HomePlug is an inustry trade group for power line communication. This organization of about 50 companies defines power line communication specifications. HomePlug 1.0 and AV are the two versions of the specification for home networking technology that connects devices to each other through the power lines in a home. HomePlug certified products connect PCs and other devices that use Ethernet, USB, and 802.11. Many devices have HomePlug built in and to connect them to a network all one has to do is to plug the device into the wall in a home with other HomePlug devices. Since surge protectors and similar devices may interfere with the high-frequency signals used by HomePlug, the directions included with HomePlug devices recommend plugging them directly into the wall outlets without using extension cords or outlet strips.