Data Communications and Networks uses a top-down, Internet-focussed approach to tackle the problem of communication system design. An integrated approach is taken to networks and data communications, with an emphasis that starts from the top level requirements and works downwards, describing how such requirements are fulfilled by lower layers of the transmission chain. While the book contains sufficient detail to provide an excellent foundation, clarity is paramount and care is taken not to swamp the reader with information to the point where the underlying concepts are obscured. The Internet is used as the principle example of a communication system, allowing the reader to follow the system from the application layers, with source coding and security, through the network, with naming and routing algorithms, down to transport and physical aspects of a communication system. Modern techniques such as mobile radio, Voice over IP, and ASDL, are covered, while more traditional aspects such as circuit switching, which still form a significant part of current systems, are not overlooked. By providing a technical introduction and including application examples, this text will have significant appeal to final year students, postgraduates and professionals with a science or engineering background wishing to gain a basic understanding of the key concepts behind data communications engineering.