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Optical/IP

Circuit Switching is Back

NEW YORK—Just when it looked as though circuit switching was on its deathbed, it’s being resurrected in a different form by a bunch of optical networking startups.

The new incarnation of circuit switching—Dynamic synchronous Transfer Mode (DTM)—is radically different from the technology used in today’s telephone networks. It provides a way of automatically setting up and tearing down circuits of up to 1-Gbit/s capacity over carrier backbones, on demand. And that promises to give carriers a way of building backbones that will handle all types of traffic, including video, while enabling them to guarantee service quality.

The downside of DTM is that it’s all or nothing. Edge equipment may be temporarily bolted out of the network if traffic exceeds capacity—forcing it to keep trying to set up a circuit until it gets through. In similar circumstances, router networks would still accept traffic, even though quality would suffer.

Two Swedish startups, Dynarc AB (http://www.dynarc.com) and Net Insight AB (http://www.netinsight.net) have been shipping DTM products for a couple of years. Now some American startups are allegedly following suit:

An anonymous source has told Light Reading that Cyras Systems Inc. (http://www.cyras.com) is using DTM in its products, though the vendor declined to comment.

And Alidian Networks Inc. (http://www.alidian.com) has already announced “Optical Service Network” developments that are “DTM-like” according to a competitor. Alidian, however, says “it’s absolutely not DTM” but declines to elaborate. (The company was founded by Dave Newman, who led development of the Accelar IP switch/router at Bay Networks.)

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