The following clauses show the requirements and information flows of IMS Restoration Procedures for the SCC-AS service interruption in each of the scenarios where they apply.
It is an optional feature to support SCC-AS restoration. If SCC-AS restoration is supported, it is required to support enhanced third part registration procedure described in 6.2.1 and enhanced service request procedure described in 6.2.2 together.
During the 3rd party registration, the SCC-AS should store extra SRVCC related information, i.e, ATCF-Path-URI, ATCF-Management-URI and g.3gpp.accesstype media feature tag if received as specified in clause 6.3.2 of TS 24.237
, in the HSS as Repository Data.
When a service request is received when assigned SCC-AS is down, the S-CSCF should forward the service request to a working SCC-AS and this SCC-AS should:
download corresponding ATCF related information previously stored in the HSS and it should notify the ATCF with its own ATU-STI for SRVCC; and
download corresponding g.3gpp.accesstype media feature tag (if exist) previously stored in the HSS and determine that PS to CS SRVCC is usable for UE as specified in clause 6.3.2 of TS 24.237.