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23.401
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4.3.32 Support for Integrated access and backhaul (IAB)
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.32.1 IAB architecture and functional entities
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Integrated access and backhaul (IAB) enables wireless in-band and out-of-band relaying of NR Uu access traffic via NR Uu backhaul links.
At high level, IAB has the following characteristics:
- IAB uses the CU/DU architecture defined in TS 38.401 [90], and the IAB operation via F1 (between IAB-donor and IAB-node) is invisible to the EPC.
- IAB performs relaying at layer-2, and therefore does not require a local S/P-GW;
- IAB supports multi-hop backhauling;
- IAB supports dynamic topology update, i.e. the IAB-node can change the parent node, e.g. another IAB-node, or the IAB-donor, during operation, for example in response to backhaul link failure or blockage.
Figure 4.3.32.1-1 shows the IAB reference architecture with two backhaul hops, when connected to EPC, where both the IAB-node and the UE connect to the EPC with Dual Connectivity as defined in TS 37.340 [85].
Figure 4.3.32.1-1: IAB architecture for EPS, with IAB-node and UE both connected to EPC
Each relay, referred to as IAB-node, consists of a gNB-DU function and a UE function (referred to as IAB-UE). The gNB-DU in the IAB-node is responsible for providing NR Uu access to UEs and child IAB-nodes. The corresponding gNB-CU function resides on the IAB-donor gNB (referred to as IAB-donor-CU), which controls IAB-node gNB-DU via the F1 interface. When a UE connects to EPC via an IAB-node, the gNB-DU of the IAB-node appears as a normal secondary gNB to the UE. When the IAB-UE of another IAB-node connects to EPC via the IAB-node, the gNB-DU of the IAB-node also appears as a secondary gNB to the IAB-UE.
The IAB-UE function reuses UE procedures to connect to:
- the gNB-DU on a parent IAB-node or IAB-donor for access and backhauling;
- the gNB-CU on the IAB-donor via RRC for control of the access and backhaul link;
- EPC, e.g. MME,
- OAM system via a PDN connection (based on implementation).
NOTE: The EPC, e.g. MME, may detect that a PDN connection for the IAB-UE is for the OAM system access, e.g. by checking the APN and/or configuration. It is up to the operator configuration to choose whether to use 1 or multiple EPS bearers for OAM traffic and the appropriate QoS parameters, e.g. using QCI=6 for software downloading, and QCI=80 or a pre-configured QCI for alarm or control traffic.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.32.2 System enhancements to support IAB
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In IAB operation, the IAB-UE interacts with the EPC using procedures defined for UE. The IAB-node gNB-DU only interacts with the IAB-donor-CU and follows the CU/DU design defined in TS 38.401 [90].
For the IAB-UE operation, the existing UE authentication methods as defined in TS 33.401 [41] apply. For EPC, only USIM based methods are allowed.
The following aspects of EPS are enhanced to support the IAB operation:
- the Attach procedure as defined in clause 5.3.2 is enhanced to indicate IAB-node's capability to the MME:
- the IAB-node provides an IAB-indication to the eNodeB when the IAB-node establishes the RRC connection. If the IAB-indication is received, the eNodeB selects an MME that supports IAB, and includes the IAB-indication in the INITIAL UE MESSAGE so that the MME can perform IAB authorization;
- the UE Subscription data as defined in clause 5.7.1 is enhanced to include the authorization information for the IAB operation;
- Authorization procedure during the UE attach procedure is enhanced to perform verification of IAB subscription information;
- If the IAB operation is not authorized, the MME may reject the IAB-UE's attach request or detach the IAB-UE, or the MME may initiate UE Context setup/Modification procedure by providing IAB authorized indication with the value set to "not authorized" to the eNodeB, but the IAB-UE is in the EMM-REGISTERED state.
- If the IAB operation is authorized, UE Context setup/modification procedure is enhanced to provide IAB authorized indication with the value set to "authorized" to eNodeB and IAB-donor gNB.
After attached or registered, the IAB-node remains in ECM-CONNECTED state if the IAB operation is authorized. In the case of radio link failure, the IAB-UE uses existing UE procedure to restore the connection with the network. The IAB-UE uses the Detach procedure defined in clause 5.3.8 to disconnect from the network.
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23.401
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4.3.32.3 Data handling and QoS support with IAB
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Control plane and user plane protocol stacks for IAB operation are defined in TS 38.300 [93].
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23.401
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4.3.32.4 Mobility support with IAB
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For UEs, all existing NR intra-RAT mobility and dual-connectivity procedures are supported with IAB. During UE mobility or dual-connectivity procedures, backhaul channels including IAB layer may be updated. This update is carried out by the IAB-donor-CU and signalled to the IAB-nodes via RRC and/or F1-C. The update is transparent to the UE.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.32.5 Charging support with IAB
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IAB-donor has all the information regarding the UE and the IAB-node and corresponding mapping of the bearers. The PDN connection for the UE and IAB-node are separate from IAB-node onwards to the core network. Therefore, the existing charging mechanism as defined in clause 5.7A can be used to support IAB.
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23.401
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4.3.33 Support for Multi-USIM UE
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.33.1 General
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A network and a Multi-USIM UE may support one or more of the following features for Multi-USIM UE operation:
- Connection Release, as described in clause 4.3.33.2.
- Paging Cause Indication for Voice Service, as described in clause 4.3.33.3.
- Reject Paging Request, as described in clause 4.3.33.4.
- Paging Timing Collision Control, as described in clause 4.3.33.5.
- Paging Restriction, as described in clause 4.3.33.6.
In the Attach procedure (as specified in clause 5.3.2.1), or in the Tracking Area Update procedure (as specified clause 5.3.3), when a Multi-USIM UE has more than one USIM active, supports and intends to use one or more Multi-USIM specific features, it indicates to the MME the corresponding Multi-USIM feature(s) are supported. Based on the received indication of supported Multi-USIM features from the UE, the MME shall indicate to the UE the support of the Multi-USIM features based on the Multi-USIM features supported by network and any preference policy by the network, if available. When a UE returns to having only one USIM active from a Multi-USIM UE that previously indicated to the network it supported Multi-USIM feature(s), the UE shall indicate all the Multi-USIM features are not supported to the network for that USIM. The MME shall only indicate the support of Paging Restriction feature together with the support of either Connection Release feature or Reject Paging Request feature.
The Multi-USIM UE includes the support of individual features for Connection Release, Paging Cause Indication for Voice Service, Reject Paging Request and Paging Restrictions as specified in clause 5.11.3.
The network shall not indicate support for any Multi-USIM feature to the UE as part of the Emergency Attach procedure or as part of Tracking Area Update for Emergency attached UE.
A Multi-USIM UE shall use a separate IMEI for each USIM when it registers with the network.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.33.2 Connection Release
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A Multi-USIM UE may request to be released to ECM-IDLE state for a USIM due to activity on another USIM if both the UE and the network indicate to each other the Connection Release feature is supported. A Multi-USIM UE indicates that it requests to be released to ECM-IDLE state for the USIM by initiating the Service Request procedure (using Extended Service Request message) or a Tracking Area Update procedure if the UE needs to perform Tracking Area Update at the same time with this network (including the case where the Tracking Area Update is performed due to mobility to a Tracking Area outside the current Tracking Area List, i.e. before detecting whether the network supports the feature in the new Tracking Area, provided that the network has already indicated support for Connection Release feature in the current Tracking Area List), by including a Release Request indication. If supported by the UE and network, the UE may also provide, together with the Release Request indication, Paging Restriction Information, as specified in clause 4.3.33.6, which requests the network to restrict paging.
NOTE: When there is no PLMN-wide support for the Connection Release feature, it can occur that upon tracking area update with Release Request indication the UE is not released by the network. The UE behaviour, when it detects that the network does not support the feature in a new TA, is outside the scope of this specification.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.33.3 Paging Cause Indication for Voice Service
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A Multi-USIM UE and the network may support the Paging Cause Indication for Voice Service feature.
The MME that supports Paging Cause Indication for Voice Service feature should provide a Voice Service Indication in the S1AP Paging message for the MMTel voice service, only if the UE indicates the Paging Cause Indication for Voice Service feature is supported. The MME determines the downlink data triggering the paging is related to a MMTel voice service based on the Paging Policy Indicator as specified in clause 4.9 for MMTel voice.
NOTE: The indication of CS voice in the CN domain indication in S1AP paging message and Uu paging message is not modified by the Paging Cause Indication for Voice Service feature.
Upon reception of the Voice Service Indication in S1AP Paging Message, an eNodeB that supports the Paging Cause Indication for Voice Service should include the Voice Service Indication the Uu Paging message to the UE.
A UE that supports the Paging Cause Indication for Voice Service feature is capable of differentiation between Paging from a network that does not support the Paging Cause Indication for Voice Service feature and Uu Paging without the Voice Service Indication. How the UE distinguishes the Paging from a RAN that does not support the Paging Cause Indication for Voice Service feature and Paging without the Voice Service Indication is defined in TS 36.331 [37]. The UE determines whether the Paging Cause Indication for Voice Service feature is supported in the current Tracking Area by EPC based on the MUSIM capability exchange with the MME, see clause 4.3.33.1. The UE determines that the Paging Cause Indication for Voice Service feature is supported if it is supported by both the RAN, as indicated in the received Uu Paging message, and by EPC, as indicated in the MUSIM capability exchange with the MME.
The UE uses the Paging Cause Indication for Voice Service as described in TS 24.301 [46] and TS 36.331 [37].
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.33.4 Reject Paging Request
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A Multi-USIM UE may respond to a page for a USIM with an indication to the MME that the UE does not accept the paging and requests to be released to ECM-IDLE state after sending this response, if both UE and network indicate to each other the Reject Paging Request feature is supported.
Upon being paged, the Multi-USIM UE attempts to send an Extended Service Request message to the paging network including the Reject Paging Indication as the response to the paging, unless it is unable to do so, e.g. due to UE implementation constraints. In addition to the Reject Paging Indication, the UE may include Paging Restriction Information as specified in clause 4.3.33.6 in the Extended Service Request message, if the Paging Restrictions are supported by UE and network.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.33.5 Paging Timing Collision Control
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To avoid possible paging occasion collision and to enhance the likelihood that paging is received successfully for different USIMs, a Multi-USIM UE may provide, for at least one USIM, a Requested IMSI Offset value that is used for the determination of paging occasions. Upon reception of a Requested IMSI Offset value from UE in Attach Request or Tracking Area Update Request, a supporting MME provides an Accepted IMSI Offset value to the UE in the Attach Accept or Tracking Area Update Accept message to acknowledge it supports the feature and provide the accepted value. The Accepted IMSI Offset Value may be different from the Requested IMSI Offset provided by the UE. The Alternative IMSI value, determined as below, is stored in the UE context in the MME. If the UE does not provide any Requested IMSI Offset value in Attach Request or Tracking Area Request, the MME removes any stored Alternative IMSI value in the UE context. The UE and the network use the Accepted IMSI Offset to determine the paging occasion. The UE and MME use the Accepted IMSI Offset value to calculate the Alternative IMSI value that is determined based on UE's IMSI as follows:
Alternative IMSI value = [MCC] [MNC] [(MSIN value + Accepted IMSI Offset) mod (MSIN address space)]
where: the MCC, MNC and MSIN value are the fields of the UE's IMSI as defined in TS 23.003 [9].
The MME uses the Alternative IMSI value to compute the UE Identity Index Value. The MME sends the UE Identity Index Value to RAN in the Paging message (see TS 36.413 [36]) for RAN to derive the paging occasions according to TS 36.304 [34].
The UE uses the Alternative IMSI value for the determination of paging occasions as specified in TS 36.304 [34].
NOTE 1: It is recommended to avoid excessive signalling load from UE due to this procedure.
NOTE 2: The MME does not remove Alternative IMSI value if the Tracking Area Update Request is for periodic Tracking Area Update.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.33.6 Paging Restriction
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A Multi-USIM UE and the network may support Paging Restriction. A Multi-USIM UE, if the MME indicates that the network supports Paging Restriction feature, may indicate Paging Restriction Information in an Extended Service Request or a Tracking Area Update Request (including the case where the Tracking Area Update is performed due to mobility to a Tracking Area outside the current Tracking Area List, i.e. before detecting whether the network supports the feature in the new Tracking Area, provided that the network has already indicated support for Paging Restrictions in the current Tracking Area List), as specified in clauses 4.3.33.2 and 4.3.33.4.
The MME may accept or reject the Paging Restriction Information requested by the UE. If the MME accepts the Paging Restriction Information from the UE, the MME stores the Paging Restriction Information from the UE in the UE context. If the MME rejects the Paging Restriction Information the MME removes any stored Paging Restriction Information from the UE context and discards the UEs requested Paging Restriction Information. The MME informs the UE about the acceptance/rejection of the requested Paging Restriction Information in the Tracking Area Update Accept or Service Accept message.
If the UE does not provide Paging Restriction Information in the Extended Service Request message or the Tracking Area Update Request message, or if the UE initiates the Service Request procedure, the MME removes any stored Paging Restriction Information from the UE context.
The Paging Restriction Information may indicate any of the following:
a) all paging is restricted, or
b) all paging is restricted, except paging for voice service (MMTel voice or CS domain voice), or
c) all paging is restricted, except for certain PDN Connection(s), or
d) all paging is restricted, except for certain PDN Connection(s) and voice service (MMTel voice or CS domain voice).
NOTE 1: The UE expects not to be paged for any purpose in case a). The UE expects to be paged only for voice service in case b). The UE expects to be paged only for certain PDN Connection(s) in case c). The UE expects be paged for voice service and certain PDN Connection(s) in case d). The MME can page the UE for mobile terminated signalling based on local policy considering the stored Paging Restriction Information, except for case a). In this case, to comply with UE provided Paging Restriction Information, the MME can trigger S1 release procedure as soon as possible after the mobile terminated signalling procedure is executed.
NOTE 2: In the case of roaming, the paging restrictions for voice service implied by bullet b) and d) depends on the existence of an agreement with the HPLMN to support voice service via IMS. Hence the support of paging restrictions in bullets b) and d) takes the IMS voice service agreement into consideration.
NOTE 3: When there is no PLMN-wide support for the Paging Restriction feature, it can occur that upon Tracking Area Update due to mobility with Paging Restriction Information the UE detects the network does not support the feature. If so, the UE assumes that no Paging Restriction is applied.
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495b59b986f98d41912141cabbec196e
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23.401
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4.3.34 Support for Time Reference Information Distribution
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Support for time reference information distribution in RRC is specified in TS 36.331 [37].
This feature is optional. When it is supported, it enables the operator to control, based on subscription, whether to deliver time reference information to a UE. The MME receives the indication from the HSS that the UE is subscribed to receive time reference information in access stratum. If the MME has received the indication that the UE is subscribed to receive time reference information, then the MME provides a Time Reference Information Distribution Indication to the eNodeB whenever the UE context is established in E-UTRAN, e.g., during the Attach procedure, Service Request procedure, TAU procedure and handover procedures. If an eNodeB receives the Time Reference Information Distribution Indication and if the eNodeB supports time reference information distribution, then the eNodeB shall provide the time reference information to the UE in a unicast RRC message as specified in TS 36.331 [37]. The UE may further distribute the time reference information to devices connected to the UE using implementation-specific means.
