JUST UNDER TWO DECADES AGO, AT A NATIONAL
Show breakfast for engineering mucketymucks
in L.A., MIT Media Lab founder
Nicholas Negroponte, who at the time
had just published Being Digital, caused
a few dozen forkfuls of scrambled eggs
to quiver with indignation.
Back then, it was a relatively new
bit of network blasphemy; today, it’s a
perennially popular theme: Bandwidth
should be free!
Fast-forward to now. The work of today’s network engineers
is the race to service the dozens of electronic
doodads in our lives, parched for broadband. For them,
bandwidth is anything but free, especially if you’re the
one girding for the growth in moving all the bits.
It’s a two-step. Analog went to digital. Digital now
goes to IP —- Internet protocol.
Going from A-to-D was one thing, and a big thing.
And it’s still in motion.
Just as analog spectrum bows to digital, digital
morphs. Once, “digital” was the thing that made it possible
to do lots more TV — remember John Malone’s
The volume of things that become quaint every two
months is simultaneously exciting and depressing.
So, back to bandwidth basics this week. The bandwidth
of IP. A typical cable system is built to 860 Megahertz
of total available bandwidth. Some go higher (1
Gigahertz); lots go lower (750 MHz). But let’s go in the
Subtract the upstream path, which represents
about 5% of total available capacity between 5 MHz
and 54 MHz. That includes guard band, so that stuff
going down doesn’t mess with stuff going up.
That leaves 811 MHz, or, about 135 “channels” —
where “channel” means a 6 MHz chunk of spectrum.
(Will the 6 MHz designation become vestigial? It appears
so. But that’s not for this column.)
Suddenly, the signal path carved out for IP traffic
— used by cable modems and voice-over-IP — needs
to grow. For more than a decade, two 6-MHz channels
carried everything an operator needed to service highspeed
Internet and voice services. Not so now.
By next year, that pool of IP-capable channels could
go to 12. Why: Because soon enough, the average
U.S. household will contain an average of six screens
that play video from an IP-based signal. That’s roughly
two times the number of TV screens accustomed to receiving
signal through a set-top box connected to a TV.
Meanwhile, the trend of making everything smaller
and lighter — a function of silicon — thrives. Hardware
cedes to software. Lines of code are the new black.
On the drawing boards or production schedules,
depending on who you ask, are chip designs that make
it possible to go “all-IP” — meaning that the entire
downstream spectrum, from 54 MHz to 860 MHz, can
be undone as 6-MHz channels, and treated as a giant
pool of IP spectrum.
That’s all a function of bonded DOCSIS 3.0 channels.
Bond them all, the logic goes. Use gateways (see
last week’s column) for the transition. In conventional
logic, this transition will take a decade.
Which means blink twice, and we’ll be there.
Stumped by gibberish? Visit Leslie Ellis at
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