Unified Messaging using SIP and RTSP

Traditional answering machines and voice mail services are closed systems, tightly coupled to a single end system, the local PBX or local exchange carrier. Even simple services, such as forwarding voice mail to another user outside the local system, are hard to provide. With the advent of Internet telephony, we need to provide voice and video mail services. This also offers the opportunity to address some of the shortcomings of existing voice mail systems. We list general requirements for a multimedia mail system for Internet telephony. We then propose an architecture using SIP (Session Initiation Protocol) and RTSP (Real-Time Streaming Protocol) and compare various alternative approaches to solving call forwarding, reclaiming and retrieval of messages. We also briefly describe our prototype implementation. Keywords—Voice mail, video mail, unified messaging, SIP, RTSP, Internet telephony.