Methods to route a bearer via circuit switching to an internet protocol multimedia system node using session initiation protocol contact header

A method of setting up a bearer over a circuit switched network, comprising:

• a user equipment sending a session initiation protocol (SIP) INVITE message that contains a uniform resource identifier (URI) of a called party, wherein the SIP INVITE message is sent to an application server;
• the user equipment receiving a SIP response message related to the SIP INVITE message, wherein the SIP response message has a contact header that contains a digit string provided by the application server, the contact header indicating a reason identifying the purpose for providing the digit string to the user equipment;
• the user equipment analyzing the contact header of the SIP response message to determine a digit sequence associated with the called party;
• and
• the user equipment sending a call set-up message for setting up the bearer over the circuit switched network using the digit sequence.

A user equipment (UE), comprising:

• a component configured to:
• transmit a session initiation protocol (SIP) INVITE message containing a uniform resource identifier (URI) of a called party and that identifies that a bearer for a call to the called party is to be set-up at least partially over a circuit switched domain, wherein the SIP INVITE message is sent to an application server,
• receive a SIP informational response message having a contact header that contains information based on a digit string provided by the application server, the contact header indicating a reason identifying the purpose for providing the information based on the digit string,
• analyze the information contained in the contact header based on the digit string to determine one of an E.164 number and a private number plan (PNP) number associated with the called party, and
• transmit a call set-up message to a mobile switching center (MSC), the call set-up message containing the one of the E.164 number and the PNP number,
• wherein the UE promotes setting-up a bearer over the circuit switched domain.

A server, comprising:

• a component to:
• receive a first session initiation protocol (SIP) INVITE message that contains a uniform resource identifier (URI) of a called party and that identifies that a bearer for a call to the called party is to be set-up at least in part over a circuit switched domain, wherein the first SIP INVITE message is sent by a user equipment
• determine one of an E.164 number and a private number plan (PNP) number associated with the URI of the called party,
• send a SIP informational response message having a contact header that contains information based on the one of the E.164 number and the PNP number, wherein the contact header indicates a reason identifying to the user equipment the purpose for providing the one of the E.164 number and the PNP number,
• receive a second SIP INVITE message that contains the information based on the one of the E.164 number and the PNP number, and
• complete call set-up between the user equipment and the called party in response to using the information based on the one of the E.164 number and the PNP number to associate the second SIP INVITE message with the first SIP INVITE message.