Session Initiation Protocol
No discussion about IP telephony is complete without covering the Session Initiation Protocol (SIP). SIP is a signaling protocol used to establish sessions in an IP network. A session can be something as complex as a collaborative voice/video/data conversation, or something as simple as a phone call. The IPT market has adopted SIP as the protocol of choice for long-term strategic direction. As of this writing, SIP remains a draft from the Internet Engineering Task Force, which is the organization responsible for developing and administering the methodology driving Internet communications. To this extent, SIP is still evolving as the IPT market matures.
SIP is important because it is simple and straightforward, and it is designed to do one thing: establish/set up sessions. SIP doesn't need to know all the variant details of a session—it just establishes the session, modifies the session, or releases the session.
SIP inherently uses other existing protocols, which means that it does not try to do everything. SIP has a role and it is designed to play that role specifically. So, by working with other protocols and not forcing additional functionality into SIP itself, this is a protocol that scales extremely well. Being modeled after HTTP and SMTP, SIP is compatible with other web-based applications.
The ability to establish these sessions enables a myriad of innovative capabilities or services. Capabilities such as web page click-to-dial, instant messaging with buddy lists, and video-embedded text are examples of functionality SIP can be expected to provide cost-effectively to the market.
The real win for companies, however, is going to be choice. That is the reason for discussing SIP in lieu of other potential protocols. Adherence to the SIP standard by manufacturers will mean a new level of choice for organizations when it comes to telephony devices. It will enable a company to deploy any number of clients it chooses from any manufacturer that has adopted SIP, knowing full well that the clients will work properly and can be managed from the same platform.
Consider a typical IP network with infrastructure equipment such as switches and routers that can be implemented from a number of manufacturers. In your own network, you might see any number of clients, ranging from IBM personal computers, to Dell servers, to Toshiba laptops—all from different manufacturers running on the same network. This is the promise of SIP. Upon being ratified by the standards bodies, SIP promises a similar environment where companies have a wider range of choices for their desktop IP telephony devices, regardless of which manufacturers' product was selected for call-control.
Finally, SIP is expected to create a host of new companies that can provide applications, devices (clients), and management capabilities without regard to manufacturer, which can benefit the entire market.
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