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Content for  TS 23.256  Word version:  19.0.0

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6.3 Functional description and information flows  6.3.1 Control and user plane stacks for NR PC5 reference point supporting A2X services  6.3.1.1 User plane for PC5 reference point supporting A2X services  6.3.1.2 Control plane for NR PC5 reference point supporting A2X services  6.3.2 Procedures for A2X service authorization and provisioning to UE  6.3.2.1 General  6.3.2.2 PCF based A2X Service Authorization and Provisioning to UE  6.3.2.3 Procedure for UE triggered A2X Policy provisioning  6.3.2.4 AF-based service parameter provisioning for A2X communications over control plane  6.3.3 Procedures for A2X communication over PC5 reference point  6.3.3.1 Broadcast mode A2X communication over NR PC5 reference point  6.3.3.2 Unicast mode A2X communication over PC5 reference point 
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6.3  Functional description and information flows  p. 93

6.3.1  Control and user plane stacks for NR PC5 reference point supporting A2X services  p. 93

6.3.1.1  User plane for PC5 reference point supporting A2X services  p. 93

Figure 6.3.1.1-1 depicts a user plane for NR PC5 reference point, i.e. PC5 User Plane Protocol stack.
Reproduction of 3GPP TS 23.256, Fig. 6.3.1.1-1: User Plane for NR PC5 reference point
Figure 6.3.1.1-1: User Plane for NR PC5 reference point
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Legend:
  • PC5-U: The SDAP/PDCP/RLC/MAC/PHY functionality is specified in TS 38.300.
  • For PDCP SDU type "Non-IP", a "Non-IP Type" header included in the SDU by upper layer to indicate the type of non-IP messages carried will be specified in stage 3 specification.
IP and Non-IP PDCP SDU types are supported for the A2X communication over PC5 reference point.
For IP PDCP SDU type, only IPv6 is supported. The IP address allocation and configuration are as defined in clause 5.6.1.1 of TS 23.287.
The Non-IP PDCP SDU contains a Non-IP Type header, which indicates the A2X message family used by the application layer.
The packets from A2X application layer are handled by the A2X layer before transmitting them to the AS layer, e.g. A2X layer maps the IP/Non IP packets to PC5 QoS Flow and marks the corresponding PFI.
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6.3.1.2  Control plane for NR PC5 reference point supporting A2X services  p. 94

The protocol stack of clause 6.1.2 of TS 23.287 applies.

6.3.2  Procedures for A2X service authorization and provisioning to UE  p. 94

6.3.2.1  General  p. 94

The procedures for service authorization and provisioning to UE may be initiated by the PCF (as described in clause 6.3.2.2), by the UE (as described in clause 6.3.2.3), or by the AF (as described in clause 6.3.2.4).

6.3.2.2  PCF based A2X Service Authorization and Provisioning to UE  p. 94

For PCF based Service Authorization and Provisioning to UE, the Registration procedures as defined in clause 4.2.2.2 of TS 23.502, UE Policy Association Establishment procedure as defined in clause 4.16.11 of TS 23.502 and UE Policy Association Modification procedure as defined in clause 4.16.12 of TS 23.502 apply with the following additions:
  • If the UE indicates A2X capability in the Registration Request message and if the UE is authorized to use A2X service based on subscription data, the AMF selects the PCF which supports A2X Policy/Parameter provisioning and establishes a UE policy association with the PCF for A2X Policy/Parameter delivery. PCF discovery and selection mechanism defined in clause 6.3.7.1 of TS 23.501 applies and the AMF may include the A2X capability indication in the Nnrf_NFDiscovery_Request message as the optional input parameter. If provided, the NRF takes the information into account for discovering the PCF instance.
  • If the AMF receives the PC5 capability for A2X in the Registration Request message from UE, the AMF further reports the PC5 capability for A2X to the selected PCF. The PCF may determine the A2X Policy/Parameter for specific PC5 RAT based on the received UE's PC5 capability for A2X.
The PCF may update the A2X Policy/parameters to the UE in following conditions:
  • UE Mobility, e.g. UE moves from one PLMN to another PLMN. This is achieved by using the procedure of UE Policy Association Modification initiated by the AMF, as defined in clause 4.16.12.1 of TS 23.502.
  • When there is a subscription change in the list of PLMNs where the UE is authorized to perform A2X communication over PC5 reference point. This is achieved by using UE Policy Association Modification initiated by the PCF procedure as defined in clause 4.16.12.2 of TS 23.502.
  • When there is a change of service specific parameter as described in clause 4.15.6.7 of TS 23.502.
If the serving PLMN is removed from the list of PLMNs in the service authorization parameters, the service authorization is revoked in the UE.
When the UE is roaming, the change of subscription resulting in updates of the service authorization parameters are transferred to the UE by H-PCF via V-PCF.
The UE may perform UE triggered Policy Provisioning procedure to the PCF, after Registration procedure has been completed, as specified in clause 6.3.2.3 when the UE determines the A2X Policy/Parameter is invalid (e.g. Policy/Parameter is outdated, missing or invalid).
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6.3.2.3  Procedure for UE triggered A2X Policy provisioning  p. 95

The UE triggered Policy Provisioning procedure is initiated by the UE to request A2X Policy/Parameter from the PCF when UE determines the A2X Policy/Parameter is invalid in the following cases:
  • if the validity timer indicated in the A2X Policy/Parameter expires;
  • if there are no valid parameters, e.g. for the A2X service type a UE wants to use, for current area, or due to abnormal situation.
Reproduction of 3GPP TS 23.256, Fig. 6.3.2.3-1: UE triggered A2X Policy provisioning procedure
Figure 6.3.2.3-1: UE triggered A2X Policy provisioning procedure
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Step 1.
The UE sends UL NAS TRANSPORT message carrying the UE Policy Container (UE A2X Policy Provisioning Request to request A2X policies) to the AMF.
Step 2.
The AMF sends the Namf_Communication_N1MessageNotify request to the PCF including the UE Policy Container received from UE.
Step 3.
The PCF receives UE Policy Container which indicates UE Policy Provisioning Request to request A2X policies. If the A2X policies are authorized based on AMF input as specified in clause 6.3.5.2 the PCF performs the UE Policy delivery procedure defined in clause 4.2.4.3 of TS 23.502.
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6.3.2.4  AF-based service parameter provisioning for A2X communications over control plane  p. 96

The A2X Application Server can provision the 5GC with A2X service parameters via NEF using the procedure defined in clause 4.15.6.7 of TS 23.502 with the following considerations:
  • The AF in TS 23.502 is considered as A2X Application Server in this specification.
  • Service Description indicates A2X service domain information.
  • Service Parameters include policy/provisioning parameters for A2X communications over PC5 and/or Uu.
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6.3.3  Procedures for A2X communication over PC5 reference point  p. 96

6.3.3.1  Broadcast mode A2X communication over NR PC5 reference point  p. 96

A2X leverages what is defined for V2X in clause 6.3.1 of TS 23.287 with the following differences:
  • V2X is replaced by A2X.
  • The applicable configuration is described in clause 6.2.1.2.
  • PC5 QoS parameters are described in clause 6.2.4.
  • QoS handling for NR based PC5 reference point is described in clause 6.2.4.1.
  • Identifiers for A2X communication over PC5 reference points are described in clause 6.2.6.1.
  • Pedestrian UE's and corresponding pedestrian UE power saving as described in clause 5.9 is not supported.
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6.3.3.2  Unicast mode A2X communication over PC5 reference point  p. 96

A2X leverages what is defined for V2X in clause 6.3.3 of TS 23.287 with the following differences:
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