Session initiation protocol (sip) router

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

• receiving a SIP INVITE for an incoming call to a target mobile device;
• identifying a first address of a serving switch, associated with the target mobile device, 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;
• 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.

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 of a serving switch, associated with the target mobile device, 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;
• 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.

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 of a serving switch, associated with the target mobile device, 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;
• 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.