計(jì)算機(jī)網(wǎng)絡(luò)

前言

　  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

內(nèi)容概要

　　本書是全球最具有權(quán)威性和經(jīng)典性的計(jì)算機(jī)網(wǎng)絡(luò)教材，我國各大專院校也廣泛采用此書作為計(jì)算機(jī)網(wǎng)絡(luò)課程的基本教材。作者tanenbaum
教授以高深的理論造詣和豐富的實(shí)踐經(jīng)驗(yàn)，在書中對計(jì)算機(jī)網(wǎng)絡(luò)的原理、結(jié)構(gòu)、協(xié)議標(biāo)準(zhǔn)與應(yīng)用等做了深入的分析與研究。
　　全書按照網(wǎng)絡(luò)協(xié)議模型（物理層、數(shù)據(jù)鏈路層、介質(zhì)訪問控制子層、網(wǎng)絡(luò)層、傳輸層和應(yīng)用層），自底向上逐層講述每一層所用的技術(shù)與協(xié)議標(biāo)準(zhǔn)，并給出大量實(shí)例。全書內(nèi)容全面詳實(shí)，體系清晰合理，敘述由簡入繁、層層深入，自底向上方法也符合人類從底層到高層的認(rèn)識規(guī)律，因此是公認(rèn)的最適合網(wǎng)絡(luò)入門的教材。
　　 隨著計(jì)算機(jī)網(wǎng)絡(luò)的發(fā)展，本版對相關(guān)內(nèi)容進(jìn)行了大量修訂、更新和補(bǔ)充，具體更新內(nèi)容如下：
　　 ·無線網(wǎng)絡(luò)（802.12和802.16）。
　　 ·智能手機(jī)使用的3g網(wǎng)絡(luò)。
　　 ·rfid和傳感器網(wǎng)絡(luò)。
　　 ·使用cdns進(jìn)行內(nèi)容分發(fā)。
　　 ·對等網(wǎng)絡(luò)。
　　 ·實(shí)時媒體。
　　 ·網(wǎng)絡(luò)電話。
　　 ·延遲容忍網(wǎng)絡(luò)。

作者簡介

Andrew S. Tanenbaum
國際知名的計(jì)算機(jī)科學(xué)家，著名的技術(shù)作家、教育家和研究者，ACM和IEEE兩會高級會員，荷蘭皇家藝術(shù)和科學(xué)院院士，荷蘭阿姆斯特丹Vrije大學(xué)計(jì)算機(jī)科學(xué)系教授。他講授計(jì)算機(jī)網(wǎng)絡(luò)、操作系統(tǒng)和計(jì)算機(jī)組成等課程30多年，教學(xué)成果卓著，其所著的多部計(jì)算機(jī)科學(xué)方面的教材已成為該領(lǐng)域內(nèi)的范本，得到學(xué)術(shù)界和教育界的廣泛認(rèn)可，多次獲得ACM及其他學(xué)術(shù)組織頒發(fā)的各項(xiàng)榮譽(yù)，包括1994年ACM
Karl V.
Karlstrom杰出教育獎、1997年ACM計(jì)算機(jī)科學(xué)教育杰出貢獻(xiàn)獎、2002年Texty****教材獎、第10屆ACM操作系統(tǒng)原理研討會杰出論文獎等，他還入選了《世界名人錄》。
David J. Wetherall
擁有美國麻省理工學(xué)院計(jì)算機(jī)科學(xué)博士學(xué)位，現(xiàn)為華盛頓大學(xué)西雅圖分校計(jì)算機(jī)科學(xué)與工程系副教授。他的研究領(lǐng)域是網(wǎng)絡(luò)系統(tǒng)，尤其是無線網(wǎng)絡(luò)和移動計(jì)算、網(wǎng)絡(luò)測量和Internet協(xié)議的設(shè)計(jì)、隱私和安全。

