This introductory text on computer networks is in three parts: the first of which deals with the basics of data communications. It answers the question as to what is information and covers basic signal characteristics, before introducing interfaces, protocols, standards and coding in the context of practical modem links. Part 2 covers transmission principles in three chapters: transmission lines, free space links and fibre optics. Understanding the physical media and the constraints they impose is very relevant to the successful operation of any computer network; this book is one of the few that cover this topic. Part 3 contains fuller discussions of networks and protocols, including: LANs, WANs, TCP/IP and new services such as ATM, frame relay, etc. There are examples and exercises throughout to facilitate self-study; answers to all exercises are given at the back, as is a useful glossary and several appendices.