Data Communication and Computer Networks deals with various aspects of the subject vis-à-vis the emerging trends in network-centric information technology. It provides the reader with an in-depth framework of the fundamental concepts. Networking involves different kinds of personal computers, the operating system, the network adapter, the adapter drivers, cabling, and the protocols connecting these items. Likewise, there are many techniques of data communication such as modulation, multiplexing and analog to digital conversion. Constant demand from IT professionals and individuals leads to rapid and unbounded growth of both data communications and networks in terms of better applications and improved opportunities. This book provides a good learning platform to the people who need to be skilled without going into the details of computer programming. An attempt has been made to explain the underlying concepts to lead students and professionals from the hardware level right up to the application level. Most currently relevant areas have been covered. A study of them will encourage inquisitiveness about the concepts, tools, technologies and applications. There are 14 chapters and an elaborate glossary for quick reference. Chapters have been organised independently with clearly set out links with previous chapters. Data communication and computer networks are extremely exciting fields and therefore a good amount of emphasis has been put to prepare objective questions so that the student may enjoy the exercises in a most effective way to test his/her understanding of the concepts.