Content for  TS 23.256  Word version:  19.0.0

The procedure for V2X Application Server discovery using broadcast MBS session as specified in clause 6.4.2 of TS 23.287 is used for A2X Application Server discovery using broadcast MBS session with the following difference:

• V2X is replaced by A2X, e.g. V2X message to A2X message, V2X Application Server to A2X Application Server, etc.

The procedure for A2X Application Server discovery using broadcast MBS session may be used by the UE only when it is configured with the information to receive A2X Application Server information via MBS as specified in clause 6.2.1.3.1.

In order to enable PC5 radio resource control in NG-RAN, per PC5 RAT A2X service authorization information and PC5 QoS parameters need to be made available in NG-RAN, this clause describes the corresponding procedures and aspects.

The Registration procedure for UE is performed as defined in TS 23.502 with the following additions:

• The UE includes the PC5 Capability for A2X (i.e. LTE PC5 only, NR PC5 only, both LTE and NR PC5) as part of the "5GMM capability" in the Registration Request message. The AMF stores this information for A2X operation. The PC5 Capability for A2X indicates whether the UE is capable of A2X communication over PC5 reference point and which specific PC5 RAT(s) it supports.
• The AMF obtains the A2X Subscription data as part of the user subscription data from UDM during UE Registration procedure using Nudm_SDM service as defined in clause 4.2.2.2.2 of TS 23.502.
• The AMF determines whether the UE is authorized to use A2X communication over PC5 reference point based on UE's PC5 Capability for A2X and the subscription data related to A2X service authorization information (i.e. "A2X services authorized" indication per PC5 RAT and UE-PC5-AMBR per PC5 RAT) received from UDM, and stores the A2X service authorization information as part of the UE context.
• The PCF provides the PC5 QoS parameters to AMF, and the AMF stores them in the UE context.
• If the UE is PC5 capable for A2X, and the UE is authorized to use A2X communication over PC5 reference point based on the subscription data, then the AMF shall include the following information in the NGAP message sent to NG-RAN:
  • a "A2X services authorized" indication per PC5 RAT, indicating the UE is authorized to use A2X communication over PC5 reference point.
  • UE-PC5-AMBR per PC5 RAT, used by NG-RAN for the resource management of UE's PC5 transmission for A2X services in network scheduled mode.
  • the PC5 QoS parameters used by the NG-RAN for the resource management of UE's PC5 transmission for A2X services in network scheduled mode.
• If the UE is authorized to use A2X communication over PC5 reference point, then the AMF should not initiate the release of the signalling connection after the completion of the Registration procedure. The release of the NAS signalling relies on the decision of NG-RAN, as specified in TS 23.502.

The Service Request procedure for UE in CM-IDLE state is performed as defined in TS 23.502 with the following additions:

• If the UE is PC5 capable for A2X, and the UE is authorized to use A2X communication over PC5 reference point, then the AMF shall include a "A2X services authorized" indication per PC5 RAT in the NGAP message.
• The AMF includes the UE-PC5-AMBR for A2X per PC5 RAT in the NGAP message to the NG-RAN as part of the UE context and NG-RAN may use in resource management of UE's PC5 transmission for A2X services in network scheduled mode.
• The AMF sends the PC5 QoS parameters for A2X to NG-RAN via N2 signalling. The PC5 QoS parameters may be stored in the UE context after the registration procedure. If the UE is authorized to use A2X communication over PC5 reference point but AMF does not have PC5 QoS parameters available, the AMF fetches the PC5 QoS parameters from the PCF.

The N2 based handover or the Inter-RAT to NG-RAN handover procedures for UE are performed as defined in TS 23.502 with the following additions:

• If the UE is PC5 capable for A2X, and the UE is authorized to use A2X communication over PC5 reference point, then the target AMF shall send the "A2X services authorized" indication per PC5 RAT, UE-PC5-AMBR per PC5 RAT and PC5 QoS parameters to the target NG-RAN as follows:
  • For the intra AMF handover, the "A2X services authorized" indication per PC5 RAT, UE-PC5-AMBR per PC5 RAT and PC5 QoS parameters are included in the NGAP Handover Request message.
  • For the inter AMF handover or Inter-RAT handover to NG-RAN, the "A2X services authorized" indication per PC5 RAT, UE-PC5-AMBR per PC5 RAT and PC5 QoS parameters are included in the NGAP Handover Request message sent to the target NG-RAN.

The Xn based handover procedures for UE are performed as defined in TS 23.502 with the following additions:

• If the "A2X services authorized" indication is included in the UE context (as described in TS 38.423), then the source NG-RAN shall include a "A2X services authorized" indication per PC5 RAT, UE-PC5-AMBR per PC5 RAT and PC5 QoS parameters in the XnAP Handover Request message to the target NG-RAN.
• If the UE is PC5 capable for A2X, and the UE is authorized to use A2X communication over PC5 reference point, then the AMF shall send the "A2X services authorized" indication per PC5 RAT, the UE-PC5-AMBR per PC5 RAT and PC5 QoS parameters to the target NG-RAN in the Path Switch Request Acknowledge message.

The procedure of Subscriber Data Update Notification to AMF is performed as defined in TS 23.502 with the following additions:

• The Nudm_SDM_Notification service operation may contain the "A2X services authorized" indication per PC5 RAT and/or the UE-PC5-AMBR per PC5 RAT.
• The AMF updates the UE Context with the above new A2X subscription data.
• When the AMF updates UE context stored at NG-RAN, the UE context contains the A2X subscription data.

The UE Policy Association Establishment procedure and UE Policy Association Modification procedure, as defined in TS 23.502, is used to provide to the AMF PC5 QoS parameters used by NG-RAN. When receiving Npcf_UEPolicyControl_Create Request from the AMF which includes the PC5 capability for A2X or when receiving the updated subscription data from UDR, the PCF generates the PC5 QoS parameters used by NG-RAN corresponding to a UE. The (V-)PCF provides the information to the AMF as follows:

• In the roaming case, the H-PCF includes the PC5 QoS parameters used by NG-RAN in the Npcf_UEPolicyControl_Create Response message or Npcf_UEPolicyControl UpdateNotify Request message sent to V-PCF in an N2 PC5 policy container, and V-PCF relays this N2 PC5 policy container as the N2 container in the Namf_Communication_N1N2MessageTransfer message sent to AMF.
• In the non-roaming case, the PCF includes the PC5 QoS parameters used by NG-RAN in an N2 container in Namf_Communication_N1N2MessageTransfer message sent to AMF.

When the AMF determines that the N2 PC5 policy container comes from (V-)PCF, the AMF stores such information as part of the UE context. In the UE Configuration Update procedure triggered by UE Policy Association Establishment or UE Policy Association Modification:

• The AMF forwards the PC5 QoS parameters in the NGAP message to the NG-RAN if a N2 PC5 policy container is received in the Namf_Communication_N1N2MessageTransfer message.
• The AMF forwards the PC5 QoS parameters in the NAS message to UE by using the UE Configuration Update procedure for transparent UE Policy delivery procedure defined in clause 4.2.4.3 of TS 23.502 if a UE Policy Container is received in the Namf_Communication_N1N2MessageTransfer message.