| 摘要 |
<p>A method of Dual Radio Access Transfer of an IP Multimedia session, IMS, in an alerting phase for the Packet Switched to Circuit Switched direction. The method comprises initiating an IMS media session towards a terminating mobile station, UE and, during a session alerting phase, making a determination at the UE that a DRVCC transfer is required from a Packet Switched, PS, to a Circuit Switched, CS, access. The method comprises sending a SIP message from the UE to a Service Centralization and Continuity Application Server, SCC-AS, over the PS access, informing the SCC-AS of the DRVCC transfer, and responding to receipt of the SIP message at the SCC-AS by sending a SIP INVITE from the SCC-AS towards a Mobile Switching Centre, MSC, serving the UE in the CS access, the INVITE including an identity of the UE as a called party identity and the STN as the calling party identity. The method further comprises responding to receipt of said INVITE at the MSC, or to receipt of associated CS signalling, by sending from the MSC to the UE a CS Setup message, whereupon the MSC is placed in a state in which it expects a CS Answer from the UE.</p> |
