Extensions to an Internet signaling protocol to support telecommunication services

We discuss extensions to the session initiation protocol (SIP) to enable a rich set of services between the cellular public switched telephone network (PSTN) and the Internet. We consider all manner of cellular endpoints, 2G, 2.5G, and early 3G endpoints. These extensions allow the PSTN endpoints to act as smart SIP user agents and participate in Internet-oriented services, such as presence and instant messaging (IM), without the endpoint itself being connected to the Internet. For cellular networks, our methodology conserves precious radio spectrum by offloading such data services from the bandwidth normally allocated to voice. Our approach is based on open standards and is not an ad-hoc or incremental solution.