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`THE INTERNE;
`
`
`
`Illustrated by MICHAEL TROLLER
`
`GOOGLE 1005
`
`GOOGLE 1005
`
`1
`
`

`

`ABOUT THE AUTHOR
`
`
`
`Preston Gralla is the awardawimiing author of 20 books, including
`How Wireless Works, How To Expand and Upgrade PCs, and The
`Complete Idiot’s Guide to Protecting Yourself Online. He is an executive
`editor and columnist for CNet and ZDNet; is a technology colum—
`nist for the Dallas Morning News; and has written about technology
`for many magazines and newspapers, including USA Today, PC
`Magazine, the Los Angeles Times, Boston Magazine, PClComputing,
`Computerworld, and FamilyPC among many others. Gralla has won
`several writing and editing awards, including one from the
`Computer Press Association for the best feature article in a com—
`puter magazine.
`
`Ala wellilcnoivn expert on computers and the Internet, he has
`appeared frequently on numerous TV and radio shows and nemorks,
`including the CBS Early Show, CNN, National Public Radio’s All
`Things Considered, MSNBC, CNBC, TechTV, and CNet Radio.
`
`He was the founding managing editor of the well—known newspaper
`PC Week and a founding editor of PC/Computing. Under his
`editorship, PC/Compua'ng was a finalist for General Excellence from
`thouNational Magazine Awards.
`
`Gralla lives in Cambridge, Massachusetts, with his wife Lydia,
`children Gabriel and Mia, and a rabbit named Polichinelle. He also
`writes the free Gralla’s Intemet Insider e—mail newsletter. To subscribe
`
`to it for free, send an e—mail to preston©gralla.com with the words
`SUBSCRIBE NETINSIDER on the subject line.
`
`2
`
`

`

`How the
`
`Internet
`
`Works
`
`Sixth Edition
`
`
`
`3
`
`

`

`
`
`4
`
`

`

`How the
`
`Internet
`
`W0rks
`
`Edltm
`
`Preston Gralla
`
`ree
`
`Indianapol iiiiiiiiii
`
`5
`
`

`

`6
`
`

`

`How the Internet Works, Sixth Edition
`Copyright © 2002 by Que
`
`Associate Publisher
`
`Acquisitions Editor
`
`Development Editor
`Managing Editor
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`Project Editor
`
`Production Editors
`
`Indexer
`
`Technical Editor
`
`Illustrator
`
`Team Coordinator
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`Page Layou:
`
`Greg Wiegand
`
`Stephanie J. McComb
`
`Nicholas J. Goetz
`Thomas F. Hayes
`
`Karen S. Shields
`
`Megan Wade
`AmyJay
`Erika Millen
`
`Chris Faust
`
`Michael Troller
`
`Sharry Lee Gregory
`
`Gloria Schurick
`
`All rights reserved. No part of this book shall be reproduced, stored in a retrieval system, or transmitted by any means,
`electronic, mechanical, photocopying, recording, or otherwise, without written permission from the publisher. No patent
`liability is assumed with respect to the use of the information contained herein. Although every precaution has been taken in
`the preparation of this book, the publisher and author assume no responsibility for errors or omissions. Nor is any liability
`assumed for damages resulting from the use of the information contained herein.
`International Standard Book Number: 0-7897-2582-7
`
`Library of Congress Catalog Card Number: 20-0I087727
`Printed in the United States of America
`
`First Printing: September, 200i
`04
`03
`02 0|
`4
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`I
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`Trademarks
`All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Que
`cannot attest to the accuracy of this information. Use of a term in this book should not be regarded as affecting the validity of
`any trademark or service mark.
`
`Warning and Disclaimer
`Every effort has been made to make this book as complete and as accurate as possible, but no warranty or fitness is implied.
`The information provided is on an “as is" basis. The author and the publisher shall have neither liability nor responsibility to any
`person or entity with respect to any loss or damages arising from the information contained in this book.
`
`7
`
`

