37-888-9999>" Service Centralization and Continuity P-CSCF I-CSCF S-CSCF SCC AS SIP REGISTER SIP REGISTER SIP REGISTER DIAMETER UAR DIAMETER UAA SIP REGISTER DIAMETER MAR SIP 401 SIP 401 SIP 401 SIP 401 DIAMETER MAA SIP REGISTER SIP REGISTER SIP REGISTER DIAMETER LIR DIAMETER LIA SIP REGISTER DIAMETER SAR SIP 200 SIP 200 DIAMETER SAA SIP 200 SIP 200 SIP REGISTER SIP 200 SIP MESSAGE SIP MESSAGE SIP 200 SIP 200 DIAMETER PUR DIAMETER PUA DIAMETER IDR DIAMETER IDA Figure 9.12. Registration for service continuity 3) At the end of the mobile's registration, the SCC AS entity receives from the S-CSCF entity the SIP REGISTER message containing the following information created by the ATCF entity: - the SIP URI identity of the ATCF entity; - the PATH URI identity for the identification of the mobile while registering; - the STN-SR session transfer number. 4) The SCC AS entity responds with SIP 200 OK message to the SIP REGISTER request. 5) The SCC AS entity communicates to the SIP URI of the ATCF entity, in the SIP MESSAGE request, additional information concerning the PATH URI identity: its own access transfer update - transfer session identifier (ATU-STI) and the mobile subscriber ISDN number (MSISDN). 262 VoLTE and ViLTE MESSAGE sip:atcf.HomeA.net SIP/2.0 <?xml version="1.0" encoding="UTF-8"?> <SRVCC-infos> <SRVCC-info - ATCF-Path- URI="sip: :termsdgfdfwe@atcf.HomeA.net": <ATU-STI>sip:sccas.HomeA.net</ATU-STI: C-MSISDN>tel:+358-50-4821437</C-MSISDN> </SRVCC-info> </SRVCC-infos> 6) The ATCF entity responds with the SIP 200 OK message to the SIP REGISTER request. 7) The SCC AS entity forwards the message DIAMETER profile- update-request (PUR) to the HSS entity to update the STN-SR session number. 8) The message DIAMETER profile-update-answer (PUA) acknowledges the received message DIAMETER PUR. 9) The HSS entity sends the message DIAMETER insert-subscriber-data- request (IDR) to the MME entity for the update of the STN-SR session number. 10) The message DIAMETER insert-subscriber-data-answer (IDA) acknowledges the receiv