Each UE participating in the Group Communication Service uses one or multiple EPS bearers for exchanging application signaling and data with the GCS AS. The EPS bearer services are specified in TS 23.401
and TS 23.203
In order to enable GCS, a PDN connection needs to be established that can be used for GC1 signaling exchange. When the PDN connection gets established the PCC functionality determines a QCI and an ARP for the default bearer, which may be used for GC1 signaling. Alternatively, during PDN connection establishment a dedicated bearer may be established for GC1 signaling by configuring PCC rules accordingly.
A GCS UE may join multiple GCS groups, which are served by one or more EPS bearers. The GCS AS determines the service characteristics of a specific Group Communication Service, e.g. media or flow description and priority, which is used by the PCRF to determine the EPS bearer configuration appropriate for GCS. The GCS AS updates the PCRF with service characteristics to initiate any required update of the EPS bearer configuration, e.g. when the UE joins or leaves a GCS group or when a GCS data exchange starts or stops.
Whenever the UE's bearer configuration needs to be updated, the GCS AS provides the updated or new service characteristics to the PCRF. From service characteristics PCRF determines the required bearer configuration, including QCI and ARP, and requests the PCEF amendment of the UE's EPS bearers accordingly. If the priority of the application Group Communication session changes, the GCS AS provides an update of the service characteristics towards the PCRF via the Rx interface. 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.
The PCRF is not aware of the GCS group(s).
To obtain the responsiveness desired for GCS the GCS UE shall signal the Idle Mode DRX value to the MME, using the procedures described in TS 23.401
. The E-UTRAN derives from the QCI the configuration for delivering an equivalent responsiveness in Connected Mode. When performing the S1 interface paging procedure for a DownlinkData Notification for a bearer associated with either QCI 65 or QCI 69 (e.g. Mission Critical Push To Talk), the Paging Priority IE needs to be set to a value such that the E-UTRAN can correctly prioritize the contents of its radio interface paging messages to enable low latency for the first downlink packet on that bearer. To enable the MME to send this Paging Priority IE on the S1 interface, the bearer(s) associated with QCI 65 and QCI 69 should have appropriate ARP(s).