Section: 8.15.1.1 Broadcast MBS Session Setup
Content: Figure 8.15.1.1-1 illustrates an exemplified interaction of NGAP, E1AP, F1AP and RRC protocol functions at Broadcast MBS Session Setup. Figure 8.15.1.1-1: Broadcast MBS Session Setup 1. The 5GC starts the broadcast session by sending the NGAP Broadcast Session Setup Request message to the gNB containing the TMGI, S-NSSAI, 5G QoS Profile, area information and transport information (for NG-U multicast transport it provides the IP multicast address and the IP source specific multicast address). 2/3. The gNB-CU-CP sets up the broadcast bearer context, providing NG-U transport information from the 5GC to the gNB-CU-UP and receiving from the gNB-CU-UP the NG-U GTP DL TEID in case NG-U unicast transport was selected and an F1-U GTP UL TEID per MRB. 4. In case of NG-U multicast transport, the gNB-CU-UP joins the NG-U multicast group. 5/6. The gNB-CU-CP establishes the Broadcast MBS Session Context at the gNB-DU, providing MRB configuration, other relevant session parameters and F1-U GTP UL TEID information, and receiving F1-U GTP DL TEID information. 7/8. The gNB-CU-CP triggers BC Bearer Context Modification Request towards the gNB-CU-UP to provide the F1-U GTP DL TEID information. 9. The gNB-DU configures broadcast resources and provides broadcast configuration information to the UEs by means of MCCH. 10. The gNB-CU CP successfully terminates the NGAP broadcast Session Setup procedure. In case the gNB has chosen NG-U unicast transport, NG-U GTP DL TEID information is provided to the 5GC. 11. The broadcast MBS media stream is provided to the UEs. 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.