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Business Data Communications and Networking

Thirteenth Edition

Jerry Fi tzGerald Jerry FitzGerald & Associates

Alan Dennis Indiana University

Alexandra Durcikova University of Oklahoma

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ACQUISITIONS EDITOR Darren Lalonde EDITORIAL MANAGER Gladys Soto CONTENT MANAGEMENT DIRECTOR Lisa Wojcik CONTENT MANAGER Nichole Urban SENIOR CONTENT SPECIALIST Nicole Repasky PRODUCTION EDITOR Padmapriya Soundararajan PHOTO RESEARCHER Billy Ray COVER PHOTO CREDIT © Wright Studio/Shutterstock

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To my son Alec, Alan

To all curious minds who want to know how today’s modern world works.

Alexandra

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ABOUT THE AUTHORS

Alan Dennis is a Fellow of the Association for Information Systems and a professor of information systems in the Kelley School of Business at Indiana University. He holds the John T. Chambers Chair in Internet Systems, which was established to honor John Chambers, president and chief executive officer of Cisco Systems, the worldwide leader of networking technologies for the Internet.

Prior to joining Indiana University, Alan spent nine years as a professor at the University of Georgia, where he won the Richard B. Russell Award for Excellence in Undergraduate Teaching. He has a bachelor’s degree in computer science from Acadia University in Nova Scotia, Canada, and an MBA from Queen’s University in Ontario, Canada. His PhD in management of information systems is from the University of Arizona. Prior to entering the Arizona doctoral program, he spent three years on the faculty of the Queen’s School of Business.

Alan has extensive experience in the development and application of groupware and Internet technologies and co-founded Courseload, an electronic textbook company whose goal is to improve learning and reduce the cost of textbooks. He has won many awards for theoretical and applied research and has published more than 150 business and research articles, including those in Management Science, MIS Quarterly, Information Systems Research, Academy of Management Journal, Organization Behavior and Human Decision Making, Journal of Applied Psychology, Communications of the ACM, and IEEE Transactions of Systems, Man, and Cybernetics. His first book was Getting Started with Microcomputers, published in 1986. Alan is also an author of two systems analysis and design books published by Wiley. He is the cochair of the Internet Tech- nologies Track of the Hawaii International Conference on System Sciences. He has served as a consultant to BellSouth, Boeing, IBM, Hughes Missile Systems, the U.S. Department of Defense, and the Australian Army.

Alexandra Durcikova is an Assistant Professor at the Price College of Business, University of Oklahoma. Alexandra has a PhD in management information systems from the University of Pittsburgh. She has earned an MSc degree in solid state physics from Comenius University, Bratislava, worked as an experimental physics researcher in the area of superconductivity and as an instructor of executive MBA students prior to pursuing her PhD. Alexandra’s research interests include knowledge management and knowledge management systems, the role of organizational climate in the use of knowledge management systems, knowledge management system characteristics, governance mechanisms in the use of knowledge management systems, and human compliance with security policy and characteristics of successful phishing attempts within the area of network security. Her research appears in Information Systems Research, MIS Quarterly, Journal of Management Information Systems, Information Systems Journal, Journal of Organizational and End User Computing, International Journal of Human-Computer Studies, International Journal of Human-Computer Studies, and Communications of the ACM.

Alexandra has been teaching business data communications to both undergraduate and grad- uate students for several years. In addition, she has been teaching classes on information technol- ogy strategy and most recently won the Dean’s Award for Undergraduate Teaching Excellence while teaching at the University of Arizona.

Dr. Jerry FitzGerald wrote the early editions of this book in the 1980s. At the time, he was the principal in Jerry FitzGerald & Associates, a firm he started in 1977.

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PREFACE

The field of data communications has grown faster and become more important than computer processing itself. Though they go hand in hand, the ability to communicate and connect with other computers and mobile devices is what makes or breaks a business today. There are three trends that support this notion. First, the wireless LAN and Bring-Your-Own-Device (BYOD) allow us to stay connected not only with the workplace but also with family and friends. Second, computers and networks are becoming an essential part of not only computers but also devices we use for other purpose, such as home appliances. This Internet of things allows you to set the thermostat in your home from your mobile phone, can help you cook a dinner, or eventually can allow you to drive to work without ever touching the steering wheel. Lastly, we see that a lot of life is moving online. At first this started with games, but education, politics, and activism followed swiftly. Therefore, understanding how networks work; how they should be set up to support scalability, mobility, and security; and how to manage them is of utmost importance to any business. This need will call not only for engineers who deeply understand the technical aspects of networks but also for highly social individuals who embrace technology in creative ways to allow business to achieve a competitive edge through utilizing this technology. So the call is for you who are reading this book—you are at the right place at the right time!

PURPOSE OF THIS BOOK Our goal is to combine the fundamental concepts of data communications and networking with practical applications. Although technologies and applications change rapidly, the fundamental concepts evolve much more slowly; they provide the foundation from which new technologies and applications can be understood, evaluated, and compared.

This book has two intended audiences. First and foremost, it is a university textbook. Each chapter introduces, describes, and then summarizes fundamental concepts and applications. Man- agement Focus boxes highlight key issues and describe how networks are actually being used today. Technical Focus boxes highlight key technical issues and provide additional detail. Mini case studies at the end of each chapter provide the opportunity to apply these technical and man- agement concepts. Hands-on exercises help to reinforce the concepts introduced in the chapter. Moreover, the text is accompanied by a detailed Instructor’s Manual that provides additional back- ground information, teaching tips, and sources of material for student exercises, assignments, and exams. Finally, our Web page contains supplements to our book.

Second, this book is intended for the professional who works in data communications and networking. The book has many detailed descriptions of the technical aspects of communica- tions from a business perspective. Moreover, managerial, technical, and sales personnel can use this book to gain a better understanding of fundamental concepts and trade-offs not presented in technical books or product summaries.

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Preface vii

WHAT’S NEW IN THIS EDITION The thirteenth edition maintains the three main themes of the twelfth edition, namely, (1) how networks work (Chapters 1–5); (2) network technologies (Chapters 6–10); and (3) network secu- rity and management (Chapters 11 and 12). In the new edition, we removed older technologies and replaced them with new ones. Accordingly, new hands-on activities and questions have been added at the end of each chapter that guide students in understanding how to select technolo- gies to build a network that would support an organization’s business needs. In addition to this overarching change, the thirteenth edition has three major changes from the twelfth edition:

First, at the end of each chapter, we provide key implications for cyber security that arise from the topics discussed in the chapter. We draw implications that focus on improving the management of networks and information systems as well as implications for cyber security of an individual and an organization.

The second major change is that in Chapter 5 we have revised the way we explain how TCP/IP works to make it clearer and more streamlined.

Third, we have revised the security chapter (Chapter 11) to consider some of the newer threats and responses.

LAB EXERCISES www.wiley.com/college/fitzgerald

This edition includes an online lab manual with many hands-on exercises that can be used in a networking lab. These exercises include configuring servers and other additional practical topics.

