Computer Networking

A Top-Down Approach

Seventh Edition

James F. Kurose

University of Massachusetts, Amherst

Keith W. Ross

NYU and NYU Shanghai

Boston Columbus Indianapolis New York San Francisco Hoboken Amsterdam Cape Town Dubai London Madrid Milan Munich Paris Montréal Toronto Delhi Mexico City São Paulo Sydney Hong Kong Seoul Singapore Taipei Tokyo

Vice President, Editorial Director, ECS: Marcia Horton

Acquisitions Editor: Matt Goldstein

Editorial Assistant: Kristy Alaura

Vice President of Marketing: Christy Lesko

Director of Field Marketing: Tim Galligan

Product Marketing Manager: Bram Van Kempen

Field Marketing Manager: Demetrius Hall

Marketing Assistant: Jon Bryant

Director of Product Management: Erin Gregg

Team Lead, Program and Project Management: Scott Disanno

Program Manager: Joanne Manning and Carole Snyder

Project Manager: Katrina Ostler, Ostler Editorial, Inc.

Senior Specialist, Program Planning and Support: Maura Zaldivar-Garcia

Cover Designer: Joyce Wells

Manager, Rights and Permissions: Ben Ferrini

Project Manager, Rights and Permissions: Jenny Hoffman, Aptara Corporation

Inventory Manager: Ann Lam

Cover Image: Marc Gutierrez/Getty Images

Media Project Manager: Steve Wright

Composition: Cenveo Publishing Services

Printer/Binder: Edwards Brothers Malloy

Cover and Insert Printer: Phoenix Color/ Hagerstown

Credits and acknowledgments borrowed from other sources and reproduced, with ­permission, in this textbook appear on appropriate page within text.

Copyright © 2017, 2013, 2010 Pearson Education, Inc. All rights reserved. Manufactured in the United States of America. This publication is protected by Copyright, and permission should be obtained from the publisher prior to any prohibited reproduction, storage in a retrieval system, or transmission in any form or by any means, electronic, mechanical, photocopying, recording, or likewise. For information regarding permissions, request forms and the appropriate contacts within the Pearson Education Global Rights & Permissions Department, please visit www.pearsoned.com/permissions/. Many of the designations by manufacturers and seller to distinguish their products are claimed as trademarks. Where those designations appear in this book, and the publisher was aware of a trademark claim, the designations have been printed in initial caps or all caps.

Library of Congress Cataloging-in-Publication Data

Names: Kurose, James F. | Ross, Keith W., 1956-

Title: Computer networking: a top-down approach / James F. Kurose, University of Massachusetts, Amherst, Keith W. Ross, NYU and NYU Shanghai.

Description: Seventh edition. | Hoboken, New Jersey: Pearson, [2017] | Includes bibliographical references and index.

Identifiers: LCCN 2016004976 | ISBN 9780133594140 | ISBN 0133594149

Subjects: LCSH: Internet. | Computer networks.

Classification: LCC TK5105.875.I57 K88 2017 | DDC 004.6-dc23

LC record available at http://lccn.loc.gov/2016004976

ISBN-10:     0-13-359414-9

ISBN-13: 978-0-13-359414-0

About the Authors

Jim Kurose

Jim Kurose is a Distinguished University Professor of Computer Science at the University of Massachusetts, Amherst. He is currently on leave from the University of Massachusetts, serving as an Assistant Director at the US National Science Foundation, where he leads the Directorate of Computer and Information Science and Engineering.

Dr. Kurose has received a number of recognitions for his educational activities including Outstanding Teacher Awards from the National Technological University (eight times), the University of Massachusetts, and the Northeast Association of Graduate Schools. He received the IEEE Taylor Booth Education Medal and was recognized for his leadership of Massachusetts’ Commonwealth Information Technology Initiative. He has won several conference best paper awards and received the IEEE Infocom Achievement Award and the ACM Sigcomm Test of Time Award.

