An Internet protocol used to:

• Set up a multimedia session
• Modify a multimedia session
• Tear down a multimedia session
• Request and deliver presence and instant messages

A protocol to establish media sessions between two end points.

SIP is an Internet protocol designed by IETF as part of the Internet Multimedia Conferencing Architecture to manage call sessions. SIP is used to set up, modify, and tear down multimedia sessions and to request and deliver presence of users and to send instant messages between users. SIP works with other Internet protocols such as Internet Protocol (IP), Domain Name Service (DNS), Transmission Control Protocol (TCP), and User Datagram Protocol (UDP). SIP was modeled after two of the most prevalent and successful protocols on the internet, HTTP and SMTP. From HTTP, SIP borrowed the client-server model and the usage of URLs and URIs. From SMTP (Simple Mail Transfer Protocol), SIP borrowed a text-encoding scheme and the header style.

An application layer protocol that is independent of content protocols and uses network layer protocols such as TCP/IP and UDP.

The SIP protocol became a standard in March 1999 and was published as RFC 2543. RFC 3261 contained bug fixes and clarification to SIP.