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DWDM ready for cable's prime time

Thu, 04/30/1998 - 8:00pm
Roger Brown, Editor

Technological advancements and cost reductions in optical dense wavelength division multiplexing technology are causing cable operators to re-examine their fiber optic architectures, and are giving them an opportunity to increase bandwidth while lowering system maintenance costs.

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TCI's new fiber optic architecture.

A case in point is cable giant Tele-Communications Inc., which last month unveiled a new approach its engineering executives have dubbed the "invisible hub" concept. By using DWDM in the 1550 nm window, TCI says it can significantly reduce the physical size of its hub sites, reduce the number of active components and convert some locations from manned to unmanned facilities.

In fact, TCI Executive VP of Engineering and Technology Operations Tony Werner and VP of Engineering Oleh Sniezko are so convinced that the approach will work, they've adopted it for all their major-market rebuilds. "We believe we're the most aggressive (deployer of DWDM equipment) on the cable side," said Werner during a briefing at TCI headquarters in late March.

DWDM equipment is already being deployed in some of TCI's largest markets, and plans call for gear to be used in 14 different major markets that cover roughly 100 communities, said Werner. Those markets include: Seattle, Denver, Dallas, St. Louis, San Francisco, Chicago, Pittsburgh and Portland, Ore., he added.

The new architecture uses eight densely-packed waves of light over a single fiber to send signals in the downstream, and four for the upstream return path. Equipment from Harmonic Lightwaves and Antec (both of whom will be showing the technology at this month's National Cable Show in Atlanta) is being used for the rebuilds.

Werner and Sniezko hatched the new architecture after determining that the physical size of some fiber cables — as well as the "secondary hubs" they feed — had simply grown too large. After investigating the costs of DWDM technology and comparing it to other approaches such as frequency stacking, and Sonet-based solutions, the two engineers decided the time was right to adopt DWDM.

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Network capacity per home passed

Sniezko, who won the 1997 Polaris Award for fiber innovation, says DWDM technology is already "at cost parity today and headed (lower)" than traditional analog 1310 electronics. So, by spending the same amount of money, TCI gets similar performance, much more capacity, a simpler hub site and perhaps millions of dollars in real estate savings. In fact, Werner projects that real estate and rent savings could be on the order of $6 to $7 per home passed.

Other considerations that TCI considers bonuses are the system's scalability and the fact that cable modem equipment, such as caching and proxy servers, can be moved back to the primary hub, which means they can be amortized over a larger number of subscribers. And because each of the eight optical wavelengths can accommodate up to 10 QAM digital video channels, TCI immediately can send 80 channels in the downstream direction. Should the day come when that's not enough, a relatively simple electronics change-out will provide even more capacity.

What made it all possible was the steep drop in laser costs. Werner says that over the years, laser costs have gone from about $1,000 per milliWatt of power to less than $200 per mW. DWDM technology is on a similar cost curve, driven by large deployments by the long-haul telecommunications carriers who are adopting the technology.

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