 ID, User Info, etc.) corresponding to the PC5 link that the DNS query message is received.
For Ethernet communication, the 5G ProSe Layer-3 UE-to-UE Relay maintains the association between PC5 links and Ethernet MAC addresses received from the 5G ProSe Layer-3 End UE.
For Unstructured traffic communication, for each pair of source and target 5G ProSe Layer-3 End UEs, the 5G ProSe Layer-3 UE-to-UE Relay maintains the 1:1 mapping between the PC5 link with source 5G ProSe Layer-3 End UE and the PC5 link with target 5G ProSe Layer-3 End UE.
12. The source 5G ProSe Layer-3 End UE communicates with the target 5G ProSe Layer-3 End UE via the 5G ProSe Layer-3 UE-to-UE Relay.
In the case of one source 5G ProSe Layer-3 End UE communicates with multiple target 5G ProSe Layer-3 End UEs, the PC5 link between the source 5G ProSe Layer-3 End UE and the 5G ProSe Layer-3 UE-to-UE Relay can be shared for multiple target 5G ProSe Layer-3 End UEs per RSC while the PC5 links may be established individually between the 5G ProSe Layer-3 UE-to-UE Relay and target 5G ProSe Layer-3 End UEs per RSC. For the shared PC5 link, the Layer-2 link modification procedure shall be used, replacing the step 3 to 4 and 9 to 10 of the procedure in Figure 6.7.1.1-1. The parameters used in the Layer-2 link modification procedure are described in clause 6.4.3.7.
In the case of multiple source 5G ProSe Layer-3 End UEs communicate with one target 5G ProSe Layer-3 End UE, the PC5 link between the 5G ProSe Layer-3 UE-to-UE Relay and the target 5G ProSe Layer-3 End UE can be shared per RSC while the PC5 links may be established individually between the source 5G ProSe Layer-3 End UEs and the 5G ProSe Layer-3 UE-to-UE Relay per RSC. For the shared PC5 link, the Layer-2 link modification procedure shall be used, replacing the step 5 to 8 of the procedure in Figure 6.7.1.1-1. The parameters used in the Layer-2 link modification procedure are described in clause 6.4.3.7.
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6.7.1.2 Link identifier update for PC5 communication via 5G ProSe Layer-3 UE-to-UE Relay
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The Link Identifier Update procedure as defined in clause 6.4.3.2 is reused between source 5G ProSe Layer-3 End UE and 5G ProSe Layer -3 UE-to-UE Relay to perform a link identifier update. When the IP address/prefix is changed, the new one is shared between source 5G ProSe Layer-3 End UE and target 5G ProSe Layer-3 End UE as depicted in Figure 6.7.1.2-1.
Figure 6.7.1.2-1: Link Identifier Update and IP address/prefix sharing via 5G ProSe Layer-3 UE-to-UE Relay
0. A PC5 link is established between a source 5G ProSe Layer-3 End UE (i.e. UE1) and a 5G ProSe Layer-3 UE-to-UE Relay (i.e. UE-to-UE Relay). Another PC5 link is established between the UE-to-UE Relay and the target 5G ProSe Layer-3 End UE (i.e. UE2). IP data may be exchanged between UE1 and UE2 via the UE-to-UE Relay over the PC5 links. During the link establishment, UE1 informs the UE-to-UE Relay that the link requires privacy.
1. As stated in clause 6.4.3.2, according to the privacy requirement, UE1 may trigger link identifier update procedure. UE1 sends a Link Identifier Update Request message to the UE-to-UE Relay including the following parameters:
- its new Layer-2 ID, new security information, new Application layer ID (if provided by the upper layer).
- If UE1's IP address/prefix needs to be changed:
- if UE 1's IP address/prefix is allocated by the UE-to-UE Relay, UE1 includes "new IP address needed" indication.
- if UE1 self-assign its IP address/prefix, UE1 includes its new IP address/prefix.
- its peer UEs information (e.g. UE2's IP address, UE2's Application layer ID), allowing the UE-to-UE Relay to inform UE1's peer UEs (e.g. UE2) about UE1's new allocated IP address/prefix.
2. UE-to-UE Relay self-assigns a new L2 ID, new security information and possibly new IP address/prefix for PC5 link with UE1.
a. If a "new IP address needed" indication is received, UE-to-UE Relay assigns a new IP address/prefix to UE1 and saves it locally.
