Q: I think I’ve got it. There are several ways to get data from one place to another. There's the switched telephone network, using copper or fiber. There's the cable TV network, using coaxial cable. And there's wireless. Right?

A: Right. But you forgot one: the electric wiring in your house, provided by the power companies.

Q: Oh? Somehow that seems pretty far-fetched. You mean send everything over the power lines in your house?

A: Most everything, yes. And think how convenient that would be. You certainly have dozens of electric outlets in your house. Wouldn't it be nice if every one of them was the entry point to the Internet?

Q: Well, yeah. But it can't be all that easy, can it?

A: No, it's not easy at all. Before I touch on the disadvantages and challenges, and problems, let's look briefly at the advantages and opportunities. First, as we mentioned above, there are electric outlets every-where. Zillions of them. Second, the transmission medium is in place. Third, (and this may not affect you or me) a power company that moves in this direction can use the network for all sorts of things: measuring the power usage in particular networks, controlling distribution facilities, and the holy grail of power companies: automated meter reading.

Q: Okay, so there are advantages. What about disadvantages? And more important, just how is it done?

A: I think we can answer both questions at once. As to how it is done, you've got to look up (or down). The backbone, or core, of the electric distribution system is the very high voltage lines, on the order of 70,000 Volts, hung from those huge towers. (Incidentally, you can't tell the voltage by looking at them, but you can get an idea by seeing how long a chain of insulators is required to provide separation between tower and line: the higher the voltage, the more insulators).

These very high voltage lines terminate in a substation, where transformers step-down the voltage to maybe 7,000 Volts. Now, here's our first problem. The lines leading to the substations are not shielded (they're not even insulated) so any high frequency signal on them would leak, and generate all sorts of interference.

Q: You mean that the high voltage lines won't be used for this data-over-power-lines business?

A: There may be exceptions, but that's about it. The medium voltage lines leaving the substation are where you might apply the data signals. There's some inter-ference from these lines, too, and some groups (e.g., radio amateurs) are protesting loudly. But the protests aren't loud enough to kill the technology.

Q: So, now we've got data signals on the lines running down the highways. Now what?

A: Now comes a big problem: transformers. Throughout this country there are transformers mounted on poles or in ground-level cabinets that lower the voltage to 220/110 Volts. Each transformer serves about 6 houses. Transformers are, essentially, low-pass filters. That is, they filter out any high frequency signals. And of course, our data signals are very high frequency.

Q: So the whole thing won't work!

A: Oh, it'll work. But it takes some effort. The most straightforward way of doing it is to put a bypass device across each of these transformers. This bypass device allows the high frequency data signals to go from the medium voltage lines to the low voltage lines.

Q: That takes a lot of pole climbing! What else?

A: In your home you plug a gadget into your electric outlet, and the other side of the gadget goes to your computer. This gadget is really just a modem.

Q: Sounds pretty good. Are there other problems?

A: Yes. The frequency capability of the technology is not yet enough to handle TV. This could be a serious problem. Because, as you know, the Triple Play is the goal of all telecommunications companies: voice, data, and video. But you can be sure that lots of people are searching for ways to overcome this problem, to go from a Double Play to a Triple Play.