Fluent Essays

Please read the file before discussion    The solution for every part should include the original formulas & a steps of calculations. The solution for every part it should include the original formulas & a steps of calculations. Problem 1 (10 points): Consider the example given in textbook pages 91-92. Figure 1 (on page 92) part (d) shows the low pass filtered signal when only the first four harmonic terms are passed through the filter. The low pass filter rejects the other higher frequency components. a) (7 points) compute the percentage of power for the signal shown in part (d) relative to the original signal shown in part (a) of the figure. b) (3 points) compute the bandwidth of the signal shown in part (d) of the figure. Assume A = 2 volts and T = 1 msec. Hint: you may want to use the table of coefficients 𝑐, 𝑎𝑛, and 𝑏𝑛 given in the powerpoint slides provided by instructor. Problem 2 (15 points): Consider the power spectral density function shown in Figure below for the periodic signal g(t). The figure shows the specific frequency components and the corresponding power. a) (10 points) specify one corresponding time-domain function g(t). b) (5 points) sketch g(t) for values of t ranging from -1 to 1 seconds. Problem 3 (15 points) A file of size 𝐾 = 100 KBytes is to be sent from Node 1 to Node 5 traversing four identical intermediate links as shown in Figure below. The data link protocol operating on node 1 requires that 𝑉 = 50 bits be added as overhead to any frame transmitted on the link. Assume the link transmission rate is 𝑅 = 80 kb/s while the link propagation time, 𝑇prop is equal to 2 msec. Node processing delay is ignored. An intermediate node can start transmitting the received frame immediately when it is fully received. a) (5 points) If the file is NOT segmented at node 1, but rather sent as a whole together with the overhead 𝑉, compute the total transmission time, 𝑇total1, till the file is completely received at Node 5. b) (10 points) For this part assume the file at node 1 is divided into frames each of size 𝐹 bits. Of course, as before V overhead bits are added to F data bits at node 1 before transmission on link 1. The figure below shows the case of dividing the frame into 𝑚 frames. Note that 𝑇𝑓 is the time to transmit the frame on the link, while 𝑇prop is the time it signal to propagate and reach the other end of the link. If the frame size F is chosen to be very small, then m is going to be large and these links are going to be transmitting overhead bits most of the time. The other extreme is when the frame size is equal to the original file size as in part (a) of this problem, then m is equal to 1. In this case the file transmission time is still not optimal. It is required to determine the best frame size that results in minimum transmission time. Hint: Let the frame size F vary from 1 bit all the way to original file size in bits, and for each value compute the corresponding T_total2. Refer to textbook problem 39 page 190 for the more general case. Problem 4 (15 points): A typical telephone channel has the bandwidth of 3100 Hz can support dial-up modems that can variable speeds depending on the quality of the links on both ends of the data call. a) (5 points) Assuming the dial-up modem is working at rate of 33.6 kb/s, compute the minimum needed Eb/N0 in dBs. b) (4 points) For part (a), what is the theoretical number of bits per symbol needed to achieve this 33.6 kb/s? c) (6 points) What are (1) the baud rate and (2) number of bits per symbol used on a standard telephone channel that operates at 33.6 kb/s. Specify the standard model that implements the above specifications for a dial-up modem. Hint: Refer to textbook pages 145-147. Problem 5 (10 points): Consider a 256 4kHz channels ADSL system operating over twisted pair as shown in Figure. The system utilizes a variety of modulation and coding schemes on each of the channels depending on the reported SNR for the channel. Assume the available modulation schemes are BPSK, QPS, 16-QAM, and 64-QAM, while the utilized coding schemes provide coding rates equal to 1/4, 1/3, 1/2, 3/4, and 5/6. Assume the POTS uses the lower 6 channels and 2 channels are reserved for control. Furthermore, ADSL uses a modulation that produces 4000 bauds per second on the channel. If 3/4 of the available ADSL channels are utilized for the downstream, compute the minimum and maximum possible downlink throughput numbers for the ADSL system? Hint: Please refer to textbook subsection on ADSL modem. 