ONLINE SUPPLEMENTS FOR INSTRUCTORS www.wiley.com/college/fitzgerald

Instructor’s supplements comprise an Instructor’s Manual that includes teaching tips, war stories, and answers to end-of-chapter questions; a Test Bank that includes true-false, multiple choice, short answer, and essay test questions for each chapter; and Lecture Slides in PowerPoint for classroom presentations. All are available on the instructor’s book companion site.

E-BOOK Wiley E-Text: Powered by VitalSource offers students continuing access to materials for their course. Your students can access content on a mobile device, online from any Internet-connected computer, or by a computer via download. With dynamic features built into this e-text, students can search across content, highlight, and take notes that they can share with teachers and classmates. Readers will also have access to interactive images and embedded podcasts. Visit www.wiley.com/college/fitzgerald for more information.

http://www.wiley.com/college/fitzgerald
http://www.wiley.com/college/fitzgerald
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viii Preface

ACKNOWLEDGMENTS Our thanks to the many people who helped in preparing this edition. Specifically, we want to thank the staff at John Wiley & Sons for their support.

Alan Dennis Bloomington, Indiana

www.kelley.indiana.edu/ardennis

Alexandra Durcikova Norman, Oklahoma

http://www.ou.edu/price/mis/people/alexandra_durcikova.html

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CONTENTS

About the Authors v Preface vi

PART ONE INTRODUCTION 1 Chapter 1

Introduction to Data Communications 1 1.1 Introduction 1 1.2 Data Communications Networks 4

1.2.1 Components of a Network 4 1.2.2 Types of Networks 5

1.3 Network Models 7 1.3.1 Open Systems Interconnection

Reference Model 7 1.3.2 Internet Model 9 1.3.3 Message Transmission Using

Layers 10 1.4 Network Standards 13

1.4.1 The Importance of Standards 13 1.4.2 The Standards-Making Process 13 1.4.3 Common Standards 15

1.5 Future Trends 16 1.5.1 Wireless LAN and BYOD 16 1.5.2 The Internet of Things 17 1.5.3 Massively Online 17

1.6 Implications for Cyber Security 18

PART TWO FUNDAMENTAL CONCEPTS 25 Chapter 2

Application Layer 25 2.1 Introduction 25 2.2 Application Architectures 26

2.2.1 Host-Based Architectures 27 2.2.2 Client-Based Architectures 28 2.2.3 Client-Server Architectures 28 2.2.4 Cloud Computing Architectures 31 2.2.5 Peer-to-Peer Architectures 33 2.2.6 Choosing Architectures 34

2.3 World Wide Web 35 2.3.1 How the Web Works 35 2.3.2 Inside an HTTP Request 36 2.3.3 Inside an HTTP Response 37

2.4 Electronic Mail 39 2.4.1 How Email Works 39 2.4.2 Inside an SMTP Packet 42 2.4.3 Attachments in Multipurpose Internet

Mail Extension 43 2.5 Other Applications 43

2.5.1 Telnet 44 2.5.2 Instant Messaging 45 2.5.3 Videoconferencing 45

2.6 Implications for Cyber Security 47

Chapter 3

Physical Layer 57 3.1 Introduction 57 3.2 Circuits 59

3.2.1 Circuit Configuration 59 3.2.2 Data Flow 60 3.2.3 Multiplexing 60

3.3 Communication Media 63 3.3.1 Twisted Pair Cable 63 3.3.2 Coaxial Cable 64 3.3.3 Fiber-Optic Cable 64 3.3.4 Radio 65 3.3.5 Microwave 66 3.3.6 Satellite 66 3.3.7 Media Selection 68

3.4 Digital Transmission of Digital Data 69 3.4.1 Coding 69 3.4.2 Transmission Modes 69

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3.4.3 Digital Transmission 71 3.4.4 How Ethernet Transmits Data 72

3.5 Analog Transmission of Digital Data 73 3.5.1 Modulation 73 3.5.2 Capacity of a Circuit 76 3.5.3 How Modems Transmit Data 76

3.6 Digital Transmission of Analog Data 77 3.6.1 Translating from Analog to Digital 77 3.6.2 How Telephones Transmit Voice

Data 77 3.6.3 How Instant Messenger Transmits

Voice Data 79 3.6.4 Voice over Internet Protocol

(VoIP) 80 3.7 Implications for Cyber Security 80

Chapter 4

Data Link Layer 88 4.1 Introduction 88 4.2 Media Access Control 89

4.2.1 Contention 89 4.2.2 Controlled Access 89 4.2.3 Relative Performance 90

4.3 Error Control 91 4.3.1 Sources of Errors 91 4.3.2 Error Prevention 93 4.3.3 Error Detection 94 4.3.4 Error Correction via

Retransmission 95 4.3.5 Forward Error Correction 95 4.3.6 Error Control in Practice 97

4.4 Data Link Protocols 97 4.4.1 Asynchronous Transmission 97 4.4.2 Synchronous Transmission 98

4.5 Transmission Efficiency 101 4.6 Implications for Cyber Security 103

Chapter 5

NETWORK AND TRANSPORT LAYERS 110 5.1 Introduction 110 5.2 Transport and Network Layer Protocols 112

5.2.1 Transmission Control Protocol (TCP) 112

5.2.2 Internet Protocol (IP) 113

5.3 Transport Layer Functions 114 5.3.1 Linking to the Application Layer 114 5.3.2 Segmenting 115 5.3.3 Session Management 116

5.4 Addressing 119 5.4.1 Assigning Addresses 120 5.4.2 Address Resolution 125

5.5 Routing 127 5.5.1 Types of Routing 128 5.5.2 Routing Protocols 130 5.5.3 Multicasting 132 5.5.4 The Anatomy of a Router 133

5.6 TCP/IP Example 134 5.6.1 Known Addresses 136 5.6.2 Unknown Addresses 137 5.6.3 TCP Connections 138 5.6.4 TCP/IP and Network Layers 139

5.7 Implications for Cyber Security 141

PART THREE NETWORK TECHNOLOGIES 159 Chapter 6

Network Design 159 6.1 Introduction 159

6.1.1 Network Architecture Components 159

6.1.2 The Traditional Network Design Process 161

6.1.3 The Building-Block Network Design Process 162

6.2 Needs Analysis 164 6.2.1 Network Architecture

Component 165 6.2.2 Application Systems 166 6.2.3 Network Users 166 6.2.4 Categorizing Network Needs 166 6.2.5 Deliverables 167

6.3 Technology Design 168 6.3.1 Designing Clients and Servers 168 6.3.2 Designing Circuits 168 6.3.3 Network Design Tools 170 6.3.4 Deliverables 171

6.4 Cost Assessment 171 6.4.1 Request for Proposal 171

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Contents xi

6.4.2 Selling the Proposal to Management 173

6.4.3 Deliverables 173 6.5 Implications for Cyber Security 173

Chapter 7

Wired and Wireless Local Area Networks 177 7.1 Introduction 177 7.2 LAN Components 178

7.2.1 Network Interface Cards 179 7.2.2 Network Circuits 179 7.2.3 Network Hubs, Switches, and Access

Points 180 7.2.4 Network Operating Systems 183

7.3 Wired Ethernet 184 7.3.1 Topology 184 7.3.2 Media Access Control 187 7.3.3 Types of Ethernet 188

7.4 Wireless Ethernet 189 7.4.1 Topology 189 7.4.2 Media Access Control 189 7.4.3 Wireless Ethernet Frame Layout 190 7.4.4 Types of Wireless Ethernet 191 7.4.5 Security 192

