Session Initiation Protocol
The Session Initiation Protocol (SIP) is a signaling protocol used to establish, modify, and tear-down communication sessions in an IP network. These sessions can be as simple as a two-way voice call or as involved as a multi-party web conference complete with audio, video, and a shared whiteboard application.
SIP was modeled after the way we access web pages on the Internet. We launch a web browser and navigate to a web server by way of an address that begins with “http.” HTTP, or Hypertext Transfer Protocol, allows the web browser to download and display text, images, links, and anything else a web page might contain. With SIP, we connect to a SIP device to obtain a real-time media stream. Since SIP is media independent, it can be used to establish sessions of nearly any media type imaginable. As communications move beyond that of a simple phone call, SIP is fully equipped to support any and all media (voice, video, instant message, SMS text, etc.) that might come along.
Built into SIP is the notion of session description which allows SIP to establish a session independent of the underlying media stream. This allows for session escalation whereby a user might start communicating with an instant message and then later on add voice, file transfer, or multi-party video. A user would no longer be required to launch separate calls to communicate in these different ways. SIP allows a single application the ability to support communications of all different types with the flexibility to move smoothly between each one.
SIP is perfect for dealing with the explosion of consumer-grade communications devices that are making their way into our lives. Imagine a world where your personal iPhone or iPad can be securely integrated into your communications system. With SIP that world exists and solutions are available today.
With the explosion of communications interfaces, a user might employ numerous different devices throughout the day. For instance, the manager of a sales department will typically have an office phone, a cell phone, a soft phone (a computer phone such as Avaya’s One-X Communicator or Microsoft’s OCS or Lync clients), and an instant messaging client. With SIP, a single application can manage that user’s devices along with the presence status generated by those devices (e.g. on a call, in an instant messaging session, etc.) . This user centric model is a break from the device centric model where each device is treated as a separate entity with no particular connection to its owner.
As digital technology in the 1980’s revolutionized the PBX, SIP is transforming the way we communicate in the new millennium. SIP allows us to untether ourselves from the confines of voice and its limitations. As communications devices become more sophisticated and the expectations of the user base more demanding, SIP has become the only protocol that can deliver on the promise of truly unified communications.