One! More! Time! IP and Bandwidth


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 “500 channels”?

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 middle.

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. (Sigh.)

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.

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