Session Initiation Protocol enabling an impressive array of communications and collaboration.

In technology jargon, a “killer app” is an application so useful that it quickly becomes almost impossible to live without. Spreadsheets, e-mail and Web browsers are all examples.

Now it appears we have a legitimate “killer protocol.”

The Session Initiation Protocol (SIP) is a signaling protocol used for establishing communications in an IP network. That definition may sound unremarkable, but SIP has in fact taken the world by storm. Not only is it now the pervasive standard in voice over IP telephony, but SIP has become an essential enabler of seamless multimedia applications like IP voice/video conferencing, instant messaging and gaming. It is seen as the base protocol for the ongoing development of so-called “next-generation networks” that will offer an immense range of services over converged voice, video, data and mobile networks.

Gaining Momentum

ABI Research predicts SIP services will become the norm after 2010 and will rapidly begin to dominate the world’s telecom markets. The firm says almost half of all telecom users will be using at least one SIP-based service by 2012 — and more likely will be using an array of SIP-enabled services from multiple devices to communicate across the Web and between private and public networks. These services include presence, click-to-dial, buddy lists, e-mail and Web access.

The firm predicts SIP will generate more than $150 billion in service revenue annually by 2012, with cumulative infrastructure capital expenditure of more than $10 billion by that date.

Why all the fuss over a protocol? After all, it is merely an agreed-upon method of communicating between two computer systems. It simply enables different types of devices such as computers, handheld gadgets and telephones to “talk” with each other seamlessly in an IP network.

Protocol Evolution

To understand why SIP has captured so much attention, it helps to understand the shortcomings of its predecessor, the H.323 suite of protocols. Like SIP, H.323 is a signaling protocol that establishes, modifies and terminates multimedia sessions between two or more points. H.323 was designed initially for videoconferencing and LAN telephony in carrier networks, so it leans toward a telco way of doing things.

In dialing numbers, for example, H.323 has to account for the varied sequences of numbers for international calls. H.323 basically has to discover and acknowledge the entire network before completing a call, so setting up a single call requires literally dozens of messages to traverse between clients, causing significant delay. Setting up multiple users compounds the problem, leading to scalability issues.

In contrast, SIP is an elegantly simple technology — it is easy to configure and it works well in different architectures and deployment scenarios. Perhaps most important, SIP is extremely Web friendly. It closely resembles HTTP and SMTP, the two Internet protocols that drive the Web and e-mail. Using SIP, telephony literally becomes yet another Web application.

“The sheer simplicity and flexibility of SIP makes it particularly easy for service developers to work with,” said Margaret Hopkins, author of a recent SIP study for telecom consultant Analysys. “As a result, we believe SIP will form the basis of many low-cost value-added services provided over the public switched telephone network and Internet protocol infrastructure.”

More Than Telephony

Because SIP is an Internet Engineering Task Force (IETF) protocol, it is inherently an open architecture — which is a big reason most major communications equipment manufacturers and software companies are embracing it. Cisco Systems and other manufacturers of IP public branch exchange (PBX) equipment are putting SIP into that hardware, while media gateway makers are adding it to network cores. Microsoft, Yahoo! and America Online have made SIP a part of instant messaging sessions. It was long ago incorporated into 3G mobile standards.

Although SIP is used to enable IP telephony, it is not merely a software-based telephony switch — it is capable of much more than that. SIP treats voice as just another medium, albeit a very important one. It is quickly becoming the backbone protocol for numerous personal and enterprise communications by enabling fixed and mobile phones to interoperate with Internet services like e-mail, the Web, instant messaging and multimedia collaboration.

SIP isn’t perfect, however. Several security issues have come to light in the past few months. For example, it has been demonstrated that a personal computer with an SIP-based softphone can be compromised with a buffer overflow attack. Cisco recently issued a security response confirming multiple SIP vulnerabilities in the Cisco 7960 IP Phones. But most experts say such incidents only reveal the need for vigilant security and are not fatal flaws to the technology.

The market has welcomed SIP. It has emerged as the de facto standard for enabling converged voice and data applications in telecommunications. More than that, it enables organizations to tie together diverse multimedia and collaboration applications into a single platform. Such a platform offers the ability to improve business objectives by speeding decision-making, shortening response times to customers and partners, and increasing employee productivity. SIP may be a simple protocol, but it has profound implications.

Learn more about Abba's converged communications services.

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