Session initiation protocol (SIP) router

1. A computer-implemented method for processing a call, the method comprising:

receiving a SIP INVITE for an incoming call to a target mobile device;

transmitting a Send Routing Information for Short Message (SRI/SM) request to a home location register (HLR) associated with a serving switch in a circuit-switched network,

wherein the serving switch is associated with the target mobile device, and

wherein the serving switch has a different address than the target mobile device;

receiving, from the HLR, a Global Title (GT) Address that uniquely identifies the serving switch,

wherein the HLR determines the GT address of the serving switch based on the transmitted SRI/SM request without communicating with the serving switch, and without determining call forwarding information;

determining, based on the GT address of the serving switch, a second address of the serving switch; and

sending, using the second address, the SIP INVITE to a SIP interface of the serving switch for processing the incoming call to the target mobile device,

wherein the sending of the SIP INVITE to the serving switch for processing the incoming call is the first transmission to the serving switch associated with the incoming call.

2. The method of claim 1 wherein the SIP INVITE is destined for termination in a circuit-switched mobile environment.

3. The method of claim 1 wherein the incoming call is a packet-switched call that a Media Gateway Control Function (MGCF)/call server can process.

4. The method of claim 1 wherein the second address is a Fully Qualified Domain Name (FQDN).

5. The method of claim 1 wherein the second address is an IP address.

6. The method of claim 1 wherein the GT Address is part of a Signalling Connection Control Part (SCCP) address, and wherein the method further comprises translating the GT address to an IP-address equivalent code that uniquely identifies the serving switch.

7. A tangible computer-readable medium comprising computer-program instructions executable by a processor for performing operations comprising:

receiving a SIP INVITE for an incoming call to a target mobile device;

identifying a first address that uniquely identifies a serving switch in a circuit-switched network by:

transmitting a Send Routing Information for Short Message (SRI/SM) request to a home location register (HLR) associated with the serving switch; and

receiving the first address from the HLR,

wherein the HLR determines the first address of the serving switch based on the transmitted SRI/SM request without communicating with the serving switch, and without determining call forwarding information,

wherein the first address is a Global Title (GT) Address,

wherein the serving switch is associated with the target mobile device,

wherein the target mobile device is currently location-updated on the serving switch, and

wherein the serving switch has a different address than the target mobile device;

determining, based on the first address of the serving switch, a second address of the serving switch; and

sending, using the second address, the SIP INVITE to a SIP interface of the serving switch for processing the incoming call to the target mobile device,

wherein the sending of the SIP INVITE to the serving switch for processing the incoming call is the first transmission to the serving switch associated with the incoming call.

8. The tangible computer-readable medium of claim 7 wherein the SIP INVITE is destined for termination in a circuit-switched mobile environment.

9. The tangible computer-readable medium of claim 7 herein the incoming call is a packet-switched call that a Media Gateway Control Function (MGCF)/call server can process.

10. The tangible computer-readable medium of claim 7 wherein the second address is an IP address or a Fully Qualified Domain Name (FQDN).

11. An apparatus comprising:

a processor; and

a memory coupled to the processor, the memory comprising computer-executable instructions that when executed by the processor performing operations including:

receiving a SIP INVITE for an incoming call to a target mobile device;

identifying a first address that uniquely identifies a serving switch in a circuit-switched network by:

transmitting a Send Routing Information for Short Message (SRI/SM) request to a home location register (HLR) associated with the serving switch; and

receiving the first address from the HLR,

wherein the HLR determines the first address of the serving switch based on the transmitted SRI/SM request without communicating with the serving switch, and without determining call forwarding information,

wherein the first address is a Global Title (GT) Address,

wherein the serving switch is associated with the target mobile device,

wherein the target mobile device is currently location-updated on the serving switch, and

wherein the serving switch has a different address than the target mobile device;

determining, based on the first address of the serving switch, a second address of the serving switch; and

sending, using the second address, the SIP INVITE to a SIP interface of the serving switch for processing the incoming call to the target mobile device,

wherein the sending of the SIP INVITE to the serving switch for processing the incoming call is the first transmission to the serving switch associated with the incoming call.

12. The apparatus of claim 11 wherein the SIP INVITE is destined for termination in a circuit-switched mobile environment.

13. The apparatus of claim 11 herein the incoming call is a packet-switched call that a Media Gateway Control Function (MGCF)/call server can process.

14. The apparatus of claim 11 wherein the second address is an IP address or a Fully Qualified Domain Name (FQDN).