People talked about a promising idea: using the electrical wiring already in the house to move data from room to room. One early application, the X10 system for controlling lights and appliances, didn't always work well. The technology was certainly not ready to be used to bring web pages to computers anywhere in the house. Along came the wireless network. For $50, you could get the Internet sprayed across the house and never be confined by a cord to the wall. It was slow in those early days, very unreliable, and open to interruption if you couldn't bother with setting up the encoded passwords. But it caught on. According to estimates made by Parks Associates, a market research firm based in Dallas, about 12.5 million homes now have wireless networks another 10 million homes, mostly newer ones, have Ethernet(以太网). Cheap and prevalent is a hard combination to beat. However, technology companies continued to work on the idea. A version for power lines called HomePlug came out in 2002, and while it hardly affected sales of wireless network equipment, it sold enough that major companies like Intel, Cisco, Sony, Sharp and Comcast created the HomePlug Alliance to push for next-generation products, with the first to come out later this year. Some companies are not waiting. Panasonic, Netgear, Marantz are already offering products that will move data through home electrical lines faster than routers(路由器) using the current Wi-Fi standard for wireless networking. Panasonic started selling its HD-PLC Ethernet adapters for power lines last month. One adapter is attached to a router with a short Ethernet cable and plugged into a nearby wall socket. The second device is plugged into a socket elsewhere in the house. When a computer is linked to it with an Ethernet cable, data is transmitted through the home's electrical wiring at speeds of up to 190 rnegabits(兆位) a second. Netgear will be selling a similar system next month for about $300. It moves data at a slightly faster rate. Marantz says its ZR6001SP receiver will send music to special speakers in another room over power lines. The system includes both devices. The music listener controls the receiver and the CD players connected to it from a control pad on the speakers. These products seem hopeless candidates. Who would like to pay two or three times expensive than wireless network? The answer lies in simplicity. 'It's why most people need us,' Robert said, noting the complexity of installing a wireless network is evident by the fact that return rates on wireless networking devices drop to nearly zero. The three products' makers said that people who cannot get whole-house coverage with a wireless system or those plagued by dead zones might find it appealing. The promising idea mentioned in the first paragraph_______.