Douglas Comer, best-selling networking author, teacher, and consultant, provides a unique and understandable overview ofnot only how to use the Internet but how it works. In the Third Edition of The INTERNET Book, the author utilizes a non-technical perspective to explain the technology of how computers communicate, what the Internet is, how the Internet works, and what the Internet can do for people. The author's Practical approach offers the reader the big picture by presenting a solid overview of networking and the Internet rather than burying the reader with details. This book shows the reader the potential ways the Internet can changer how we conduct our personal and professional lives. Comer assumes no prior background knowledge in computer networking or the Internet.

Douglas Comer is a professor of comPuter science at Purdue University, where he teaches courses on comPuter operang systems and internetworking. One of the researchers who contributed to the Internet as it was being formed in the late 1970s and 1980s, he has served as a member of the Internet Architecture Board, the group responsible for guiding the Inteme's development. In addition, he has written a popular series of textbooks that describe the technical details of the Internet, and Presents lectures on the subject around the world. He is a Fellow of The Association for Compuhng Machinery (the maor Professional society in computer science) and editor of the scientific journal, Software--Practice and ExPerience.
　　Professor Come has had Intemet access from his home since the late 1970s, has had a direct connechon with twenty-four hour per day servlce smce 198l, and uses the Internet daily. His connection currently Operasat 2.24 million bitS per second, appoximately fifty hmes faster than a dial-up modem. He wrote this book as a response to everyone who has asked him for an explanation of the Internet that is both technically correct and easily understood by anyone. An Intemet enthusiasL Comer displays MT on the license plate of his car.
　　More infOnnaon can be found at:
　　http://www.cs. purdue. edu/people/comer

The Internet Book explains how computers cornmunicate, what the Internet is, how the Internet works, and what services the Internet offers you. It is designed for readers who do not have a strong techoical background--early chapters cleary explain the terndnology and concepts needed to understand all the services. When you finish reading,you will understand the technology behind the Internet, will appreciate how the Internet can be used, and discover why People find it so exciting. In addition, you will understand the origins of the Internet and see how rapidly it has grown.
　　Instead of using mathematics, algorithIns, or computer programs, the book uses analogies from everyday life to explain technology. For examPle, to explain why digital conununication is superior to analog, the text uses an analogy of sending signals throgh fog with a flashlight. To explain how audio can be plnyed back for the user at a steady rate when packets arrive in clumps, the text uses th6 analogy of many gallons of milk Arriving at a supermarket in one shipment, but being sold one gallon at a time.
　　In addihon to explaining the services users encounter such as e-mail, file transfer,and web browsing, the text covers key networking concepts such as packet switching,Local fora Networks, Protocol software, and domain names. More important, the text builds on fundamentals -- it describes basic Internet communication faCilihes first, and then shows how the basic facilities are used to provide a variety of services. Finally,the book includes an extensive glossny of technical terms with easy-to-understand definitions; readers are encouraged to consult the glossare as they read.
　　The third edition retains the same generai str'UctUre as the previous edihon, but ds four new chapters and updates material throughout. Chapter 2 surveys a variety of Web sites, and encourages readers to begin exploring the Web while they read. The other for new chapters are espeCially significant. Chapter 14 covers Internet connection technologies, including ADSL and cable modems, technologies which are now available to consumers. Chapters 29 and 30 cover the related topics of security and ecommerce, both of which are increasingly important. Chapter 29 explains encryption technology,and Chapter 30 shows how the technology is used to conduct business.
　　As with the previous edihon, the book is divided into four main parts. The first part begins with fundamental concepts such as digital and analog comznunicaton. It bo iwtuces packet switching, and explains the Local Ar6a Network techoologies that are used in most businesses.
　　The second part of the book gives a short history of the Internet rescarch Project and the development of the Internet. Although most of the history can be skipped,readers should pay attention to the Phenomenal growth rate, which demnstrates that the technology was designed incredibly well -- no other communication technology has remained as unchanged through such rapid growth.
　　The thitd part of the book explains how the Internet works, including a description of the two fundrnental Protocols used by all services: the Internet Protocol(IP) and the Transmission Control Protocol (TCP). Although they omit technical detalls, the chapters in this pat allow students to understand the essenhal role of each protocol and gain perspechve on the overall design.
　　The fourth part of the boOk exarnines services available on the Internet. In addihon to covering browsers, plugins, CGI, and seareh engines used with the Word Wide Web, chaPters discuss e-mail, network newsgfOups, file and fax transfer, and audio and video conununicahon. In each case, the text explains how the service oPerates and how it uses facilihes in the underiying system.
　　The Internet Book makes an excellent reference text for a college-Ievel course on the Internet. Although Presented in a nonteChnical manner, the materiai is scientifically accurate. More important, in the twenty-first century, an educated person will need to know more than how to use a browser or set up a Web page -- they should have some understanding of what goes on behind the scenes. They can acquire such knowledge from this text.
　　Instructors are encouraged to combine classroom lectures with laboratory sessions in which students see and use the technology first-hand. In all courses, eary labs should focus on exPloring a vedety of services, including sending e-mail, using a browser, using a search engine, downloading files via FTP, listening to audio, and using an IP telephone, if one is available. I encourage all students, even those who have no interest in computers, to build a trivial Wed page by hand. In eddihon to helping them see the relahonship between tags in an HTML document and thC resulting displny, it shows students how a server transfers files on a computer disk to a browser. Seeing the relahonship in labs helps students better understand as they reed about the underiying process.
　　Lab projects later in the semester dePend on the type of course. Business-oriented courses often focus stUdents on using the Internet -- labs require studentS to search the Internet for iofonnation and then use the information to write a short paper. Other courses use labs to focus on tools such as Programs used to create a Web page. Some courses combine both by having students search for information and then create a Web page that contalns linds to the ioformation. In any case, we have found that stubents enter Internet courses with genuine enthusiasm and motivation; a professor's task is merely to provide perspective and reInind students throughout the semester why the Intemt is so exciting.
　　The author thanks many People who have contributed to editions of this book.John Lin, Keith Rovell, Rob Slade, and ChristoPh Schuba read early versions and mede suggeshons. Dwight Baznette, George Polyzo, Donald Knudson, Daie Musser, and Dennis Rny sent the publisher reviews Of a Previous edhon. Scott Comer Provided a student persPeCtive. As always, my wife, Chris, carefully edited the manuscript, solved many probems, and improved the wording.