Based on peer UE's information, UE-to-UE Relay then sends a PC5 Relay Update Request message to each peer UE (e.g. UE2), including: UE1's old IP address/prefix, UE1's old and new Application layer ID, UE1's new IP address/prefix.
3. UE2 receives the PC5 Relay Update Request message and saves UE1's new IP address/prefix. UE2 sends a PC5 Relay Update Response message to the UE-to-UE Relay including all parameters received on the PC5 Relay Update Request message.
UE2 continues to receive IP data with UE1's old IP address (transit packets sent prior to UE1's receiving its new IP address) until an IP packet using UE1's new IP address is received. At this point, UE2 starts using UE1's new IP address and may forget UE1's old IP address.
4. UE-to-UE Relay sends a Link Identifier Update Response message to UE1 including UE1's new IP address/prefix, UE-to-UE Relay's new Layer-2 ID, new security information and possibly new IP address/prefix and/or new Application layer ID.
5. UE1 saves its new IP address/prefix and UE-to-UE Relay's new parameters and sends a Link Identifier Update ACK message to the UE-to-UE Relay, including its new IP address received on the Link Identifier Update Response message. UE1 and UE-to-UE Relay start using the new Layer-2 IDs and new security information for PC5 communication. UE1 starts using its new IP address for IP data exchange with UE2.
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6.7.1.3 Layer-2 link release for PC5 communication via 5G ProSe Layer-3 UE-to-UE Relay
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Figure 6.7.1.3-1 shows the Layer-2 link release procedure via 5G ProSe Layer-3 UE-to-UE Relay.
Figure 6.7.1.3-1: Layer-2 Link Release procedure via 5G ProSe Layer-3 UE-to-UE Relay
0. The source 5G ProSe Layer-3 End UE and the 5G ProSe Layer-3 UE-to-UE Relay and the 5G ProSe Layer-3 UE-to-UE Relay and the target 5G ProSe Layer-3 End UE have a unicast link established as described in clause 6.7.1.1.
1. The source 5G ProSe Layer-3 End UE sends a Disconnect Request message to the 5G ProSe Layer-3 UE-to-UE Relay in order to release the layer-2 link and deletes all context data associated with the layer-2 link.
2. Upon reception of the Disconnect Request message, the 5G ProSe Layer-3 UE-to-UE Relay shall respond with a Disconnect Response and deletes all context data associated with the layer-2 link.
3a. Upon reception of the Disconnect Request message, the 5G ProSe Layer-3 UE-to-UE Relay sends a Disconnect Request message to the target 5G ProSe Layer-3 End UE(s), which has a unicast link for the communication with the source 5G ProSe Layer-3 End UE if there are no other UEs using the layer-2 link.
4a. Upon reception of the Disconnect Request message, the target 5G ProSe Layer-3 End UE shall respond with a Disconnect Response message.
3b. Upon reception of the Disconnect Request message, the 5G ProSe Layer-3 UE-to-UE Relay sends a Link Modification Request message to the target 5G ProSe Layer-3 End UE(s), which has a unicast link for the communication with the source 5G ProSe Layer-3 End UE if there are other UEs using the layer-2 link in order to release the PC5 QoS Flow(s) and deletes the context data associated with the PC5 QoS Flow(s).
4b. Upon reception of the Link Modification Request message, the target 5G ProSe Layer-3 End UE shall respond with a Link Modification Accept message and deletes the context data associated with the PC5 QoS Flow(s) used for the communication with the source 5G ProSe Layer-3 End UE.
The ProSe layer of the 5G ProSe Layer-3 UE-to-UE Relay and the target 5G ProSe Layer-3 End UE provides information about the unicast link modification to the AS layer, which enables the AS layer to update the context related to the modified unicast link.
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6.7.1.4 Layer-2 link modification for PC5 communication via 5G ProSe Layer-3 UE-to-UE Relay
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Figure 6.7.1.4-1 shows the Layer-2 link modification procedure via Layer-3 UE-to-UE Relay. This procedure is used to add/modify/remove PC5 QoS Flow(s) in the existing PC5 unicast link as described in clause 6.4.3.7.3.
Figure 6.7.1.4-1: Layer-2 link modification procedure via Layer-3 UE-to-UE Relay
0. UE-1 and UE-to-UE Relay and UE-to-UE Relay and UE-2 have a unicast link established as described in clause 6.7.1.1.
1. UE-1 sends a Link Modification Request to UE-to-UE Relay as described in clause 6.4.3.7.3.
2. Upon reception of the Link Modification Request message from UE-1, the UE-to-UE Relay sends a Link Modification Request to UE-2 as described in clause 6.4.3.7.3.
