How DOCSIS Plays Plug-and-Play

As the dance between cable and consumer-electronics companies quickens, so does the gathering of the number of gadgets that might include the arrangement of circuits and software we've all come to know as a cable modem.

More specifically, we've come to know this cable modem by its strained, industrial acronym: "DOCSIS," for Data Over Cable Service Interface Specification.

It starts with the cable modem inside the digital set-top, or the digital TV that has a built-in set-top.

It daydreams more widely: Recordable DVD players, digital video recorders, or media centers that link all the entertainment-oriented devices, and all the pictures on all the memory sticks, in the house.

In these musings, the inclusion of a DOCSIS modem is an inextricable point of conversation, especially among the people at work on the "hows" of things.

Not just a modem

Stop. If you're like me, your brain probably already took you to a very specific place when it processed the word — because let's face it, it has become a word — "DOCSIS." It whisked you off to imagine those gathering gadgets. All contained an embedded, very fast, always on, cable-delivered, broadband Internet connection.


Partly. It turns out that DOCSIS also shows strong colors as an extra signal path for the "boring work stuff" of two-way cable communications. Moving a click to the Internet, or a packet full of interactive guide data, or a software download, requires a fast, unclogged passageway.

Many technologists see DOCSIS as a natural for that passageway, especially for the devices that spill from the "plug-and-play" agreement between cable and consumer-electronics companies.

Put another way: If you were to play a game of word association with a coworker right now, chances are unmistakably high that if you said "DOCSIS," they'd say "cable modem," and then "Internet."

Yet, knowing DOCSIS only as a means to rocket people around the Internet is like knowing electricity only as a way to turn on the lights — or knowing a Swiss army knife only for the corkscrew.

Quietly percolating

That's OK. Either we're all dummies, or this signal path thing has been brewing in the background and hasn't needed wider attention until now. (I'm partial to the latter idea.)

The reality is that it has
been brewing in the background.

The flourish of the Internet, it turns out, brewed utility for both consumers and
enterprise. The successes of broadband Internet service, and the billions of dollars of revenue it represents, are obvious. Less obvious is the success of finding a signal path built for two-way communications.

The contents of cable's two-way signal path are what other industries would call "enterprise data." It's the day-to-day stuff that makes the business run. For set-tops, it's a profusion of system information, ranging from fresh guide data, to code revisions, to conditional access info to VOD sessions.

In today's world, this data free-wheels from a centrally located carousel, broadcast-style, into either an "in-band" or "out-of-band" signal path to the boxes. (See "In Band, Out-of-Band, What's the Difference," May 28, 2001.)

"In-band" means the work stuff rides in a unique area of a 6 Megahertz channel, or a digital multiplex within a 6 MHz channel.

At the box, the stuff riding "in-band" with the video and audio is plucked off and put to use.

"Out-of-band" means the work-stuff rides in a spectral area that isn't correlated to a particular channel — it traverses a path that is unrelated to the frequencies that carry video.

Why it's superior

Aficionados of cable's signal paths — in-band, out-of-band and DOCSIS — call DOCSIS superior because it was built for two-way transit.

In other words, it wasn't tacked on later, when two-way services (like video-on-demand, or whatever interactive TV is forever becoming) came to life.

Broadband Internet service is inherently real-time and two-way. Building a fast, sturdy two-way path into DOCSIS was a critical — and inalienable — design goal.

Those same aficionados lament that DOCSIS is singularly synonymous with broadband Internet access, because of what happens in people's minds when the gathering gadget storm is described as including a cable modem, or a DOCSIS cable modem.

The mind locks on Internet access via the TV, or Internet access through whatever the device is.

That could (or could not) happen. But it occludes the primary purpose, which is that two-way path.

In reality, future digital TV sets, outfitted to meet the second part of the plug-and-play agreement — two-way services — could benefit from a cable modem and its real-time, two-way signaling.

But just because a device contains a cable modem doesn't mean its main use is to get to the Internet at high speeds.

For as long as DOCSIS has been around, people have lauded its existence and rued its name.

Maybe now is the time to make the shift to a new moniker, if only to resolve the unintended myopia that bonds "DOCSIS" to "broadband Internet service."

Marketers, what say ye? Now's your chance.

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