Content for  TS 23.434  Word version:  19.4.2

In case of multicast MBS sessions, the members affiliated to a certain VAL service group need to initiate a UE session join request towards the 5GC in order to receive the VAL media sent via the associated MBS session. The UE session join request enables the reservation of NG-RAN resources for the members of the VAL group. However, it is not necessary that the VAL media is delivered over the whole time the multicast MBS session is associated to the group under consideration. Therefore, the VAL server is able to efficiently utilize and control the reservation of radio resources based on the availability of VAL data to be delivered via the activation and de-activation procedure with NRM server. This presents more flexibility and efficient use of resources different from LTE. The most suitable scenario to activate/de-activate a certain multicast MBS session is based on whether there is a VAL group communication, taking place over that associated session to the VAL service group. In this manner, the VAL server can activate the associated multicast session once a VAL group communication takes place, then deactivate it once the VAL group communication is over. Whether the multicast session is activated (i.e., in an active state), or de-activated (in an inactive state), the VAL group is associated to the multicast session and its members are within a UE session join. The activation or de-activation request is initiated by the VAL server towards the NRM server which further interacts either directly with the MB-SMF or indirectly with NEF/MBSF.

The procedure shown in Figure 14.3.4A.5.2-1 presents the multicast MBS session activation procedure initiated by the VAL server. Pre-conditions:

• NRM clients are attached to the 5GS, registered and affiliated to the same VAL service group X.
• The NRM server has directly performed (or via NEF/MBSF) an MB-SMF discovery and selection, unless the corresponding information is locally configured.
• The multicast MBS session for NRM group communications associated to VAL service group X.
• The MBS session is created and announced to address VAL group communication related to the associated VAL service group X with certain service requirements and optionally with a certain service area.

The procedure shown in Figure 14.3.4A.5.3-1 presents the multicast MBS session activation procedure initiated by the VAL server. Pre-conditions:

• NRM clients are attached to the 5GS, registered and affiliated to the same VAL service group X.
• The NRM server has directly performed (or via NEF/MBSF) an MB-SMF discovery and selection, unless the corresponding information is locally configured.
• A multicast MBS session is created and announced to address the corresponding VAL service group with certain service requirements and optionally with a certain multicast service area.
• The VAL UE have already joined the multicast MBS session and are able to receive the VAL data over the associated MBS session.

The VAL server can decide to configure an MBS session per VAL service group to transmit the media related to the corresponding VAL 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 NRM 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 communication should be handled with a higher priority than normal group communication. 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 VAL media to the associated VAL service group, and the latter indicates their deactivation as no VAL media is being transmitted. The VAL server may initiate the activation of multicast MBS sessions once the VAL service group is established and active, as well as once the VAL media is available for transmission. For this purpose, the VAL server sends a multicast MBS session activation request towards the NRM indicating the MBS session ID to be activated, and the NRM server further interacts with the 5GS to complete the MBS session activation. Similar to the use of eMBMS, the NRM server shall provide the associated information between a specific group communication and the stream to be used within an MBS session to the UE. 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 14.3.4A.6.2-1 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 14.3.4A.2.2 and the dynamic MBS session case as described in 14.3.4A.2.3. For simplicity, the Figure 14.3.4A.6.2-1 shows that the MBS session is pre-created prior to the group communication establishment. Pre-conditions:

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

The VAL server may use an 5G MBS session for application level control signalling. An 5G MBS session 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, for example:

• MBS session announcement for media sessions
• Group application paging
• Group dynamic data (e.g. status of the group)

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 NRM client shall not send responses to group-addressed application level control signalling unless instructed or configured to respond.

The procedure in Figure 14.3.4A.7.2-1 shows only one of the receiving VAL UE using a 5G MBS session.