As with DSL and phone-line networking, power-line technology uses your existing AC wiring as a transport for a data carrier frequency. Power-line networks use an exclusive set of radio frequencies that won’t interfere with remote-controlled on-off switches.

The raw data rate is about 20 Mbps, but error correction and other overhead subtracts from that, leaving an actual rate of about 14 Mbps. It won’t affect your electric bill and it’s even more convenient than using phone lines, because you probably have empty electrical outlets all over your house.

The hardware typically consists of an adapter that attaches to the computer, usually through the parallel port or a USB connector, and a proprietary interface that plugs into the AC outlet. The adapter will have its own surge protection built in.You will need one adapter/interface set for each PC you intend to connect.

As with Wi-Fi, privacy is a concern with this technology. The signal can migrate through the incoming power lines to other nearby homes. It will not jump an electrical distribution transformer to the world at large, but as many as six other homes may be tied into a single distribution leg, and more than that may exist in an apartment complex.

The power-line standard, however, does include packet encryption. Power lines are even noisier than the telephone lines described and are extremely noisy under the best of circumstances. They change constantly too, as customers plug in some appliances and remove others.

Some of the devices being powered are inherently noisy by themselves, such as fluorescent lights, switching power supplies, and dimmer switches. The circuit breakers in power panels are signal sponges.

HomePlug technology deals with the hostile data environment by adapting to changing conditions, pushing high throughput on some channels, and slowing down on others to plow through noise. Also, it uses thorough error detection and automatic repeat requests (ARQs) to ensure that the line appears reliable to the driving software.

The HomePlug specification uses the same Orthogonal Frequency Division Multiplexing (OFDM) that is used in the newer 802.11a Wi-Fi networking standard. Basically, the HomePlug specification works by sending most of the data on the clearest of 84 channels (between 4.3 to 20.9 MHz), dynamically shifting data to alternates if some of them become swamped with noise.

The data signal has no effect on your home’s electricity, which is immensely more powerful. The age of the wiring in a house does not appear to be a factor. The software will automatically detect your plugged-in nodes.

Adapters are available to provide printer sharing, and routers are available for interfacing multiple home PCs to a single Internet link. Many adapters have AC sockets built in, so that you won’t lose a place to plug in a desk lamp when you plug in an adapter. Depending on the brand, the resulting networks can be client/server or peer to peer.

The advantages for using your power lines for networking are as follows:

• You already have multiple AC outlets in every room.
• It won’t interfere with other home networking technologies.
• It’s cheap.
• It works the world over, even on older wiring.
• It’s easy to install.
• It’s easy to add more nodes.

Before you buy it, make certain that it has been tested as conforming to the specifications of the HomePlug Powerline Alliance. As with the Wi-Fi Alliance and the HomePNA organizations, the Powerline Alliance conducts tests to guarantee interoperability between manufacturers.