This page intentionally left blank COMPUTER NETWORKS FIFTH EDITION This page intentionally left blank COMPUTER NETWORKS FIFTH EDITION ANDREW S. TANENBAUM Vrije Universiteit Amsterdam, The Netherlands DAVID J. WETHERALL University of Washington Seattle, WA PRENTICE HALL Boston Columbus Indianapolis NewYork SanFrancisco UpperSaddleRiver Amsterdam CapeTown Dubai London Madrid Milan Paris Montreal Toronto Delhi MexicoCity Sao Paulo Sydney HongKong Seoul Singapore Tapei Tokyo Editorial Director: Marcia Horton Art Director: Linda Knowles Editor-in-Chief: Michael Hirsch Cover Designer: Susan Paradise Executive Editor: Tracy Dunkelberger Cover Illustration: Jason Consalvo Assistant Editor: Melinda Haggerty Interior Design: Andrew S. Tanenbaum Editorial Assistant: Allison Michael AV Production Project Manager: Vice President, Marketing: Patrice Jones Gregory L. Dulles Marketing Manager: Yezan Alayan Interior Illustrations: Laserwords, Inc. Marketing Coordinator: Kathryn Ferranti Media Editor: Daniel Sandin Vice President, Production: Vince O’Brien Composition: Andrew S. Tanenbaum Managing Editor: Jeff Holcomb Copyeditor: Rachel Head Senior Operations Supervisor: Alan Fischer Proofreader: Joe Ruddick Manufacturing Buyer: Lisa McDowell Printer/Binder: Courier/Westford Cover Direction: Andrew S. Tanenbaum, Cover Printer: Lehigh-Phoenix Color/ David J. Wetherall, Tracy Dunkelberger Hagerstown Credits and acknowledgments borrowed from other sources and reproduced, with permission, in this textbook appear on appropriate page within text. Many of the designations by manufacturers and sellers 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. Copyright © 2011, 2003, 1996, 1989, 1981 Pearson Education, Inc., publishing as Prentice Hall. 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. To obtain permission(s) to use material from this work, please submit a written request to Pearson Education, Inc., Permissions Department, 501 Boylston Street, Suite 900, Boston, Massachusetts 02116. Library of Congress Cataloging-in-Publication Data Tanenbaum, Andrew S., 1944- Computer networks / Andrew S. Tanenbaum, David J. Wetherall. -- 5th ed. p. cm. Includes bibliographical references and index. ISBN-13: 978-0-13-212695-3 (alk. paper) ISBN-10: 0-13-212695-8 (alk. paper) 1. Computer networks. I. Wetherall, D. (David) II. Title. TK5105.5.T36 2011 004.6--dc22 2010034366 10 9 8 7 6 5 4 3 2 1—CRW—14 13 12 11 10 To Suzanne, Barbara, Daniel, Aron, Marvin, Matilde, andthe memory of Bram, andSweetie π (AST) To Katrin, Lucy, andPepper (DJW) This page intentionally left blank CONTENTS PREFACE xix 1 INTRODUCTION 1 1.1USES OFCOMPUTER NETWORKS, 3 1.1.1Business Applications, 3 1.1.2HomeApplications, 6 1.1.3Mobile Users, 10 1.1.4Social Issues, 14 1.2NETWORK HARDWARE, 17 1.2.1Personal Area Networks, 18 1.2.2Local Area Networks, 19 1.2.3MetropolitanArea Networks, 23 1.2.4Wide Area Networks, 23 1.2.5Internetworks, 28 1.3NETWORK SOFTWARE, 29 1.3.1Protocol Hierarchies, 29 1.3.2Design Issues fortheLayers, 33 1.3.3Connection-OrientedVersus ConnectionlessService, 35 1.3.4Service Primitives,38 1.3.5The Relationship ofServices toProtocols, 40 1.4REFERENCE MODELS, 41 1.4.1The OSIReference Model, 41 1.4.2The TCP/IP Reference Model, 45 1.4.3The ModelUsedinThisBook,48 vii viii CONTENTS 1.4.4AComparison oftheOSIandTCP/IP Reference Models*, 49 1.4.5ACritiqueoftheOSI ModelandProtocols*, 51 1.4.6ACritiqueoftheTCP/IP Reference Model*, 53 1.5EXAMPLE NETWORKS, 54 1.5.1The Internet, 54 1.5.2Third-Generation Mobile PhoneNetworks*, 65 1.5.3Wireless LANs: 802.11*,70 1.5.4RFID andSensor Networks*, 73 1.6NETWORK STANDARDIZATION*,75 1.6.1Who’sWhointheTelecommunications World, 77 1.6.2Who’sWhointheInternational Standards World, 78 1.6.3Who’sWhointheInternet Standards World, 80 1.7METRIC UNITS, 82 1.8OUTLINE OFTHEREST OFTHE BOOK,83 1.9SUMMARY, 84 2 THE PHYSICAL LAYER 89 2.1THE THEORETICAL BASIS FOR DATA COMMUNICATION, 90 2.1.1Fourier Analysis, 90 2.1.2Bandwidth-Limited Signals, 90 2.1.3The Maximum Data Rate ofaChannel, 94 2.2GUIDED TRANSMISSION MEDIA, 95 2.2.1Magnetic Media, 95 2.2.2Twisted Pairs, 96 2.2.3Coaxial Cable, 97 2.2.4Power Lines, 98 2.2.5Fiber Optics, 99 2.3WIRELESSTRANSMISSION, 105 2.3.1The Electromagnetic Spectrum, 105 2.3.2Radio Transmission, 109 2.3.3Microwave Transmission, 110 2.3.4Infrared Transmission, 114 2.3.5LightTransmission, 114