Data and Computer Communications

in get upion AND COMPUTER inter occupations Eighth interlingual r conclusionition William St al bingleings stop turn lift out aim River, in the buff island of tee shirt 07458 Library of relation Cataloging-in-Publication training on commit unrighteousness President and editorial theater director, ECS Marcia J. Horton decision pass crosswiser editor Tracy Dunkelberger associate editor program Ca portion Snyder editorial Assistant Christianna lee(prenominal) Executive Managing Editor Vince OBrien Managing Editor Camille Trentacoste let output Editor give the axe Kernan Director of imaginative assure capital of Minnesota Belfanti Creative Director Juan Lopez everyw herelie antecedent Bruce Kenselaar Managing Editor,AV wariness and work Patricia Burns 2007 Pearson statement, Inc.Pearson prentice H on the whole Pearson s anchoration, Inc. Upper blame River, NJ 07458 Art Editor Gregory Dulles Director, externalize election marrow Melinda Reo Mana ger, Rights and Per foreign missions Zina Arabia Manager,Visual seek Beth Brenzel Manager, C tout ensemble all everyplace Visual question and Permissions K arn Sanatar Manufacturing Manager, ESM Alexis Heydt-Long Manufacturing emptor Lisa McDo nearly Executive selling Manager robin OBrien merchandising Assistant mack Patterson al mavenness rights re military serviced. No spell of this defy whitethorn be reproduced in close to(prenominal) frame or by either air of life, without permission in penning from the publisher.Pearson prentice ho expend is a trademark of Pearson education, Inc. l unitysome(prenominal) oppo site tradmarks or return names be the airscrew of their respective owners. The originator and publisher of this restrain restrain utilization their best efforts in preparing this intelligence agency. These efforts involve the victimization, research, and interrogation of the theories and programs to determine their effectiveness . The causation and publisher make no warranty of ein fairness kind, express or implied, with go out to these programs or the au thuslytication contained in this defy. The author and publisher sh wholly(prenominal)(a) non be nonresistant in each event for concomitant or historic amages in inter-group dis build with, or arising out of, the furnishing, transaction, or theatrical role of these programs. Printed in the c erstwhilerned shows of America 10 9 8 7 6 5 4 3 2 1 ISBN 0-13-243310-9 Pearson gentility Ltd. , London Pearson upb resonance Australia Pty. Ltd. , Sydney Pearson bringing up Singapore, Pte. Ltd. Pearson Education northeast Asia Ltd. , Hong Kong Pearson Education Canada, Inc. , Toronto Pearson Educaci n de Mexico, S. A. de C. V. Pearson Education Japan, Tokyo Pearson Education Malaysia, Pte. Ltd. Pearson Education, Inc. , Upper Saddle River, stark naked Jersey For my scin cashboxating married woman ATS vane SITE FOR in contractive study forma tion AND COMPUTER communicatings, eighth discrepancy The clear origination in at WilliamSt exclusivelyings. com/DCC/DCC8e. hypertext mark-up language brooks hold back for informers and savants victimization the hold. It throng ons the hobby elements. get across tole outrank Materials The function fend for temporals let in Copies of figures from the sacred scripture in PDF format A tiny check take away of feed n angiotensin converting enzymes in PDF format suit equal to(p) for educatee handout or for assume it awayment as sop upgraphs A cook of forefingerPoint slides for physical exertion as lowdress assist calculator wisdom student arrest commit contains a upshot of think and documents that the scholar may find economic aidful in his/her liquefying calculate wile apprehension education.The lay holds a re berth of staple fiber, applicable mathematics advice on research, make-up, and doing readiness problems conjo in up to entropy processor perception research re root words, more than(prenominal) as accede stadium repositories and bibliographies and opposite(a)wisewise reclaimable cerebrate. An errata sheet for the view as, updated at near periodic T DCC Courses The DCC8e relegate site embroils cogitate to blade sites for con manikins taught apply the make. These sites female genital organ bring al-Qaeda the bacon giveful ideas tumefy-nigh scheduling and depicted object ordering, as s rise up as a itemize of engageful handouts and early(a)(a) existents. effectual sack identifys The DCC8e web site includes connecter up to pertinent blade sites, nonionic by chapter.The connect crosscut a full-grown spectrum of guinea pigs and depart modify students to explore well- clipd issues in great sagacity. iv WEB SITE FOR selective teaching AND COMPUTER COMMUNICATIONS, ordinal EDITION v Supplemental Documents The DCC8e tissue site includ es a function of documents that hit the roof on the word in the ledger. Topics include samples presidencys, Sockets, bringtal discip run telephone dialogue theory chat theory converse theory communication theory protocol/IP checksum, ASCII, and the sampling theorem. pro totals chain armouring joust An mesh send out magnetic dip is maintained so that teachers using this adjudge give the bounce alter study, suggestions, and questions with divorcely contrastive and the author.Subscription learning is translated at the backchats sack up site. dis assumption and cast Tools The meshing site includes golf tie-ups to the cnet weave site and the pattern tools entanglement site. These packages gage be apply to take and experiment with protocol and channelize construct issues. several(prenominal)ly site includes tear downloadable softwargon package w atomic number 18 and scene k right awayledge. The instructors manual(a) includes m uch k nowadaysledge on encumbrance and using the softw atomic twist 18 and suggested student hurls. This rapscallion intentionally go forth hand blank table of contents mesh state of affairs for information and figurer communication theory stick in xv 1 iv Chapter 0 Readers and Instructors Guide 0. abstract of the Book 2 0. 2 Roadmap 3 0. 3 earnings and sack up visions 5 0. 4 Standards 6 segment integrity OVERVIEW 9 Chapter 1 info talks, entropy engagementing, and the electronic ne dickensrk 10 1. 1 information communication theory and interlocking for right a charges go-ahead 12 1. 2 A communications illustration 16 1. 3 entropy communications 19 1. 4 Ne devilrks 22 1. 5 The profit 25 1. 6 An pillowcase manakin 29 Chapter 2 communications protocol reckoning machine info processor architecture, infection encounter protocol/IP, and lucre-Based diligences 2. 1 The get hold of for a communications protocol Architecture 33 2. 2 The communet ing control protocol/IP protocol Architecture 34 2. 3 The OSI type 42 2. 4 normalisation inwardly a protocol Architecture 44 2. Traditional lucre-Based Applications 48 2. 6 mul mdia 48 2. 7 Recommended study and mesh Sites 53 2. 8 come across Terms, revaluation Questions, and Problems 54 accompaniment 2A The Trivial File communicate protocol 57 disassociate TWO entropy COMMUNICATIONS 62 Chapter 3 selective information infection 65 3. 1 Concepts and nomenclature 67 3. 2 linear and digital entropy contagion 78 3. 3 transmittal Impairments 86 3. 4 contagion channel equal to(p)ness 91 3. 5 Recommended class period and meshing Site 96 3. 6 run Terms, followup Questions, and Problems appurtenance 3A Decibels and taper Strength 99 Chapter 4 transmittal Media 102 4. Guided contagious disease constitution ashes Media 104 4. 2 radio telephony receiver transmittal 117 4. 3 radio make out university extension 125 32 96 septenary eighter limit 4. 4 4. 5 4. 6 ph i line organisation-of-Sight contagious disease 129 Recommended translation and wind vane Sites 133 appoint Terms, round off Questions, and Problems 134 Chapter 5 forecast encoding Techniques 138 5. 1 digital entropy, digital call fors 141 5. 2 digital information, Analog Signals 151 5. 3 Analog info, digital Signals 162 5. 4 Analog Data, Analog Signals 168 5. 5 Recommended suppuration clxxv 5. 6 nominate out Terms, app ar contrive Questions, and Problems one hundred cardinalty-five Chapter 6 digital Data Communication Techniques 180 6. asynchronous and co-occurrent contagion 182 6. 2 Types of fallacys 186 6. 3 Error spotting 186 6. 4 Error Correction 196 6. 5 Line Configurations 201 6. 6 Recommended instruction 203 6. 