When concerns about interference are paramount, a wired network makes the most sense. The easiest systems to install are those that use the wires already embedded in the walls. By the end of this year, there are likely to be gateways on the market that work through ordinary electrical wires. At this time, however, the only way to piggyback onto existing circuits is through conventional telephone wiring. As long as the wires have been properly installed and haven't deteriorated with age, it's just a matter of plugging each device into a phone jack and installing the necessary software. Standard telephone wire can handle current high-speed Internet traffic just fine, but with access speeds steadily increasing, its 10-Mbps transmission capacity (the same as wireless systems) is all but certain to become a digital bottleneck. Electrical contractor Allen Gallant, who has worked on several This Old House projects, no longer installs this wire when he's working on new homes and additions, even if his customers plan to use the lines only to make telephone calls. Instead, he specifies Category 5 enhanced cable, a souped-up telephone wire that can simultaneously handle up to 100 Mbps of high-speed data. Cat 5 is nearly four times as expensive as everyday telephone wire, but that amounts to a mere 15 cents per foot — a bargain considering the transmission speeds it offers. And it has to be handled with care. Pulling the wires too hard, bending them too sharply, or shoving them through too tight an opening can alter the way they twist inside their plastic jacket, reducing performance. "You don't have to treat them like eggs," Gallant says, "but you do have to use some common sense. To put it simply: Don't force it." Shortcuts are also out. Each computer jack, which looks like a phone jack, needs its own separate cable run from the central gateway; it can't have any splices along the way. Nor can Cat 5 cable slink alongside electrical wires. The electromagnetic fields that the wires generate when in use can interfere with the relatively weak digital signals in the cable. Keeping the two lines at least a foot apart protects against such interference.

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