Handover delay optimization

1. A method of anchoring an Internet Protocol (IP) Multimedia Subsystem (IMS) multimedia session of a subscriber, the method executed by a control node of a home network of the subscriber and comprising:

receiving, by the control node and via an IMS call session control function in the home network, a request for setup of the IMS multimedia session of the subscriber; and

anchoring, by the control node, the IMS multimedia session in an access transfer function of a visited network of the subscriber.

2. The method according to claim 1 , wherein said anchoring comprises sending information from the control node to the access transfer function for anchoring the IMS multimedia session in that access transfer function and for anchoring a media path in a transmission node of the visited network.

3. The method according to claim 2 , wherein said sending comprises sending at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

4. The method according to claim 1 , wherein the method comprises anchoring a signaling path for the IMS multimedia session in the access transfer function.

5. The method according to claim 1 , wherein said anchoring comprises identifying the access transfer function, wherein said identifying comprises at least one of:

using a configured Public Service Identifier (PSI) of the access transfer function; and

requesting information about the access transfer function from the home network.

6. The method according to claim 5 , wherein said requesting comprises requesting a Mobile Station Roaming Number (MSRN) from at least one of a Home Location Register (HLR) and a Home Subscriber Server (HSS) of the home network.

7. The control node according to claim 5 , wherein the control node comprises a Service Centralization and Continuity Application Server (SCC AS) of the home network of the subscriber.

8. A control node of a home network of a subscriber for anchoring an Internet Protocol (IP) Multimedia Subsystem (IMS) multimedia session of the subscriber, the control node comprising:

a processor and a memory, the memory containing instructions executable by the processor whereby the control node is configured to:

receive, via an IMS call session control function in the home network, a request for setup of the IMS multimedia session of the subscriber; and

anchor the IMS multimedia session in an access transfer function of a visited network of the subscriber.

9. The control node according to claim 8 , wherein the control node comprises a Service Centralization and Continuity Application Server (SCC AS) of the home network.

10. The control node according to claim 8 , wherein the memory contains instructions executable by the processor whereby the control node is configured to send information to the access transfer function for anchoring the IMS multimedia session in that access transfer function and for anchoring a media path in a transmission node of the visited network.

11. The control node according to claim 10 , wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

12. The control node according to claim 8 , wherein the memory contains instructions executable by the processor whereby the control node is configured to anchor a signaling path for the IMS multimedia session in the access transfer function.

13. The control node according to claim 8 , wherein the memory contains instructions executable by the processor whereby the control node is configured to identify the access transfer function by at least one of:

using a configured Public Service Identifier (PSI) of the access transfer function; and

requesting information about the access transfer function from the home network.

14. A method of anchoring an Internet Protocol (IP) Multimedia Subsystem (IMS) multimedia session of a subscriber, the method executed by a Mobile Switching Center server (MSC-S) implementing an access transfer function of a visited network of the subscriber, the method comprising:

determining by the MSC-S that the IMS multimedia session is to be anchored in the access transfer function of the visited network; and

responsive to said determining, anchoring the IMS multimedia session in the access transfer function of the visited network implemented by the MSC-S.

15. The method according to claim 14 , further comprising receiving information from a control node of a home network of the subscriber for anchoring the IMS multimedia session in the access transfer function and for anchoring a media path in a transmission node of the visited network.

16. The method according to claim 15 , wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

17. The method according to claim 14 , further comprising receiving a handover request and, responsive to the handover request, instructing a transmission node of the visited network to transfer a source access leg of the IMS multimedia session associated with packet switched access to a target access leg of the IMS multimedia session associated with a circuit switched access.

18. The method according to claim 17 , further comprising using information received from a control node of a home network of the subscriber to correlate the IMS multimedia session with the handover request, wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

19. A Mobile Switching Center Server (MSC-S) implementing an access transfer function of a visited network of a subscriber for anchoring an Internet Protocol (IP) Multimedia Subsystem (IMS) multimedia session of the subscriber, the MSC-S comprising:

a processor and a memory, the memory containing instructions executable by the processor whereby the MSC-S is configured to:

determine that the IMS multimedia session is to be anchored in the access transfer function of the visited network implemented by the MSC-S; and

responsive to said determining, anchor the IMS multimedia session in the access transfer function of the visited network implemented by the MSC-S.

20. The MSC-S according to claim 19 , wherein the memory contains instructions executable by the processor whereby the MSC-S is configured to receive information from a control node of a home network of the subscriber for anchoring the IMS multimedia session in the access transfer function and for anchoring a media path in a transmission node of the visited network.

21. The MSC-S according to claim 20 , wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.

22. The MSC-S according to claim 19 , wherein the memory contains instructions executable by the processor whereby the MSC-S is configured to receive a handover request and, responsive to the handover request, instruct a transmission node of the visited network to transfer a source access leg of the IMS multimedia session associated with packet switched access to a target access leg of the IMS multimedia session associated with a circuit switched access.

23. The MSC-S according to claim 22 , wherein the memory contains instructions executable by the processor whereby the MSC-S is configured to use information received from a control node of a home network of the subscriber to correlate the IMS multimedia session with the handover request, wherein the information comprises at least one of a Correlation Mobile Station International Number (C-MSISDN), an International Mobile Subscriber Identity (IMSI), and a media description.