Data Communication and Networks is designed as a textbook for undergraduate engineering students of computer science, information technology (IT), electronics and communications, and electrical disciplines as well as those pursuing MCA and B Sc (IT) and M Sc (IT). The book provides exhaustive and up-to-date coverage of all the topics in data communication and networks. It lays emphasis on conceptual understanding and follows the layered approach for discussing the various network layers. The book first acquaints the readers with the fundamentals of data communication and computer networks and then moves on to discuss the network layers in detail. The book covers cryptography and network security in separate chapters. The text is interspersed with several analogies to enable easy understanding of concepts. At the end of every chapter, many exercises including review questions, numerical problems, and multiple-choice questions are provided to assess students’ understanding of the concepts learnt.