Network entity for interconnecting SIP end-points of different capabilities

1. A method for operating a Session Initiation Protocol (SIP) network entity in a communication channel between a first SIP user agent and a second SIP user agent in a packet based communication network with available a first set of communication features supported by the first SIP user agent and available a second set of communication features supported by the second SIP user agent, including at least one communication feature in the second set of communication features which is not supported by the first SIP user agent, comprising:

acting as a client application for the first SIP user agent and as a server application for the second SIP user agent; and

arranging to exchange signaling information with the first and second user agents to enable the second SIP user agent to utilize the at least one communication feature which is unsupported by the first SIP user agent during communications with the first SIP user agent.

2. The method as claimed in claim 1 , wherein a call routing addresses signaling information that is exchanged between the SIP network entity and the first and second SIP user agents or the SIP network entity and the communication network.

3. The method as claimed in claim 2 , wherein a payload routing addresses payload data received at the SIP network entity for routing to the first or second SIP user agents.

4. A network entity for operating a Session Initiation Protocol (SIP) network in a communication channel between two end points in a packet based communication network, comprising:

a first SIP user agent being a first end point and supporting a basic SIP communication feature set;

a second SIP user agent being a second end point and supporting an enhanced SIP communication feature set; and

a SIP Basic Call Enhancer located within the communication channel between the first and second SIP user agents that enables the second SIP user agent to utilize the enhanced SIP communication feature set which is unavailable to the first SIP user agent when communicating with the first SIP user agent.

5. The network entity as claimed in claim 4 , wherein the basic SIP communication feature set supports session initiation and termination.

6. The network entity as claimed in claim 4 , wherein the enhanced SIP communication feature set supports session initiation and termination, and an enhanced set of telephony features selected from the group consisting of: call waiting, call transfer, conference calling, call hold, and music on hold.

7. The network entity as claimed in claim 4 , wherein the SIP Basic Call Enhancer comprises:

a user agent server part that exchanges messages with the first SIP user agent,

a user agent client part that exchanges messages with the second SIP user agent,

a local configuration store that stores information required for the Basic Call Enhancer to route messages,

a call router that involves the first and second SIP user agents in an enhanced SIP session,

a session controller that transfers messages from the user agent server part to the call router and from the call router to the user agent client part to keep track of session states and progress, and

a payload router that manages media streams so that the Basic Call Enhancer functions as a virtual end point to both the first and second SIP user agents in respect of the media streams.

8. The network entity as claimed in claim 4 , wherein the SIP Basic Call Enhancer functions as a client application for the first end point.

9. The network entity as claimed in claim 4 , wherein the SIP Basic Call Enhancer functions as a server application for the second endpoint.