ABSTRACT
The Physical layer is responsible for turning some medium into a bit pipe. Copper cabling is the most common data-networking medium of LANs and in the local loop, while fiber optic cabling is prevalent in most wide area networks-and is perhaps the local-loop and the LAN medium of the future. Radio frequency bands also play a role in some data networks, including signals that are relayed via satellites. Some local networks and point-topoint links employ infrared signals propagated through space, and visible light lasers are sometimes used to transmit data without the aid of a fiber optic cable.
