Session Initiation Protocol is an IETF draft for managing the handshake procedures for beginning and ending IP communications between end points.
SIP is a text-based protocol, similar to HTTP and SMTP, for initiating interactive communication sessions between users. Such sessions are designed to include voice, video, chat, interactive games, and virtual reality.The important protocol, Session Initiation Protocol (SIP), has quickly developed substantial industry infrastructure to encourage and promote its use.
The IETF has chartered the Session Initiation Protocol (SIP) working group to continue the development of SIP, currently specified as proposed standard RFC 2543. SIP originated as a development of the MMUSIC Multiparty Multimedia Session Control workgroup, and maintains active communications with MMUSIC. That’s because the main MIME (Multipart Internet Mail Extension) type carried in SIP messages, the Session Description Protocol which is specified in RFC 2327 was developed by MMUSIC and they are also developing a successor to SDP which SIP will also use. For such a simple protocol, SIP relies or influences a huge chunk of the work of the IETF. There are 131 SIP-related IETF drafts. By comparison, other IETF protocols, such as AS2 (Applicability Statement 2), which is Electronic Data Interchange over the Internet (EDIINT) have only ten.
Also while the SIP working group takes care of the IETF standardization processes, a related, interoperability, implementation & promotion body, the SIP Forum has complementary responsibilities.