Call charging notification

1. A communication system for providing charging information of a call established over a data network, the system comprising:

a user agent configured to initiate a call to another user agent according to a Session Initiation Protocol; and

a network element configured to assist in establishing the call and to forward the charging information indicating that the call is chargeable according to the Session Initiation Protocol, the charging information being forwarded to the user agent.

2. A system according to claim 1 , wherein the user agent provides at least one of a visual indicator and an audio indicator based on the forwarded charging information.

3. A system according to claim 1 , wherein the charging information is provided prior to completion of the call.

4. A system according to claim 1 , wherein the charging information is provided before the establishment of the call.

5. A method for providing charging information of a call established over a data network, the method comprising:

establishing a call between a user agent and another user agent according to a Session Initiation Protocol; and

forwarding the charging information to the user agent according to the Session Initiation Protocol, the charging information indicating that the call is chargeable to the user agent.

6. A method according to claim 5 , wherein the user agent in the forwarding step provides at least one of a visual indicator and an audio indicator based on the forwarded charging information.

7. A method according to claim 5 , wherein the charging information in the forwarding step is provided prior to completion of the call.

8. A method according to claim 5 , wherein the charging information in the forwarding step is provided before the establishment of the call.

9. A communication system for providing charging information of a call established over a data network, the system comprising:

means for establishing a call between a user agent and another user agent according to a Session Initiation Protocol; and

means for forwarding the charging information to the user agent according to the Session Initiation Protocol, the charging information indicating that the call is chargeable to the user agent.

10. A system according to claim 9 , wherein the user agent provides at least one of a visual indicator and an audio indicator based on the forwarded charging information.

11. A system according to claim 9 , wherein the charging information is provided prior to completion of the call.

12. A system according to claim 9 , wherein the charging information in the forwarding step is provided before the establishment of the call.

13. A network apparatus for providing charging information of a call established over a data network, the apparatus comprising:

a communications interface configured to receive a message from a user agent to establish a call to another user agent according to a Session Initiation Protocol; and

a processor coupled to the communications interface and configured to instruct the communications interface to forward the charging information to the user agent according to the Session Initiation Protocol, the charging information indicating that the call is chargeable to the user agent.

14. An apparatus according to claim 13 , wherein the user agent provides at least one of a visual indicator and an audio indicator based on the forwarded charging information.

15. An apparatus according to claim 13 , wherein the charging information is provided prior to completion of the call.

16. An apparatus according to claim 13 , wherein the charging information is provided before the establishment of the call.

17. A computer-readable medium carrying one or more sequences of one or more instructions for providing charging information of a call established over a data network, the one or more sequences of one or more instructions including instructions which, when executed by one or more processors, cause the one or more processors to perform the steps of:

establishing a call between a user agent and another user agent according to a Session Initiation Protocol; and

forwarding the charging information to the user agent according to the Session Initiation Protocol, the charging information indicating that the call is chargeable to the user agent.

18. A computer-readable medium according to claim 17 , wherein the user agent in the forwarding step provides at least one of a visual indicator and an audio indicator based on the forwarded charging information.

19. A computer-readable medium according to claim 17 , wherein the charging information in the forwarding step is provided prior to completion of the call.

20. A computer-readable medium according to claim 17 , wherein the charging information in the forwarding step is provided before the establishment of the call.

21. A method for supporting charging of a Session Initiation Protocol (SIP) call, the method comprising:

receiving a message from a source device, the message requesting establishment of the SIP call with a destination device; and

transmitting a provisional response message, according to the Session Initiation Protocol (SIP), to the source device, wherein the provisional response message notifies the source device that the SIP call has a charge applicable to the source device.

22. A method according to claim 21 , further comprising:

receiving an options message requesting charging information associated with the SIP call, wherein the charging information corresponds to a most economical one of a plurality of paths to the destination device over the data network; and

establishing the SIP call with the destination device using the one path.

23. A method according to claim 21 , further comprising:

establishing the SIP call with the destination device if the source device acknowledges that the charge is acceptable.