Company Limited Molly Millars Lane Wokingham, Berkshire RG11 2PY, England Van Nostrand Reinhold 480 Latrobe Street Melbourne, Victoria 3000, Australia Macmillan of Canada Division of Gage Publishing Limited 164 Commander Boulevard Agincourt, Ontario MIS 3C7, Canada Library of Congress Cataloging in Publication Data Coughlin, Vince. Telecommunications, equipment fundamentals and net- work structures. Includes index. 1. Telecommunication. I. Title. TK5101.C694 621.38 84-3521 TO SPECIAL AGENTS OF HAPPINESS: My Mother, Nicholetta Carol Ware Coughlin Almira Figueira PREFACE Modern technology began in the 1950's and 1960's, with the devel- opment of transistor technology. At first it was useful in improving the performance of voice communications. But then it made possible extraordinary computer capability in manageable size-and at man- ageable cost. First came large mainframe computers for only the largest companies; and later the microcomputer as we know it today. The increasing use of computers, in the 1960's with their ability to manipulate and store vast quantities of information, stimulated the need for computers to communicate with one another and SO tele- phone circuits had to be segregated and conditioned specifically for computer traffic, using the modem. Computers ushered in a new era of business communications in which data could be developed, ma- nipulated, stored or transmitted with remarkable ease. The recent pace of technological advancement has been breath- taking and, today, the distinction between communications and computers is no longer even necessary. Computers, at the very core of communications networks, route and control communications on major common carriers. The decade of the 1980's is bearing the fruits of the marriage of computers and communications. For the first time networks are en- abling organizations to utilize the combined processing power of computers and communications equipment. Hence both engineering and communications managers must have a thorough knowledge of telecommunication