NOTE: If an operator wants to prevent unsubscribed UE(s) from receiving the time reference information, then the operator is expected to configure the eNB to not broadcast time reference information using SystemInformationBlockType16 (TS 36.331 [37]) but to use unicast delivery of time reference information to only the subscribed UE(s).
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495b59b986f98d41912141cabbec196e
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23.401
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4.4 Network elements
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.1 E-UTRAN
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E-UTRAN is described in more detail in TS 36.300 [5].
In addition to the E-UTRAN functions described in TS 36.300 [5], E-UTRAN functions include:
- Header compression and user plane ciphering and integrity protection (for user plane data sent across S1-U);
- MME selection when no routing to an MME can be determined from the information provided by the UE;
- UL bearer level rate enforcement based on UE-AMBR and MBR via means of uplink scheduling
(e.g. by limiting the amount of UL resources granted per UE over time);
- DL bearer level rate enforcement based on UE-AMBR;
- UL and DL bearer level admission control;
- Transport level packet marking in the uplink, e.g. setting the DiffServ Code Point, based on the QCI, and optionally the ARP priority level, of the associated EPS bearer;
- ECN-based congestion control.
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.2 MME
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MME functions include:
- NAS signalling;
- NAS signalling security;
- Inter CN node signalling for mobility between 3GPP access networks (terminating S3);
- UE Reachability in ECM-IDLE state (including control, execution of paging retransmission and optionally Paging Policy Differentiation);
- Tracking Area list management;
- Mapping from UE location (e.g. TAI) to time zone, and signalling a UE time zone change associated with mobility,
- PDN GW and Serving GW selection;
- MME selection for handovers with MME change;
- SGSN selection for handovers to 2G or 3G 3GPP access networks;
- Roaming (S6a towards home HSS);
- Authentication;
- Authorization;
- Bearer management functions including dedicated bearer establishment;
- Lawful Interception of signalling traffic;
- Warning message transfer function (including selection of appropriate eNodeB);
- UE Reachability procedures;
- Support Relaying function (RN Attach/Detach);
- Change of UE presence in Presence Reporting Area reporting upon PCC request,
- in the case of Change of UE presence in Presence Reporting Area reporting, management of Core Network pre-configured Presence Reporting Areas.
- For the Control Plane CIoT EPS Optimisation:
a) transport of user data (IP, Non-IP and Ethernet));
b) local Mobility Anchor point;
c) header compression (for IP user data);
d) ciphering and integrity protection of user data;
e) Lawful Interception of user traffic not transported via the Serving GW (e.g. traffic using T6a).
NOTE: The Serving GW and the MME may be implemented in one physical node or separated physical nodes. For CIoT EPS Optimisation, the Serving GW and the MME can be implemented in one physical node (e.g. C-SGN) or separated physical nodes. The C-SGN can also encompass the PDN GW function.
The MME shall signal a change in UE Time Zone only in the case of mobility and in the case of UE triggered Service Request, PDN Disconnection and UE Detach. If the MME cannot determine whether the UE Time Zone has changed (e.g. the UE Time Zone is not sent by the old MME during MME relocation), the MME should not signal a change in UE Time Zone. A change in UE Time Zone caused by a regulatory mandated time change (e.g. daylight saving time or summer time change) shall not trigger the MME to initiate signalling procedures due to the actual change. Instead the MME shall wait for the UE's next mobility event or Service Request procedure and then use these procedures to update the UE Time Zone information in the PDN GW.
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.3 Gateway
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.3.1 General
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Two logical Gateways exist:
- Serving GW (S‑GW);
- PDN GW (P‑GW).
NOTE: The PDN GW and the Serving GW may be implemented in one physical node or separated physical nodes.
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.3.2 Serving GW
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The Serving GW is the gateway which terminates the user plane interface towards E-UTRAN (except when user data is transported using the Control Plane CIoT EPS Optimisation).
For each UE associated with the EPS, at a given point of time, there is a single Serving GW.
The functions of the Serving GW, for both the GTP-based and the PMIP-based S5/S8, include:
- the local Mobility Anchor point for inter-eNodeB handover (except when user data is transported using the Control Plane CIoT EPS Optimisation);
- sending of one or more "end marker" to the source eNodeB, source SGSN or source RNC immediately after the Serving GW switches the path during inter-eNodeB and inter-RAT handover, especially to assist the reordering function in eNodeB.
- Mobility anchoring for inter-3GPP mobility (terminating S4 and relaying the traffic between 2G/3G system and PDN GW);
- ECM-IDLE mode downlink packet buffering and initiation of network triggered service request procedure and optionally Paging Policy Differentiation;
- Lawful Interception;
- Packet routing and forwarding;
- Transport level packet marking in the uplink and the downlink, e.g. setting the DiffServ Code Point, based on the QCI, and optionally the ARP priority level, of the associated EPS bearer;
- Accounting for inter-operator charging. For GTP-based S5/S8, the Serving GW generates accounting data per UE and bearer;
- Interfacing OFCS according to charging principles and through reference points specified in TS 32.240 [51];
- Forwarding of "end marker" to the source eNodeB, source SGSN or source RNC when the "end marker" is received from PDN GW and the Serving GW has downlink user plane established. Upon reception of "end marker", the Serving GW shall not send Downlink Data Notification.
Additional Serving GW functions for the PMIP-based S5/S8 are captured in TS 23.402 [2].
Connectivity to a GGSN is not supported.
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.3.3 PDN GW
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The PDN GW is the gateway which terminates the SGi interface towards the PDN.
If a UE is accessing multiple PDNs, there may be more than one PDN GW for that UE, however a mix of S5/S8 connectivity and Gn/Gp connectivity is not supported for that UE simultaneously.
PDN GW functions include for both the GTP-based and the PMIP-based S5/S8:
- Per-user based packet filtering (by e.g. deep packet inspection);
- Lawful Interception;
- UE IP address allocation;
- Transport level packet marking in the uplink and downlink, e.g. setting the DiffServ Code Point, based on the QCI, and optionally the ARP priority level, of the associated EPS bearer;
- Accounting for inter-operator charging: for home routed roaming, the P-GW shall collect and report the uplink and downlink data volume (per EPS bearer) as received from and sent to the serving node;
- UL and DL service level charging as defined in TS 23.203 [6]
(e.g. based on SDFs defined by the PCRF, or based on deep packet inspection defined by local policy);
- Interfacing OFCS through according to charging principles and through reference points specified in TS 32.240 [51].
- UL and DL service level gating control as defined in TS 23.203 [6];
- UL and DL service level rate enforcement as defined in TS 23.203 [6]
(e.g. by rate policing/shaping per SDF);
- UL and DL rate enforcement based on APN-AMBR
(e.g. by rate policing/shaping per aggregate of traffic of all SDFs of the same APN that are associated with Non-GBR QCIs);
- DL rate enforcement based on the accumulated MBRs of the aggregate of SDFs with the same GBR QCI
(e.g. by rate policing/shaping);
- DHCPv4 (server and client) and DHCPv6 (client and server) functions;
- The network does not support PPP bearer type in this version of the specification. Pre-Release 8 PPP functionality of a GGSN may be implemented in the PDN GW;
- The PDN GW may support Non-IP data transfer (e.g. with CIoT EPS Optimisations);
- The PDN GW (when acting as a combined PDN GW+SMF as specified in TS 23.501 [83]) may support Ethernet data transfer;
- packet screening;
- sending of one or more "end marker" to the source SGW immediately after switching the path during SGW change;
- PCC related features (e.g. involving PCRF and OCS) as described in TS 23.203 [6].
Additionally the PDN GW includes the following functions for the GTP-based S5/S8:
- UL and DL bearer binding as defined in TS 23.203 [6];
- UL bearer binding verification as defined in TS 23.203 [6];
- Functionality as defined in RFC 4861 [32];
- Accounting per UE and bearer.
The P‑GW provides PDN connectivity to both GERAN/UTRAN only UEs and E‑UTRAN capable UEs using any of E‑UTRAN, GERAN or UTRAN. The P‑GW provides PDN connectivity to E‑UTRAN capable UEs using E‑UTRAN only over the S5/S8 interface.
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495b59b986f98d41912141cabbec196e
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23.401
|
4.4.4 SGSN
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In addition to the functions described in TS 23.060 [7], SGSN functions include:
- Inter EPC node signalling for mobility between 2G/3G and E-UTRAN 3GPP access networks;
- PDN and Serving GW selection: the selection of S‑GW/P‑GW by the SGSN is as specified for the MME;
- Handling UE Time Zone as specified for the MME;
- MME selection for handovers to E-UTRAN 3GPP access network.
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.5 GERAN
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GERAN is described in more detail in TS 43.051 [15].
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.6 UTRAN
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UTRAN is described in more detail in TS 25.401 [16].
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.7 PCRF
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.7.1 General
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PCRF is the policy and charging control element. PCRF functions are described in more detail in TS 23.203 [6].
In non-roaming scenario, there is only a single PCRF in the HPLMN associated with one UE's IP-CAN session. The PCRF terminates the Rx interface and the Gx interface.
In a roaming scenario with local breakout of traffic there may be two PCRFs associated with one UE's IP-CAN session:
- H-PCRF that resides within the H-PLMN;
- V-PCRF that resides within the V-PLMN.
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495b59b986f98d41912141cabbec196e
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23.401
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4.4.7.2 Home PCRF (H-PCRF)
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The functions of the H-PCRF include:
- terminates the Rx reference point for home network services;
- terminates the S9 reference point for roaming with local breakout;
- associates the sessions established over the multiple reference points (S9, Rx), for the same UE's IP-CAN session (PCC session binding).
The functionality of H-PCRF is described in TS 23.203 [6].
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4.4.7.3 Visited PCRF (V-PCRF)
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The functions of the V-PCRF include:
- terminates the Gx and S9 reference points for roaming with local breakout;
- terminates Rx for roaming with local breakout and visited operator's Application Function.
The functionality of V-PCRF is described in TS 23.203 [6].
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4.4.8 PDN GW's associated AAA Server
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The PDN Gateway may interact with a AAA server over the SGi interface. This AAA Server may maintain information associated with UE access to the EPC and provide authorization and other network services. This AAA Server could be a RADIUS or Diameter Server in an external PDN network, as defined in TS 29.061 [38]. This AAA Server is logically separate from the HSS and the 3GPP AAA Server.
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4.4.9 HeNB subsystem
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A HeNB subsystem consists of a HeNB, optionally a HeNB GW and optionally a Local GW.
The Local IP Access and SIPTO at the Local Network with L-GW function collocated with the HeNB functions are achieved using a Local GW (L-GW) collocated with the HeNB.
Figure 4.4.9-1 illustrates the architecture for LIPA and/or SIPTO at the Local Network with L-GW function collocated with the HeNB.
Figure 4.4.9-1: Architecture for LIPA or SIPTO at the Local Network with L-GW collocated with the HeNB
NOTE 1: The optional HeNB GW is not shown in the figure for simplicity.
The HeNB subsystem is connected by means of the standard S1 interface to the EPC (Evolved Packet Core), more specifically to the MME (Mobility Management Entity) by means of the S1-MME interface and to the Serving Gateway (S-GW) by means of the S1-U interface. When LIPA or SIPTO at the Local Network with L-GW function collocated with the HeNB is activated, the L-GW has a S5 interface with the S-GW.
NOTE 2: In this specification and for simplification the term eNodeB refers to the HeNB subsystem if the UE accesses the network via a HeNB unless stated otherwise.
NOTE 3: Detailed functions of HeNB and HeNB GW are described in TS 36.300 [5].
NOTE 4: An L-GW collocated with a HeNB may support LIPA, or SIPTO@LN, or both.
The Local GW is the gateway towards the IP networks (e.g. residential/enterprise networks, Internet) associated with the HeNB. The Local GW has the following PDN GW functions:
- UE IP address allocation;
- DHCPv4 (server and client) and DHCPv6 (client and server) functions;
- Packet screening;
- Functionality as defined in RFC 4861 [32].
Additionally, the Local GW has the following functions:
- ECM-IDLE mode downlink packet buffering;
- ECM-CONNECTED mode direct tunnelling towards the HeNB.
NOTE 5: The architecture for SIPTO at the Local Network with L-GW function collocated with a HeNB depicted in Figure 4.4.9-1 also applies to SIPTO at the Local Network with L-GW function collocated with an eNodeB.
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4.4.10 DeNB
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DeNB function is described in more detail in TS 36.300 [5].
DeNB provides the necessary S/P‑GW functions for the operation of RNs connected to the DeNB.
In order to provide the Relay Function the DeNB shall support the following P-GW functions:
- IP address allocation for the UE functionality of the RN;
- Downlink transport level packet mapping between the DSCP value used over S1-U of the UE (which is the SGi interface of the PDN GW function in the DeNB) and the EPS bearers with an appropriate QCI value and optionally ARP priority level value, established between the PDN GW function in the DeNB and the UE function of the RN;
- Uplink transport level packet mapping between QCI value and optionally ARP priority level value, of the EPS bearers (established between the PDN GW function in the DeNB and the UE function of the RN) and the DSCP value used over S1-U of the UE (which is the SGi interface of the PDN GW function in the DeNB).
In order to provide the Relay Function the DeNB shall support the following S-GW functions:
- Termination the S11 session of the MME(RN).
S-GW functions related to ECM-IDLE are not required.
S-GW functions related to mobility management are not supported.
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4.4.11 CSG Subscriber Server
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CSG Subscriber Server (CSS) is an optional element that stores CSG subscription data for roaming subscribers. The CSS stores and provides VPLMN specific CSG subscription information to the MME. The CSS is accessible from the MME via the S7a interface. The CSS is always in the same PLMN as the current MME.
If the same CSG ID exists in both CSS subscription data and HSS subscription data, the CSG subscription data from the HSS shall take precedence over the data from CSS.
Figure 4.4.11-1 illustrates CSS connected to MME.
Figure 4.4.11-1: CSS connected to MME
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4.4.12 RAN Congestion Awareness Function
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The RAN Congestion Awareness Function (RCAF) is an element that provides RAN User Plane Congestion Information (RUCI) to the PCRF to enable the PCRF to take the RAN user plane congestion status into account for policy decisions.
The RCAF collects information related to user plane congestion from the RAN's OAM system based on which the RCAF determines the congestion level (and the identifier) of an eNodeB or E-UTRAN cell.
Via the Nq interface the RCAF determines the UEs served by a congested eNodeB or congested E-UTRAN cell and retrieves the APNs of the active PDN connections of those UEs. The decision whether the RCAF operates on eNodeB or E-UTRAN cell level is up to operator configuration.
Via the Np reference point, the RCAF sends the RUCI to the PCRFs serving the UEs' PDN connections.
NOTE 1: The details of congestion reporting to the PCRF and the Np reference point are specified in TS 23.203 [6].
NOTE 2: In the case of roaming or RAN sharing as specified in TS 23.251 [24], Np is an inter-operator reference point. Whether Np applies in the case of roaming and RAN sharing is subject to inter-operator agreements.
Figure 4.4.12-1 illustrates the RCAF connected to the MME. The RCAF is located in the same PLMN as the serving MME except in network sharing scenarios where the RCAF belongs to the RAN operator.