Dr. Kurose is a former Editor-in-Chief of IEEE Transactions on Communications and of IEEE/ACM Transactions on Networking. He has served as Technical Program co-Chair for IEEE Infocom, ACM SIGCOMM, ACM Internet Measurement Conference, and ACM SIGMETRICS. He is a Fellow of the IEEE and the ACM. His research ­interests include network protocols and architecture, network measurement, multimedia communication, and modeling and performance ­evaluation. He holds a PhD in Computer Science from Columbia University.

Keith Ross

Keith Ross is the Dean of Engineering and Computer Science at NYU Shanghai and the Leonard J. Shustek Chair Professor in the Computer Science and Engineering Department at NYU. Previously he was at University of Pennsylvania (13 years), Eurecom Institute (5 years) and Polytechnic University (10 years). He received a B.S.E.E from Tufts University, a M.S.E.E. from Columbia University, and a Ph.D. in Computer and Control Engineering from The University of Michigan. Keith Ross is also the co-founder and original CEO of Wimba, which develops online multimedia applications for e-learning and was acquired by Blackboard in 2010.

Professor Ross’s research interests are in privacy, social networks, peer-to-peer networking, Internet measurement, content distribution networks, and stochastic modeling. He is an ACM Fellow, an IEEE Fellow, recipient of the Infocom 2009 Best Paper Award, and recipient of 2011 and 2008 Best Paper Awards for Multimedia Communications (awarded by IEEE Communications Society). He has served on numerous journal editorial boards and conference program committees, including IEEE/ACM Transactions on Networking, ACM SIGCOMM, ACM CoNext, and ACM Internet Measurement Conference. He also has served as an advisor to the Federal Trade Commission on P2P file sharing.

To Julie and our three precious ones—Chris, Charlie, and Nina

JFK

A big THANKS to my professors, colleagues, and students all over the world.

KWR

Preface

Welcome to the seventh edition of Computer Networking: A Top-Down Approach. Since the publication of the first edition 16 years ago, our book has been adopted for use at many hundreds of colleges and universities, translated into 14 languages, and used by over one hundred thousand students and practitioners worldwide. We’ve heard from many of these readers and have been overwhelmed by the ­positive ­response.

What’s New in the Seventh Edition?

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.

Audience

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.

What Is Unique About This Textbook?

The subject of computer networking is enormously complex, involving many concepts, protocols, and technologies that are woven together in an intricate manner. To cope with this scope and complexity, many computer networking texts are often organized around the “layers” of a network architecture. With a layered organization, students can see through the complexity of computer networking—they learn about the distinct concepts and protocols in one part of the architecture while seeing the big picture of how all parts fit together. From a pedagogical perspective, our personal experience has been that such a layered approach indeed works well. Nevertheless, we have found that the traditional approach of teaching—bottom up; that is, from the physical layer towards the application layer—is not the best approach for a modern course on computer networking.

A Top-Down Approach

Our book broke new ground 16 years ago by treating networking in a top-down ­manner—that is, by beginning at the application layer and working its way down toward the physical layer. The feedback we received from teachers and students alike have confirmed that this top-down approach has many advantages and does indeed work well pedagogically. First, it places emphasis on the application layer (a “high growth area” in networking). Indeed, many of the recent revolutions in ­computer networking—including the Web, peer-to-peer file sharing, and media streaming—have taken place at the application layer. An early emphasis on application-layer issues differs from the approaches taken in most other texts, which have only a small amount of material on network applications, their requirements, application-layer paradigms (e.g., client-server and peer-to-peer), and application programming ­interfaces. ­Second, our experience as instructors (and that of many instructors who have used this text) has been that teaching networking applications near the beginning of the course is a powerful motivational tool. Students are thrilled to learn about how networking applications work—applications such as e-mail and the Web, which most students use on a daily basis. Once a student understands the applications, the student can then understand the network services needed to support these applications. The student can then, in turn, examine the various ways in which such services might be provided and implemented in the lower layers. Covering applications early thus provides motivation for the remainder of the text.

