What is SIP?

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Editor/Publisher: Tony Dennis

Tone's Blog

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What is SIP (Session Initiation Protocol)?

The Session Initiation Protocol (SIP) is a text-based protocol, similar to HTTP and SMTP, for initiating interactive communication sessions between users. It has been developed under the auspices of the IETF (Internet Engineering Task Force). See Glossary. SIP sessions include voice, video, chat, interactive games, and virtual reality. SIP's main usage to date has been for Instant Messaging (IM) and 'Presence'. Plus most VoIP (Voice over IP) services utilise SIP. Presence not only includes details as to a devices location but what type of session is in progress (ie a mobile Internet session).

SIP was first developed within the Multiparty Multimedia Session Control (MMUSIC). This is particularly important since the main MIME type carried in SIP messages, the Session Description Protocol (SDP), is developed by MMUSIC and because MMUSIC is developing a successor to SDP which SIP will also use.

There's a SIPPING WG (Work Group) which is analysing the requirements for application of SIP to several different tasks, and a SIMPLE WG (Work Group), which is concentrating on using SIP for messaging and presence. AOL 's IM offering is SIMPLE (SIP for Instant Messaging and Presence Leveraging Extensions) based, for example.

Other relevant associations include the IP telephony (IPTEL) WG (Work Group), whose Call Processing Language (CPL) relates to many features of SIP; will continue to consider the requirements and specifications previously established by the PSTN and Internet Internetworking (PINT) working group;: and will consider input from the Distributed Call Signaling (DCS) Group of the PacketCable Consortium for distributed telephony services, and from 3GPP, 3GPP2, and MWIF (Mobile Wireless Internet Forum) [no Web site for MWIF] for third-generation wireless network requirements.