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 New York San Francisco Upper Saddle River Amsterdam Cape Town Dubai London Madrid Milan Paris Montreal Toronto Delhi Mexico City Sao Paulo Sydney Hong Kong Seoul Singapore Tapei Tokyo Editorial Director: Marcia Horton Editor-in-Chief: Michael Hirsch Executive Editor: Tracy Dunkelberger Assistant Editor: Melinda Haggerty Editorial Assistant: Allison Michael Vice President, Marketing: Patrice Jones Marketing Manager: Yezan Alayan Marketing Coordinator: Kathryn Ferranti Vice President, Production: Vince O’Brien Managing Editor: Jeff Holcomb Senior Operations Supervisor: Alan Fischer Manufacturing Buyer: Lisa McDowell Cover Direction: Andrew S. Tanenbaum, David J. Wetherall, Tracy Dunkelberger Art Director: Linda Knowles Cover Designer: Susan Paradise Cover Illustration: Jason Consalvo Interior Design: Andrew S. Tanenbaum AV Production Project Manager: Gregory L. Dulles Interior Illustrations: Laserwords, Inc. Media Editor: Daniel Sandin Composition: Andrew S. Tanenbaum Copyeditor: Rachel Head Proofreader: Joe Ruddick Printer/Binder: Courier/Westford Cover Printer: Lehigh-Phoenix Color/ 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, and the memory of Bram, and Sweetie π (AST) To Katrin, Lucy, and Pepper (DJW) This page intentionally left blank CONTENTS PREFACE xix 1 INTRODUCTION 1 1.1 USES OF COMPUTER NETWORKS, 3 1.1.1 Business Applications, 3 1.1.2 Home Applications, 6 1.1.3 Mobile Users, 10 1.1.4 Social Issues, 14 1.2 NETWORK HARDWARE, 17 1.2.1 Personal Area Networks, 18 1.2.2 Local Area Networks, 19 1.2.3 Metropolitan Area Networks, 23 1.2.4 Wide Area Networks, 23 1.2.5 Internetworks, 28 1.3 NETWORK SOFTWARE, 29 1.3.1 Protocol Hierarchies, 29 1.3.2 Design Issues for the Layers, 33 1.3.3 Connection-Oriented Versus Connectionless Service, 35 1.3.4 Service Primitives, 38 1.3.5 The Relationship of Services to Protocols, 40 1.4 REFERENCE MODELS, 41 1.4.1 The OSI Reference Model, 41 1.4.2 The TCP/IP Reference Model, 45 1.4.3 The Model Used in This Book, 48 vii viii CONTENTS 1.4.4 A Comparison of the OSI and TCP/IP Reference Models*, 49 1.4.5 A Critique of the OSI Model and Protocols*, 51 1.4.6 A Critique of the TCP/IP Reference Model*, 53 1.5 EXAMPLE NETWORKS, 54 1.5.1 The Internet, 54 1.5.2 Third-Generation Mobile Phone Networks*, 65 1.5.3 Wireless LANs: 802.11*, 70 1.5.4 RFID and Sensor Networks*, 73 1.6 NETWORK STANDARDIZATION*, 75 1.6.1 Who’s Who in the Telecommunications World, 77 1.6.2 Who’s Who in the International Standards World, 78 1.6.3 Who’s Who in the Internet Standards World, 80 1.7 METRIC UNITS, 82 1.8 OUTLINE OF THE REST OF THE BOOK, 83 1.9 SUMMARY, 84 2 THE PHYSICAL LAYER 89 2.1 THE THEORETICAL BASIS FOR DATA COMMUNICATION, 90 2.1.1 Fourier Analysis, 90 2.1.2 Bandwidth-Limited Signals, 90 2.1.3 The Maximum Data Rate of a Channel, 94 2.2 GUIDED TRANSMISSION MEDIA, 95 2.2.1 Magnetic Media, 95 2.2.2 Twisted Pairs, 96 2.2.3 Coaxial Cable, 97 2.2.4 Power Lines, 98 2.2.5 Fiber Optics, 99 2.3 WIRELESS TRANSMISSION, 105 2.3.1 The Electromagnetic Spectrum, 105 2.3.2 Radio Transmission, 109 2.3.3 Microwave Transmission, 110 2.3.4 Infrared Transmission, 114 2.3.5 Light Transmission, 114 CONTENTS ix 2.4 COMMUNICATION SATELLITES*, 116 2.4.1 Geostationary Satellites, 117 2.4.2 Medium-Earth Orbit Satellites, 121 2.4.3 Low-Earth Orbit Satellites, 121 2.4.4 Satellites Versus Fiber, 123 2.5 DIGITAL MODULATION AND MULTIPLEXING, 125 2.5.1 Baseband