VoIP at Butler University

Butler University identified weaknesses in the existing campus communication systems. Chief Information Office (CIO) Scott Kincaid's identified the need to upgrade or replace the Centrex system as Butler student enrollment and administrative data communication needs had outgrown its usefulness. Arguments for the Centrex system were that users found the system reliability to be beneficial. Once employees have a system that meets their current needs, some are reluctant to go embrace the next step to enhancing Job capabilities.The majority of students liked having campus rovided email even though 92% had cell phones. Various problems were associated with the existing system but it was not without failure. For no other reason than advances in technology, the current analog system had become outdated and hard to customize. Moving lines was labor intensive with student and administrative shifts. Changes become labor intensive and difficult to perform because not only is the hardware diffic ult to repair, at a certain point the system will be so antiquated that it won't be compatible with new vendor technology upgrades outside of Butler.A large amount of administrative time was spent reconciling the current billing system each month showing that again unnecessary labor was a hindrance to efficiency. Changes aren't without risk and administrative staff viewed merging data and voice networks was viewed as risky. A major concern was regarding the voice quality of VoIP technology. The IT department also knew that network security risks were a concern addressing other data network risk concerns post 9/1 1 . An efficient and flexible integrated emergency notification system was required to remedy this concern.Campus administration also feared virus attacks that commonly affected data networks. Unified communications is a term used to describe a system that integrates call and data communication applications that are interactive and collaborative with real- time and transacti onal capabilities. Butler hired the Dietrich Lockard Group, a telecommunications-consulting firm, to address the primary issues and needs of the university and to recommend a unified communications solution.To pinpoint the real needs of the university, Dietrich formed an advisory group comprised of dministrative staff from a variety of departments around campus who required a high-level of data usage and accuracy from the system. Those departments were admissions, financial services, student life, facilities management, the libraries, and department faculty. The advisory group and technical staff were taught about VoIP and steps that can be taken to mitigate its risks.The strategic plan involving integrating these five goals: improve student communications, improve handling of callers, leverage new services to assist staff and improve training on these systems, emain competitive with other institutions regarding the level of student services offered, and to provide more immediate ac cess to key Butler personnel. The options presented to Butler were to continue with the existing systems and make no changes. Many people find the system reliable.Another solutions would be to continue upgrading the existing system and equipment. Although expensive, IT staff was familiar with the system and, while difficult, upgrades were possible – at least in the system and integrate and independent VoIP for a few selected offices. This would llow Butler to make a small-scale technology change without compromising the entire communications network. The last and most expensive option is to acquire a new in-house PBX system for unified communications.The concern with this option is if Butler were to invest in a new PBX system would it have a limited life? With Dietrich's guidance, Butler drafted an RFP and put the project out for bid. Vendor selection would be based on the an analysis of the variables effecting choices, the vendor's ability meet the universitys needs as defin ed in the RFP, cost, availability of ocal support once the network was installed, and the vendor's experience with new VoIP and other enterprise systems.A vendor was selected and a very aggressive implementation schedule was initiated. Staff and students found the changeover simple and the pilot program made training fun. The IT department described the changeover as the â€Å"week from hell†. Phone system registration was labor intensive when each needed to be registered manually. Other problems were malfunctioning equipment, the 2,000 additional phone numbers provided by SBC came up missing nd required a 45-day window to fix the problem and food service and the bookstore didn't have Ethernet wiring.The biggest problem was that department safety alarm wiring was not compatible with new VoIP and the old system needed to be recreated to make them work. My concern with the alarm system was based on 1970's technology and should have been updated. I would consider the upgrade to be a wise decision on Butler's choice. Analog systems are antiquated and had they not made the change now, it may have been more costly in the future. Technology ntegration with outside source such as telecommunications companies and software support for financial and accounting systems.Any department that required data sharing and collaboration, mixed media messaging was at an operational risk had the change-over not been implemented. By converging systems for a unified communication solution, Butler had taken the proactive approach. It wasn't without unanticipated costs – a new IT staff position was created, and the unforeseen costs to the department alarm system and Ethernet cabling to food services and the bookstore were substantial. What Butler gained was collaborative applications, improved communications and convenience.Having a different call centers around campus, Butler could now examine call records and identify inefficacies within a specific area. The economy of i mproving these areas will be cost and improved university services. I believe Butler made the correct choice in moving forward with a new system. The only fault I found was in their not revamping the existing alarm system. The problems experienced during the changeover were minimal and solvable without reconstructing the plan. Again, a solid strategic and farsighted plan.

Culture Lens

Culture lens Ford went through a hard time, not just because of the outside gloomy economics, but also the pressure of a dysfunctional, often defeatist culture. In Ford’s long business history, culture is not constant; it evolves, the business culture had been changed generation by generation in the economic progress and globalization. Both of essence and dross has been passed down in a grown bureaucracy, where people lost their innovation and structure is messy. The new chief executive of Ford Motor Co. , Alan R. Mulally was taking a culture revolution in this giant machine in order to pull it out of the deep mud.Organization values †¢Pioneered modern management techniques Period 1: Ford is the birthplace of the assembly line and home of the celebrated Whiz Kids, which highly increase the efficiency in the production and copied by the other companies. Period 2: After 1960s, Ford fell into a reverse way and has degenerated into a symbol of inefficiency. Right now, it has four parallel operating units and the company has more than 30 engineering platforms worldwide, each with its own costly bureaucracy, factories, and product development staff.Period 3: Mulally took a big step and would like to reduce the level of complexity. He wants to get that number down to five or six platforms, similar to Honda. More importantly, Ford tries to eliminate all of its unnecessary duplication. †¢Cooperation and efficiency Period 1: After assembly line been introduced to the world, Ford impressed all of their competitors by their highly cooperated work and their efficiency, employees worked together and impede the flaws passing to the next connection. Until the mid-'60s, Ford was considered a management shrine.Period 2: The bureaucracy at Ford grew, and managers took refuge in the structure when things got tough rather than innovate or try new ideas that seemed risky. Personal ties became important in Ford, ambitious managers focused increasingly on kissing the right rings instead of racking up results, which discouraged collaboration. Period 3: With Mulally’s idea, moving job tenures to a long tenure, collaboration would become more important in the future production and management. He has made it a top priority to encourage his team to admit mistakes, to share more information, and to cooperate across divisions †¢Customer focusPeriod 1: Ford focused on customer needs, developed scientific consumer research techniques, which was one of the first auto companies to create products that were based on hard data rather than the personal tastes of executives. Period 2: Employees consider more about their logics than customers’ needs. The tendency of employees is to rationalize mistakes instead of fixing them. Period 3: Mulally wants managers to think more about customers than their own careers. Shared assumptions †¢Rationalize problem instead of fixing problemsIn the example, it is easy to tell that employees’ log ic with problems, rationalizing mistakes instead of fixing them and focusing on customers’ needs. †¢Royal hierarchy Within almost half century’s development, Ford has been fallen into a costly bureaucracy structure. People in the organization have their own status, and it is not allowed to share information freely, manager focus on their rings more than their jobs. †¢Mediocrity is acceptable Weary corporate lifers have become all too comfortable with the idea of losing money.They do not think about to fix problems or try new ideas that seemed risk but took refuge in the structure when things got tough. †¢Resist with outsiders Ford is a place that's notorious for destroying auto industry outsiders–and Mulally is admittedly no car guy. Despite Bill Ford's strong backing, employees are looks arrogant and resist the revolution from outside. Symbols †¢blue oval logo Ford’s logo is highly impressive by their customers, even in the economic c risis, Ford still can pledge their icon to finance enough money from banks and bondholders to turnaround. Assembly line This new product line created quite a stir when it had been introduced to product line; it changed the way manufacturing factory to run their business. What’s more, it is still significantly influence the world and operated in almost all of the manufacturing business. †¢Henry Ford Henry Ford obviously is an outstanding personage in business area, he invented auto business and changed the way people assemble their products. Even right now, when people talk about Ford, we still cannot ignore his impact in the auto area. †¢Bureaucratic organizationThere are no other companies like Ford, has a high level of complexity within their organization structure. There are four parallel operating units and more than 30 engineering platforms worldwide. On the other side, duplication was common in the company; no two vehicles in Ford's lineup share the same mirro rs, headlamps, or even such mundane pieces as the springs and hinges for the hood. Changes in culture system can be slow and painful for an organization, especially in the high developed bureaucracy. However, the importance to take the revolution is obviously, with regard to globalization and fierce competition.

