Optical fibers can be used to transmit light and, therefore, information over long distances. Fiber-based systems have largely replaced radio transmitter systems for the transmission of long-distance optical data. They are widely used for telephony, but also for Internet traffic, long-distance local area networks (LAN), cable TV (CATV) and, increasingly, also for shorter distances within buildings. In most cases, silica fibers are used, except for very short distances, where plastic optical fibers can be advantageous.