7.2.8 Service request procedure

23.2473GPPArchitectural enhancements for 5G multicast-broadcast servicesRelease 18TS

If the multicast MBS session is in Inactive state, the UE can go to CM-IDLE state or the user plane of the associated PDU Session may be deactivated even when the UE is in CM-CONNECTED state. When user plane of the associated PDU session is activated again, the SMF sends the MBS session information to NG-RAN during Service Request procedure as specified in TS 23.502 [6]. The MBS session information indicates that this MBS session is in Inactive state; and:

– For the MBS supporting NG-RAN node, the NG-RAN establish the shared tunnel with the MB-UPF as usual. However, as the MBS session is in Inactive state, the NG-RAN node will not allocate related radio resource.

– For the non-MBS supporting NG-RAN node, the unicast QoS flow associated with the MBS session are not established.

If the multicast MBS session is in Active state, the UE can go to CM-IDLE state due to AN release as specified in TS 23.502 [6]. When the UE communicates with the network again, the SMF provides the MBS session information indicating that the UE joined the MBS session to the NG-RAN within N2 SM container for the associated PDU Session.

NOTE: Network triggered Service Request, if triggered for other reason, can also be used by the SMF to provide that MBS session information to NG-RAN.