The Group Communication (GC) Service is defined for use with LTC/EPC in TS 23.468. 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.

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.

The use of MBS User Services in collaboration with the 5G Media Streaming architecture [7] is for further study.

Figure A.3-1 depicts a collaboration in which the MBS Application Provider (AF/AS) is deployed within the Trusted DN.

1. The AF/AS uses the Nmbsf service directly at reference point Nmb10.
2. The MBSTF injects packets into the MB-UPF via reference point Nmb9.

Figure A.4-1 depicts a collaboration in which the MBS Application Provider (AF/AS) is deployed within the External DN.

1. The AF/AS invokes the Nnef service at reference point N33 to access the MBSF via the NEF. The NEF, in turn, invokes the Nmbsf service on the MBSF at reference point Nmb5 on behalf of the AF/AS.
2. The MBSTF injects packets into the MB-UPF via reference point Nmb9.

Figure A.5-1 depicts a transport-only deployment in which the MBS Application Provider (AF/AS) hosts an "MBSF-like" function that mimics the MBSF at reference point MBS-5 and an "MBSTF-like" function that mimics the MBSTF at reference point MBS-4-MC. The "MBSF-like", "MBSTF-like" and "MBS AS-like" functions produce data streams which are compliant with the present document. Although the 5G System sets up a Transport-only Mode (see configuration option 1 in Annex A of TS 23.247), the MBS Client in the UE follows the procedures defined in the present document.

1. The MBSF-like function provisions MBS Services in the MB-SMF via the Nnef service at reference point N33.
2. The MBS Application Provider (AF/AS) uses an MBSTF-like function to produce packet data compliant with reference point MBS-4-MC. The packets are injected directly into the MB-UPF at reference point N6mb (not shown).
3. An MBS Application Provider (AF/AS) in an External DN uses an MBSF-like function to generate a Service Announcement for MBS User Services.
4. The MBS Application Provider (AF/AS) makes object repair available from an MBS AS-like function that is compliant with reference point MBS-4-UC.