We think one important reason for this success has been that our book continues to offer a fresh and timely approach to computer networking instruction. We’ve made changes in this seventh edition, but we’ve also kept unchanged what we believe (and the instructors and students who have used our book have confirmed) to be the most important aspects of this book: its top-down approach, its focus on the Internet and a modern treatment of computer networking, its attention to both principles and practice, and its accessible style and approach toward learning about computer networking. Nevertheless, the seventh edition has been revised and updated substantially.

Long-time readers of our book will notice that for the first time since this text was published, we’ve changed the organization of the chapters themselves. The network layer, which had been previously covered in a single chapter, is now covered in Chapter 4 (which focuses on the so-called “data plane” component of the network layer) and Chapter 5 (which focuses on the network layer’s “control plane”). This expanded coverage of the network layer reflects the swift rise in importance of software-defined networking (SDN), arguably the most important and exciting advance in networking in decades. Although a relatively recent innovation, SDN has been rapidly adopted in practice—so much so that it’s already hard to imagine an introduction to modern computer networking that doesn’t cover SDN. The topic of network management, previously covered in Chapter 9, has now been folded into the new Chapter 5. As always, we’ve also updated many other sections of the text to reflect recent changes in the dynamic field of networking since the sixth edition. As always, material that has been retired from the printed text can always be found on this book’s Companion Website. The most important updates are the following:

• Chapter 1 has been updated to reflect the ever-growing reach and use of the ­Internet.

• Chapter 2, which covers the application layer, has been significantly updated. We’ve removed the material on the FTP protocol and distributed hash tables to make room for a new section on application-level video streaming and ­content distribution networks, together with Netflix and YouTube case studies. The socket programming sections have been updated from Python 2 to Python 3.

• Chapter 3, which covers the transport layer, has been modestly updated. The ­material on asynchronous transport mode (ATM) networks has been replaced by more modern material on the Internet’s explicit congestion notification (ECN), which teaches the same principles.

• Chapter 4 covers the “data plane” component of the network layer—the per-router forwarding function that determine how a packet arriving on one of a router’s input links is forwarded to one of that router’s output links. We updated the material on traditional Internet forwarding found in all previous editions, and added material on packet scheduling. We’ve also added a new section on generalized forwarding, as practiced in SDN. There are also numerous updates throughout the chapter. Material on multicast and broadcast communication has been removed to make way for the new material.

• In Chapter 5, we cover the control plane functions of the network layer—the ­network-wide logic that controls how a datagram is routed along an end-to-end path of routers from the source host to the destination host. As in previous ­editions, we cover routing algorithms, as well as routing protocols (with an updated treatment of BGP) used in today’s Internet. We’ve added a significant new section on the SDN control plane, where routing and other functions are implemented in so-called SDN controllers.

• Chapter 6, which now covers the link layer, has an updated treatment of Ethernet, and of data center networking.

• Chapter 7, which covers wireless and mobile networking, contains updated ­material on 802.11 (so-called “WiFi) networks and cellular networks, including 4G and LTE.

• Chapter 8, which covers network security and was extensively updated in the sixth edition, has only modest updates in this seventh edition.

• Chapter 9, on multimedia networking, is now slightly “thinner” than in the sixth edition, as material on video streaming and content distribution networks has been moved to Chapter 2, and material on packet scheduling has been incorporated into Chapter 4.

• Significant new material involving end-of-chapter problems has been added. As with all previous editions, homework problems have been revised, added, and removed.

As always, our aim in creating this new edition of our book is to continue to provide a focused and modern treatment of computer networking, emphasizing both principles and practice.

This textbook is for a first course on computer networking. It can be used in both computer science and electrical engineering departments. In terms of programming languages, the book assumes only that the student has experience with C, C++, Java, or Python (and even then only in a few places). Although this book is more precise and analytical than many other introductory computer networking texts, it rarely uses any mathematical concepts that are not taught in high school. We have made a deliberate effort to avoid using any advanced calculus, probability, or stochastic process concepts (although we’ve included some homework problems for students with this advanced background). The book is therefore appropriate for undergraduate courses and for first-year graduate courses. It should also be useful to practitioners in the telecommunications industry.

Although we dropped the phrase “Featuring the Internet” from the title of this book with the fourth edition, this doesn’t mean that we dropped our focus on the Internet. Indeed, nothing could be further from the case! Instead, since the Internet has become so pervasive, we felt that any networking textbook must have a significant focus on the Internet, and thus this phrase was somewhat unnecessary. We continue to use the Internet’s architecture and protocols as primary vehicles for studying fundamental computer networking concepts. Of course, we also include concepts and protocols from other network architectures. But the spotlight is clearly on the Internet, a fact reflected in our organizing the book around the Internet’s five-layer architecture: the application, transport, network, link, and physical layers.