7.5 The Best Practice LAN Design 193 7.5.1 Designing User Access with Wired

Ethernet 194 7.5.2 Designing User Access with Wireless

Ethernet 195 7.5.3 Designing the Data Center 197 7.5.4 Designing the e-Commerce Edge 199 7.5.5 Designing the SOHO

Environment 200 7.6 Improving LAN Performance 202

7.6.1 Improving Server Performance 203 7.6.2 Improving Circuit Capacity 204 7.6.3 Reducing Network Demand 204

7.7 Implications for Cyber Security 205

Chapter 8

Backbone Networks 214 8.1 Introduction 214 8.2 Switched Backbones 215 8.3 Routed Backbones 218

8.4 Virtual LANs 221 8.4.1 Benefits of VLANs 221 8.4.2 How VLANs Work 223

8.5 The Best Practice Backbone Design 226 8.6 Improving Backbone Performance 227

8.6.1 Improving Device Performance 227 8.6.2 Improving Circuit Capacity 228 8.6.3 Reducing Network Demand 228

8.7 Implications for Cyber Security 228

Chapter 9

Wide Area Networks 237 9.1 Introduction 237 9.2 Dedicated-Circuit Networks 238

9.2.1 Basic Architecture 238 9.2.2 T-Carrier Services 241 9.2.3 SONET Services 243

9.3 Packet-Switched Networks 243 9.3.1 Basic Architecture 243 9.3.2 Frame Relay Services 245 9.3.3 IP Services 246 9.3.4 Ethernet Services 246

9.4 Virtual Private Networks 247 9.4.1 Basic Architecture 247 9.4.2 VPN Types 248 9.4.3 How VPNs Work 248

9.5 The Best Practice WAN Design 251 9.6 Improving WAN Performance 252

9.6.1 Improving Device Performance 252 9.6.2 Improving Circuit Capacity 253 9.6.3 Reducing Network Demand 253

9.7 Implications for Cyber Security 254

Chapter 10

The Internet 265 10.1 Introduction 265 10.2 How the Internet Works 266

10.2.1 Basic Architecture 266 10.2.2 Connecting to an ISP 268 10.2.3 The Internet Today 269

10.3 Internet Access Technologies 270 10.3.1 Digital Subscriber Line 270 10.3.2 Cable Modem 271 10.3.3 Fiber to the Home 273 10.3.4 WiMax 274

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10.4 The Future of the Internet 274 10.4.1 Internet Governance 274 10.4.2 Building the Future 276

10.5 Implications for Cyber Security 277

PART FOUR NETWORK MANAGEMENT 284 Chapter 11

Network Security 284 11.1 Introduction 284

11.1.1 Why Networks Need Security 286 11.1.2 Types of Security Threats 286 11.1.3 Network Controls 287

11.2 Risk Assessment 288 11.2.1 Develop Risk Measurement

Criteria 289 11.2.2 Inventory IT Assets 290 11.2.3 Identify Threats 291 11.2.4 Document Existing Controls 293 11.2.5 Identify Improvements 296

11.3 Ensuring Business Continuity 296 11.3.1 Virus Protection 296 11.3.2 Denial-of-Service Protection 297 11.3.3 Theft Protection 300 11.3.4 Device Failure Protection 301 11.3.5 Disaster Protection 302

11.4 Intrusion Prevention 305 11.4.1 Security Policy 306 11.4.2 Perimeter Security and Firewalls 306 11.4.3 Server and Client Protection 312 11.4.4 Encryption 315 11.4.5 User Authentication 321 11.4.6 Preventing Social Engineering 324

11.4.7 Intrusion Prevention Systems 325 11.4.8 Intrusion Recovery 327

11.5 Best Practice Recommendations 328 11.6 Implications for Your Cyber Security 330

Chapter 12

Network Management 340 12.1 Introduction 340 12.2 Designing for Network Performance 341

12.2.1 Managed Networks 341 12.2.2 Managing Network Traffic 345 12.2.3 Reducing Network Traffic 346

12.3 Configuration Management 349 12.3.1 Configuring the Network and Client

Computers 349 12.3.2 Documenting the Configuration

350 12.4 Performance and Fault Management 351

12.4.1 Network Monitoring 351 12.4.2 Failure Control Function 353 12.4.3 Performance and Failure

Statistics 355 12.4.4 Improving Performance 358

12.5 End User Support 358 12.5.1 Resolving Problems 358 12.5.2 Providing End User Training 360

12.6 Cost Management 360 12.6.1 Sources of Costs 360 12.6.2 Reducing Costs 363

12.7 Implications for Cyber Security 364

Appendices (Online) Glossary (Online) Index 373

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PART ONE INTRODUCTION

C H A P T E R 1

INTRODUCTION TO DATA COMMUNICATIONS

This chapter introduces the basic concepts of data communications. It describes why it is impor- tant to study data communications and introduces you to the three fundamental questions that this book answers. Next, it discusses the basic types and components of a data communications network. Also, it examines the importance of a network model based on layers. Finally, it describes the three key trends in the future of networking.

OBJECTIVES ◾ Be aware of the three fundamental questions this book answers ◾ Be aware of the applications of data communications networks ◾ Be familiar with the major components of and types of networks ◾ Understand the role of network layers ◾ Be familiar with the role of network standards ◾ Be aware of cyber security issues ◾ Be aware of three key trends in communications and networking

OUTLINE 1.1 Introduction 1.2 Data Communications Networks

1.2.1 Components of a Network 1.2.2 Types of Networks

1.3 Network Models 1.3.1 Open Systems Interconnection

Reference Model 1.3.2 Internet Model 1.3.3 Message Transmission Using Layers

1.4 Network Standards

1.4.1 The Importance of Standards 1.4.2 The Standards-Making Process 1.4.3 Common Standards

1.5 Future Trends 1.5.1 Wireless LAN and BYOD 1.5.2 The Internet of Things 1.5.3 Massively Online

1.6 Implications for Cyber Security Summary

1.1 INTRODUCTION What Internet connection should you use? Cable modem or DSL (formally called Digital Sub- scriber Line)? Cable modems are supposedly faster than DSL, providing data speeds of 50 Mbps to DSL’s 1.5–25 Mbps (million bits per second). One cable company used a tortoise to represent DSL in advertisements. So which is faster? We’ll give you a hint. Which won the race in the fable, the tortoise or the hare? By the time you finish this book, you’ll understand which is faster and why, as well as why choosing the right company as your Internet service provider (ISP) is probably more important than choosing the right technology.

Over the past decade or so, it has become clear that the world has changed forever. We con- tinue to forge our way through the Information Age—the second Industrial Revolution, according

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2 Chapter 1 Introduction to Data Communications

to John Chambers, CEO (chief executive officer) of Cisco Systems, Inc., one of the world’s leading networking technology companies. The first Industrial Revolution revolutionized the way people worked by introducing machines and new organizational forms. New companies and industries emerged, and old ones died off.

