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Understanding SIP

Initiation is SIP's middle name ? it's also what AV pros can expect to go through over the next few years.

Rob Smith and his colleagues had a clean slate and some simple goals: Design a state-of-the-art AV system that would allow entrepreneurs at a Canadian innovation center to collaborate effortlessly with everything from videoconferencing to virtual whiteboards. For the foundation, they chose Session Initiation Protocol (SIP), a communication standard that's increasingly common in the telecom world but a newcomer in pro AV.

“Our whole telecom infrastructure is also SIP-compliant,” says Smith, technology consultant for the MaRS Discovery District, whose Collaboration Centre opened in downtown Toronto in May 2005. “So now we're able to connect what would be the traditional AV world, which usually sits on one side of the fence, and telecom, which sits on the other side.”

For example, MaRS' offices are equipped with a variety of SIP-equipped endpoints, including desk phones and PCs. These endpoints interact with a variety of MaRS infrastructure, including presence servers — which track a person's whereabouts and the capabilities of the office they're in at that particular moment — and its Private Branch Exchange (PBX), which routes phone calls.

“When your phone rings, a little window will pop up on your screen,” Smith says. “If that person happens to be ‘on network,' you now have the opportunity to do instant collaboration using tools such as whiteboarding or desktop sharing. You can do instant videoconferencing.”

Plays well with others

SIP started showing up in videoconferencing endpoints more than a year ago but currently isn't as widely used as incumbent protocols such as H.323, which is the most common IP-videoconferencing standard. But based on AV vendors' product roadmaps and on the positive experiences of early adopters such as MaRS, SIP is a protocol that most AV pros will have to master sooner or later.

Robert Smith, technology consultant for MaRS Discovery District, Toronto, sets up a multipoint videoconference using SIP endpoints in conjunction with the MaRS Discovery District's Tandberg MPS 800 Multipoint Control Unit (MCU).Photo by Christie Spicoluk

Developed by the Internet Engineering Task Force (IETF), SIP's primary function is to broker communications between devices, including instant messaging (IM), voice over IP (VoIP) phone calls, and videoconferences. Those communications can be between just two devices or between multiple ones, such as a media server feeding video to a mall's digital signage.

“It's very computer-network-focused as opposed to telecom-network-focused,” says Jim Smith, a systems engineer with Polycom, a Pleasanton, CA-based maker of conferencing equipment. “Its goal is to allow smart devices to talk to each other rather than trying to network together dumb devices.”

For integrators, one benefit is that SIP allows videoconferencing to interact with firewalls in a way that's less likely to violate a company's IT-security policies. Trying to accommodate those policies with older protocols can affect the user experience.

“H.323 requires certain firewall ports to be open and says that traffic has to pass a particular way: Voice has to go on one port, data on another, and video on another,” says Smith, whose company has been selling SIP-equipped videoconferencing gear for more than a year. “You end up with all these strange interactions that can make for an unpleasant conferencing experience.”

Another benefit is that SIP can reduce videoconferencing's impact on an enterprise's telephone system, particularly those that use VoIP.

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