Method and apparatus for completing a circuit switched service call in an internet protocol network

A non-transitory computer-readable medium storing a plurality of instructions which, when executed by a processor of a serving-call session control function, cause the processor to perform operations for processing a session request in an internet protocol network, the operations comprising:

• receiving the session request from a calling party to a called party, wherein the called party uses a registered user endpoint device;
• querying a telephone numbering mapping server for the called party of the session request for a naming authority pointer resource record associated with the called party, wherein the naming authority pointer resource record comprises a session initiation protocol universal resource identifier and a telephone universal resource identifier;
• processing the session request using the session initiation protocol universal resource identifier, wherein the session initiation protocol universal resource identifier returned in the naming authority pointer resource record associated with the called party is received from the telephone numbering mapping server;
• determining whether the processing of the session request using the session initiation protocol universal resource identifier resulted in a successful call completion;
• and
• processing the session request using the telephone universal resource identifier, when the processing of the session request using the session initiation protocol universal resource identifier resulted in an unsuccessful call completion.

An apparatus for processing a session request in an Internet protocol network, the apparatus comprising:

• a processor of a serving-call session control function;
• and
• a computer-readable medium storing a plurality of instructions which, when executed by the processor, cause the processor to perform operations, the operations comprising:
• receiving the session request from a calling party to a called party, wherein the called party uses a registered user endpoint device;
• querying a telephone numbering mapping server for the called party of the session request for a naming authority pointer resource record associated with the called party, wherein the naming authority pointer resource record comprises a session initiation protocol universal resource identifier and a telephone universal resource identifier;
• processing the session request using the session initiation protocol universal resource identifier, wherein the session initiation protocol universal resource identifier returned in the naming authority pointer resource record associated with the called party is received from the telephone numbering mapping server;
• determining whether the processing of the session request using the session initiation protocol universal resource identifier resulted in a successful call completion;
• and
• processing the session request using the telephone universal resource identifier, when the processing of the session request using the session initiation protocol universal resource identifier resulted in an unsuccessful call completion.