The Ovum View: SIP sets the web generation talking

Session initiation protocol (SIP) promises to turn the internet we know today into a fully-fledged multimedia communications network, says John Delaney, senior analyst at Ovum.

You've taken delivery of the little yellow sports car you ordered all those months ago and you're on the phone to your friend Dave, telling him about it. The mag wheel trims are like nothing you've seen before but you're having trouble describing them. So you take some pictures of them with the phone's integrated camera and send it to Dave.

"Wow, they look fantastic," says Dave when the pictures arrive on his phone two seconds later. "We have to show them to Jeff."

You check Jeff's status on your friends list and he's available for calls, so you click on his name to set up a three-way conference. When he answers, you send him the pictures and the three of you spend the next 15 minutes discussing the car.

When your monthly bill arrives it shows a single session comprising a five-minute phone call, a 15-minute three-way conference and three photo messages.

Sound far-fetched? This kind of spontaneous, everyday multimedia conferencing is some way off - but the basic technology needed to support it exists today and it's starting to be used in live carrier networks. Session initiation protocol (SIP) is the key.

Among the growing number of people interested in using the internet to carry phone calls, the Internet Engineering Task Force's SIP has long been recognised as a slimmer, smarter way to do IP telephony.

The existing IP telephony standard, H.323, a product of the International Telecommunications Union (ITU), is cumbersome, hard to program and even harder to scale up to the millions of users that real phone networks have to support.

By contrast, SIP is based on hypertext transfer protocol (HTTP), one of the technologies that underpin the web - and familiar to an enormous community of programmers worldwide.

SIP takes a minimalist approach, confining itself to the basic functions of setting up, controlling and tearing down communications sessions over the web. What those sessions are, and how they behave, is determined by SIP extensions, which are service application programs that use the basic functions provided by SIP to deliver a wide variety of communications services.

This extensible design makes SIP much more flexible and scalable than H.323. There's nothing in the protocol that dictates the nature of a SIP session. It could be a two-way phone call, a multi-party phone call, or a real-time videoconference and it could change from one to another of these types on the fly.

The purpose of H.323 is to get the internet to behave like a telephone network - but to SIP's developers this is like looking through the wrong end of a telescope. The basic purpose of SIP is to enrich web services with communications capabilities, rather than simply offering a new way to build a telephone network.

These can range from simple point applications - such as clicking on an address book entry to set up a phone call - through to complex enterprise services like a web-enabled call centre suite.

Complete IP telephony solutions based on SIP are still rare but an increasing number of carriers are investigating the use of SIP as an access protocol. Several large carriers have announced live network deployments of SIP, most notably Level 3, Sonera, Telia and WorldCom.

Specialist service providers are also using SIP to add value to carriers' basic access products. Players such as Estara, GoBeam, Telverse and Vonage are offering services including: ad hoc and multimedia conferencing, unified communications, desktop call management, virtual IP-based private branch exchanges (PBXes), intelligent connection, and web-enabled call centres.

There are still some issues holding SIP back, including lack of support for some of the phone network's features and billing interfaces - and the fact that many enterprise firewalls block the traffic streams that SIP generates.

The highest hurdle to jump is the fact that not many end users have SIP devices yet. This is set to change as SIP phones and PBXs aimed at business users are now coming onto the market, both from specialists like Pingtel and from heavyweights like Avaya and Cisco.

In the consumer market, Microsoft has just put its weight behind SIP. Windows XP incorporates SIP for use in real-time conferencing, application sharing and online collaboration. This move has caused excitement in some quarters over the coming proliferation of SIP endpoints and unease in others - with suspicions that Microsoft may be aiming to build up a new line of business as a communications service provider.

But Microsoft's game plan aside, if you're using Windows XP, then you're using a SIP client - and pretty soon, millions of people will be doing just that. And that's when things will start to get really interesting.

For further information see Ovum's advisory service: IP-Services@Ovum or the Ovum report Softswitches: The Keys to the Next-generation IP Network Opportunity. Or email: info@ovum.com

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