Data and Computer Communications

DATA AND COMPUTER COMMUNICATIONS Eighth Edition William Stallings Upper Saddle River, New Jersey 07458 Library of Congress Cataloging-in-Publication Data on File Vice President and Editorial Director, ECS: Marcia J. Horton Executive Editor: Tracy Dunkelberger Assistant Editor: Carole Snyder Editorial Assistant: Christianna Lee Executive Managing Editor: Vince O’Brien Managing Editor: Camille Trentacoste Production Editor: Rose Kernan Director of Creative Services: Paul Belfanti Creative Director: Juan Lopez Cover Designer: Bruce Kenselaar Managing Editor,AV Management and Production: Patricia Burns  ©2007 Pearson Education, Inc.Pearson Prentice Hall Pearson Education, Inc. Upper Saddle River, NJ 07458 Art Editor: Gregory Dulles Director, Image Resource Center: Melinda Reo Manager, Rights and Permissions: Zina Arabia Manager,Visual Research: Beth Brenzel Manager, Cover Visual Research and Permissions: Karen Sanatar Manufacturing Manager, ESM: Alexis Heydt-Long Manufacturing B uyer: Lisa McDowell Executive Marketing Manager: Robin O’Brien Marketing Assistant: Mack Patterson All rights reserved. No part of this book may be reproduced in any form or by any means, without permission in writing from the publisher.Pearson Prentice Hallâ„ ¢ is a trademark of Pearson Education, Inc. All other tradmarks or product names are the property of their respective owners. The author and publisher of this book have used their best efforts in preparing this book. These efforts include the development, research, and testing of the theories and programs to determine their effectiveness. The author and publisher make no warranty of any kind, expressed or implied, with regard to these programs or the documentation contained in this book. The author and publisher shall not be liable in any event for incidental or consequential amages in connection with, or arising out of, the furnishing, performance, or use of these programs. Printed in the United States of America 10 9 8 7 6 5 4 3 2 1 ISBN: 0-13-243310-9 Pearson Education Ltd. , London Pearson Education Australia Pty. Ltd. , Sydney Pearson Education Singapore, Pte. Ltd. Pearson Education North 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, New Jersey For my scintillating wife ATSWEB SITE FOR DATA AND COMPUTER COMMUNICATIONS, EIGHTH EDITION The Web site at WilliamStallings. com/DCC/DCC8e. html provides support for instructors and students using the book. It includes the following elements. Course Support Materials The course support materials include †¢ Copies of figures from the book in PDF format †¢ A detailed set of course notes in PDF format suitable for student handout or for use as viewgraphs †¢ A set of PowerPoint slides for use as lecture aids †¢ Computer Science Student Support Site: contains a number of links and documents that the student may find useful in his/her ongoing computer science education.The site includes a review of basic, relevant mathematics; advice on research, writing, and doing homework problems; links to computer science research resources, such as report repositories and bibliographies; and other useful links. †¢ An errata sheet for the book, updated at most monthly T DCC Courses The DCC8e Web site includes links to Web sites for courses taught using the book. These sites can provide useful ideas about scheduling and topic ordering, as well as a number of useful handouts and other materials. Useful Web Sites The DCC8e Web site includes links to relevant Web sites, organized by chapter.The links cover a broad spectrum of topics and will enable students to explore timely issues in greater depth. iv WEB SITE FOR DATA AND COMPUTER COMMUNICATIONS, EIGHTH EDITION v Supplemental Documents The DCC8e Web site includes a number of documents that expand on the treatment in the book. Topics include standards organizations, Sockets, TCP/IP checksum, ASCII, and the sampling theorem. Internet Mailing List An Internet mailing list is maintained so that instructors using this book can exchange information, suggestions, and questions with each other and the author.Subscription information is provided at the book’s Web site. Simulation and Modeling Tools The Web site includes links to the cnet Web site and the modeling tools Web site. These packages can be used to analyze and experiment with protocol and network design issues. Each site includes downloadable software and background information. The instructor’s manual includes more information on loading and using the software and suggested student projects. This page intentionally left blank CONTENTS Web Site for Data and Computer Communications Preface xv 1 iv Chapter 0 Reader’s and Instructor’s Guide 0. Outline of the Book 2 0. 2 Roadmap 3 0. 3 Internet and Web Resources 5 0. 4 Standards 6 PART ONE OVERVIEW 9 Chapter 1 Data Communications, Data Networking, and the Internet 10 1. 1 Data Communications and Networking for Today’s Enterprise 12 1. 2 A Communications Model 16 1. 3 Data Communications 19 1. 4 Networks 22 1. 5 The Internet 25 1. 6 An Example Configuration 29 Chapter 2 Protocol Architecture, TCP/IP, and Internet-Based Applications 2. 1 The Need for a Protocol Architecture 33 2. 2 The TCP/IP Protocol Architecture 34 2. 3 The OSI Model 42 2. 4 Standardization within a Protocol Architecture 44 2. Traditional Internet-Based Applications 48 2. 6 Multimedia 48 2. 7 Recommended Reading and Web Sites 53 2. 8 Key Terms, Review Questions, and Problems 54 Appendix 2A The Trivial File Transfer Protocol 57 PART TWO DATA COMMUNICATIONS 62 Chapter 3 Data Transmission 65 3. 1 Concepts and Terminology 67 3. 2 Analog and Digital Data Transmission 78 3. 3 Transmission Impairments 86 3. 4 Channel Capacity 91 3. 5 Recommended Reading and Web Si te 96 3. 6 Key Terms, Review Questions, and Problems Appendix 3A Decibels and Signal Strength 99 Chapter 4 Transmission Media 102 4. Guided Transmission Media 104 4. 2 Wireless Transmission 117 4. 3 Wireless Propagation 125 32 96 vii viii CONTENTS 4. 4 4. 5 4. 6 Line-of-Sight Transmission 129 Recommended Reading and Web Sites 133 Key Terms, Review Questions, and Problems 134 Chapter 5 Signal Encoding Techniques 138 5. 1 Digital Data, Digital Signals 141 5. 2 Digital Data, Analog Signals 151 5. 3 Analog Data, Digital Signals 162 5. 4 Analog Data, Analog Signals 168 5. 5 Recommended Reading 175 5. 6 Key Terms, Review Questions, and Problems 175 Chapter 6 Digital Data Communication Techniques 180 6. Asynchronous and Synchronous Transmission 182 6. 2 Types of Errors 186 6. 3 Error Detection 186 6. 4 Error Correction 196 6. 5 Line Configurations 201 6. 6 Recommended Reading 203 6. 7 Key Terms, Review Questions, and Problems 204 Chapter 7 Data Link Control Protocols 207 7. 1 Flow Control 209 7. 2 Error Control 216 7. 3 High-Level Data Link Control (HDLC) 222 7. 4 Recommended Reading 228 7. 5 Key Terms, Review Questions, and Problems 229 Appendix 7A Performance Issues 232 Chapter 8 Multiplexing 239 8. 1 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 Reading and Web Sites 269 8. 7 Key Terms, Review Questions, and Problems 270 Chapter 9 Spread Spectrum 274 9. 1 The Concept of Spread Spectrum 276 9. 2 Frequency Hopping Spread Spectrum 277 9. 3 Direct Sequence Spread Spectrum 282 9. 4 Code-Division Multiple Access 287 9. 5 Recommended Reading and Web Site 290 9. 6 Key Terms, Review Questions, and Problems 291 CONTENTS ix PART THREE WIDE AREA NETWORKS 295 Chapter 10 Circuit Switching and Packet Switching 297 10. Switched Communications Networks 299 10. 2 Circuit Switching Networks 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 Frame Relay 319 10. 8 Recommended Reading and Web Sites 324 10. 9 Key Terms, Review Questions, and Problems 325 Chapter 11 Asynchronous Transfer Mode 328 11. 1 Protocol Architecture 329 11. 2 ATM Logical Connections 331 11. 3 ATM Cells 335 11. 4 Transmission of ATM Cells 340 11. 5 ATM Service Categories 345 11. 6 Recommended Reading and Web Sites 348 11. Key Terms, Review Questions, and Problems 349 Chapter 12 Routing in Switched Networks 351 12. 1 Routing in Packet-Switching Networks 352 12. 2 Examples: Routing in ARPANET 362 12. 3 Least-Cost Algorithms 367 12. 4 Recommended Reading 372 12. 5 Key Terms, Review Questions, and Problems 373 Chapter 13 Congestion Control in Data Networks 377 13. 1 Effects of Congestion 379 13. 2 Congestion Control 383 13. 3 Traffic Management 386 13. 4 Congestion Control in Packet-Switching Networks 13. 5 Frame Relay Congestion Control 388 13. 6 ATM Traff ic Management 394 13. 7 ATM-GFR Traffic Management 406 13. Recommended Reading 409 13. 9 Key Terms, Review Questions, and Problems 410 Chapter 14 Cellular Wireless Networks 413 14. 1 Principles of Cellular Networks 415 14. 2 First Generation Analog 427 14. 3 Second Generation CDMA 429 14. 4 Third Generation Systems 437 14. 5 Recommended Reading and Web Sites 440 14. 6 Key Terms, Review Questions, and Problems 441 387 x CONTENTS PART FOUR LOCAL AREA NETWORKS 444 Chapter 15 Local Area Network Overview 446 15. 1 Background 448 15. 2 Topologies and Transmission Media 451 15. 3 LAN Protocol Architecture 457 15. 4 Bridges 465 15. 5 Layer 2 and Layer 3 Switches 473 15. Recommended Reading and Web Site 478 15. 7 Key Terms, Review Questions, and Problems 479 Chapter 16 High-Speed LANs 482 16. 1 The Emergence of High-Speed LANs 483 16. 2 Ethernet 485 16. 3 Fibre Channel 500 16. 4 Recommended Reading and Web Sites 504 16. 5 Key Terms, Review Questions, and Problems 506 Appendix 16A Digital Sig nal Encoding for LANs 508 Appendix 16B Performance Issues 514 Appendix 16C Scrambling 518 Chapter 17 Wireless LANs 522 17. 1 Overview 523 17. 2 Wireless LAN Technology 528 17. 3 IEEE 802. 11 Architecture and Services 531 17. 4 IEEE 802. 11 Medium Access Control 535 17. 5 IEEE 802. 1Physical Layer 543 17. 6 IEEE 802. 11 Security Considerations 549 Recommended Reading and Web Sites 550 17. 7 17. 8 Key Terms, Review Questions, and Problems 551 PART FIVE INTERNET AND TRANSPORT PROTOCOLS Chapter 18 Internetwork Protocols 556 18. 1 Basic Protocol Functions 558 18. 2 Principles of Internetworking 566 18. 3 Internet Protocol Operation 569 18. 4 Internet Protocol 576 18. 5 IPv6 586 18. 6 Virtual Private Networks and IP Security 596 18. 7 Recommended Reading and Web Sites 599 18. 8 Key Terms, Review Questions, and Problems 600 Chapter 19 Internetwork Operation 603 19. 1 Multicasting 605 19. Routing Protocols 614 19. 3 Integrated Services Architecture 625 19. 4 Differentiated Services 636 554 CONTENTS xi 19. 5 19. 6 19. 7 19. 8 Service Level Agreements 645 IP Performance Metrics 646 Recommended Reading and Web Sites 649 Key Terms, Review Questions, and Problems 651 657 Chapter 20 Transport Protocols 655 20. 1 Connection-Oriented Transport Protocol Mechanisms 20. 2 TCP 674 20. 3 TCP Congestion Control 683 20. 4 UDP 693 20. 5 Recommended Reading and Web 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. INTERNET APPLICATIONS 699 Network Security 701 Security Requirements and Attacks 703 Confidentiality with Conventional Encryption 705 Message Authentication and Hash Functions 713 Public-Key Encryption and Digital Signatures 720 Secure Socket Layer and Transport Layer Security 727 IPv4 and IPv6 Security 732 Wi-Fi Protected Access 737 Recommended Reading and Web Sites 739 Key Terms, Review Questions, and Problems 740 Chapter 22 Internet Applications—Electronic Mail and Network Managemen t 22. 1 Electronic Mail: SMTP and MIME 745 22. 2 Network Management: SNMP 760 22. 3 Recommended Reading and Web Sites 770 22. Key Terms, Review Questions, and Problems 771 743 Chapter 23 Internet Applications—Internet Directory Service and World Wide Web 23. 1 Internet 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 Internet Applications—Multimedia 799 24. 1 Audio and Video Compression 800 24. 2 Real-Time Traffic 808 24. 3 Voice Over IP and Multimedia Support—SIP 811 24. 4 Real-Time Transport 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 Appendix A Fourier Analysis 835 A. 1 Fourier Series Representation of Periodic Signals 836 A. 2 Fourier Transform Representation of Aperiodic Signals 837 A. 3 Recommended Reading 840 Appendix B Projects for Teaching Dat a and Computer Communications B. 1 Practical Exercises 842 B. 2 Sockets Projects 843 B. 3 Ethereal Projects 843 B. 4 Simulation and Modeling Projects 844 B. 5 Performance Modeling 844 B. 6 Research Projects 845 B. 7 Reading/Report Assignments 845 B. 8 Writing Assignments 845 B. 9 Discussion Topics 846 References Index 858 ONLINE APPENDICES WilliamStallings. om/DCC Appendix C Sockets: A Programmer’s Introduction C. 1 Versions of Sockets C. 2 Sockets, Socket Descriptors, Ports, and Connections The Client/Server Model of Communication C. 3 C. 4 Sockets Elements C. 5 Stream and Datagram Sockets C. 6 Run-Time Program Control C. 7 Remote Execution of a Windows Console Application Appendix D Standards Organizations D. 1 The Importance of Standards D. 2 Standards and Regulation D. 3 Standards-Setting Organizations Appendix E Appendix F The International Reference Alphabet Proof of the Sampling Theorem 847 841 Appendix G Physical-Layer Interfacing G. 1 V. 24/EIA-232-F G. ISDN Physical Interface Appendix H The OSI Model H. 1 The Model H. 2 The OSI Layers CONTENTS xiii 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 TCP/IP Checksum K. 1 Ones-Complement Addition K. 2 Use in TCP and IP Appendix L TCP/IP Example Appendix M Uniform Resource Locators (URLs) and Uniform Resource Identifiers (URIs) M. 1 Uniform Resource Locator M. 2 Uniform Resource Identifier M. 3 To Learn More Appendix N Glossary Augmented Backus-Naur FormThis page intentionally left blank PREFACE Begin at the beginning and go on till you come to the end; then stop. —Alice in Wonderland, Lewis Carroll OBJECTIVES This book attempts to provide a unified overview of the broad field of data and computer communications. The organization of the book reflects an attempt to break this massive subject into comprehensible parts and to build, piece by piec e, a survey of the state of the art. The book emphasizes basic principles and topics of fundamental importance concerning the technology and architecture of this field and provides a detailed discussion of leading-edge topics.The following basic themes serve to unify the discussion: †¢ Principles: Although the scope of this book is broad, there are a number of basic principles that appear repeatedly as themes and that unify this field. Examples are multiplexing, flow control, and error control. The book highlights these principles and contrasts their application in specific areas of technology. †¢ Design approaches: The book examines alternative approaches to meeting specific communication requirements. †¢ Standards: Standards have come to assume an increasingly important, indeed dominant, role in this field.An understanding of the current status and future direction of technology requires a comprehensive discussion of the related standards. INTENDED AUDIENCE The book is intended for both an academic and a professional audience. For the professional interested in this field, the book serves as a basic reference volume and is suitable for self-study. As a textbook, it can be used for a one-semester or two-semester course. It covers the material in Networking (NET), a core area in the Information Technology body of knowledge, which is part of the Draft ACM/IEEE/AIS Computing Curricula 2005.The book also covers the material in Computer Networks (CE-NWK), a core area in Computer Engineering 2004 Curriculum Guidelines from the ACM/IEEE Joint Task Force on Computing Curricula. PLAN OF THE TEXT The book is divided into six parts (see Chapter 0): †¢ Overview †¢ Data Communications †¢ Wide Area Networks xv xvi PREFACE †¢ Local Area Networks †¢ Internet and Transport Protocols †¢ Internet Applications In addition, the book includes an extensive glossary, a list of frequently used acronyms, and a bibliography. Each chapter inc ludes problems and suggestions for further reading.The chapters and parts of the book are sufficiently modular to provide a great deal of flexibility in the design of courses. See Chapter 0 for a number of detailed suggestions for both top-down and bottom-up course strategies. INSTRUCTIONAL SUPPORT MATERIALS To support instructors, the following materials are provided: †¢ Solutions Manual: Solutions to all end-of-chapter Review Questions and Problems. †¢ PowerPoint Slides: A set of slides covering all chapters, suitable for use in lecturing. †¢ PDF files: Reproductions of all figures and tables from the book. Projects Manual: Suggested project assignments for all of the project categories listed below. Instructors may contact their Pearson Education or Prentice Hall representative for access to these materials. In addition, the book’s Web site supports instructors with: †¢ Links to Webs sites for other courses being taught using this book †¢ Sign up i nformation for an Internet mailing list for instructors INTERNET SERVICES FOR INSTRUCTORS AND STUDENTS There is a Web site for this book that provides support for students and instructors.The site includes links to other relevant sites, transparency masters of figures in the book, and sign-up information for the book’s Internet mailing list. The Web page is at WilliamStallings. com/DCC/DCC8e. html; see the section, Web Site for Data and Computer Communications, preceding the Table of Contents, for more information. An Internet mailing list has been set up so that instructors using this book can exchange information, suggestions, and questions with each other and with the author. As soon as typos or other errors are discovered, an errata list for this book will be available at WilliamStallings. om. PROJECTS AND OTHER STUDENT EXERCISES For many instructors, an important component of a data communications or networking course is a project or set of projects by which the student gets hands-on experience to reinforce concepts from