计算机通信与网络技术（影印版）

.chapter review materials 72
analog and digital communications concepts 76
3.1 representing data as analog signals 77
3.2 representing data as digital signals 87
3.3 data rate and baud rate redux 92
3.4 digital carrier systems 93
end-of-chapter commentary 100
chapter review materials 100
ii physical, data link, and network layer concepts 107
4 physical layer concepts 108
4.1 what is the physical layer? 109
4.2 the physical and electrical characteristics of wire 110
4.3 copper media 116
4.4 fiber-optic media 120
4.5 wireless communications 124
4.6 satellite communications 129
4.7 structured cabling systems 133
end-of-chapter commentary 135
chapter review materials 135
5 data link layer concepts and ieee lan standards 139
5.1 what is the data link layer? 140
5.2 the logical link control (llc) sublayer 142
5.3 the media access control(mac) sublayer 158
5.4 data prioritization and quality of service 163
end-of-chapter commentary 166
chapter review materials 166
6 network hardware components (layers 1 and 2) 170
6.1 what are connectors? 171
6.2 transceivers and media converters 174
6.3 repeaters 177
6.4 network interface cards and pc cards 179
6.5 bridges 182
6.6 switches 188
end-of-chapter commentary 192
chapter review materials 192
7 internetworking and network layer concepts and components 195
7.1 internetworking concepts 196
7.2 the network layer and routing concepts 200
7.3 sample routing protocols 208
7.4 routers and switches 215
7.5 virtual private networks (vpns) 218
end-of-chapter commentary 223
chapter review materials 223
8 the internet and tcp/ip 229
8.1 what is the internet? 230
8.2 internet history 231
8.3 internet administration 240
8.4 what is tcp/ip? 243
8.5 tcp/ip's transport and network layer protocols 248
8.6 ip addresses 263
8.7 ipv6 274
8.8 tcp/ip application level protocols 281
end-of-chapter commentary 304
chapter review materials 304
iii local and wide area networking technologies 311
9 ethernet and ieee 802.3 networks 312
9.1 the history of ethernet 313
9.2 10-mbps ethernet/802.3 lans 316
9.3 switched ethernet, full-duplex ethernet, and virtual lans 328
9.4 100-mbps ethernet lans 337
9.5 gigabit ethernet 346
9.6 other ethernet-related projects 354
end-of-chapter commentary 355
chapter review materials 355
10 token ring 361
10.1 what is token ring? 362
10.2 physical layer specifications 364
10.3 frame formats 365
10.4 priority and reservation 368
16.5 monitor stntions 369
10.6 second-generationtokenring 370
16.7 token ring versus token bus 374
end-of-chapter commentary 375
chapter review materials 376
11 fiber distributed data interface (fddi) 378
11.1 what is fddi? 379
112 physicnl layer specifications 381
11.3 frame formats and medium access specifications 382
11.4 configuration and design issues 386
11.5 interconnecting fddi with ethernet/802.3 or atm networks 388
11.6 the future of fddi 390
end-of-chapter commentary 390
chapter review materials 391
12 integrated services digital network (isdn) 393
12.1 what is isdn? 394
12.2 isdn components 398
12.3 isdn channel types 400
12.4 basic and primary rate interfaces 402
12.5 isdn protocols 404
12.6 isdn features, services, and applications 406
12.70therlsdn initiatives 410
end-of-chapter commentary 411
chapter review materials 412
13 frame relay 416
13.1 what is fram relay?