Figure 4.4.12-1: RCAF connected to MME
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4.4.13 UCMF
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The UCMF is used for storage of dictionary entries corresponding to either PLMN-assigned or UE manufacturer-assigned UE Radio Capability IDs. An MME may subscribe with the UCMF to obtain from the UCMF new values of UE Radio Capability ID that the UCMF assigns for the purpose of caching them locally.
Provisioning of UE manufacturer-assigned UE Radio Capability ID entries in the UCMF is performed from an AS that interacts with the UCMF either directly or via the SCEF (or via Network Management) (see TS 23.682 [74] for further information). A UCMF that serves both EPS and 5GS shall require provisioning the UE Radio Capability ID with the TS 38.331 [89] format or the TS 36.331 [37] format or both the formats of the UE radio capabilities.
For PLMN-assigned UE Radio Capability ID the UCMF also is the entity that assigns the UE Radio Capability ID values.
Figure 4.4.13-1: UCMF connected to MME
Each PLMN-assigned UE Radio Capability ID is also associated to the IMEI/TAC of the UE model(s) that it is related to. When an MME requests the UCMF to assign a UE Radio Capability ID for a set of UE radio capabilities, it indicates the IMEI/TAC of the UE that the UE Radio Capability information is related to.
The UCMF may be provisioned with a dictionary of UE manufacturer-assigned UE Radio Capability IDs which include a "Vendor ID" that applies to the Manufacturers of these UE, and a list of IMEI/TACs for which the PLMN has obtained UE manufacturer-assigned UE Radio Capability IDs.
A PLMN-assigned UE Radio Capability IDs is kept in the UCMF storage as long as it is associated with at least a IMEI/TAC value. When a IMEI/TAC value is related to a UE model that is earmarked for operation based on UE manufacturer-assigned UE Radio Capability IDs, this IMEI/TAC value is disassociated in the UCMF from any PLMN assigned UE Radio Capability IDs.
For the case the PLMN is configured to store PLMN assigned IDs in the UE manufacturer-assigned operation requested list defined in clause 5.11.3a, the UCMF does not remove from UE manufacturer-assigned operation requested list any PLMN assigned UE Radio Capability ID no longer used, and rather quarantines it to avoid any future reassignment.
The UCMF stores a Version ID value for the PLMN assigned UE Radio Capability IDs so it is included in the PLMN assigned UE Radio Capability IDs it assigns. This shall be configured in the UCMF.
A UCMF dictionary entry shall include also the related UE Radio Capability for Paging for each RAT.
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4.5 Void
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4.6 EPS Mobility Management and Connection Management states
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4.6.1 General
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The EPS Mobility Management (EMM) states describe the Mobility Management states that result from the mobility management procedures e.g. Attach and Tracking Area Update procedures.
Two EMM states are described in this document:
- EMM-DEREGISTERED.
- EMM-REGISTERED.
NOTE 1: Other specifications may define more detailed EMM states (see e.g. TS 24.301 [46]).
The EPS Connection Management (ECM) states describe the signalling connectivity between the UE and the EPC.
Two ECM states are described in this document:
- ECM-IDLE.
- ECM-CONNECTED.
NOTE 2: The ECM-CONNECTED and ECM-IDLE states used in this document correspond respectively to the EMM-CONNECTED and EMM-IDLE modes defined in TS 24.301 [46].
In general, the ECM and EMM states are independent of each other. Transition from EMM-REGISTERED to EMM-DEREGISTERED can occur regardless of the ECM state, e.g. by explicit detach signalling in ECM-CONNECTED or by implicit detach locally in the MME during ECM-IDLE. However there are some relations, e.g. to transition from EMM-DEREGISTERED to EMM-REGISTERED the UE has to be in the ECM-CONNECTED state.
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4.6.2 Definition of main EPS Mobility Management states
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4.6.2.1 EMM-DEREGISTERED
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In the EMM‑DEREGISTERED state, the EMM context in MME holds no valid location or routing information for the UE. The UE is not reachable by a MME, as the UE location is not known.
In the EMM-DEREGISTERED state, some UE context can still be stored in the UE and MME, e.g. to avoid running an AKA procedure during every Attach procedure.
During the successful Inter-RAT TAU/RAU/handover procedure and ISR activated is not indicated to the UE, the old S4 SGSN/old MME changes the EMM state of the UE to GPRS-IDLE/PMM-DETACHED/EMM-DEREGISTERED.
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4.6.2.2 EMM-REGISTERED
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The UE enters the EMM-REGISTERED state by a successful registration with an Attach procedure to either E-UTRAN or GERAN/UTRAN. The MME enters the EMM-REGISTERED state by a successful Tracking Area Update procedure for a UE selecting an E-UTRAN cell from GERAN/UTRAN or by an Attach procedure via E-UTRAN. In the EMM-REGISTERED state, the UE can receive services that require registration in the EPS.
NOTE: The UE employs a single combined state machine for EMM and GMM states.
The UE location is known in the MME to at least an accuracy of the tracking area list allocated to that UE (excluding some abnormal cases).
In the EMM-REGISTERED state, the UE shall:
- always have at least one active PDN connection (unless the UE supports "Attach without PDN connectivity");
- setup the EPS security context.
After performing the Detach procedure, the state is changed to EMM-DEREGISTERED in the UE and in the MME. Upon receiving the TAU Reject and Attach Reject messages the actions of the UE and MME depend upon the 'cause value' in the reject message, but, in many cases the state is changed to EMM-DEREGISTERED in the UE and in the MME.
If all the bearers belonging to a UE that does not support "Attach without PDN connectivity" are released (e.g., after handover from E‑UTRAN to non-3GPP access), the MME shall change the MM state of that UE to EMM-DEREGISTERED. If the UE that does not support "Attach without PDN connectivity" camps on E-UTRAN and the UE detects that all of its bearers are released, the UE shall change the MM state to EMM-DEREGISTERED. If all the bearers (PDP contexts) belonging to a UE are released, while the UE camps on GERAN/UTRAN, the UE shall deactivate ISR by setting its TIN to "P-TMSI" as specified in TS 23.060 [7]. This ensures that the UE performs Tracking Area Update when it re-selects E-UTRAN. If the UE switches off its E‑UTRAN interface when performing handover to non-3GPP access, the UE shall automatically change its MM state to EMM-DEREGISTERED.
The MME may perform an implicit detach any time after the Implicit Detach timer expires. The state is changed to EMM-DEREGISTERED in the MME after performing the implicit detach.
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4.6.3 Definition of EPS Connection Management states
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4.6.3.1 ECM-IDLE
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A UE is in ECM-IDLE state when no NAS signalling connection between UE and network exists. In ECM-IDLE state, a UE performs cell selection/reselection according to TS 36.304 [34] and PLMN selection according to TS 23.122 [10].
Except for UEs that have had their RRC connection suspended, as described in clause 5.3.4A, there exists no UE context in E-UTRAN for the UE in the ECM-IDLE state. There is no S1_MME and no S1_U connection for the UE in the ECM-IDLE state.
In the EMM-REGISTERED and ECM-IDLE state, the UE shall:
- perform a tracking area update if the current TA is not in the list of TAs that the UE has received from the network in order to maintain the registration and enable the MME to page the UE;
- perform the periodic tracking area updating procedure to notify the EPC that the UE is available;
- perform a tracking area update if the RRC connection was released with release cause "load balancing TAU required";
- perform a tracking area update when the UE reselects an E-UTRAN cell and the UE's TIN indicates "P-TMSI";
- perform a tracking area update for a change of the UE's Core Network Capability information or the UE specific DRX parameter;
- perform a tracking area update when a change in conditions in the UE require a change in the extended idle mode DRX parameters previously provided by the MME.
- perform a tracking area update when the UE manually selects a CSG cell, and the CSG ID and associated PLMN of that cell is absent from both the UE's Allowed CSG list and the UE's Operator CSG list;
- answer to paging from the MME by performing a service request procedure or, if the UE has had its RRC connection suspended, the UE initiates the Connection Resume procedure (clause 5.3.5A);
- perform the service request procedure in order to establish the radio bearers when uplink user data is to be sent, or uplink NAS signalling is to be sent for UE requested bearer modification procedure (clause 5.4.5), UE requested PDN connectivity (clause 5.10.2), UE requested PDN disconnection (clause 5.10.3), or if the UE has had its RRC connection suspended the UE initiates the Connection Resume procedure (clause 5.3.5A).
The UE and the MME shall enter the ECM-CONNECTED state when the signalling connection is established between the UE and the MME. Initial NAS messages that initiate a transition from ECM-IDLE to ECM-CONNECTED state are Attach Request, Tracking Area Update Request, Service Request or Detach Request. A successful completion of the Connection Resume procedure, described in clause 5.3.5.A, initiates at UE and MME a state transition from ECM-IDLE to ECM-CONNECTED.
When the UE is in ECM‑IDLE state, the UE and the network may be unsynchronized, i.e. the UE and the network may have different sets of established EPS bearers. When the UE and the MME enter the ECM‑CONNECTED state, the set of EPS Bearers is synchronized between the UE and network.
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4.6.3.2 ECM-CONNECTED
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The UE location is known in the MME with an accuracy of a serving eNodeB ID. The mobility of UE is handled by the handover procedure, except for when the NB-IoT is being used, in which case there are no handover procedures.
The UE performs the tracking area update procedure when the TAI in the EMM system information is not in the list of TA's that the UE registered with the network, or when the UE handovers to an E‑UTRAN cell and the UE's TIN indicates "P-TMSI".
For a UE in the ECM-CONNECTED state, there exists a signalling connection between the UE and the MME. The signalling connection is made up of two parts: an RRC connection and an S1_MME connection.
The UE shall enter the ECM-IDLE state when its signalling connection to the MME has been released or broken. This release or failure is explicitly indicated by the eNodeB to the UE or detected by the UE.
The S1 release procedure or, if the UE is enabled to use User Plane CIoT EPS Optimisation the S1 Connection Suspend procedure (clause 5.3.4A) changes the state at both UE and MME from ECM-CONNECTED to ECM-IDLE.
NOTE 1: The UE may not receive the indication for the S1 release, e.g. due to radio link error or out of coverage. In this case, there can be temporal mismatch between the ECM-state in the UE and the ECM-state in the MME.
After a signalling procedure, the MME may decide to release the signalling connection to the UE, after which the state at both the UE and the MME is changed to ECM-IDLE.
NOTE 2: There are some abnormal cases where the UE transitions to ECM-IDLE.
When a UE changes to ECM‑CONNECTED state and the network initiates establishment of data radio bearers, then if a data radio bearer cannot be established, or the UE cannot maintain a data radio bearer in the ECM-CONNECTED state during handovers, the corresponding EPS bearer is deactivated. An exception to this is when the UE has been informed by the MME that a specific EPS bearer will never use a data radio bearer (e.g. because that EPS bearer is for a connection to the SCEF).
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4.6.4 State transition and functions
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Figure 4.6.4-1: EMM state model in UE
Figure 4.6.4-2: EMM state model in MME
Figure 4.6.4-3: ECM state model in UE
Figure 4.6.4-4: ECM state model in MME
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4.7 Overall QoS concept
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4.7.1 PDN connectivity service
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The Evolved Packet System provides connectivity between a UE and a PLMN external packet data network. This is referred to as PDN Connectivity Service.
The IP PDN Connectivity Service supports the transport of traffic flow aggregate(s), consisting of one or more Service Data Flows (SDFs).
NOTE: The concept of SDF is defined in the context of PCC, TS 23.203 [6], and is not explicitly visible in the NAS signalling.
A PDN connection to an SCEF has the following characteristics:
- It is only supported for WB-EUTRA, LTE-M and NB-IoT RAT types;
- It applies only when Control Plane CIoT EPS Optimisation are applicable;
- It does not support the transport of traffic flow aggregate(s);
- It does not support Emergency Services.
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4.7.2 The EPS bearer
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4.7.2.1 The EPS bearer in general
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For E-UTRAN access to the EPC the PDN connectivity service is provided by an EPS bearer for GTP-based S5/S8, and if IP is in use, by an EPS bearer concatenated with IP connectivity between Serving GW and PDN GW for PMIP-based S5/S8.
In this release of the specifications, dedicated bearers are only supported for the IP and Ethernet PDN Connectivity Service.
When User Plane (S1-U) is used for data traffic, then an EPS bearer uniquely identifies traffic flows that receive a common QoS treatment between a UE and a PDN GW for GTP-based S5/S8, and between UE and Serving GW for PMIP-based S5/S8. The packet filters signalled in the NAS procedures are associated with a unique packet filter identifier on per-PDN connection basis.
NOTE 1: The EPS Bearer Identity together with the packet filter identifier is used to reference which packet filter the UE intends to modify or delete, i.e. it is used to implement the unique packet filter identifier.
An EPS bearer is the level of granularity for bearer level QoS control in the EPC/E-UTRAN. That is, all traffic mapped to the same EPS bearer receive the same bearer level packet forwarding treatment (e.g. scheduling policy, queue management policy, rate shaping policy, RLC configuration, etc.). Providing different bearer level packet forwarding treatment requires separate EPS bearers.
NOTE 2: In addition but independent to bearer level QoS control, the PCC framework allows an optional enforcement of service level QoS control on the granularity of SDFs independent of the mapping of SDFs to EPS bearers.
One EPS bearer is established when the UE connects to a PDN, and that remains established throughout the lifetime of the PDN connection to provide the UE with always-on connectivity to that PDN. That bearer is referred to as the default bearer. Any additional EPS bearer that is established for the same PDN connection is referred to as a dedicated bearer.
The EPS bearer traffic flow template (TFT) is the set of all packet filters associated with that EPS bearer. An UpLink Traffic Flow Template (UL TFT) is the set of uplink packet filters in a TFT. A DownLink Traffic Flow Template (DL TFT) is the set of downlink packet filters in a TFT. Every dedicated EPS bearer is associated with a TFT. A TFT may be also assigned to the default EPS bearer. The UE uses the UL TFT for mapping traffic to an EPS bearer in the uplink direction. The PCEF (for GTP-based S5/S8) or the BBERF (for PMIP-based S5/S8) uses the DL TFT for mapping traffic to an EPS bearer in the downlink direction. The UE may use the UL TFT and DL TFT to associate EPS Bearer Activation or Modification procedures to an application and to traffic flow aggregates of the application. Therefore the PDN GW shall, in the Create Dedicated Bearer Request and the Update Bearer Request messages, provide all available traffic flow description information (e.g. source and destination IP address and port numbers and the protocol information).
For the UE, the evaluation precedence order of the packet filters making up the UL TFTs is signalled from the P‑GW to the UE as part of any appropriate TFT operations.
NOTE 3: The evaluation precedence index of the packet filters associated with the default bearer, in relation to those associated with the dedicated bearers, is up to operator configuration. It is possible to "force" certain traffic onto the default bearer by setting the evaluation precedence index of the corresponding filters to a value that is lower than the values used for filters associated with the dedicated bearers.
Further details about the TFT and the TFT operations are described in clause 15.3 of TS 23.060 [7]. The details about the TFT packet filter(s) are described in clause 15.3.2 of TS 23.060 [7] for PDN connections of IP type and in clause 5.7.6.3 of TS 23.501 [83] for PDN connections of Ethernet type.
