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the field of science and technology encompassing both the study of telephone-communication principles and the development of telephone equipment.
As a scientific and technological discipline, telephony comprises a number of activities. It studies the properties and characteristics of the sound field, by which interaction occurs between the organs of speech and hearing on the one hand and electroacoustic transducers (telephone transmitter and receiver) on the other. Telephony also investigates the physics of these interaction processes and develops transducers and telephone sets having specified parameters (sensitivity, amplitude-frequency response, level of intrinsic noise, extent of sidetone reduction). In addition, it develops equipment for multichannel communication and establishes criteria for evaluating the quality of speech transmission of telephone sets and telephone circuits (intelligibility, loudness, naturalness).
Telephony also includes the design and construction of switching and control equipment for telephone central offices (selectors, connectors, registers, markers) and the design of telephone networks. Networks must be designed to handle a particular volume of traffic and deliver a certain quality of service, and the design work involves determination of the number of channels and control devices to be used and of the placement of central offices and switching centers. Telephony also concerns itself with developing methods of monitoring, and improving the reliability of, switching equipment.
Improvements in telephone technology have been associated with the development of multichannel systems (with both frequency- and time-division multiplexing) possessing high operational reliability and stability of electrical and other characteristics and with the introduction of high-speed switching and control apparatus for automatic central offices. Of special interest is the development of methods for encoding address and speech information for systems where line multiplexing and channel switching are based on the principle of time division of channels, for example, using pulse-code modulation. Advances in electronics and computer technology have made possible the creation of highly efficient equipment for telephone communication, prime examples of which are quasi-electronic and electronic switching facilities, including automatic central offices with programmed control of switching operations.
Many problems in telephony draw on the principles and techniques of the electromagnetic analogy theory (design of transducers), the theory of linear and nonlinear circuits (design of telephone-set circuits and of control circuits in automatic central offices), probability theory, and queuing theory.
REFERENCESSee references under .
Z. S. KOKHANOVA and O. I. PANKRATOVA