Computer Networks is designed as a textbook for undergraduate students of computer science engineering as well as students pursuing courses MCA and IT. The book covers the fundamentals of Computer Networks and provides the tools that will help in simplifying the concepts and protocols for the students. Beginning with network fundamentals such as types of networks, network components etc, and an overview of data communications, the books moves on to provide a layer approach to building a computer network. Exhaustive description of the physical layer, data link layer, medium access sub layer, transport layer, and application layer is provided. The book also provides separate coverage of security issues. Key concepts of OSI model, its layers and their applications, TCP/IP, UDP, fiber optic communication, IEEE 802 wireless standard, various network protocols, and other advanced concepts are covered in detail. Using a simple approach with plenty of interesting analogies, the book provides a rich mix of examples and exercises to help students assimilate the theory.