Content for  TS 38.401  Word version:  18.3.0

Figure 8.15.1.1-1 illustrates an exemplified interaction of NGAP, E1AP, F1AP and RRC protocol functions at Broadcast MBS Session Setup.

On NG-U, in case of location dependent broadcast MBS Sessions, multiple shared NG-U transport tunnels may need to be setup, one per Area Session ID served by the gNB. In case of shared NG-U termination,

• the gNB-CU-UP may provide the gNB-CU-CP at E1 setup or configuration update about established shared NG-U terminations, indicated by one or several MBS Session IDs.
• at establishment of the BC bearer context in the gNB-CU-UP, the gNB-CU-CP may request the gNB-CU-UP to either apply the available MRB configuration of the shared NG-U termination, or to apply the MRB configuration requested by the gNB-CU-CP. The gNB-CU-UP provides the MRB configuration to the gNB-CU-CP if the MRB configuration requested by the gNB-CU-CP and the available MRB configuration of the shared NG-U termination are different.

Figure 8.15.1.1a-1 illustrates an exemplified interaction of NGAP, E1AP, F1AP and RRC protocol functions at Broadcast MBS Session Setup with the support of resource efficiency for MOCN.

Afterwards, if the gNB-CU-CP decides (e.g., in case the 5GC1 triggers Broadcast Session Release) to establish shared NG-U resources with the 5GC2 with which the shared NG-U was not established:

• in case of multicast transport, the gNB-CU-CP triggers BC Bearer Context Modification Request towards the gNB-CU-UP providing the stored multicast address received from the 5GC2. Then the gNB-CU-UP joins the NG-U multicast group of 5GC2 accordingly;
• in case of unicast transport, the gNB-CU-CP triggers Broadcast Session Transport Request towards the core network providing the unicast transport address received from the gNB-CU-UP.

Figure 8.15.1.1b-1 illustrates an exemplified interaction of NGAP, E1AP, F1AP and RRC protocol functions at Broadcast MBS Session Setup with the support of resource efficiency for RAN sharing with multiple cell-ID broadcast. The gNB-DU1/2 entity shown in Figure 8.15.1.1b-1 is a simplified representation of the gNB-DU1 of PLMN 1, the gNB DU2 of PLMN 2 and respective radio resources of the shared cell.

Afterwards, if the gNB-DU1/2 decides (e.g., upon receiving the Broadcast Context Release Command from gNB-CU-CP1 in case the 5GC1 triggers Broadcast Session Release) to establish the shared F1-U tunnel for PLMN2 which was not established:

• the gNB-DU2 triggers Broadcast Transport Resource Request towards the gNB-CU-CP2 and providing the F1-U TNL at DU;
• and then, the gNB-CU-CP2 triggers the BC Bearer Context Modification Request towards the gNB-CU-UP2 providing the F1-U TNL at DU,
• in case of multicast transport, the gNB-CU-CP2 also provides the stored NG-U multicast transport address received from 5GC2. Then the gNB-CU-UP2 joins the NG-U multicast group of 5GC2 accordingly;
• in case of unicast transport, the gNB-CU-CP2 triggers the Broadcast Session Transport procedure towards the 5GC2 providing the stored NG-U unicast transport address received from gNB-CU-UP2.

Figure 8.15.1.2-1 illustrates an exemplified interaction of NGAP, E1AP, F1AP and RRC protocol functions for Multicast MBS Session Context Establishment with a UE joining an active multicast session as the first UE joining in its serving gNB.

On NG-U, in case of location dependent multicast MBS Sessions, multiple shared NG-U transport tunnels may need to be setup, one per Area Session ID served by the gNB. In case of shared NG-U termination,

• the gNB-CU-UP may provide the gNB-CU-CP at E1 setup or configuration update about established shared NG-U terminations, indicated by one or several MBS Session IDs.
• at establishment of the MC bearer context in the gNB-CU-UP, the gNB-CU- CP may request the gNB-CU-UP to either apply the available MRB configuration of the shared NG-U termination, or to apply the MRB configuration requested by the gNB-CU-CP. The gNB-CU-UP provides the MRB configuration to the gNB-CU-CP if the MRB configuration requested by the gNB-CU-CP and the available MRB configuration of the shared NG-U termination are different.