Transmission, 125 2.5.2 Passband Transmission, 130 2.5.3 Frequency Division Multiplexing, 132 2.5.4 Time Division Multiplexing, 135 2.5.5 Code Division Multiplexing, 135 2.6 THE PUBLIC SWITCHED TELEPHONE NETWORK, 138 2.6.1 Structure of the Telephone System, 139 2.6.2 The Politics of Telephones, 142 2.6.3 The Local Loop: Modems, ADSL, and Fiber, 144 2.6.4 Trunks and Multiplexing, 152 2.6.5 Switching, 161 2.7 THE MOBILE TELEPHONE SYSTEM*, 164 2.7.1 First-Generation (coco1G) Mobile Phones: Analog Voice, 166 2.7.2 Second-Generation (2G) Mobile Phones: Digital Voice, 170 2.7.3 Third-Generation (3G) Mobile Phones: Digital Voice and Data, 174 2.8 CABLE TELEVISION*, 179 2.8.1 Community Antenna Television, 179 2.8.2 Internet over Cable, 180 2.8.3 Spectrum Allocation, 182 2.8.4 Cable Modems, 183 2.8.5 ADSL Versus Cable, 185 2.9 SUMMARY, 186 3 THE DATA LINK LAYER 193 3.1 DATA LINK LAYER DESIGN ISSUES, 194 3.1.1 Services Provided to the Network Layer, 194 3.1.2 Framing, 197 3.1.3 Error Control, 200 3.1.4 Flow Control, 201 x CONTENTS 3.2 ERROR DETECTION AND CORRECTION, 202 3.2.1 Error-Correcting Codes, 204 3.2.2 Error-Detecting Codes, 209 3.3 ELEMENTARY DATA LINK PROTOCOLS, 215 3.3.1 A Utopian Simplex Protocol, 220 3.3.2 A Simplex Stop-and-Wait Protocol for an Error-Free Channel, 221 3.3.3 A Simplex Stop-and-Wait Protocol for a Noisy Channel, 222 3.4 SLIDING WINDOW PROTOCOLS, 226 3.4.1 A One-Bit Sliding Window Protocol, 229 3.4.2 A Protocol Using Go-Back-N, 232 3.4.3 A Protocol Using Selective Repeat, 239 3.5 EXAMPLE DATA LINK PROTOCOLS, 244 3.5.1 Packet over SONET, 245 3.5.2 ADSL (Asymmetric Digital Subscriber Loop), 248 3.6 SUMMARY, 251 4 THE MEDIUM ACCESS CONTROL SUBLAYER 257 4.1 THE CHANNEL ALLOCATION PROBLEM, 258 4.1.1 Static Channel Allocation, 258 4.1.2 Assumptions for Dynamic Channel Allocation, 260 4.2 MULTIPLE ACCESS PROTOCOLS, 261 4.2.1 ALOHA, 262 4.2.2 Carrier Sense Multiple Access Protocols, 266 4.2.3 Collision-Free Protocols, 269 4.2.4 Limited-Contention Protocols, 274 4.2.5 Wireless LAN Protocols, 277 4.3 ETHERNET, 280 4.3.1 Classic Ethernet Physical Layer, 281 4.3.2 Classic Ethernet MAC Sublayer Protocol, 282 4.3.3 Ethernet Performance, 286 4.3.4 Switched Ethernet, 288 CONTENTS xi 4.3.5 Fast Ethernet, 290 4.3.6 Gigabit Ethernet, 293 4.3.7 10-Gigabit Ethernet, 296 4.3.8 Retrospective on Ethernet, 298 4.4 WIRELESS LANS, 299 4.4.1 The 802.11 Architecture and Protocol Stack, 299 4.4.2 The 802.11 Physical Layer, 301 4.4.3 The 802.11 MAC Sublayer Protocol, 303 4.4.4 The 802.11 Frame Structure, 309 4.4.5 Services, 311 4.5 BROADBAND WIRELESS*, 312 4.5.1 Comparison of 802.16 with 802.11 and 3G, 313 4.5.2 The 802.16 Architecture and Protocol Stack, 314 4.5.3 The 802.16 Physical Layer, 316 4.5.4 The 802.16 MAC Sublayer Protocol, 317 4.5.5 The 802.16 Frame Structure, 319 4.6 BLUETOOTH*, 320 4.6.1 Bluetooth Architecture, 320 4.6.2 Bluetooth Applications, 321 4.6.3 The Bluetooth Protocol Stack, 322 4.6.4 The Bluetooth Radio Layer, 324 4.6.5 The Bluetooth Link Layers, 324 4.6.6 The Bluetooth Frame Structure, 325 4.7 RFID*, 327 4.7.1 EPC Gen 2 Architecture, 327 4.7.2 EPC Gen 2 Physical Layer, 328 4.7.3 EPC Gen 2 Tag Identification Layer, 329 4.7.4 Tag Identification Message Formats, 331 4.8 DATA LINK LAYER SWITCHING, 332 4.8.1 Uses of Bridges, 332 4.8.2 Learning Bridges, 334 4.8.3 Spanning Tree Bridges, 337 4.8.4 Repeaters, Hubs, Bridges, Switches, Routers, and Gateways, 340 4.8.5 Virtual LANs, 342 4.9 SUMMARY, 349 xii CONTENTS 5 THE NETWORK LAYER 355 5.1 NETWORK LAYER DESIGN ISSUES, 355 5.1.1 Store-and-Forward Packet Switching, 356 5.1.2 Services Provided to the Transport Layer, 356 5.1.3 Implementation of Connectionless Service, 358 5.1.4 Implementation of Connection-Oriented Service, 359 5.1.5 Comparison of Virtual-Circuit and Datagram Networks, 361 5.2 ROUTING ALGORITHMS, 362 5.2.1 The Optimality Principle, 364 5.2.2 Shortest Path Algorithm, 366 5.2.3 Flooding, 368 5.2.4 Distance Vector Routing, 370 5.2.5 Link State Routing, 373 5.2.6 Hierarchical