A.13 Handling of MCPTT priority call

29.2143GPPPolicy and charging control over Rx reference pointRelease 17TS

A.13.1 General

Within the framework of MCPTT, when the SIP Core (3GPP TS 23.379 [54]) is implemented by an IMS core network, if the P-CSCF receives a SIP request message including a Resource-Priority header field with a namespace field and priority value defined for MCPTT for adjusting the priority of an MCPTT session, the P-CSCF shall provide the Reservation-Priority AVP and the MCPTT-Identifier AVP in the AA-Request command as defined in clause A.13.2 to allow the PCRF to set the corresponding PCC rule(s) according to the prioritized MCPTT service. Additionally, if PrioritySharing feature is supported, the P-CSCF may provide the Priority-Sharing-Indicator AVP within the Media-Component-Description AVP as described in clause A.1. For MCPTT the service priority and the priority sharing indicator are defined in 3GPP TS 23.379 [54].

NOTE 1: The process of adjusting priority may occur several times during the course of one session, e.g. a normal MCPTT group call elevated to an MCPTT emergency group call, returned to a normal priority MCPTT group call, elevated to an MCPTT imminent peril group call and returned to a normal priority MCPTT group call.

NOTE 2: Upon reception of a request that requires the adjustment of the MCPTT priority, the PCRF is expected to derive the PCC Rules corresponding to the this MCPTT session, as appropriate according to operator policies.

NOTE 3: The PCRF can identify an MCPTT call using the IMS Communication Service Identifier specific to MCPTT, which is provided by the P-CSCF in the AF-Application-Identifier AVP in the AA-Request sent to PCRF.

A.13.2 Determination of MCPTT priority parameter values

When the P-CSCF receives an authorized Resource-Priority header field containing an appropriate namespace and priority value used for MCPTT in SIP signaling, the P-CSCF shall include the MCPTT-Identifier AVP and Reservation-Priority AVP in the AAR command towards the PCRF.

The MCPTT-Identifier AVP shall include the namespace defined for MCPTT as received within the Resource-Priority header field.

NOTE: Two different values are defined for the MCPTT-Identifier AVP, one for each namespace value defined for MCPTT (see IETF RFC 8101 [45]).

The Reservation-Priority AVP shall contain the priority value of the Resource-Priority header; the lowest priority shall be mapped to to DEFAULT (0), the next after the lowest to PRIORITY-ONE (1), and so on up to the highest priority which shall be mapped to PRIORITY-FIFTEEN (15).

Additionally, when the P-CSCF receives information about priority sharing from an MCPTT server that supports simultaneous sessions and that needs to share a common priority for several MCPTT sessions and if PrioritySharing feature is supported, the P-CSCF may include the Priority-Sharing-Indicator AVP within the Media-Component-Description AVP in the AAR command. See 3GPP TS 23.379 [54] for further information.