The IMS: IP Multimedia Concepts And Services, Second Edition

12.1. Background

SIP is an application layer protocol that is used for establishing, modifying and terminating multimedia sessions in an Internet Protocol (IP) network. It is part of the multimedia architecture whose protocols are continuously being standardized by the Internet Engineering Task Force (IETF). Its applications include, but are not limited to, voice, video, gaming, messaging, call control and presence.

The idea of a session signalling protocol over IP dates back to 1992 where multicast conferencing was being considered. SIP itself originated in late 1996 as a component of the IETF Mbone (multicast backbone), an experimental multicast network on top of the public Internet. It was used by IETF for the distribution of multimedia content, including IETF meetings, seminars and conferences. Due to its simplicity and extensibility, SIP was later adopted as a Voice over IP (VoIP) signalling protocol, finally becoming an IETF-proposed standard in 1999 as [RFC2543]. SIP was further enhanced to take into account interoperability issues, better design and new features. The actual document was re-written entirely for clarity. The protocol remains mostly backward compatible with [RFC2543]. This newly created document became the proposed standard as [RFC3261] in 2002, making [RFC2543] obsolete.