Method and system for enabling number portability in IMS networks

1. A method for enabling number portability in a communication session between a caller and a callee when the callee moves from a terminating home network to a target home network, the method comprising:

contacting a border element of the terminating home network of a first service provider by a serving node from an originating home network upon receiving a call request initiated by the caller, the call request comprising at least a first public identification number associated with the callee;

obtaining a second public identification number associated with the callee and assigned by the target home network of a different service provider from a user location function module by the border element based on the first public identification number for communication session redirection;

based on the second public identification number, performing a handshake between the originating home network and the target home network of the different service provider to establish a direct communication between the originating home network and the target home network of the different service provider without involving the terminating home network of the first service provider, wherein the terminating home network of the first service provider communicates one or more messages with the target home network of the different service provider, the one or more messages indicate that the terminating home network of the first service provider does not need to stay involved for communication session redirection in future communications between the caller and the callee, and

wherein the terminating home network of the first service provider and the target home network of the different service provider are IMS networks.

2. The method of claim 1 , wherein the border element of the terminating home network and the user location function exchanges an LIR and a LIAS messages for providing the second public identification number.

3. The method of claim 1 , wherein the first or second public identification number is of a telephone uniform resource identification format.

4. The method of claim 1 , wherein the first or second public identification number is of a session initial protocol uniform resource identification format.

5. The method of claim 1 wherein the first public identification number is a universal public identification number that is not associated with any operator.

6. The method of claim 1 wherein the user location function module is operated independent of operators of the originating, terminating, or target home network.

7. The method of claim 1 wherein the originating network is a call session based (CS) network, and the border element further includes a media gateway control function module (MGCF) that converts a first initial address message (IAM) message to a session initial protocol (SIP) message.

8. The method of claim 7 wherein the MGCF contacts the target network through a second IAM message after obtaining the second public identification number.

9. A system for enabling number portability in a communication session between a caller and a callee when the callee moves from a terminating home network to a target home network, the system comprising:

an originating home network having a serving node, the serving node configured to contact a border element of the terminating home network of a first service provider upon receiving a call request initiated by the caller, wherein the call request comprises at least a first public identification number associated with the callee;

the border element of the terminating home network of the first service provider configured to obtain a second public identification number associated with the callee for routing messages based on the first public identification number from a user location function module;

the originating home network and the target home network of a different service provider configured to perform a handshake between the originating home network and the target home network of the different service provider to establish a direct communication between the originating home network and the target home network of the different service provider without involving the terminating home network of the first service provider based on the second public identification number, wherein the terminating home network of the first service provider is further configured to communicate one or more messages with the target home network of the different service provider, the one or more messages indicate that the terminating home network of the first service provider does not need to stay involved for communication session redirection in future communications between the caller and the callee, and

wherein the terminating home network of the first service provider and the target home network of the different service provider are IMS networks.

10. The system of claim 9 , wherein the border element of the terminating home network and the user location function exchanges an LIR and a LIAS messages for providing the second public identification number.

11. The system of claim 9 , wherein the first or second public identification number is of a telephone uniform resource identification format.

12. The method of claim 9 , wherein the first or second public identification number is of a session initial protocol uniform resource identification format.

13. The system of claim 9 , wherein the first public identification number is a universal public identification number that is not associated with any operator.

14. The system of claim 9 , wherein the user location function module is operated independent of operators of the originating, terminating, or target home network.

15. The system of claim 9 , wherein the originating network is a call session based (CS) network, and the border element further includes a media gateway control function module (MGCF) that converts a first initial address message (IAM) message to a session initial protocol (SIP) message.

16. The system of claim 15 , wherein the MGCF contacts the target network through a second IAM message after obtaining the second public identification number.

17. The system of claim 9 , wherein the terminating home network is further configured to receive a confirmatory message from the target home network and send the confirmatory massage to the originating home network;

the originating home network is further configured to receive the confirmatory massage and send an acknowledgement signal to the target home network to establish a direct communication between the originating home network and the target home network without involving the terminating home network.

18. The method of claim 1 , wherein performing a handshake between the originating home network and the target home network to establish a direct communication between the originating home network and the target home network without involving the terminating home network comprising:

based on the second public identification number, communicating, by the terminating home network, the one or more messages with the target home network;

receiving, by the terminating home network, a confirmatory message from the target home network and sending the confirmatory massage to the originating home network;

sending, by the originating home network an acknowledgement signal to the target home network to establish a direct communication between the originating home network and the target home network without involving the terminating home network.

19. The method of claim 1 , wherein the one or more messages indicates an exclusion of the border element for communication session redirection.

20. The method of claim 1 , wherein the user location function module directs whether the border element should stay involved for communication session redirection.

21. The system of claim 9 , wherein the user location function module directs whether the border element should stay involved for communication session redirection.