SIP

Session Initiation Protocol (SIP) was designed by Henning Schulzrinne (Columbia University) and Mark Handley (UCL) in 1996. SIP is believed to be the next logical step in internet communications and is designed to be independent of the transport layer. In essence, SIP can work on TCP (Transmission Control Protocol), UDP (User Datagram Protocol) and SCTP (Stream Control Transmission Protocol). To make this article as simple as possible and target a wider audience, the technical details will be kept to the bare minimum.

SIP is not a single protocol but instead a combination of numerous protocols that allow effective combining of voice, text and video data over a single network. Unlike ISDN, that has separate ‘channels’ for voice, video and data, SIP allows transmission of different types of data over a single internet connection. Today, one of the biggest applications of SIP is VoIP (Voice over IP) or internet telephony. Let’s assume that 4 internet users wish to enter into a voice chat online, SIP does not carry out the data transfer but actually facilitates the voice chat. SIP will initiate all the voice sessions, decide on which data transmission technique is best, and will ensure that the voice chat is carried out at optimum settings. SIP will also manage features like addition and removal of people from the conference voice chat.
It is important to note that SIP has nothing to do with the quality of the call or with the rate of data transfer, SIP is merely choosing the best way to initiate the call and ensuring that all 4 internet users involved can communicate with each other. In essence, SIP is not the internet telephony solution but a vital component of a larger internet telephony solution. What makes SIP so indispensable to video conferencing and VoIP is that SIP initiates and facilitates smooth flow of communications. Apart from the protocols mentioned in the beginning of the article, SIP can work with other internet protocols like SOAP, HTTP, XML, VXML, WSDL and UDDI.

SIP is the reason that high speed mobile technologies like 3G have come into existence. Instead, of using a separate channel for voice and data, SIP allows 3G users to make video calls, voice calls and browse the internet using the same connection. SIP has another feature that makes it indispensable to new age communications, SIP actually negotiates advanced network features like different topologies and data networks seamlessly. To put the power of SIP into perspective, SIP can actually switch a user from a 3G network to a GSM network without any user input whatsoever. In addition, SIP can also negotiate calls between a VoIP phone and a mobile phone seamlessly.

What makes SIP so powerful is that it is loosely defined, and does not require strict adherence to any single international coding standard. Also, SIP is not designed to be run on any single platform and SIP’s scalability is what makes it one of the most powerful innovations in present day internet based communication systems and the wide spread implementation of SIP is inevitable.

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Gareth Taylor is the author of this article on SIP. Find more information about SIPhere.

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