3. UE-2 responds with a Link Modification Accept message to the UE-to-UE Relay as described in clause 6.4.3.7.3.
4. Upon reception of the Link Modification Accept message from UE-2, the UE-to-UE Relay responds with a Link Modification Accept message to the UE-1 as described in clause 6.4.3.7.3.
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6.7.1.5 Layer-2 link maintenance for PC5 communication via 5G ProSe Layer-3 UE-to-UE Relay
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The Layer-2 link maintenance over the PC5 reference point procedure as described in clause 6.4.3.5 can be used for the Layer-2 link established between the source 5G ProSe Layer-3 End UE and the 5G ProSe Layer-3 UE-to-UE Relay and between the 5G ProSe Layer-3 UE-to-UE Relay and the target 5G ProSe Layer-3 End UE.
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6.7.2 5G ProSe Communication via 5G ProSe Layer-2 UE-to-UE Relay
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This procedure applies to 5G ProSe Layer-2 UE-to-UE Relay.
Figure 6.7.2-1: 5G ProSe Communication via 5G ProSe Layer-2 UE-to-UE Relay
Service authorization and provisioning has been performed for the 5G ProSe Layer-2 UE-to-UE Relay and the 5G ProSe End UEs as described in clause 6.2 before this procedure.
1. Model A or Model B 5G ProSe UE-to-UE Relay Discovery as described in clause 6.3.2.4 is performed and a source 5G ProSe End UE selects a suitable 5G ProSe Layer-2 UE-to-UE Relay for the communication with a target 5G ProSe End UE.
2. The source 5G ProSe End UE decides whether to use an existing PC5 link with the 5G ProSe UE-to-UE Relay for the required service. If an existing PC5 link is used then the Layer-2 link modification procedure as specified in clause 6.4.3.7 is used towards a 5G ProSe UE-to-UE Relay, otherwise a Layer-2 link establishment procedure is used towards a 5G ProSe UE-to-UE Relay.
This procedure is towards the selected 5G ProSe UE-to-UE Relay and for Layer-2 link establishment, the security establishment is performed before step 3 is initiated.
NOTE: The source 5G ProSe Layer-2 End UE does not initiate any Layer-2 link establishment or Layer-2 link modification procedure towards the same 5G ProSe Layer-2 UE-to-UE Relay for a different target 5G ProSe Layer-2 End UE unless the current Layer-2 link establishment or Layer-2 link modification procedure has been completed including reception of the PC5-RRC message from the 5G ProSe Layer-2 UE-to-UE Relay as specified in TS 38.300 [12]. Therefore, the source 5G ProSe Layer-2 End UE can recognize the target 5G ProSe Layer-2 End UE of the Layer-2 ID provided by the 5G ProSe Layer-2 UE-to-UE Relay.
3. The 5G ProSe Layer-2 UE-to-UE Relay decides whether to use an existing PC5 link between the 5G ProSe UE-to-UE Relay and the target 5G ProSe End UE for the required service and initiates Layer-2 link establishment procedure or Layer-2 link modification procedure as specified in clause 6.4.3.7 with the target 5G ProSe End UE.
If the Layer-2 link establishment procedure is performed towards the target 5G ProSe End UE then either a broadcast or a unicast Layer-2 ID is used as the Destination Layer-2 ID. A Unicast Layer-2 ID is used if the Layer-2 ID of the target 5G ProSe Layer-2 End UE associated with the user info (i.e. Application Layer ID) of target 5G ProSe Layer-2 End UE is known to the 5G ProSe Layer-2 UE-to-UE Relay.
If the Layer-2 link modification procedure is performed towards the target 5G ProSe End UE, it uses the unicast Layer-2 ID of target 5G ProSe End UE as the Destination Layer-2 ID.
The 5G ProSe Layer-2 UE-to-UE Relay sends a Direct Communication Accept message or Link Modification Accept message to the source 5G ProSe End UE after step 3 is completed.
4. The source 5G ProSe End UE establishes an end-to-end connection for unicast mode communication with the target 5G ProSe End UE as described in clause 6.4.3.7.
The data and End-to-End PC5-S signalling are transferred between the source 5G ProSe End UE and the target 5G ProSe End UE via the 5G ProSe Layer-2 UE-to-UE Relay. The 5G ProSe Layer-2 UE-to-UE Relay forwards all the data traffic and End-to-End PC5-S signalling between the source 5G ProSe End UE and the target 5G ProSe End UE, as specified in TS 38.300 [12].
