Activating the reverse path for two-way services like
high-speed data and telephony will pick up momentum this summer, as MSOs across the
country free up the funds that are necessary to complete critical upstream projects.
The subject is clearly an important one for network
operators, both from a training stance and a deployment stance. At next week's
Society of Cable Telecommunications Engineers Cable Tec-Expo in Denver, for example,
several return-path technical and training sessions are scheduled so that the
industry's hands-on technical ranks can learn and compare notes on the subject.
And most of the top five MSOs now frequently discuss their
two-way plans as a regular part of their prepared briefings to financial analysts and
The upshot: Between 40 percent and 65 percent of U.S. plant
will be outfitted to carry two-way services this year, if the predictions of
Tele-Communications Inc., Time Warner Cable, Cox Communications Inc., Comcast Corp. and
MediaOne are aggregated and averaged.
Kinetic Strategies Inc., a Scottsdale, Ariz.-based
analytical firm focused on broadband data, predicted that 10 million homes will be
actively passing two-way signals and ready for high-speed-data services by year end, said
its president, Michael Harris.
"That's definitely a number that makes you pick
whether the glass is half-full or half-empty," Harris said, putting himself in the
half-full category. "Operators are moving along at a decent clip" with respect
to two-way activations, he added.
TCI will take the largest leap, agreeing to dramatically
boost its two-way-project load this year. Instead of outfitting 500,000 homes with two-way
plant, as originally planned, TCI now intends to install reverse amplifiers in plant
serving 3.9 million homes, said Tony Werner, executive vice president of engineering for
TCI, during a recent briefing.
"It's a heavy pull this year," Werner said
of the plans, explaining TCI's desire to prepare more of its metro properties for the
@Home Network service.
Plus, he said, a continued aggressive rollout of digital
television is also triggering the need for two-way because of the operational
inefficiencies of installing telephone jacks in homes for upstream signaling.
Other MSOs are similarly ambitious. MediaOne said 30
percent of its plant is already available for two-way services, and it is aiming for 60
percent by the end of this year.
Time Warner Cable was at "a little over 50
percent" of two-way readiness, or about 9 million homes passed, by the end of last
year, said James Chiddix, chief technical officer for the MSO. That number will grow by
another 3 million homes per year through the end of the century.
"We're still planning to be completed [with
hybrid fiber-coaxial two-way upgrades] by the year 2000," Chiddix said.
And smaller MSOs are just as busy. Ken Wright, chief
technical officer for InterMedia Partners, which has been actively clustering its systems
in the Southeast, said just under one-half of its plant was two-way active by the end of
"And by the end of next year, we'll be at the 90
percent mark," he added.
Most engineers said last year went well in terms of two-way
upgrades, because extensive testing allowed them to focus on how to find and correct the
myriad problems lurking in the 5- to 40-megahertz reverse path.
"There was a time when people were saying that [the
reverse path] wouldn't work, but that was wishful thinking on their part,"
Werner said. "It's going to take attention, but it's not rocket science, by
The use of the upstream-signal path is key to the
performance of interactive video, telephony and high-speed-data services. But the upstream
has always been problematic because the 5- to 40-MHz chunk of spectrum reserved for
home-to-headend transmissions is highly susceptible to "ingress" noise -- when
signals leak into the upstream path -- and to electrical spikes known as "impulse
noise" that happen when in-home appliances, from hair dryers to furnaces, kick on.
A 73-page document now exists, written by both MSO and
vendor executives, that outlines the most common and most obscure problems that can
strangle upstream communications, according to Dick Shimp, director of technical marketing
for ComSonics Inc. and chairman of the National Cable Television Association's
Engineering Committee's Recommended Practices subcommittee.
What does it take to activate the upstream path? The short
answer: installing reverse modules into plant amplifiers, carefully balancing the system
and, in some cases, placing filters onto or near homes.
Engineers are still at odds about the best ways to overcome
electrical noise and signal leakage into the upstream spectrum. Some advocated the use of
band-stop filters, which are used on homes that don't subscribe to two-way services
so that any noise originating in those homes doesn't leak into the upstream network.
Another option is the band-pass filter, which is designed
for use on homes that subscribe to two-way services. A band-pass filter works by trapping
any noise or signal leakage in the home, while passing on some upstream signals that are
critical to the two-way application.
Still other engineers are adamant that pristine plant is
the best cure.
And yet another option is a technique known as
"reverse equalization," where loss is added selectively in the reverse plant so
that the transmit levels from all homes are roughly the same and set at the maximum
MSOs familiar with two-way activation said that nowadays,
return-path activations are reaching a manageable gait, because technical staffers
organized into "two-way teams" are becoming more and more comfortable with the