Routing, 378 5.2.7 Broadcast Routing, 380 5.2.8 Multicast Routing, 382 5.2.9 Anycast Routing, 385 5.2.10 Routing for Mobile Hosts, 386 5.2.11 Routing in Ad Hoc Networks, 389 5.3 CONGESTION CONTROL ALGORITHMS, 392 5.3.1 Approaches to Congestion Control, 394 5.3.2 Traffic-Aware Routing, 395 5.3.3 Admission Control, 397 5.3.4 Traffic Throttling, 398 5.3.5 Load Shedding, 401 5.4 QUALITY OF SERVICE, 404 5.4.1 Application Requirements, 405 5.4.2 Traffic Shaping, 407 5.4.3 Packet Scheduling, 411 5.4.4 Admission Control, 415 5.4.5 Integrated Services, 418 5.4.6 Differentiated Services, 421 5.5 INTERNETWORKING, 424 5.5.1 How Networks Differ, 425 5.5.2 How Networks Can Be Connected, 426 5.5.3 Tunneling, 429 CONTENTS xiii 5.5.4 Internetwork Routing, 431 5.5.5 Packet Fragmentation, 432 5.6 THE NETWORK LAYER IN THE INTERNET, 436 5.6.1 The IP Version 4 Protocol, 439 5.6.2 IP Addresses, 442 5.6.3 IP Version 6, 455 5.6.4 Internet Control Protocols, 465 5.6.5 Label Switching and MPLS, 470 5.6.6 OSPF—An Interior Gateway Routing Protocol, 474 5.6.7 BGP—The Exterior Gateway Routing Protocol, 479 5.6.8 Internet Multicasting, 484 5.6.9 Mobile IP, 485 5.7 SUMMARY, 488 6 THE TRANSPORT LAYER 495 6.1 THE TRANSPORT SERVICE, 495 6.1.1 Services Provided to the Upper Layers, 496 6.1.2 Transport Service Primitives, 498 6.1.3 Berkeley Sockets, 500 6.1.4 An Example of Socket Programming: An Internet File Server, 503 6.2 ELEMENTS OF TRANSPORT PROTOCOLS, 507 6.2.1 Addressing, 509 6.2.2 Connection Establishment, 512 6.2.3 Connection Release, 517 6.2.4 Error Control and Flow Control, 522 6.2.5 Multiplexing, 527 6.2.6 Crash Recovery, 527 6.3 CONGESTION CONTROL, 530 6.3.1 Desirable Bandwidth Allocation, 531 6.3.2 Regulating the Sending Rate, 535 6.3.3 Wireless Issues, 539 6.4 THE INTERNET TRANSPORT PROTOCOLS: UDP, 541 6.4.1 Introduction to UDP, 541 6.4.2 Remote Procedure Call, 543 6.4.3 Real-Time Transport Protocols, 546 xiv CONTENTS 6.5 THE INTERNET TRANSPORT PROTOCOLS: TCP, 552 6.5.1 Introduction to TCP, 552 6.5.2 The TCP Service Model, 553 6.5.3 The TCP Protocol, 556 6.5.4 The TCP Segment Header, 557 6.5.5 TCP Connection Establishment, 560 6.5.6 TCP Connection Release, 562 6.5.7 TCP Connection Management Modeling, 562 6.5.8 TCP Sliding Window, 565 6.5.9 TCP Timer Management, 568 6.5.10 TCP Congestion Control, 571 6.5.11 The Future of TCP, 581 6.6 PERFORMANCE ISSUES*, 582 6.6.1 Performance Problems in Computer Networks, 583 6.6.2 Network Performance Measurement, 584 6.6.3 Host Design for Fast Networks, 586 6.6.4 Fast Segment Processing, 590 6.6.5 Header Compression, 593 6.6.6 Protocols for Long Fat Networks, 595 6.7 DELAY-TOLERANT NETWORKING*, 599 6.7.1 DTN Architecture, 600 6.7.2 The Bundle Protocol, 603 6.8 SUMMARY, 605 7 THE APPLICATION LAYER 611 7.1 DNS—THE DOMAIN NAME SYSTEM, 611 7.1.1 The DNS Name Space, 612 7.1.2 Domain Resource Records, 616 7.1.3 Name Servers, 619 7.2 ELECTRONIC MAIL*, 623 7.2.1 Architecture and Services, 624 7.2.2 The User Agent, 626 7.2.3 Message Formats, 630 7.2.4 Message Transfer, 637 7.2.5 Final Delivery, 643 CONTENTS xv 7.3 THE WORLD WIDE WEB, 646 7.3.1 Architectural Overview, 647 7.3.2 Static Web Pages, 662 7.3.3 Dynamic Web Pages and Web Applications, 672 7.3.4 HTTP—The HyperText Transfer Protocol, 683 7.3.5 The Mobile Web, 693 7.3.6 Web Search, 695 7.4 STREAMING AUDIO AND VIDEO, 697 7.4.1 Digital Audio, 699 7.4.2 Digital Video, 704 7.4.3 Streaming Stored Media, 713 7.4.4 Streaming Live Media, 721 7.4.5 Real-Time Conferencing, 724 7.5 CONTENT DELIVERY, 734 7.5.1 Content and Internet Traffic, 736 7.5.2 Server Farms and Web Proxies, 738 7.5.3 Content Delivery Networks, 743 7.5.4 Peer-to-Peer Networks, 748 7.6 SUMMARY, 757 8 NETWORK SECURITY 763 8.1 CRYPTOGRAPHY, 766 8.1.1 Introduction to Cryptography, 767 8.1.2 Substitution Ciphers, 769 8.1.3 Transposition Ciphers, 771 8.1.4 One-Time Pads, 772 8.1.5 Two Fundamental Cryptographic Principles, 776 8.2 SYMMETRIC-KEY ALGORITHMS, 778 8.2.1 DES—The Data Encryption Standard, 780 8.2.2 AES—The