the text. This book provides an unparalleled degree of support for including a projects component in the course. The instructor’s supplement not only includes guidance on how to assign and structure the projects but also includes a set of User’s PREFACE xvii Manuals for various project types plus specific assignments, all written especially for this book.Instructors can assign work in the following areas: †¢ Practical exercises: Using network commands, the student gains experience in network connectivity. †¢ Sockets programming projects: The book is supported by a detailed description of Sockets available at the book’s Web site. The Instructors supplement includes a set of programming projects. Sockets programming is an â€Å"easy† topic and one that can result in very satisfying hands-on projects for students. †¢ Ethereal projects: Ethereal is a protocol analyzer that enables students to study the behavior of protocols. Simulation projects: The student can use the simulation package cnet to analyze network behavior. †¢ Performance modeling projects: Two performance modeling techniques are provided a tools package and OPNET. †¢ Research projects: The instructor’s supplement includes a list of suggested research projects that would involve Web and literature searches. †¢ Reading/report assignments: The instructor’s supplement includes a list of papers that can be assigned for reading and writing a report, plus suggested assignment wording. Writing assignments: The instructor’s supplement includes a list of writing assignments to facilitate learning the material. †¢ Discussion topics: These topics can be used in a classroom, chat room, or message board environment to explore certain areas in greater depth and to foster student collaboration. This diverse set of projects and other student exercises enables the instructor to use t he book as one component in a rich and varied learning experience and to tailor a course plan to meet the specific needs of the instructor and students. See Appendix B for details.WHAT’S NEW IN THE EIGHTH EDITION This eighth edition is seeing the light of day less than four years after the publication of the seventh edition. During that time, the pace of change in this field continues unabated. In this new edition, I try to capture these changes while maintaining a broad and comprehensive coverage of the entire 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 result is that, in many places, the narrative has been clarified and tightened, and illustrations have been improved.Also, a number of new â€Å"field-tested† problems have been added. Beyond these refinements to improve pedagogy and user friendliness, there have been major substantive changes throughout the book . Every chapter has been revised, new chapters have been added, and the overall organization of the book has changed. Highlights include: †¢ Updated coverage of Gigabit Ethernet and 10-Gbps Ethernet: New details of these standards are provided. †¢ Updated coverage of WiFi/IEEE 802. 11 wireless LANs: IEEE 802. 11 and the related WiFi specifications have continued to evolve. viii PREFACE †¢ New coverage of IP performance metrics and service level agreements (SLAs): These aspects of Quality of Service (QoS) and performance monitoring are increasingly important. †¢ Address Resolution Protocol (ARP): This important protocol is now covered. †¢ New coverage of TCP Tahoe, Reno, and NewReno: These congestion control algorithms are now common in most commercial implementations. †¢ Expanded coverage of security: Chapter 21 is more detailed; other chapters provide overview of security for the relevant topic.Among the new topics are Wi-Fi Protected Access (WPA) and the secure hash algorithm SHA-512. †¢ Domain Name System (DNS): This important scheme is now covered. †¢ New coverage of multimedia: Introductory section in Chapter 2; detailed coverage in Chapter 24. Topics covered include video compression, SIP, and RTP. †¢ Online appendices: Fourteen online appendices provide additional detail on important topics in the text, including Sockets programming, queuing models, the Internet checksum, a detailed example of TCP/IP operation, and the BNF grammar.In addition, throughout the book, virtually every topic has been updated to reflect the developments in standards and technology that have occurred since the publication of the seventh edition. ACKNOWLEDGMENTS This new edition has benefited from review by a number of people, who gave generously of their time and expertise. The following people reviewed all or a large part of the manuscript: Xin Liu- (UC, Davis), Jorge Cobb, Andras Farago, Dr. Prasant Mohapatra (UC Davis), Dr. Jingxi an Wu (Sonoma State University), G. R.Dattareya (UT Dallas), Guanling Chen (Umass, Lowell), Bob Roohaprvar (Cal State East Bay), Ahmed Banafa (Cal State East Bay), Ching-Chen Lee (CSU Hayward), and Daji Qaio (Iowa State). Thanks also to the many people who provided detailed technical reviews of a single chapter: Dave Tweed, Bruce Lane, Denis McMahon, Charles Freund, Paul Hoadley, Stephen Ma, Sandeep Subramaniam, Dragan Cvetkovic, Fernando Gont, Neil Giles, Rajesh Thundil, and Rick Jones. In addition, Larry Owens of California State University and Katia Obraczka of the University of Southern California provided some homework problems.Thanks also to the following contributors. Zornitza Prodanoff of the University of North Florida prepared the appendix on Sockets programming. Michael Harris of the University of South Florida is responsible for the Ethereal exercises and user’s guide. Lawrie Brown of the Australian Defence Force Academy of the University of New South Wales produc ed the PPT lecture slides. Finally, I would like to thank the many people responsible for the publication of the book, all of whom did their usual excellent job.This includes the staff at Prentice Hall, particularly my editor Tracy Dunkelberger, her assistants Christianna Lee and Carole Snyder, and production manager Rose Kernan. Also, Patricia M. Daly did the copy editing. CHAPTER READER’S AND INSTRUCTOR’S GUIDE 0. 1 0. 2 0. 3 0. 4 Outline of the Book Roadmap Internet and Web Resources Standards 0 1 2 CHAPTER 0 / READER’S AND INSTRUCTOR’S GUIDE â€Å"In the meanwhile, then,† demanded Li-loe, â€Å"relate to me the story to which reference has been made, thereby proving the truth of your assertion, and at the same time affording n entertainment of a somewhat exceptional kind. † â€Å"The shadows lengthen,† replied Kai Lung, â€Å"but as the narrative in question is of an inconspicuous span I will raise no barrier against your flatter ing request, especially as it indicates an awakening taste hitherto unexpected. † —Kai Lung’s Golden Hours, Earnest Bramah This book, with its accompanying Web site, covers a lot of material. Here we give the reader some basic background information. 0. 1 OUTLINE OF THE BOOK The book is organized into five parts: Part One. Overview: Provides an introduction to the range of topics covered in the book.This part includes a general overview of data communications and networking and a discussion of protocols, OSI, and the TCP/IP protocol suite. Part Two. Data Communications: Concerned primarily with the exchange of data between two directly connected devices. Within this restricted scope, the key aspects of transmission, interfacing, link control, and multiplexing are examined. Part Three. Wide Area Networks: Examines the internal mechanisms and user-network interfaces that have been developed to support voice, data, and multimedia communications over long-distance ne tworks.The traditional technologies of packet switching and circuit switching are examined, as well as the more recent ATM and wireless WANs. Separate chapters are devoted to routing and congestion control issues that are relevant both to switched data networks and to the Internet. Part Four. Local Area Networks: Explores the technologies and architectures that have been developed for networking over shorter distances. The transmission media, topologies, and medium access control protocols that are the key ingredients of a LAN design are explored and specific standardized LAN systems examined.Part Five. Networking Protocols: Explores both the architectural principles and the mechanisms required for the exchange of data among computers, workstations, servers, and other data processing devices. Much of the material in this part relates to the TCP/IP protocol suite. Part Six. Internet Applications: Looks at a range of applications that operate over the Internet. A more detailed, chapte r-by-chapter summary of each part appears at the beginning of that part. 0. 2 / ROADMAP 3 0. 2 ROADMAP Course EmphasisThe material in this book is organized into four broad categories: data transmission and communication; communications networks; network protocols; and applications and security. The chapters and parts of the book are sufficiently modular to provide a great deal of flexibility in the design of courses. The following are suggestions for three different course designs: †¢ Fundamentals of Data Communications: Parts One (overview) and Two (data communications) and Chapters 10 and 11 (circuit switching, packet switching, and ATM). Communications Networks: If the student has a basic background in data communications, then this course could cover Parts One (overview), Three (WAN), and Four (LAN). †¢ Computer Networks: If the student has a basic background in data communications, then this course could cover Part One (overview), Chapters 6 and 7 (data communication techniques and data link control), Part Five (protocols), and part or all of Part Six (applications). In addition, a more streamlined course that covers the entire book is possible by eliminating certain chapters that are not essential on a first reading.Chapters that could be optional are Chapters 3 (data transmission) and 4 (transmission media), if the student has a basic understanding of these topics; Chapter 8 (multiplexing); Chapter 9 (spread spectrum); Chapters 12 through 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. After reading Part One, the other parts can be read in a number of possible sequences.Figure 0. 1a shows the bottom-up approach provided by reading the book from front to back. With this approach, each part builds on the material in the previous part, so that it is always clear how a given layer of functionality is supporte d from below. There is more material than can be comfortably covered in a single semester, but the book’s organization makes it easy to eliminate some chapters and maintain the bottom-up sequence. Figure 0. 1b suggests one approach to a survey course.Some readers, and some instructors, are more comfortable with a top-down approach. After the background material (Part One), the reader continues at the application level and works down through the protocol layers. This has the advantage of immediately focusing on the most visible part of the material, the applications, and then seeing, progressively, how each layer is supported by the next layer down. Figure 0. 1c is an example of a comprehensive treatment and Figure 0. 1d is an example of a survey treatment. 4 CHAPTER 0 / READER’S AND INSTRUCTOR’S GUIDEPart One Overview Part Two Data Communications Part Three Wide Area Networks Part Four Local Area Networks Part Five Internet and Transport Protocols Part Six Inter net Applications (a) A bottom-up approach Part One Overview Chapter 18 The Internet Protocol Part Six Internet Applications Part Five TCP/IP Part Three WANs Part Four LANs Part Two Data Communications (c) A top-down approach (d) Another top-down approach (b) Another 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) Figure 0. 1 Suggested Reading Orders Finally, it is possible to select chapters to reflect specific teaching objectives by not sticking to a strict chapter ordering. We give two examples used in courses taught with the seventh edition.One course used the sequence Part One (Overview); Chapter 3 (Data Transmission); Chapter 6 (Digital Data Communications Techniques); Chapter 7 (Data Link Control); Chapter 15 (LAN Overview); Cha pter 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 used 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 / INTERNET 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 INTERNET AND WEB RESOURCES There are a number of resources available on the Internet and the Web to support this book and to help one keep 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 beginning of this book for a detailed description of that site. As soo n as any typos or other errors are discovered, an errata list for this book will be available at the Web site. Please report any errors that you spot. Errata sheets for my other books are at WilliamStallings. com. I also maintain the Computer Science Student Resource Site, at WilliamStallings. com/StudentSupport. html. The purpose of this site is to provide documents, information, and links for computer science students and professionals.Links and documents are organized into four categories: †¢ Math: Includes a basic math refresher, a queuing analysis primer, a number system primer, and links to numerous math sites †¢ How-to: Advice and guidance for solving homework problems, writing technical reports, and preparing technical presentations †¢ Research resources: Links to important collections of papers, technical reports, and bibliographies †¢ Miscellaneous: A variety of useful documents and links Other Web Sites There are numerous Web sites that provide informa tion related to the topics of this book. In subsequent chapters, pointers to specific Web sites can be found in the Recommended Reading and Web Sites section. Because the addresses for Web sites tend to change frequently, I have not included URLs in the book. For all of the Web sites listed in the book, the appropriate link can be found at this book’s Web site. Other links not mentioned in this book will be added to the Web site over time.The following are Web sites of general interest related to data and computer communications: †¢ Network World: Information and links to resources about data communications and networking. †¢ IETF: Maintains archives that relate to the Internet and IETF activities. Includes keyword-indexed library of RFCs and draft documents as well as many other documents related to the Internet and related protocols. 6 CHAPTER 0 / READER’S AND INSTRUCTOR’S GUIDE †¢ Vendors: Links to thousands of hardware and software vendors who currently have Web sites, as well as a list of thousands of computer and networking companies in a phone directory. †¢ IEEE Communications Society: Good way to keep up on conferences, publications, and so on. ACM Special Interest Group on Communications (SIGCOMM): Good way to keep up on conferences, publications, and so on. †¢ International Telecommunications Union: Contains a listing of ITU-T recommendations, plus information on obtaining ITU-T documents in hard copy or on DVD. †¢ International Organization for Standardization: Contains a listing of ISO standards, plus information on obtaining ISO documents in hard copy or on CD-ROM. †¢ CommWeb: Links to vendors, tutorials, and other useful information. †¢ CommsDesign: Lot of useful articles, tutorials, and product information. A bit hard to navigate, but worthwhile. USENET Newsgroups A number of USENET newsgroups are devoted to some aspect of data communications, networks, and protocols.As with virtually all USENET groups, there is a high noise-to-signal ratio, but it is worth experimenting to see if any meet your needs. The most relevant are as follows: †¢ comp. dcom. lans, comp. dcom. lans. misc: General discussions of LANs †¢ comp. dcom. lans. ethernet: Covers Ethernet, Ethernet-like systems, and the IEEE 802. 3 CSMA/CD standards †¢ comp. std. wireless: General discussion of wireless networks, including wireless LANs †¢ comp. security. misc: Computer security and encryption †¢ comp. dcom. cell-relay: Covers ATM and ATM LANs †¢ comp. dcom. frame-relay: Covers frame relay networks †¢ comp. dcom. net-management: Discussion of network management applications, protocols, and standards †¢ comp. rotocols. tcp-ip: The TCP/IP protocol suite 0. 4 STANDARDS It has long been accepted in the telecommunications industry that standards are required to govern the physical, electrical, and procedural characteristics of communication equipment. In the past, this view has not been embraced by the computer industry. Whereas communication equipment vendors recognize that their 0. 