Douglas E. Comer
March, 2000

Douglas E.Comer：Douglas E.Comer: 美国普度大学教授，著名的网络技术专家。他每年都要向学生、专业人士等讲授计算机网络和Internet课程。他编写的《TCP/IP网际互联》（3卷本）、《计算机网络和因特网》等都是非常受欢迎的著作。他是对20世纪70年代末期和80年代因特网的形成有杰出贡献的研究人员之一。他还供职于因特网体系结构委员会（负责指导因特网发展的团体），是美国计算机学会的会员。

Chapter 1 The Internet Has Arrived
The World Is Changing
Numbers Do Not Tell The Story
Learning About The Internet
Undersranding The Big Picture
Terminology And Technology
Growth And Adaptability
The Impact of The Internet
Organization OfThe Book
A Personal Note
Chapter 2 Getting Staned: Hande-On Experience
Introduction
The Web: Sites And Pages
Web Browsers and Browsing
Using A Browser
Examples of Web Sites And Services
Summary
PART I Introduction To Networking
Chapter a Telephones Everywhere
Introduction
A Communication Service
Selling Communlcatlon
Limited Access
High Cost
The Difficulr Transition
Ubiquitous Access
Relevance To The Internet
Chapter 4 The World Was Once Analog
Introduction
Sound, Vibrations, And Analog Recording
Analog Electronic Devices
Many Electronic Devices Are Analog
The First Analog Communication
Analog Is Simple But Inaccurate
Sending An Analog Signal Across A Wire
Digital Music
The Digital Revolution
Computers Are Digital
Digital Recording
Using Digital To Recreate Analog
Why Digital Music
Summary
Chapter 5 The Once And Future Digital Network
Introduction
The World Was Once Digital
A Telegraph Is Digital
Morse Code
Letters And Digits In Morse Code
Users Did Not Encounter Morse Code
Virtually Instant Communication
Speed Is Relative
The Telephone Became Digital
Relevance To The Internet
Binary Encoding Of Data On The Internet
Why Use Two Symbols
Summary
Chapter 6 Basic Communication
Introduction
Communication Using Electricity
Signals On Wires
Information Coding
Modems Allow Two-Way Traffic
A Character Code For Digital Information
Dctecting Errors
Summary
Chapter 7 The Local Area Network Arrives
Introduction
Motivation
Interchangeable Media
A Computer Consists of Circuit Boards
Circuit Boards Plug Into A Computer
Connecting One Computer To Another
LAN Technologies
Connecting A Computer To A LAN
The Iniportance Of LAN Technology
Relationship To The Internet
PART II A Brief History Of The Internet
Chapter 8 Internet: The Early Yeare
Many Independent Networks
The Proliferation of LANs
Facts About LANs
LANs Are Incompatible
Wide Area Technologies Exist
Few WANs, Many LANs
WANs and LANs Are Incompatible
The Desirability Of A Single Network
The Department Of Defense Had Multiple Networks
Connecting Disconnected Machines
The Internet Emerges
The ARPANET Backbone
Intermet Software
The Name Is TCP/IP
The Shock Of An Open System
Open Systems Are Necessary
TCP/IP Documentation Is Online
The Militaty AdoptS TCP/IP
Summary
A Personal Note
Chapter 9 Two Decades Of Inctedible Growth
Introduction
Disseminating The Software
Meanwhile, Back In Computer Science
The Internet Meets UNIX
The U.S. Military Makes A Commionent
The Internet Doubles In Size In One Year
Every Computer Science Department
Graduate Students Volunteer Their Time
The IAB evolves
The IETF
Doubling Again In A Year
The Internet Improves Science
NSF Takes ,4 Leadership Role
Target: AII of Science And Engineering
NSF's Approach
The NSFNET Backbone
The ANS Backbone
Exponential Growth
A Commercial Assessment
The End of Growth
Chapter 10 The Global Internet
Introduction
Early ARPA Networks
Electronic Mail Among Computers
BITNET And FIDONET
Networks In Europe
EBONE: The Internet In Europe
Backbones And Internet Hierarchy
Internet On All Continents
The World Of lnternet after 1998
A Personal Note
Chapter 11 A Global Information Infrastrueture
Introduction
Existing Infrastructure
Communication Inpastructure
The Internet Infrastructure
The Internet Offers Diverse Informatiou Services
TCP/IP Provides Commmlication Facilities
A Personal Note
PART III How The Internet Works
Chapter 12 Paeket Switching
Introduction
Sharing Saves Money
Sharing Introduces Delays
Sharing Wires
Selectable Channels
Sharing By Taking Turns