A TFT of an uplink unidirectional EPS bearer is only associated with UL packet filter(s) that matches the uplink unidirectional traffic flow(s) A TFT of a downlink unidirectional EPS bearer is associated with DL packet filter(s) that matches the unidirectional traffic flow(s) and a UL packet filter that effectively disallows any useful packet flows (see clause 15.3.3.4 in TS 23.060 [7] for an example of such packet filter.
The UE routes uplink packets to the different EPS bearers based on uplink packet filters in the TFTs assigned to these EPS bearers. The UE evaluates for a match, first the uplink packet filter amongst all TFTs that has the lowest evaluation precedence index and, if no match is found, proceeds with the evaluation of uplink packet filters in increasing order of their evaluation precedence index. This procedure shall be executed until a match is found or all uplink packet filters have been evaluated. If a match is found, the uplink data packet is transmitted on the EPS bearer that is associated with the TFT of the matching uplink packet filter. If no match is found, the uplink data packet shall be sent via the EPS bearer that has not been assigned any uplink packet filter. If all EPS bearers (including the default EPS bearer for that PDN) have been assigned one or more uplink packet filters, the UE shall discard the uplink data packet.
NOTE 4: The above algorithm implies that there is at most one EPS bearer without any uplink packet filter. Therefore, some UEs may expect that during the lifetime of a PDN connection (where only network has provided TFT packet filters) at most one EPS bearer exists without any uplink packet filter.
To ensure that at most one EPS bearer exists without any uplink packet filter, the PCEF (for GTP-based S5/S8) or the BBERF (for PMIP-based S5/S8) maintains a valid state for the TFT settings of the PDN connection as defined in clause 15.3.0 of TS 23.060 [7] and if necessary, adds a packet filter which effectively disallows any useful packet flows in uplink direction (see clause 15.3.3.4 in TS 23.060 [7] for an example of such a packet filter) to the TFT of a dedicated bearer.
NOTE 5: The default bearer is the only bearer that may be without any uplink packet filter and thus, a packet filter which effectively disallows any useful packet flows in uplink direction will not be added by the PCEF/BBERF.
The initial bearer level QoS parameter values of the default bearer are assigned by the network, based on subscription data (in E-UTRAN the MME sets those initial values based on subscription data retrieved from HSS).
In a non-roaming scenario, the PCEF may change the QoS parameter value received from the MME based on interaction with the PCRF or based on local configuration. When the PCEF changes those values, the MME shall use the bearer level QoS parameter values received on the S11 reference point during establishment or modification of the default bearer.
In a roaming scenario, based on local configuration, the MME may downgrade the ARP or APN-AMBR and/or remap QCI parameter values received from HSS to the value locally configured in MME (e.g. when the values received from HSS do not comply with services provided by the visited PLMN).
At inter-PLMN mobility the source MME shall provide the EPS bearer QoS parameters used in the source MME to the target MME.
The PCEF may change the QoS parameter values received from the MME based on interaction with the PCRF or based on local configuration. Alternatively, the PCEF may reject the bearer establishment.
NOTE 6: For certain APNs (e.g. the IMS APN defined by the GSMA) the QCI value is strictly defined and therefore remapping of QCI is not permitted.
NOTE 7: In roaming scenarios, the ARP/APN-AMBR/QCI values provided by the MME for a default bearer may deviate from the subscribed values depending on the roaming agreement. If the PCC/PCEF rejects the establishment of the default bearer, this implies that Attach via E-UTRAN will fail. Similarly, if the PCEF (based on interaction with the PCRF or based on local configuration) upgrades the ARP/APN-AMBR/QCI parameter values received from the MME, the default bearer establishment and attach may be rejected by the MME.
NOTE 8: Subscription data related to bearer level QoS parameter values retrieved from the HSS are not applicable for dedicated bearers.
For WB-E-UTRA, the decision to establish or modify a dedicated bearer can only be taken by the EPC, and the bearer level QoS parameter values are always assigned by the EPC.
Dedicated bearers are not supported over NB-IoT. The PDN GW uses the RAT Type to ensure that no dedicated bearers are active when the UE is accessing over NB-IoT. In the case of inter-RAT mobility from WB-EUTRA to NB-IoT, the UE and MME indicate local deactivation of non-default EPS bearers at TAU as specified in TS 24.301 [46].
The MME shall not modify the bearer level QoS parameter values received on the S11 reference point during establishment or modification of a default or dedicated bearer (except when the conditions described in NOTE 9 or NOTE 10 apply). Consequently, "QoS negotiation" between the E-UTRAN and the EPC during default or dedicated bearer establishment / modification is not supported. Based on local configuration, the MME may reject the establishment or modification of a default or dedicated bearer if the bearer level QoS parameter values sent by the PCEF over a GTP based S8 roaming interface do not comply with a roaming agreement.
NOTE 9: If the EPS QoS parameters are not compliant with the roaming agreement, the MME, based on local policies, can downgrade the ARP priority level, ARP pre-emption capability, ARP pre-emption vulnerability, APN-AMBR or MBR (for GBR bearers) parameters received over S8 and allow the bearer establishment or modification of a default or dedicated bearer. The HPLMN is expected to set EPS QoS parameters compliant with roaming agreements, therefore the HPLMN is not informed about any downgrade of EPS bearer QoS parameters. The consequences of such a downgrading APN-AMBR and MBR are that APN-AMBR and MBR enforcement at the HPLMN and at the UE will not be aligned. The consequence of downgrading the ARP is that the EPS bearer ARP at the HPLMN and at the eNodeB will not be aligned, and multiple EPS bearers created can possibly have the same EPS bearer ARP in the eNodeB.
NOTE 10: In the case of QCI remapping at inter-PLMN mobility is needed for certain EPS bearers, the remapping that is done is implementation specific according to an inter-PLMN agreement between the involved operators. The remapping can include QCI values in the operator-specific QCI value range. If remapping of QCI at inter-PLMN mobility is to be performed, the target PLMN chooses the QCI value based on inter-PLMN agreement among operators involved. If the source MME provides a QCI value which is not part of the inter-PLMN agreement between the target PLMN and the HPLMN, the target PLMN can choose a QCI value based on local policy. The remapping of the QCI value based on local policy can result in service degradation. The target PLMN MME informs the SGW (and the SGW updates the PGW) the selected QCI value by using the procedure in clause 5.4.2.2.
NOTE 11: In a Home Routed roaming scenario, if the QCI value an MME receives from PGW via SGW during EPS bearer establishment or modification is not part of the inter-PLMN agreement between the serving PLMN and the HPLMN, the MME can remap QCI value. The remapping of the QCI value based on local policy can result in service degradation. The MME informs the SGW (and the SGW updates the PGW) of the selected QCI value by using the procedure in clause 5.4.2.2. Hence the same QCI value is associated with the PDN connection in the serving PLMN and HPLMN.
NOTE 12: In roaming scenarios, for IMS voice service (e.g. the IMS APN defined by the GSMA), the MME, based on local policy, can override the ARP (i.e. ARP priority level, ARP pre-emption capability, ARP pre-emption vulnerability) received over S8 if the ARP indicates lower priority than the local policy. The purpose of ARP override in the serving PLMN is to apply the same allocation and retention priority for IMS voice service for all users (i.e. roamers and non-roamers) and to apply the same allocation and retention priority for all MPS service users (clause 4.3.18) when roaming agreements are in place and where regulatory requirements apply.
At inter-RAT mobility, based on local configuration, the MME may perform a mapping of QCI values for which there is no mapping defined in Table E.3 or which are not supported in the target RAT.
NOTE 13: The PCRF ensures that the EPS bearer QCI values are aligned with the QCI values mapped by the MME for the current RAT as described in clause A.4.1.2 of TS 23.203 [6].
The distinction between default and dedicated bearers should be transparent to the access network (e.g. E-UTRAN).
An EPS bearer is referred to as a GBR bearer if dedicated network resources related to a Guaranteed Bit Rate (GBR) value that is associated with the EPS bearer are permanently allocated (e.g. by an admission control function in the eNodeB) at bearer establishment/modification. Otherwise, an EPS bearer is referred to as a Non-GBR bearer.
NOTE 14: Admission control can be performed at establishment / modification of a Non-GBR bearer even though a Non-GBR bearer is not associated with a GBR value.
A dedicated bearer can either be a GBR or a Non-GBR bearer. A default bearer shall be a Non-GBR bearer.
NOTE 15: A default bearer provides the UE with connectivity throughout the lifetime of the PDN connection. That motivates the restriction of a default bearer to bearer type Non-GBR.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.2.2 The EPS bearer with GTP-based S5/S8
|
Figure 4.7.2.2-1: Two Unicast EPS bearers (GTP-based S5/S8)
An EPS bearer is realized by the following elements:
- In the UE, the UL TFT maps a traffic flow aggregate to an EPS bearer in the uplink direction;
- In the PDN GW, the DL TFT maps a traffic flow aggregate to an EPS bearer in the downlink direction;
- A radio bearer (defined in TS 36.300 [5]) transports the packets of an EPS bearer between a UE and an eNodeB. If a radio bearer exists, there is a one-to-one mapping between an EPS bearer and this radio bearer;
- An S1 bearer transports the packets of an EPS bearer between an eNodeB and a Serving GW;
- An E-RAB (E-UTRAN Radio Access Bearer) refers to the concatenation of an S1 bearer and the corresponding radio bearer, as defined in TS 36.300 [5].
- An S5/S8 bearer transports the packets of an EPS bearer between a Serving GW and a PDN GW;
- A UE stores a mapping between an uplink packet filter and a radio bearer to create the mapping between a traffic flow aggregate and a radio bearer in the uplink;
- A PDN GW stores a mapping between a downlink packet filter and an S5/S8 bearer to create the mapping between a traffic flow aggregate and an S5/S8 bearer in the downlink;
- An eNodeB stores a one-to-one mapping between a radio bearer and an S1 Bearer to create the mapping between a radio bearer and an S1 bearer in both the uplink and downlink;
- A Serving GW stores a one-to-one mapping between an S1 Bearer and an S5/S8 bearer to create the mapping between an S1 bearer and an S5/S8 bearer in both the uplink and downlink.
The PDN GW routes downlink packets to the different EPS bearers based on the downlink packet filters in the TFTs assigned to the EPS bearers in the PDN connection. Upon reception of a downlink data packet, the PDN GW evaluates for a match, first the downlink packet filter that has the lowest evaluation precedence index and, if no match is found, proceeds with the evaluation of downlink packet filters in increasing order of their evaluation precedence index. This procedure shall be executed until a match is found, in which case the downlink data packet is tunnelled to the Serving GW on the EPS bearer that is associated with the TFT of the matching downlink packet filter. If no match is found, the downlink data packet shall be sent via the EPS bearer that does not have any TFT assigned. If all EPS bearers (including the default EPS bearer for that PDN) have been assigned a TFT, the PDN GW shall discard the downlink data packet.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.2.3 The EPS bearer with PMIP-based S5/S8
|
See clause 4.10.3 in TS 23.402 [2].
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.3 Bearer level QoS parameters
|
The EPS bearer QoS profile includes the parameters QCI, ARP, GBR and MBR, described in this clause. This clause also describes QoS parameters which are applied to an aggregated set of EPS Bearers: APN‑AMBR and UE‑AMBR.
Each EPS bearer (GBR and Non-GBR) is associated with the following bearer level QoS parameters:
- QoS Class Identifier (QCI);
- Allocation and Retention Priority (ARP).
A QCI is a scalar that is used as a reference to access node-specific parameters that control bearer level packet forwarding treatment (e.g. scheduling weights, admission thresholds, queue management thresholds, link layer protocol configuration, etc.), and that have been pre-configured by the operator owning the access node (e.g. eNodeB). A one-to-one mapping of standardized QCI values to standardized characteristics is captured in TS 23.203 [6]. A QCI may have an operator-specific QCI value and the mapping of such a QCI value to the QoS characteristics is defined by the operator.
NOTE 1: On the radio interface and on S1, each PDU (e.g. RLC PDU or GTP-U PDU) is indirectly associated with one QCI via the bearer identifier carried in the PDU header. The same applies to the S5 and S8 interfaces if they are based on GTP.
NOTE 2: When required by operator policy, the eNodeB can be configured to also use the ARP priority level in addition to the QCI to control bearer level packet forwarding treatment in the eNodeB for SDFs having high priority ARPs.
The ARP shall contain information about the priority level (scalar), the pre-emption capability (flag) and the pre-emption vulnerability (flag). The primary purpose of ARP is to decide whether a bearer establishment / modification request can be accepted or needs to be rejected due to resource limitations (typically available radio capacity for GBR bearers). The priority level information of the ARP is used for this decision to ensure that the request of the bearer with the higher priority level is preferred. In addition, the ARP can be used (e.g. by the eNodeB) to decide which bearer(s) to drop during exceptional resource limitations (e.g. at handover). The pre-emption capability information of the ARP defines whether a bearer with a lower ARP priority level should be dropped to free up the required resources. The pre-emption vulnerability information of the ARP defines whether a bearer is applicable for such dropping by a pre-emption capable bearer with a higher ARP priority level.
Once a bearer has been successfully established, the packet handling (e.g. scheduling and rate control) within the eNodeB, PDN GW, and Serving GW should be solely determined by the following EPS bearer QoS parameters: QCI, GBR and MBR, and by the AMBR parameters. However, when required by operator policy, the eNodeB can be configured to also use a bearer's ARP priority level in addition to the QCI to determine the relative priority of the SDFs for packet handling (e.g. scheduling and rate control) in the eNodeB as defined in TS 23.203 [6] clause 6.1.7.2. This configuration applies only for bearers with high priority ARPs as defined in TS 23.203 [6] clause 6.1.7.3.
The ARP priority level may be used in addition to the QCI to determine the transport level packet marking, e.g. to set the DiffServ Code Point. The ARP is not included within the EPS QoS Profile sent to the UE.
NOTE 3: The ARP should be understood as "Priority of Allocation and Retention"; not as "Allocation, Retention, and Priority".
NOTE 4: Video telephony is one use case where it may be beneficial to use EPS bearers with different ARP values for the same UE. In this use case an operator could map voice to one bearer with a higher ARP, and video to another bearer with a lower ARP. In a congestion situation (e.g. cell edge) the eNodeB can then drop the "video bearer" without affecting the "voice bearer". This would improve service continuity.
NOTE 5: The ARP may also be used to free up capacity in exceptional situations, e.g. a disaster situation. In such a case the eNodeB may drop bearers with a lower ARP priority level to free up capacity if the pre-emption vulnerability information allows this.
Each GBR bearer is additionally associated with the following bearer level QoS parameters:
- Guaranteed Bit Rate (GBR);
- Maximum Bit Rate (MBR).
The GBR denotes the bit rate that can be expected to be provided by a GBR bearer. The MBR limits the bit rate that can be expected to be provided by a GBR bearer (e.g. excess traffic may get discarded by a rate shaping function). See clause 4.7.4 for further details on GBR and MBR.
GBR bearers are not supported by NB-IoT. The PDN GW uses the RAT Type to ensure that GBR bearers are not active when the UE is using NB-IoT.