4 / STANDARDS 7 equipment will generally interface to and communicate with other vendors’ equipment, computer vendors have traditionally attempted to monopolize their customers. The proliferation of computers and distributed processing has made that an untenable position.Computers from different vendors must communicate with each other and, with the ongoing evolution of protocol standards, customers will no longer accept special-purpose protocol conversion software development. The result is that standards now permeate all of the areas of technology discussed in this book. There are a number of advantages and disadvantages to the standards-making process. We list here the most striking ones. The principal advantages of standards are as follows: †¢ A standard assures that there will be a large market for a particular piece of equipment or software. Thi s encourages mass production and, in some cases, the use of large-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 selection and use. The principal disadvantages are as follows: †¢ A standard tends to freeze the technology. By the time a standard is developed, subjected to review and compromise, and promulgated, more efficient techniques are possible. †¢ There are multiple standards for the same thing. This is not a disadvantage of standards per se, but of the current way things are done. Fortunately, in recent years the various standards-making organizations have begun to cooperate more closely. Nevertheless, there are still areas 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 commun ications. Various organizations have been involved in the development or promotion of these standards. The following are the most important (in the current context) of these organizations: †¢ Internet Society: The Internet SOCiety (ISOC) is a professional membership society with more than 150 organizational and 6000 individual members in over 100 countries. It provides leadership in addressing issues that confront 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 Internet Architecture Board (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 Committee develops local area network standards and metropolitan area network standards. The most widely used standards are for the Ethernet family, wireless LAN, bridging, a nd virtual bridged LANs. An individual working group provides the focus for each area. 8 CHAPTER 0 / READER’S AND INSTRUCTOR’S GUIDE †¢ ITU-T: The International Telecommunication Union (ITU) is an international organization within the United Nations System where governments and the private sector coordinate global telecom networks and services.The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors of the ITU. ITU-T’s mission is the production of standards covering all fields of telecommunications. †¢ ATM Forum: The ATM Forum is an international nonprofit organization formed with the objective of accelerating the use of ATM (asynchronous transfer mode) products and services through a rapid convergence of interoperability specifications. In addition, the Forum promotes industry cooperation and awareness. †¢ ISO: The International Organization for Standardization (ISO)1 is a worldwide federation of national standards bod ies 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 exchange of goods and services, and to developing cooperation in the spheres of intellectual, scientific, technological, and economic activity. ISO’s 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, meaning equal. PART ONE Overview The purpose of Part One is to provide a background and context for the remainder of this book. The broad range of topics that are encompassed in the field of data and computer communications is introduced, and the fundamental concepts of protocols and protocol architectures are examined.ROAD MAP FOR PART ONE Chapter 1 Data Communicati ons, Data Networks, and The Internet Chapter 1 provides an overview of Parts Two through Four of the book, giving the â€Å"big picture. † 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 preview of the first three 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 immediately 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 Interconnection (OSI) model and TCP/IP. Although the OSI model is often used as the framework for discourse in this area, it is the TCP/IP protocol suite that is the basis for most commercially available interoperable products and that is the focus of Parts Five and Six of this book. 9 CHAPTER DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET 1. 1 1. 2 1. 3 1. 4 1. 5 1. 6 Data Communications and Networking for Today’s Enterprise A Communications Model Data Communications Networks The Internet An Example Configuration 1 10 The fundamental problem of communication is that of reproducing at one point either exactly or approximately a message selected at another point. The Mathematical Theory of Communication, Claude Shannon KEY POINTS †¢ The scope of this book is broad, covering three general areas: data communications, networking, and protocols; the first two are introduced in this chapter. Data communications deals with the transmission of signals in a reliable and efficient manner. Topics covered include signal transmission, transmission media, signal encoding, interfacing, data link control, and multiplexing. Networking deals with the technology and architecture of the communications networks used to interconnect communicating devices. This field is generally divided into the topics of local area networks (LANs) and wide area networks (WANs). †¢ †¢The 1970s and 1980s saw a merger of the fields of computer science and data communications that profoundly changed the technology, products, and companies of the now combined computer-communications industry. The computercommunications revolution has produced several remarkable facts: †¢ There is no fundamental difference between data processing (computers) and data communications (transmission and switching equipment). †¢ There are no fundamental differences among data, voice, and video communications. †¢ The distinction among single-processor computer, multiprocessor computer, local network, metropolitan network, and long-haul network has blurred.One effect of these trends has been a growing overlap of the computer and communications industries, from component fabrication to system integration. Another resul t 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 driving toward integrated public systems that make virtually all data and information sources around the world easily 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 break this massive subject into comprehensible parts and to build, piece by piece, a survey of the state of the art.This introductory chapter begins with a general model of communications. Then a brief discussion introduces each of the Parts Two through Four of this book. Chapter 2 provides an overview to Parts Five and Six 11 12 CHAPTER 1 / DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET 1. 1 DATA COMMUNICATIONS AND NETWORKING FOR TODAY’S ENTERPRISE Effective and efficient data communication and networking facilitie s are vital to any enterprise. In this section, we first look at trends that are increasing the challenge for the business manager in planning and managing such facilities. Then we look specifically at the requirement for ever-greater transmission speeds and network capacity. TrendsThree different forces have consistently driven the architecture and evolution of data communications and networking facilities: traffic growth, development of new services, and advances in technology. Communication traffic, both local (within a building or building complex) and long distance, both voice and data, has been growing at a high and steady rate for decades. The increasing emphasis on office automation, remote access, online transactions, and other productivity measures means that this trend is likely to continue. Thus, managers are constantly struggling to maximize capacity and minimize transmission costs. As businesses rely more and more on information technology, the range of services expand s. This increases the demand for high-capacity networking and transmission facilities.In turn, the continuing growth in high-speed network offerings with the continuing drop in prices encourages the expansion of services. Thus, growth in services and growth in traffic capacity go hand in hand. Figure 1. 1 gives some examples of information-based services and the data rates needed to support them [ELSA02]. Finally, trends in technology enable the provision of increasing traffic capacity and the support of a wide range of services. Four technology trends are particularly notable: 1. The trend toward faster and cheaper, both in computing and communications, continues. In terms of computing, this means more powerful computers and clusters of computers capable of supporting more demanding applications, such as multimedia applications.In terms of communications, the increasing use of optical fiber has brought transmission prices down and greatly increased capacity. For example, for long-d istance telecommunication and data network links, recent offerings of dense wavelength division multiplexing (DWDM) enable capacities of many terabits per second. For local area networks (LANs) many enterprises now have Gigabit Ethernet backbone networks and some are beginning to deploy 10-Gbps Ethernet. 2. Both voice-oriented telecommunications networks, such as the public switched telephone network (PSTN), and data networks, including the Internet, are more â€Å"intelligent† than ever. Two areas of intelligence are noteworthy.First, today’s networks can offer differing levels of quality of service (QoS), which include specifications for maximum delay, minimum throughput, and so on. Second, today’s networks provide a variety of customizable services in the areas of network management and security. 1. 1 / DATA COMMUNICATIONS AND NETWORKING FOR TODAY’S ENTERPRISE Speed (kbps) Transaction processing Messaging/text apps Voice Location services Still image t ransfers Internet/VPN access Database access Enhanced Web surfing Low-quality video Hifi audio Large file transfer Moderate video Interactive entertainment High-quality video Performance: Poor Adequate Good 9. 6 14. 4 28 64 144 384 2000 13 VPN: virtual private network Figure 1. 1 Services versus Throughput Rates 3.The Internet, the Web, and associated applications have emerged as dominant features of both the business and personal 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 isolate their proprietary information free from unwanted access. 4. There has been a trend toward ever-increasing mobility for decades, liberating workers from the confines 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.T he 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 isolated facility internal to an enterprise; an extranet extends a company’s intranet out onto the Internet to allow selected customers, suppliers, and mobile workers to access the company’s private data and applications. 14 CHAPTER 1 / DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET Data Transmission and Network Capacity RequirementsMomentous changes in the way organizations do business and process information have been driven by changes in networking technology and at the same time have driven those changes. It is hard to separate chicken and egg in this field. Similarly, the use of the Internet by both businesses and individuals reflects this cycli c dependency: the availability of new image-based services on the Internet (i. e. , the Web) has resulted in an increase in the total number of users and the traffic volume generated by each user. This, in turn, has resulted in a need to increase the speed and efficiency of the Internet. On the other hand, it is only such increased speed that makes the use of Web-based applications palatable 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 forced the pace of networking development. Then we look at business WAN requirements. Finally we offer a few words about the effect of changes in commercial electronics on network requirements. The Emergence of High-Speed LANs Personal computers and microcomputer workstations began to achieve widespread acceptance in business computing in the early 1980s and have now achieved virtu ally the status of the telephone: an essential tool for office workers.Until relatively recently, office LANs provided basic connectivity services—connecting personal computers and terminals to mainframes and midrange systems that ran corporate applications, and providing workgroup connectivity at the departmental or divisional level. In both cases, traffic patterns were relatively light, with an emphasis on file transfer and electronic mail. The LANs that were available for this type of workload, primarily Ethernet and token ring, are well suited to this environment. In the 1990s, two significant trends altered the role of the personal computer and therefore the requirements on the LAN: 1. The speed and computing power of personal computers continued to enjoy explosive growth. These more powerful platforms support graphics-intensive applications and ever more elaborate graphical user interfaces to the operating system. . MIS (management information systems) organizations hav e recognized the LAN as a viable and essential computing platform, resulting in the focus on network computing. This trend began with client/server computing, which has become a dominant architecture in the business environment and the more recent Webfocused intranet trend. Both of these approaches involve the 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 acceptable delay on data transfers.The earlier generation of 10-Mbps Ethernets and 16-Mbps token rings was simply not up to the job of supporting these requirements. The following are examples of requirements that call for higher-speed LANs: †¢ Centralized server farms: In many applications, there is a need for user, or client, systems to be able to draw huge amounts of data from multiple centralized servers, called server farms. An example is a color publishing operation, in 1. 1 / DATA COMMUNICATIONS AND NETWORKING FOR TODAY’S ENTERPRISE 15 which servers typically contain tens of gigabytes of image data that must be downloaded to imaging workstations. As the performance of the servers themselves has increased, the bottleneck has shifted to the network. Power workgroups: These groups typically 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. Corporate Wide Area Networking Needs As recently as the ear ly 1990s, there was an emphasis in many organizations on a centralized data processing model.In a typical environment, there might be significant computing facilities at a few regional offices, consisting of mainframes or well-equipped midrange systems. These centralized facilities could handle most corporate applications, including basic finance, accounting, and personnel 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 personal 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 funda mentally restructured the organizational data processing environment. There is now much more reliance on personal computers, workstations, and servers and much less use of centralized mainframe and midrange systems. Furthermore, the virtually universal deployment of graphical user interfaces to the desktop 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 mouse can trigger huge volumes of data, traffic patterns have become more unpredictable while the average 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 accepted that in the typical business environment, about 80% of the traffic remains local and about 20% traverses wide area links. But this rule no longer applies to most companies, with a greater percentage of the traffic going into the WAN environment [COHE 96]. This traffic flow shift places a greater burden 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 creation of high-speed 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 versatile disks (DVDs) and digital still cameras. With the capacious DVD, the electronics industry has at last 16 CHAPTER 1 / DATA COMMUNICATIONS, DATA NETWORKS, AND THE INTERNET found an acceptable replacement for the analog 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 di gital age. It delivers movies with picture quality that outshines laser disks, and it can be randomly accessed like audio CDs, which DVD machines can also play. Vast volumes of data can be crammed onto the disk, currently seven times as much as a CDROM. With DVD’s 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 incorporated 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 MODEL This section introduces a simple model of communications, illustrated by the block diagram in Figure 1. 2a. The fundamental purpose of a communications system is the exchange of data between two parties. Figure 1. 2b presents one particular example, which is communication between a workstation and a server over a public telephone network. Another example is the exchange of voice signals between two telephones over the same network. The key elements of the model are as follows: †¢ Source.This device generates the data to be transmitted; examples are telephones and personal computers. Source system Destination system Source Transmitter Transmission System (a) General block diagram Receiver Destination Workstation Modem Public telephone network (b) Example Modem Server Figure 1. 2 Simplified 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 transmitter 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 system: 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 incoming data from the receiver.This simple 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 somewhat arbitrary: Elements could be added; items on the list could be merged; and some items repr esent several tasks that are performed at different â€Å"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 transmission facilities that are typically shared among a number of communicating devices.Various techniques (referred to as multiplexing) are used to allocate the total capacity of a transmission medium among a number of users. Congestion control techniques may be required 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 required 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) interpretable 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 form of synchronization Table 1. 1 Communications Tasks Transmission system utilization Interfacing Signal generation Synchronization Exchange management Error detection and correction Flow control Addressing Routing Recovery 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 arrive and when it ends. It must also know the duration of each signal element.Beyond the basic matter of deciding on the nature and timing 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 exchanged 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 party must dial the number of the other, causing signals to be generated that result in the ringing of the called phone. The called party completes a connection by lifting the receiver. For data processing devices, more will be needed 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

