SIP is defined in RFC 2543 (March 99) of the MMUSIC (Multiparty Multimedia Session Control) working group of the IETF.
The MMUSIC working group is focused on loosely coupled conferences as they exist today on the MBONE (see Chapter 8 for additional details on the MBONE) and is working on a complete framework based on the following protocols:
The Session Description Protocol (SDP) and the Session Announcement Protocol (SAP);
The Real-Time Stream protocol (RTSP) to control real-time data servers;
The Simple Conference Control Protocol (SCCP) for tightly coupled conferences. This work has just begun with the definition of a message bus between conferencing systems;
So far ...