The second Industrial Revolution is revolutionizing the way people work through network- ing and data communications. The value of a high-speed data communications network is that it brings people together in a way never before possible. In the 1800s, it took several weeks for a message to reach North America by ship from England. By the 1900s, it could be transmitted within an hour. Today, it can be transmitted in seconds. Collapsing the information lag to Internet speeds means that people can communicate and access information anywhere in the world regard- less of their physical location. In fact, today’s problem is that we cannot handle the quantities of information we receive.

Data communications and networking is a truly global area of study, both because the technology enables global communication and because new technologies and applications often emerge from a variety of countries and spread rapidly around the world. The World Wide Web, for example, was born in a Swiss research lab, was nurtured through its first years primarily by European universities, and exploded into mainstream popular culture because of a development at an American research lab.

One of the problems in studying a global phenomenon lies in explaining the different polit- ical and regulatory issues that have evolved and currently exist in different parts of the world. Rather than attempt to explain the different paths taken by different countries, we have chosen simplicity instead. Historically, the majority of readers of previous editions of this book have come from North America. Therefore, although we retain a global focus on technology and its business implications, we focus mostly on North America.

This book answers three fundamental questions. First, how does the Internet work? When you access a website using your computer, laptop,

iPad, or smartphone, what happens so that the page opens in your Web browser? This is the focus in Chapters 1–5. The short answer is that the software on your computer (or any device) creates a message composed in different software languages (HTTP, TCP/IP, and Ethernet are common) that requests the page you clicked. This message is then broken up into a series of smaller parts that we call packets. Each packet is transmitted to the nearest router, which is a special-purpose computer whose primary job is to find the best route for these packets to their final destination. The packets move from router to router over the Internet until they reach the Web server, which puts the packets back together into the same message that your computer created. The Web server reads your request and then sends the page back to you in the same way—by composing a message using HTTP, TCP/IP, and Ethernet and then sending it as a series of smaller packets back through the Internet that the software on your computer puts together into the page you requested. You might have heard a news story that the U.S. or Chinese government can read your email or see what websites you’re visiting. A more shocking truth is that the person sitting next you at a coffee shop might be doing exactly the same thing—reading all the packets that come from or go to your laptop. How is this possible, you ask? After finishing Chapter 5, you will know exactly how this is possible.

Second, how do I design a network? This is the focus of Chapters 6–10. We often think about networks in four layers. The first layer is the Local Area Network, or the LAN (either wired or wireless), which enables users like you and me to access the network. The second is the backbone network that connects the different LANs within a building. The third is the core network that connects different buildings on a company’s campus. The final layer is connections we have to the other campuses within the organization and to the Internet. Each of these layers has slightly different concerns, so the way we design networks for them and the technologies we use are

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Introduction 3

slightly different. Although this describes the standard for building corporate networks, you will have a much better understanding of how your wireless router at home works. Perhaps more importantly, you’ll learn why buying the newest and fastest wireless router for your house or apart- ment is probably not a good way to spend your money.

Finally, how do I manage my network to make sure it is secure, provides good performance, and doesn’t cost too much? This is the focus of Chapters 11 and 12. Would it surprise you to learn that most companies spend between $1,500 and $3,500 per computer per year on network man- agement and security? Yup, we spend way more on network management and security each year than we spend to buy the computer in the first place. And that’s for well-run networks; poorly run networks cost a lot more. Many people think network security is a technical problem, and, to some extent, it is. However, the things people do and don’t do cause more security risks than not hav- ing the latest technology. According to Symantec, one of the leading companies that sell antivirus software, about half of all security threats are not prevented by their software. These threats are called targeted attacks, such as phishing attacks (which are emails that look real but instead take you to fake websites) or ransomware (software apps that appear to be useful but actually lock your computer and demand a payment to unlock it). Therefore, network management is as much a people management issue as it is a technology management issue.

By the time you finish this book, you’ll understand how networks work, how to design net- works, and how to manage networks. You won’t be an expert, but you’ll be ready to enter an organization or move on to more advanced courses.

MANAGEMENT

FOCUS

1-1 Career Opportunities

It’s a great time to be in information technology (IT)! The technology-fueled new economy has dramatically increased the demand for skilled IT professionals. Accord- ing to the U.S. Bureau of Labor Statistics and Career Profiles (http://www.careerprofiles.info), 2 out of 10 fastest grow- ing occupations are computer network administrator and computer systems analyst, which is expected to grow by 22% over the next 10 years with an annual median salary of $72,500—not counting bonuses. There are two reasons for this growth. First, companies have to continuously upgrade their networks and thus need skilled employees to support their expanding IT infrastructure. Second, people are spending more time on their mobile devices, and because employers are allowing them to use these personal devices at work (i.e., BYOD, or bring your own device), the network infrastructure has to support the data that flow from these devices as well as to make sure that they don’t pose a security risk.

With a few years of experience, there is the possibility to work as an information systems manager, for which the median annual pay is as high as $117,780. An information systems manager plans, coordinates, and directs IT-related

activities in such a way that they can fully support the goals of any business. Thus, this job requires a good understanding not only of the business but also of the technology so that appropriate and reliable technology can be implemented at a reasonable cost to keep everything operating smoothly and to guard against cybercriminals.

Because of the expanding job market for IT and networking-related jobs, certifications become important. Most large vendors of network technologies, such as the Microsoft Corporation and Cisco Systems Inc., provide certification processes (usually a series of courses and formal exams) so that individuals can document their knowledge. Certified network professionals often earn $10,000 to $15,000 more than similarly skilled uncertified professionals—provided that they continue to learn and maintain their certification as new technologies emerge.

Adapted from: http://jobs.aol.com, “In Demand Careers That Pay $100,00 a Year or More”; www.careerpath.com, “Today’s 20 Fastest-Growing Occupations”; www.cnn.com, “30 Jobs Needing Most Workers in Next Decade,” http://www.careerprofiles.info/top-careers.html.

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4 Chapter 1 Introduction to Data Communications

1.2 DATA COMMUNICATIONS NETWORKS Data communications is the movement of computer information from one point to another by means of electrical or optical transmission systems. Such systems are often called data communications networks. This is in contrast to the broader term telecommunications, which includes the transmission of voice and video (images and graphics) as well as data and usually implies longer distances. In general, data communications networks collect data from personal computers and other devices and transmit those data to a central server that is a more powerful personal computer, minicomputer, or mainframe, or they perform the reverse process, or some combination of the two. Data communications networks facilitate more efficient use of computers and improve the day-to-day control of a business by providing faster information flow. They also provide message transfer services to allow computer users to talk to one another via email, chat, and video streaming.

TECHNICAL

FOCUS

1-1 Internet Domain Names

Internet address names are strictly controlled; otherwise, someone could add a computer to the Internet that had the same address as another computer. Each address name has two parts, the computer name and its domain. The general format of an Internet address is therefore com- puter.domain. Some computer names have several parts separated by periods, so some addresses have the format computer.computer.computer.domain. For example, the main university Web server at Indiana University (IU) is called www.indiana.edu, whereas the Web server for the Kelley School of Business at IU is www.kelley.indiana.edu.