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Satire and Political Life in Canada - Essay Example Politics is a practise that has been practised for a long time in Canada, though it has incessantly evolved. Satire has been in practise for even longer, dating back centuries. However, the relationship between the two is more recent as the ‘freedom of expression’ has continually become more adhered to by the authorities. It can also be said that the accessibility of effective communication channels to the people has also made the relationship even stronger. Satire and politics have hence of late formed a bond that has got many understanding one through the other (Fisher, 2013). Perhaps the most famous Canadian of 2013, Toronto Mayor Mr. Rob Ford, brought out a new and more advanced context of satire in politics. It is fitting to use this example since many people can identify with it, and consequently understand the extent to which satire and politics are presently entangled. After the mayor admitted to using drugs, comedians from all across the country and in specific parts of the world were prompt to pick it up and bend the admission to their favour. In fact, so many picked it up that some audience started viewing Ford as a victim of mockery. It got to a point where people taking drugs got sympathy from a newly formed population with the mind-set that taking is a sickness rather than a crime (CBCNews, 2013). However, a majority of the people found the ‘mockery’ as hilarious and in a way understood politics through this perspective. It is a further emphasis on the burly bond between satire and politics in the current Canadian society. This is an example that most without the knowledge of the bond can use to realize what it is all about. However, it is appropriate to state that there are many more angles that the same relationship can be understood. The fact that views on political matters can be expressed freely means that the ‘limits’ of political satire are limitless. Some of