Advanced Encryption Standard, 783 8.2.3 Cipher Modes, 787 8.2.4 Other Ciphers, 792 8.2.5 Cryptanalysis, 792 xvi CONTENTS 8.3 PUBLIC-KEY ALGORITHMS, 793 8.3.1 RSA, 794 8.3.2 Other Public-Key Algorithms, 796 8.4 DIGITAL SIGNATURES, 797 8.4.1 Symmetric-Key Signatures, 798 8.4.2 Public-Key Signatures, 799 8.4.3 Message Digests, 800 8.4.4 The Birthday Attack, 804 8.5 MANAGEMENT OF PUBLIC KEYS, 806 8.5.1 Certificates, 807 8.5.2 X.509, 809 8.5.3 Public Key Infrastructures, 810 8.6 COMMUNICATION SECURITY, 813 8.6.1 IPsec, 814 8.6.2 Firewalls, 818 8.6.3 Virtual Private Networks, 821 8.6.4 Wireless Security, 822 8.7 AUTHENTICATION PROTOCOLS, 827 8.7.1 Authentication Based on a Shared Secret Key, 828 8.7.2 Establishing a Shared Key: The Diffie-Hellman Key Exchange, 833 8.7.3 Authentication Using a Key Distribution Center, 835 8.7.4 Authentication Using Kerberos, 838 8.7.5 Authentication Using Public-Key Cryptography, 840 8.8 EMAIL SECURITY*, 841 8.8.1 PGP—Pretty Good Privacy, 842 8.8.2 S/MIME, 846 8.9 WEB SECURITY, 846 8.9.1 Threats, 847 8.9.2 Secure Naming, 848 8.9.3 SSL—The Secure Sockets Layer, 853 8.9.4 Mobile Code Security, 857 8.10 SOCIAL ISSUES, 860 8.10.1 Privacy, 860 8.10.2 Freedom of Speech, 863 8.10.3 Copyright, 867 8.11 SUMMARY, 869 CONTENTS xvii 9 READING LIST AND BIBLIOGRAPHY 877 9.1 SUGGESTIONS FOR FURTHER READING*, 877 9.1.1 Introduction and General Works, 878 9.1.2 The Physical Layer, 879 9.1.3 The Data Link Layer, 880 9.1.4 The Medium Access Control Sublayer, 880 9.1.5 The Network Layer, 881 9.1.6 The Transport Layer, 882 9.1.7 The Application Layer, 882 9.1.8 Network Security, 883 9.2 ALPHABETICAL BIBLIOGRAPHY*, 884 INDEX 905 This page intentionally left blank PREFACE This book is now in its fifth edition. Each edition has corresponded to a dif- ferent phase in the way computer networks were used. When the first edition ap- peared in 1980, networks were an academic curiosity. When the second edition appeared in 1988, networks were used by universities and large businesses. When the third edition appeared in 1996, computer networks, especially the Internet, had become a daily reality for millions of people. By the fourth edition, in 2003, wire- less networks and mobile computers had become commonplace for accessing the Web and the Internet. Now, in the fifth edition, networks are about content dis- tribution (especially videos using CDNs and peer-to-peer networks) and mobile phones are small computers on the Internet. New in the Fifth Edition Among the many changes in this book, the most important one is the addition of Prof. David J. Wetherall as a co-author. David brings a rich background in net- working, having cut his teeth designing metropolitan-area networks more than 20 years ago. He has worked with the Internet and wireless networks ever since and is a professor at the University of Washington, where he has been teaching and doing research on computer networks and related topics for the past decade. Of course, the book also has many changes to keep up with the: ever-changing world of computer networks. Among these are revised and new material on Wireless networks (802.12 and 802.16) The 3G networks used by smart phones RFID and sensor networks Content distribution using CDNs Peer-to-peer networks Real-time media (from stored, streaming, and live sources) Internet telephony (voice over IP) Delay-tolerant networks A more detailed chapter-by-chapter list follows. xix xx PREFACE Chapter 1 has the same introductory function as in the fourth edition, but the contents have been revised and brought up to date. The Internet, mobile phone networks, 802.11, and RFID and sensor networks are discussed as examples of computer networks. Material on the original Ethernet—with its vampire taps— has been removed, along with the material on ATM. Chapter 2, which covers the physical layer, has expanded coverage of digital modulation (including OFDM as widely used in wireless networks) and 3G net- works (based on CDMA). New technologies