A.5 Indication of Emergency Registration and Session Establishment

29.2143GPPPolicy and charging control over Rx reference pointRelease 17TS

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, the P-CSCF may request the PCRF to provide the EPC-level identities (MSISDN, IMSI, IMEI(SV)) available for that IP-CAN session using the procedure as specified in this clause (for an IMS emergency registration) or A.1 (for an IMS emergency session establishment). An P-CSCF may request the PCRF to provide the EPC-level identities (MSISDN, IMSI, IMEI(SV)) available for that IP-CAN session when no service information is available in the AF.To do so, the P-CSCF shall open an Rx Diameter session with the PCRF for the AF signalling using an AA-Request command. The P-CSCF shall provide the UE’s IP address (using either the Framed-IP-Address AVP or the Framed-Ipv6-Prefix AVP) and the AF-Requested-Data AVP set to "EPC-level identities required". The AF shall include the Service-URN AVP set to the value "sos", in order to indicate that the new AF session relates to emergency traffic that is not related to a specific emergency service.

When the PCRF receives an AA-Request command as described in the preceding paragraphs from the P-CSCF, the PCRF shall perform session binding as described in 3GPP TS 29.213 [9]. When the PCRF receives the Service-URN AVP indicating an emergency session, the PCRF may apply special policies, for instance prioritising service flows relating to the AF session or allowing these service flows free of charge. When the Service-URN AVP indicates that the AF session relates to emergency traffic and the AF-Requested-Data AVP is received indicating "EPC-level Identities required", the PCRF shall provide the requested available user information (MSISDN, IMSI) for the IP-CAN session within the Subscription-Id AVP(s) and/or the IMEI(SV) within the User-Equipment-Info AVP or the User-Equipment-Info-Extension AVP if the User-Equipment-Info-Extension feature is supported, in the AA-Answer command.

When the P-CSCF receives the AA-Answer with the EPC-level identities from the PCRF, the P-CSCF stores the information received within the Subscription-Id AVP(s) and/or User-Equipment-Info AVP or User-Equipment-Info-Extension AVP if the User-Equipment-Info-Extension feature is supported, provided by the PCRF and behaves as defined in 3GPP TS 24.229 [17].

NOTE:  The user information received within the User-Equipment-Info AVP or the User-Equipment-Info-Extension AVP if the User-Equipment-Info-Extension feature is supported, and/or Subscription-Id AVP(s) can be used to support PSAP callback functionality for anonymous IMS emergency sessions. See 3GPP TS 23.167 [53] for further information.

The P-CSCF may decide to terminate the Rx session at any time. In that case, the AF shall use a Session-Termination-Request (STR) command to the PCRF, which shall be acknowledged with a Session-Termination-Answer (STA) command.

A SIP INVITE request can contain a service URN as defined in IETF RFC 5031 [21] 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 Service-URN AVP towards the PCRF. The P-CSCF may also provision possible information about other services received within the service URN.