How Far External Auditors are Committed to Code of Conduct in Saudi Thesis

How Far External Auditors are Committed to Code of Conduct in Saudi Arabia, and the Ways which Encourage them to Follow Professional Behaviour - Thesis Example Scope of the study: The study will cover a wide area of auditors’ ethics. This research will involve a detailed study of the accounting and external auditing standards of Saudi Arabia. The code of conduct of the country’s accounting standards will also be studied. Study about the external auditor’s commitment to such code of ethics is the major area of study. Finally, this research will suggest a set of important recommendations that might help to improve the professional behaviour of external auditors in Saudi Arabia, and encourage them to commit code of conduct. World over very few studies were conducted in the field of personal values and accounting ethics. One among such few studies is ‘Effects of personal values on auditors’ ethical decisions.’ The study was mainly conducted among practicing auditors. The study however revealed that personal values and preferences do not influence the ethical decisions in accounting. It explains that other than personal values it is contextual factors that promote unethical behavior in accounting. Another study on ethics and auditing is, ‘Testing the bases of ethical decision-making: a study of the New Zealand auditing profession.’ The study showed that most of the auditors did not avoid a difficult situation. The study also showed that demographic factors like age, gender, job profile, etc. did not influence a person’s ethical behavior in their profession. There was another study that was done to find the relationship between cultural influences on professional ju dgment and auditor client-conflict resolution. The study was focused on auditing professionals of Australia, China, Malaysia and India. There was clear difference witnessed in the behavior of Australian auditors compared to that of the Asian counterparts. This is a slightly different view than the study, ‘Effects of personal values on auditors’ ethical decisions.’ â€Å"New corporate governance rules