are discussed, including Fiber to the Home and power-line networking. Chapter 3, on point-to-point links, has been improved in two ways. The mater- ial on codes for error detection and correction has been updated, and also includes a brief description of the modern codes that are important in practice (e.g., convo- lutional and LDPC codes). The examples of protocols now use Packet over SONET and ADSL. Sadly, the material on protocol verification has been removed as it is little used. In Chapter 4, on the MAC sublayer, the principles are timeless but the tech- nologies have changed. Sections on the example networks have been redone accordingly, including gigabit Ethernet, 802.11, 802.16, Bluetooth, and RFID. Also updated is the coverage of LAN switching, including VLANs. Chapter 5, on the network layer, covers the same ground as in the fourth edi- tion. The revisions have been to update material and add depth, particularly for quality of service (relevant for real-time media) and internetworking. The sec- tions on BGP, OSPF and CIDR have been expanded, as has the treatment of multicast routing. Anycast routing is now included. Chapter 6, on the transport layer, has had material added, revised, and re- moved. New material describes delay-tolerant networking and congestion control in general. The revised material updates and expands the coverage of TCP con- gestion control. The material removed described connection-oriented network lay- ers, something rarely seen any more. Chapter 7, on applications, has also been updated and enlarged. While mater- ial on DNS and email is similar to that in the fourth edition, in the past few years there have been many developments in the use of the Web, streaming media and content delivery. Accordingly, sections on the Web and streaming media have been brought up to date. A new section covers content distribution, including CDNs and peer-to-peer networks. Chapter 8, on security, still covers both symmetric and public-key crypto- graphy for confidentiality and authenticity. Material on the techniques used in practice, including firewalls and VPNs, has been updated, with new material on 802.11 security and Kerberos V5 added. Chapter 9 contains a renewed list of suggested readings and a comprehensive bibliography of over 300 citations to the current literature. More than half of these are to papers and books written in 2000 or later, and the rest are citations to classic papers. PREFACE xxi List of Acronyms Computer books are full of acronyms. This one is no exception. By the time you are finished reading this one, the following should ring a bell: ADSL, AES, AJAX, AODV, AP, ARP, ARQ, AS, BGP, BOC, CDMA, CDN, CGI, CIDR, CRL, CSMA, CSS, DCT, DES, DHCP, DHT, DIFS, DMCA, DMT, DMZ, DNS, DOCSIS, DOM, DSLAM, DTN, FCFS, FDD, FDDI, FDM, FEC, FIFO, FSK, FTP, GPRS, GSM, HDTV, HFC, HMAC, HTTP, IAB, ICANN, ICMP, IDEA, IETF, IMAP, IMP, IP, IPTV, IRTF, ISO, ISP, ITU, JPEG, JSP, JVM, LAN, LATA, LEC, LEO, LLC, LSR, LTE, MAN, MFJ, MIME, MPEG, MPLS, MSC, MTSO, MTU, NAP, NAT, NRZ, NSAP, OFDM, OSI, OSPF, PAWS, PCM, PGP, PIM, PKI, POP, POTS, PPP, PSTN, QAM, QPSK, RED, RFC, RFID, RPC, RSA, RTSP, SHA, SIP, SMTP, SNR, SOAP, SONET, SPE, SSL, TCP, TDD, TDM, TSAP, UDP, UMTS, URL, VLAN, VSAT, WAN, WDM, and XML. But don’t worry. Each will appear in boldface type and be carefully defined before it is used. As a fun test, see how many you can identify before reading the book, write the number in the margin, then try again after reading the book. How to Use the Book To help instructors use this book as a text for courses ranging in length from quarters to semesters, we have structured the chapters into core and optional ma- terial. The sections marked with a ‘‘*’’ in the table of contents are the optional ones. If a major section (e.g., 2.7) is so marked, all of its subsections are optional. They provide material on network technologies that is useful but can be omitted from a short course without loss of continuity. Of