The Session Initiation Protocol (SIP) owes its existence more to the telephony industry than to the computer industry. The telephony industry conceived SIP to improve the setup and handling of telephone calls, but computer technologists have been quick to adopt SIP as a protocol to simplify all forms of realtime communications. The lines of demarcation between what was once strictly telephony turf and what's now Internet-based communications are hard to distinguish.

The original drafts of what was to become the SIP standard started back in February 1996. The first Internet Engineering Task Force (IETF) draft, which was titled "draft-ietf-mmusic-sip-00," included only one request type, which was a call setup request. (By the way, mmusic isn’t the name of a new pop group but rather is an acronym for Multiparty Multimedia Session Control.) Revisions of this draft led to the publication of "draft-ietf-mmusic-sip-01" in December 1996. This draft would still be unrecognizable to most people as the precursor to SIP. Eleven versions and 3 years later, the draft took shape as the SIP with which people are now familiar. The IETF published this draft, which was called "draft-ietf-mmusic-sip-12," in January 1999. It contained the six requests that SIP has today. From "draft-ietf-mmusic-sip-12" to SIP’s publication as RFC 2543 in March 1999 was a small step.

SIP revisions have been ongoing in recent years. Perhaps more important, new working groups have been formed to exploit SIP’s potential. Most notable is the SIP for Instant Messaging and Presence Leveraging Extensions (SIMPLE) Working Group. This working group expanded the original SIP specification so that it included the delivery of Instant Messaging (IM) information through the use of the MESSAGE request. Primarily, this request is the mechanism by which the Microsoft Real Time Communications (RTC) Server provides its IM capability.