'Telecommunications, Switching, Traffic And Networks ' Preface The communication of information over distance is essential to civilization. This communication is increasingly provided by electronic means, in order to transport large amounts of information very rapidly. Thus, telecommunications services are extensively used in business, in social life and for entertainment. The importance of telecommunications is reflected by the inclusion of Communication Engineering as a subject in Electrical and Electronic Engineering courses. Most users of telecommunications obtain the services they require from a telecommunications network provided by a public operator. A telecommunications network conveys traffic by means of transmission links connected by switching systems. However, conventional first degree and diploma courses in Communication Engineering, and most undergraduate textbooks, are mainly devoted to the technology of information transmission. Networks, traffic and switching have largely been ignored. There are signs of change. Some recent undergraduate textbooks on telecommunications contain a chapter on networks and their components. There are also advanced texts, suitable for postgraduate students and for practising engineers, on networks, traffic, switching systems and signalling; however, these are too specialized for undergraduate courses. It is hoped that this book will help to fill the gap between the detailed treatments in the advanced texts and the brief treatments of these subjects in existing undergraduate textbooks. The book contains much that the author learned while working in industry, so it is hoped that it will be of interest to practising engineers as well as to students. The book deals with switching, signalling and traffic in the context of telecommunications networks. The first chapter provides an introduction to telecommunications networks and the final chapter treats them in more detail, showing the application of technology described in preceding chapters. Both circuit switching and packet switching are treated in some depth. The reader is led through the evolution of switching systems, from manual and electromechanical systems to stored-programcontrolled digital systems and future broadband systems. This approach enables fundamental ideas to be introduced progressively and explained by means of real