Packet Switching Avoids Delays
Each Packct Must Be Labeled
Computers Have Addresses
Packets Are Not All The Same Size
Packet Transmission Seems Instantaneous
Sharing Is Automatic
Network Hardware Handles Sharing
Many Devices Can Use Packet Switching
Relevance To The Internet
Summary
Chapter 19 Internet: A Network Of Networks
Introduction
Network Technologies Are Incompatible
Coping With Incompatibility
Two Fundamental Concepts
Using A Computer To Interconnect Networks
Interconnecting Computers Pass Packets
Interconnecting Computers Are Called Routers
Routers Are The Building Blocks of The Internet
Routers Acconunadate Multiple Types Of Networks
Routers Can Interconnect WAVs And LANs
Interconnecting Networks Was Revolutionary
Summary
Chapter 14 ISPs And Network Conneetions
Introduction
Internet Service Providers And Fees
Customer Connections Form The Last Mile
Lased Circuits Are Exprensive
Most Individuals Choose Dial-up Access
The Important Concept of Continuous Connectivity
Instantaneous Access Changes Use
Newer Technologies Offer Inexpensive Dedicated Access
Wireless Can Reach Everyone
A Personal Note
Chapter 15 IP: Software To Create A Virtual Network
Introduction
Protocol: An Agreement For Communication
Basic Functionality: The Internet Protocol
IP Software On Every Machine
Internet Packets Are Called Datagrams
The Illusion Of A Giant Network
The Reality Of lnternal Structure
Datagrams Travel In Packets
Every Computer Is Assigned A Unique Address
Internet Addresses
An Odd IP Address Syntax
IP Addresses Are Not Random
An Example Trip Through The Internet
Summary
Chapter 16 TCP: Software Fer Rellable Communicatien
Introduction
A Packet Switching System Can Be Overrun
TCP Helps IP Guarantee Delivery
TCP Provides A Connection Between Computer Programs
The Magic Of Recovering Last Datagrams
TCP Retransmission Is Automatic
TCP And IP Work Together
Summary
Chapter 17 Clients + Servere = Distributed Computing
Introduction
Large Computers Use Networks For Input And Output
Small Computers Use Networks To Interact
Distributed Computing On The Internet
A Single Paradigm Explains AIl Distributed Computing
Progrants Are Clients Or Servers
A Server Must Always Run
Summary
Chapter 18 Names For Computers
Introduction
People Prefer Names To Numbers
Naming A Computer Can Be Difficult Or Fun
Computer Names Must Be Unique
Suffixes On Compufer Names
Names With Many Parts
Domain Names Outside The US
Translating A Name To An Equivalent IP Address
Domain Name System Works Like Directory Assistance
Computer Name Lookup Is Automatic
IP Addresses And Domain Names Are Unrelated
Summary
Chapter 19 Why The Internet Worke Well
Introduction
The Internet Work Well
IP Provides Flexibility
TCP Provides Reliability
TCP/IP Software Was Engineered For Efficiency
TCP/IP Research Emphasized Practical Results
The Formula For Success
Summary
PART IV Services Available On The Internet
Chapter 20 Electronie Mail
Introduction
Description Of Functionality
The Best Of All Worlds
Each User Has A Mailbox For E-mail
Sending An E-mail Message
Notification That E-mail has Arrived
Reading An E-mail Message
E-mail Messages Look Like Interoffice Memos
E-mail Software Fills In Header Information
How E-mail Works
Using E-mail From A Personal Computer
Mailbox Address Format
Abbreviations Make E-mail Friendly
Aliases Permit Arbitrary Abbreviations
Aliases Shared By All Users Of A Computer System
Sending To Multiple Recipients
Mailing List: An Alias for Multiple Recipients
Public Mailing Lists And Mail Exploders
E-mail To And From Non-Internet Sites
Access To Services Via E-mail
Speed, Reliability, And Expectations
Impact And Significance OIP Electronic Mail
Joining A Mailing List
Chapter 21 Bulletin Board Serviee (Network News)
Introduction
Description of Functionalify
Many Bulletin Boards With Diverse Topics
Network News
Newsgroup Names
Obtaining Network News And The Software To Read Articles
How Network News Appears To A User
Checking For News Articles
Article Expiration