Since the Internet began in the United States, the American address board was the first to assign domain names to indicate types of organizations. Some common U.S. domain names are as follows:

EDU for an educational institution, usually a university

COM for a commercial business GOV for a government department or agency MIL for a military unit ORG for a nonprofit organization

As networks in other countries were connected to the Internet, they were assigned their own domain names. Some international domain names are as follows:

CA for Canada AU for Australia UK for the United Kingdom DE for Germany

New top-level domains that focus on specific types of businesses continue to be introduced, such as the following:

AERO for aerospace companies MUSEUM for museums NAME for individuals PRO for professionals, such as

accountants and lawyers BIZ for businesses

Many international domains structure their addresses in much the same way as the United States does. For example, Australia uses EDU to indicate academic institu- tions, so an address such as xyz.edu.au would indicate an Australian university.

For a full list of domain names, see www.iana.org/domains/root/db.

1.2.1 Components of a Network There are three basic hardware components for a data communications network: a server (e.g., personal computer, mainframe), a client (e.g., personal computer, terminal), and a circuit (e.g., cable, modem) over which messages flow. Both the server and client also need special-purpose network software that enables them to communicate.

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Data Communications Networks 5

File server

Web server

Mail server

Client computers

Wireless access point

Printer

Client computers

To other networks (e.g., the Internet)

SwitchSwitch

Router

FIGURE 1-1 Example of a local area network (LAN)

The server stores data or software that can be accessed by the clients. In client–server com- puting, several servers may work together over the network with a client computer to support the business application.

The client is the input–output hardware device at the user’s end of a communication circuit. It typically provides users with access to the network and the data and software on the server.

The circuit is the pathway through which the messages travel. It is typically a copper wire, although fiber-optic cable and wireless transmission are becoming common. There are many devices in the circuit that perform special functions such as switches and routers.

Strictly speaking, a network does not need a server. Some networks are designed to connect a set of similar computers that share their data and software with each other. Such networks are called peer-to-peer networks because the computers function as equals, rather than relying on a central server to store the needed data and software.

Figure 1-1 shows a small network that has several personal computers (clients) connected through a switch and cables (circuit) and wirelessly through a wireless access point(AP). In this network, messages move through the switch to and from the computers. The router is a special device that connects two or more networks. The router enables computers on this network to communicate with computers on the same network or on other networks (e.g., the Internet).

The network in Figure 1-1 has three servers. Although one server can perform many functions, networks are often designed so that a separate computer is used to provide different services. The file server stores data and software that can be used by computers on the network. The Web server stores documents and graphics that can be accessed from any Web browser, such as Internet Explorer. The Web server can respond to requests from computers on this net- work or any computer on the Internet. The mail server handles and delivers email over the network. Servers are usually personal computers (often more powerful than the other personal computers on the network) but may be mainframes too.

1.2.2 Types of Networks There are many different ways to categorize networks. One of the most common ways is to look at the geographic scope of the network. Figure 1-2 illustrates three types of networks: local area

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6 Chapter 1 Introduction to Data Communications

Records building

Hangars

Fire station

Flight building

Runway checkout

Backbone network (BN) at the McClellan Air Force Base—one node of the Sacramento

metropolitan area network (MAN).

Gateway to Sacramento metropolitan area network

Main gate

Records Local area network (LAN) at the Records Building—one node

of the McClellan Air Force Base backbone network (BN).

Web server

Router

Switch

Wide area network (WAN) showing Sacramento connected to nine other cities throughout the United States.

Evanston, Ill.

Miami, Fla. Houston, Tex.

Phoenix, Ariz.

Sacramento, Calif. (Capitol)

Portland, Oreg.

Seattle, Wash.

Golden, Colo.

Ontario, N.Y.

Sudbury, Mass.

FIGURE 1-2 The hierarchical relationship of a LAN to a BN to a WAN. BAN = backbone network; LAN = local area network; WAN = wide area network

networks (LANs), backbone networks (BNs), and wide area networks (WANs). The distinctions among these are becoming blurry because some network technologies now used in LANs were originally developed for WANs, and vice versa. Any rigid classification of technologies is certain to have exceptions.

A local area network (LAN) is a group of computers located in the same general area. A LAN covers a clearly defined small area, such as one floor or work area, a single building, or a group of buildings. The upper-left diagram in Figure 1-2 shows a small LAN located in the records building at the former McClellan Air Force Base in Sacramento. LANs support high-speed data transmission compared with standard telephone circuits, commonly operating 100 million bits per second (100 Mbps). LANs and wireless LANs are discussed in detail in Chapter 6.

Most LANs are connected to a backbone network (BN), a larger, central network connecting several LANs, other BNs, MANs, and WANs. BNs typically span from hundreds of feet to several miles and provide very high-speed data transmission, commonly 100–1,000 Mbps. The second diagram in Figure 1-2 shows a BN that connects the LANs located in several buildings at McClellan Air Force Base. BNs are discussed in detail in Chapter 7.

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Network Models 7

Wide area networks (WANs) connect BNs and MANs (see Figure 1-2). Most organizations do not build their own WANs by laying cable, building microwave towers, or sending up satellites (unless they have unusually heavy data transmission needs or highly specialized requirements, such as those of the Department of Defense). Instead, most organizations lease circuits from IXCs (e.g., AT&T, Sprint) and use those to transmit their data. WAN circuits provided by IXCs come in all types and sizes but typically span hundreds or thousands of miles and provide data transmission rates from 64 Kbps to 10 Gbps. WANs are discussed in detail in Chapter 8.

Two other common terms are intranets and extranets. An intranet is a LAN that uses the same technologies as the Internet (e.g., Web servers, Java, HTML [Hypertext Markup Language]) but is open to only those inside the organization. For example, although some pages on a Web server may be open to the public and accessible by anyone on the Internet, some pages may be on an intranet and therefore hidden from those who connect to the Web server from the Internet at large. Sometimes, an intranet is provided by a completely separate Web server hidden from the Internet. The intranet for the Information Systems Department at Indiana University, for example, provides information on faculty expense budgets, class scheduling for future semesters (e.g., room, instructor), and discussion forums.

An extranet is similar to an intranet in that it, too, uses the same technologies as the Internet but instead is provided to invited users outside the organization who access it over the Internet. It can provide access to information services, inventories, and other internal organizational databases that are provided only to customers, suppliers, or those who have paid for access. Typically, users are given passwords to gain access, but more sophisticated technologies such as smart cards or special software may also be required. Many universities provide extranets for Web-based courses so that only those students enrolled in the course can access course materials and discussions.

1.3 NETWORK MODELS There are many ways to describe and analyze data communications networks. All networks pro- vide the same basic functions to transfer a message from sender to receiver, but each network can use different network hardware and software to provide these functions. All of these hardware and software products have to work together to successfully transfer a message.

One way to accomplish this is to break the entire set of communications functions into a series of layers, each of which can be defined separately. In this way, vendors can develop software and hardware to provide the functions of each layer separately. The software or hardware can work in any manner and can be easily updated and improved, as long as the interface between that layer and the ones around it remains unchanged. Each piece of hardware and software can then work together in the overall network.

