Take A Rhetorical Journey to Network’s Edge

3/13/2005 7:00 PM Eastern

Trends can dawn suddenly. You observe yet another of your friends wearing eyeglasses. She ordinarily wears contacts. You somehow already know this to be a pre-surgery requirement, and ask when she’s going in. It dawns on you: this Lasik thing is really taking off.

For me, it’s the word “edge.” It’s one of those words that crisscrosses between everyday talk and industrial tech-speak: There’s the edge of the kitchen counter, and then there’s the edge of the network. One is something you bump into; the other, an invisible boundary.

The “edge” dawning arrived during a recent conversation with a cable system honcho, who made this sage, if slightly exasperated, observation: “It seems there’s always something going on at the edge of the network.” (We had been talking about Things That Cost Money.)


The remark made me wonder: Where is the edge, anyway?

The answer, delivered as a sort of verbal pocket map, was the original intent of this week’s translation.

Alas, in order to make a map, you need directions. And it turns out that there are nearly as many “edges of the network” as there are people to ask about it.

Over the past several weeks, I’ve conducted an unofficial survey of this industry’s brighter tech-side brains. The questions: Where (oh where) is the edge of the network? If you were to draw us a map, where would we wind up, and what would we see?

From the onset, it seemed pretty clear that the answer depended on who was talking. In the technical community, as in all communities, there are knowledge precincts: Network engineers see edges differently than software engineers, data engineers or plant engineers.

Put any specialist in front of a white board, for example, and 95% of the writable surface quickly takes on the context of his known world — told in boxes, lines, letters and lists. Usually there’s a short line to a tiny cloud, in an upper, outer corner. The “edge” is that short line. The cloud is somebody else’s knowledge precinct.


Here’s a sampling of the “Where’s the edge?” responses:

“The edge is at the end of the core.”

“The edge is where RF goes to IP, or visa versa.”

“The edge is the distribution hub.”

“The edge is where the QAMs [quadrature amplitude modulators] are.”

“The edge is the output of the set-top box.”

“The edge is after the headend, before the eyeball.”

And, my personal favorite: “It’s where the bits fall off.” (Ten bonus points to Time Warner Cable tech guru Steve Johnson for deadpanning that one.)

The crazy thing is, everybody’s right. The edge, it turns out, is in the eye of the beholder.

One way to grasp the tapestry of edges in a contemporary cable system is to visually walk it. Say you’re standing in the headend. It, in a sense, is a network edge: Internet traffic and satellite signals make big junctions there. It is the core, so its “head” and its “end” are both edges.

You step outside to walk to the next edge. In this example, you’re magically able to follow the fiber optic plant to the nearest distribution hub. Let’s say the hub is 10 miles away (actual mileage varies predictably; pack a lunch.) Hubs are edges for lots of things: Advertising zones, node clusters, signal handoffs.

You keep on walking. You want to visit one of the 40 or so nodes fed by the hub, because nodes are edges. They’re where the light on the fiber-optic cables drops off, and the signals are moved onto the RF (radio-frequency) plant.

You’re now in the zone of “the last mile,” although the last mile usually isn’t a linear mile. It’s a collection of cable lengths which, when summed, can be a mile. You follow one of them from the metal box that is the node.


You wind up at somebody’s house. It’s a good customer: Inside is a digital set-top box, a cable modem, and a voice-over-IP device. Each are edges.

How do you know what people are talking about, then, when they say things like “more intelligence at the edge,” or “edge QAMs?” A tip: Most technologists wound up describing the node when asked about the edge. The point where light goes to RF came in first, by far.

But if it’s a case of “edge intelligence,” then the in-home equipment certainly qualifies. The edge becomes the place where network-based intelligence hands off. In the case of cable modems and VoIP devices, the intelligence could be anything aided by QoS (quality of service). In digital set-tops, it’s any of the advanced features fetched over that upstream path, from remote servers.

All of this makes “the edge” one of those trick words, because it puts its onus on you to decide what and where it is. Translation: If someone drops “the edge” on you in a conversation, you might want to ask which one.

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