What is SIP?

Session Initiation Protocol (SIP) is one of the most common protocols used in VoIP technology. It is an application layer protocol that works in conjunction with other application layer protocols to control multimedia communication sessions over the Internet.

VoIP Technology

Before moving further, let us first understand a few points about VoIP.
  • VOIP is a technology that allows you to deliver voice and multimedia (videos, pictures) content over the Internet. It is one of the cheapest way to communicate anytime, anywhere with the Internet’s availability.
  • Some advantages of VOIP include:
    • Low cost
    • Portability
    • No extra cables
    • Flexibility
    • Video conferencing
  • For a VOIP call, all that you need is a computer/laptop/mobile with internet connectivity. The following figure depicts how a VoIP call takes place.


With this much fundamental, let us get back to SIP.

SIP – Overview

Given below are a few points to note about SIP:
  • SIP is a signalling protocol used to create, modify, and terminate a multimedia session over the Internet Protocol. A session is nothing but a simple call between two endpoints. An endpoint can be a smartphone, a laptop, or any device that can receive and transmit multimedia content over the Internet.
  • SIP is an application layer protocol defined by IETF (Internet Engineering Task Force) standard. It is defined in RFC 3261.
  • SIP is incorporated with two widely used internet protocols: HTTP for web browser and SMTP used for email. From HTTP, SIP borrowed the client-server architecture and the use of URL and URI. From SMTP, it borrowed a text encoding scheme and a header style.
  • SIP takes the help of SDP (Session Description Protocol) which describes a session and RTP (Real Time Transport Protocol) used for delivering voice and video over IP network.
  • SIP can be used for two-party (unicast) or multiparty (multicast) sessions.
  • Other SIP applications include file transfer, instant messaging, video conferencing, online games, and steaming multimedia distribution.
Source – Tutorials Point

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