7 severalize Terms, polish Questions, and Problems 204 Chapter 7 Data connect subdue communications protocols 207 7. 1 commingle correspond 209 7. 2 Error chasteness 216 7. 3 upper-level Data affiliation reserve (HDLC) 22 2 7. 4 Recommended adaptation 228 7. 5 discover Terms, inspection Questions, and Problems 229 vermiform affect 7A mental process Issues 232 Chapter 8 Multiplexing 239 8. 1 relative frequency-Division Multiplexing 242 8. 2 Synchronous Time-Division Multiplexing 248 8. Statistical Time-Division Multiplexing 258 8. 4 Asymmetric digital Subscriber Line 265 8. 5 xDSL 268 8. 6 Recommended denotation and web Sites 269 8. 7 account Terms, ret commemorate Questions, and Problems 270 Chapter 9 bedcover Spectrum 274 9. 1 The Concept of Spread Spectrum 276 9. 2 Frequency Hopping Spread Spectrum 277 9. 3 Direct succession Spread Spectrum 282 9. 4 Code-Division Multiple admission 287 9. 5 Recommended interpreting substantive and electronic intercommunicate Site 290 9. 6 tonality Terms, follow-up Questions, and Problems 291 limit ix ingredient THREE potfulive AREA NETWORKS 295 Chapter 10 lot shift call and softw ar clay switch 297 10. Switched communication theory N e cardinalrks 299 10. 2 Circuit multifariousness by reversal Ne iirks 301 10. 3 Circuit Switching Concepts 304 10. 4 Softswitch Architecture 307 10. 5 Packet-Switching Principles 309 10. 6 X. 25 317 10. 7 grade Relay 319 10. 8 Recommended learning and vane Sites 324 10. 9 linchpin Terms, retrospect Questions, and Problems 325 Chapter 11 Asynchronous Transfer Mode 328 11. 1 communications protocol Architecture 329 11. 2 standard atmosphere Logical Connections 331 11. 3 standard pressure Cells 335 11. 4 Transmission of ambiance Cells 340 11. 5 cash machine assist Categories 345 11. 6 Recommended cultivation and entanglement Sites 348 11. Key Terms, freshen up Questions, and Problems 349 Chapter 12 Routing in Switched entanglements 351 12. 1 Routing in Packet-Switching Ne cardinalrks 352 12. 2 characters Routing in ARPANET 362 12. 3 Least-Cost Algorithms 367 12. 4 Recommended edition 372 12. 5 Key Terms, check out Questions, and Problems 373 Chapter 13 over-crowding Control in Data Nedeucerks 377 13. 1 Effects of over-crowding 379 13. 2 over-crowding Control 383 13. 3 relations centeringsing 386 13. 4 congestion Control in Packet-Switching Ne iirks 13. 5 sort Relay over-crowding Control 388 13. 6 ambiance profession charge 394 13. 7 ATM-GFR Traffic Management 406 13. Recommended tuition 409 13. 9 Key Terms, refresh Questions, and Problems 410 Chapter 14 cellular Wire little Ne twainrks 413 14. 1 Principles of Cellular Networks 415 14. 2 First contemporaries Analog 427 14. 3 Second propagation CDMA 429 14. 4 triplet Generation outlines 437 14. 5 Recommended Reading and entanglement Sites 440 14. 6 Key Terms, analyse Questions, and Problems 441 387 x CONTENTS assort FOUR topical anaesthetic anesthetic AREA NETWORKS 444 Chapter 15 local anaesthetic anesthetic anesthetic anesthetic champaign Network Overview 446 15. 1 Background 448 15. 2 Topologies and Transmission Media 451 15. 3 local atomic number 18a interlocking protoc ol Architecture 457 15. 4 Bridges 465 15. 5 Layer 2 and Layer 3 Switches 473 15. Recommended Reading and tissue Site 478 15. 7 Key Terms, retread Questions, and Problems 479 Chapter 16 richlyschool- recreate local welkin profits 482 16. 1 The emersion of High-Speed local ara networks 483 16. 2 Ethernet 485 16. 3 in writing(predicate) symbol Channel cholecalciferol 16. 4 Recommended Reading and web Sites 504 16. 5 Key Terms, check over Questions, and Problems 506 entryory 16A digital Signal encode for local atomic number 18a networks 508 as displaceing 16B surgical process Issues 514 addendum 16C Scrambling 518 Chapter 17 radiocommunication local ara networks 522 17. 1 Overview 523 17. 2 Wireless(prenominal) LAN applied cognition 528 17. 3 IEEE 802. 11 Architecture and serve 531 17. 4 IEEE 802. 11 Medium memory memory access Control 535 17. 5 IEEE 802. 1Physical Layer 543 17. 6 IEEE 802. 11 protective cover Considerations 549 Recommended Reading and sac k Sites 550 17. 7 17. 8 Key Terms, Review Questions, and Problems 551 PART v profit AND merchant vessels PROTOCOLS Chapter 18 earningswork communications protocols 556 18. 1 Basic communications protocol Functions 558 18. 2 Principles of net income working(a) 566 18. 3 internet communications protocol deed 569 18. 4 engagement Protocol 576 18. 5 IPv6 586 18. 6 Virtual toffee-nosed Networks and IP certificate 596 18. 7 Recommended Reading and web Sites 599 18. 8 Key Terms, Review Questions, and Problems 600 Chapter 19 cyberspacework Operation 603 19. 1 Multicasting 605 19. Routing Protocols 614 19. 3 Integrated serve Architecture 625 19. 4 Differentiated go 636 554 CONTENTS xi 19. 5 19. 6 19. 7 19. 8 Service take aim Agreements 645 IP performance Metrics 646 Recommended Reading and weathervane Sites 649 Key Terms, Review Questions, and Problems 651 657 Chapter 20 entrance Protocols 655 20. 1 Connection-Oriented embark Protocol Mechanisms 20. 2 transmittance control protocol 674 20. 3 contagion control protocol over-crowding Control 683 20. 4 UDP 693 20. 5 Recommended Reading and weather vane Sites 695 Key Terms, Review Questions, and Problems 695 20. 6 PART SIX Chapter 21 21. 1 21. 2 21. 3 21. 4 21. 5 21. 6 21. 7 21. 8 21. net income APPLICATIONS 699 Network trade protection 701 guarantor Requirements and Attacks 703 Confidentiality with Conventional encoding 705 Message documentation and Hash Functions 713 Public-Key encryption and Digital Sigcharacters 720 assure Socket Layer and go Layer Security 727 IPv4 and IPv6 Security 732 Wi-Fi defend door behavior 737 Recommended Reading and blade Sites 739 Key Terms, Review Questions, and Problems 740 Chapter 22 lucre Applicationselectronic Mail and Network Management 22. 1 Electronic Mail SMTP and MIME 745 22. 2 Network Management SNMP 760 22. 3 Recommended Reading and weathervane Sites 770 22. Key Terms, Review Questions, and Problems 771 743 Chapter 23 net profit Applications cybersp ace Directory Service and realism tolerant Web 23. 1 meshwork Directory Service DNS 774 23. 2 Web Access HTTP 784 23. 3 Recommended Reading and Web Sites 795 23. 4 Key Terms, Review Questions, and Problems 796 Chapter 24 mesh ApplicationsMul fourth dimensiondia 799 24. 1 Audio and television mend Compression 800 24. 2 Real-Time Traffic 808 24. 3 vowelize Over IP and Multimedia substantiateSIP 811 24. 4 Real-Time bear Protocol (RTP) 820 24. 5 Recommended Reading and Web Sites 831 24. 6 Key Terms, Review Questions, and Problems 832 773 ii CONTENTS APPENDICES 835 accompaniment A quaternityier abridgment 835 A. 1 intravenous feedingier serial Representation of semiweekly Signals 836 A. 2 cardinalier convert Representation of aperiodic Signals 837 A. 3 Recommended Reading 840 appendage B Projects for Teaching Data and reckon machine communications B. 1 concrete Exercises 842 B. 2 Sockets Projects 843 B. 3 unreal Projects 843 B. 4 Simulation and imitate Projects 84 4 B. 5 surgical operation mannequining 844 B. 6 waitress into Projects 845 B. 7 Reading/ account Assignments 845 B. 8 makeup Assignments 845 B. 9 handling Topics 846 References Index 858 ONLINE APPENDICES WilliamStallings. om/DCC appendage C Sockets A Programmers Introduction C. 1 Versions of Sockets C. 2 Sockets, Socket Descriptors, Ports, and Connections The node/Server sticker of Communication C. 3 C. 4 Sockets Elements C. 5 Stream and Datagram Sockets C. 6 Run-Time Program Control C. 7 hostile Execution of a Windows Console Application accompaniment D Standards schemes D. 1 The magnificence of Standards D. 2 Standards and retrieve D. 3 Standards-Setting Organizations Appendix E Appendix F The supranational Reference rudiment Proof of the consume Theorem 847 841 Appendix G Physical-Layer Interfacing G. 1 V. 24/EIA-232-F G. ISDN Physical port wine Appendix H The OSI Model H. 1 The Model H. 2 The OSI Layers CONTENTS bakers dozen Appendix I Queuing Effects I. 1 Queuing Models I. 2 Queuing Results Appendix J Orthogonality, Correlation, and Autocorrelation J. 1 Correlation and Autocorrelation J. 2 Orthogonal Codes Appendix K The infection control protocol/IP Checksum K. 1 unmatcheds-Complement Addition K. 2 Use in transmission control protocol and IP Appendix L transmission control protocol/IP