This book covers the topics related to physical layer, data link layer, network layer and application layer. The book also explains router configuration and different lan technologies in a very simple language. Separate chapters are added on atm, isdn and frame relay containing many illustrations. Network security concepts are explained with easy to-understand language. Concept of transmission control protocol and user datagram protocol are discussed in a matter that the students of various streams can easily understand these complex topics. Ample number of diagrams are used to illustrate that answers for easy understanding. A glossary of numerous technical terms is included at the end of this book for easy understanding of the subject matter. A comprehensive index is included for quick access to all the topics in the book, thus reducing the reader's valuable time in searching any topics. A set of review questions with answers added at the end of each chapter so that the reader can eva