QAM

If All-IP Is Where We’re Going, Where Are We Right Now?

Over the course of the summer, while co-teaching a class about how cable technology works, one question came up, every time: “If all-IP (Internet Protocol) is where we’re going, where are we right now?”

As television milestones go, all-IP is arguably as significant as the shift to color from black-and-white TVs, in the early ‘50s, and when satellite transmissions began, in 1975, and when analog ceded to digital, in the mid-‘90s.

Each phase sparked major growth. Color TVs bumped sales of TVs in general. Satellite distribution opened the door to national scale, which begat the hundreds of TV channels available to us now. Digital made room for high-definition, then broadband services. Broadband is innately IP, so making room for more of it is what this transition is all about.

Which brings us back to the question. If all-IP is where we’re going, where are we now? If you asked an engineering colleague this question, you’d likely get one of two answers: “QAM,” or “MPEG transport.”

The first (QAM) is technically wrong, as direct comparisons go, but nonetheless right because we’ve all used it for so long. It just stuck.

The other (MPEG transport) is confusing because it’s also the term people use to describe digital video compression.

Let’s look at the “P” part of “IP.” Protocol. Protocols are sets of rules that define how data is transmitted and received, so that two or more machines can talk to each other.

What size are the packets? How are errors handled – with forward error correction (FEC), or by re-sending? What’s the data to do when a piece of the transmission path goes kaflooey?

In that case, then, the correct answer for where we’re coming from, as we head to all IP, is “MPEG transport.” MPEG stands for Moving Pictures Experts Group, and is the standards body that gave us MPEG-2 and MPEG-4 compression.

Part of the MPEG compression standard defines transit. Hence “MPEG transport.” It’s the protocol underlying every fielded digital set-top, cable modem, gateway and voice adaptor out there. And lots of consumer devices.

Still, people often refer to where we are now as “QAM.” Quadrature Amplitude Modulation. Modulation, in general, defines how signals get imprinted onto a communications carrier, to get from here to there. Protocols define how the end points talk to each other. So, even when things are “all-IP,” they’ll still (in cable) move using QAM.

It was at the 2003 Cable Show when Bill Gates and Brian Roberts got to talking about whether and when the cable industry would go from all-digital, to all-IP. At the time, the conversation prompted headlines like “What The Heck Was Bill Gates Talking About?”

And here we are, a decade later. All-IP is still a matter of “when,” not “if.” It’s still the destination. And it’s still going to take a really long time to get there.

This column originally appeared in the Platforms section of Multichannel News.

 

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How to Talk to People Who Use the Word “Orthogonal”

by Leslie Ellis // September 04 2012

Here’s one that’s sauntering back into tech-speak: Orthogonal.

Orthogonal is an oldie-but-goodie tech term, sure to imbue the person who utters it with an unmistakable whiff of tech intelligence. (It has nothing to do with your feet or shoes.)

As an everyday term, though, “orthogonal” is still largely inscrutable: A (math) term, meaning “at right angles.” Generally speaking, when people say “orthogonal” and they’re not talking about OFDM (yes there are people who say “orthogonal” conversationally), they mostly mean “irrelevant.” One thing doesn’t affect or disaffect the other thing.

In cable tech-talk, listen for “orthogonal” in tech-talk from broadband-side technologists working on what comes next with the DOCSIS cable modem specification. One of the potential expansions: OFDM, or, Orthogonal Frequency Division Multiplexing.

Know going in that OFDM is an upstream modulation thing, just as is QAM (quadrature amplitude modulation), QPSK (quaterny phase shift key), and S-CDMA (synchronous code division multiple access.)

Refresher: Modulation is the process of imprinting information onto a communications carrier, itself an electro-magnetic wave, so as to move that information from one physical location to another.

So, people talk about OFDM in the context of getting more stuff upstream, or responding to faster upstream speeds. (OFDM could be used for downstream modulation, too, but that’s not the initial application.)

OFDM, with improved error correction, could kick up some serious capacity – half as much again as what’s already down there. Which is good, because the upstream path is a slender five percent of total available capacity on any cable system.

How to earn style points when talking to engineers about OFDM: Ask the person who utters “OFDM” what they think Hedy Lamarr would say, if asked how it compares to her invention of CDMA. (A variation of which – Synchronous CDMA, or S-CDMA — is still used in cable modems.)

Lamarr, a celebrated MGM actress in the ‘30s and ‘40s, was romantically involved with a ranking military official in Europe, and endured the tedium of being treated as a bubblehead long enough to collect the facts she needed to develop what is now CDMA. (It also goes by “spread spectrum.”)

CDMA works by compartmentalizing a signal into a series of packets, which are smeared across a chunk of spectrum for transmission. It was initially used by the Dept. of Defense to transmit coded information. It’s like OFDM in that it codes data to move over smaller spectral slices.

But in every other sense, OFDM is essentially orthogonal to your everyday life.

This column originally appeared in the Platforms section of Multichannel News.