s technology to meet the challenges of assembling such networks. These professionals will shape the electronic products and systems that will allow such activ- viii PREFACE ities as banking, education, travel, manufacturing and medical di- agnostics to be performed more efficiently. By adding communica- tions capability to these systems, users can benefit from having fast and direct access to the enormous power of the computer. The attempt of this book is to set in perspective the operating prin- ciples that underlie the various telecommunications equipment and network structures used to grow these systems. Having understood the basics, the communications manager can make the proper tech- nology choice for his applications. The book also serves as a user guide to equipment that can fulfill requirements for setting up such networks. A special thank you to Debby Garcia for her assistance in typing and preparation of this work. Vince Coughlin CONTENTS Preface / vii The Medium and the Market-An Overview / 1 1.1 A Telecommunications Overview / 1 1.1.1 Smart Telecom Banking Card Systems / 2 1.2 Understanding the Basics / 3 1.2.1 Parallel and Serial Transmission / 4 1.2.2 Channels and Facilities / 4 1.2.3 Digital Versus Analog Transmission / 6 1.2.4 Asynchronous and Synchronous Transmission / 8 A Bright Future with Fiber Optics / 9 1.3.1 Fiber Selection / 10 1.3.2 Light Source Emitters and Detectors / 12 A View from the Business Side / 13 1.4.1 How to Set your Requirements / 14 1.4.2 Minimizing Line Costs / 14 Modems and Multiplexers / 16 Introduction / 16 The Role of Modems / 17 2.3 Modem Applications / 19 2.4 Industry Standards / 20 2.5 Modem Features / 20 2.6 Multiplexing Reduces Communications Cost / 22 Multiplexer Technology / 24 2.8 Statistical Multiplexer / 29 2.8.1 Bandsplitter / 31 X CONTENTS Protocols and Codes / 32 What is a Protocol? / 32 Protocol Hierarchy / 32 Physical Electrical Interface / 34 3.3.1 Handshaking / 35 Link Control Structure / 37 3.4.1 Data Transparency / 37 3.4.2 Connection and Disconnectio