Session Initiation Protocol (SIP) is a communication protocol widely used to initiate, control and terminate multimedia sessions over the Internet.
SIP is widely used in enterprises to power VoIP communication systems and most VoIP hardware is SIP-compatible.
In fact, any consumer or business considering VoIP calling for their needs has probably heard of it.
But what makes it so attractive? One of the biggest reasons for the popularity of SIP is the fact that it is an open project with public domain reference implementations.
It is not controlled by a single company and vendors are free to incorporate it into their devices.
Naturally, this has helped in its widespread adoption and SIP is currently the most popular protocol for implementing VoIP systems.
SIP enjoys many other advantages as well: 1.
Simple and lightweight SIP messages are small and do not require much bandwidth.
It is very easy to program and implement and is designed to work in conjunction with other protocols such as RTP.
2.
Extensible The SIP protocol is text-based and it is very easy for programmers to extend its capabilities.
It is extremely flexible so that developers can add new features while making sure that it remains compatible with earlier versions.
There are many SIP-based protocols such as XMPP and SIMPLE which bring additional functionality such as presence capabilities for instant messaging apps or VoIP systems.
3.
Security Although SIP does not provide complete end-to-end encryption, a more secure version called SIPS is commonly used (similar to HTTP and HTTPS).
SIPS mandates that every hop until the SIP endpoint has to be secured using TLS.
The media streams can also be encrypted by using SRTP instead of RTP.
4.
Scalability SIP relies on peer to peer architecture and very little modification is required to the underlying network in order to support it.
The PSTN network uses a centralized network model and the call endpoints are typically dumb units which do not have any processing capability.
The SIP protocol on the other hand distributes the call processing capabilities to the endpoints.
This makes it easy to scale communications systems to the needs of the business or consumer.
SIP can also be used to modify sessions while they are in progress so that a normal call can easily be converted into a conference call.
SIP endpoints can be any device such as a cell phone or a softphone installed on a computer.
Although it does have limitations, the protocol looks set to become the standard for multimedia implementations over the next few years.