Alternative Solutions to Change of Google Corporation Essay

Alternative Solutions to Change of Google Corporation - Essay Example In 2004 a company that was already millions of dollars in revenue decided to go public to spur the company long-term growth potential. The Google IPO on April 30, 2004, raised $2.7 billion dollars (Monica, 2004). Today Google is the market leader in search engine industry with a 50% market share and also controls 70% of all internet based advertising revenue. During the 3rd quarter of 2008 Google generated $5.54 billion dollars in revenues (Google, 2008). Â  Google handle half the traffic over the internet today. Its information system has access to nearly 25 billion web pages. The information technology (IT) infrastructure the company utilizes is composed of 450,000 inexpensive servers spread around 25 nations worldwide. The system is very cost effective because not only is the company achieving cost savings in hardware, the software utilized to program the servers is a customized version of the freeware Linux operating system. Google’s superior MIS design provides the company a 3 to 1 cost advantage in comparison with its competitor in order to achieve a comparable computing power. There are three key software applications that optimize the efficiency of the system. The MapReduce software system provides a programming model that simplifies processing. The WorkQueue system allows grouping of queries and schedules to perform distributed processing, while the Google File System serves the function of safe proofing the data by k eeping copies of the data in several places to prevent loss of information in case part of the system crashes. Â  Google has excelled in the online advertisement industry. Google has a technology that creates a correlation between the contents of a page and the potential advertisers. The technology creates online ad campaigns that are more relevant than the competitors can provide.

HW Assignment Example | Topics and Well Written Essays - 250 words

HW - Assignment Example Kodak has a legal obligation to sue companies that infringe on its patents. Kodak is among the oldest companies in the market that is slowly dying. Patents give the company to exclusively benefit from its innovations. Kodak sues the companies’ infringing on its patents to be compensated for its products. The company has to sue to deter other companies from infringing on its patents. Kodak has an exclusive right to produce the product for 20 years before other companies can duplicate. The company sues to ensure that it retains this right. Kodak can market its products in the market to gain market dominance before its patents expire. The company should invest in market penetration to ensure that it attains a loyal client base before the 20-year patent period. The company can also diversify it product range to compete with other players in the market. Positioning is key for the company, the management should ensure that the company is well positioned in the

Art Education Essay Example | Topics and Well Written Essays - 750 words - 1

Art Education - Essay Example Dancing is another form of art which emphasizes on the movement of the body in rhythm to the music. Dancing is used for expression of emotions, energy release, and being joyful of the movement itself. Riitta Pasanen Willberg introduces somatic choreography approach in relating the ideas of dancers with their choreographers on performances. Her aim is to evaluate the effectiveness of the exercises on the dancers in order to assess if the goals of the choreography were attained. Somatic practices are intended to raise kinesthetic awareness and to listen to one’s physical sensations, unlike just focusing on the visual view, imitation, and repetition of movements. Theatre Arts is a form of art wherein the actions of the body particularly facial expressions and human voices are used by performers in interpreting and creating drama in a story. It uses several elements like the architecture, lighting, stage craft, and sound design. John William Sommers argues that theatre can stimulate changes in art, a belief that is contradictory to U.S. Cornerstone Theatre Company Artistic Director Bill Rauch’s idea that one cannot predict art changes. He introduces the term Applied Drama which involves an application of direct experiences to create changes. In his study, he concludes that change is possible through the creation of situations in which people will experience favorable conditions where changes in values, knowledge, and attitudes can happen. Visual Arts is another form of art which focuses on presentations that are seen and appreciated by the naked eye. These presentations are in the form of paintings, sculptures, collages, etc. Terrence McCraw discusses about the distinction of arts from crafts. He provides one instance that explains the distinction. It was during the Reformation where embroidery became popular with more focus on the different designs. McCraw cites that the embroidery production created shared features with arts and crafts which made them similar. However according to him, the connotations of crafts in the modern period are still present in the embroidery works that were produced domestically which makes the point above confusing. III. RECOMMENDATION For music, the studies on musical therapy and the effects of music on the human brain function are significant topics that can be discussed and expounded in art education. For dancing, the study of somatics is also an interesting mechanism for effective body movement and coordination. In theatre arts the notion of Applied Drama is an essential tool for art change for versatility. Lastly, the distinction of arts from crafts is a good topic for debate when understanding the nature of art and its disciplines.

Metropolis Movie Essay Example | Topics and Well Written Essays - 1250 words

Metropolis Movie - Essay Example It was quite popular and among one of a kind movie to ever grace theatres and cinemas. Fritz Lang was a master of expressionism in German. This shows why he adopted and directed such an ambitious and eye catching movie to air in the 1920s. He adopts a futuristic dystopia that has two distinct approaches. The distinct classes are that of workers and thinkers. The movie depicts struggles between the two conflicting entities. It incorporates symbolism to a large extent. That said, the sci-fi perspective that is shown in this movie does not come close to defining reality. The fact that it was set in 1927 makes it seem eerily near reality. This is one of the many distinctive features with the movies of current times. However, the blame does not fall on Fritz as the provisions of that time only possessed the characteristics that feature in the movie. It is a good trial to depict reality. The visual impressions created are laudable though there is a considerable change and advancement of th e same since 1927. The movie is credited as having taken up a large amount of resources to make. In fact, it was the biggest budgeted movie in Germany during that time. There is a critic on the issue of budgeting. The movie was shot for a period of 310 days (close to a year) with an unmatched production design and members of the cast summing up to 36,000 extras. This is the reason why a huge amount of money was used up in its production. The amount spent on this movie translates to a better visually and acting equipped movie in current times. There is no denying that acquisition of the provisions that facilitated production of metropolis at that time was an expensive endeavor. There has been progress in the budgeting of movies of the same kind such as metropolis. They are not as demanding and the provisions are readily available. The movie world has instituted favorable technologies to oversee the production of science fiction movies. Similarly, the movie world has developed ways to manage the number of cast involved in the –production. Current science fiction movies certainly do not use such a huge number of extra casts. This means that production of such a movie in recent times is not a pioneering practice as in the case of metropolis. The cast are continuously being reduced to a manageable level and the rest of the cast requirement facilitated by technological features. Therefore, cost effectiveness in production of science fiction movies has been noticed over time since 1927(Lopate 22). . The movies possess a commendable attribute of linking science fiction with common and existing phenomena. This attribute is not common with movies of such kind in current times. The movie captures the conflicts of two groups. The workers are depicted as mentally exhausted and submissive. They walk in crowds creating the impression that they can be easily deceived. The masses are portrayed as incapable of challenging for anything. This description of the masses by F ritz Lang, coincidences with the notion created by leaders of that time. For instance, Hitler is quoted as saying â€Å"How fortunate for leaders that men do not think†. Other politicians also viewed the description as worth accreditation. This is a physically approved attribute that assures the movie plot is quite relevant to the social and political settings of that time. However, this does not mean that current science fic

Classification and division Essay Example | Topics and Well Written Essays - 500 words

Classification and division - Essay Example Thus schools are classified mainly into three broad categories; Elementary school, middle school and high school, for educating the children of different ages in a proper manner. Elementary schools are institutions in which children get their initial education. It is also referred as primary schools in some parts of the world. Elementary education includes kindergarten education or pre-primary education and primary education. Children within the age group of 3-11 are usually admitted in the elementary schools. Story telling methods are usually adopted in elementary teaching because of the interests of elementary school children in hearing stories. Problem solving or analytical methods cannot be applied in elementary school stages because of the difficulty of small aged children in grasping topics through such methods. Elementary education usually ends in the fifth standard. At the end of elementary education, middle school education starts. Middle schools are institutions in which th e children of 11 to 14 years old undergo the learning process. Usually, education from grade sixth to eighth is included in middle schools. â€Å"Young people undergo more rapid and profound personal changes between the ages 10 and 15 than at any other time in their lives.

Building Positive Relationships in Children Essay Example for Free

Building Positive Relationships in Children Essay To help your child understand feelings you could do a feeling chart or make a feeling tree in your home. To make a feelings chart just draw out faces with how there expression might be when they are feeling that way an do the expressions yourself when showing them. This will give your child a better understanding of their feelings and how they can express them through facial expressions. For a feeling tree its much the same idea as a feeling card but you just take in a branch from a tree and stick the faces with the expressions on it. this will help a child express themselves when they can’t do it through facial expressions. The Significance of friendship Buy them some books with plenty of colourful pictures with the theme of friendship and them to them.this will help show them how nice it is to have friends and how to make them and keep them. It is only after the age of three that children can incorperate other children into their playtime activities so at around this age ask other parents if they would like to make a playdate for their child and yours n a regular basis.this will get your child used to other childrens company.you can also talk about what they did together at dinner or quiet time alone and encourage them to do it again. Communication and Respect To help your child with communication you need to be a good example to them.talk to them as much as you can about your day and ask how theirs was.even talking about their favourite tv programme would be good as they will be more likely to talk about something that they’re interested in. To teach them about respect you need to set a good example for this as well. Giving them boundaries will also help and treating them with respect will encourage them to do the same to you. Factors that impact/Motivate children Tou tourself have a major impact on your child.they learn from how you react to situations and other peaople and will use this as a guide for themselves. Also the tv programmes that they watch will make an impact on them and can also motivate them to try new things that they wouldn’t of thought of themselves. .