There are many different ways in which the network layers can be designed. The two most important network models are the Open Systems Interconnection Reference (OSI) model and the Internet model. Of the two, the Internet model is the most commonly used; few people use the OSI model, although understand it is commonly required for network certification exams.

1.3.1 Open Systems Interconnection Reference Model The Open Systems Interconnection Reference model (usually called the OSI model for short) helped change the face of network computing. Before the OSI model, most commercial networks used by businesses were built using nonstandardized technologies developed by one vendor (remember that the Internet was in use at the time but was not widespread and certainly was not commercial). During the late 1970s, the International Organization for Standardization (ISO) created the Open System Interconnection Subcommittee, whose task was to develop a framework of standards for computer-to-computer communications. In 1984, this effort produced the OSI model.

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FIGURE 1-3 Network models. OSI = Open Systems Interconnection Reference

OSI Model

7. Application Layer

6. Presentation Layer

5. Session Layer

4. Transport Layer

3. Network Layer

2. Data Link Layer

1. Physical Layer

Internet Model Groups of Layers

5. Application Layer Application

Layer

Internetwork Layer

Hardware Layer

Examples

Internet Explorer and Web pages

TCP/IP software

Ethernet port, Ethernet cables,

and Ethernet software drivers

4. Transport Layer

3. Network Layer

2. Data Link Layer

1. Physical Layer

The OSI model is the most talked about and most referred to network model. If you choose a career in networking, questions about the OSI model will be on the network certification exams offered by Microsoft, Cisco, and other vendors of network hardware and software. However, you will probably never use a network based on the OSI model. Simply put, the OSI model never caught on commercially in North America, although some European networks use it, and some network components developed for use in the United States arguably use parts of it. Most networks today use the Internet model, which is discussed in the next section. However, because there are many similarities between the OSI model and the Internet model, and because most people in networking are expected to know the OSI model, we discuss it here. The OSI model has seven layers (see Figure 1-3).

Layer 1: Physical Layer The physical layer is concerned primarily with transmitting data bits (zeros or ones) over a communication circuit. This layer defines the rules by which ones and zeros are transmitted, such as voltages of electricity, number of bits sent per second, and the physical format of the cables and connectors used.

Layer 2: Data Link Layer The data link layer manages the physical transmission circuit in layer 1 and transforms it into a circuit that is free of transmission errors as far as layers above are con- cerned. Because layer 1 accepts and transmits only a raw stream of bits without understanding their meaning or structure, the data link layer must create and recognize message boundaries; that is, it must mark where a message starts and where it ends. Another major task of layer 2 is to solve the problems caused by damaged, lost, or duplicate messages so the succeeding layers are shielded from transmission errors. Thus, layer 2 performs error detection and correction. It also decides when a device can transmit so that two computers do not try to transmit at the same time.

Layer 3: Network Layer The network layer performs routing. It determines the next computer to which the message should be sent, so it can follow the best route through the network and finds the full address for that computer if needed.

Layer 4: Transport Layer The transport layer deals with end-to-end issues, such as procedures for entering and departing from the network. It establishes, maintains, and terminates logical connec- tions for the transfer of data between the original sender and the final destination of the message. It is responsible for breaking a large data transmission into smaller packets (if needed), ensuring that all the packets have been received, eliminating duplicate packets, and performing flow control

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Network Models 9

to ensure that no computer is overwhelmed by the number of messages it receives. Although error control is performed by the data link layer, the transport layer can also perform error checking.

Layer 5: Session Layer The session layer is responsible for managing and structuring all sessions. Session initiation must arrange for all the desired and required services between session partici- pants, such as logging on to circuit equipment, transferring files, and performing security checks. Session termination provides an orderly way to end the session, as well as a means to abort a session prematurely. It may have some redundancy built in to recover from a broken transport (layer 4) connection in case of failure. The session layer also handles session accounting so the correct party receives the bill.

Layer 6: Presentation Layer The presentation layer formats the data for presentation to the user. Its job is to accommodate different interfaces on different computers so the application program need not worry about them. It is concerned with displaying, formatting, and editing user inputs and outputs. For example, layer 6 might perform data compression, translation between different data formats, and screen formatting. Any function (except those in layers 1 through 5) that is requested sufficiently often to warrant finding a general solution is placed in the presentation layer, although some of these functions can be performed by separate hardware and software (e.g., encryption).

Layer 7: Application Layer The application layer is the end user’s access to the network. The primary purpose is to provide a set of utilities for application programs. Each user pro- gram determines the set of messages and any action it might take on receipt of a message. Other network-specific applications at this layer include network monitoring and network management.

1.3.2 Internet Model The network model that dominates current hardware and software is a more simple five-layer Internet model. Unlike the OSI model that was developed by formal committees, the Internet model evolved from the work of thousands of people who developed pieces of the Internet. The OSI model is a formal standard that is documented in one standard, but the Internet model has never been formally defined; it has to be interpreted from a number of standards. The two models have very much in common (see Figure 1-3); simply put, the Internet model collapses the top three OSI layers into one layer. Because it is clear that the Internet has won the “war,” we use the five-layer Internet model for the rest of this book.

Layer 1: The Physical Layer The physical layer in the Internet model, as in the OSI model, is the physical connection between the sender and receiver. Its role is to transfer a series of electrical, radio, or light signals through the circuit. The physical layer includes all the hardware devices (e.g., computers, modems, and switches) and physical media (e.g., cables and satellites). The physical layer specifies the type of connection and the electrical signals, radio waves, or light pulses that pass through it. Chapter 3 discusses the physical layer in detail.

Layer 2: The Data Link Layer The data link layer is responsible for moving a message from one computer to the next computer in the network path from the sender to the receiver. The data link layer in the Internet model performs the same three functions as the data link layer in the OSI model. First, it controls the physical layer by deciding when to transmit messages over the media. Second, it formats the messages by indicating where they start and end. Third, it detects and may correct any errors that have occurred during transmission. Chapter 4 discusses the data link layer in detail.

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Layer 3: The Network Layer The network layer in the Internet model performs the same func- tions as the network layer in the OSI model. First, it performs routing, in that it selects the next computer to which the message should be sent. Second, it can find the address of that computer if it doesn’t already know it. Chapter 5 discusses the network layer in detail.

Layer 4: The Transport Layer The transport layer in the Internet model is very similar to the transport layer in the OSI model. It performs two functions. First, it is responsible for linking the application layer software to the network and establishing end-to-end connections between the sender and receiver when such connections are needed. Second, it is responsible for breaking long messages into several smaller messages to make them easier to transmit and then recombining the smaller messages back into the original larger message at the receiving end. The transport layer can also detect lost messages and request that they be resent. Chapter 5 discusses the transport layer in detail.

Layer 5: Application Layer The application layer is the application software used by the net- work user and includes much of what the OSI model contains in the application, presentation, and session layers. It is the user’s access to the network. By using the application software, the user defines what messages are sent over the network. Because it is the layer that most people under- stand best and because starting at the top sometimes helps people understand better, Chapter 2 begins with the application layer. It discusses the architecture of network applications and several types of network application software and the types of messages they generate.