書籍目錄

about the authors
1 introduction
　1.1 uses of computer networks,
　　1.1.1 business applications,
　　1.1.2 home applications,
　　1.1.3 mobile users,
　　1.1.4 social issues,
　1.2 network hardware,
　　1.2.1 personal area networks,
　　1.2.2 local area networks,
　　1.2.3 metropolitan area networks,
　　1.2.4 wide area networks,
　　1.2.5 internetworks,
　1.3 network software,
　　1.3.1 protocol hierarchies,
　　1.3.2 design issues for the layers,
　　1.3.3 connection-oriented versus connectionless service,
　　1.3.4 service primitives,
　　1.3.5 the relationship of services to protocols,
　1.4 reference models,
　　1.4.1 the osi reference model,
　　1.4.2 the tcp/ip reference model,
　　1.4.3 the model used in this book,
　　1.4.4 a comparison of the osi and tcp/ip reference models,
　　1.4.5 a critique of the osi model and protocols,
　　1.4.6 a critique of the tcp/ip reference model,
　1.5 example networks,
　　1.5.1 the internet,
　　1.5.2 third-generation mobile phone networks,
　　1.5.3 wireless lans: 802.11,
　　1.5.4 rfid and sensor networks,
　1.6 network standardization,
　　1.6.1 who’s who in the telecommunications world,
　　1.6.2 who’s who in the international standards world,
　　1.6.3 who’s who in the internet standards world,
　1.7 metric units,
　1.8 outline of the rest of the book,
　1.9 summary,
2 the physical layer
　2.1 the theoretical basis for data communication,
　　2.1.1 fourier analysis,
　　2.1.2 bandwidth-limited signals,
　　2.1.3 the maximum data rate of a channel,
　2.2 guided transmission media,
　　2.2.1 magnetic media,
　　2.2.2 twisted pairs,
　　2.2.3 coaxial cable,
　　2.2.4 power lines,
　　2.2.5 fiber optics,
　2.3 wireless transmission,
　　2.3.1 the electromagnetic spectrum,
　　2.3.2 radio transmission,
　　2.3.3 microwave transmission,
　　2.3.4 infrared transmission,
　　2.3.5 light transmission,
　　contents?
　2.4 communication satellites,
　　2.4.1 geostationary satellites,
　　2.4.2 medium-earth orbit satellites,
　　2.4.3 low-earth orbit satellites,
　　2.4.4 satellites versus fiber,
　2.5 digital modulation and multiplexing,
　　2.5.1 baseband transmission,
　　2.5.2 passband transmission,
　　2.5.3 frequency division multiplexing,
　　2.5.4 time division multiplexing,
　　2.5.5 code division multiplexing,
　2.6 the public switched telephone network,
　　2.6.1 structure of the telephone system,
　　2.6.2 the politics of telephones,
　　2.6.3 the local loop: modems, adsl, and fiber,
　　2.6.4 trunks and multiplexing,
　　2.6.5 switching,
　2.7 the mobile telephone system,
　　2.7.1 first-generation (1g) mobile phones: analog voice,
　　2.7.2 second-generation (2g) mobile phones: digital voice,
　　2.7.3 third-generation (3g) mobile phones: digital voice and
data,
　　2.8 cable television,
　2.8.1 community antenna television,
　　2.8.2 internet over cable,
　　2.8.3 spectrum allocation,
　　2.8.4 cable modems,
　　2.8.5 adsl versus cable,
　2.9 summary,
3 the data link layer
　3.1 data link layer design issues,
　　3.1.1 services provided to the network layer,
　　3.1.2 framing,
　　3.1.3 error control,
　　3.1.4 flow control,
　3.2 error detection and correction,
　　3.2.1 error-correcting codes,
　　3.2.2 error-detecting codes,
　　3.3 elementary data link protocols,
　　3.3.1 a utopian simplex protocol,
　3.3.2 a simplex stop-and-wait protocol for an error-free
channel,
　　3.3.3 a simplex stop-and-wait protocol for a noisy channel,
　3.4 sliding window protocols,
　　3.4.1 a one-bit sliding window protocol,
　　3.4.2 a protocol using go-back-n,
　　3.4.3 a protocol using selective repeat,
　3.5 example data link protocols,
　　3.5.1 packet over sonet,
　　3.5.2 adsl (asymmetric digital subscriber loop),
　　3.6 summary,
4 the medium access control sublayer
　4.1 the channel allocation problem,
　　4.1.1 static channel allocation,
　　4.1.2 assumptions for dynamic channel allocation,
　4.2 multiple access protocols,
　　4.2.1 aloha,
　　4.2.2 carrier sense multiple access protocols,
　　4.2.3 collision-free protocols,
