B.5 Indication of Emergency Registration and Session Establishment

29.5143GPP5G SystemPolicy Authorization ServiceRelease 18Stage 3TS

When the P-CSCF receives an initial REGISTER SIP message for an IMS emergency registration or an INVITE SIP message for an emergency session and the P-CSCF determines that there are no IMS-level roaming interfaces, and the "IMS_SBI" feature is supported the P-CSCF may request the PCF to provide the 5GS-Level UE identities (GPSI, SUPI, PEI) available for that PDU session in the serving network (either a PLMN or an SNPN) using the procedure as specified in this clause (for an IMS emergency registration) or B.1 (for an IMS emergency session establishment).

A P-CSCF may request the PCF to provide the 5GS-level identities (GPSI, SUPI, PEI) available for that PDU session when no service information is available in the P-CSCF. To do so, the P-CSCF shall create an "Individual Application Session Context" resource in the PCF for the AF signalling using an Npcf_PolicyAuthorization_Create service operation. The P-CSCF shall provide the UE’s IP address (using either the "ueIpv4" attribute or the "ueIpv6" attribute) and the "afReqData" attribute set to "UE_IDENTITY". The P-CSCF shall include the "servUrn" attribute set to the value "sos", in order to indicate that the new AF session context relates to emergency traffic that is not related to a specific emergency service.

If the P-CSCF supports the SBI Message Priority mechanism for an emergency session, it shall include the "3gpp‑Sbi‑Message‑Priority" custom HTTP header towards the PCF as described in clause 6.8.2 of 3GPP TS 29.500 [5].

NOTE 1: If the P-CSCF supports the SBI Message Priority mechanism for an emergency session, the P-CSCF includes the "3gpp-Sbi-Message-Priority" custom HTTP header based on P-CSCF policies in relation to valid values of the "servUrn" attribute. The highest user priority value is mapped to the corresponding lowest value of the "3gpp-Sbi-Message-Priority" custom HTTP header.

When the PCF receives an Npcf_PolicyAuthorization_Create service operation as described in the preceding paragraphs from the P-CSCF, the PCF shall perform session binding as described in 3GPP TS 29.513 [7]. When the PCF receives the "servUrn" attribute indicating an emergency session, the PCF may apply special policies, for instance prioritising service flows relating to the AF session context or allowing these service flows free of charge.

When the "servUrn" attribute indicates that the AF session context relates to emergency traffic and the "afReqData" attribute is received indicating "UE_IDENTITY", the PCF shall provide the requested available user information (MSISDN, IMSI (for PLMN access) or either IMSI or NAI (for SNPN access), IMEI(SV)) for the PDU session within "ueIds" attribute within the "ascRespData" in the HTTP "201 Created" response.

When the P-CSCF receives the HTTP "201 Created" response with the 5GS-level UE identities from the PCF, the P-CSCF stores the "ueIds" received within "Individual Application Session Context" resource returned in the HTTP "201 Created" response and behaves as defined in 3GPP TS 24.229 [32].

NOTE 2: The user information received within the "ueIds" attribute can be used to support PSAP callback functionality for anonymous IMS emergency sessions. See 3GPP TS 23.167 [40] for further information.

The P-CSCF may decide to delete the "Individual Application Session Context" resource at any time. In that case, the Npcf_PolicyAuthorization_Delete service operation, as described in clause 4.2.4.2.

A SIP INVITE request can contain a service URN as defined in IETF RFC 5031 [34] within the request URI. If the service within this URN is "sos", possibly with additional sub-service information, the P-CSCF shall provision this service and sub-service information within the "servUrn" attribute towards the PCF. The P-CSCF may also provision possible information about other services received within the service URN.