Chapter 7 - Data Communications

Abstract

Data communications is the transmission of data between computer systems. At present, the trend is toward networks of computers that share information. Recent government rulings have tended to increase competition in the data communications industry. Because a computer transmits digital data and telephone lines transmit analog data, modems must be used to convert data between these different formats. The data communications controller receives signals from transmission lines, converts them into computerized form, and passes them onto the central computer system, thus relieving the central computer system of these chores. Simplex lines allow transmission in only one direction; half-duplex lines allow two-way transmission but in only one direction at a time; and full-duplex lines allow transmission in both directions simultaneously. Leased lines are dedicated to the user who is charged for the undivided attention of the line. Switched lines are available through the regular telephone switching system. Each terminal might be connected to the computer by a different set of communication lines each time the user dials the number of the computer system.