Each APN access, by a UE, is associated with the following QoS parameter:
- per APN Aggregate Maximum Bit Rate (APN-AMBR).
The subscribed APN‑AMBR is a subscription parameter stored per APN in the HSS, which applies as APN-AMBR unless the APN-AMBR is modified by the MME (e.g in roaming scenarios and/or for usage of NB-IoT) or the PDN GW, based on local policy (e.g. for RAT Type = NB-IoT) or PCRF interactions. The APN-AMBR limits the aggregate bit rate that can be expected to be provided across all Non‑GBR bearers and across all PDN connections of the same APN (e.g. excess traffic may get discarded by a rate shaping function). Each of those Non‑GBR bearers could potentially utilize the entire APN‑AMBR, e.g. when the other Non‑GBR bearers do not carry any traffic. GBR bearers are outside the scope of APN‑AMBR. The P‑GW enforces the APN‑AMBR in downlink. Enforcement of APN‑AMBR in uplink is done in the UE and additionally in the P‑GW.
NOTE 6: All simultaneous active PDN connections of a UE that are associated with the same APN shall be provided by the same PDN GW (see clauses 4.3.8.1 and 5.10.1).
APN-AMBR applies to all PDN connections of an APN. For the case of multiple PDN connections of an APN, if a change of APN-AMBR occurs due to local policy or the PDN GW is provided the updated APN-AMBR for each PDN connection from the MME or PCRF, the PDN GW initiates explicit signalling for each PDN connection to update the APN-AMBR value.
Each UE in state EMM-REGISTERED is associated with the following bearer aggregate level QoS parameter:
- per UE Aggregate Maximum Bit Rate (UE-AMBR).
The UE‑AMBR is limited by a subscription parameter stored in the HSS. The MME shall set the UE‑AMBR to the sum of the APN‑AMBR of all active APNs up to the value of the subscribed UE‑AMBR. The UE‑AMBR limits the aggregate bit rate that can be expected to be provided across all Non‑GBR bearers of a UE (e.g. excess traffic may get discarded by a rate shaping function). Each of those Non‑GBR bearers could potentially utilize the entire UE‑AMBR, e.g. when the other Non‑GBR bearers do not carry any traffic. GBR bearers are outside the scope of UE AMBR. The E‑UTRAN enforces the UE‑AMBR in uplink and downlink except for PDN connections using the Control Plane CIoT EPS Optimisation.
The GBR and MBR denote bit rates of traffic per bearer while UE-AMBR/APN-AMBR denote bit rates of traffic per group of bearers. Each of those QoS parameters has an uplink and a downlink component. On S1_MME the values of the GBR, MBR, and AMBR refer to the bit stream excluding the GTP-U/IP header overhead of the tunnel on S1_U.
The HSS defines, for each PDN subscription context, the 'EPS subscribed QoS profile' which contains the bearer level QoS parameter values for the default bearer (QCI and ARP) and the subscribed APN-AMBR value. The subscribed ARP shall be used to set the priority level of the EPS bearer parameter ARP for the default bearer while the pre-emption capability and the pre-emption vulnerability information for the default bearer are set based on MME operator policy. In addition, the subscribed ARP shall be applied by the P-GW for setting the ARP priority level of all dedicated EPS bearers of the same PDN connection unless a different ARP priority level setting is required (due to P-GW configuration or interaction with the PCRF).
NOTE 7: The ARP parameter of the EPS bearer can be modified by the P‑GW (e.g. based on interaction with the PCRF due to e.g. MPS user initiated session) to assign the appropriate pre-emption capability and the pre-emption vulnerability setting.
The ARP pre-emption vulnerability of the default bearer should be set appropriately to minimize the risk of unnecessary release of the default bearer.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.4 Support for Application / Service Layer Rate Adaptation
|
The E‑UTRAN/UTRAN and the UE support the RFC 3168 [55] Explicit Congestion Notification (ECN), as described in TS 36.300 [5], TS 25.401 [16] and TS 26.114 [56]. The IP level ECN scheme enables the E‑UTRAN/UTRAN to trigger a rate adaptation scheme at the application / service / transport layer. To make sufficient time available for end-to-end codec rate adaptation the E-UTRAN/UTRAN should attempt to not drop any packets on a bearer for a default grace period of at least 500 ms after it has indicated congestion with ECN on the bearer for packets within the packet delay budget. During this ECN grace period the E-UTRAN/UTRAN should also attempt to meet the QCI characteristics / QoS class associated with the bearer.
NOTE 1: Note that the receiving end-point should interpret all ECN-CE signals received within one end-to-end round-trip time as one "congestion event" (see IETF RFC 3168 [55] and TS 26.114 [56]).
The MBR of a particular GBR bearer may be set larger than the GBR.
NOTE 2: Enforcement of APN-AMBR / UE-AMBR is independent of whether the MBR of a particular GBR bearer has been set larger than the GBR (see clause 4.7.3).
The EPC does not support E-UTRAN/UTRAN-initiated "QoS re-negotiation". That is, the EPC does not support an eNodeB/RNC initiated bearer modification procedure. If an eNodeB/RNC can no longer sustain the GBR of an active GBR bearer then the eNodeB/RNC should simply trigger a deactivation of that bearer.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.5 Application of PCC in the Evolved Packet System
|
The Evolved Packet System applies the PCC framework as defined in TS 23.203 [6] for QoS policy and charging control. PCC functionality is present in the AF, PCEF and PCRF.
An EPS needs to support both PCEF and PCRF functionality to enable dynamic policy and charging control by means of installation of PCC rules based on user and service dimensions. However, an EPS may only support PCEF functionality in which case it shall support static policy and charging control.
NOTE: The local configuration of PCEF static policy and charging control functionality is not subject to standardization. The PCEF static policy and control functionality is not based on subscription information.
The following applies to the use of dynamic policy and charging control in EPS:
- The service level (per SDF) QoS parameters are conveyed in PCC rules (one PCC rule per SDF) over the Gx reference point. The service level QoS parameters consist of a QoS Class Identifier (QCI) Allocation and Retention Priority (ARP) and authorised Guaranteed and Maximum Bit Rate values for uplink and downlink. The QCI is a scalar that represents the QoS characteristics that the EPS is expected to provide for the SDF. ARP is an indicator of the priority for the SDF that is used to decide about the assignment of resources due to resource limitations. The service level ARP assigned by PCRF in a PCC rule may be different from the bearer level ARP stored in subscription data;
- The set of standardized QCIs and their characteristics that the PCRF in an EPS can select from is provided in TS 23.203 [6]. It is expected that the PCRF selects a QCI in such a way that the IP-CAN receiving it can support it;
- It is not required that an IP-CAN supports all standardized QCIs;
- In the case of IP address configuration subsequent to initial attachment, i.e. through DHCP mechanism to complete the IP address configuration, the PDN GW/PCEF shall notify the PCRF of the UE's IP address by means of an IP-CAN Session Modification procedure or IP-CAN Session Establishment procedure as defined in TS 23.203 [6] when it is assigned. If the PCRF response leads to an EPS bearer modification the PDN GW should initiate a bearer update procedure;
- For local breakout, the visited network has the capability to reject the QoS authorized by the home network based on operator policies.
The following applies regardless of whether dynamic or static policy and charging control is used in EPS:
- For E-UTRAN the value of the ARP of an EPS bearer is identical to the value of the ARP of the SDF(s) mapped to that EPS bearer;
- For the same UE/PDN connection: SDFs associated with different QCIs or with the same service-level QCI but different ARP shall not be mapped to the same EPS bearer;
- The bearer level QCI of an EPS bearer is identical to the value of the QCI of the SDF(s) mapped to that EPS bearer.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.6 Bearer Control Mode in EPC
|
The Bearer Control Mode (BCM) for E-UTRAN access is always UE/NW. Hence, explicit signalling between the UE and the network to determine BCM for E-UTRAN access does not occur.
GERAN/UTRAN/E-UTRAN capable UEs negotiate the BCM of a PDN Connection applicable for GERAN/UTRAN access during E-UTRAN Initial Attach and during UE Requested PDN Connectivity procedure. Such UEs provide the Network Request Support UE (NRSU) parameter to the PDN GW in PCO. The PDN GW derives the BCM applicable to GERAN/UTRAN access based on the NRSU and operator policy. The selected BCM, valid for GERAN/UTRAN, is provided back to the UE in PCO IE in the E-UTRAN Attach Accept or PDN Connectivity Accept message. The selected BCM is also stored in the PDN GW and the UE, and applied by UE upon moving to GERAN or UTRAN access unless explicitly informed by PDN GW of a change in BCM (see TS 23.060 [7]) via PCO IE.
NOTE 1: In Rel‑8 it was not mandatory for GERAN/UTRAN/E-UTRAN capable UEs to provide NRSU to the PDN GW during E-UTRAN Initial Attach and UE Requested PDN Connectivity procedure.
When a GERAN/UTRAN/E-UTRAN capable UE moves from UTRAN or GERAN access to E-UTRAN access, it stores the BCM used in UTRAN or GERAN access to be used again when the UE moves back to UTRAN or GERAN access unless explicitly informed by PDN GW of a change in BCM (see TS 23.060 [7]) via the PCO IE.
If PCC is deployed, the PDN GW requests PCRF to perform BCM selection for the RAT the UE is accessing at IP‑CAN session establishment and IP-CAN session modification. The PCRF, determines the applicable BCM, based on a number of factors (see TS 23.203 [6]), and informs the PDN GW. If the BCM has changed, the PDN GW informs the UE of the new BCM via the PCO IE.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.7 Support of rate control of user data using CIoT EPS Optimisation
| |
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.7.1 General
|
The rate of user data sent to and from a UE (e.g. a UE using CIoT EPS Optimisations) can be controlled in two different ways:
- Serving PLMN Rate Control
- APN Rate Control
Serving PLMN Rate Control is intended to allow the Serving PLMN to protect its MME and the Signalling Radio Bearers in the E-UTRAN from the load generated by NAS Data PDUs.
APN Rate Control is intended to allow HPLMN operators to offer customer services such as "maximum of Y messages per day".
NOTE: Existing AMBR mechanisms are not suitable for such a service since, for radio efficiency and UE battery life reasons, an AMBR of e.g. > 100kbit/s is desirable and such an AMBR translates to a potentially large daily data volume.
The PDN GW in the visited PLMN may send the APN rate control parameter for an emergency PDN connection.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.7.2 Serving PLMN Rate Control
|
The Serving PLMN Rate Control value is configured in the MME.
NOTE 1: Homogeneous support of Serving PLMN Rate Control in a network is assumed.
At PDN connection establishment, the MME may inform the UE and PDN GW/SCEF (as specified in TS 24.301 [46] and TS 29.274 [43]) of any per PDN connection local Serving PLMN Rate Control that the Serving PLMN intends to enforce for NAS Data PDUs. The MME shall only indicate Serving PLMN Rate Control command to the PDN GW if the PDN connection is using S11-U and set to Control Plane only. The MME shall only indicate Serving PLMN Rate Control command to the SCEF if that PDN connection is using SCEF.
This rate control is operator configurable and expressed as "X NAS Data PDUs per deci hour" where X is an integer that shall not be less than 10. There are separate limits for uplink and downlink NAS Data PDUs:
- The UE shall limit the rate at which it generates uplink NAS Data PDUs to comply with the Serving PLMN policy. In the UE the indicated rate control applies only on the PDN connection where it was received, and therefore the UE shall limit the rate of its uplink NAS Data PDUs to comply with the rate that is indicated for the PDN connection. The indicated rate is valid until the PDN connection is released.
- The PDN GW/SCEF shall limit the rate at which it generates downlink Data PDUs. In the PDN GW/SCEF the indicated rate control applies only on the PDN connection where it was received, and therefore the PDN GW/SCEF shall limit the rate of its downlink Data PDUs to comply with the rate that is indicated for the PDN connection.
- The MME may enforce these limits per PDN connection by discarding or delaying packets that exceed this these limits. The Serving PLMN Rate does not include SMS sent via NAS Transport PDUs. The MME starts the Serving PLMN Rate Control when the first NAS Data PDU is received.
NOTE 2: If the UE/PDN GW/SCEF start the Serving PLMN rate control at a different time than the MME, PDUs sent within the limit enforced at the UE/PDN GW/SCEF can still exceed the limit enforced by the MME.
NOTE 3 It is assumed that the Serving PLMN Rate is sufficiently high to not interfere with the APN Rate Control as the APN Rate Control, if used, is assumed to allow fewer messages. NAS PDUs related to exception reports are not subject to the Serving PLMN Rate Control.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.7.3 APN Rate Control
|
The APN Rate Control is configured in the PDN GW or in the SCEF. The PDN GW or SCEF can send an APN Uplink Rate Control command to the UE using the PCO information element.
The APN Uplink Rate Control applies to data PDUs sent on that APN by either Data Radio Bearers (S1-U) or Signalling Radio Bearers (NAS Data PDUs).
The rate control information is separate for uplink and downlink and in the form of:
- a positive integer 'number of packets per time unit', and
- an indication as to whether or not exception reports can still be sent if this rate control limit has been met, and
- if the UE indicated support for it, an integer 'number of additional allowed exception report packets per time unit' once the rate control limit has been reached.
UEs supporting APN Rate Control shall support the 'number of additional allowed exception report packets per time unit' and shall provide an indication to the CN at PDN connection establishment.
NOTE 1: Pre-Rel‑14 UEs do not support the 'number of additional allowed exception report packets per time unit' and do not send an indication to the CN at PDN connection establishment.
The UE shall comply with this uplink rate control instruction. If the UE exceeds the uplink 'number of packets per time unit', the UE may still send uplink exception reports if allowed and the 'number of additional allowed exception reports per time unit' has not been exceeded. The UE shall consider this rate control instruction as valid until it receives a new one from either PDN GW or from SCEF.
When the last PDN connection using a given APN is released, the APN Rate Control Status (including the number of packets still allowed in the given time unit, the number of additional exception reports still allowed in the given time unit and the termination time of the current APN Rate Control validity period) may be stored in the MME so that it can be retrieved for a subsequent re-establishment of a new first PDN connection for that given APN.
At subsequent establishment of a new first PDN connection for that given APN, the PDN GW/SCEF may receive the previously stored APN Rate Control Status and, if the first APN Rate Control validity period has not expired, it applies the received APN Rate Control Status and provides the related parameters to the UE in the PCO (instead of the configured APN Rate Control parameters). If the initially applied parameters differ from the configured APN Rate Control parameters, the PDN GW/SCEF uses the configured APN Rate Control parameters once the first APN Rate Control validity period expires, and sends an update to the UE with the configured APN Rate Control parameters.
NOTE 2: The storage of the APN Rate Control Status information for very long time intervals can be implementation specific.
The PDN GW or SCEF realises the APN rate control based on a 'maximum allowed rate' per direction. If PDN GW or SCEF provided the 'number of additional allowed exception report packets per time unit' to the UE, then the 'maximum allowed rate' is equal to the 'number of packets per time unit' plus the 'number of additional allowed exception report packets per time unit'. Otherwise, the 'maximum allowed rate' is equal to the 'number of packets per time unit'.