13.2 fram relay circuits 420
13.3 technical overview and data link layer issues 427
13.4 additional frame relay information 434
end-nf-chapter commentary 437
chapter review materials 437
14 switched multimegabit data service (smds) 441
14.1 what is smds? 442
14.2 smds technical overview 444
14.3 the smds interface protocol (sip) 447
14.4 smdsaddressing 451
14.5 smds versus other lan-to-lan technologies 452
14.6 status of smds today 453
end-of-chapter commentary 455
chapter review materials 455
15 asynchronous transfer mode (atm) 458
15.1 what is atm? 459
15.2 general concepts and operation 461
15.3 atm interface standards 463
15.4 atm cells, virtual connections, and addressing 465
15.5 atm adaptation layer (aal) 470
15.6 atm and convergence technology 472
15.7 atm versus other technologies and services 473
end-of-chapter commentary 477
chapter review materials 477
related networking concepts, applications, and technologies
16 dialup and home networking 482
16.1 what is dialup networking? 483
16.2 analog modem concepts 485
16.3 dslservice 490
16.4 cable modems 498
16.5 home networking concepts and issues 501
end-of-chapter commentary 507
chapter review materiels 508
17 network security issues 512
17.1 what is network security? 513
17.2 threat assessment 513
17.3 network attacks and security measures considerations 518
17.4 firewalls 524
17.5 encryption methods 528
17.6 authentication and access control measures 537
17.7 virtual private networks and internet security 539
end-of-chaptar commentary 545
chapter review materials 545
18 network convergence 549
18.1 what is network convergence? 550
18.2 networking issues and convergence 554
18.2 effects of network convergence on businesses 559
18.4 convergence at home 565
end-of-chaptar commentary 566
chapter review materials 567
a vendor ethernet/802.3 prefixes 570
b using parity for single-bit error correction 571
c guidelines for installing utp cable 574
d network design and analysis guidelines; network politics 576
e x.25
glossary 587
index 617

.　　 Intemet and the TCP/IP protocol suite including TCP/IP's two transport protocols,UDP and TCP. This part of the book provides students with the core networking concepts that are fundamental to the various local and wide area computer networks and networking technologies presented in Part III.
　　 Part HI: Local and Wide Area Networking Technologies. Chapters 9 through 15 examine specific LAN or WAN protocols, technologies, and services. Although most students' perception of computer networks revolves around the Internet and Ethernet, this is not the reality they will face when working in the field. Yes, nearly every organization has an Internet connection, and yes, nearly every organization has a local area Ethernet network. However, many organizations also have fully operational first-generation networks such as token ring or outdated second-generation networks such as FDDI. Furthermore, some of these same organizations also have frame relay, ATM, or ISDN connections. Given the diversity of networking technologies that exist in the field, we have provided separate chapters on the common ones students will most likely encounter. These include Ethernet (Chapter 9), Token Ring (Chapter 10), FDDI (Chapter 11), ISDN (Chapter 12), Frame Relay (Chapter 13), SMDS (Chapter 14), and ATM (Chapter 15).
　　 Part IV: Related Networking Concepts, Applications, and Technologies, The final three chapters provide information about several related networking topics: dialup and home networking (Chapter 16), network security issues (Chapter 17), and network convergence (Chapter 18), the merging of the technologies and applications discussed in all the previous chapters. Among the topics discussed in Chapter 18 is the current trend toward multiservice networking, which integrates traditional voice, video, and data applications.
　　 Each chapter concludes with an End-of-Chapter Commentary. These commentaries consist of transitional material that identifies other chapters in the book containing additional information related to the current discussion. In a sense, they provide a notion of "where we are presently, where we were, and where we are going." As a result, students are able to link key concepts and issues from the current chapter to other chapters. A Chapter Review is provided at the end of each chapter. This section consists of a bulleted-item list that summarizes the salient aspects of the chapter, a vocabulary check that contains key words and phrases introduced in the chapter, approximately 400 review exercises throughout, and suggested readings and references. Finally, five appendixes and a comprehensive 700-word glossary complement the book's nucleus.
　　Appendix A contains information about vendor Ethernet prefixes. Appendix B presents a detailed example of how parity is used for single-bit error correction. Appendix C has guidelines for installing unshielded twisted-pair cable. Appendix D provides information about designing and analyzing networks as well as how to deal with network politics. Appendix E contains a brief overview of X.25.
　　 Although the chapters are structured logically to follow each other and build on previously learned knowledge, this does not preclude their being read in any order. We wrote the chapters to be independent of each other. Throughout every chapter, key terms or concepts that were presented in an earlier chapter or discussed in a later chapter are explained in the current context with either a forward or backward reference that specifies the appropriate chapter or chapters where the term or concept is discussed more completely. These cross-references enable students to take a break from the current discussion so they can either refresh their knowledge of previously presented material or jump ahead to gain further insight into a specific topic. Thus, the cross-
　　references effectively facilitate a deeper understanding of a given concept in the current
　　context. Finally, throughout the entire presentation, illustrations, tables, and special boxed text items are included to promote further knowledge.
