TABLE OF CONTENTS Many consider the Session Initiation Protocol (SIP) a powerful alternative to H.323. They claim that SIP is a more flexible solution, simpler than H.323, easier to implement, better suited to the support of intelligent user devices, and better suited to the implementation of advanced features. These factors are of major importance to any equipment vendor or network operator. Simplicity means that products and advanced services can be developed faster and made available to subscribers sooner. The features themselves mean that operators are better able to attract and retain customers, and they also offer the potential for new revenue streams.
SIP is designed to be a part of the overall Internet Engineering Task Force (IETF) multimedia data and control architecture. As such, SIP is used in conjunction with several other IETF protocols such as the Session Description Protocol (SDP), the Real-Time Streaming Protocol (RTSP), and the Session Announcement Protocol (SAP).
Originally developed in the Multiparty Multimedia Session Control (MMUSIC) working group of the IETF, great interest in SIP led to the creation of a separate SIP working group. SIP was defined in Request for Comments (RFC) 2543, which has seen a number of revisions as the specification has proceeded from proposed standard status towards draft standard status. The number of proposed enhancements to SIP as it proceeds along the standards track is one indication of the attention it has received. Many developers are including SIP in their products without waiting...
