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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.

“Right now, when a videoconferencing system goes onto a VoIP network, they have to partition the network so that part of it is running H.323,” Smith says. “Then they lose all of the features and functionality they've come to enjoy with their phone system.”

But with SIP, there's no need for network partitioning. “All of the neat features in their SIP-based call manager environment can migrate into the videoconferencing world very nicely,” Smith says.

SIP also integrates more easily with IP-based PBXs. (Older PBXs that use Time Division Multiplexing, or TDM, can work with SIP with the addition of a gateway.)

“Often video systems are set up to be independent of the phone system,” says Cullen Jennings, a Cisco distinguished engineer at San Jose, CA-based networking equipment provider Cisco Systems. “But because the SIP signaling is like a normal phone call, it doesn't matter if it's an audio or video call through the PBX. There's a higher degree of being able to take advantage of the phone system.”

Keeping the legacy alive

Although SIP may be the future, it still has to respect the past. One reason is because it's not yet the dominant protocol. “SIP and H.323 started around the same time, but today 323 has a much larger installed base, at least in video,” says Sean Lessman, senior director of advanced technologies at Tandberg, a visual communications solutions provider based in New York and Oslo, Norway. “But things are moving toward SIP. We believe they'll co-exist. So all of our products will have dual stacks to share the same feature sets over both protocols.”

Gateways are one option for adding SIP and its enhanced features to an AV system where there's no business case for replacing functional equipment that uses older protocols. The gateway sits somewhere in the network or next to the legacy device and translates the SIP-based traffic into a protocol that the older device can handle. For example, MaRS uses bridges to enable collaboration with people who use H.323 equipment. “They create the value of being able to aggregate a variety of different technologies and connect people,” Smith says.

A second option is to add SIP support to the legacy device via a software upgrade. That's not always possible, however, unless the vendor designed the product to be flexible enough to handle those upgrades. In those cases, the product is essentially acting as its own gateway to handle protocol conversion.

“Occasionally you'll get a vendor that adds SIP to a product as an afterthought,” says Alan Hawrylyshen, director of VoIP Protocols at Ditech Networks, a Mountain View, CA-based manufacturer of networking products. “Underneath the skin, they're still doing things the old way. We see that all the time.”

AV vendors such as Tandberg say that they recognize the importance of such interoperability.

“The idea this year is to be as interoperable as possible with everything that's on the market,” Lessman says. “Next year, our focus will be on parity: A lot of the features we have in H.320 and H.323, we want to make sure that they're extended to the SIP side of the product, as well. The customer shouldn't care about the protocol they're running. If the feature is there in one protocol, it should be available with the others.”

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