Groups of Layers The layers in the Internet are often so closely coupled that decisions in one layer impose certain requirements on other layers. The data link layer and the physical layer are closely tied together because the data link layer controls the physical layer in terms of when the physical layer can transmit. Because these two layers are so closely tied together, decisions about the data link layer often drive the decisions about the physical layer. For this reason, some people group the physical and data link layers together and call them the hardware layers. Likewise, the transport and network layers are so closely coupled that sometimes these layers are called the internetwork layers. (see Figure 1-3). When you design a network, you often think about the network design in terms of three groups of layers: the hardware layers (physical and data link), the internetwork layers (network and transport), and the application layer.

1.3.3 Message Transmission Using Layers Each computer in the network has software that operates at each of the layers and performs the functions required by those layers (the physical layer is hardware, not software). Each layer in the network uses a formal language, or protocol, that is simply a set of rules that define what the layer will do and that provides a clearly defined set of messages that software at the layer needs to understand. For example, the protocol used for Web applications is HTTP (Hypertext Transfer Protocol, which is described in more detail in Chapter 2). In general, all messages sent in a network pass through all layers. All layers except the physical layer create a new Protocol Data Unit (PDU) as the message passes through them. The PDU contains information that is needed to transmit the message through the network. Some experts use the word packet to mean a PDU. Figure 1-4 shows how a message requesting a Web page would be sent on the Internet.

Application Layer First, the user creates a message at the application layer using a Web browser by clicking on a link (e.g., get the home page at www.somebody.com). The browser translates the user’s message (the click on the Web link) into HTTP. The rules of HTTP define a specific PDU—called an HTTP packet—that all Web browsers must use when they request a Web page.

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Network Models 11

Application Layer

Transport Layer

Network Layer

Data Link Layer Ethernet IP TCP RequestHTTP

IP TCP RequestHTTP

TCP RequestHTTP

Request Packet

Segment

Packet

Frame

Bit

HTTP

Physical Layer

Sender PDU Receiver

Application Layer

Transport Layer

Network Layer

Data Link Layer Ethernet IP TCP RequestHTTP

IP TCP RequestHTTP

TCP RequestHTTP

RequestHTTP

Physical Layer

FIGURE 1-4 Message transmission using layers. IP = Internet Protocol; HTTP = Hypertext Transfer Protocol; TCP = Transmission Control Protocol

For now, you can think of the HTTP packet as an envelope into which the user’s message (get the Web page) is placed. In the same way that an envelope placed in the mail needs certain informa- tion written in certain places (e.g., return address, destination address), so too does the HTTP packet. The Web browser fills in the necessary information in the HTTP packet, drops the user’s request inside the packet, then passes the HTTP packet (containing the Web page request) to the transport layer.

Transport Layer The transport layer on the Internet uses a protocol called TCP (Transmission Control Protocol), and it, too, has its own rules and its own PDUs. TCP is responsible for breaking large files into smaller packets and for opening a connection to the server for the transfer of a large set of packets. The transport layer places the HTTP packet inside a TCP PDU (which is called a TCP segment), fills in the information needed by the TCP segment, and passes the TCP segment (which contains the HTTP packet, which, in turn, contains the message) to the network layer.

Network Layer The network layer on the Internet uses a protocol called IP (Internet Protocol), which has its rules and PDUs. IP selects the next stop on the message’s route through the net- work. It places the TCP segment inside an IP PDU, which is called an IP packet, and passes the IP packet, which contains the TCP segment, which, in turn, contains the HTTP packet, which, in turn, contains the message, to the data link layer.

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12 Chapter 1 Introduction to Data Communications

Data Link Layer If you are connecting to the Internet using a LAN, your data link layer may use a protocol called Ethernet, which also has its own rules and PDUs. The data link layer formats the message with start and stop markers, adds error checks information, places the IP packet inside an Ethernet PDU, which is called an Ethernet frame, and instructs the physical hardware to trans- mit the Ethernet frame, which contains the IP packet, which contains the TCP segment, which contains the HTTP packet, which contains the message.

Physical Layer The physical layer in this case is network cable connecting your computer to the rest of the network. The computer will take the Ethernet frame (complete with the IP packet, the TCP segment, the HTTP packet, and the message) and send it as a series of electrical pulses through your cable to the server.

When the server gets the message, this process is performed in reverse. The physical hard- ware translates the electrical pulses into computer data and passes the message to the data link layer. The data link layer uses the start and stop markers in the Ethernet frame to identify the message. The data link layer checks for errors and, if it discovers one, requests that the message be resent. If a message is received without error, the data link layer will strip off the Ethernet frame and pass the IP packet (which contains the TCP segment, the HTTP packet, and the message) to the network layer. The network layer checks the IP address and, if it is destined for this computer, strips off the IP packet and passes the TCP segment, which contains the HTTP packet and the message, to the transport layer. The transport layer processes the message, strips off the TCP seg- ment, and passes the HTTP packet to the application layer for processing. The application layer (i.e., the Web server) reads the HTTP packet and the message it contains (the request for the Web page) and processes it by generating an HTTP packet containing the Web page you requested. Then the process starts again as the page is sent back to you.

The Pros and Cons of Using Layers There are three important points in this example. First, there are many different software packages and many different PDUs that operate at different layers to successfully transfer a message. Networking is in some ways similar to the Russian matryoshka, nested dolls that fit neatly inside each other. This is called encapsulation, because the PDU at a higher level is placed inside the PDU at a lower level so that the lower-level PDU encapsulates the higher-level one. The major advantage of using different software and protocols is that it is easy to develop new software, because all one has to do is write software for one level at a time. The developers of Web applications, for example, do not need to write software to perform error checking or routing, because those are performed by the data link and network layers. Developers can simply assume those functions are performed and just focus on the application layer. Similarly, it is simple to change the software at any level (or add new application protocols), as long as the interface between that layer and the ones around it remains unchanged.

Second, it is important to note that for communication to be successful, each layer in one com- puter must be able to communicate with its matching layer in the other computer. For example, the physical layer connecting the client and server must use the same type of electrical signals to enable each to understand the other (or there must be a device to translate between them). Ensur- ing that the software used at the different layers is the same as accomplished by using standards. A standard defines a set of rules, called protocols, that explain exactly how hardware and software that conform to the standard are required to operate. Any hardware and software that conform to a standard can communicate with any other hardware and software that conform to the same standard. Without standards, it would be virtually impossible for computers to communicate.

Third, the major disadvantage of using a layered network model is that it is somewhat inef- ficient. Because there are several layers, each with its own software and PDUs, sending a message involves many software programs (one for each protocol) and many PDUs. The PDUs add to the

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Network Standards 13

total amount of data that must be sent (thus increasing the time it takes to transmit), and the different software packages increase the processing power needed in computers. Because the pro- tocols are used at different layers and are stacked on top of one another (take another look at Figure 1-4), the set of software used to understand the different protocols is often called a protocol stack.

1.4 NETWORK STANDARDS 1.4.1 The Importance of Standards Standards are necessary in almost every business and public service entity. For example, before 1904, fire hose couplings in the United States were not standard, which meant a fire department in one community could not help in another community. The transmission of electric current was not standardized until the end of the nineteenth century, so customers had to choose between Thomas Edison’s direct current (DC) and George Westinghouse’s alternating current (AC).

