Content for  TS 38.401  Word version:  18.3.0

The overall architecture specified in clause 6.1.1 and 6.1.2 applies for NR MBS. Upon establishment of a MBS Session resource by the 5GC, the gNB-CU triggers the establishment of MRBs, involving the gNB-DU. If E1 is deployed, the gNB-CU-CP triggers establishment of respective MBS UP resources in the gNB-CU-UP. The gNB-DU assigns the G-RNTI. A shared F1-U tunnel is used between the gNB-CU and the gNB-DU forMRB with PTM transmission. UE dedicated F1-U tunnels are used between the gNB-CU and the gNB-DU for data transmission of PTP retransmission and PTP forwarding of an MRB. For an MRB configured with PTP only transmission either a shared F1-U or a UE dedicated F1-U tunnel is used, dependent on the lower layer configuration. The gNB-DU assigns the DL GTP-U TEID and provides it to the gNB-CU. If E1 is deployed the gNB-CU-CP forwards it to the gNB-CU-UP. For both broadcast and multicast, DL flow control maybe used for the shared F1-U tunnel established for the MRB, as specified in TS 38.425.

The protocol stacks for the user plane and control plane of L2 U2N Relay architecture are described in Figure 6.1.6-1 and Figure 6.1.6-2, respectively. The Uu SRAP is terminated between U2N relay UE and gNB-DU.