Corvis goes the distance

Last week, Corvis announced that Williams Communications Group has successfully tested its ultralong-haul transport equipment, using it to transmit optical signals over 6,400 kilometers without electrical regeneration.

"It's a major milestone for the industry because it allows carriers to offer all-optical networks that span coast to coast," says Chris Nicoll, vice president of Current Analysis, in Corvis' release.

What's more, it doubles the distance Williams claimed in an earlier field trial with Corvis. Like the earlier field trial, the one announced last week uses the CorWave family of products, which are based on Raman amplification.

The fact that the trial was carried out on installed fiber is significant. In laboratory experiments it's possible to select and tweak the properties of every inch of fiber in the setup for best results. That's obviously not practicable in a real-world network.

However, it's worth noting that the trial did not run over just any old fiber. Instead, it was conducted over a portion of what Williams calls its Multi-Service Broadband Network; a network that Williams appears to have built specifically to be compatible with Corvis equipment.

The question is whether other carriers will have the same success using the equipment over their installed networks.

Corvis says the answer is yes -- and that its products are compatible with all fiber types, although newer fibers will give better results.

However, the age of the installed fiber is not the only parameter to take into account when engineering a network. Bandwidth, speed, fiber type and amplifier spacing all need to be considered. "Williams, Broadwing and Qwest have networks that are optimized to bring in ultralong-haul capabilities," a source inside Corvis says. Specifically, the amplifier spacing is slightly shorter in their networks than is standard, he adds.

The upshot seems to be that while Corvis can eliminate costly optical-electrical-optical conversion inside regenerators, it does so at the expense of needing additional amplifier points in the network. That's necessary to make sure the signal is always stronger than the noise introduced by the amplifiers.

And because regeneration is expensive, reducing the number of times this needs to be done is a big plus and that it is hoped it will lower costs for end users.

Details of the bandwidth per channel, number of channels and speed were not given. Williams says merely that it used "multiple channels." Corvis declined to comment.

It would be useful to know these details because it would provide more insight into the trade-offs among bandwidth, speed and distance. On its Web site, Corvis notes that whether carriers use 2.5G or 10G bit/sec, the CorWave system still tops out at the same aggregate capacity: 400G bit/sec. But since these numbers are based on a system that's billed as going 3,200 km, it's not clear if the same capacity can be achieved with a 6,400-km system.

Corvis does say that it will be possible to combine new developments - namely, the launch next quarter of a product based on the soliton technology it acquired from Algety - with CorWave to sidestep these trade-offs and boost capacity significantly.

This story, "Corvis goes the distance " was originally published by Network World.

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