NOTE 3: Pre-Rel‑14 UEs understand only the 'number of packets per time unit', and, if an indication that exception reports are allowed has been sent to such UEs, there is a risk that exception report packets are discarded by the PDN GW or SCEF. To overcome this problem, the PDN GW or SCEF can still apply a configured 'number of additional allowed exception report packets per time unit' even though not sent to pre-Rel‑14 UEs.
The PDN GW or SCEF may enforce the uplink rate by discarding or delaying packets that exceed the 'maximum allowed rate'. The PDN GW or SCEF shall enforce the downlink rate by discarding or delaying packets that exceed the downlink part of the 'maximum allowed rate'.
NOTE 4: It is assumed that the Serving PLMN Rate is sufficiently high to not interfere with the APN Rate Control as the APN Rate Control, if used, is assumed to allow fewer messages. NAS PDUs related to exception reports are not subject to the Serving PLMN Rate Control.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.7.8 Inter-UE QoS for NB-IoT UEs using Control Plane CIoT EPS Optimisation
|
To allow the E-UTRAN to prioritise resource allocation between different NB-IoT UEs when some of the UEs are using the Control Plane CIoT EPS Optimisation, the eNodeB may request, based on configuration, the MME to supply the eNodeB with the negotiated QoS profile for any UE that is using the Control Plane CIoT EPS Optimisation.
The QoS profile sent to the eNodeB by the MME consists of the E-RAB Level QoS Parameter in the E-RAB to be Setup List IE (see TS 36.413 [36]).
In order to reduce signalling load on the MME, the eNodeB may be configured to request the QoS profile from the MME by using the UE's S-TMSI as identifier, e.g., when the eNodeB's NB-IoT load exceeds certain threshold(s) or when the eNodeB needs to cache the QoS profile.
If the UE has more than one EPS bearer active, the MME sends QoS profile for only one EPS bearer to the eNodeB. In this case the MME uses local configuration (e.g. considering table 6.1.7 in TS 23.203 [6], the MME chooses the non-GBR EPS bearer with the QCI corresponding to the highest Priority Level) to determine which EPS bearer's QoS to send to the eNodeB. If the MME has no EPS bearers active for the UE, then this fact is indicated to the eNodeB.
The eNodeB can use the QoS profile to assist with resource prioritisation decisions between different NB-IoT UEs (irrespective of whether the UE/eNodeB is using the Control Plane CIoT EPS Optimisation, or, the User Plane CIoT EPS Optimisation).
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495b59b986f98d41912141cabbec196e
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23.401
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4.8 Compatibility Issues
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495b59b986f98d41912141cabbec196e
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23.401
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4.8.1 Network Configuration for Interaction with UTRAN/GERAN
|
GPRS idle mode mobility within GERAN or UTRAN and also between GERAN and UTRAN specifies a set of sequence number handling functions, e.g. the exchange of sequence numbers during Routing Area Update procedures. EPS idle mode mobility procedures don't specify any such sequence number mappings for IRAT mobility scenarios. To avoid interoperation issues a network that deploys E-UTRAN together with GERAN and/or UTRAN shall not configure usage of the GPRS feature "reordering required" for PDP contexts of PDP type IPv4, IPv6 or IPv4v6. Also the network shall not configure usage of lossless PDCP of UTRAN and the GERAN SGSN shall not configure usage of acknowledged mode LLC/NSAPI/SNDCP.
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495b59b986f98d41912141cabbec196e
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23.401
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4.9 Paging Policy Differentiation
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Paging policy differentiation is an optional feature that allows the MME, based on operator configuration, to apply different paging strategies as defined in clause 5.3.4.3 for different traffic or service types provided within the same PDN connection.
When it supports Paging Policy Differentiation feature, the Serving GW provides a Paging Policy Indication in the Downlink Data Notification. The Paging Policy Indication is based on information received with the downlink packet that triggers the Downlink Data Notification. For example, as defined in TS 23.228 [52], the P-CSCF may support Paging Policy Differentiation by marking packet(s) to be sent towards the UE that relate to specific IMS services (e.g. conversational voice as defined in IMS multimedia telephony service).
NOTE 1: This Paging Policy Differentiation feature can be used to determine the Paging Cause Indication for Voice Service, as described in clause 4.3.33.3.
The PDN GW shall not modify the received downlink IP packet e.g. the DSCP (IPv4) / TC (IPv6). Unconditionally, for each bearer and for each packet of PDN type IPv4, IPv6 or IPv4v6 that triggers a Downlink Data Notification, the SGW shall send the DSCP in TOS (IPv4) / TC (IPv6) information received in the IP payload of the GTP-U packet from the PDN GW in the Paging Policy Indication in the Downlink Data Notification.
It shall be possible for the operator to configure the MME in such a way that the Paging Policy Indicator only applies to certain HPLMNs and/or APNs and/or QCIs.
NOTE 2: Network configuration needs to ensure that the information used as a trigger for Paging Policy Indication is not changed within the EPS.
NOTE 3: Network configuration needs to ensure that the specific DSCP in TOS (IPv4) / TC (IPv6) value, used as a trigger for Paging Policy Indication, is managed correctly in order to avoid the accidental use of certain paging policies.
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495b59b986f98d41912141cabbec196e
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23.401
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4.10 Introduction of CIoT EPS Optimisations
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CIoT EPS Optimisations provide improved support of small data transfer. One optimisation is based on User Plane transport of user data and is referred to as User Plane CIoT EPS Optimisation. Another optimisation, known as Control Plane CIoT EPS Optimisation, transports user data or SMS messages via MME by encapsulating them in NAS, reducing the total number of control plane messages when handling a short data transaction. For EPC Mobile Originated Location Request (EPC-MO-LR) and EPC Mobile Terminated Location Request (EPC-MT-LR) when the UE and network support Control Plane CIoT EPS Optimisation, Control Plane Service Request is used. These optimisations can be used separately e.g. if the UE or the network supports one of them, or in parallel if the UE and the network supports both. If both the Control Plane and User Plane CIoT EPS Optimisations are supported for a UE, the PDN connections that only use the Control Plane CIoT EPS Optimisation, i.e. the MME has included Control Plane Only Indicator in the ESM request, will only be handled via the Control Plane CIoT EPS Optimisation. All other PDN connections are handled using Control Plane or User Plane CIoT EPS Optimisations. In addition, the Control Plane CIoT Optimisation can be used to support PDN connections to an SCEF, while regular S1-U data transfer is used independently to support PDN connections to P-GW. The MME shall consistently include Control Plane Only Indicator either in all SGi PDN connections of a UE or in none of them. All the SGi PDN connections of a UE shall either use S11-U or S1-U at any point in time.
The CIoT data could include e.g. status information, measurement data from Machine-to-Machine applications.
Several types of MME are envisaged, e.g.
- an MME that supports either User Plane or Control Plane CIoT EPS Optimisation;
- an MME that supports both User Plane and Control Plane CIoT EPS Optimisations;
- an MME that does not support any CIoT EPS Optimisations.
The E-UTRAN shall support the routeing of UEs to an MME that can process the request from the UE.
The CIoT EPS Optimisations are negotiated as described in clause 4.3.5.10 "Preferred and Supported Network Behaviour".
CIoT EPS Optimisations may be supported also by UEs that are not limited to low complexity and low throughput applications for Machine Type Communications.
If Control Plane CIoT EPS Optimisation applies, separation of S11-U from S1-U may be required, and if required, the MME and the Serving GW shall handle the IP address and TEID for the S1-U and the address and TEID for the S11-U separately.
NOTE: Homogeneous support of separation of S11-U from S1-U in the MMEs and Serving GWs is assumed.
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495b59b986f98d41912141cabbec196e
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23.401
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4.11 User Plane CIoT EPS Optimisation
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The User Plane CIoT EPS Optimisation functionality enables support for transfer of user plane data without the need for using the Service Request procedure to establish Access Stratum (AS) context in the serving eNodeB and UE.
If the following preconditions are met:
- UE and MME support User Plane CIOT EPS Optimisation as defined in clause 4.3.5.10,
- MME indicates "UE User Plane CIoT Support Indicator" IE to "supported" as defined in TS 36.413 [36],
- and the UE performs an initial connection establishment that establishes the AS bearers and the AS security context in the network and UE,
then the RRC connection can be suspended by means of a Connection Suspend Procedure (see clause 5.3.4A).
Based on trigger from the NAS layer when UE is in ECM-IDLE including if it attempts to send data using Control Plane CIoT EPS Optimisation as defined in clause 5.3.4B, the UE shall attempt the Connection Resume procedure, see clause 5.3.5A and TS 24.301 [46]. If the Connection Resume procedure fails, the UE initiates the pending NAS procedure, see TS 24.301 [46]. To maintain support for User Plane CIoT EPS Optimisation at UE mobility between cells configured on different eNodeBs, the AS Context should be transferred between the eNodeBs, see TS 36.300 [5] and TS 36.423 [76].
Early Data Transfer (EDT) for User Plane CIOT EPS Optimisation is defined in TS 36.300 [5] and clause 5.3.5A.
If the UE is in ECM-IDLE state with AS information stored, and the UE attempts to send data using Control Plane CIoT EPS Optimisation as defined in clause 5.3.4B, the UE shall attempt the Connection Resume procedure without Early Data Transfer.
By using the Connection Suspend procedure, see clause 5.3.5A and TS 36.300 [5]:
- the UE at transition into ECM-IDLE stores the AS information;
- the eNodeB stores the AS information, the S1AP association and the bearer context for that UE;
- MME stores the S1AP association and the bearer context for that UE and enters ECM-IDLE.
In the context of this functionality, the UE and the eNodeB store the relevant AS information at transition into ECM-IDLE.
By using the Connection Resume procedure, see clause 5.3.5A and TS 36.300 [5]:
- the UE resumes the connection with the network using the AS information stored during the Connection Suspend procedure;
- the, potentially new, eNodeB notifies the MME that the connection with the UE has been securely resumed and the MME enters ECM-CONNECTED.
If a MME has a S1AP association stored for a UE and the MME receives for that UE a EMM procedure over another UE-associated logical S1-connection or at Tracking Area Update procedure with MME change, or SGSN Context Request, when the UE has re-attached, or when the UE has been Detached, the MME and the previously involved eNodeB shall delete that stored S1AP association using the S1 Release procedure, see clause 5.3.5 and TS 36.413 [36].
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495b59b986f98d41912141cabbec196e
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23.401
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4.12 Supporting up to 15 EPS bearers per UE
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A UE attached to WB-E-UTRAN access, including for dual connectivity using E-UTRAN access as described in clause 4.3.2a, may support 8 or 15 EPS bearers. To enable support of establishing 15 EPS bearers, it requires the EPC connected to the E-UTRAN access to support 15 EPS bearers for such UEs.
If the UE supports 15 EPS bearers, then the UE shall indicate this to the MME in NAS signalling as defined in TS 24.301 [46].
The network shall support E-UTRAN idle mode mobility and handover procedures in such PLMNs, where only part of the network nodes have been upgraded to support 15 EPS bearers. In the case of mobility procedures involving target nodes not supporting 15 EPS bearers, additional bearers not supported by the non-upgraded nodes should be thus released.
The network shall homogeneously support 15 EPS bearers per UE, at least per MME pool area/SGW serving area, in order to avoid EPS bearer deactivations and attempts from services to re-activate the deactivated EPS bearers caused by UE mobility within that area, by defining the tracking areas accordingly (see clause 4.3.5.3).
The MME shall provide the UE with a TAI List such that it triggers the UE to perform the TAU procedure, as defined in clause 5.3.3.0, when the UE enters and exits the area with support for 15 EPS bearers per UE. The TAU procedure execution enables the nodes in the supporting area to identify a supporting UE when it enters the area. When exiting the area, also enables the nodes to remove bearer resources for the UE towards nodes without support for 15 EPS bearers per UE.
NOTE 1: In order for the above TAI List handling to be fully successful, the network requires the PGWs the UE is connected to from these MME pool area/SGW serving area to be upgraded to support 15 EPS bearers.
For a UE supporting 15 EPS bearers, mobility to UTRAN or GERAN may also lead to selective release of EPS bearers, due to the lack of support of 15 PDP contexts in the GPRS core network and Radio Access networks.
NOTE 2: EPS bearers need to be released either because the UE has more than 8 active EPS bearers, or because they are identified by EPS Bearer Identities not supported.
In order to minimize the impact from release of bearers not supported by the target nodes during mobility, the MME should be able to allocate the EPS bearer IDs in such way that the bearers with higher operator preference will be preserved in the case of mobility involving legacy target nodes. This prioritised bearer allocation should be based on, at least, the Allocation Retention Priority of the EPS bearers and may take other bearer parameters (e.g. QCI, APN) into consideration.
All PDN GWs in a PLMN shall support 15 EPS bearers. MME may be configured to take into account additional PDN GW information such as whether the HPLMN supports 15 EPS bearers when selecting PDN GW (e.g. in the case of roaming users Home Routed PDN GW selection) for UEs supporting 15 EPS bearers.
For inter-PLMN handover, support of 15 EPS bearers is based on MME configuration according to operator policy (e.g. bilateral agreements between operators).
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495b59b986f98d41912141cabbec196e
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23.401
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4.13 Introduction of satellite support for Cellular IoT
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495b59b986f98d41912141cabbec196e
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23.401
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4.13.1 General
|
This clause describes the functionality for supporting Cellular IoT over satellite access. Support for WB-E-UTRAN, NB-IoT and LTE-M satellite access is specified in TS 36.300 [5]. The description for satellite access in this specification is applicable to both transparent satellite payload and regenerative satellite payload, unless otherwise stated.
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495b59b986f98d41912141cabbec196e
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23.401
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4.13.2 Support of RAT types defined in EPC for satellite access
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In the case of satellite access with WB-E-UTRAN, NB-IoT or LTE-M, the RAT Types values "WB-E-UTRAN(LEO)", "WB-E-UTRAN(MEO)", " WB-E-UTRAN(GEO)", " WB-E-UTRAN(OTHERSAT)", "NB-IoT(LEO)", "NB-IoT(MEO)", "NB-IoT(GEO)", "NB-IoT(OTHERSAT)", "LTE-M(LEO)", "LTE-M(MEO)", "LTE-M(GEO)" and "LTE-M(OTHERSAT)" are used in EPC to distinguish the different WB-E-UTRAN, NB-IoT and LTE-M satellite access types.
In order to enable efficient enforcement of mobility restrictions:
- Cells of each NB-IoT satellite RAT type (NB-IoT(LEO), NB-IoT(MEO), NB-IoT(GEO) or NB-IoT(OTHERSAT)) need to be deployed in TAs that are:
- different from TAs for other NB-IoT satellite RAT types; and
- different from TAs supporting terrestrial NB-IoT RAT type; and
- different from TAs for WB-E-UTRAN satellite RAT types; and
- different from TAs for WB-E-UTRAN terrestrial RAT types.
The MME may initiate Detach of the UE when an S1 UE Context Release Request is received with Cause indicating the release is requested due to a UE using satellite access moved out of PLMN serving area, as specified in TS 36.413 [36].
NOTE: The transparent satellite payload and regenerative satellite payload share the same set of RAT type values specified in this clause. If there is a need for differentiating between the payload types, the determination of what kind of payload is based on operator configuration.
