anumeric display. Display which shows characters as well as Wavelength Division Multiple Access. (Multiple ac- numbers. cess technique.) Alternate routing. A feature of a telecommunication element Windows, Icons, Mouse and Pointer. (Display and which enables it to send information via an alternate route if the manipulation technique for graphical interfaces, e.g. prime route is unavailable, such as due to congestion. Often as used for network management.) used as a route protection measure. World Meteorological Organisation. Ameritech. One of the seven regional Bell operating companies Work Station. covering the mid-Western region of the US. Glossary of terms 62/19 Amplifier. A device which increaces the level of the signal. Am- Usually this is on the basis of the least cost and is referred to as plification may be of current, voltage or power, of electrical or least cost routing. light signals. Autorate. Facility within a device, such as a modem, which en- Amplitude modulation. A method of encoding the transmitted ables it to automatically adjust its transmission rate to suit the information by variations in the level of voltage or current in requirements of the device located at the other end of the the signal. transmission line. Amplitude distortion. The unwanted change in the amplitude of a Availability. In telecommunications it usually refers to the per- signal waveform, usually due to the effect of non-linear com- centage of time that a piece of equipment is operational. ponents in the communication network. Azimuth angle. The angle between the meridian plane and the Analogue. A system in which information is represented by a antenna beam, when measured along the horizontal plane. continuous variation of a parameter, e.g. a voltage level. The sender selects a level to represent his information and the receiver interprets this as an approximation of the encoded value. Backbone network. A high speed transmission network which is Analogue cellular radio. Cellular system which uses digital sig- used to intercon