course, students should be encouraged to read those sections as well, to the extent they have time, as all the material is up to date and of value. Instructors’ Resource Materials The following protected instructors’ resource materials are available on the publisher’s Web site at www.pearsonhighered.com/tanenbaum. For a username and password, please contact your local Pearson representative. Solutions manual PowerPoint lecture slides Students’ Resource Materials Resources for students are available through the open-access Companion Web site link on www.pearsonhighered.com/tanenbaum, including Web resources, links to tutorials, organizations, FAQs, and more Figures, tables, and programs from the book Steganography demo Protocol simulators www.pearsonhighered.com/tanenbaum www.pearsonhighered.com/tanenbaum xxii PREFACE Acknowledgements Many people helped us during the course of the fifth edition. We would espe- cially like to thank Emmanuel Agu (Worcester Polytechnic Institute), Yoris Au (University of Texas at Antonio), Nikhil Bhargava (Aircom International, Inc.), Michael Buettner (University of Washington), John Day (Boston University), Kevin Fall (Intel Labs), Ronald Fulle (Rochester Institute of Technology), Ben Greenstein (Intel Labs), Daniel Halperin (University of Washington), Bob Kinicki (Worcester Polytechnic Institute), Tadayoshi Kohno (University of Washington), Sarvish Kulkarni (Villanova University), Hank Levy (University of Washington), Ratul Mahajan (Microsoft Research), Craig Partridge (BBN), Michael Piatek (University of Washington), Joshua Smith (Intel Labs), Neil Spring (University of Maryland), David Teneyuca (University of Texas at Antonio), Tammy VanDe- grift (University of Portland), and Bo Yuan (Rochester Institute of Technology), for providing ideas and feedback. Melody Kadenko and Julie Svendsen provided administrative support to David. Shivakant Mishra (University of Colorado at Boulder) and Paul Nagin (Chim- borazo Publishing, Inc.) thought of many new and challenging end-of-chapter problems. Our editor at Pearson, Tracy Dunkelberger, was her usual helpful self in many ways large and small. Melinda Haggerty and Jeff Holcomb did a good job of keeping things running smoothly. Steve Armstrong (LeTourneau Univer- sity) prepared the PowerPoint slides. Stephen Turner (University of Michigan at Flint) artfully revised the Web resources and the simulators that accompany the text. Our copyeditor, Rachel Head, is an odd hybrid: she has the eye of an eagle and the memory of an elephant. After reading all her corrections, both of us won- dered how we ever made it past third grade. Finally, we come to the most important people. Suzanne has been through this 19 times now and still has endless patience and love. Barbara and Marvin now know the difference between good textbooks and bad ones and are always an inspiration to produce good ones. Daniel and Matilde are welcome additions to our family. Aron is unlikely to read this book soon, but he likes the nice pictures on page 866 (AST). Katrin and Lucy provided endless support and always man- aged to keep a smile on my face. Thank you (DJW). ANDREW S. TANENBAUM DAVID J. WETHERALL 1 INTRODUCTION Each of the past three centuries was dominated by a single new technology. The 18th century was the era of the great mechanical systems accompanying the Industrial Revolution. The 19th century was the age of the steam engine. During the 20th century, the key technology was information gathering, processing, and distribution. Among other developments, we saw the installation of worldwide telephone networks, the invention of radio and television, the birth and unpre- cedented growth of the computer industry, the launching of communication satel- lites, and, of course, the Internet. As a result of rapid technological progress, these areas are rapidly converging in the 21st century and the differences between collecting, transporting, storing, and processing information are quickly