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495b59b986f98d41912141cabbec196e
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23.401
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4.13.3 Network/Access selection for satellite access
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Network/Access selection principles specified in clause 4.3.2.2 also apply for satellite access for Cellular IoT.
In the case of satellite access for Cellular IoT, a UE with location capability (i.e. GNSS capability) should use its awareness of its location to select a PLMN that is allowed to operate the UE location as specified in TS 23.122 [10].
In order to ensure that regulatory requirements are met, the network may be configured to enforce this UE choice by verifying the UE location as specified in clause 4.13.4.
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495b59b986f98d41912141cabbec196e
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23.401
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4.13.4 Verification of UE location
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In order to ensure that the regulatory requirements are met, the network may be configured to enforce that the selected PLMN is allowed to operate in the current UE location by verifying the UE location during EMM and ESM procedures. In this case, when the MME receives the User Location Information (ULI) for a UE using satellite access for Cellular IoT, the MME may decide to verify the UE location.
In the case of satellite NB-IoT, the UE and the MME may support reporting of Coarse Location Information (with the format defined in TS 24.301 [46]) from the UE to MME in the NAS Security Mode Command procedure. As described for the Attach procedure (clause 5.3.2.1), TAU procedures (clauses 5.3.3.1 and 5.3.3.2) and Service Request procedure (clause 5.3.4.1), in the case of NB-IoT, the MME may, if supported by the UE and if the MME has obtained user consent based on proprietary mechanisms depending on local regulations, request the UE, in a NAS Security Mode Command message, to report its Coarse Location Information. If requested, the UE provides its Coarse Location Information in the NAS Security Mode Complete message. The MME provides the received Coarse Location Information to the E-SMLC as described in clause 9.1.17 of TS 23.271 [57]. The UE indicates its support for providing Coarse Location Information in the UE Network Capability IE, as described in clause 5.11.3.
NOTE 1: Provisioning of coarse UE location information in the SMC procedure as described above is intended to enable basic support for UE location verification. If additional accuracy or other positioning features are needed it is assumed that the UE and the network support LPP and the procedures defined in TS 23.271 [57].
NOTE 2: In order to ensure that the regulatory requirements are met, based on operator configuration, the MME can prevent the UE from accessing certain services (e.g. services related with NAS messages initiated by UE or network except services related with UE location procedures or NAS procedures required for location verification) while location determination is ongoing (i.e. UE location procedure is on going). This can be done by, for example, the MME using functionality such as NAS level congestion control described in clause 4.3.7.4.2.
If the MME determines based on the Selected PLMN ID and the identity of the cell serving, or based on the reply from the E-SMLC in case of NB-IoT and Coarse Location Information was provided to E-SMLC, that this UE that it is not allowed to operate at the present UE location the MME should reject any NAS request with a suitable Cause value. If the UE is already registered to the network when the MME determines that the UE is not allowed to operate at the present UE location, the MME may initiate an explicit detach of the UE. The MME should not reject the request or detach the UE unless it has sufficiently accurate UE location information to determine that the UE is located in a geographical area where the PLMN is not allowed to operate.
NOTE 2: The area where the PLMN is allowed to operate can be determined based on local regulations and licensing conditions.
If the MME is not able to determine the UE location with sufficient accuracy to make a decision or if the received ULI is not sufficiently reliable, the MME proceeds with the Mobility Management or Session Management procedure and may initiate UE location procedure after the Mobility Management or Session Management procedure is complete, as specified in clause 9.1.17 of TS 23.271 [57], to determine the UE location. The MME shall be prepared to detach the UE if the information received from the E SMLC indicates that the UE is registered to a PLMN that is not allowed to operate in the UE location. In case of a NAS procedure, the MME should either reject any NAS request targeted towards a PLMN that is not allowed to operate in the known UE location and indicate a suitable cause value, or accept the NAS procedure and initiate the Detach procedure once the UE location is known. In the Detach Request message to the UE, the MME shall include a suitable cause value.
NOTE 3: In the case of NB-IoT, whether to trigger interaction with E-SMLC during a NAS procedure based on location information received by MME, or trigger interaction with E-SMLC after the NAS procedure, is based on operator configuration.
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495b59b986f98d41912141cabbec196e
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23.401
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4.13.5 Use of extended NAS timers
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Whenever the UE is accessing the network using a satellite RAT, the MME and the UE shall set the NAS timers long enough according to this satellite RAT, as specified in TS 24.301 [46].
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495b59b986f98d41912141cabbec196e
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23.401
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4.13.6 Support of Tracking Area Update
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A moving cell for NB-IoT, LTE-M or WB-E-UTRAN satellite access may indicate support for one or more Tracking Areas Codes (TACs) for each PLMN (see clause 4.13.7). A UE that is registered with a PLMN may access a cell and does not need to perform a Tracking Area Update procedure for mobility reasons as long as at least one supported TAC for the RPLMN or equivalent to the RPLMN indicated in the cell is part of the UE's Tracking Area List. A UE shall perform a Tracking Area Update procedure when entering a cell where none of the supported TACs for the RPLMN or equivalent to the RPLMN indicated in the cell are part of the UE's Tracking Area List.
When indicating a last visited TAI in an Attach Request or a TAU Request, a UE shall indicate the last selected TAI supported in the last visited cell for that RPLMN or PLMN equivalent to the RPLMN, as specified in TS 24.301 [46].
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495b59b986f98d41912141cabbec196e
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23.401
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4.13.7 Tracking Area handling
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For Cellular IoT over satellite access with moving cells, in order to ensure that each TA is Earth-stationary, even if the radio cells are moving across the Earth's surface, the E-UTRAN may change the TAC values that are broadcast in a cell's system information as the cell moves, as described in TS 36.331 [37].
E-UTRAN may broadcast in a cell a single TAC per PLMN and change this TAC value as the cell moves. Alternatively, the E-UTRAN may broadcast in a cell more than one TAC for a PLMN and add or remove TAC values as the cell moves. The eNodeB provides either the single broadcast TAI or all broadcast TAIs corresponding to the Selected PLMN as described in TS 36.413 [36] to the MME as part of the ULI, whenever the TAI is included in the S1-AP message as described in TS 36.413 [36]. The eNodeB indicates, if known, also the TAI where the UE is geographically located.
NOTE: The MME can take into account the TAI where the UE is geographically located, and the last visited TAI to generate a suitable Tracking Area List for the UE.
The MME considers the UE to be in a forbidden area if the only TAI or all TAIs received from the eNodeB are forbidden based on subscription data. The UE considers it is in a cell within a forbidden area if the only TAI or all TAIs broadcast in this cell for the selected PLMN are forbidden. In a PLMN, the UE considers it is not in a cell within a forbidden area if at least one broadcast TAI for this PLMN in this cell is not forbidden.
If the MME receives multiple TAIs from E-UTRAN and determines that some, but not all, TAIs in the received list of TAIs are forbidden by subscription or by operator policy, the MME shall send the forbidden TAI(s) to UE as described in clause 5.3.2, 5.3.3 and 5.3.4. The UE stores the TAI(s) in the appropriate Forbidden Area list and removes the TAI(s) from the TAI list.
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495b59b986f98d41912141cabbec196e
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23.401
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4.13.8 Enhanced support of discontinuous network coverage for satellite access
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495b59b986f98d41912141cabbec196e
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23.401
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4.13.8.1 General
|
Basic support for discontinuous coverage is specified in clause 4.3.5.2 and clause 4.3.17.7. The present clause 4.13.8 provides additional optional enhancements to discontinuous coverage:
- Mobility management and power saving optimization, see clause 4.13.8.2; and
- Coverage availability information provisioning to the UE, see clause 4.13.8.3; and
- Coverage availability information provisioning to the MME, see clause 4.13.8.4; and
- Paging, see clause 4.13.8.5; and
- Overload control, see clause 4.13.8.6.
In the following, "Enhanced Discontinuous Coverage" functionality includes the following enhancements as listed above: Mobility management and power saving optimization described in clause 4.13.8.2, and Overload control described in clause 4.13.8.6.
During Attach or TAU procedures, a UE supporting Enhanced Discontinuous Coverage provides "Enhanced Discontinuous Coverage Support" indication as part of UE Core Network Capability in the Attach Request or TAU Request message to the MME. The MME receiving an Attach Request or a TAU Request message from the UE including "Enhanced Discontinuous Coverage Support" indicates whether Enhanced Discontinuous Coverage is supported by providing the "Enhanced Discontinuous Coverage Support" indication to the UE in the Attach Accept or TAU Accept message.
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495b59b986f98d41912141cabbec196e
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23.401
|
4.13.8.2 Mobility Management and UE Power Saving Optimization
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For satellite access that provides discontinuous network coverage, and in case both the UE and the network support Enhanced Discontinuous Coverage, then the Mobility Management and UE Power Saving Optimization functionality may be used.
If both the UE and the network indicate support for "Enhanced Discontinuous Coverage Support" and if the UE determines it will lose coverage and will become unavailable, and decides to remain in no service during that time, then:
- The UE may be able to determine, including considering current and expected future locations of the UE, a Start of Unavailability Period and/or Unavailability Period Duration for when it expects to be out of coverage.
NOTE 1: A UE, based on implementation, can combine successive periods of no satellite coverage into a single continuous period that is notified to the network if the UE does not require network access during this period.
NOTE 2: UE informing the network of coverage gaps would increase signalling and UE power consumption if coverage gaps are more frequent than UE's communication period.
- The UE triggers a TAU procedure and includes an indication of upcoming loss of coverage in the TAU Request message to the MME. If the UE is able to determine a Start of Unavailability Period and/or Unavailability Period Duration it also includes them in the TAU Request message.
- The UE should trigger the TAU procedure early enough such that the procedure, under normal conditions, is able to complete before the start of the unavailability period.
- The UE and the MME re-negotiate unavailability at every TAU procedure, if it is required. If Start of Unavailability Period and/or Unavailability Period Duration is not included in a TAU Request message any pending loss of coverage configuration stored in the UE context at MME is discarded.
- If the UE determines an upcoming loss of coverage to the network no longer applies or determines a new Start of Unavailability Period or Unavailability Period Duration related to the upcoming loss of coverage, the UE sends a new TAU Request to the MME to update the Start of Unavailabililty Period and/or Unavailability Period Duration.
Upon receiving a TAU Request message from the UE including an indication of upcoming loss of coverage or Attach request message:
- If the UE did not include a Start of Unavailability Period in the TAU Request message, the MME considers implicitly the Start of Unavailability Period to be the time at which it has received the TAU Request message from the UE. If the UE included a Start of Unavailability Period, the Start of Unavailability Period indicates the time at which the UE determines it expects to lose coverage, i.e. time until which the UE determines it is available.
- The MME may determine, if not provided by the UE, or update the Unavailability Period Duration and/or the Start of Unavailability Period.
If the MME knows an Unavailability Period Duration and/or the Start of Unavailability Period (e.g. based on information available to the MME as described in clause 4.13.8.4) for the UE, and the UE not include an Unavailability Period Duration and/or the Start of Unavailability Period or included an Unavailability Period Duration and/or the Start of Unavailability Period different to the Unavailability Period Duration and/or the Start of Unavailability Period known to the MME, the MME should include the Unavailability Period Duration and/or the Start of Unavailability Period known to the MME in the TAU Accept or Attach Accept message and use those values in subsequent steps of this procedure. How the UE treats the MME provided Unavailability Period Duration and/or the Start of Unavailability Period is up to UE implementation e.g. to help to determine when to return to coverage after a discontinuous coverage period, whether to listen to paging in eDRX, not to initiate any NAS signalling (including Service Request for MO data) within the discontinuous coverage period in case of any UL signalling/data request or the UE may deactivate its Access Stratum functions for satellite access in order to optimise power consumption until coverage returns, etc.
The MME indicates to the UE in the Attach Accept or TAU Accept whether the UE is not required to perform a TAU procedure when the unavailability period has ended.
- The MME stores the information that the UE is unavailable at the Start of Unavailability Period in the UE context, and considers the UE is unreachable from then until the UE enters ECM_CONNECTED state.
NOTE 3: The UE does not include indication of upcoming loss of coverage, Unavailability Period Duration and the Start of Unavailability Period in Attach Request message.
If the UE requests power saving features the MME uses procedures defined in other clauses to provide the UE with timers (e.g. periodic TAU timer, extended idle mode DRX (see clause 5.13a), and PSM mode configuration (see clause 4.3.22)), and may also consider the Unavailability Period Duration (if available) and Start of Unavailability Period (if available).
Unless the MME indicated that the UE is not required to perform a TAU procedure when the unavailability period has ended, then once the event which makes the UE unavailable is completed in the UE, the UE triggers a TAU procedure. If the event which makes the UE unavailable is delayed to a future time or cancelled or unavailability period deviates from negotiated value in the UE, the UE triggers TAU procedure.
The MME should adjust the mobile reachable timer or Implicit Detach timer or both such that the MME does not implicitly detach the UE while the UE is out of coverage, see clause 4.3.5.2. Features described for High latency communication in clause 4.3.17.7 may be used to handle mobile terminated (MT) communication with UEs being unreachable due to satellite access with discontinuous coverage and the Unavailability Period Duration (if available) and Start of Unavailability Period (if available) may be used when determining the Downlink Buffering Duration time.
The UE may send Tracking Area Update request message to inform the network of its UE unavailability period even if Mobility Management back-off timer is running.
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495b59b986f98d41912141cabbec196e
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23.401
|
4.13.8.3 Coverage availability information provisioning to the UE
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A UE may use satellite coverage availability information for satellite access to support discontinuous coverage operations. Satellite coverage availability information can be provided to a UE by an external server via a PDN Connection or SMS. The protocol and format of satellite coverage availability information via PDU Connection or SMS is not defined in this release of the specification, but some examples on the information that constitutes the satellite coverage availability information is defined in Annex N.
NOTE: The satellite coverage availability information provisioned to the UE describes when and where satellite coverage with both service link and feeder link connectivity is expected or not expected to be available in an area.
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495b59b986f98d41912141cabbec196e
|
23.401
|
4.13.8.4 Coverage availability information provisioning to the MME
|
The MME may use satellite coverage availability information to support satellite access by UEs with discontinuous coverage operation. Satellite coverage availability information may be provisioned to the MME by O&M.
NOTE 1: In this release of the specification there is no support for provisioning of satellite coverage availability information to an MME from an AF.
NOTE 2: The satellite coverage availability information provisioned to the MME describes when and where satellite coverage with both service link and feeder link connectivity is expected or not expected to be available in an area.
The satellite coverage availability information is not UE specific and can be applied by the MME for any UE in the affected area.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.13.8.5 Paging
|
In the case of satellite access that provides discontinuous network coverage, the MME may utilize sub-area paging (e.g. first page in the last known ECGI or TA and retransmission in all registered TAs). The MME may utilize the location information as received at or before the S1 release due to the discontinuous coverage for paging optimisation.
