Internet Multimedia Subsystem (ims) Control Over Session Transfer Between Communication Networks

1. A method of operating a communication system to transfer a media session for User Equipment (UE) between communication networks, the method comprising: in a session control server, receiving a session request for the UE over a first one of the communication networks and exchanging first control signaling with the UE and a transfer control server to establish the media session for the UE over the first communication network; in a transfer control server and in response to the first control signaling, transferring an association of the UE and the transfer control server for delivery to a translation server; in the translation server, individually associating the UE with the transfer control server in the data structure responsive to the association from the transfer control server; in the translation server, receiving a transfer request for the UE from a second one of the communication networks and processing the data structure to identify the transfer control server that is associated with the UE and transferring the transfer request for delivery to the transfer control server; and in the transfer control server, exchanging second control signaling with the second communication network responsive to the transfer request to transfer the media session for the UE from the first communication network to the second communication network.

2. The method of claim 1 wherein receiving and transferring the session transfer request comprises translating a UE identifier into a session transfer number for the transfer control server.

3. The method of claim 1 wherein receiving and transferring the session transfer request comprises translating a UE identifier into a session transfer number for an Internet Multimedia Subsystem (IMS) Emergency Access Transfer Function (EATF).

4. The method of claim 1 wherein receiving the session request for the UE comprises receiving a Session Initiation Protocol (SIP) message into an Internet Multimedia Subsystem (IMS).

5. The method of claim 1 wherein the first communication network comprises a Long Term Evolution (LTE) network and the second communication network comprises one of a Code Division Multiple Access (CDMA) network and a Global System for Mobile communications (GSM) network.

6. The method of claim 1 wherein the session control server comprises an Internet Multimedia Subsystem (IMS) server.

7. The method of claim 1 wherein the session control server comprises an Internet Multimedia Subsystem (IMS) Call Session Control Functions (CSCF).

8. The method of claim 1 wherein the session control server comprises an Internet Multimedia Subsystem (IMS) Emergency Call Session Control Function (E-CSCF).

9. The method of claim 1 wherein the transfer control server comprises an Internet Multimedia Subsystem (IMS) server.

10. The method of claim 1 wherein the transfer control server comprises an Internet Multimedia Subsystem (IMS) Emergency Access Transfer Function (EATF).

11. A communication system to transfer a media session for User Equipment (UE) between communication networks, the communication system comprising: a session control server configured to receive a session request for the UE over a first one of the communication networks and to exchange first control signaling with the UE and with a transfer control server to establish the media session for the UE over the first communication network; the transfer control server configured, in response to the first control signaling, to transfer an association of the UE and the transfer control server for delivery to a translation server; the translation server configured to individually associate the UE with the transfer control server in the data structure responsive to the association from the transfer control server, receive a transfer request for the UE from a second one of the communication networks, process the data structure to identify the transfer control server that is associated with the UE, and transfer the transfer request for delivery to the transfer control server; and the transfer control server configured to exchange second control signaling with the second communication network responsive to the transfer request to transfer the media session for the UE from the first communication network to the second communication network.

12. The communication system of claim 11 wherein the translation server is configured to translate a UE identifier into a session transfer number for the transfer control server.

13. The communication system of claim 11 wherein the translation server is configured to translate a UE identifier into a session transfer number for an Internet Multimedia Subsystem (IMS) Emergency Access Transfer Function (EATF).

14. The communication system of claim 11 wherein the session request comprises a Session Initiation Protocol (SIP) message for an Internet Multimedia Subsystem (IMS).

15. The communication system of claim 11 wherein the first communication network comprises a Long Term Evolution (LTE) network and the second communication network comprises one of a Code Division Multiple Access (CDMA) network and a Global System for Mobile communications (GSM) network.

16. The communication system of claim 11 wherein the session control server comprises an Internet Multimedia Subsystem (IMS) server.

17. The communication system of claim 11 wherein the session control server comprises an Internet Multimedia Subsystem (IMS) Call Session Control Functions (CSCFs).

18. The communication system of claim 11 wherein the session control server comprises Internet Multimedia Subsystem (IMS) Emergency Call Session Control Function (E-CSCF).

19. The communication system of claim 11 wherein the transfer control server comprises an Internet Multimedia Subsystem (IMS) server.

20. The communication system of claim 11 wherein the transfer control server comprises an Internet Multimedia Subsystem (IMS) Emergency Access Transfer Function (EATF).