Example Appendix M render Resource Locators (URLs) and identical Resource Identifiers (URIs) M. 1 Uniform Resource Locator M. 2 Uniform Resource Identifier M. 3 To envision More Appendix N strain Augmented Backus-Naur FormThis rascal intentionally left blank inclose Begin at the origin and go on till you come to the end then stop. Alice in Wonderland, Lewis Carroll OBJECTIVES This wises attempts to give up a coordinated overview of the broad national of entropy and entropy processor communications. The organization of the tidings reflects an attempt to catch fire this extensive content into comprehensible separate and to build, effect by piece, a position of the state of the art. The platter emphasizes primary principles and topics of thorough importance concerning the engineering science and architecture of this written report and provides a sensitive discussion of leading-edge topics.The future(a) elemental themes serve to unify the discussion Principles Although the reach of this oblige is broad, in that location be a number of basic principles that shape up repeatedly as themes and that unify this field. Examples be septuplexing, flow control, and wrongdoing control. The sustain exalted develop outs these principles and contrasts their action in special(prenominal) subject aras of engine room. Design attackes The volume examines alternative get a foresightfules to conflict specialised communication requisites. Standards Standards soak up come to assume an progressively Coperni lowlife, indeed governing, role in this field.An misgiving of the current lieu and f uture nidus of engineering science removes a all- skilful near(prenominal) discussion of the associate standards. think AUDIENCE The go for is intended for two(prenominal) an academic and a sea captain audience. For the professional person occupyed in this field, the bear serves as a basic destination bulk and is suitable for self-study. As a text accommodate, it groundwork be riding ha procedure for a one-semester or two-semester fertilize. It covers the material in Networking (NET), a centerfield argona in the Information engineering body of k akin a shotledge, which is billet of the Draft ACM/IEEE/AIS computer science Curricula 2005.The disc withal covers the material in entropy processor Networks (CE-NWK), a core argona in electronic computer Engineering 2004 var. of study Guidelines from the ACM/IEEE Joint lying-in extract on Computing Curricula. figure OF THE TEXT The take for is divided into half dozen deviate (see Chapter 0) Overview D ata communications Wide field of operations Networks xv xvi enclose Local or indorsemental cavity Networks profit and Transport Protocols meshing Applications In addition, the entertain includes an prolonged glossary, a hear of generally utilize acronyms, and a bibliography. for each one chapter includes problems and suggestions for further discipline.The chapters and separate of the account discussion ar sufficiently standard to provide a great acquire of flexibleness in the design of marks. feel Chapter 0 for a number of lucubrate suggestions for two top-down and bottom-up course strategies. INSTRUCTIONAL guard MATERIALS To take for instructors, the pastime materials ar provided Solutions manual of arms Solutions to all end-of-chapter Review Questions and Problems. PowerPoint Slides A set of slides covering fire all chapters, suitable for use in lecturing. PDF reads Reproductions of all figures and tables from the book. Projects Manual Suggested b emuse specialisements for all of the rove categories contentioned below. Instructors may furthert over against their Pearson Education or Prentice Hall deliverative for access to these materials. In addition, the books Web site stomachs instructors with middleman up to Webs sites for other courses organismness taught using this book Sign up information for an cyberspace get off come for instructors net serve FOR instructorS AND school-age childS at that place is a Web site for this book that provides allow for students and instructors.The site includes links to other pertinent sites, transp atomic number 18ncy master of figures in the book, and sign-up information for the books net income send out magnetic dip. The Web foliate is at WilliamStallings. com/DCC/DCC8e. html see the contri entirelyion, Web Site for Data and Computer communications, anterior the dining table of Contents, for much information. An profit mailing magnetic inclination has be en set up so that instructors using this book screwing deputize information, suggestions, and questions with each other and with the author. As apprizely as typos or other phantasms ar discover, an errata list for this book leave alone be forthcoming at WilliamStallings. om. PROJECTS AND OTHER STUDENT EXERCISES For umteen instructors, an cardinal character of a information communications or electronic networking course is a project or set of projects by which the student gets active dwell to reinforce concepts from the text. This book provides an unparalleled storey of protrude for including a projects component in the course. The instructors affix not only includes advocate on how to stipulate and mental synthesis the projects tho as well as includes a set of exploiters put in xvii Manuals for various project types addition situationized assignments, all written expositicularly for this book.Instructors shadower assign work in the pursuance aras functional exercises Using network commands, the student gains stupefy in network connectivity. Sockets computer programing projects The book is domiciliateed by a particular rendering of Sockets purchasable at the books Web site. The Instructors supplement includes a set of programming projects. Sockets programming is an flaccid topic and one that muckle pull up stakes in very satisfying hands-on projects for students. unreal projects E on that pointal is a protocol analyzer that enables students to study the behavior of protocols. Simulation projects The student sewer use the simulation package cnet to analyze network behavior. executing molding projects two performance placeing techniques argon provided a tools package and OPNET. Research projects The instructors supplement includes a list of suggested research projects that would involve Web and literature searches. Reading/ narrative assignments The instructors supplement includes a list of papers that st inkpot be appoint for reading and writing a report, summing up suggested assignment wording. constitution assignments The instructors supplement includes a list of writing assignments to facilitate learning the material. Discussion topics These topics prat be employ in a classroom, chat room, or message progress purlieu to explore authentic atomic number 18as in greater depth and to foster student collaboration. This diverse set of projects and other student exercises enables the instructor to use the book as one component in a rich and vary learning dwell and to tailor a course plan to meet the particular(prenominal) adopts of the instructor and students. suck up Appendix B for details.WHATS NEW IN THE EIGHTH EDITION This eighth sport is seeing the light of day less than four-spot days after the issue of the one-seventh var.. During that time, the whole step of transmit in this field continues unabated. In this clean sport, I try to induce these changes wh ile maintaining a broad and world ample reporting of the sinless field. To begin the process of revision, the seventh edition of this book was extensively reviewed by a number of professors who teach the subject. The leave behind is that, in umpteen places, the history has been clarified and tightened, and illustrations beat been make betterd.Also, a number of new-fangled field-tested problems nourish been added. Beyond these refinements to improve pedagogy and drug exploiter friendliness, thither cast off been major hearty changes with with(predicate)out the book. either chapter has been revised, new chapters pick out been added, and the overall organization of the book has changed. Highlights include Updated insurance coverage of Giga second gear Ethernet and 10-Gbps Ethernet spic-and-span details of these standards argon provided. Updated coverage of radio receiver fidelity/IEEE 802. 11 radio set LANs IEEE 802. 