`

`vi
`
`TABLE 05? tam-EN 18
`
`Introduction
`
`Part I: Understanding the
`Internet’s Underlying
`Architecture
`
`Chapter 1
`What Is the Internet?
`
`Chapter 2
`How Computer Networks Send Data
`Across the Internet
`
`Chapter 3
`How TCP/IP Works
`
`Chapter 4
`Understanding the Internet’s Software
`Structure
`
`Chapter 5
`How Internet Addresses and
`Domains Work
`
`Chapter 6
`How Routers Work
`
`Chapter 7
`How Internet File Types Work
`
`Chapter 13
`How You Connect to the Internet from
`
`Online Services
`
`Chapter 14
`How Wireless and Palmtop Connections
`Work
`
`Chapter 15
`How Home Networks Work
`
`64
`
`68
`
`78
`
`Part 3: Communicating on
`the Internet
`
`84
`
`12
`
`16
`
`20
`
`28
`
`32
`
`Chapter 16
`How E—mail Works
`
`Chapter 17
`How E—mail Spam Works
`
`Chapter 18
`How Newsgroups Work
`
`Chapter 18
`How Internet Chat and Instant
`
`Messaging Work
`
`Chapter 20
`How Internet Phone Calls Work
`
`88
`
`100
`
`106
`
`110
`
`116
`
`Part 2: Connecting to the
`Internet
`
`36
`
`Part 4: Using the World
`Wide Web
`
`I 22
`
`Chapter 8
`How Computers Connect to
`the Internet
`
`Chapter 9
`How a Modern Works
`
`Chapter 10
`How Internet/Television Connections
`Work
`
`Chapter 11
`How the Digital Subscriber Line (DSL)
`Works
`
`Chapter 12
`How ISDN Works
`
`4O
`
`44
`
`48
`
`56
`
`60
`
`Chapter 21
`How Web Pages Work
`
`Chapter 22
`How Web Browsers Work
`
`Chapter 23
`How Markup Languages Work
`
`Chapter 24
`How Hypertext Works
`
`Chapter 25
`How URLs Work
`
`Chapter 26
`How Image Maps and Interactive
`Forms Work
`
`126
`
`134
`
`140
`
`148
`
`152
`
`156
`
`8
`
`

`

`Chapter 27
`How Web Host Servers Work
`
`Chapter 28
`How Web Sites Work with Databases
`
`Chapter 29
`How InternetrBased Software Works
`
`160
`
`164
`
`168
`
`Part 5: Using Common
`Internet Tools
`
`I 72
`
`Chapter 30
`How Tenet Works
`
`Chapterfl31
`How FTP Downloading Works
`
`Chapter 32
`How Internet Searching Works
`
`Chapter 33
`How Agents Work
`
`Chapter 34
`How Java, ActiveX, and JavaScript
`Work
`
`Chapter 35
`How CGI Scripting Works
`
`176
`
`180
`
`186
`
`192
`
`196
`
`204
`
`Part 6: Enjoying
`Entertainment and
`
`Multimedia on the
`
`Internet
`
`208
`
`Chapter 36
`How Music and Audio Work on
`
`the Internet
`
`~Chapter31..
`How Napster and File Sharing Work
`
`Chapter 38
`How Video on the Internet Works
`
`Chapter 39
`How Multicast IP and the MBone
`Work
`
`212
`
`220
`
`224
`
`232
`
`Chapter 40
`How Virtual Reality Works
`
`Chapter 41
`Animation on the Web
`
`236
`
`240
`
`Part 7: Shopping and Doing
`Business on the
`
`lnte rnet
`
`248
`
`Chapter 42
`How Intranets Work
`
`Chapter 43
`Shopping on the Internet
`
`252
`
`258
`
`Part 8: Protecting Yourself
`on the Internet
`268
`
`Chapter 44
`How Firewalls Work
`
`Chapter 45
`How Hackers Can Cripple the Internet
`and Attack Your PC
`
`Chapter 46
`How Viruses Work
`
`Chapter 47
`How Internet Sites Can Invade
`
`Your Privacy
`
`Chapter 48
`Cryptography, Privacy, and Digital
`Certificates
`
`Chapter 49
`How the FBI’s “Carnivore” Program
`Works
`
`cameras
`Parental Controls on the Internet
`
`Glossary
`
`Index
`
`272
`
`280
`
`286
`
`292
`
`302
`
`308
`
`312
`
`3 16
`
`326
`
`9
`
`

