PREFACE
    This book is now in its fifth edition. Each edition has corresponded to a different phase in the way computer networks were used. When the first edition appearedin 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, wireless networks and mobile computers had become commonplace for accessing the Web and the Internet. Now, in the fifth edition, networks are about content distribution(especially videos using CDNs and peer-to-peer networks) and mobile phones are small computers on the Internet.

    Among the many changes in this book, the most important one is the addition f Prof. David J. Wetheall as a co-author. David brings a rich background in networking,having cut his teeth designing metropolitan-area networks more than 20years 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.

    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 networks (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 material 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., convolutional 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 technologies 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 edition.

    .　　The revisions have been to update material and add depth, particularly for quality of service (relevant for real-time media) and internetworking. The sections 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 removed.
    New material describes delay-tolerant networking and congestion control in general. The revised material updates and expands the coverage of TCP congestion control. The material removed described connection-oriented network layers, something rarely seen any more.
    Chapter 7, on applications, has also been updated and enlarged. While material 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 cryptography 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.

    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 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.
    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 material.
    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.

    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

    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

    Many people helped us during the course of the fifth edition. We would especially 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 VanDegrift (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 (Chimborazo
    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 University) 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 wondered 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 884 (AST). Katrin and Lucy provided endless support and always managed to keep a smile on my face.
    Thank you (DJW).
    ANDREW S. TANENBAUM
    DAVID J.WETHERALL