　　4.2.4 limited-contention protocols,
　　4.2.5 wireless lan protocols,
　4.3 ethernet,
　　4.3.1 classic ethernet physical layer,
　　4.3.2 classic ethernet mac sublayer protocol,
　　4.3.3 ethernet performance,
　　4.3.4 switched ethernet,
　　4.4.4 the 802.11 frame structure,
　　4.4.5 services,
　4.5 broadband wireless,
　　4.5.1 comparison of 802.16 with 802.11 and 3g,
　　4.5.2 the 802.16 architecture and protocol stack,
　　4.5.3 the 802.16 physical layer,
　　4.5.4 the 802.16 mac sublayer protocol,
　　4.5.5 the 802.16 frame structure,
　4.6 bluetooth,
　　4.6.1 bluetooth architecture,
　　4.6.2 bluetooth applications,
　　4.6.3 the bluetooth protocol stack,
　　4.6.4 the bluetooth radio layer,
　　4.6.5 the bluetooth link layers,
　　4.6.6 the bluetooth frame structure,
　4.7 rfid,
　　4.7.1 epc gen 2 architecture,
　　4.7.2 epc gen 2 physical layer,
　　4.7.3 epc gen 2 tag identification layer,
　　4.7.4 tag identification message formats,
　4.8 data link layer switching,
　　4.8.1 uses of bridges,
　　4.8.2 learning bridges,
　　4.8.3 spanning tree bridges,
　　4.8.4 repeaters, hubs, bridges, switches, routers, and
gateways,
　　4.8.5 virtual lans,
　4.9 summary,
5 the network layer
　5.1 network layer design issues,
　　5.1.1 store-and-forward packet switching,
　　5.1.2 services provided to the transport layer,
　　5.1.3 implementation of connectionless service,
　　5.1.4 implementation of connection-oriented service,
　　5.1.5 comparison of virtual-circuit and datagram networks,
　5.2 routing algorithms,
　　5.2.1 the optimality principle,
　　5.2.2 shortest path algorithm,
　　5.2.3 flooding,
　　5.2.4 distance vector routing,
　　5.2.5 link state routing,
　　5.2.6 hierarchical routing,
　　5.2.7 broadcast routing,
　　5.2.8 multicast routing,
　　5.2.9 anycast routing,
　　5.2.10 routing for mobile hosts,
　　5.2.11 routing in ad hoc networks,
　5.3 congestion control algorithms,
　　5.3.1 approaches to congestion control,
　　5.3.2 traffic-aware routing,
　　5.3.3 admission control,
　　5.3.4 traffic throttling,
　　5.3.5 load shedding,
　5.4 quality of service,
　　5.4.1 application requirements,
　　5.4.2 traffic shaping,
　　5.4.3 packet scheduling,
　　5.4.4 admission control,
　　5.4.5 integrated services,
　　5.4.6 differentiated services,
　5.5 internetworking,
　　5.5.1 how networks differ,
　　5.5.2 how networks can be connected,
　　5.5.3 tunneling,
　　5.5.4 internetwork routing,
　　5.5.5 packet fragmentation,
　5.6 the network layer in the internet,
　　5.6.1 the ip version 4 protocol,
　　5.6.2 ip addresses,
　　5.6.3 ip version 6,
　　5.6.4 internet control protocols,
　　5.6.5 label switching and mpls,
　　5.6.6 ospf—an interior gateway routing protocol,
　　5.6.7 bgp—the exterior gateway routing protocol,
　　5.6.8 internet multicasting,
　　5.6.9 mobile ip,
　5.7 summary,
6 the transport layer
　6.1 the transport service,
　　6.1.1 services provided to the upper layers,
　　6.1.2 transport service primitives,
　　6.1.3 berkeley sockets,
　　6.1.4 an example of socket programming: an internet file
server,
　6.2 elements of transport protocols,
　　6.2.1 addressing,
　　6.2.2 connection establishment,
　　6.2.3 connection release,
　　6.2.4 error control and flow control,
　　6.2.5 multiplexing,
　　6.2.6 crash recovery,
　6.3 congestion control,
　　6.3.1 desirable bandwidth allocation,
　　6.3.2 regulating the sending rate,
　　6.3.3 wireless issues,
　6.4 the internet transport protocols: udp,
　　6.4.1 introduction to udp,
　　6.4.2 remote procedure call,
　　6.4.3 real-time transport protocols,
　6.5 the internet transport protocols: tcp,
　　6.5.1 introduction to tcp,
　　6.5.2 the tcp service model,
　　6.5.3 the tcp protocol,
　　6.5.4 the tcp segment header,
　　6.5.5 tcp connection establishment,
　　6.5.6 tcp connection release,
　　6.5.7 tcp connection management modeling,
　　6.5.8 tcp sliding window,
　　6.5.9 tcp timer management,
　　6.5.10 tcp congestion control,
　　6.5.11 the future of tcp,
　6.6 performance issues,
　　6.6.1 performance problems in computer networks,
