Comcast Corp. has become the second major MSO to deploy a
dense-wave-division-multiplexing solution for boosting transmission capacity on fiber from
an upgraded system's hubs to its headends.
The installation of Harmonic Lightwaves Inc.'s
"METROLink" system in a portion of Comcast's recently upgraded Sarasota,
Fla., market represents a much more limited deployment than Harmonic's initial
rollout in several markets with Tele-Communications Inc.
But the vendor said landing another big fish is a strong
signal that more MSOs may be accepting DWDM solutions as they look for cost-effective ways
to create the capacity needed to offer more bandwidth-demanding enhanced services.
"The drivers for that are Internet access and things
like digital video -- mainly on the forward path, but also on the return path for things
like VOD [video-on-demand]," said Colin Boyd, Harmonic's vice president of North
American sales and worldwide marketing. "DWDM makes for more efficient uses of
As deployed for Comcast, the METROLink system provides an
eight-wavelength digital transmission over 1550-nanometer fiber, enabling the operator to
provide its directed services from the headend, instead of from its hubs.
Harmonic said DWDM solutions are relatively more expensive
than some fiber-enhancing alternatives such as radio-frequency stacking, but DWDM provides
better transmission performance, while enabling operators to locate complex equipment
needed for services such as Internet access at the headend.
Requiring minimal equipment at the hub, in turn, cuts real
estate costs -- equipment can be housed in a cabinet, rather than in a building -- and
lowers maintenance expenses by making equipment accessible to technicians who are already
at the headend.
"It can tolerate more ingress noise, while still
maintaining a good bit-error rate on the return," said John Trail, Harmonic's
director of product-line management for transmission systems. "And if you can pull
equipment back to the headend, that's a big advantage."
Harmonic, General Instrument Corp., Scientific-Atlanta
Inc., ADC Telecommunications Inc., Antec Corp. and other vendors began rolling out DWDM
products for the cable industry last year, citing the technology's cost advantage
compared with the expense of adding more fiber where capacity became an issue.
They also pointed to TCI's announcement last year of
its strategy of using DWDM solutions in 14 of its major markets as the means for boosting
capacity and cutting its electronics-maintenance costs.
Boyd said TCI has deployed DWDM technology at about 30 hubs
so far, for eight-wavelength transmission on both the forward and return paths.