`

`
`
`Acknowledgments
`
` book like the Internet, is a collaborative work My name might be on the cover, but I am far
`from the only person involved in its creation
`
`Development editor Nick Goetz managcd to pull together all the elements of a complex project, all
`the while keeping a cool head, improving the illustrations, and offering editorial insight and help. And
`acquisitions editor Stephanie McComb was instrumental in getting the book off the ground, and as al—
`ways, was a pleasure to work with.
`
`The illustrator for the book, Michael Troller, deserves much thanks. Not only did he create new il’
`lustrations from scratch specifically for this book, he redid all the ones from past books and made this
`edition a more coherent, richer, more visually pleasing experience.
`
`Thanks also go to illustrators of past editions: Mina Reimer, Sarah Ishida, Shelly Norris, and Stephen
`Adams. And many thanks to the entire team at Que who produced the book, including Karen Shields,
`Megan Wade, Amy Jay, Gloria Schurick, and Erika Millen.
`
`Thanks also have to go to the many, many people I interviewed for this book. People from
`Quarterdeck Corporation, Chaco Communications, Progressive Networks, White Pine Software,
`Microsoft, Netscape, Headspace, Surf\X/atch Software, WebTV, Accrue, VDONet Corporation, America
`Online, Yahool, Hilgraeve, Fairmarket, eWallet, and Nuborn Technologies are only a few of the folks
`who gave their time to help me understand the nitty—gritty of how various Internet technologies work.
`Tim Smith from ZDNet offered me Vital help as well.
`
`I gleaned much information from the many FAQs and similar documents widely available on the
`Internet. I’d like to thank the anonymous authors of those documents, whoever they are.
`
`Many thanks go to Chris Faust, the technical editor for the book, who did a superb job of ensuring
`that I always got the information right
`
`Finally, big thanks have to go to my wife, Lydia She put up with those occasionnal glassy=eyed looks
`that were replies to simple questions like,Did you leave your keysin the refrigerator again?” She also
`endured my extreme absent'mindedness while I was figuring out ways to explain how firewalls, ISDN, or
`Web robots work when I should have been concentrating on more immediate matters.
`
`10
`
`10
`
`

`

`Tell Us What You Think!
`
`Al the reader of this book, you are our most important critic and commentator. We value your opinion
`and want to know what we’re doing right, what we could do better, what areas you’d like to see us pub;
`fish in, and any other words of wisdom you’re willing to pass our way.
`
`As an associate publisher for Que, I welcome your comments. You can fax, email, or write me di»
`rectly to let me know what you did or didn’t like about this book—as well as what we can do to make
`our books stronger.
`
`Please note that I cannot help you with technical problems related to the topic of this book, and
`that due to the high volume of mail I receive, 1 might not be able to reply to every message.
`
`When you write, please be sure to include this book’s title and author as well as your name and
`phone or fax number. I will carefully review your comments and share them with the author and editors
`who worked on the book.
`
`Fax:
`
`317681—4666
`
`E—mail:
`
`feedback@quepublishing.com
`
`Mail:
`
`Greg Wiegand
`Associate Publisher
`
`Que
`201 West 103rd Street
`
`Indianapolis, IN 46290 USA
`
`11
`
`11
`
`

