Introduction to Session Initiation Protocol | SIP Protocol Introduction by Venkatesh Macha · Published March 25, 2014 · Updated February 27, 2017 Spread the love SIP Protocol : SIP protocol is an application Layer protocol, used to Establish and modify and Terminate Multimedia sessions. These sessions may be audio sessions , Video sessions, e- learning sessions,.. etc. SIP is Text-based protocol similar to HTTP. SIP was standardized by Internet Engineering Task Force(IETF). SIP also documented as RFC 3261. The main function of SIP is Establishing and maintaining and terminating calls(Multimedia sessions).