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6.7.3 5G ProSe UE-to-UE Relay Communication with integrated Discovery
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6.7.3.1 General
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5G ProSe Communication via 5G ProSe UE-to-UE Relay with integrated Discovery is supported.
For 5G ProSe UE-to-UE Relay Communication with integrated Discovery, when a UE allows a UE-to-UE relay to be involved in the Direct Communication Request to the other UE, the UE indicates it by including a relay_indication in the broadcasted Direct Communication Request message.
When a UE-to-UE relay receives a Direct Communication Request including a relay_indication, it decides whether to send a Direct Communication Request message including its own User Info according to e.g. Relay Service Code if there is any, ProSe Service Info, operator policy per Relay Service Code, signal strength and local policy.
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6.7.3.2 Procedure for Communication via Layer-3 UE-to-UE Relay
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Figure 6.7.3.2-1: 5G ProSe UE-to-UE Relay Communication with integrated Discovery via Layer-3 UE-to-UE Relay
0. 5G ProSe End UEs are authorized and provisioned with parameters to use the service provided by the 5G ProSe UE-to-UE Relays. 5G ProSe UE-to-UE Relays are authorized and provisioned with parameters to provide service of relaying traffic among 5G ProSe End UEs.
1. The source 5G ProSe End UE (i.e. UE-1) wants to establish a unicast communication with the target 5G ProSe End UE (i.e. UE-2) and broadcasts a Direct Communication Request. The parameters included in the Direct Communication Request message are described in clause 6.4.3.7.
The relay_indication in the Direct Communication Request is used to indicate whether 5G ProSe UE-to-UE Relay can forward the Direct Communication Request message (i.e. send a Direct Communication Request based on the received Direct Communication Request message) or not. It is also used to limit the number of hops of 5G ProSe UE-to-UE Relay by removing relay_indication in the Direct Communication Request message from the 5G ProSe UE-to-UE Relay.
The Source Layer-2 ID and Destination Layer-2 ID used for the Direct Communication Request message are defined in clause 5.8.5.
The source 5G ProSe End UE gets application information and optional ProSe Application Requirements from ProSe application layer and determines the end-to-end QoS parameters as described in clause 5.6.3.1.
NOTE 1: The data type of relay_indication can be determined in Stage 3.
2. When receiving Direct Communication Request with relay_indication from UE-1, the 5G ProSe UE-to-UE Relay (i.e. Relay-1 and Relay-2) may decide to participate in the procedure and broadcast a Direct Communication Request message in its proximity without relay_indication. The parameters included in the Direct Communication Request message are described in clause 6.4.3.7.
The Source Layer-2 ID and Destination Layer-2 ID used for the Direct Communication Request message are defined in clause 5.8.5.
3. When UE-2 receives a Direct Communication Request from one or multiple 5G ProSe UE-to-UE Relays, UE-2 select a 5G ProSe UE-to-UE Relay which UE-2 will respond. UE-2 may select the 5G ProSe UE-to-UE Relay according to e.g. the signal strength, local policy, operator policy per Relay Service Code if any.
4. The security establishment happens between UE-2 and the selected 5G ProSe UE-to-UE Relay (here Relay-1), if needed.
If the existing PC5 link can be reused, Link Modification Request and Link Modification Accept messages are used.
NOTE 2: The conflict between Link Modification Request and Direct Communication Request can be determined in Stage 3.
5. UE-2 replies Direct Communication Accept message to Relay-1. The parameters included in the Direct Communication Accept message are described in clause 6.4.3.7.
6. For IP traffic, IPv6 prefix or IPv4 address is allocated for the target 5G ProSe Layer-3 End UE as defined in clause 5.5.1.4.
7. Security establishment happens between UE-1 and Relay-1, if needed.
8. For 5G ProSe UE-to-UE Relay Communication with integrated Discovery, after receiving QoS Info of the end-to-end QoS from UE-1, Relay-1 provides the QoS info of the second hop QoS to UE-2 with Link Modification Request message.
9. For 5G ProSe UE-to-UE Relay Communication with integrated Discovery, UE-2 responds with a Link Modification Accept message.
10. Relay-1 responds with Direct Communication Accept to the UE-1. The parameters included in the Direct Communication Accept message are described in clause 6.4.3.7.
