A device that transmits signals with light, instead of over radio frequency waves. Literally, “laser” is an acronym: “Light Amplification by Stimulated Emission of Radiation.” The laser, in modern fiber optic systems, is the transmitter, which pulses signals over fiber optic transmission media, to be received by a photo detector (receiver) at the destination.

Light, in and of its own, is an energy form: An electromagnetic radiation similar to other familiar electromagnetic types, like TV, radio and microwave signals. The difference is that lightwave radiation is much higher in frequency, making its wavelengths correspondingly shorter. In comparison, coaxial cables carry usable bandwidths of up to 1 GHz; radio-based systems vary with available spectrum, and lightwave systems can carry upwards of 100 GHz per kilometer of fiber.

Lasers work by launching light signals, imprinted with signals along specific wavelengths –usually 1310 nanometers or 1550 nanometers, in cable systems. The light signals launch into strands of fiber optic cable. At the other end of the fiber, a receiver detects the photons on the fiber, and translates them back into their native format.

A collection of coaxial cable lengths that drop individually drop off to subscribing homes. When summed, those lengths can equal a mile, but the last mile is almost never a linear mile. And, building a mile almost always requires more than a miles worth of materials.

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

Adding a fourth wire, to carry services that overlap with what’s on the other three wires, is expensive. For cable, a mile of plant costs between $19,000-$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, where the guts of amplifiers are removed and replaced, usually with modules that afford a higher bandwidth.

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 — thick ropes of steel, and the 3-bolt clamps to fasten it to telephone poles. Feeder cable — coaxial cable that’s wider of girth than the stuff used inside homes. Wire, to lash the coaxial cable to the strand, and 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 reactions strand and coaxial cable have to temperature changes. “Taps,” usually delineated by the number of ports they contain, adjoin fatter feeder cable to the skinnier cable that drops off to homes. And, of course, amplifiers, which boost signal levels as they inevitably wane over distance.

Then there are tools. Lots and lots of tools: To drill holes, to cut tree limbs, and to tighten bolts. 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 off 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,” and necessary 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 of the planning, design and especially the construction of the last mile. Forget a “drip loop,” for example, 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.

One thing is certain: It’s not easy 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 delay, or lateness, in getting signals or information from origination to destination. Examples are plentiful: In early digital TV systems, “latency” showed as seconds of blank time between channel changes. In telephony, latency’s symptom is blank spots in conversation, such that one feels the need to say “over” after completing a sentence or thought. On the Internet, latency is how to describe a slow-loading Web page.

In short, anything that moves from one place to another as part of its usual routine is subject to latency.

What happens when RF signals spill out of a transmission media. In coaxial cable, leakage can occur for a variety of reasons: Cracked or chewed cable lines, bad shielding of TV tuners, or improperly crimped connectors.

No matter how you look at it, leakage is bad. Not only does it weaken the strength of the transmitted signal as it tries to get from one place to another (i.e., from the home to the headend, or visa versa). In cable’s case, signal leakage also can create problems for the Federal Aviation Administration, which uses some of the same frequencies as cable, but for air traffic control.

Because cable is inherently a closed system, it theoretically doesn’t interfere with FAA signals. But in the ’80s, the FCC found enough evidence of RF seepage into the air that it mandated a series of regularly occurring “cumulative leakage index” tests, to force cable operators into fixing signal leaks. Not surprisingly, when CLI tests were conducted, and leaks repaired, cable system reliability rose.

Companies that provide local telephone service to businesses and residences. Also called Independent Local Exchange Carriers (ILECs), Regional Bell Operating Companies (RBOCs), “Baby Bells,” and “telcos.”

The process of making an analog telephone wire, extending from the telco central office to the home or office, suitable for handling digital information, such as DSL (digital subscriber line) services.

The pair of copper wires that extend from a telco central office, to a home or business, thus forming a loop between homes/businesses and telco switching equipment.

When homes require additional lines, as in for Internet access, home faxes, or teenagers, telcos install additional loops. Notably, local loops were designed over 100 years ago to do one thing: Carry analog, electrical signals across a pair of wires, to make a voice conversation happen at both ends. The technology works quite well at doing that one thing. But, doing more — digital anything — taxes the very local loops that make phone calls possible.

The brightness and contrast level of a television picture, as opposed to its color, which is designated by “chrominance.” In color television, signals are generally described by their luminance and chrominance. In general, the human eye is more sensitive to luminance/brightness detail than it is to color detail.

Usage: Because the human eye notices brightness and contrast more so than color, many digital video compression techniques allocate more pixel coding muscle to the luminance than the chrominance information.”