e is the response to the PRACK request. Alice's mobile proceeds with the establishment of the bearer in the CS- mode network (SETUP) indicating the PSI identity as destination. 11), 13) The MSC server entity generates the SIP INVITE request to the identity PSI. Service Centralization and Continuity 251 The header P-Asserted-Identity contains the phone number of the caller. The header Accept-Contact indicates that the MSC server entity supports supplementary telephone services. INVITE tel : +1-212-555-6666 SIP/2.0 P-Asserted-Identity: <tel:+358-50-4821437> Accept-Contact: *; +g.3gpp.icsi-ref="urn%3Aurn-7%3gpp service.ims.icsi.mmtel" The SIP INVITE request contains an SDP offer that contains the characteristics of the audio stream provided by the MSC GW entity. 12), 14) Each entity responds with the SIP 100 Trying response that allows for blocking the retransmission timer of the SIP INVITE request. 15), 17) The SCC AS entity generates the SIP INVITE request to Bob located in the domain HomeB.net. The SCC AS entity replaces the PSI identity by the TEL URI identity of Bob that was recorded during the first SIP INVITE message. INVITE tel: +1-212-555-2222 SIP/2.0 16), 18) Each entity responds with the SIP 100 Trying response that allows for blocking the retransmission timer of the SIP INVITE request. 19), 20) The SCC AS entity receives from the domain HomeB. net the SIP 180 Ringing message indicating that Bob's phone is ringing. 21), 22) The SCC AS entity responds with the SIP 180 Ringing message to the INVITE request received from Alice's UA entity. 23), 24) The SCC AS entity receives from the domain HomeB. net the SIP 200 OK message indicating that Bob picked up the phone. The SIP 200 OK message contains the SDP message with the characteristics of the audio stream. VoLTE and ViLTE 25), 26) The SCC AS entity responds to the SIP INVITE request of the MSC server entity with the SIP 200 OK message in which the SCC AS entity forwards the SDP message received from the domain HomeB.net. Upon receipt of the SIP 200 OK messag