Gettin' Jiggy with Gig-E


Most who cleave to technological matters are occasionally guilty of making nouns out of verbs, like saying "transport" to describe things that move signals from one place to another. It goes like this, conversationally: "It's part of the transport," or "it's a transport issue."

In cable, when people say "transport," they mean the devices and paths linking headends and distribution hubs more often than they mean the "last mile" of coaxial cable conveying signals to homes.

Distribution hubs are part of cable's regional network. They connect the headend to the last mile. One hub generally serves around 200,000 homes passed, and from it, signals are sent to smaller, 500-ish home nodes.

Other industries would call this region a "metropolitan area network." Links between a headend and its distribution hubs can span a few kilometers, or 40 kilometers, depending on geography.


"Transport" discussions invariably evoke the brainiac language of fiber optics: wave division multiplexing (WDM) and dense wave division multiplexing (DWDM), for example. Both shove more bits into more "colors" of light, along the same fiber optic cable.

Despite the waning mound of capital dollars earmarked for network rebuilds and upgrades in U.S. cable systems, suppliers of transport equipment are always coming up with new paraphernalia. Using it, mercifully, doesn't involve digging up streets. It usually means changing out the smallish metal boxes on each end of an installed length of fiber.

The logic works: Keep the expensive part of the investment right where it is. (The expensive part of building a shiny, new, $30,000 mile of hybrid-fiber coax plant is the labor required to suspend or bury cables.) Boost the ends with better stuff that can either accommodate more, go farther, or both.

The new stuff of today's transport discussions is "gigabit Ethernet." Its shortened version is "Gig-E," as in, rhymes with Ziggy. "Giga" means billion, so a "gigabit" is a billion bits transmitted each second. A bit is digital's lowest common denominator. Essentially, it's the one or the zero — a binary digit, minus the "nary" and the "digi."

Which brings us to the Ethernet part of Gig-E.

Conversationally, Ethernet is often the magic, if inscrutable, answer. "How does it work?" you say. "It's Ethernet," you're told.


As though saying "Ethernet," with a solemn, knowing nod will fill the knowledge gaps and make everything okay.


What is Ethernet? It's a tried-and-true specification, now 29-years-old, for hooking stuff up together to work as a group. It started out with links between PCs and printers in offices, which came to be known as "local area networks."

Ethernet's identifying characteristics are things like data rate (a billion bits per second, in this case), maximum link length (about 500 meters for coax, and 100 meters for twisted-pair copper), media type (coax, fiber or twisted pair) and topology (the "shape" of the network — bus, star, point-to-point).

Ethernet also describes how interconnected things communicate.

Say you're a device that speaks Ethernet. You're at a cocktail party with 30 other Ethernet devices. Mostly, everyone stands, sips and listens (to nothing, because no one is talking.)

Suddenly, you have something to say. If you happen to blurt your packets at the same time someone else is blurting packets, your blurts collide. You stop talking, wait a random amount of time (measured in microseconds) and then repeat what you said. So does the other person.

The random wait interval helps to assure that you don't collide again.

Couple gigabit speeds with Ethernet, and you've got a way to move digital information really fast, from one place to another.


Watch for discussions about Gig-E to heat up in lockstep with the notion of on-demand video beyond films. Right now, most operators place video servers in multiple distribution hubs, and replicate the contents periodically. The thinking is that there won't be sufficient storage, nor will there be a way to quickly refresh the servers when regular television (i.e., not just movies) shifts to on demand.

There's ample reason to move carefully into Gig-E, our industry's more cautious technologists suggest. One of the reasons Gig-E is suddenly warming to cable is the meltdown of the competitive local exchange carriers, or CLECs. When your customer base evaporates, you find a new one. Cable is the new one. That doesn't necessarily mandate the use of Gig-E.

Also, some technologists warn: If it sounds too good to be true, then it probably is. Particularly the most common rose that sweetens Gig-E discussions: It's cheap. Commoditized.

Making sure it's as cheap as everyone says involves modeling how bandwidth usage may change in the face of an on-demand TV surge. More on that topic next time.