Location-based S-CSCF selection in an IMS network

1. A method implemented on an interrogating call session control function (I-CSCF) server, the method comprising:

receiving a request to register a user equipment (UE) to use an IP multimedia service, the request including geographic information of the UE;

determining, based at least in part on the geographic information, that the UE is located in a first region;

determining, based at least in part on the request, that the UE is previously registered through a different region;

comparing an authorized S-CSCF server associated with the previous registration of the UE with a set of S-CSCF servers located in the first region; and

determining, based on the comparing, that there is no match between the authorized S-CSCF server and the set of S-CSCF servers;

based on determining that there is no match, disregarding the authorized S-CSCF and determining a serving call session control function (S-CSCF) server from the set of S-CSCF servers to provide the IP multimedia service to the UE; and

registering the UE on the S-CSCF server.

2. The method of claim 1 , wherein determining the S-CSCF server from the set of S-CSCF servers to provide the IP multimedia service to the UE further comprises: querying a domain name server (DNS) for the S-CSCF server located in the first region.

3. The method of claim 1 , further comprising:

retrieving, from the request, an identifier related to the previous registration of the UE, wherein the identifier includes one of an evolved universal mobile telecommunications system terrestrial radio access (EUTRA) cell global identity (CGI) or a new radio (NR) CGI.

4. The method of claim 3 , wherein determining, based at least in part on the request, that the UE is previously registered through the different region further comprises:

comparing, as a comparison, the identifier with a set of identifiers associated with the first region; and

determining, based on the comparison, that there is no match between the identifier and the set of identifiers.

5. The method of claim 1 , further comprising:

querying a home subscriber server (HSS) for the authorized S-CSCF server; and

receiving, from the HSS, a response including information of the authorized S-CSCF server.

6. The method of claim 1 , further comprising:

sending a second request to the authorized S-CSCF server, the second request causing a de-registration of the UE from the authorized S-CSCF server.

7. The method of claim 1 , wherein the first region is one of a plurality of regions in an IP multimedia subsystem (IMS) network.

8. The method of claim 1 , further comprising:

determining, from the set of S-CSCF servers located in the first region, the S-CSCF server based at least in part on respective capabilities of the set of S-CSCF servers.

9. A server comprising:

one or more processors, and

a non-transitory memory storing instructions executed by the one or more processors to perform actions including:

receiving a request to register a user equipment (UE) to use an IP multimedia service, the request including geographic information of the UE;

determining, based at least in part on the geographic information, that the UE is located in a first region;

determining, based at least in part on the request, that the UE is previously registered through a different region;

comparing an authorized S-CSCF server associated with the previous registration of the UE with a set of S-CSCF servers located in the first region; and

determining, based on the comparing, that there is no match between the authorized S-CSCF server and the set of S-CSCF servers;

based on determining that there is no match, disregarding the authorized S-CSCF and determining a serving call session control function (S-CSCF) server of the set of S-CSCF servers to provide the IP multimedia service to the UE; and

registering the UE on the S-CSCF server.

10. The server of claim 9 , wherein the instructions are executed by the processor to further perform actions including:

querying a domain name server (DNS) for the S-CSCF server located in the first region.

11. The server of claim 9 , wherein the instructions are executed by the processor to further perform actions including: retrieving, from the request, an identifier identity related to the previous registration of the UE, wherein the identifier includes one of an evolved universal mobile telecommunications system terrestrial radio access (EUTRA) cell global identity (CGI) or a new radio (NR) CGI.

12. The server of claim 11 , wherein the instructions are executed by the processor to further perform actions including:

comparing, as a comparison, the identifier with a set of identifiers associated with the first region; and

determining, based on the comparison, that there is no match between the identifier and the set of identifiers.

13. The server of claim 9 , wherein the instructions are executed by the processor to further perform actions including:

querying a home subscriber server (HSS) for the authorized S-CSCF server; and

receiving, from the HSS, a response including information of the authorized S-CSCF server.

14. The server of claim 9 , wherein the instructions are executed by the processor to further perform actions including:

sending a second request to the authorized S-CSCF server, the second request causing a de-registration of the UE from the authorized S-CSCF server.

15. One or more non-transitory computer-readable storage media storing computer-readable instructions, that when executed by one or more processors, cause the one or more processors to perform actions comprising:

receiving a request to register a user equipment (UE) to use an IP multimedia service, the request including geographic information of the UE;

determining, based at least in part on the geographic information, that the UE is located in a first region;

determining, based at least in part on the request, that the UE is previously registered through a different region;

comparing an authorized S-CSCF server associated with the previous registration of the UE with a set of S-CSCF servers located in the first region; and

determining, based on the comparing, that there is no match between the authorized S-CSCF server and the set of S-CSCF servers;

based on determining that there is no match, disregarding the authorized S-CSCF and determining a serving call session control function (S-CSCF) server of the set of S-CSCF servers to provide the IP multimedia service to the UE; and

registering the UE on the S-CSCF server.

16. The one or more non-transitory computer-readable storage media of claim 15 , wherein the instructions are executed by the one or more processors to further perform actions including:

querying a domain name server (DNS) for the S-CSCF server located in the first region.

17. The one or more non-transitory computer-readable storage media of claim 15 , wherein the instructions are executed by the one or more processors to further perform actions including:

retrieving, from the request, an identifier identity related to the previous registration of the UE, wherein the identifier includes one of an evolved universal mobile telecommunications system terrestrial radio access (EUTRA) cell global identity (CGI) or a new radio (NR) CGI

comparing, as a comparison, the identifier identity with a set of identifiers associated with the first region; and

determining, based on the comparison, that there is no match between the identifier and the set of identifiers.

18. The one or more non-transitory computer-readable storage media of claim 15 , wherein the instructions are executed by the one or more processors to further perform actions including:

querying a home subscriber server (HSS) for the authorized S-CSCF server;

receiving, from the HSS, a response including information of the authorized S-CSCF server.