System and method for providing early ringback by a home legacy mobile station domain network

1 . A method of providing call progress to a calling party, comprising:

receiving a circuit-switched call origination message in a home legacy mobile station domain, wherein circuit-switched the call origination message specifies a destination terminal device having a directory number assigned with the home legacy mobile station domain;

identifying a serving legacy mobile station domain in which the terminal device is registered;

transmitting, from the home legacy mobile station domain to the serving legacy mobile station domain, a call origination message that requests the terminal device to a call with the calling party;

receiving, by the home legacy mobile station domain from the serving legacy mobile station domain, a first message that requests the home legacy mobile station domain to provide a call progress signal to the calling party; and

providing, by the home legacy mobile station domain, a first call progress signal to the calling party.

2 . The method of claim 1 , wherein receiving the circuit-switched call origination message comprises receiving an Integrated Services User Part call origination message.

3 . The method of claim 1 , wherein transmitting the call origination message comprises transmitting a session initiation protocol INVITE message that allows for encapsulation of Integrated Services User Part information.

4 . The method of claim 1 , wherein receiving the first message comprises receiving a Session Initiation Protocol 180 Ringing provisional response message.

5 . The method of claim 1 , further comprising receiving, by the home legacy mobile station domain from the serving legacy mobile station domain, a second message providing a request for the home legacy mobile station domain to discontinue the first call progress signal, wherein the serving legacy mobile station domain sends the second message after receiving a paging response from the terminal device.

6 . The method of claim 5 , wherein receiving the second message comprises receiving a session initiation protocol provisional response message.

7 . The method of claim 6 , further comprising providing, by the serving legacy mobile station domain, a second call progress signal to the calling party after the home legacy mobile station domain discontinues the first call progress signal.

8 . A computer-readable medium having computer-executable instructions for execution by a processing system, the computer-executable instructions for performing a method of providing call progress to a calling party, comprising:

instructions for interpreting a circuit-switched call origination message in a home legacy mobile station domain, wherein the circuit-switched call origination message specifies a destination terminal device having a directory number assigned to the home legacy mobile station domain;

instructions for identifying a serving legacy mobile station domain in which the terminal device is registered;

instructions for constructing and transmitting, from the home legacy mobile station domain to the serving legacy mobile station domain, a call origination message that requests the terminal device to join a call with the calling party;

instructions for receiving, by the home legacy mobile station domain from the serving legacy mobile station domain, a first message that requests the home legacy mobile station domain to provide a call progress signal to the calling party; and

instructions for providing, by the home legacy mobile station domain, a first call progress signal to the calling party.

9 . The computer-readable medium of claim 8 , wherein the instructions for interpreting a circuit-switched call origination message comprise instructions for interpreting an Integrated Services User Part call origination message.

10 . The computer-readable medium of claim 8 , wherein the instructions for constructing and transmitting the call origination message comprise instructions for constructing and transmitting a session initiation protocol INVITE message that allows for encapsulation of Integrated Services User Part information.

11 . The computer-readable medium of claim 8 , wherein the instructions for receiving the first message comprise instructions that receive a session initiation protocol 180 Ringing provisional response message.

12 . The computer-readable medium of claim 8 , further comprising instructions for receiving and interpreting, by the home legacy mobile station domain from the serving legacy mobile station domain, a second message providing a request for the home legacy mobile station domain to discontinue the first call progress signal, wherein the serving legacy mobile station domain sends the second message after receiving a paging response from the terminal device.

13 . The computer-readable medium of claim 12 , wherein the instructions for receiving and interpreting the second message comprise instructions that receive and interpret a Session Initiation Protocol provisional response message.

14 . The computer-readable medium of claim 13 , further comprising instructions for providing, by the serving legacy mobile station domain, a second call progress signal to the calling party after the home legacy mobile station domain discontinues the first call progress signal.

15 . A telecommunications system for connecting a circuit-switched calling party and a terminal device registered in a legacy mobile station domain, comprising:

a serving legacy mobile station domain in which the terminal device is registered; and

a home legacy mobile station domain having a directory number of the terminal device assigned thereto that receives a circuit-switched call origination message from the calling party and transmits a call origination message to the serving legacy mobile station domain that requests the terminal device to join a call with the calling party and that, in response to receipt of a first message from the serving legacy mobile station domain that requests the home legacy mobile station to provide call progress to the calling party, provides a first call progress signal to the calling party.

16 . The telecommunications system of claim 15 , wherein the circuit-switched call origination message comprises an Integrated Services User Part call origination message.

17 . The telecommunications system of claim 15 , wherein the call origination message transmitted from the home legacy mobile station domain to the serving legacy mobile station domain comprises a Session Initiation Protocol INVITE message.

18 . The telecommunications system of claim 15 , wherein the serving legacy mobile station domain comprises a serving mobile switching center emulation and the home legacy mobile station domain comprises a home mobile switching center emulation, and wherein the serving mobile switching center emulation transmits a second message to the home mobile switching center emulation that provides a request for the home legacy mobile station domain to discontinue the first call progress signal provided to the calling party.

19 . The telecommunications system of claim 18 , wherein the second message comprises a session initiation protocol provisional response message.

20 . The telecommunications system of claim 18 , wherein the serving legacy mobile station domain provides a second call progress signal to the calling party responsive to the home legacy mobile station domain discontinuing the first call progress signal.