Patent ID: 8472376

Claim:
A method of operating a communication system comprising an Internet Protocol Multimedia Subsystem (IMS) network, the method comprising: interposing a terminal agent between a plurality of Session Initiation Protocol (SIP) User Agents and a Serving Call/Session Control Function (S-CSCF) of the IMS network; registering a contact address of the terminal agent with the S-CSCF on behalf of the SIP User Agents; emulating by the terminal agent, a single SIP User Agent to the S-CSCF; receiving a SIP REGISTER message in the IMS network from a given SIP User Agent; and in response to receipt of the SIP REGISTER message, selectively delegating Home SIP Registrar functions for the given SIP User Agent to allow the terminal agent to perform IMS network registrations and de-registrations on behalf of the given SIP User Agent, wherein the Home SIP Registrar functions are selectively delegated based upon Initial Filter Criteria (IFC) obtained by the S-CSCF for a user.