Data communications is still the fastest-growing aspect of computing. The subject has always been made artificially complex, and modern developments tend to complicate the issue even more. Satellite communications, local area networks, optical fibres, digital networks, the integrated services digital network, and the open system interconnection are examples of the rapid growth in the communications industry. Regardless of where you live, there are still universal principles that lie at the heart of all data communications. This book deals with these principles and addresses them in simple terms and in a logical sequence so that we will be able to locate easily the essential information we need to know to have a good understanding of data communications.