25 P-CSCF restoration

29.1653GPPInter-IMS Network to Network Interface (NNI)Release 18TS

25.1 General

Based on inter-operator agreement, P-CSCF restoration may be supported over the II-NNI.

The P-CSCF restoration defines two optional mechanisms:

– a PCRF or PCF based mechanism; and

NOTE 1: In 5GS the mechanism is called "PCF based P-CSCF restoration" since the PCF takes the role of the PCRF.

– an HSS or UDM/HSS based mechanism.

NOTE 2: In 5GS the mechanism is called "UDM/HSS based P-CSCF restoration" since the UDM participates in the procedure.

The support of either one of the mechanisms is based on operator agreements.

If a mechanism is supported, the related procedures from the 3GPP TS 24.229 [5] shall be applied with the requirements in the relevant clause below.

25.2 PCRF or PCF based P-CSCF restoration

The procedures in 3GPP TS 24.229 [5] shall be applied and the capabilities below shall be provided at the II-NNI.

The Restoration-Info header field containing IMSI information defined in 3GPP TS 24.229 [5] in the home-to-visited initial INVITE request shall be supported on the roaming II-NNI.

25.3 HSS or UDM/HSS based P-CSCF restoration

The procedures in 3GPP TS 24.229 [5] shall be applied and the capabilities below shall be provided at the II-NNI.

The Restoration-Info header field containing information about failed node defined in 3GPP TS 24.229 [5] in the 408 (Request Timeout) response to the home-to-visited initial INVITE request and in the 504 (Server Time-out) response to the MESSAGE request, NOTIFY request, OPTIONS request, PUBLISH request, REFER request and the SUBSCRIBE request shall be supported on the roaming II-NNI.