Content for  TS 23.468  Word version:  18.0.0

A Group Communication Session that requires to be prioritized over other Group Communication Sessions or non-Group Communication Sessions includes both the priority level and the GCS identifier in a service authorization request to the PCRF and to the BM-SC. The priority level and the GCS identifier are defined at the application layer for priority and pre-emption purposes. The GCS AS provides the priority level and the GCS identifier to the PCRF and the BM-SC. It is mapped by the PCRF and the BM-SC to the ARP priority level, pre-emption capability and pre-emption vulnerability indication under the consideration of the respective EPS network. In the case of Unicast Delivery, the PCRF translates the service characteristics to PCC policies and forwards its policy decision to the PCEF. The PCEF determines, based on policies provided by the PCRF, whether the PCEF modifies already established bearers or whether the PCEF establishes dedicated bearer(s) with the determined bearer characteristics. If the priority of a particular application Group Communication session changes, the GCS AS provides an update of the service characteristics towards the PCRF via the Rx interface. The PCRF updates the PCC policies and forwards them to the PCEF. The PCEF modifies already established bearers or establishes dedicated bearer(s) accordingly. The PCRF shall, at the reception of service authorization from the GCS AS including an indication that is a prioritized GC Session and priority level, ensure that the ARP priority level of the default bearer is assigned a prioritized value which is at least as high as the highest priority of all Group Communication Sessions within the same IP-CAN session. The PCRF shall also ensure that the ARP pre-emption capability and pre-emption vulnerability indication of the default bearer satisfies the strongest requirements of all Group Communication Sessions within the same IP-CAN session. When the PCRF detects that all prioritized Group Communication Sessions within the same IP-CAN session are released, the PCRF shall assign the ARP of the default bearer as appropriate. In the case of MBMS Delivery, if the priority of an MBMS bearer needs to be changed, based upon a GCS AS decision to change the priority level, the GCS AS performs either:

• The Modify MBMS Bearer procedure in clause 5.1.2.4; or
• A new Activate MBMS Bearer procedure and a Deactivate MBMS Bearer procedure replacing the old MBMS bearer service with a new one.

In certain network conditions such as congestion, the bearer used for group communication service may be pre-empted.

• In the case of Unicast Delivery, the GCS AS is notified by the PCRF of unicast bearer release.
• In the case of MBMS Delivery, the related MBMS bearer may be 'suspended' by E-UTRAN and the UE becomes aware in either of the following ways:
• packets are dropped at the eNB. In this case the UE can detect that MBMS delivery is no longer available when the related TMGI is removed from MCCH.
• The UE receives an explicit indication broadcast from the eNB in the MBMS Scheduling Information (see TS 36.300 and TS 36.321), where it is informed that transmission for the MBMS bearer is going to be, or has been, suspended.
  The procedure used by the UE in these scenarios is depicted in Figure 5.4-1.

For MBMS Delivery, the architecture requirement for charging defined for MBMS broadcast service for E-UTRAN in TS 23.246 shall apply. For Unicast Delivery, the architecture requirement for charging defined for EPS bearer services in TS 23.401 shall apply.

Security requirements for supporting the MB2 reference point for GCS are defined in TS 33.246. No additional security requirement is defined for supporting GCS with Unicast Delivery.