Englewood, Colo. -- Tele-Communications Inc.'s
engineering brain trust detailed a new optical-networking plan last week that will wring
more capacity out of existing fiber while dramatically lowering costs associated with
electronics maintenance.
In what TCI's senior engineers called "invisible
hubs," the MSO is using dense-wave-division multiplexing to take the next step beyond
the massive headend-consolidation projects that were conducted last year.
During a briefing at TCI's headquarters here last
week, the executives described their aggressive plans to deploy DWDM in 14 major markets,
representing 100 communities, starting this month. Doing the briefing were Tony Werner,
executive vice president of engineering and technology operations, and Oleh Sniezko, vice
president of engineering.
Some of the markets targeted for DWDM include: Seattle, the
San Francisco Bay area, Denver, Dallas, St. Louis, Chicago, Pittsburgh and Portland, Ore.
The plan, already proven in one TCI system, is to increase
by eightfold the downstream capacity of its already-installed fiber optic cable, while
providing a nearly limitless amount of network capacity for advanced services.
In all cases, the move will lessen the amount of physical
space needed in "secondary hubs" that branch out from TCI's main headends.
In some cases, entire buildings -- some as large as 1,000 square feet -- won't be
needed, since the use of DWDM trims the physical-space requirement to that of a small,
node-sized cabinet.
"This is a going-forward story," Werner said.
Sniezko launched the effort last summer, when he embarked
on a search for a technological solution that would minimize the electronics-maintenance
needs in the secondary hubs of one of the MSO's systems.
Sniezko contacted several vendors to assist in the design
process, and he wound up working closely with Antec Corp.'s Antec Network
Technologies and with Harmonic Lightwaves Inc. on the project.
What they came up with was a scheme that links primary
headends to secondary hubs in the downstream direction using 8-DWDM. This means that eight
separate optical wavelengths, or colors of light, can carry information on one piece of
dual-mode, 1310/1550-nanometer glass.
For the upstream path, TCI and its vendor partners used
4-WDM, Sniezko said. Ultimately, 4-DWDM in the 5- to 40-megahertz upstream path could
increase the skinny 35 MHz of bandwidth in that spectral area to 200 MHz, he said.
The system is practically a passive optical network, with
amplification via erbium-doped fiber amplifiers placed at the invisible hub, which also
improves overall system reliability, Sniezko added.
So far, the use of DWDM techniques in cable systems has
been mostly limited to experimentation, because it was deemed too expensive to deploy
widely.
But recently, the cost of DWDM components has dropped
dramatically, Sniezko said.
"The capacity is larger, the cost is heading toward
better and you save all of the money in real estate," Sniezko said. "And the
biggest bonus is that you have this simplistic site that is totally transparent at either
end."
Werner said lasers, which are priced on a per-milliwatt
basis, have dropped from $1,000 per milliwatt a few years ago to under $200, and prices
are still falling.
Plus, each wavelength can hold as many as 10 QAM
(quadrature-amplitude-modulation) channels in the downstream direction, making it
expandable for new services.
Also, key pieces of electronics equipment -- like
cable-modem-termination systems and caching and proxy servers -- can be moved higher up
into the network, Werner said.
But the project wasn't without its technical hurdles.
Sniezko said the most challenging aspect was the minimization of second-order distortions,
like chromatic dispersion, which are caused by laser chirp.
"We believe that we're the most aggressive [cable
operator] doing this," Werner said.
Executives with Antec and Harmonic agreed, but they said
the technology is well-suited for other MSOs, as well. Both vendors plan to bring products
to market at next month's National Show that have their roots in TCI's design.
"It's a very innovative sort of way [to design a
network]," said John Trail, project manager of transmission systems for Harmonic.
Trail said Harmonic's version of invisible-hubs-based
DWDM "is working in the lab now," and field trials are anticipated.
Jack Bryant, division president of Antec Network
Technologies, said that prior to being contacted by TCI, he had considered DWDM as
"something to watch from a research-and-design perspective." He said the TCI
project, presented to Antec in September, "put it on the front burner for us."
Once commercially available, DWDM and invisible hubs will
have "real broad appeal, domestically and internationally," Bryant said.
Antec also plans to detail its new optical-networking
products at next month's National Show.