disappearing. Organizations with hun- dreds of offices spread over a wide geographical area routinely expect to be able to examine the current status of even their most remote outpost at the push of a button. As our ability to gather, process, and distribute information grows, the de- mand for ever more sophisticated information processing grows even faster. Although the computer industry is still young compared to other industries (e.g., automobiles and air transportation), computers have made spectacular pro- gress in a short time. During the first two decades of their existence, computer systems were highly centralized, usually within a single large room. Not infre- quently, this room had glass walls, through which visitors could gawk at the great electronic wonder inside. A medium-sized company or university might have had 1 2 INTRODUCTION CHAP. 1 one or two computers, while very large institutions had at most a few dozen. The idea that within forty years vastly more powerful computers smaller than postage stamps would be mass produced by the billions was pure science fiction. The merging of computers and communications has had a profound influence on the way computer systems are organized. The once-dominant concept of the ‘‘computer center’’ as a room with a large computer to which users bring their work for processing is now totally obsolete (although data centers holding thou- sands of Internet servers are becoming common). The old model of a single com- puter serving all of the organization’s computational needs has been replaced by one in which a large number of separate but interconnected computers do the job. These systems are called computer networks. The design and organization of these networks are the subjects of this book. Throughout the book we will use the term ‘‘computer network’’ to mean a col- lection of autonomous computers interconnected by a single technology. Two computers are said to be interconnected if they are able to exchange information. The connection need not be via a copper wire; fiber optics, microwaves, infrared, and communication satellites can also be used. Networks come in many sizes, shapes and forms, as we will see later. They are usually connected together to make larger networks, with the Internet being the most well-known example of a network of networks. There is considerable confusion in the literature between a computer network and a distributed system. The key distinction is that in a distributed system, a collection of independent computers appears to its users as a single coherent sys- tem. Usually, it has a single model or paradigm that it presents to the users. Of- ten a layer of software on top of the operating system, called middleware, is responsible for implementing this model. A well-known example of a distributed system is the World Wide Web. It runs on top of the Internet and presents a model in which everything looks like a document (Web page). In a computer network, this coherence, model, and software are absent. Users are exposed to the actual machines, without any attempt by the system to make the machines look and act in a coherent way. If the machines have different hard- ware and different operating systems, that is fully visible to the users. If a user wants to run a program on a remote machine, he† has to log onto that machine and run it there. In effect, a distributed system is a software system built on top of a network. The software gives it a high degree of cohesiveness and transparency. Thus, the distinction between a network and a distributed system lies with the software (es- pecially the operating system), rather than with the hardware. Nevertheless, there is considerable overlap between the two subjects. For ex- ample, both distributed systems and computer networks need to move files around. The difference lies in who invokes the movement, the system or the user. † ‘‘He’’ should be read as ‘‘he or she’’ throughout this book. SEC. 1.1 USES OF COMPUTER NETWORKS 3 …