Method for re-assignment of S-CSCF services to registered IMS users of a home subscriber servers HSS

1. A method for re-assigning Serving Call Session Control Function (S-CSCF) services to a user of a Home Subscriber Server (HSS), in a telecommunications network, the method comprising:

i) assigning a first S-CSCF to the user during an internet protocol multimedia subsystem (IMS) registration procedure;

ii) uploading dynamic registration information from the first S-CSCF to the HSS during the IMS registration procedure, wherein the dynamic registration information comprises information created during the IMS registration procedure;

iii) storing the dynamic registration information in the HSS; and

iv) downloading the stored dynamic registration information from the HSS to a second S-CSCF during a S-CSCF re-assignment procedure for the user;

wherein the dynamic registration information comprises at least one of a binding address, a binding duration, a path header value, Expires header, Contact header.

2. The method of claim 1 , further comprising providing re-assignment information to a Proxy Call Session Control Function (P-CSCF), which acts as an outbound proxy for an internet protocol multimedia subsystem (IMS) terminal.

3. The method of claim 2 , wherein the providing the S-CSCF assignment information to the P-CSCF via extended procedure for the subscription of a Reg Event package further comprises sending by the P-CSCF a SIP SUBSCRIBE request to an I-CSCF which then forwards the SIP SUBSCRIBE request to the newly selected S-CSCF, providing by the S-CSCF- 2 the S-CSCF assignment information to the P-CSCF updating by the P-CSCF the stored S-CSCF assignment information, which the P-CSCF uses to connect the IMS user with the newly assigned S-CSCF- 2 .

4. The method of claim 1 , wherein the uploading dynamic registration information to the HSS is performed via Server Assignment Request/Server Assignment Answer (Cx-SAR/SAA) operation, which automatically includes the dynamic registration information in the Server Assignment request.

5. The method of claim 4 , wherein every new Cx-SAR request triggers the dynamic registration information stored at the HSS to be updated.

6. The method of claim 5 , wherein if no dynamic registration information is contained in the Cx-SAR request, previously stored dynamic registration at the HSS is deleted.

7. The method of claim 1 , wherein said S-CSCF reassignment for registered IMS users via a Cx-SAR/SAA operation comprises, when the second S-CSCF is selected and receives a non-REGISTER request for an unknown IMS user, the second S-CSCF treats the user as an unregistered user and downloads a user profile from the HSS via the Cx-SAR operation.

8. The method of claim 7 , wherein the HSS checks whether the registration status of the IMS user at the HSS is “registered”, and when the user is registered, but in the Cx-SAR request the IMS user is marked as “unregistered”, the HSS recognizes the inconsistence between the HSS and the S-CSCF about the registration status of the IMS user.

9. The method of claim 8 , wherein the HSS checks whether the dynamic registration information is stored at the HSS for the IMS user, if it is the case that the dynamic registration information is stored at the HSS for the IMS user, the HSS further treat the IMS user as “registered” and provide the stored registration information to the S-CSCF in the Cx-SAA operation, together with a user profile.

10. The method of claim 9 , wherein if it is not the case that dynamic registration information is stored at the HSS for the user, the HSS treat the user as “unregistered” and only provides the user profile to the S-CSCF, and when the S-CSCF receives the dynamic registration information from the HSS, S-CSCF knows that the user was already registered in IMS, the S-CSCF treat the IMS user as “registered” and build information for serving the registered IMS user from the received dynamic registration information.

11. A Home Subscriber Server (HSS), in an Internet Protocol (IP), Multimedia subsystem (IMS), comprising:

a receiver configured to receive dynamic registration information from a first Serving Call Session Control Function (S-CSCF), during an IMS registration procedure of a user, wherein the dynamic registration information comprises information created during the IMS registration procedure;

storage configured to store the dynamic registration information;

the receiver configured to receive a request from a second Serving Call Session Control Function (S-CSCF), requesting a user profile for the user;

a transmitter configured to transmit, responsive to receiving the request, the dynamic registration information to the second Serving Call Session Control Function (S-CSCF);

wherein the dynamic registration information comprises at least one of a binding address, a binding duration, a path header value, Expires header, Contact header.

12. The Home Subscriber Server (HSS), of claim 11 , wherein the transmitter is configured to transmit the dynamic registration information to the second Serving Call Session Control Function (S-CSCF), only if following conditions are met:

registration status of the user according to the Home Subscriber Server, HSS, database indicates that the user is registered, and

in the received request the user is marked as unregistered.

13. The Home Subscriber Server (HSS), of claim 11 , further configured to update the stored dynamic registration information if updated dynamic registration information is received from the first Serving Call Session Control Function (S-CSCF), during the registration procedure of the user.

14. The Home Subscriber Server (HSS), of claim 11 , further configured to delete the stored dynamic registration information if no dynamic registration information is received from the first Serving Call Session Control Function (S-CSCF), during the registration procedure of the user.