The primary reason for standards is to ensure that hardware and software produced by different vendors can work together. Without networking standards, it would be difficult—if not impossible—to develop networks that easily share information. Standards also mean that customers are not locked into one vendor. They can buy hardware and software from any vendor whose equipment meets the standard. In this way, standards help to promote more competition and hold down prices.

The use of standards makes it much easier to develop software and hardware that link different networks because software and hardware can be developed one layer at a time.

1.4.2 The Standards-Making Process There are two types of standards: de jure and de facto. A de jure standard is developed by an official industry or a government body and is often called a formal standard. For example, there are de jure standards for applications such as Web browsers (e.g., HTTP, HTML), for network layer soft- ware (e.g., IP), for data link layer software (e.g., Ethernet IEEE 802.3), and for physical hardware (e.g., V.90 modems). De jure standards typically take several years to develop, during which time technology changes, making them less useful.

De facto standards are those that emerge in the marketplace and are supported by several ven- dors but have no official standing. For example, Microsoft Windows is a product of one company and has not been formally recognized by any standards organization, yet it is a de facto standard. In the communications industry, de facto standards often become de jure standards once they have been widely accepted.

The de jure standardization process has three stages: specification, identification of choices, and acceptance. The specification stage consists of developing a nomenclature and identifying the problems to be addressed. In the identification of choices stage, those working on the standard iden- tify the various solutions and choose the optimum solution from among the alternatives. Accep- tance, which is the most difficult stage, consists of defining the solution and getting recognized industry leaders to agree on a single, uniform solution. As with many other organizational pro- cesses that have the potential to influence the sales of hardware and software, standards-making processes are not immune to corporate politics and the influence of national governments.

International Organization for Standardization One of the most important standards-making bodies is the International Organization for Standardization (ISO), which makes technical rec- ommendations about data communication interfaces (see www.iso.org). ISO is based in Geneva,

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14 Chapter 1 Introduction to Data Communications

Switzerland. The membership is composed of the national standards organizations of each ISO member country.

International Telecommunications Union-Telecommunications Group The International Telecommunications Union-Telecommunications Group (ITU-T) is the technical standards- setting organization of the United Nations International Telecommunications Union, which is also based in Geneva (see www.itu.int). ITU is composed of representatives from about 200 member countries. Membership was originally focused on just the public telephone companies in each country, but a major reorganization in 1993 changed this, and ITU now seeks members among public- and private-sector organizations who operate computer or communications networks (e.g., RBOCs) or build software and equipment for them (e.g., AT&T).

American National Standards Institute The American National Standards Institute (ANSI) is the coordinating organization for the U.S. national system of standards for both technology and nontechnology (see www.ansi.org). ANSI has about 1,000 members from both public and private organizations in the United States. ANSI is a standardization organization, not a standards-making body, in that it accepts standards developed by other organizations and publishes them as Amer- ican standards. Its role is to coordinate the development of voluntary national standards and to

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1-2 How Network Protocols Become Standards

There are many standards organizations around the world, but perhaps the best known is the Internet Engineering Task Force (IETF). IETF sets the standards that govern how much of the Internet operates.

The IETF, like all standards organizations, tries to seek consensus among those involved before issuing a standard. Usually, a standard begins as a protocol (i.e., a language or set of rules for operating) developed by a vendor (e.g., HTML). When a protocol is proposed for standardization, the IETF forms a working group of technical experts to study it. The working group examines the protocol to identify potential problems and possible extensions and improve- ments, and then issues a report to the IETF.

If the report is favorable, the IETF issues a Request for Comment (RFC) that describes the proposed standard and solicits comments from the entire world. Most large software companies likely to be affected by the proposed standard prepare detailed responses. Many “regular” Inter- net users also send their comments to the IETF.

The IETF reviews the comments and possibly issues a new and improved RFC, which again is posted for more comments. Once no additional changes have been identi- fied, it becomes a proposed standard.

Usually, several vendors adopt the proposed standard and develop products based on it. Once at least two ven- dors have developed hardware or software based on it and it has proven successful in operation, the proposed stan- dard is changed to a draft standard. This is usually the final specification, although some protocols have been elevated to Internet standards, which usually signifies mature stan- dards not likely to change.

The process does not focus solely on technical issues; almost 90% of the IETF’s participants work for manufacturers and vendors, so market forces and politics often complicate matters. One former IETF chairperson who worked for a hardware manufacturer has been accused of trying to delay the standards process until his company had a product ready, although he and other IETF members deny this. Likewise, former IETF directors have complained that members try to standardize every product their firms produce, leading to a proliferation of standards, only a few of which are truly useful.

Sources: “How Networking Protocols Become Standards,” PC Week, March 17, 1997; “Growing Pains,” Network World, April 14, 1997.

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Network Standards 15 MANAGEMENT

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1-3 Keeping Up with Technology

The data communications and networking arena changes rapidly. Significant new technologies are introduced and new concepts are developed almost every year. It is there- fore important for network managers to keep up with these changes.

There are at least three useful ways to keep up with change. First and foremost for users of this book is the website for this book, which contains updates to the book, additional sections, teaching materials, and links to useful websites.

Second, there are literally hundreds of thousands of websites with data communications and networking

information. Search engines can help you find them. A good initial starting point is the telecom glossary at http:// www.atis.org. Three other useful sites are http://www.zdnet .com, http://www.networkcomputing.com, and http://www .zdnet.com.

Third, there are many useful magazines that discuss computer technology in general and networking tech- nology in particular, including Network Computing, Info World, Info Week, and CIO Magazine.

interact with the ISO to develop national standards that comply with the ISO’s international rec- ommendations. ANSI is a voting participant in the ISO.

Institute of Electrical and Electronics Engineers The Institute of Electrical and Electronics Engineers (IEEE) is a professional society in the United States whose Standards Association (IEEE-SA) develops standards (see www.standards.ieee.org). The IEEE-SA is probably most known for its standards for LANs. Other countries have similar groups; for example, the British counterpart of IEEE is the Institution of Electrical Engineers (IEE).

Internet Engineering Task Force The Internet Engineering Task Force (IETF) sets the stan- dards that govern how much of the Internet will operate (see www.ietf.org). The IETF is unique in that it doesn’t really have official memberships. Quite literally anyone is welcome to join its mail- ing lists, attend its meetings, and comment on developing standards. The role of the IETF and other Internet organizations is discussed in more detail in Chapter 8; also, see the box entitled “How Network Protocols Become Standards.”

1.4.3 Common Standards There are many different standards used in networking today. Each standard usually covers one layer in a network. Some of the most commonly used standards are shown in Figure 1-5. At this point, these models are probably just a maze of strange names and acronyms to you, but by the end of the book, you will have a good understanding of each of these. Figure 1-5 provides a brief road map for some of the important communication technologies we discuss in this book.

For now, there is one important message you should understand from Figure 1-5: For a net- work to operate, many different standards must be used simultaneously. The sender of a message must use one standard at the application layer, another one at the transport layer, another one at the network layer, another one at the data link layer, and another one at the physical layer. Each layer and each standard is different, but all must work together to send and receive messages.