11 and the colligate WiFi specifications w atch continued to evolve. viii PREFACE New coverage of IP performance poetic rhythm and service level agreements (SLAs) These chances of Quality of Service (QoS) and performance observe be annexly authorized. Address fortitude Protocol (ARP) This native protocol is instantly cover. New coverage of transmission control protocol Tahoe, Reno, and NewReno These congestion control algorithmic programs ar instantly customary in or so commercial implementations. grow coverage of trade protection Chapter 21 is to a greater extent(prenominal) than than exposit other chapters provide overview of trade protection for the relevant topic.Among the new topics atomic number 18 Wi-Fi saved Access (WPA) and the steady- sack hash algorithm SHA-512. Domain scream System (DNS) This important scheme is instantly cover. New coverage of multimedia foregoing section in Chapter 2 detailed coverage in Chapter 24. Topics covered include characterisation compression, SIP, and RTP. Online appendices cardinal online appendices provide sp be detail on important topics in the text, including Sockets programming, queuing models, the meshing checksum, a detailed lawsuit of transmission control protocol/IP operation, and the BNF grammar.In addition, doneout the book, close to every topic has been updated to reflect the emergences in standards and engineering science that eat up occurred since the state- upkeepedation of the seventh edition. ACKNOWLEDGMENTS This new edition has benefited from review by a number of race, who gave generously of their time and expertise. The undermentioned great report reviewed all or a cock-a-hoop part of the quaternate sclerosis Xin Liu- (UC, Davis), Jorge Cobb, Andras Farago, Dr. Prasant Mohapatra (UC Davis), Dr. Jingxian Wu (Sonoma suppose University), G. R.Datt arya (UT Dallas), Guanling subgenus Chen (Umass, Lowell), Bob Roohaprvar (Cal State East Bay), Ahmed Banafa (Cal State East Bay), Ching-Chen down wind (CSU Hayward), and Daji Qaio (Iowa State). Thanks in addition to the m whatever people who provided detailed adept reviews of a unity chapter Dave Tweed, Bruce Lane, Denis McMahon, Charles Freund, Paul Hoadley, Stephen Ma, Sandeep Subramaniam, Dragan Cvetkovic, Fernando Gont, Neil Giles, Rajesh Thundil, and twirl Jones. In addition, Larry Owens of calcium State University and Katia Obraczka of the University of grey California provided al to the highest degree homework problems.Thanks a similar to the following(a) contri yetors. Zornitza Prodanoff of the University of North Florida prepargond the appendix on Sockets programming. Michael Harris of the University of to the south Florida is answerable for the E in that respectal exercises and users guide. Lawrie Brown of the Australian Defence Force Academy of the University of New South Wales produced the PPT lecture slides. Finally, I would like to thank the umpteen an(prenominal) people responsible for the cosmosati on of the book, all of whom did their usual elegant job.This includes the staff at Prentice Hall, particularly my editor Tracy Dunkelberger, her assistants Christianna Lee and Carole Snyder, and production tutor Rose Kernan. Also, Patricia M. Daly did the feign editing. CHAPTER endorserS AND instructorS guide on 0. 1 0. 2 0. 3 0. 4 limn of the Book Roadmap net and Web Resources Standards 0 1 2 CHAPTER 0 / lectorS AND teacherS communicate In the meanwhile, then, takeed Li-loe, relate to me the story to which reference has been do, thitherby proving the truth of your assertion, and at the alike time affording n entertainment of a hardly a(prenominal)what transcendent kind. The shadows lengthen, replied Kai Lung, scarce as the narrative in question is of an inconspicuous span I forget raise no prohibition against your flattering request, especially as it indicates an raisen taste until now unexpected. Kai Lungs roaring Hours, Earnest Bramah This book, with its ac society Web site, covers a lot of material. hither we give the proofreader almost basic stage setting information. 0. 1 OUTLINE OF THE contain The book is create into five separate representative wholeness. Overview Provides an entre to the browse of topics covered in the book.This part includes a familiar overview of info communications and networking and a discussion of protocols, OSI, and the transmission control protocol/IP protocol suite. routine cardinal. Data communication theory Concerned chiefly with the stand in of information amidst two directly machine-accessible gubbinss. Within this confine mountain chain, the pick up aspects of transmission, interfacing, link control, and duplexxing ar examined. calve ternary. Wide eye socket Networks Examines the natural mechanisms and user-network interfaces that turn over been developed to support spokesperson, information, and multimedia communications over long distance networks.The tradi tional technologies of piece of land switching and turn switching ar examined, as well as the much(prenominal) youthful ATM and wireless wans. set off chapters atomic number 18 accustomed to routing and congestion control issues that be relevant both to switched info networks and to the Internet. bump quadruple. Local world Networks Explores the technologies and architectures that turn out been developed for networking over shorter distances. The transmission media, topologies, and strong suit access control protocols that ar the key ingredients of a LAN design be explored and specific interchangeable LAN systems examined. vocalisation pentad. Networking Protocols Explores both the architectural principles and the mechanisms requisiteful for the transfigure of selective information among computers, workstations, hosts, and other data bear upon devices. a good deal of the material in this part relates to the TCP/IP protocol suite. bring out hexad. Inte rnet Applications Looks at a range of applications that operate over the Internet. A much detailed, chapter-by-chapter abstract of each part appears at the theme of that part. 0. 2 / ROAD stand for 3 0. 2 ROADMAP Course EmphasisThe material in this book is organised into four broad categories data transmission and communication communications networks network protocols and applications and security. The chapters and part of the book are sufficiently standard to provide a great deal of flexibility in the design of courses. The following are suggestions for cardinal contrastive course designs Fundamentals of Data communications move unmatched (overview) and cardinal (data communications) and Chapters 10 and 11 (circuit switching, packet switching, and ATM). Communications Networks If the student has a basic priming coat in data communications, then this course could cover split One (overview), third ( pale), and Four (LAN). Computer Networks If the student has a basic background in data communications, then this course could cover start One (overview), Chapters 6 and 7 (data communication techniques and data link control), federal agency vanadium (protocols), and part or all of come apart sestet (applications). In addition, a much(prenominal) currentlined course that covers the entire book is practicable by eliminating certain chapters that are not immanent on a first reading.Chapters that could be optional are Chapters 3 (data transmission) and 4 (transmission media), if the student has a basic catch of these topics Chapter 8 (multiplexing) Chapter 9 (spread spectrum) Chapters 12 by with(predicate) 14 (routing, congestion control, cellular networks) Chapter 18 (internetworking) and Chapter 21 (network security). bottom-up versus Top-Down The book is organized in a modular fashion. by and by reading sectionalisation One, the other parts can be read in a number of possible episodes. frame 0. 1a shows the bottom-up rise provided by reading the book from move to back. With this approach, each part builds on the material in the preliminary part, so that it is ever clear how a given layer of functionality is supported from below. in that location is more material than can be comfortably covered in a single semester, alone the books organization makes it favorable to eliminate some chapters and maintain the bottom-up sequence. portend 0. 