Content for  TS 23.289  Word version:  19.0.0

The MC service server can decide to configure an MBS session per MC service group to transmit the media related to the corresponding MC service group communications. Such group communications can comprise different service requirements. For that, multicast and broadcast MBS sessions need to be configured with multiple MBS QoS flows to address different service requirements, e.g., different required QoS, provided by the MC service server. For instance, application-level control messages or media associated to a group communication can comprise different QoS requirements. Also, different type of group communications can comprise different QoS requirements, e.g., emergency group calls should be handled with a higher priority than normal group calls. The configuration of multiple MBS QoS flows to address different service requirements is associated to the assignment of different streams (e.g., different ports) within an MBS session. The established multicast MBS session can either be in active or inactive state, where the former indicates the activation of radio resources hence transmitting the MC media to the associated MC service group, and the latter indicates their deactivation as no MC media is being transmitted. The MC service server may trigger the activation of multicast MBS sessions once the MC service group is established and active, as well as once the MC media is available for transmission. For this purpose, the MC service server sends a multicast MBS session activation request towards the 5GC indicating the MBS session ID to be activated. Similar to the use of eMBMS, the MC service server shall provide the associated information between a specific group communication and the stream to be used within an MBS session. This information could be sent in advance in an MBS session announcement or could be provided on demand in an additional signalling message for the MBS session, e.g., MapGroupToSessionStream (similar to the MapGroupToBearer in eMBMS).

The procedure in Figure 7.3.3.5.2-1 describes how media related to a specific group communication can be distributed over a configured MBS session which consist of multiple QoS flows, i.e. addressing different service requirements. The procedure is applicable for both the pre-created MBS session case as described in clause 7.3.3.1.2 and the dynamic MBS session case as described in clause 7.3.3.1.3. For simplicity, the Figure 7.3.3.5.2-1 shows that the MBS session is pre-created prior to the group communication establishment. Pre-conditions:

• MC service clients 1 to n are attached to the 5GS, registered and affiliated to the same MC service group X.
• The MC service server has decided to use an MBS session for MC service group communications associated to MC service group X.

The MC service server may use an 5G MBS session for application level control signalling. An 5G bearer for application level control signalling is typically used for the purposes beyond the benefit for using 5G for resource efficiency, e.g. for improved MC service performance (KPIs), handling of high load scenarios. Similar to the usage of eMBMS, both broadcast and multicast 5MBS session for application level control signalling may be used to transmit the following messages,

• Transmission control (e.g. call setup and floor control)
• MBS session announcement for media sessions
• Group application paging
• Group dynamic data (e.g. status of the group)
• Group state (e.g. emergency alerts)

Similar to the usage of eMBMS bearer in TS 23.280, 5G MBS session for application level control signalling is created in a service area that is larger than the estimated service for media MBS session. The service area for the media sessions is mainly based on counting of group members in each defined service area. The MBS session for application level control signalling is also created with a QoS that is better than MBS media session since the packet loss requirements are much stricter. The MC service client shall not send responses to group-addressed application level control signalling unless instructed or configured to respond.

The procedure in Figure 7.3.3.6.2-1 shows only one of the receiving MC service clients using an 5G MBS session.