The Tool That Sees Around Corners


Innovation can happen in
the strangest places. Latest
example: a tool built from a
tangent of the DOCSIS cablemodem
specification, which
lets cable operators find, map
and fix network problems —
before they affect consumers.

Up until now, technicians
could see “green-yellow-red”
notifications about network
impairments, but not their
precise location. (Squirrels and rats don’t typically tweet
their whereabouts when chewing through wires.)

The source of the invention are the “pre-equalization”
techniques within the DOCSIS specification (versions 1.1
and above), which anticipate and correct distortions between
cable modems and the headend.

Turns out those same distortion “signatures” can be
mined to triangulate where a problem is. On a map. Which
makes this a tool that can see around corners.

Or, in tech terms, it means that every fielded cable modem
becomes a network analyzer, a tool that goes for about
$10K otherwise.

I saw the invention in action last week, when an engineering
pal at Comcast (we’ll call him Larry, because that’s his
name) showed me, on my New York-situated laptop screen,
that the cable modems in my Denver office were working
just fine. All green.

He then switched the screen to show the diagnostics
from his house — an older home, with older wiring. Uh-oh:
yellow lights. Why? Larry’s modem’s upstream transmit levels
were huffing and puffing, trying to push the data through
the aged wires.

That tool designed for customer-care people — plus
one tailored to line techs and another that shows network
health, by region — are all built on top of a foundational tool
Comcast calls the “network scout.” (Internally, it also goes
by “flux capacitor.”)

Next, Larry showed me a “ripple,” shorthand for a microreflection caused by an impedance mismatch. (Those happen
when connectors aren’t connected right, or when coax
gets kinked or squished.)

And then — poof! — he overlaid the ripple data onto a
network map, showing major plant components (nodes, amplifiers). From there, he overlaid a street map, with the precise
location of the fault.

The scout tool stems from a CableLabs effort called “Proactive
Network Maintenance,” which was “productized” by
Comcast. (Cox Communications, Charter Communications
and others built or are building versions, too.)

Anything that can see around corners is spooky, in my
book. Fixing problems before they occur? Spooky-cool.

Stumped by gibberish? Visit Leslie Ellis at or