Content for  TS 23.289  Word version:  19.3.0

The main purpose of 5G Multicast-Broadcast Service (MBS) use by mission critical services is to provide efficient downlink delivery of user traffic in group calls and communications. The architectural Figures in this clause are aligned with the 5GS architecture for MBS shown in Figure 5.1-2 of TS 23.247, which identifies both mandatory and optional functional entities and interfaces, in reference point representation, available for use by the MC services. Multicast and broadcast communication services in 5G for MC group communications rely on the creation and establishment of MBS sessions to deliver user data in downlink. Shared and individual delivery from the MC service server to multiple MC users (i.e., users affiliated to a certain MC group) is supported either as point-to-point or point-to-multipoint over the radio. The MBS sessions are either broadcast or multicast type and consist of one or multiple QoS flows for different service requirements. For the broadcast MBS session or local MBS session, the MBS service area is configured with the MBS session. Within this arrangement, the MC service server decides whether to create broadcast or multicast MBS sessions to be associated with certain MC groups. The 5GC adaptively decides whether to deliver the MBS traffic from the MB-UPF in the form of shared delivery or individual delivery, where the latter is applicable to multicast MBS sessions only. The NG-RAN decides to utilize point-to-point or point-to-multipoint delivery methods applicable for shared delivery only. MBS provides reliability enhancements and minimizes loss of information, e.g., due to mobility and handover. MBS group scheduling mechanism enables simultaneous reception of MBS and unicast user traffic by the MC service UEs. The UEs can receive broadcast MBS sessions irrespective of their RRC state (i.e., connected, inactive or idle) and multicast sessions only in RRC-CONNECTED and RRC-INACTIVE state. The following capabilities (non-exhaustive list) provided by MBS could be used by MC service servers as described in TS 23.247:

• MBS session creation;
• MBS session update;
• MBS session release;
• MBS session ID allocation;
• Transparent MBS Data forwarding;
• Dynamic PCC control for MBS session;
• UE's MBS assistance information provision.

Figure 4.7.2-1 presents a high-level architectural view of mission critical services when using MBS. The shown architecture is consistent with TS 23.501 and TS 23.247. MC services use MBS control plane capabilities by initiating access via Nmb13, Nmb10 or N33. MBS user plane capabilities can be accessed via N6mb or Nmb8. MC service servers can initiate access to MBS PCC capabilities supported by PCF via N5 or N33. If the MC service server and the 5GS are in different trust domains with respect to MBS, N33 needs to be used to gain access to the MBS control plane capabilities and the PCC capabilities. The 5G-GC1 reference point, which exists between the MC service client and the MC service server, is used for application layer signalling for the control of mission critical service delivery over MBS session. The functions of this reference point are defined in clause 7.3.