ABSTRACT
The Session Initiation Protocol (SIP) emerged in the mid-1990s from the research of Henning Schulzrinne, associate professor in the Department of Computer Science at Columbia University, and his team. A coauthor of the Real-Time Transport Protocol (RTP) for transmitting real-time data via the Internet, Schulzrinne also co-wrote the Real-Time Streaming Protocol (RTSP), a proposed standard for controlling streaming audiovisual content over the web. Schulzrinne’s intent was to define a standard for Multiparty Multimedia Session Control (MMUSIC). In 1996, he submitted a draft to the Internet Engineering Task Force (IETF) that contained the key elements of SIP. In 1999, he removed extraneous components regarding media content in a new submission, and the IETF issued the first SIP specifications, RFC 2543 (Handley et al. 1999). While some vendors expressed concerned that protocols such as H.323 (ITU 2009) and Gateway Control Protocol (GCP) could jeopardize their investments in SIP services, the IETF continued its work and issued SIP specifications (RFC 3261; Rosenberg et al. 2002) in 2001. The advent of RFC 3261 signaled that the fundamentals of SIP were in place. Since then, enhancements to security and authentication, among other areas, have been issued in several additional RFCs. RFC 3262 (Rosenberg and Schulzrinne 2002b), for example, governs the reliability of provisional responses. RFC 3263 (Rosenberg, and Schulzrinne 2002c) establishes rules to locate SIP proxy servers. RFC 3264 (Rosenberg and Schulzrinne 2002a) provides an offer–answer model, and RFC 3265 (Roach 2002) determines specific event notification.