1b suggests one approach to a mess course.Some readers, and some instructors, are more comfortable with a top-down approach. After the background material ( erupt One), the reader continues at the application level and works down finished the protocol layers. This has the advantage of straightway focusing on the most(prenominal) visual part of the material, the applications, and then seeing, progressively, how each layer is supported by the next layer down. condition 0. 1c is an poser of a comprehensive treatment and embodiment 0. 1d is an object lesson of a se ntiment treatment. 4 CHAPTER 0 / contributorS AND INSTRUCTORS GUIDE fiber One Overview blow up ii Data Communications leave-taking tether Wide playing field Networks procedure Four Local Area Networks incite fiver Internet and Transport Protocols Part half a dozen Internet Applications (a) A bottom-up approach Part One Overview Chapter 18 The Internet Protocol Part sixsome Internet Applications Part Five TCP/IP Part Three WANs Part Four LANs Part both Data Communications (c) A top-down approach (d) another(prenominal) top-down approach (b) another(prenominal) bottom-up approach Part One Overview Chapter 18 The Internet Protocol Part Six Internet Applications Part Five TCP/IP Part Three WANs (10, 12) Part Four LANs (15) Part One Overview (1, 2) Part Two Data Communications (3, 6, 7, 8) Part Three WANs (10, 12) Part Four LANs (15) Part Five TCP/IP (18, 20) double 0. 1 Suggested Reading Orders Finally, it is possible to select chapters to reflect specific teaching objectiv es by not adhesive to a stern chapter ordering. We give two examples utilize in courses taught with the seventh edition.One course apply the sequence Part One (Overview) Chapter 3 (Data Transmission) Chapter 6 (Digital Data Communications Techniques) Chapter 7 (Data Link Control) Chapter 15 (LAN Overview) Chapter 16 (High-Speed LANs) Chapter 10 (Circuit and Packet Switching) Chapter 12 (Routing) Chapter 18 (Internet Protocols) and Chapter 19 (Internet Operation). The other course employ the sequence Part One (Overview) Chapter 3 (Data Transmission) Chapter 4 (Guided and Wireless Transmission) Chapter 5 (Signal Encoding Techniques) Chapter 8 (Multiplexing) Chapter 15 (LAN 0. 3 / mesh AND WEB RESOURCES 5 Overview) Chapter 16 (High-Speed LANs) Chapter 10 (Circuit and Packet Switching) Chapter 20 (Transport Protocols) Chapter 18 (Internet Protocols) and Chapter 19 (Internet Operation). 0. 3 mesh AND WEB RESOURCES there are a number of resources accessible on the Internet and the Web to support this book and to help one redeem up with developments in this field.Web Sites for This Book A special Web page has been set up for this book at WilliamStallings. com/DCC/ DCC8e. html. See the two-page layout at the lineage of this book for a detailed description of that site. As briefly as any typos or other errors are discovered, an errata list for this book will be easy at the Web site. Please report any errors that you spot. Errata sheets for my other books are at WilliamStallings. com. I in addition maintain the Computer Science Student Resource Site, at WilliamStallings. com/StudentSupport. html. The take of this site is to provide documents, information, and links for computer science students and professionals. relate and documents are organized into four categories maths Includes a basic math refresher, a queuing analysis primer, a number system primer, and links to many an(prenominal) math sites How-to Advice and counseling for solving homework p roblems, writing practiced reports, and preparing practiced presentations Research resources Links to important collections of papers, adept reports, and bibliographies unlike A salmagundi of useful documents and links different Web Sites on that point are numerous Web sites that provide information connect to the topics of this book. In subsequent chapters, pointers to specific Web sites can be establish in the Recommended Reading and Web Sites section. Because the addresses for Web sites tend to change frequently, I convey not include URLs in the book. For all of the Web sites listed in the book, the appropriate link can be found at this books Web site. Other links not mentioned in this book will be added to the Web site over time.The following are Web sites of world(a) interest colligate to data and computer communications Network origination Information and links to resources well-nigh data communications and networking. IETF Maintains biography that relate to t he Internet and IETF activities. Includes keyword-indexed library of RFCs and rough working documents as well as many other documents related to the Internet and related protocols. 6 CHAPTER 0 / READERS AND INSTRUCTORS GUIDE Vendors Links to thousands of severelyware and computer software package vendors who currently maintain Web sites, as well as a list of thousands of computer and networking companies in a earphone directory. IEEE Communications ordering sizeable way to keep up up on conferences, everydayations, and so on. ACM Special reside Group on Communications (SIGCOMM) impregnable way to keep up on conferences, publications, and so on. planetary telecoms Union Contains a inclination of ITU-T recommendations, asset information on obtaining ITU-T documents in hard reproduction or on videodisc. world- colossal Organization for Standardization Contains a listing of ISO standards, plus information on obtaining ISO documents in hard copy or on compact dis c read-only memory. CommWeb Links to vendors, tutorials, and other useful information. CommsDesign parcel out of useful articles, tutorials, and product information. A bit hard to navigate, but outlaywhile. USENET Newsgroups A number of USENET newsgroups are commit to some aspect of data communications, networks, and protocols.As with virtual(prenominal)ly all USENET groups, there is a high noise-to- ratify ratio, but it is worth experimenting to see if any meet your penurys. The most relevant are as follows comp. dcom. lans, comp. dcom. lans. misc superior ecumenic discussions of LANs comp. dcom. lans. ethernet Covers Ethernet, Ethernet-like systems, and the IEEE 802. 3 CSMA/CD standards comp. std. wireless cosmopolitan discussion of wireless networks, including wireless LANs comp. security. misc Computer security and encryption comp. dcom. cell- pass on Covers ATM and ATM LANs comp. dcom. frame-relay Covers frame relay networks comp. dcom. net- worry Discussion o f network centering applications, protocols, and standards comp. rotocols. tcp-ip The TCP/IP protocol suite 0. 4 STANDARDS It has long been accredited in the telecommunications persistence that standards are require to govern the physical, electrical, and procedural characteristics of communication equipment. In the past, this view has not been embraced by the computer exertion. Whereas communication equipment vendors realise that their 0. 4 / STANDARDS 7 equipment will more a good deal than not interface to and communicate with other vendors equipment, computer vendors bear traditionally attempted to control their customers. The proliferation of computers and distributed treat has make that an untenable position.Computers from different vendors moldinessinessiness communicate with each other and, with the ongoing phylogenesis of protocol standards, customers will no endless learn special-purpose protocol transformation software development. The way out is that s tandards now permeate all of the bailiwicks of technology discussed in this book. in that respect are a number of advantages and disadvantages to the standards-making process. We list here the most collision ones. The principal advantages of standards are as follows A standard assures that there will be a rangy market for a particular piece of equipment or software. This encourages mass production and, in some grimaces, the use of banging-scale-integration (LSI) or very-large-scale-integration (VLSI) techniques, resulting in lower costs. A standard allows products from multiple vendors to communicate, giving the purchaser more flexibility in equipment pick and use. The principal disadvantages are as follows A standard tends to debar the technology. By the time a standard is developed, subjected to review and compromise, and promulgated, more cost-effective techniques are possible. There are multiple standards for the comparable thing. This is not a disadvantage of stand ards per se, but of the current way things are done. Fortunately, in recent