Introduction To Cricket In The 21st Century History Essay

Introduction To Cricket In The 21st Century History Essay When considering the extensive amount of research that has been directed toward the sporting world from a mathematical, statistical and operational research perspective, the Duckworth/Lewis method (Duckworth and Lewis, 1998, 2004) perhaps stands alone as the most significant contribution to sport. The common practice in dealing with interrupted one-day cricket matches until 1992 was to compare the run rates (the total number of runs scored divided by the number of completed overs) of the competing teams; the team with the higher run rate was declared the winner. However, this rule tended to benefit the team batting second (Team 2) at the expense of the team batting first (Team 1), leading to the common practice of inviting the other team to bat first if rain was expected. The difficulty with run rates is that targets are determined by taking the remaining overs into account, while ignoring the number of lost wickets. As is well known, batsmen tend to bat less aggressively and score fewer runs when more wickets have been taken. The first team does not have the same strategic options as the second team and, in that sense, the rule does not provide both teams with equal opportunities. Realising that this rule is biased towards the side batting second, the Australian Cricket Board introduced its most productive overs rule during the 1992/93 season. This rule calculates the target for Team 2 by taking the n highest scoring overs of Team 1 where n is the number of played overs (for example, 40 if 10 overs are lost due to rain). Ironically, this rule was now considered as tending to favour the side batting first and transparently unfair to the team batting second. To illustrate, Suppose that Team 2 requires 20 off 19 balls to win, when a short shower takes three overs away. The reset target would now be 20 off 1 ball since the three least productive overs are deduced from the original target (which we may believe were three maiden overs in this case). However, this seems to be unfair and even ironic: the second teams excellent bowling (three maiden overs) in the first innings is now turning against them; it would have been better for Team 2 in this case if Team 1 had reached the same total score without any maidens. The Duckworth/Lewis method was utilised and gained prominence during the 1999 World Cup, and since that time, it has been adopted by every major cricketing board and competition. In one-day cricket, the Duckworth/Lewis method is based on the recognition that at the beginning of a match, each side has resources available (typically 50 overs and 10 wickets). When the match is shortened, the resources of one or both teams are reduced and the two teams usually have different resources for their innings. In this case, in an attempt to be fair, a revised target for the team batting second is set. The determination of the target using resources is known as the Duckworth/Lewis method. What makes the adoption of the Duckworth/Lewis method remarkable is that the method is widely perceived by the public as a black box procedure. Generally, people do not understand how the targets are set but they do agree that the targets are sensible or at least preferable to the approach based on run rates. Although the Duckworth/Lewis (D/L) method was designed for one-day cricket, it has also been applied to Twenty20 cricket. Twenty20 is a relatively new version of limited overs cricket with only 20 overs per side. In contrast to the one-day game and first-class cricket (which can take up to five days to complete), Twenty20 matches have completion times that are comparable to other popular team sports. With the introduction of the biennial World Twenty20 tournament in 2007 and the Indian Premier League in 2008, Twenty20 cricket has gained widespread popularity. Although Twenty20 (t20) cricket is similar to one-day cricket, there exist subtle variations in the rules (e.g. fielding restrictions, limits on bowling, etc) between the two versions of cricket. The variations in the rules, and most importantly, the reduction of overs from 50 to 20 suggest that scoring patterns in t20 may differ from the one-day game. In particular, t20 is seen as a more explosive game where the ability to score 4s and 6s is more highly valued than in one-day cricket. Since the D/L method (and its associated resource table) is based on the scoring patterns in one-day cricket, it is therefore reasonable to ask whether the D-L method is appropriate for t20. With the rise of Twenty20, an investigation of the D/L method applied to t20 is timely. Up until this point in time, such an investigation might not have been possible due to the dearth of t20 match results. Now analysts have at their disposal nearly 200 international matches, and through the use of efficient estimation procedures, the question may be at least partially addressed. Also, since t20 matches have a shorter duration, to date, few matches have been interrupted and resumed according to D/L. Consequently, if there is a problem with D/L applied to t20, it may not have yet manifested itself. This was true before the third editon of the World t20 in May 2010 when a controversial outcome occurred in a game between England and the West Indies. The criticism directed at the usage and appropriateness of the method by players, commentators and fans provide sufficient motivation to adjust the table in this project. In Section 2, the construction of the Duckworth/Lewis resource table is reviewed as well as its effective inception relative to past rain rules. Some comments are provided on aspects of the table and the limitations of the method. In Section 3, an alternative Twenty20 resource table is obtained using a non-parametric approach based on Gibbs sampling. The data used in the construction of the new table consist of all international Twenty20 matches to date involving Test-playing nations as recognised by the International Cricket Council (ICC). The project concludes with a short discussion in Section 4. A heat map is provided to facilitate comparisons between the two tables. 2. For their eyes only: Evaluation of the current method and its appropriateness A condensed version of the Duckworth/Lewis resource table (Standard Edition) is shown in Table 1 (taken from the ICC Playing Handbook 2008-09). In an uninterrupted innings of one-day cricket, a team starts batting with maximum resources available, equivalent to 50 overs and zero wickets taken. Reflect now on a one-day match where Team 1 scores 276 runs at the end of its 50 overs, as a simple example of the use of the Duckworth/Lewis resource table. Before Team 2 has a chance to start their chase of Team 1s total, it rains and they only receive 30 overs for their innings. A look at the resource table shows that Team 2 has only 75.1% of their resources in hand and, consequently, their target for winning the match is set at 276(0.751)=208 runs. Contrast the Duckworth/Lewis target with the unreasonably low target of 276(30/50)=166 runs based on run rates. Table 1. Abbreviated version of the Duckworth-Lewis resource table (Standard Edition) Overs available Wickets lost 0 1 2 3 4 5 6 7 8 50 100.0 93.4 85.1 74.9 62.7 49.0 34.9 22.0 11.9 40 89.3 84.2 77.8 69.6 59.5 47.6 34.6 22.0 11.9 30 75.1 71.8 67.3 61.6 54.1 44.7 33.6 21.8 11.9 25 66.5 63.9 60.5 56.0 50.0 42.2 32.6 21.6 11.9 20 56.6 54.8 52.4 49.1 44.6 38.6 30.8 21.2 11.9 10 32.1 31.6 30.8 29.8 28.3 26.1 22.8 17.9 11.4 5 17.2 17.0 16.8 16.5 16.1 15.4 14.3 12.5 9.4 1 3.6 3.6 3.6 3.6 3.6 3.5 3.5 3.4 3.2 0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 0.0 The table entries indicate the percentage of resources remaining in a match with the specified number of wickets lost and overs available. The D/L method has several advantages, which make it undoubtedly preferable to all previously used retargeting rules: completeness (it is able to handle all kinds of interruptions, even multiple interruptions and other unusual situations); the underlying mathematical model is internally consistent; tables are easily accessible/the computer programme is user-friendly; and the method compared to previous rules preserves the chance of winning by providing a relatively realistic reset target. Duckworth and Lewis (1998) only make available incomplete information relating to the creation of the resource table. Nevertheless, they do reveal that the table entries are based on the estimation of the 20 parameters Z0(w) and b(w), w=0, †¦, 9 corresponding to the function where Z(u,w) is the average total score obtained in u overs in an unlimited overs match where w wickets have been taken. While the utility of the Duckworth/Lewis table in one-day cricket cannot be questioned, a number of questions arise based on (1) and the estimates found in Table 1: Is (1) the best curve when considering that there are several parametric curves that could be fit? Is there any benefit in using a non-parametric fit to derive the table entries? The function (1) refers to unlimited overs cricket but is formed from a basis of one-day rules. Since one-day cricket is limited overs cricket, is there an advantage in taking the structure of the one-day game into account? How are the parameters estimated? If the 10 curves corresponding to w=0, †¦, 9 are fit separately, there are little data available beyond u=30 for fitting the curve with w=9. Also, the asymptotes for the curves with w=0,1,2 (see Figure 1 of Duckworth and Lewis (1998)) fall beyond the range of the data. In Table 1, the last two columns have many identical entries going down the columns. Although very few matches occur under these conditions, is it really sensible for resources to remain constant as the available overs decrease? This is a consequence of the asymptote imposed by (1). Although the D/L method maintains the margin of victory, it does not preserve the probability of victory. The resource table employed by the D/L method, and throughout its several updates, is based on detailed information from a large number of first innings scoring patterns. Therefore, the method assumes that the expected proportion of overall scoring for a particular over when a given number of wickets have been lost is the same in both innings. The validity of this assumption (that scoring patterns are the same in both innings) can be questioned. It has been found that there are a greater relative proportion of runs scored in the early and late overs of second innings, than in the first innings. The rule assumes that run-scoring accelerates right from the beginning of the innings so that runs come at a faster rate for every over completed; an exponential relationship between runs and overs is assumed. Although this captures the fact that run-scoring accelerates at the end of an innings, the moment of stabilisation somewhere after the relaxing of fielding restrictions is overlooked. 50 overs has been the standard format for a One-day International (ODI) for so long (over 20 years) that there is a period between the end of the fifteenth over and the start of the 41st where the batting side keep the scorecard ticking over through nudged and nurdled singles whilst the fielding side are perfectly happy to concede. Furthermore, no consideration is given to powerplay overs in which fielding restrictions are in place. Losing two overs during a period of fielding restrictions reduces a teams resources more than when a team loses the same couple of overs somewhere between, say, overs 25 and 30. The D/L method does not reflect the fact that the first period has a much higher run-scoring capacity than the second. The asymmetry between the equations for resetting targets impairs the quality of impartiality and may even lead to strategic options which are not equally open to both teams. When the target is large and Team 2 forsees a substantial reduction of its innings, Team 2 could take the strategic option to keep as many wickets as possible in hand, even if the scoring rate is less than required: a score of 99/1 (or 110/2, 123/3†¦) after 25 overs in the second innings against a target of 286 for 50 overs would win if no further play is possible. This distorted result is not merely due to the scaling of limited early data but also stems from an idealised assumption of how batting sides deploy their resources during an innings. The D/L method, like other (target) prediction algorithms, tries to fit historical data into a function curve, and uses this to predict future match states. Although this approach is generic and scales well, the specificity of the match is lost. For example, say in two instances a match is interrupted in the first innings with the score at 100/3 after 25 overs. The prediction (extrapolation) for both the matches will be the same. However, if one of the teams were 90/0 after 15 overs and the other team were 40/3 at the same stage, it is highly probable that the second team would have gone on to score more than the first. 3. Turn the tables: A new model for Twenty20 matches For ease of discussion, it is convenient to convert the Duckworth/Lewis resource table to the context of Twenty20; the resource table is shortened to 20 overs and the entries scaled so that an innings beginning with 20 overs and zero wickets corresponds to 100% resources. Table 2 gives the full Duckworth/Lewis resource table (Standard Edition) for Twenty20 where the entries are obtained by dividing the corresponding entry in Table 1 by 0.566 (the resources remaining in a 1-day match where 20 overs are available and zero wickets taken). Table 2. The Duckworth/Lewis resource table (Standard Edition) scaled for Twenty20 Overs available Wickets lost 0 1 2 3 4 5 6 7 8 20 100.0 96.8 92.6 86.7 78.8 68.2 54.4 37.5 21.3 19 96.1 93.3 89.2 83.9 76.7 66.6 53.5 37.3 21.0 18 92.2 89.6 85.9 81.1 74.2 65.0 52.7 36.9 21.0 17 88.2 85.7 82.5 77.9 71.7 63.3 51.6 36.6 21.0 16 84.1 81.8 79.0 74.7 69.1 61.3 50.4 36.2 20.8 15 79.9 77.9 75.3 71.6 66.4 59.2 49.1 35.7 20.8 14 75.4 73.7 71.4 68.0 63.4 56.9 47.7 35.2 20.8 13 71.0 69.4 67.3 64.5 60.4 54.4 46.1 34.5 20.7 12 66.4 65.0 63.3 60.6 57.1 51.9 44.3 33.6 20.5 11 61.7 60.4 59.0 56.7 53.7 49.1 42.4 32.7 20.3 10 56.7 55.8 54.4 52.7 50.0 46.1 40.3 31.6 20.1 9 51.8 51.1 49.8 48.4 46.1 42.8 37.8 30.2 19.8 8 46.6 45.9 45.1 43.8 42.0 39.4 35.2 28.6 19.3 7 41.3 40.8 40.1 39.2 37.8 35.5 32.2 26.9 18.6 6 35.9 35.5 35.0 34.3 33.2 31.4 29.0 24.6 17.8 5 30.4 30.0 29.7 29.2 28.4 27.2 25.3 22.1 16.6 4 24.6 24.4 24.2 23.9 23.3 22.4 21.2 18.9 14.8 3 18.7 18.6 18.4 18.2 18.0 17.5 16.8 15.4 12.7 2 12.7 12.5 12.5 12.4 12.4 12.0 11.7 11.0 9.7 1 6.4 6.4 6.4 6.4 6.4 6.2 6.2 6.0 5.7 The table entries indicate the percentage of resources remaining in a match with the specified number of wickets lost and overs available. To build a resource table for Twenty20 (t20), it is imperative to consider the scoring patterns specific to the shortest version of the game. Hence, consider the 141 international t20 matches involving ICC full member teams that have taken place from the first in 17 February 2005 through to 14 January 2011 (details of these matches can be accessed from ESPN Cricinfo). The shortened matches where the Duckworth/Lewis method was present have been excluded along with the t20 matches involving non-test playing nations (ICC Associates); the latter disqualification is in place to ensure matches are of a consistently high standard. Since scoring patterns in the second innings show a level of dependency to the number of runs scored by Team 1, consider first innings data only in the examination of t20 scoring patterns. Note that in their development of a simulator for one-day cricket match results, Swartz et al (2009) consider batting behaviour in the second innings. Match summary results are obtainable from ESPN Cricinfos statistics website but this study calls for ball-by-ball data. For this, Stephen Lynch (statistician) took pains to compose the associated commentary log for each match and store the data in a tabular form for easy access. For each match, define z(u,w(u)) as the runs scored from the point in the first innings where u overs remain and w(u) wickets have been taken until the conclusion of Team 1s innings. Calculate z(u,w(u)) for all values of u that occur in the first innings for each match beginning with u=20 and w(u)=w(20)=0. Next calculate the matrix T=(tuw) where tuw is the estimated percentage of resources remaining when u overs are available and w wickets have been taken. Calculate (100%) tuw by averaging z(u,w(u)) over all matches where w(u)=w and dividing by the average of z(20, 0) over all matches; the denominator is the average score by a side batting first in a t20 match. In the case of u=0, set tuw=t0w=0.0%. Table 3 displays the matrix T, an initial attempt at a resource table for t20. Note that t20,0=100% as desired. Although T is a non-parametric estimate of resources and makes no assumptions concerning the scoring patterns in t20, it is less than ideal. First, there are many table entries where there are missing data for the given situation. In addition, Table 3 does not exhibit the monotonicity expected. Logically, there is a requirement for a resource table that is non-decreasing from left to right along rows and a requirement for a resource table that is non-decreasing down columns. Also o bserve some conspicuous entries in Table 3, particularly the entry of 110.2% resources corresponding to 19 overs available and two wickets taken. This entry is clearly misleading and should be less than 100%. It arises due to the small sample size (three matches) corresponding to the given situation. For this non-parametric resource table (upcoming), the estimation procedure is robust to observations based on small sample sizes as the surrounding observations based on larger sample sizes have greater influence in the determination of the table. Therefore, there is retention of conspicuous observations such as 110.2%. This investigation of Duckworth/Lewis in Twenty20 should be viewed as one of discovery rather than an attempt to replace the Duckworth/Lewis table. Table 3. The matrix R=(r ow) of estimated resources for Twenty20 Overs available Wickets lost 0 1 2 3 4 5 6 7 8 20 100.0 19 93.6 83.0 110.2 18 90.4 85.8 78.3 17 86.7 80.5 82.8 53.7 16 81.7 74.5 81.9 70.7 32.8 15 76.5 71.4 71.5 65.9 59.9 14 68.3 69.1 67.6 66.2 58.4 13 63.8 68.2 62.4 62.9 59.0 24.3 12 62.1 62.3 60.6 57.3 58.8 44.1 11 60.5 56.3 57.0 53.6 61.0 39.7 10 57.6 49.6 52.1 52.8 48.1 38.6 41.0 35.2 9 54.9 52.1 43.6 49.0 44.1 33.8 35.0 29.7 8 51.0 46.4 41.7 42.2 41.2 36.7 27.5 28.7 7 48.6 45.8 38.9 35.9 39.1 34.8 24.1 25.5 6 54.0 37.9 36.6 30.3 36.2 31.3 20.9 21.4 26.7 5 44.0 32.5 25.4 28.7 29.4 23.9 17.1 14.9 4 28.2 23.4 22.5 22.2 20.9 14.3 10.6 3 20.6 19.9 16.9 17.8 15.8 12.4 7.6 2 21.2 17.6 11.9 13.4 10.6 11.0 7.2 1 8.7 5.2 7.3 6.0 5.5 6.0   The table entries indicate the percentage of resources remaining in a match with the specified number of wickets lost and overs available. Note: Missing entries correspond to match situations where data are unavailable. To impose the monotonicity constraints in the rows and columns, refer to the general problem of isotonic regression. For these purposes, consider the minimisation of with respect to the matrix Y=(yuw) where the double summation corresponds to u=1, †¦, 20 and w=0, †¦, 9, the quw are weights and the minimisation is subject to the constraints yuwgreater than or equal toyu,w+1 and yu,wgreater than or equal toyu−1,w. In addition, impose y20,0=100, y0,w=0 for w=0, †¦, 9 and yu,10=0 for u=1, †¦, 20. Although the fitting of Y is completely non-parametric, there are some arbitrary choices that have been made in the minimisation of (2). First, not only was the choice of squared error discrepancy in (2) convenient for computation, minimisation of the function F with squared error discrepancy corresponds to the method of constrained maximum likelihood estimation where the data ruw are independently normally distributed with means yuw and variances 1/quw. Second, a matrix Y: 20 10 based on overs is chosen. Alternatively, a larger matrix Y: 120 10 based on balls could have been considered. The overs formulation is preferred as it involves less missing data and leads to a less computationally intensive optimization. With a matrix Y based on overs, it is possible to interpolate on a ball-by-ball basis if required. Third, a simple choice has been made with respect to the weights quw. 1/quw is set equal to the sample variance used in the calculation of ruw divided by the sample size. The rationale is that when ruw is less variable, there is stronger belief that yuw should be close to ruw. Table 4 gives a non-parametric resource table based on the minimisation of (2). An algorithm for isotonic regression in two variables was first introduced by Dykstra and Robertson (1982). Fortran code was subsequently developed by Bril et al (1984). An R code implementation has been used that is available from the Iso package on the Cran website (www.cran.r-project.org). The programme requires 27 iterations to achieve convergence. What is unsatisfactory about Table 4 is that it suffers from the same criticism that was directed at the Duckworth-Lewis resource table. There is a considerable number of adjacent entries in Table 4 that have the same value. Again, it is not sensible for resources to remain constant as available overs decrease or wickets increase. The problem is that in the minimization of (2), various fitted ys occur on the boundaries imposed by the monotonicity constraints. Table 4 is also unsatisfactory from the point of view that it is incomplete; missing values corresp ond to match situations where data are unavailable. To address the above criticisms, it is necessary take a slightly different approach to estimation. As previously mentioned, it can been seen that (2) arises from the normal likelihood Therefore, consider a Bayesian model where the unknown parameters in (3) are the ys. A flat default prior is assigned to the ys subject to the monotonicity constraints. It follows that the posterior density takes the form (3) and that Gibbs sampling can be carried out via sampling from the full conditional distributions subject to the local constraints on yuw in the given iteration of the algorithm. Sampling from (4) is easily carried out using a normal generator and rejection sampling according to the constraints. Although in statistical terminology, (3) takes a parametric form, the approach is referred to as non-parametric since no functional relationship is imposed on the ys. Table 4. A non-parametric resource table for Twenty20 based on isotonic regression Overs available Wicket lost 0 1 2 3 4 5 6 7 8 20 100.0 19 93.6 85.5 85.5 18 90.4 85.5 80.8 17 86.7 80.8 80.8 64.7 16 81.7 77.4 77.4 64.7 55.9 15 76.5 71.5 71.5 64.7 55.9 14 68.8 68.8 67.6 64.7 55.9 13 66.6 66.6 62.6 62.6 55.9 38.4 12 62.2 62.2 60.6 57.3 55.9 38.4 11 60.5 56.8 56.8 54.8 54.8 38.4 10 57.6 52.1 52.1 52.1 48.1 38.4 34.1 29.3 9 54.9 52.1 46.5 46.5 44.1 36.3 34.1 29.3 8 51.0 46.4 42.0 42.0 41.2 36.3 28.6 28.6 7 48.6 45.8 38.9 37.3 37.3 34.8 25.3 25.3 6 39.7 39.7 36.6 32.8 32.8 31.3 23.0 21.4 21.4 5 39.7 32.5 28.0 28.0 28.0 23.0 17.1 15.5 4 27.9 23.4 22.5 22.2 20.9 14.3 10.7 3 20.7 19.9 17.4 17.4 15.8 12.4 7.7 2 20.7 17.6 12.5 12.5 10.8 10.8 7.2 1 8.7 6.6 6.6 6.0 5.7 5.7 The table entries indicate the percentage of resources remaining in a match with the specified number of wickets lost and overs available. Missing entries correspond to match situations where data are unavailable. In Table 5, the estimated posterior means of the ys obtained through Gibbs sampling are given, and these provide an alternative resource table for t20. The computations pose no difficulties and the estimates stabilize after 50,000 iterations. For cases of missing data, the Duckworth/Lewis table entries are used to impute the missing rs. The imputation is in the spirit of a Bayesian approach where prior information is utilised. Unlike Table 4, Table 5 is a complete table. Also, there are no longer adjacent table entries with identical values and this is due to the sampling approach. Finally, it can be stated that the methodology allows the input of expert opinion. For example, suppose that there is expert consensus that a table entry yij ought to be tied down to a particular value a. To force this table entry, all that is required is to set rij=a and assign a sufficiently small standard deviation Unfortunately we are unable to provide accessible alternative text for this. If you requi re assistance to access this image, please contact [emailprotected] or the author Table 5. A non-parametric resource table for Twenty20 based on Gibbs sampling Overs available Wickets lost 0 1 2 3 4 5 6 7 8 20 100.0 96.9 93.0 87.9 81.3 72.2 59.9 44.8 29.7 19 95.6 90.9 87.7 83.0 76.9 68.3 56.5 42.0 27.2 18 91.7