Understanding Data Communications [antikvár]

Preface The communication of information of all kinds by means of binary signals—the ones and zeros that are used by computers—has gained such an important place in American society that it is fair to say that successful operation of the U.S. economy would be impossible without it. Information sent using data communications controls a major portion of the long-distance telephone network, enables the rapid authorization of credit purchases and cashing of checks, and provides for the inventory and ordering of goods in stores of all kinds, from fast-food franchises to photo finishers. Data communications technology allows the simultaneous printing in widely separated cities of national magazines and newspapers, whose entire text and picture copy is transmitted from a central source to the city in which the publications are to be printed daily. A basic knowledge of such a pervasive force in our lives is as necessary for all of us as is some knowledge of the working of the automobile. I have attempted to cover the basic principles of data communications and to explain those areas of application that have a daily impact: communications between terminals and computers, including local area networks and packet networks; communication of telephone conversations and control of the telephone network; and the use of light rays and satellites for carrying the ever-in-creasing volume of data that helps make our lives more comfortable and sometimes a great deal more confusing. This book is arranged somewhat like a textbook. Each chapter starts by saying what it covers, ends by saying what has been covered, and provides a short multiple-choice quiz on the chapter's contents. Like other books in the series, this book builds understanding step-by-step. Try to master each chapter before going on to the next one. If your objective is to obtain general information about the subject, you can bypass the more detailed portions of the text and the quiz. This will enable you to absorb the information more easily and, hopefully, enjoy the style of presentation. If you need more basic information about the telephone system and telephone electronics, a companion book in the series, titled Understanding Telephone Electronics, should be helpful. For more detailed and more advanced information about data communications, refer to the books listed in the bibliography. G.H.