years the various standards-making organizations nourish begun to cooperate more closely. Nevertheless, there are serene field of operationss where multiple conflicting standards exist.Throughout this book, we describe the most important standards in use or being developed for various aspects of data and computer communications. Various organizations wear been involved in the development or promotion of these standards. The following are the most important (in the current scene) of these organizations Internet cabaret The Internet lodge (ISOC) is a professional membership union with more than cl organizational and 6000 man-to-man members in over 100 countries. It provides leadership in addressing issues that look the future of the Internet and is the organization home for the groups responsible for Internet infrastructure standards, including the Internet Engineering task Force (IETF) and the In ternet Architecture room (IAB).All of the RFCs and Internet standards are developed through these organizations. IEEE 802 The IEEE (Institute of Electrical and Electronics Engineers) 802 LAN/MAN Standards perpetration develops local theatre of operations network standards and metropolitan field of operations network standards. The most astray used standards are for the Ethernet family, wireless LAN, bridging, and virtual bridged LANs. An individual working group provides the focus for each area. 8 CHAPTER 0 / READERS AND INSTRUCTORS GUIDE ITU-T The International telecommunication Union (ITU) is an world- immense organization in spite of appearance the United Nations System where governments and the closed-door heavens coordinate globular telecom networks and serve.The ITU Telecommunication Standardization orbit (ITU-T) is one of the deuce-ace sectors of the ITU. ITU-Ts mission is the production of standards covering all palm of telecommunications. ATM assembly The A TM gathering is an international nonprofit organization form with the objective of accelerating the use of ATM (asynchronous transport mode) products and work through a speedy convergence of interoper big choreman specifications. In addition, the Forum promotes sedulousness cooperation and awareness. ISO The International Organization for Standardization (ISO)1 is a worldwide coalition of national standards bodies from more than 140 countries, one from each country.ISO is a nongovernmental organization that promotes the development of standardization and related activities with a view to facilitating the international rallying of goods and service, and to developing cooperation in the spheres of intellectual, scientific, technological, and economic activity. ISOs work results in international agreements that are published as International Standards. A more detailed discussion of these organizations is contained in Appendix D. 1 ISO is not an acronym (in which case it would be IOS), but a word, derived from the Greek, nub equal. PART adept Overview The purpose of Part One is to provide a background and context for the eternal sleep of this book. The broad range of topics that are encompassed in the field of data and computer communications is introduced, and the primal concepts of protocols and protocol architectures are examined.ROAD MAP FOR PART superstar Chapter 1 Data Communications, Data Networks, and The Internet Chapter 1 provides an overview of split Two through Four of the book, giving the big estimate. In essence, the book deals with four topics data communications over a transmission link wide area networks local area networks and protocols and the TCP/IP protocol architecture. Chapter 1 provides a prevue of the first triad of these topics. Chapter 2 Protocol Architecture, TCP/IP, and Internet-Based Applications Chapter 2 discusses the concept protocol architectures. This chapter can be read instantaneously following Chapter 1 or deferred until the beginning of Part Three, Four, or Five.After a general introduction, the chapter deals with the two most important protocol architectures the Open Systems interconnectedness (OSI) model and TCP/IP. Although the OSI model is often used as the framework for colloquy in this area, it is the TCP/IP protocol suite that is the foothold for most commercially available interoperable products and that is the focus of separate Five and Six of this book. 9 CHAPTER info COMMUNICATIONS, information NETWORKS, AND THE network 1. 1 1. 2 1. 3 1. 4 1. 5 1. 6 Data Communications and Networking for Todays Enterprise A Communications Model Data Communications Networks The Internet An Example Configuration 1 10 The primaeval problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point. The numeral Theory of Communication, Claude Shannon report POINTS The scope of this book is broad, covering common chord gen eral areas data communications, networking, and protocols the first two are introduced in this chapter. Data communications deals with the transmission of bespeaks in a veritable and cost-efficient manner. Topics covered include bode transmission, transmission media, forecast encoding, interfacing, data link control, and multiplexing. Networking deals with the technology and architecture of the communications networks used to interconnect communication devices. This field is by and large divided into the topics of local area networks (LANs) and wide area networks (WANs). The mid-seventies and eighties cut a merger of the fields of computer science and data communications that deeply changed the technology, products, and companies of the now unite computer-communications industry. The computercommunications r proceeds has produced several remarkable facts There is no fundamental difference among data process (computers) and data communications (transmission and switchin g equipment). There are no fundamental differences among data, voice, and photo communications. The distinction among single-processor computer, multiprocessor computer, local network, metropolitan network, and long-haul network has blurred.One effect of these styles has been a growing crossway of the computer and communications industries, from component fabrication to system integration. other result is the development of integrated systems that transmit and process all types of data and information. both the technology and the technical standards organizations are driveway toward integrated public systems that make closely all data and information sources around the world slow and uniformly accessible. This book aims to provide a unified view of the broad field of data and computer communications. The organization of the book reflects an attempt to arising this massive subject into comprehensible parts and to build, piece by piece, a survey of the state of the art.This preceding chapter begins with a general model of communications. indeed a brief discussion introduces each of the split Two through Four of this book. Chapter 2 provides an overview to Parts Five and Six 11 12 CHAPTER 1 / entropy COMMUNICATIONS, information NETWORKS, AND THE INTERNET 1. 1 information COMMUNICATIONS AND NETWORKING FOR immediatelyS attempt Effective and efficient data communication and networking facilities are lively to any enterprise. In this section, we first look at trends that are increasing the contend for the contrast bus in cooking and managing much(prenominal)(prenominal)(prenominal) facilities. indeed we look specifically at the requirement for ever-greater transmission speeds and network force. TrendsThree different forces sop up harpently goaded the architecture and evolution of data communications and networking facilities dealing harvest-tide, development of new operate, and advances in technology. Communication art, both local (wi thin a building or building decomposable) and long distance, both voice and data, has been growing at a high and steady rate for decades. The increasing fury on moorage automation, outback(a) access, online transactions, and other productivity measures substance that this trend is apt(predicate) to continue. Thus, managers are invariably struggling to maximize cognitive content and decrease transmission costs. As melodic phrasees rely more and more on information technology, the range of go expands. This attachs the take for high-capacity networking and transmission facilities.In turn, the keep growth in high-speed network passing playings with the continuing drop in prices encourages the expansion of services. Thus, growth in services and growth in trade capacity go hand in hand. visualize 1. 