11. For IP traffic, IPv6 prefix or IPv4 address is allocated for the source 5G ProSe Layer-3 End UE as defined in clause 5.5.1.4.
12. For IP communication, the 5G ProSe Layer-3 UE-to-UE Relay may store an association of user info (i.e. Application Layer ID) and the IP address of target 5G ProSe Layer-3 End UE into its DNS entries and the 5G ProSe Layer-3 UE-to-UE Relay may act as a DNS server to other UEs. The source 5G ProSe Layer-3 End UE may send a DNS query to the 5G ProSe Layer-3 UE-to-UE Relay to request IP address of target 5G ProSe Layer-3 End UE after step 11 if the IP address of target 5G ProSe Layer-3 End UE is not received in step 10 and the 5G ProSe Layer-3 UE-to-UE Relay returns the IP address of the target 5G ProSe Layer-3 End UE to the source 5G ProSe Layer-3 End UE.
For Ethernet communication, the 5G ProSe Layer-3 UE-to-UE Relay is acting as an Ethernet switch by maintaining the association between PC5 links and Ethernet MAC addresses received from the 5G ProSe Layer-3 End UE.
For Unstructured traffic communication, for each pair of source and target 5G ProSe Layer-3 End UEs, the 5G ProSe Layer-3 UE-to-UE Relay maintains the 1:1 mapping between the PC5 link with source 5G ProSe Layer-3 End UE and the PC5 link with target 5G ProSe Layer-3 End UE.
The source 5G ProSe Layer-3 End UE communicates with the target 5G ProSe Layer-3 End UE via the 5G ProSe Layer-3 UE-to-UE Relay.
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6.7.3.3 Procedure for Communication via Layer-2 UE-to-UE Relay
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Figure 6.7.3.3-1: 5G ProSe UE-to-UE Relay Communication with integrated Discovery via Layer-2 UE-to-UE Relay
0-5. It is the same as steps 0-5 of Figure 6.7.3.2-1.
6. It is the same as step 7 of Figure 6.7.3.2-1.
7. It is the same as step 10 of Figure 6.7.3.2-1.
The parameters included in the above messages are described in clause 6.4.3.7.4.
8. For 5G ProSe UE-to-UE Relay Communication via Layer-2 UE-to-UE Relay, UE-1 establishes an end-to-end connection for unicast mode communication with UE-2.
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6.7.4 5G ProSe UE-to-UE Relay reselection
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6.7.4.1 General
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After being connected to the 5G ProSe UE-to-UE Relay, the 5G ProSe End UEs may trigger the 5G ProSe UE-to-UE Relay reselection based on conditions (e.g. the measured signal strength of PC5 unicast link with the 5G ProSe UE-to-UE Relay) as specified in TS 38.300 [12]. For 5G ProSe multi-hop Layer-3 UE-to-UE Relay for non-IP PDU, when a 5G ProSe UE-to-UE Relay in the path detects link failure or link quality degradation to its adjacent 5G ProSe UE-to-UE Relay, it sends Relay reselection indication and optionally a cause value to 5G ProSe End UE. After receving the reselection indication the 5G ProSe End UE may trigger the multi-hop Layer-3 UE-to-UE Relay reselection.
For 5G ProSe UE-to-UE Relay reselection, a 5G ProSe UE-to-UE Relay may be discovered by either the discovery procedures defined in clause 6.3.2.4 or by the negotiated 5G ProSe UE-to-UE Relay reselection procedure defined in clause 6.7.4.2 or clause 6.7.4.3. For 5G ProSe multi-hop Layer3 UE-to-UE Relay for non-IP, in addition, a 5G ProSe UE-to-UE Relay may be discovered by the discovery procedure defined in clause 6.3.2.6.3, by the negotiated 5G ProSe multi-hop Layer3-UE-to-UE Relay reselection for non-IP type PDU defined in clause 6.7.4.4.
In the negotiated UE-to-UE Relay reselection defined in clause 6.7.4.2 or clause 6.7.4.3, one 5G ProSe End UE initiates the UE-to-UE Relay reselection procedure, the 5G ProSe End UEs can negotiate a new 5G ProSe UE-to-UE Relay using the existing connection and to establish the communication via the reselected 5G ProSe UE-to-UE Relay prior to releasing the communication via the current 5G ProSe UE-to-UE Relay.
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6.7.4.2 Negotiated 5G ProSe Layer-2 UE-to-UE Relay reselection
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Depicted in Figure 6.7.4.2-1 is the procedure for the negotiated 5G ProSe Layer-2 UE-to-UE Relay reselection.
