"Computer Networks, 4/e" is the only introductory computer networking book written by authors who have had first-hand experience with many of the protocols discussed in the book, who have actually designed some of them as well, and who are still actively designing the computer networks today. This newly revised edition continues to provide an enduring, practical understanding of networks and their building blocks through rich, example-based instruction. The authors' focus is on the why of network design, not just the specifications comprising today's systems but how key technologies and protocols actually work in the real world to solve specific problems. The new edition makes less use of computer code to explain protocols than earlier editions. Moreover, this new edition shifts the focus somewhat higher in the protocol stack where there is generally more innovative and exciting work going on at the application and session layers than at the link and physical layers. It is completely updated with new sidebars discussing successes/failures of previously deployed networks. It features thorough companion website with downloadable OpNet network simulation software and lab experiments manual. It includes expanded coverage of topics of utmost importance to today's networking professionals, e.g., security, wireless, multimedia applications.