Denver -- Com21 Inc. last week described a way to
selectably deliver multiple upstream data streams traveling on hybrid fiber-coaxial
At a briefing here, Com21's vice president of
marketing, Buck Gee, said its new "return-path multiplexer" solves upstream
noise funneling and "dramatically reduces" headend capital investments for data
The approach will also help operators to fire up an entire
market area for data services, and not just go neighborhood by neighborhood, Gee said.
Gee noted that some MSOs have found that even though their
networks are two-way-active, their headend data receivers -- regardless of manufacturer --
can only handle so many incoming upstream channels. That, in turn, can make for steep
By deploying the RPM -- essentially, a high-speed switch
with protocol-control software -- operators can cleanly combine up to 96 return-path
channels, Gee said.
Operators familiar with the RPM said they liked the
"This addresses the problem of reverse-path
scaling," said Tom Jokerst, senior vice president of engineering for Charter
Communications Inc. "If you want to do broad-based marketing ... you quickly get into
an area where you're supporting more [headend] equipment than you have actual
That's because most upstream lasers top out at a
multiplexing level of about four to eight upstream signals before they become inadequate.
So a 200,000-homes-passed network with nodes configured to serve 1,000 homes could, at
best, anticipate 50 upstream channels, at 4-to-1, combining at the laser.
Without an RPM, and with most headend data receivers
designed to accept around six upstream channels, that translates into a need for about
eight controller-receiver boxes in the headend.
"In order not to go broke and run out of headend space
buying data receivers, this is a great option," Jokerst said.
Dan Pike, vice president of science and technology for
Prime Cable, said that as traffic loads increase, techniques like Com21's RPM will
become more commonplace.
The RPM uses "intelligent multiplexing" that
allows signals to talk to the headend receiver one return path at a time. By doing that,
any noise from the other return-path channels is blocked at the RPM, Gee said. When a
signal needs to move from a node to the headend receiver, the RPM opens an RF switch that
lets data pass.
Gee said Com21 plans to demonstrate the RPM, which is
priced at $9,500, at the National Show next month. Field trials are planned for early this
summer, probably in Charter's Pasadena, Calif., system.