　　This textbook is designed for use in a one-semester or one-quarter course. Ample material is included to provide you with a great amount of flexibility for its use. Clearly, the chapters you cover will be determined to a large extent by how the course is structured.
　　Following are three suggestions for presenting this material based on one of the authors' teaching experiences.
　　 Accompanying the textbook is an instructor's resource and solutions manual, which contains chapter outlines and answers to all of the chapter exercises. Additionally, sample chapter examinations with solutions are provided to facilitate test construction. You may find more support online at www. brookscole.com.
　　Computer Communications and Networking Technologies serves as an excellent foundation on which future and current network managers and administrators can build a solid knowledge base of data communications standards and present and emerging network technologies. After reading this book, you will have accrued a greater understanding of and appreciation for networks and networking. This book will help you understand basic networking terminology, components, applications, protocols, architectures, standards, and implementation strategies. Please note that this is not a "how-to" book. We do not provide specific information relative to network management or configurations. Thus, the material contained here will not help you perform such tasks as setting up a domain name server, configuring a network printer, or installing or managing an office network. However, your knowledge, appreciation, comprehension, and awareness of the concepts in-
　　volved in such activities will be more acute after reading this book. To quote a former student who was taught using earlier drafts of this material in a data communications and networking course: "The material cleared a lot of things up for me. It tied together a lot of loose ends I had for 10 years as a network administrator."
　　 Additionally, a companion textbook published by Digital Press, Networking Explained, is available as a supplementary resource. Networking Explained covers essentially the same material contained in this textbook except it employs an easy-to-follow question-and-answer format. We structured the question-answer format to emulate a conversation between a networking professional and the reader. The questions are representative of those asked by individuals who are interested in computer networks and who wish to gain additional understanding of the subject. Users of Networking Explained have found the conversational tone engaging, informative, and entertaining.
　　Acknowledgments Many people contributed considerably, either directly or indirectly, in the preparation of this material. It is therefore justifiable that these individuals be acknowledged. First of all, we are grateful to the authors of the articles, books, RFCs, and other reference material listed at the end of each chapter. These publications served as invaluable resources for
　　confirming that our illustrations and material are accurate, complete, and up-to-date. Next, we thank the many reviewers of the manuscript for their suggestions and thoughtprovoking comments. They did a yeoman's job and their constructive criticisms strengthened the quality of this book greatly. They include Prasad Aloni of Drexel University, Ron Fulle of Rochester Institute of Technology, Arnold Meltzer of George Washington University, Krishna Sivalingam of Washington State University, Eugene Styer of Eastern Kentucky University, and Michael Whitman of Kennesaw State University.
　　 It is with pleasure that we also acknowledge and thank the editorial staff of Brooks/Cole. In particular, an especially warm "thank you" is extended to our editor, Kallie Swanson, who, on a routine follow-up to a several years' earlier submission, actively solicited this project. We are also extremely appreciative of the collaboration among Kallie, publisher Bill Stenquist of Brooks/Cole, and associate editor Pam Chester and former publisher Phil Sutherland of Digital Press. Through a unique, cooperative arrangement between the two publishing companies, we were permitted to use our trade book, Networking Explained, which is published by Digital Press, as the basis for much of the material contained within this textbook. A note of gratitude is also extended to production editor Dustine Friedman of The Book Company and to production coordi-
　　nator Kelsey McGee of Brooks/Cole, who were together responsible for the overall production of this book. We are particularly grateful to copy editor Frank Hubert.
　　 This book also benefited from the contributions of many former students at Rollins College and Florida Institute of Technology, as well as from participants of seminars and workshops we conducted at various regional and national conferences.
　　 Finally, we extend our personal gratitude to our wives, Jane and Margenia, for their support, patience, understanding, and love throughout this entire project.
　　 Michael A. Gallo
　　 William M. Hancock