B.10 Handling of MCPTT priority call

29.5143GPP5G SystemPolicy Authorization ServiceRelease 18Stage 3TS

B.10.1 General

Within the framework of MCPTT, when the SIP Core (3GPP TS 24.379 [41]) 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 "resPrio" attribute and the "mcpttId" in the Npcf_PolicyAuthorization_Create request as defined in clause B.13.2 to allow the PCF 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 "prioSharingInd" attribute within the media component included in the "medComponents" attribute as described in clause B.1. For MCPTT the service priority and the priority sharing indicator are defined in 3GPP TS 24.379 [41].

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 PCF is expected to derive the PCC Rules corresponding to the this MCPTT session, as appropriate according to operator policies.

NOTE 3: The PCF can identify an MCPTT call using the IMS Communication Service Identifier specific to MCPTT, which is provided by the P-CSCF in the "afAppId" attribute in the Npcf_PolicyAuthorization_Create request sent to PCF.

B.10.2 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 signalling, the P-CSCF shall include the "mcpttId" attribute and the "resPrio" attribute in the corresponding Npcf_PolicyAuthorization service operation towards the PCF.

The "mcpttId" attribute 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 [42]).

The "resPrio" attribute shall contain the priority value of the Resource-Priority header; the lowest priority shall be mapped to PRIO_1 (Resource-Priority header value 0), the next after the lowest to PRIO_2 (Resource-Priority header value 1), and so on up to the highest priority which shall be mapped to PRIO_16 (Resource-Priority header value 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 "prioSharingInd" attribute within the media component received in the "medComponents" attribute in the corresponding Npcf_PolicyAuthorization service operation. See 3GPP TS 24.379 [41] for further information.