System and method for providing user mobility handling in a network telephony system

1. A method for providing user mobility handling in a network telephony system, comprising in combination:

receiving a register request from a network entity on a first domain, wherein the register request includes a user identifier, and wherein the user identifier is associated with a second domain;

modifying the register request to form a modified register request, wherein the modified register request includes a modified user identifier, and wherein the modified user identifier is associated with the first domain;

updating a registration database associated with the first domain to include the modified user identifier;

transmitting the modified register request via a network to a network telephony server on the second domain;

receiving a register response via the network from the network telephony server on the second domain, wherein the register response includes a challenge;

transmitting the register response to the network entity on the first domain;

receiving a challenge response from the network entity on the first domain;

transmitting the challenge response via the network to the network telephony server on the second domain; and

determining whether a confirmation is received from the network telephony server on the second domain.

2. A computer readable medium containing instructions to cause a processor to assist in carrying out the method of claim 1 .

3. The method of claim 1 , further comprising deleting the modified user identifier from the registration database, upon determining that the confirmation is not received.

4. The method of claim 1 , wherein the network telephony server updates a registration database associated with the second domain to include the modified user identifier.

5. The method of claim 1 , wherein the register request, the modified register request, and the challenge response are Session Initiation Protocol (SIP) register requests, wherein the register response is a SIP 401 Unauthorized message, and wherein the confirmation is a SIP 200 OK message.

6. The method of claim 1 , wherein the network entity on the first domain is selected from the group consisting of a network phone, a wireless base station, and a computer.

7. The method of claim 1 , wherein the user identifier and the modified user identifier are Universal Resource Indicators according to the Session Initiation Protocol.

8. The method of claim 1 , wherein the registration database is maintained by a registration server, and wherein updating the registration database includes instructing the registration server to modify the registration database.

9. The method of claim 1 , wherein the data network is the Internet.

10. The method of claim 1 , wherein the network telephony server on the second domain is selected from the group consisting of a registration server and a proxy server.

11. The method of claim 1 , wherein transmitting the modified register request includes transmitting the modified register request to an intermediate clearinghouse proxy server.

12. The method of claim 1 , wherein the challenge and the challenge response compose an authentication process.

13. The method of claim 1 , wherein the challenge response includes a password encrypted according to the challenge.

14. A method for providing user mobility handling at a first network telephony server, wherein the first network telephony server is operable to implement at least a portion of the Session Initiation Protocol, comprising in combination:

receiving a register request from a network entity on a first domain, wherein the register request includes a user identifier in a To field and an address associated with the network entity in a Contact field, and wherein the user identifier is associated with a second domain;

modifying the register request to form a modified register request so that the Contact field includes a modified user identifier, wherein the modified user identifier is associated with the first domain;

updating a registration database to include the modified user identifier;

transmitting the modified register request via a network to a second network telephony server on the second domain;

receiving an unauthorized response via the network from the second network telephony server, wherein the unauthorized response includes a challenge;

transmitting the unauthorized response to the network entity;

receiving a register response from the network entity, wherein the register response includes the user identifier in a To field and the address associated with the network entity in a Contact field, and wherein the register response includes a challenge response;

modifying the register response to form a modified register response so that the Contact field includes the modified user identifier;

transmitting the modified register response via the network to the second network telephony server;

determining whether a confirmation is received from the second network telephony server; and

deleting the modified user identifier from the registration database in response to determining that the confirmation is not received.

15. A computer readable medium containing instructions to cause a processor to assist in carrying out the method of claim 14 .

16. The method of claim 14 , wherein the first network telephony server is a proxy server.

17. The method of claim 15 , wherein the network entity is selected from the group consisting of a network phone, a wireless base station, and a computer.

18. The method of claim 14 , wherein the address associated with the network entity includes a username associated with a user of the network entity and a network address of the network entity, wherein the user identifier is a Universal Resource Indicator including the username and a domain address of the second domain, and wherein the modified user identifier includes the username, at least a portion of the domain address of the second domain, and a domain address of the first domain.