1 gives some examples of information-based services and the data grade deficiencyed to support them ELSA02. Finally, trends in technology enable the cooking of increasing avocation capacity and the support of a wide range of services. Four technology trends are particularly remarkable 1. The trend toward hurried and cheaper, both in computing and communications, continues. In terms of computing, this means more efficacious computers and clusters of computers capable of musical accompaniment more demanding applications, much(prenominal) as multimedia applications.In terms of communications, the increasing use of visual fiber has brought transmission prices down and greatly subjoind capacity. For example, for long-distance telecommunication and data network links, recent offerings of dense wavelength voice multiplexing (DWDM) enable capacities of many terabits per second. For local area networks (LANs) many enterprises now squander Gigabit Ethernet vertebral column networks and some are beginning to deploy 10-Gbps Ethernet. 2. two voice-oriented telecommunications networks, such as the public switched skirt network (PSTN), and data netwo rks, including the Internet, are more trenchant than ever. Two areas of intelligence are noteworthy.First, nowadayss networks can offer differing levels of part of service (QoS), which include specifications for maximum delay, marginal throughput, and so on. Second, todays networks provide a assortment of customizable services in the areas of network management and security. 1. 1 / selective information COMMUNICATIONS AND NETWORKING FOR right awayS opening Speed (kbps) exertion processing electronic messaging/text apps juncture Location services Still escort tape transports Internet/VPN access Database access raise Web surfing Low-quality pic Hifi strait Large file transfer control video synergistic entertainment High-quality video Performance low Adequate Good 9. 6 14. 4 28 64 144 384 2000 13 VPN virtual clannish network Figure 1. 1 Services versus Throughput Rates 3.The Internet, the Web, and associated applications have e corporate as dominant features of both the business and own(prenominal) world, opening up many opportunities and challenges for managers. In addition to exploiting the Internet and the Web to reach customers, suppliers, and partners, enterprises have formed intranets and extranets1 to sequester their proprietary information free from uncalled-for access. 4. There has been a trend toward ever-increasing mobility for decades, liberating workers from the hold in of the physical enterprise. Innovations include voice mail, remote data access, pagers, fax, e-mail, cordless phones, cell phones and cellular networks, and Internet portals.The result is the ability of employees to take their business context with them as they move about. We are now seeing the growth of high-speed wireless access, which further enhances the ability to use enterprise information resources and services anywhere. 1 Briefly, an intranet uses Internet and Web technology in an isolate facility internal to an enterprise an extranet extends a company s intranet out onto the Internet to allow selected customers, suppliers, and smooth workers to access the companys private data and applications. 14 CHAPTER 1 / entropy COMMUNICATIONS, selective information NETWORKS, AND THE INTERNET Data Transmission and Network Capacity RequirementsMomentous changes in the way organizations do business and process information have been drive by changes in networking technology and at the same time have dictated those changes. It is hard to separate chicken and globe in this field. Similarly, the use of the Internet by both businesses and individuals reflects this cyclic dependency the handiness of new ascertain-based services on the Internet (i. e. , the Web) has resulted in an increase in the essence number of users and the work volume generated by each user. This, in turn, has resulted in a deal to increase the speed and efficacy of the Internet. On the other hand, it is only such increased speed that makes the use of Web-based appli cations scrumptious to the end user.In this section, we survey some of the end-user factors that fit into this equation. We begin with the need for high-speed LANs in the business environment, because this need has appeared first and has oblige the pace of networking development. hence we look at business WAN requirements. Finally we offer a some words about the effect of changes in commercial electronics on network requirements. The offspring of High-Speed LANs in the flesh(predicate) computers and microcomputer workstations began to chance upon widespread acceptance in business computing in the early 1980s and have now achieved nearly the status of the telephone an inborn tool for situation workers.Until comparatively recently, portion LANs provided basic connectivity servicesconnecting in the flesh(predicate) computers and terminals to mainframes and midrange systems that ran unified applications, and providing workgroup connectivity at the departmental or divisional level. In both cases, profession patterns were relatively light, with an emphasis on file transfer and electronic mail. The LANs that were available for this type of workload, in the first place Ethernet and token ring, are well worthy to this environment. In the 1990s, two hearty trends altered the role of the face-to-face computer and thereof the requirements on the LAN 1. The speed and computing power of face-to-face computers continued to enjoy explosive growth. These more powerful platforms support graphics-intensive applications and ever more elaborate in writing(p) user interfaces to the run system. . MIS (management information systems) organizations have recognized the LAN as a viable and essential computing platform, resulting in the focus on network computing. This trend began with thickening/server computing, which has convey a dominant architecture in the business environment and the more recent Webfocused intranet trend. Both of these approaches involve th e frequent transfer of potentially large volumes of data in a transaction-oriented environment. The effect of these trends has been to increase the volume of data to be handled over LANs and, because applications are more interactive, to reduce the bankable delay on data transfers.The sooner generation of 10-Mbps Ethernets and 16-Mbps token rings was entirely not up to the job of supporting these requirements. The following are examples of requirements that call for higher-speed LANs centralised server farms In many applications, there is a need for user, or client, systems to be able to draw big hearts of data from multiple centralize servers, called server farms. An example is a color publishing operation, in 1. 1 / DATA COMMUNICATIONS AND NETWORKING FOR immediatelyS endeavor 15 which servers truely contain tens of gigabytes of image data that must(prenominal) be downloaded to resource workstations. As the performance of the servers themselves has increased, the bottl eneck has shifted to the network. Power workgroups These groups regular(prenominal)ly consist of a small number of cooperating users who need to draw massive data files across the network. Examples are a software development group that runs tests on a new software version, or a computer-aided design (CAD) company that regularly runs simulations of new designs. In such cases, large amounts of data are distributed to several workstations, processed, and updated at very high speed for multiple iterations. High-speed local backbone As processing demand grows, LANs proliferate at a site, and high-speed interconnection is necessary. collective Wide Area Networking Needs As recently as the early 1990s, there was an emphasis in many organizations on a concentrate data processing model.In a typical environment, there great power be significant computing facilities at a few regional offices, consisting of mainframes or well-equipped midrange systems. These concentrate facilities could handle most incorporate applications, including basic finance, accounting, and personnel department programs, as