Figure 6.7.4.2-1: Negotiated 5G ProSe Layer-2 UE-to-UE Relay reselection
1. A PC5 unicast link is established between the 5G ProSe End UEs via a 5G ProSe UE-to-UE Relay, based on the procedure defined in clause 6.7.2.
2. The initiating 5G ProSe End UE determines, e.g. based on PC5 signal strength, to perform UE-to-UE Relay reselection and obtains a list of candidate UE-to-UE Relays per RSC. The initiating 5G ProSe End UE may receive UE-to-UE Relay Discovery Announcement messages from 5G ProSe UE-to-UE Relays or initiate the 5G ProSe UE-to-UE Relay discovery procedures to find the candidate 5G ProSe UE-to-UE Relays. The initiating 5G ProSe End UE determines the candidate 5G ProSe UE-to-UE Relays e.g. based on the PC5 signal strength of the received UE-to-UE Relay Discovery Announcement message, RSC within the UE-to-UE Relay Discovery Announcement message. The candidate 5G ProSe UE-to-UE Relays support the same RSC which is associated with the PC5 unicast link between the initiating 5G ProSe End UE and the 5G ProSe UE-to-UE Relay.
3. The initiating 5G ProSe End UE sends a Link Modification Request message to the responding 5G ProSe End UE which includes a Relay re-selection indication, the User Info ID(s) of the candidate 5G ProSe UE-to-UE Relay(s) and optionally the Layer-2 ID(s) of the candidate 5G ProSe UE-to-UE Relay(s) and security information.
4. The responding 5G ProSe End UE selects a new 5G ProSe UE-to-UE Relay from the candidate 5G ProSe UE-to-UE Relays per RSC, based on the Relay re-selection indication in the Link Modification Request message. If the responding 5G ProSe End UE has not received a UE-to-UE Relay Discovery Announcement message from a candidate 5G ProSe UE-to-UE Relay (e.g. during a previous 5G ProSe UE-to-UE Relay Discovery procedure) or does not have a PC5 connection with the candidate 5G ProSe UE-to-UE Relay associated with the same RSC, then the responding 5G ProSe End UE may perform the Candidate 5G ProSe UE-to-UE Relay Discovery procedure defined in clause 6.3.2.4.4. The responding 5G ProSe End UE sets the candidate relay User Info ID to that of a candidate 5G ProSe UE-to-UE Relay in the discovery message and may set the Layer-2 ID of the candidate 5G ProSe UE-to-UE Relay, if received at step 3, as the Destination Layer-2 ID to carry the discovery message. The PC5 signal strength of the UE-to-UE Relay Discovery Announcement message or UE-to-UE Relay Discovery Response message may be used to select the new 5G ProSe UE-to-UE Relay.
5. The responding 5G ProSe End UE sends a Link Modification Accept message to the initating 5G ProSe End UE, including the User Info ID of the new 5G ProSe UE-to-UE Relay and security information.
6. 5G ProSe End UEs set up PC5 unicast links, if not already set up, with the new 5G ProSe UE-to-UE Relay, by reusing the procedure defined in clause 6.7.2 and the PC5 unicast is link established between 5G ProSe End UEs via the new 5G ProSe UE-to-UE Relay. The 5G ProSe End UEs switch the data traffic via the new 5G ProSe UE-to-UE Relay. The security information is used to verify that the new link has been set up successfully.
NOTE 1: The security information contents and usage will be defined by SA WG3.
NOTE 2: Whether a 5G ProSe End UE releases a PC5 unicast link with the original 5G ProSe UE-to-UE Relay after reselection depends on whether the PC5 unicast link is still required and UE implementation.
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6.7.4.3 Negotiated 5G ProSe Layer-3 UE-to-UE Relay reselection
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Depicted in Figure 6.7.4.3-1 is the procedure for the negotiated 5G ProSe Layer-3 UE-to-UE Relay reselection.
Figure 6.7.4.3-1: Negotiated 5G ProSe Layer-3 UE-to-UE Relay reselection
1. 5G ProSe End UEs have set up PC5 unicast links with a 5G ProSe UE-to-UE Relay, based on the procedure defined in clause 6.7.1.
2. The 5G ProSe End UEs have additionally set up PC5 unicast links with a 5G ProSe UE-to-UE Relay, based on the procedure defined in clause 6.7.1.
