In Spring, Talk Turns To Phone Power

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Spring is here, which makes it seem timely to update one of the perennials in cable engineering: Powering, as in, powering for cable telephone services.

Powering discussions go way, way back, and they’ll go way, way forward: Juice is juice, and just about everything needs it. But over the last few years, cable’s powering conversations have morphed.

For starters, it used to be about how best to power the “network interface units” clamped to the side of the house, and linked via cable plant to those “big iron” class-5 switches.

Back then, engineers used to worry whether it was safe, not to mention economical, to boost network voltage from 60 volts to 90 volts.

They wondered if power could even be carried on the center conductor of a coaxial cable without “galvanic corrosion,” a metal decay problem. (Imagine gunked-up car battery terminals.)


These days, engineers are still working on powering issues. It’s still about making sure customers can make and receive calls when the power is out.

But with voice-over-IP (VoIP), as with most things that depart from “traditional analog” activities, there’s a distinction.

The distinction is this: With VoIP, figuring out how to power the devices that do cable telephony no longer includes the cable plant as an option.

All VoIP devices, known in the lingo as “E-MTAs,” for “embedded multimedia terminal adaptors,” get power when they get plugged into a power outlet inside the house.

In short, it’s a safety thing. Asking a trained cable technician to run 90 volts of power into a box sitting on the side of the house is one thing. It’s another thing entirely to expect consumers to handle a live wire. Plus, it’s expensive. Just ask Cox.

As the acknowledged pioneer in cable telephony, Cox learned early on that it’s not the “big iron” class-5 switches that top the cost line for circuit-switched telephony. Nope. It’s the cost of network power.

Yet still, all operators planning VoIP deployments need to decide what their approach will be when it comes to power outages.

If you’re like me, you had to rummage through boxes in the basement during the last major power outage to find a phone that plugged directly into the phone jack. (It was in a box next to the furnace, under loops of phone and Ethernet cables.)

And now this from the Department of the Obvious: Most of us have cell phones. That means the search for the old phone happens only after the cell phone batteries give up.

The point here is that our steady accumulation of cordless and cellular phones made most of us ditch the “black phones” we used a decade or two ago. And if the power goes out, those cordless phones don’t work.

Which brings us to this not-so-shocking conclusion: Batteries dominate today’s powering conversations.

If a cable operator is offering VoIP-styled phone service — and describes it as “LEC replacement,” “primary line” or “lifeline” — batteries will be nearby.


At $10 to $15 per device, batteries assure that the E-MTA works for four to 10 hours, if there’s a big power outage. (This assumes that network hubs contain good, non-electric generators, too.)

Batteries also trigger a whole new, if predictable, spate of operational issues for cable operators. How often do they get replaced? How is that handled — are they sent to the house? By mail or by truck?

And after customers have received the batteries, have they installed them? Again, if your house is like mine, you try to be mindful of the rule about changing the fire detector batteries when the clock changes in spring and autumn: You always mean to do it, anyway.

That’s the latest bloom in cable’s perennial powering discussion.

Next time, the answer to the VoIP question you maybe don’t want to ask, because you don’t people to think you don’t already know the answer.

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