 transfer of Alice's communication to a CS network. 3) The ATCF entity establishes a new dialogue with the SCC AS entity by sending a new SIP INVITE request. The URI identity of the query contains the ATU-STI identity of the entity SCC AS entity recovered during registration. The SIP INVITE message incorporates a Require header with the value tdialog to mean that the header Target-Dialog is required. The header Target-Dialog specifies that the existing dialogue (Call - ID header, tag parameters of the headers From and To) must be connected with the dialogue established by the ATCF entity. The P-Asserted-Identity header contains Alice's phone number (MSISDN). INVITE sip:sccas.HomeA.net SIP/2.0 Require: tdialog Target-Dialog: me03a0s09a2sdfgjk1491777; remote- tag=774321; local-tag=64727891 P-Asserted-Identity: <tel:+358-50-4821437> Service Centralization and Continuity The body of the SDP message contains the characteristics of the RTP stream provided by the ATGW entity of the domain HomeA. net (IPv4 address 200.1.1.2 and port number 8899) while establishing the session. As the SDP message body has not changed, there is no need to make an update for the domain HomeB.net 4) The SIP 200 OK response incorporates the SDP message communicated by ATGW entity of the domain HomeB. net (IPv4 address 200.2.2.2 and port number 6544) that the SCC AS entity had retained. 5) The SCC AS entity sends the SIP BYE request to complete the initial dialogue in the P-CSCF and ATCF entities and possibly in Alice's UA entity if it has carried out for the SIP flow the inter-system PS-PS handover simultaneously with the PS-CS inter-system handover. In the case where Alice's UA entity may not respond with a message SIP 200 OK, the ending of the dialogue takes place at the initiative of the entities concerned network. 9.2.2.6. Emergency call 9.2.2.6.1. Session establishment for an emergency call The procedure for establishing the emergency call by implementing the e-SRVCC function is illustrated in Figure 9.17. P-CSCF E-CSCF SIP INVITE SIP IN