3. The 5G ProSe End UEs are transferring traffic via the 5G ProSe UE-to-UE Relay.
4. The initiating 5G ProSe End UE determines, e.g. based on PC5 signal strength, to perform UE-to-UE Relay reselection and obtains a list of candidate UE-to-UE Relays per RSC. The initiating 5G ProSe End UE may receive UE-to-UE Relay Discovery Announcement messages from 5G ProSe UE-to-UE Relays or initiate the 5G ProSe UE-to-UE Relay discovery procedures to find the candidate 5G ProSe UE-to-UE Relays. The initiating 5G ProSe End UE determines the candidate 5G ProSe UE-to-UE Relays e.g. based on the PC5 signal strength of the received UE-to-UE Relay Discovery Announcement message, RSC within the UE-to-UE Relay Discovery Announcement message. The candidate 5G ProSe UE-to-UE Relays support the same RSC which is associated with the PC5 unicast link between the initiating 5G ProSe End UE and the 5G ProSe UE-to-UE Relay.
5. The initiating 5G ProSe End UE sends a Link Modification Request message to the responding 5G ProSe UE-to-UE Relay, which includes a Relay re-selection indication, the User Info ID(s) of the candidate 5G ProSe UE-to-UE Relay(s), the IP addresses of the responding 5G ProSe End UEs and optionally the Layer-2 ID(s) of the candidate 5G ProSe UE-to-UE Relay(s).
Multiple 5G ProSe End UEs IP addresses may be included when the initiating 5G ProSe End UE is communicating with multiple 5G ProSe End UEs via the 5G ProSe UE-to-UE Relay.
6. 5G ProSe UE-to-UE Relay determines the responding 5G ProSe End UE based on the IP address received from the initiating 5G ProSe End UE and sends a Link Modification Request message to the responding 5G ProSe End UE. The Link Modification Request message includes a Relay re-selection indication, User Info ID(s) of the candidate 5G ProSe UE-to-UE Relay(s), IP address of the initiating 5G ProSe End UE and optionally the Layer-2 ID(s) of the candidate 5G ProSe UE-to-UE Relay(s).
If multiple 5G ProSe End UEs are specified in the Link Modification Request message received from the initiating 5G ProSe End UE, the 5G ProSe UE-to-UE Relay sends a PC5 Link Modification Request to each of the 5G ProSe End UEs.
7. The responding 5G ProSe End UE selects a new 5G ProSe UE-to-UE Relay from the candidate 5G ProSe UE-to-UE Relays per RSC, based on the Relay re-selection indication in the Link Modification Request message. If the responding 5G ProSe End UE has not received a UE-to-UE Relay Discovery Announcement message from a candidate 5G ProSe UE-to-UE Relay (e.g. during a previous 5G ProSe UE-to-UE Relay Discovery procedure) or does not have a PC5 connection with the candidate 5G ProSe UE-to-UE Relay associated with the same RSC, then the responding 5G ProSe End UE may perform the Candidate 5G ProSe UE-to-UE Relay Discovery procedure defined in clause 6.3.2.4.4. The responding 5G ProSe End UE sets the candidate relay User Info ID to that of a candidate 5G ProSe UE-to-UE Relay in the discovery message and may set the Layer-2 ID of the candidate 5G ProSe UE-to-UE Relay, if received at step 6, as the Destination Layer-2 ID to carry the discovery message. The responding 5G ProSe End UE may initiate the procedure to set up PC5 unicast links with the new 5G ProSe UE-to-UE Relay, by reusing the procedure defined in clause 6.7.1. The PC5 signal strength of the UE-to-UE Relay Discovery Announcement message or UE-to-UE Relay Discovery Response message may be used to select the new 5G ProSe UE-to-UE Relay.
8. The responding 5G ProSe End UE sends a Link Modification Accept message to the 5G ProSe UE-to-UE Relay, including the User Info ID of the new 5G ProSe UE-to-UE Relay, IP address of the initiating 5G ProSe End UE, IP address of the responding 5G ProSe End UE for communication via the newly selected 5G ProSe UE-to-UE Relay and Relay re-selection indication.
9. 5G ProSe UE-to-UE Relay sends a Link Modification Accept message to the initating 5G ProSe End UE, including the User Info ID of the new 5G ProSe UE-to-UE Relay, IP address of the responding 5G ProSe End UE, IP address of the responding 5G ProSe End UE for communication via the newly selected 5G ProSe UE-to-UE Relay and Relay re-selection indication.
