Computer Networks: A Systems Approach, Fifth Edition, discusses the key principles of computer networking. It focuses on the underlying concepts and technologies that make the Internet work. Topics covered include network design and architecture; the ways users can connect to a network; the concepts of switching, routing, and internetworking; end-to-end protocols; congestion control and resource allocation; end-to-end data; network security; and network applications such as e-mail and the Web, IP telephony and video streaming, and peer-to-peer file sharing. Each chapter includes a problem statement, which introduces issues to be examined; shaded sidebars that elaborate on a topic or introduce a related advanced topic; What's Next? discussions that deal with emerging issues in research, the commercial world, or society; and exercises. This book is written for graduate or upper-division undergraduate classes in computer networking. It will also be useful for industry professionals retraining for network-related assignments, as well as network practitioners seeking to understand the workings of network protocols and the big picture of networking.