Session Initiation Protocol
lastmod 2024-05-31created 2021-11-102 edits
The Session Initiation Protocol (SIP) is a signaling protocol defined by the IETF that is widely used to control multimedia sessions such as voice and video calls. It is an application-layer signaling protocol that specifies the procedures by which intelligent terminals (phones, internet conferencing, instant messengers, etc.) that want to communicate over the internet identify each other, locate one another, and create, delete, or modify multimedia communication sessions between them. Here, modification means changing port addresses, inviting more participants, and adding or removing multimedia streams, and it can be applied to video conferencing, streaming video distribution, messengers, subscriber presence information, file transfer, and online games.
SIP was originally designed by Henning Schulzrinne and Mark Handley in 1996. The latest version of the specification is RFC 3261 from the IETF Network Working Group. In November 2000, SIP was adopted as the 3GPP signaling protocol and the IP Multimedia Subsystem (IMS) architecture for IP-based streaming multimedia services in cellular systems.
As a request/response architecture that controls the creation, modification, and termination of multimedia service sessions such as internet-based conferencing, telephony, voice mail, event notification, and instant messaging, it can be used over both TCP and UDP. Because it uses SIP URLs, similar to email addresses, to distinguish users, services are provided without depending on IP addresses. It is text-based, developed by reusing much of HTTP and SMTP as is, so it is easy to implement, and it has the flexibility and extensibility to create a variety of services by combining with many other protocols used on the internet. It is a simpler protocol corresponding to ITU-T's H.323. After it was proposed as RFC 2543 by the IETF MMUSIC (Multiparty Multimedia Session Control) working group in 1999, revision work proceeded in the separately split-off ITEF SIP working group, and the RFC 3261 standard was established in July 2002.