n the most com- pression. B/D link (bridge/diagonal link) A link that interconnects two mated pairs of STP. It car- ries signaling messages beyond the initial point of entry to the signaling network, toward the intended destination. backbone A central network that connects several other, usually lower-bandwidth, networks SO that those networks can pass data to each other. The backbone network is usually composed of a high-capacity communications medium, such as fiber optics or microwave. backhaul backhaul The practice of routing telecommunications traffic beyond its intended destination and then back to the intended destination, usually to take advantage of tariffs or prices that are lower than those afforded by direct routing. In telecommunications, the term has evolved into more generic meaning used to define a way to get data to a point from which it can be distrib- uted over a network. In satellite technology, backhaul means to transmit data to a point from which it can be uplinked to a satellite. In the context of broadcast TV, backhaul refers to pro- gram content that is transmitted to a TV station or receiving entity, where it will be integrated into a finished show. backplane The board that contains a bus. backup The provision of facilities, logical or physical, to speed the process of restart and recovery following failure. backup copy A copy of information, usually on a floppy disk, zip disk, or CD-ROM, that is kept and can be used if the original information is lost or destroyed. bandpass filter A circuit that is designed to allow a single band of frequencies to pass, nei- ther of the cutoff frequencies being zero or infinity. bandwidth The transmission capacity of a telecommunications pathway, electronic or opti- cal. Bandwidth refers to the range of frequencies, expressed in Hertz (Hz), that comprise a given transmission channel; in other words, it is the difference between the lowest and highest fre- quencies carried on the channel. The bandwidth determines the rate at which information can be trans