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Cable’s Fiber-Deep Options

This being the week of Halloween, it seemed a good time to peer into the web of fiber-optic and coaxial cables that comprise a contemporary HFC (hybrid fiber coax) cable system, to see what lurks there.

Specifically, we’ll look at whether it’s technically and economically possible to carve the “H” and the “C” off the traditional “HFC” plant, and just go with the “F.” That’d be the fiber.

This idea goes by several rather awkward acronyms. Its broad intent is to create a roadmap for a cable fiber-to-the-home (FTTH) offering. So yes, it’s partly about how to migrate the plant, over the long term, to be competitive with telco offerings of that hue. And yes, that means Verizon Communications’ various shades of PON. (“PON” stands for passive optical network, and is usually pronounced to rhyme with “gone.”)

Marketers, brace yourselves. Here we go with the awkward acronyms.

Some call this cable FTTH idea “RFOG,” for “radio frequency over glass” (the glass being the fiber). They say it as the letter R, then the word “fog.” Others call it “DOCSIS PON,” or “D-PON.”

There’s also an “RF PON,” for “radio frequency passive optical network.”

Still others call a similar method “node plus zero,” or “N plus 0.” In this one, the zero refers to amplifiers — after the node, no amplification of the signal, as it rides toward homes. (This one isn’t necessarily all fiber, but has similar transmission attributes.)

Again. Engineers tend to name things for what they do, not how marketable they are. This is unlikely to change. Pick your battles.


A very busy vendor community stands at the ready with gear for this fiber-deep proposition, populated by companies well known in the transmission side of cable technology: Arris, Aurora Networks, Cisco Systems, CommScope, Harmonic, Hitachi and Motorola. This alone signifies a credible level of activity.

Those vendors say that an FTTH offering for cable plays well in two areas: New housing developments, and in areas where home density is low. Plus, they say, they can preserve the doings in the back office — meaning that going to a DOCSIS PON, as one example, doesn’t require changing how things like service provisioning and device provisioning are handled. (That’s big.)

How much curb appeal does a direct fiber link add? In new subdivisions and in high-rises, some developers think they can add as much as $12,000 to the price tag of a home, if it has fiber.

The density argument goes like this: In areas where homes are spread farther than 80 per mile, longer lengths of coaxial cable are needed to serve them. Longer coax means more amplifiers. More amplifiers means more cost — for the amp and the power.

Fiber, by contrast, doesn’t have the same signal-loss attributes as coax. It goes farther before needing amplification.

On the service-provider side, MSO engineers agree the fiber-deep approach can make economic sense — in specific places. Like where a trench is already open, in a new housing division. The current state of the U.S. housing market, though, makes this a longer-term consideration.


The tale of how close cable’s fiber is to homes probably bears repeating. It goes like this: Two decades ago, when cable engineers began planning to replace coaxial super trunks with fiber, a big question was how far fiber could go before it became morbidly costly.

In the late 1980s, costs were a function of the fiber itself, plus the stuff on either ends. Installing the fiber involved a decision: Aerial or underground? Underground means digging. Digging means expensive.

Then, there were the costs of the items on each end of a fiber-optic cable: laser transmitters and receivers. Because the cable industry was first to figure out how to use fiber to deliver video, and because everything was thus new, costs were higher — for everything. Again, this was the late ’80s.

In drawing the fiber routes, and comparing them against the costs, it became evident that the sweet spot, technically and economically, was in the center of a circle with a 1-kilometer radius. With typical home densities (80 homes per mile), it turned out that there were about 500 homes within that circle. Hence the 500-home node.

In practice, this means that in the average U.S. neighborhood, the fiber installed by cable providers is somewhere within a three-block walk of any given house. (Don’t be fooled by “the last mile,” as people often refer to the coaxial portion of an HFC plant. It’s hardly ever a linear mile, but rather a grouping of lengths that, when summed, can add up to a mile.)

Verizon chose a fiber-deep PON architecture, to deliver higher and higher bandwidth directly to homes. AT&T picked a cheaper path, trying to squeeze more life out of the twisted-pair copper plant, but a fiber-to-the-home network provides far more runway.

For cable, a FTTH roadmap is well underway, from a sturdy supplier group of equipment suppliers. That answers the “technically possible” question. Which brings it back to the economics — always the tricky part. As one MSO engineer put it: “Tell me again — what do I get, to spend money to put fiber at the side of the house, versus in the neighborhood?”

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