What is SIP (Session Initiation Protocol)?

SIP is the abbreviation for Session Initiation Protocol. This is a signaling protocol for IP telephony that is used to establish, modify and terminate VoIP telephone calls. SIP was developed and standardized in RFC 3261 by IETF (Internet Engineering Task Force).

SIP makes it possible to establish a phone call by describing the communication that is needed for this purpose. You can find more information about this process in the What is SDP article.


Figure 1 - The communication channel of a SIP system

In the world of VoIP, the SIP made revolutional changes. This protocol is similar to the HTTP protocol: it is text based, and very opened and flexible. Due to this, SIP protocol has largely replaced the H323 standard.

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