By 1996, the Internet Engineering Task Force (IETF) had already developed the basics for multimedia on the Internet (see Chapter 14, “SIP Conferencing”) in the Multi-Party, Multimedia Working Group. Two proposals, the Simple Conference Invitation Protocol (SCIP) by Henning Schulzrinne and the Session Initiation Protocol (SIP) by Mark Handley, were announced and later merged to form Session Initiation Protocol.
The new protocol also preserved the HTTP orientation from the initial SCIP proposal that later proved to be crucial to the merging of IP communications on the Internet. Schulzrinne focused on the continuing development of SIP with the objective of “re-engineering the telephone system from ground up,” an “opportunity that appears only once in 100 years,” as we heard him argue at a time when few believed this was practical.
SIP was initially approved as RFC  number 2543 in the IETF in March 1999. Because of the tremendous interest and the increasing number of contributions to SIP, a separate SIP Working Group (WG) was formed in September 1999. The SIP for Instant Messaging and Presence Leveraging (SIMPLE) was formed in March 2001, followed by SIPPING for applications and their extensions in 2002.
The specific needs of SIP developers and service providers have led to an increasing number of new working groups. This very large body of work attests both to the creativity of the Internet communications engineering community, and also to the vigor of the newly created industry. We will shorten the narrative on the history of SIP by listing the related working groups (WG) in chronological order in Table 1.2.
We have listed for simplicity the year of the first RFC published by the WG, though the WG was sometimes formed one to two years earlier. Years denote a new WG that has not yet produced any RFC.