A SIP/H.323 Signaling Gateway Implementation for IP Telephony

The Internet has truly become the ubiquitous communication infrastructure, bringing many benefits to the users and making the communication over IP the predominant protocol architecture for data and multimedia transmission (Web). The regular telephone service shall, in a near future, converge to the Internet, giving place to a single integrated voice and data network. IP telephony is growing, following this expected trend, and different protocol standards, as SIP and H.323, are available for this new service. In order to guarantee interoperability and give users the freedom of choosing from equipment and applications based on these protocols, a SIP/H.323 gateway has to exist. We present the implementation of a SIP/H.323 gateway, which allows a transparent interoperation to the users. The implementation unites the two protocol stacks over a simple signaling message channel, allowing partial utilization of two existing open source codes: OpenH323 Opengatekeeper and SIP client IPTele, developed at the Helsinki University of Technology (HUT). The modular approach allows using developed modules for implementing other gateways.