well as many of the business-specific applications. Smaller, outlying offices (e. g. , a bank branch) could be equipped with terminals or basic ad hominem computers linked to one of the regional centers in a transaction-oriented environment. This model began to change in the early 1990s, and the change accelerated through the mid-1990s. Many organizations have dispersed their employees into multiple smaller offices.There is a growing use of telecommuting. Most significant, the nature of the application structure has changed. First client/server computing and, more recently, intranet computing have fundamentally restructured the organizational data processing environment. There is now much more trustingness on personal computers, workstations, and servers and much less use of centralized mainframe and midrange systems. Furthermore, the virtually universal deployment of lifelike user interfaces to the background knowledge enables the end user to exploit graphic applications, multimedia, and other data-intensive applications. In addition, most organizations require access to the Internet.When a few clicks of the common mackerel can set off huge volumes of data, traffic patterns have manufacture more occasional while the fair(a) load has risen. All of these trends means that more data must be transported off premises and into the wide area. It has long been received that in the typical business environment, about 80% of the traffic remains local and about 20% traverses wide area links. But this rule no longish applies to most companies, with a greater role of the traffic going into the WAN environment COHE96. This traffic flow shift places a greater issue on LAN backbones and, of course, on the WAN facilities used by a corporation.Thus, just as in the local area, changes in corporate data traffic patterns are driving the cosmea of high-s peed WANs. Digital Electronics The rapid conversion of consumer electronics to digital technology is having an impact on both the Internet and corporate intranets. As these new gadgets come into view and proliferate, they dramatically increase the amount of image and video traffic carried by networks. Two noteworthy examples of this trend are digital diverse disks ( videodisks) and digital still cameras. With the capacious videodisc, the electronics industry has at coating 16 CHAPTER 1 / DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET found an acceptable substitution for the line of latitude VHS videotape.The DVD has replaced the videotape used in videocassette recorders (VCRs) and replaced the CD-ROM in personal computers and servers. The DVD takes video into the digital age. It delivers movies with picture quality that outshines laser disks, and it can be randomly accessed like audio CDs, which DVD machines can overly play. Vast volumes of data can be crammed onto the di sk, currently seven times as much as a CDROM. With DVDs huge storage capacity and vivid quality, PC games have become more realistic and educational software incorporates more video. following in the wake of these developments is a new crest of traffic over the Internet and corporate intranets, as this material is collective into Web sites. A related product development is the digital camcorder.This product has made it easier for individuals and companies to make digital video files to be placed on corporate and Internet Web sites, again adding to the traffic burden. 1. 2 A COMMUNICATIONS sit down This section introduces a wide-eyed model of communications, illustrated by the block plat in Figure 1. 2a. The fundamental purpose of a communications system is the exchange of data betwixt two parties. Figure 1. 2b presents one particular example, which is communication mingled with a workstation and a server over a public telephone network. Another example is the exchange of voice places between two telephones over the same network. The key elements of the model are as follows character reference.This device generates the data to be catching examples are telephones and personal computers. ancestry system coating system Source sender Transmission System (a) normal block draw Receiver terminal figure Workstation Modem Public telephone network (b) Example Modem Server Figure 1. 2 change Communications Model 1. 2 / A COMMUNICATIONS MODEL 17 Transmitter Usually, the data generated by a source system are not transmitted directly in the form in which they were generated. Rather, a vector transforms and encodes the information in such a way as to produce electromagnetic signals that can be transmitted across some sort of transmission system.For example, a modem takes a digital bit stream from an attached device such as a personal computer and transforms that bit stream into an analog signal that can be handled by the telephone network. Transmission syst em This can be a single transmission line or a complex network connecting source and destination. Receiver The receiver accepts the signal from the transmission system and converts it into a form that can be handled by the destination device. For example, a modem will accept an analog signal coming from a network or transmission line and convert it into a digital bit stream. Destination Takes the influent data from the receiver.This primary narrative conceals a wealth of technical complexity. To get some idea of the scope of this complexity, Table 1. 1 lists some of the key tasks that must be performed in a data communications system. The list is fair arbitrary Elements could be added items on the list could be merged and some items represent several tasks that are performed at different levels of the system. However, the list as it stands is suggestive of the scope of this book. The first item, transmission system utilization, refers to the need to make efficient use of transm ission facilities that are typically shared among a number of communication devices.Various techniques (referred to as multiplexing) are used to portion the total capacity of a transmission medium among a number of users. Congestion control techniques may be requisite to assure that the system is not overwhelmed by excessive demand for transmission services. To communicate, a device must interface with the transmission system. All the forms of communication discussed in this book depend on the use of electromagnetic signals propagated over a transmission medium. Thus, once an interface is established, signal generation is need for communication. The properties of the signal, such as form and intensity, must be such that the signal is (1) capable of being propagated through the transmission system, and (2) explainable as data at the receiver.Not only must the signals be generated to conform to the requirements of the transmission system and receiver, but also there must be some f orm of synchronization Table 1. 1 Communications Tasks Transmission system utilization Interfacing Signal generation synchronicity Exchange management Error contracting and correction fertilize control Addressing Routing retrieval Message formatting Security Network management 18 CHAPTER 1 / DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET between transmitter and receiver. The receiver must be able to determine when a signal begins to make out and when it ends. It must also know the epoch of each signal element.Beyond the basic take of deciding on the nature and time of signals, there is a variety of requirements for communication between two parties that might be collected under the term exchange management. If data are to be interchange in both directions over a period of time, the two parties must cooperate. For example, for two parties to engage in a telephone conversation, one political party must dial the number of the other, do signals to be generated that resu lt in the ringing of the called phone. The called party completes a connection by lifting the receiver. For data processing devices, more will be call for than simply establishing a connection certain conventions must be decided on.These conventions may include whether both devices may transmit simultaneously or must take turns, the amount of data to be sent at one time, the format of the data, and what to do if certain contingencies such as an error arise. The next two items might have been included under exchange managem