Third, a top-down approach enables instructors to introduce network application development at an early stage. Students not only see how popular applications and protocols work, but also learn how easy it is to create their own network ­applications and application-level protocols. With the top-down approach, students get early ­exposure to the notions of socket programming, service models, and ­protocols—important concepts that resurface in all subsequent layers. By providing socket programming examples in Python, we highlight the central ideas without confusing students with complex code. Undergraduates in electrical engineering and computer science should not have difficulty following the Python code.

An Internet Focus

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.

Teaching Networking Principles

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.

The Website

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.

Pedagogical Features

We have each been teaching computer networking for more than 30 years. Together, we bring more than 60 years of teaching experience to this text, during which time we have taught many thousands of students. We have also been active researchers in computer networking during this time. (In fact, Jim and Keith first met each other as master’s students in a computer networking course taught by Mischa Schwartz in 1979 at Columbia University.) We think all this gives us a good perspective on where networking has been and where it is likely to go in the future. Nevertheless, we have resisted temptations to bias the material in this book towards our own pet research projects. We figure you can visit our personal Web sites if you are interested in our research. Thus, this book is about modern computer networking—it is about contemporary protocols and technologies as well as the underlying principles behind these protocols and technologies. We also believe that learning (and teaching!) about networking can be fun. A sense of humor, use of analogies, and real-world examples in this book will hopefully make this material more fun.

Supplements for Instructors

We provide a complete supplements package to aid instructors in teaching this course. This material can be accessed from Pearson’s Instructor Resource Center (http://www.pearsonhighered.com/irc). Visit the Instructor Resource Center for ­information about accessing these instructor’s supplements.

  • PowerPoint® slides. We provide PowerPoint slides for all nine chapters. The slides have been completely updated with this seventh edition. The slides cover each chapter in detail. They use graphics and animations (rather than relying only on monotonous text bullets) to make the slides interesting and visually appealing. We provide the original PowerPoint slides so you can customize them to best suit your own teaching needs. Some of these slides have been contributed by other instructors who have taught from our book.

  • Homework solutions. We provide a solutions manual for the homework problems in the text, programming assignments, and Wireshark labs. As noted ­earlier, we’ve introduced many new homework problems in the first six chapters of the book.

Chapter Dependencies

The first chapter of this text presents a self-contained overview of computer networking. Introducing many key concepts and terminology, this chapter sets the stage for the rest of the book. All of the other chapters directly depend on this first chapter. After completing Chapter 1, we recommend instructors cover Chapters 2 through 6 in sequence, following our top-down philosophy. Each of these five chapters leverages material from the preceding chapters. After completing the first six chapters, the instructor has quite a bit of flexibility. There are no interdependencies among the last three chapters, so they can be taught in any order. However, each of the last three chapters depends on the material in the first six chapters. Many instructors first teach the first six chapters and then teach one of the last three chapters for “dessert.”

One Final Note: We’d Love to Hear from You

We encourage students and instructors to e-mail us with any comments they might have about our book. It’s been wonderful for us to hear from so many instructors and students from around the world about our first five editions. We’ve incorporated many of these suggestions into later editions of the book. We also encourage instructors to send us new homework problems (and solutions) that would complement the current homework problems. We’ll post these on the instructor-only portion of the Web site. We also encourage instructors and students to create new Java applets that illustrate the concepts and protocols in this book. If you have an applet that you think would be appropriate for this text, please submit it to us. If the applet (including notation and terminology) is appropriate, we’ll be happy to include it on the text’s Web site, with an appropriate reference to the applet’s authors.

So, as the saying goes, “Keep those cards and letters coming!” Seriously, please do continue to send us interesting URLs, point out typos, disagree with any of our claims, and tell us what works and what doesn’t work. Tell us what you think should or shouldn’t be included in the next edition. Send your e-mail to and .

Acknowledgments

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.