Columbia University
Columbia University: Session Initiation Protocol (Sip)
This is a very complete, academic site covering the SIP protocol. Find out an overview of the topic, news, features, grammar, implementations, service providers and more.
Wikimedia
Wikipedia: Session Initiation Protocol (Sip)
An introduction to Session Initiation Protocol (SIP)that involves multimedia elements such as video, voice, instant messaging, online games, and virtual reality. It is one of the leading signaling protocols for Voice over IP.