A.1 Group Communication

26.5023GPP5G Multicast-Broadcast User Service ArchitectureRelease 17TS

The Group Communication (GC) Service is defined for use with LTC/EPC in TS 23.468 [14]. In order to allow GC Services to interwork with an MBS System, the MBSF also supports reference point MB2‑C and the MBSTF also supports reference point MB2‑U, as defined in clause 5.2 and annex C of TS 23.247 [5].

Figure A.1‑1: User Plane protocol stack for Group Communication services

The following MBS Distribution Session properties (see clause 4.5.6) are used by the MBSF at reference point Nmb2 to provision this setup in the MBSTF:

– Distribution method is set to Packet.

– Operating mode is set to Forward-only.

– Packet ingest method is set to Unicast.

– User plane traffic flow information is omitted because ingested multicast packets are not modified.

– The tunnel endpoint addresses of the MBMS-GW (SGi-mb) and/or MB-UPF (Nmb9).

– FEC configuration information is provided if AL‑FEC protection was requested by the GCS AS in the MBMS bearer allocation request at MB2-C.

– The MBSTF provides the MBSTF ingest endpoint addresses (representing the BM‑SC address and BM‑SC port) via the MBSF to the GCS AS at reference point MB2‑C so that the GCS AS can establish a UDP/IP tunnel with the MBSTF at MB2-U and start sending tunnelled IP packets.

– The MBSTF provides forward error protection according to the FEC configuration for downlink IP packets ingested from GCS AS, and then sends the source packets and any FEC packets to the MBMS GW at reference point SGi-mb.