h- nique that combines OFDM with error-correcting codes, adaptive equalization, and reconfig- urable modulation to provide many beneficial properties, including resistance to multipath, phase distortion, fading, and burst noise. COFDM is used in Europe and other places where the DAB standard has been adopted for digital radio broadcasting and for terrestrial DTV. It is also used in ADSL transmission. collision Overlapping transmissions that interfere with one another. A collision occurs when two or more devices attempt to transmit at or about the same instant. collision domain A small cluster in a LAN where collisions occur. Collision domains are used to reduce collisions throughout a network. command A signal or group of signals that cause a computer to execute an operation or series of operations. command-driven Programs requiring that the task to be performed be described in a special language with strict adherence to syntax. common-battery signaling A method by which supervisory and telephone address informa- tion is sent to an exchange by depressing and releasing the switch on the cradle of the handset. common carrier An organization in the business of providing regulated telephone, tele- graph, Telex, and data communications services. common control common control An automatic switching arrangement in which the control equipment nec- essary for the establishment of connections is shared and is associated with a given call only dur- ing the period required to accomplish the control function. communication adapter A hardware feature that permits telecommunication lines to be attached to the processor. communication line A link (e.g., wire, telephone circuit, microwave, satellite) used to transmit data between computers and/or remote devices. communications controller (1) A hardware device for attaching either communication lines, ASCII devices, or a LAN to the processing unit. (2) A dedicated device with special pro- cessing capabilities for organizing and checking data and handling information traffic to and