What's in the Last Mile? (Part 1)


It's tough being the last mile. Lashed pole to pole, it ambles into neighborhoods, and there it stays. Through ice storms and squirrel bites and drive-by shootings, the last mile is a mute and patient witness to everyday life. When it comes upon someone who wants what it carries, it faithfully slings off a line to that house.

Like mail carriers and the office IT department, the last mile only gets noticed when something isn't right, and never when things are going fine.

The last mile is also the first thing competitors covet when they size up the cable-television industry. After all, there are only three wires that carry stuff into consumers' homes: Power, phone and cable.

It's expensive to add a fourth wire just to carry services that overlap with what's on the other three. For cable, a mile of plant costs between $19,000 and $35,000, depending on whether that mile is to be hung from a telephone pole ("aerial") or buried beneath the streets ("underground").

Costs also vary depending on what type of mile it is. There are "line extension" miles, which nudge into new neighborhoods. There are "rebuild" miles, where most everything that's up comes down — a total makeover. Then there are "upgrade" miles, in which the guts of amplifiers are removed and replaced, usually with modules that afford a higher bandwidth.

Cable's last mile, while acknowledged as the main taproot to customers, is hardly a new story. Most MSOs, with the exception of maybe AT&T Broadband and Adelphia Communications Corp., are past the big push toward rebuilds and upgrades. All the technological action these days is happening at either end of the plant — at the headend or in the home.

So, partly in an effort to beckon spring — when plant work heats up — and partly because refresher courses never hurt, a composition on what constitutes the last mile seems useful.

For starters, the last mile isn't really a mile. It's a collection of cable lengths that, when summed together, can become
a mile. But the last mile is almost never a linear mile, and building a mile almost always requires more than a mile's worth of materials.

For purposes of this discussion, the last mile starts at the output of the fiber-optic node, and ends at the side of the house. Building it takes a lot of stuff: Strand, or thick ropes of steel, and the 3-bolt clamps to fasten them to telephone poles; feeder cable, or coaxial cable that's wider of girth than the stuff used inside homes; and wire, to lash the coaxial cable to the strand — appropriately called "lashing wire."

(In the field, underestimating the amount of lashing wire needed to do the job is punishable in cases, not six-packs, of beer. Running out means starting over, because there's no way to adjoin lengths of lashing wire.)

There are expansion loops, installed to resolve the different ways that strand and coaxial cable react to changes in temperature. There are "taps," usually delineated by the number of ports they contain, and used to adjoin fatter feeder cable to the skinnier cable that drops off to homes. And, of course, there are amplifiers to boost signal levels as they inevitably wane over distance.

Then there are tools: Lots and lots of tools used to drill holes, cut tree limbs and tighten bolts. There are dynomometers to double-check the tension of the hung cable. Meters, to check signal levels.

For the cable itself, there are tools that strip back its protective jacket, and core it to expose the "stinger" — the center conductor — and the medium that carries signals to homes. Another tool cleans the dielectric foam that otherwise protects the stinger.

But mostly, building the last mile takes people. A different breed of people, engineers say. Rugged people. The kind of people who attach braces to their shins with sharp spikes at the ends, called "gaffs," which you need to climb telephone poles. (In the hierarchy of cable construction, the people who've been at it the longest are usually the ones that get to use the bucket truck.)

Not surprisingly, craftsmanship matters at every step in planning, designing and especially constructing the last mile. For example, forget a "drip loop" when installing a tap, and the next rainstorm will assuredly pour water directly into the tap housing — not good. Allowing a kink almost always means having to revisit that section of plant later. Incorrectly bolting strand to the pole opens risk of what skiers call a "yard sale" — falling down and losing everything.

That's the stuff of the last mile. Next time, how a last mile is planned and built.

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