The MME may e.g. receive UE location from eNodeB during the Attach or TAU procedure e.g. triggered for Mobility Management and Power Saving Optimization for discontinuous network coverage as described in clause 4.13.8.2, or the MME may request the Location Reporting Procedure when the UE is in ECM_CONNECTED state as described in clause 5.9.1.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.13.8.6 Overload control
|
The MME and UE may only use the procedure defined in this clause if both the UE and MME indicate "Enhanced Discontinuous Coverage Support", see clause 4.13.8.1.
In order to avoid a large number of UEs causing excessive signalling load on the network when leaving coverage or re-gaining coverage after being out of coverage, the MME may determine a Maximum Time Offset controlling when UEs are allowed to initiate NAS signalling with the network, as described in this clause.
In this case, the MME determines this Maximum Time Offset based on network configuration, high priority access and priority services. The MME sends this Maximum Time Offset to individual UEs during the Attach or TAU procedures.
If the UE receives this Maximum Time Offset from the network in an Attach or TAU Accept, the UE shall replace any previously received Maximum Time Offset on the same RAT type and PLMN with this one.
When the UE knows a later time at which coverage will be lost and when the UE does not send a TAU Request to the MME in advance (see clause 4.13.8.2), the UE determines a random value up to the minimum of the latest Maximum Time Offset for this PLMN and RAT type and the time until coverage will be lost. The UE shall send the TAU Request at the time when coverage will be lost less the random value to the MME indicating the loss of coverage.
Upon returning to coverage after being out of coverage due to discontinuous coverage, the UE sets the discontinuous coverage wait timer value to a random value up to and including the latest Maximum Time Offset for this PLMN and RAT type, and starts this timer. The UE shall not initiate any NAS signalling on that RAT Type and PLMN while the discontinuous coverage wait timer is running.
The UE shall stop the discontinuous coverage wait timer and initiate NAS signalling if the UE receives paging message, has pending emergency services or when UE enters a Tracking Area outside the current Tracking Area List.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.13.9 Support of Store and Forward Satellite operation
| |
495b59b986f98d41912141cabbec196e
|
23.401
|
4.13.9.1 General
|
The Store and Forward Satellite operation applies in E-UTRAN with satellite access and is suitable for delay-tolerant communication services (e.g. CIoT/MTC, SMS, etc.). If the satellite does not support Store and Forward Satellite operation and there is no feeder link connection to the ground network, then the satellite cannot provide any service to any UEs. When both the service link and feeder link are available, all services can be provided. To support Store and Forward Satellite operation, eNodeB and some network functionalities need to be deployed on the satellite.
Example deployments are described in Annex O.
Figure 4.13.9.1-1: Store and Forward Satellite operation
NOTE 1: In Figure 4.13.9.1-1, the NTN Gateway belongs to the satellite deployment and is not subject to 3GPP specifications.
In Store and Forward Satellite operation, the end-to-end exchange of signalling/data traffic is handled in a sequence of steps reflecting the intermittent availability of the service link when the satellite can exchange data with the UE and of the intermittent availability of the feeder link when the satellite can exchange data with the core network. This is depicted in Figure 4.13.9.1-1.
For example, a simple sequence of events for the transmission of data from the UE to a server on the ground may involve two steps: firstly, when service link is available (e.g. location L1 in Figure 4.13.9.1-1) the UE sends the data to the satellite. Subsequently (e.g. location L2 in Figure 4.13.9.1-1), the satellite carrying the payload connects to the ground network and delivers the UE data to the network.
Downlink data can be stored onto the same or a different satellite and provided to the UE later using the first step and the process is repeated.
When an on-board MME supports Store and Forward Satellite operation and is operating in S&F Mode, the on-board eNodeB broadcasts an indication of operating in S&F Mode as described in TS 36.300 [5], which the UE uses to determine the current operation mode of the satellite. If a satellite is operating in S&F Mode and if a UE is enabled for Store and Forward Satellite operation, then the UE indicates the S&F capability during Attach and Tracking Area Update.
NOTE 2: A satellite operating in S&F mode implies that the on-board eNodeB deployed on it is operating in S&F mode and is connected with an on-board MME that is also operating in S&F mode.
NOTE 3: Some deployments cannot support all system features, for example user plane establishment and user plane data transfer cannot be supported, when a satellite is operating in S&F Mode with the split MME deployment described in Annex O.
The MME may adapt periodic update timer, mobile reachable timer and Implicit Detach timer to the fact that the UE is served by an MME operating in S&F Mode.
For a UE which indicates support of Store and Forward Satellite operation and when an MME is operating in S&F Mode:
- If the MME cannot complete a NAS procedure with the information currently available on the satellite e.g. when the MME does not have UE security context or, if the MME needs to retrieve UE-specific authentication vectors or subscription information from the ground network, it shall reject the NAS procedure. In this case, the MME shall include a reject cause indicating the NAS rejection is due to Store and Forward Satellite operation.
- If the UE is rejected with a reject cause indicating it is due to S&F operation, the UE's EMM state shall remain unchanged.
- The MME may provide to the UE a S&F Wait Timer, a S&F Monitoring List or both when accepting or rejecting a NAS procedure.
NOTE 4: How the MME determines the S&F Wait Timer and S&F Monitoring List is up to MME implementation, e.g. based on feeder link (un)availability period, service link (un)availability period, UE power saving requirements, Communication Pattern parameters, UE location, UE mobility, etc.
- When the S&F Wait Timer expires, the UE may perform a NAS procedure, which can be a subsequent NAS procedure or a reattempt of a NAS procedure previously rejected with a S&F reject cause.
NOTE 5: When the S&F Wait Timer is running, the power consumption optimization behaviours, if any, are left for UE implementation e.g. whether to listen to paging or deactivate its Access Stratum functions.
The S&F Monitoring List includes satellite(s) which belong to the same PLMN and indicates the satellite(s) that the UE may (re)attempt NAS procedures or receive MT data from.
- The MME may indicate to the UE that it should delete any previously provided S&F Monitoring List for the current PLMN. When the S&F Monitoring List is deleted then the UE may use any satellite(s).
NOTE 6: The S&F Wait Timer or S&F Monitoring List doesn't affect the UE when accessing an eNodeB that does not broadcast an indication of operating in S&F Mode.
NOTE 7: How UE behaves when receiving the S&F Monitoring List is up to UE implementation. When a UE receives a S&F Monitoring List and the UE access a satellite that supports Store and Forward Satellite operation that is not on the S&F Monitoring List there is increased probability that it will not be able to complete the NAS procedure. The UE can continue to use the previously provided S&F Monitoring List, if the MME did not send one and the UE has previously been provided with one.
- The MME may indicate to the UE an Estimated S&F UL Delivery Time in a NAS accept messages (i.e. Attach Accept, TAU Accept or Service Accept messages).
NOTE 8: The Estimated S&F UL Delivery Time is an estimate of the time required to deliver the data or signalling sent by the UE to the ground. The Estimated S&F UL Delivery Time is associated with the satellite that provides it and how UE uses this information is left for UE implementation.
The MME may provide S&F Monitoring List to the UE as part of detach procedure.
If the UE did not indicate Store and Forward capability in NAS signalling, if the network determines to reject the UE, the network shall reject the UE request with a cause non-specific to S&F Mode.
The MME may trigger an Update Location procedure with the HSS along with the authentication procedure to fetch subscription information from the HSS. The MME may indicate the timestamp information to HSS during the Update Location procedure. This timestamp information shall be used by the HSS to ensure that newer location for that UE is not cancelled. If MME makes an Update Location Request before the completion of the authentication procedure, it shall include an indication that this Location Update is provisional, i.e. the HSS shall not consider the UE as registered until it receives the final Update Location Request (without indication that the Location Update is provisional). The timestamp information is the time when the on-board of satellite MME part has received the NAS procedure from the UE. The HSS compares the timestamp received in the Update Location Request with any stored timestamp of a previous Update Location Request and determines whether to accept or reject the request. If the received Update Location Request does not include a timestamp, the HSS assumes the present time as the timestamp of the received Update Location Request. The HSS shall reject the Update Location Request, if the timestamp associated with this request is older than the stored timestamp. If the HSS accepts the Update Location Request, the HSS shall store the timestamp associated with the latest Update Location Request. If the HSS does not support the timestamp, the MME shall reject a UE Attach request for S&F Mode.
NOTE 9: The timestamp information is used by the HSS to ensure that interactions with MMEs for a UE are handled in the correct order.
NOTE 10: The absence of timestamp in the Update Location Request can occur e.g. when the UE is connecting from a network that does not operate in S&F mode.
The EPS may expose whether a UE is served by an MME operating in S&F Mode and provide to the SCS/AS related timing information to guide the SCS/AS decision when to try to contact the UE. This is further described in clause 5.6.3.10 of TS 23.682 [74].
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.13.9.2 Transition between S&F mode and non S&F mode
|
If a UE is attached to a PLMN using satellite operating in S&F mode, the UE follows the existing AS and NAS procedures to access a satellite that is not operating in S&F mode (either TN or NTN eNodeB) and vice versa.
In order to ensure smooth idle mode transition from S&F mode to non S&F mode, if the old (S&F capable) MME in inter MME mobility has the knowledge that the UE context is not up to date (e.g. based on implementation) then the old (S&F capable) MME rejects the MM context transfer.
If a satellite has no feeder link connectivity, it can only operate in S&F Mode. When a satellite supporting S&F mode obtains a feeder link, then, the satellite may cease to operate in S&F Mode depending on operator policy and regulatory requirement.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.13.10 UE Coarse Location information for NB-IoT satellite access
|
As described in clause 4.13.4, in the case of NB-IoT, the MME may request the UE to report its Coarse Location Information for location verification purposes. In addition, as described in TS 36.300 [5] and TS 36.413 [36], the eNB may request, in a S1-AP Initial UE message, the MME to provide the Coarse Location Information to eNB. In that case, the MME provides, if available, the Coarse Location Information to the eNB as described in TS 36.413 [36].
|
495b59b986f98d41912141cabbec196e
|
23.401
|
4.13.11 S1 interface and connection management for regenerative satellite payload
|
The S1 Removal procedure defined in TS 36.413 [36] can be used to remove the interface between an eNodeB and an MME in a controlled manner, e.g. when the eNodeB is leaving the service area of an MME when using regenerative satellite payload.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
5 Functional description and information flows
| |
495b59b986f98d41912141cabbec196e
|
23.401
|
5.1 Control and user planes
| |
495b59b986f98d41912141cabbec196e
|
23.401
|
5.1.0 General
|
NOTE:
- Refer to TS 23.402 [2] for the corresponding protocol stack for PMIP based S5/S8.
- Refer to TS 23.203 [6] for the corresponding protocol stack for Policy Control and Charging (PCC) function related reference points.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
5.1.1 Control Plane
| |
495b59b986f98d41912141cabbec196e
|
23.401
|
5.1.1.1 General
|
The control plane consists of protocols for control and support of the user plane functions:
- controlling the E-UTRA network access connections, such as attaching to and detaching from E-UTRAN;
- controlling the attributes of an established network access connection, such as activation of an IP address;
- controlling the routing path of an established network connection in order to support user mobility; and
- controlling the assignment of network resources to meet changing user demands.
The following control planes are used in E-UTRAN mode.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
5.1.1.2 eNodeB - MME
|
Legend:
- S1 Application Protocol (S1-AP): Application Layer Protocol between the eNodeB and the MME.
- Stream Control Transmission Protocol (SCTP): This protocol guarantees delivery of signalling messages between MME and eNodeB (S1). SCTP is defined in RFC 4960 [35].
Figure 5.1.1.2-1: Control Plane for S1-MME Interface
NOTE: Refer to TS 36.300 [5] for the corresponding control plane for the HeNB Subsystem - MME.
|
495b59b986f98d41912141cabbec196e
|
23.401
|
5.1.1.3 UE - MME
|
Legend:
- NAS: The NAS protocol supports mobility management functionality and user plane bearer activation, modification and deactivation. It is also responsible of ciphering and integrity protection of NAS signalling.
- LTE-Uu: The radio protocol of E-UTRAN between the UE and the eNodeB is specified in TS 36.300 [5].
Figure 5.1.1.3-1: Control Plane UE - MME
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495b59b986f98d41912141cabbec196e
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23.401
|
5.1.1.4 SGSN - MME
|
Legend:
- GPRS Tunnelling Protocol for the control plane (GTP‑C): This protocol tunnels signalling messages between SGSN and MME (S3).
- User Datagram Protocol (UDP): This protocol transfers signalling messages. UDP is defined in RFC 768 [26].
Figure 5.1.1.4-1: Control Plane for S3 Interface
|
495b59b986f98d41912141cabbec196e
|
23.401
|
5.1.1.5 SGSN - S‑GW
|
Legend:
- GPRS Tunnelling Protocol for the control plane (GTP‑C): This protocol tunnels signalling messages between SGSN and S‑GW (S4).
- User Datagram Protocol (UDP): This protocol transfers signalling messages. UDP is defined in RFC 768 [26].
Figure 5.1.1.5-1: Control Plane for S4 interface
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495b59b986f98d41912141cabbec196e
|
23.401
|
5.1.1.6 S‑GW - P‑GW
|
Legend:
- GPRS Tunnelling Protocol for the control plane (GTP‑C): This protocol tunnels signalling messages between S‑GW and P‑GW (S5 or S8).
- User Datagram Protocol (UDP): This protocol transfers signalling messages between S‑GW and P‑GW. UDP is defined in RFC 768 [26].
Figure 5.1.1.6-1: Control Plane for S5 and S8 interfaces
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495b59b986f98d41912141cabbec196e
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23.401
|
5.1.1.7 MME - MME
|
Legend:
- GPRS Tunnelling Protocol for the control plane (GTP‑C): This protocol tunnels signalling messages between MMEs (S10).
- User Datagram Protocol (UDP): This protocol transfers signalling messages between MMEs. UDP is defined in RFC 768 [26].
Figure 5.1.1.7-1: Control Plane for S10 interface
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495b59b986f98d41912141cabbec196e
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23.401
|
5.1.1.8 MME - S‑GW
|
Legend:
- GPRS Tunnelling Protocol for the control plane (GTP‑C): This protocol tunnels signalling messages between MME and S‑GW (S11).
- User Datagram Protocol (UDP): This protocol transfers signalling messages. UDP is defined in RFC 768 [26].
Figure 5.1.1.8-1: Control Plane for S11 interface
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495b59b986f98d41912141cabbec196e
|
23.401
|
5.1.1.9 MME - HSS
|
Legend:
- Diameter: This protocol supports transferring of subscription and authentication data for authenticating/authorizing user access to the evolved system between MME and HSS (S6a). Diameter is defined in RFC 3588 [31].
- Stream Control Transmission Protocol (SCTP): This protocol transfers signalling messages. SCTP is defined in RFC 4960 [35].
Figure 5.1.1.9-1: Control Plane for S6a interface
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495b59b986f98d41912141cabbec196e
|
23.401
|
5.1.1.10 MME - EIR
|
Legend:
- Diameter: This protocol supports UE identity check procedure between MME and EIR (S13). Diameter is defined in RFC 3588 [31].
- Stream Control Transmission Protocol (SCTP): This protocol transfers signalling messages. SCTP is defined in RFC 4960 [35].
Figure 5.1.1.10-1: Control Plane for S13 interface
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495b59b986f98d41912141cabbec196e
|
23.401
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5.1.1.11 Void
|
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