Another benefit of spotlighting the Internet is that most computer science and electrical engineering students are eager to learn about the Internet and its protocols. They know that the Internet has been a revolutionary and disruptive technology and can see that it is profoundly changing our world. Given the enormous relevance of the Internet, students are naturally curious about what is “under the hood.” Thus, it is easy for an instructor to get students excited about basic principles when using the Internet as the guiding focus.

Two of the unique features of the book—its top-down approach and its focus on the Internet—have appeared in the titles of our book. If we could have squeezed a third phrase into the subtitle, it would have contained the word principles. The field of networking is now mature enough that a number of fundamentally important issues can be identified. For example, in the transport layer, the fundamental issues include reliable communication over an unreliable network layer, connection establishment/ teardown and handshaking, congestion and flow control, and multiplexing. Three fundamentally important network-layer issues are determining “good” paths between two routers, interconnecting a large number of heterogeneous networks, and managing the complexity of a modern network. In the link layer, a fundamental problem is sharing a multiple access channel. In network security, techniques for providing confidentiality, authentication, and message integrity are all based on cryptographic fundamentals. This text identifies fundamental networking issues and studies approaches towards addressing these issues. The student learning these principles will gain knowledge with a long “shelf life”—long after today’s network standards and protocols have become obsolete, the principles they embody will remain important and relevant. We believe that the combination of using the Internet to get the student’s foot in the door and then emphasizing fundamental issues and solution approaches will allow the student to quickly understand just about any networking technology.

Each new copy of this textbook includes twelve months of access to a Companion ­Website for all book readers at http://www.pearsonhighered.com/cs-resources/, which includes:

• Interactive learning material. The book’s Companion Website contains ­VideoNotes—video presentations of important topics throughout the book done by the authors, as well as walkthroughs of solutions to problems similar to those at the end of the chapter. We’ve seeded the Web site with VideoNotes and ­online problems for Chapters 1 through 5 and will continue to actively add and update this material over time. As in earlier editions, the Web site contains the interactive Java applets that animate many key networking concepts. The site also has interactive quizzes that permit students to check their basic understanding of the subject matter. Professors can integrate these interactive features into their lectures or use them as mini labs.

• Additional technical material. As we have added new material in each edition of our book, we’ve had to remove coverage of some existing topics to keep the book at manageable length. For example, to make room for the new ­material in this ­edition, we’ve removed material on FTP, distributed hash tables, and multicasting, Material that appeared in earlier editions of the text is still of ­interest, and thus can be found on the book’s Web site.

• Programming assignments. The Web site also provides a number of detailed programming assignments, which include building a multithreaded Web ­server, building an e-mail client with a GUI interface, programming the sender and ­receiver sides of a reliable data transport protocol, programming a distributed routing algorithm, and more.

• Wireshark labs. One’s understanding of network protocols can be greatly ­deepened by seeing them in action. The Web site provides numerous Wireshark assignments that enable students to actually observe the sequence of messages exchanged between two protocol entities. The Web site includes separate Wireshark labs on HTTP, DNS, TCP, UDP, IP, ICMP, Ethernet, ARP, WiFi, SSL, and on tracing all protocols involved in satisfying a request to fetch a Web page. We’ll continue to add new labs over time.

In addition to the Companion Website, the authors maintain a public Web site, http://gaia.cs.umass.edu/kurose_ross/interactive, containing interactive exercises that create (and present solutions for) problems similar to selected end-of-chapter problems. Since students can generate (and view solutions for) an unlimited number of similar problem instances, they can work until the material is truly mastered.

Since we began writing this book in 1996, many people have given us invaluable help and have been influential in shaping our thoughts on how to best organize and teach a networking course. We want to say A BIG THANKS to everyone who has helped us from the earliest first drafts of this book, up to this seventh edition. We are also very thankful to the many hundreds of readers from around the world—students, faculty, practitioners—who have sent us thoughts and comments on earlier editions of the book and suggestions for future editions of the book. Special thanks go out to:

We also want to thank the entire Pearson team—in particular, Matt Goldstein and Joanne Manning—who have done an absolutely outstanding job on this seventh ­edition (and who have put up with two very finicky authors who seem congenitally ­unable to meet deadlines!). Thanks also to our artists, Janet Theurer and Patrice Rossi Calkin, for their work on the beautiful figures in this and earlier editions of our book, and to Katie Ostler and her team at Cenveo for their wonderful production work on this edition. Finally, a most special thanks go to our previous two editors at ­Addison-Wesley—Michael Hirsch and Susan Hartman. This book would not be what it is (and may well not have been at all) without their graceful management, constant encouragement, nearly infinite patience, good humor, and perseverance.