Terminating Sessions for SRVCC with ATCF

For initial SIP requests, the ATCF identifies SIP INVITE requests with the ATCF URI for terminating requests in the topmost Route header field. These are called terminating SIP INVITE requests.

When it receives a terminating SIP INVITE, the ATCF does the following if the INVITE has a Record-Route header field with the g.3gpp.srvcc media feature tag:

• The ATCF inserts a Record-Route header field with its own SIP URI
• If the latest SRVCC information received for a session contains a C-MSISDN and ATU-STI,
  • The ATCF associates the session being established with the C-MSISDN and ATU-STI bound to the registration, and
  • The ATCF replaces the SDP offer in the originating SIP INVITE with updated SDP provided by the ATGW. Replacement occurs if the terminating SIP INVITE contains an SDP offer and a determination to anchor media has been made (according to the operator policy as specified in the 3GPP standard).