10-11. Link Modification Ack is sent from the initating 5G ProSe End UE to the responding the 5G ProSe End UE via the 5G ProSE UE-to-UE Relay, including the IP address of the initiating 5G ProSe End UE for communication via the newly selected 5G ProSe UE-to-UE Relay, the IP address of the responding 5G ProSe End UE and Relay re-selection indication.
12. The 5G ProSe End UEs transfer traffic via the newly selected 5G ProSe UE-to-UE Relay.
NOTE: Whether a 5G ProSe End UE releases a PC5 unicast link with the original 5G ProSe UE-to-UE Relay after reselection depends on whether the PC5 unicast link is still required and UE implementation.
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6.7.4.4 Negotiated 5G ProSe multi-hop Layer-3 UE-to-UE Relay Reselection for Non-IP type PDU
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Depicted in Figure 6.7.4.4-1 is the procedure for the negotiated 5G ProSe multi-hop Layer-3 UE-to-UE Relay reselection.
Figure 6.7.4.4.-1. Negotiated multihop Layer-3 UE-to-UE Relay reselection procedure.
1. 5G ProSe End UEs have set up PC5 unicast links with one or multiple 5G ProSe UE-to-UE Relay, based on the procedure defined in clause 6.7.5.
2. 5G ProSe End UEs are transferring data traffic e.g. Ethernet traffic, via 5G ProSe UE-to-UE Relay(s).
3. The initiating 5G ProSe End UE determines, e.g. based on PC5 signal strength, to perform U2U Relay reselection.
4. The initiating 5G ProSe End UE may discover new multi-hop U2U relay path(s) to the target 5G ProSe End UE.(refer to clause 6.3.2.6.3) as candidate path(s).
5. The initiating 5G ProSe End UE sends a Link Modification Request to the responding 5G ProSe UE-to-UE Relay, which include a Relay re-selection indication and the candidate path information(s) and the User Info ID of the responding 5G ProSe End UEs.
6. 5G ProSe UE-to-UE Relay determines the responding 5G ProSe End UE based on the received User Info ID of End UEs in step 5 and sends a Link Modification Request message to the responding End UEs (via other UE-to-UE Relay(s) if the responding End UE is connected via other UE-to-UE Relay(s)).
The Link Modification Request message includes a Relay re-selection indication, the candidate path information(s).
7. The responding 5G ProSe End UE may select a path from the candidate path information(s) in the received link modification as the newly selected multi-hop path.
8. The responding 5G ProSe End UE may initiate PC5 connection setup or modification procedure for communication with the initiating 5G ProSe End UE with path info for the selected multi-hop path in step 7 (refer to clause 6.7.5.2.2). For Ethernet traffic, MAC address of the initiating 5G ProSe End UE and MAC address of the responding 5G ProSe End UE are included.
9. The responding 5G ProSe End UE sends a Link Modification Accept message via the existing multi-hop 5G ProSe UE-to-UE Relay(s) to the initiating 5G ProSe End UE. Link Modification Accept message includes the newly selected multi-hop path info, User Info ID of the iniating End UE, User Info ID of the responding End UE and Relay re-selection indication.
10. The responding 5G ProSe UE-to-UE Relay sends a Link Modification Accept message to the initiating 5G ProSe End UE. The Link Modification Accept message includes the newly selected multi-hop path, User Info ID of the initiating End UE, User Info ID of the responding End UE and Relay re-selection indication.
11. The initiating 5G ProSe UE-to-UE Relay sends Link Modification Ack to the responding 5G ProSe UE-to-UE Relay.
12. The 5G ProSe UE-to-UE Relay sends Link Modification Ack to the responding 5G ProSe End UE. Link Modification Ack includes User Info ID of the iniating End UE, User Info ID of the responding End UE and Relay re-selection indication.
13. 5G ProSe End UEs transfer traffic via the newly selected multi-hop path. For Ethernet traffic, existing MAC address of 5G ProSe End UEs are reused.
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6.7.5 5G ProSe Communication via 5G ProSe Layer-3 Multi-hop UE-to-UE Relay
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6.7.5.1 General
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5G ProSe Communication via 5G ProSe Layer-3 Multi-hop UE-to-UE Relay supports IP type of traffic or non-IP type of traffic, depending on the RSCs associated with the relays.
For one RSC, only one type of traffic and corresponding procedures should be used for the communicaiton.
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6.7.5.2 Communication via 5G ProSe Layer-3 Multi-hop UE-to-UE-Relays (IP type)
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