　　6.6.2 network performance measurement,
　　6.6.3 host design for fast networks,
　　6.6.4 fast segment processing,
　　6.6.5 header compression,
　　6.6.6 protocols for long fat networks,
　6.7 delay-tolerant networking,
　　6.7.1 dtn architecture,
　　6.7.2 the bundle protocol,
　6.8 summary,
7 the application layer
　7.1 dns—the domain name system,
　　7.1.1 the dns name space,
　　7.1.2 domain resource records,
　　7.1.3 name servers,
　7.2 electronic mail,
　　7.2.1 architecture and services,
　　7.2.2 the user agent,
　　7.2.3 message formats,
　　7.2.4 message transfer,
　　7.2.5 final delivery,
　7.3 the world wide web,
　　7.3.1 architectural overview,
　　7.3.2 static web pages,
　　7.3.3 dynamic web pages and web applications,
　　7.3.4 http—the hypertext transfer protocol,
　　7.3.5 the mobile web,
　　7.3.6 web search,
　7.4 streaming audio and video,
　　7.4.1 digital audio,
　　7.4.2 digital video,
　　7.4.3 streaming stored media,
　　7.4.4 streaming live media,
　　7.4.5 real-time conferencing,
　7.5 content delivery,
　　7.5.1 content and internet traffic,
　　7.5.2 server farms and web proxies,
　　7.5.3 content delivery networks,
　　7.5.4 peer-to-peer networks,
　7.6 summary,
8 network security
　8.1 cryptography,
　　8.1.1 introduction to cryptography,
　　8.1.2 substitution ciphers,
　　8.1.3 transposition ciphers,
　　8.1.4 one-time pads,
　　8.1.5 two fundamental cryptographic principles,
　8.2 symmetric-key algorithms,
　　8.2.1 des—the data encryption standard,
　　8.2.2 aes—the advanced encryption standard,
　　8.2.3 cipher modes,
　　8.2.4 other ciphers,
　　8.2.5 cryptanalysis,
　　20?contents
　8.3 public-key algorithms,
　　8.3.1 rsa,
　　8.3.2 other public-key algorithms,
　8.4 digital signatures,
　　8.4.1 symmetric-key signatures,
　　8.4.2 public-key signatures,
　　8.4.3 message digests,
　　8.4.4 the birthday attack,
　8.5 management of public keys,
　　8.5.1 certificates,
　　8.5.2 x.509,
　　8.5.3 public key infrastructures,
　8.6 communication security,
　　8.6.1 ipsec,
　　8.6.2 firewalls,
　　8.6.3 virtual private networks,
　　8.6.4 wireless security,
　8.7 authentication protocols,
　　8.7.1 authentication based on a shared secret key,
　　8.7.2 establishing a shared key: the diffie-hellman key
exchange,
　　8.7.3 authentication using a key distribution center,
　　8.7.4 authentication using kerberos,
　　8.7.5 authentication using public-key cryptography,
　8.8 email security,
　　8.8.1 pgp—pretty good privacy,
　　8.8.2 s/mime,
　8.9 web security,
　　8.9.1 threats,
　　8.9.2 secure naming,
　　8.9.3 ssl—the secure sockets layer,
　　8.9.4 mobile code security,
　8.10 social issues,
　　8.10.1 privacy,
　　8.10.2 freedom of speech,
　　8.10.3 copyright,
　　8.11 summary,
9 reading list and bibliography
　9.1 suggestions for further reading,
　　9.1.1 introduction and general works,
　　9.1.2 the physical layer,
　　9.1.3 the data link layer,
　　9.1.4 the medium access control sublayer,
　　9.1.5 the network layer,
　　9.1.6 the transport layer,
　　9.1.7 the application layer,
　　9.1.8 network security,
　9.2 alphabetical bibliography,
index

章節(jié)摘錄

版權(quán)頁：插圖：Before we start to examine the technical issues in detail, it is worth devotingsome time to pointing out why people are interested in computer networks andwhat they can be used for.After all, if nobody were interested in computer net-works,few of them would be built. We will start with traditional uses at com-panies,then move on to home networking and recent developments regardingmobile users, and finish with social issues.1.1.1 usiness Applications Most companies have a substantial number of computers. For example, acompany may have a computer for each worker and use them to design products,write brochures, and do the payroll.Initially, some of these computers may haveworked in isolation from the others, but at some point, management may havedecided to connect them to be able to distribute information throughout the com-pany.

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