`

`
`
`Introduction
`
`3% the course of cruising the World Wide Web and clicking a link, have you ever wondered,
`
`“How does that work?” Or perhaps this question popped into your mind while you were trans—
`
`ferring a file to your computer via FTP, or reading a newsgroup message. or when you first
`
`heard about technologies such as spam, cookies, and firewalls. Maybe you’ve wondered how
`
`a message sent from your computer travels through the vastness of cyberspace and ends up
`
`in the right email box halfway across the world. Have you ever wanted to know how search
`
`tools find the exact piece of information you want out of the millions of pieces of information
`
`on the whole Internet.7 How can you listen to music and view animations while surfing the
`Web?
`
`This book is designed for everyone interested in the Internet. Its guiding principle is this:
`
`No matter how much of a cyberpro you are—or how much of a novice—there’s a lot you
`
`don’t understand about the Internet. Here’s just one small example. I have a friend who has
`
`made his living with companies involved with the Internet for many years. He’s a complete
`
`cyberpro who lives and breathes the Internet. One day, he almost whispered to me, “I don’t
`
`like to admit this, but I don’t know what a proxy server is. How does it work, anyway?”
`
`He’s not alone. The Internet changes so quickly and the technology advances so rapidly
`
`that it can seem almost impossible to keep up with all of it. If you’re like just about everyone
`
`else involved in the Internet, your questions are similar to those of my friend. You’ll find your
`answers here.
`
`In Part 1, “Understanding the Internet’s Underlying Architecture,” I explain the underlyr
`
`ing basics of the Internet: who runs it, how TCP/IP works, how to understand Internet
`
`addresses and domains, and similar topics. Here’s where you’ll find out about things such as
`
`routers and how the client/server architecture underpins virtually every aspect of the Internet.
`
`Part 2, “Connecting to the Internet,” depicts the various ways you can connect your com—
`
`puter to the Internet. Here’s where to turn if you’re interested in any of the following topics:
`
`how a cable modem, a digital subscriber line (DSL), or ISDN works; how online services cone
`
`nect to the Internet; how you can connect by satellite to the Internet; how “palmtop” com~
`
`puters, such as 3COM’s Palm, can browse the Web; how a modem works; how you can access
`
`the Internet from your own home network; and a host of similar subjects.
`
`Part 3, “Communicating on the Internet,” covers every aspect of Internet communica’
`
`tions. It shows how email and newsgroups work, how IRC chat works, what email “spam” is
`
`and what you can do to prevent it, how instant messaging works, and how you can use the
`
`Internet to make telephone calls anywhere in the world.
`
`12
`
`12
`
`

`

`
`
`Part 4, “Using the World Wide Web,” covers what has become by far the most popular
`
`part of the Internet—the World Wide Web. You’ll learn virtually every aspect of how the
`
`Web works. It delves into how browsers work, how Web server software works, and how
`
`Hypertext Markup Language (HTML) works. This section also covers the ways in which the
`
`Web is becoming integrated directly into your computer, how Web pages are published and
`
`organized on a site, and every other aspect of the Web that is likely to be of interest to you.
`
`Part 5, “Using Common Internet Tools,” takes a close look at common Internet tools.
`
`Here’s the place to learn about basic tools and services, such as telnet, and what happens
`
`when you use FTP to download a file to your computer. You’ll also learn how search engines
`
`and search tools work. And it’s the section of the book that covers cutting’edge Internet
`technology. You’ll find out about how push technology works, how the Java and ActiveX pro—
`
`gramming languages work, how JavaScript works, how agents can silently do your bidding for
`
`you, and how the Common Gateway Interface (CGI) works, which is a little’known but vital
`
`part of the Internet.
`
`Part 6, “Enjoying Entertainment and Multimedia on the Internet,” shows you how some
`
`of the most exciting parts of the Internet work—the various multimedia technologies.
`
`Whether you want to know how virtual reality or animations work, how streaming video
`
`works, how videoconferencing works, or how similar technologies work, you’ll find it all here.
`
`Part 7, “Shopping and Doing Business on the Internet,” covers intranets, how the
`
`Internet works with the outside world, and how you can shop online. You’ll see how compa’
`
`nies use Internet technologies to build their own private networks, called intranets. And you’ll
`
`take a close look at the underlying technologies that let you shop on the Web, which
`
`accounts for billions of dollars a year in sales.
`
`Finally, Part 8, “Protecting Yourself on the Internet,” covers security concerns. It explains
`
`the controversial cookie technology that lets Web servers put bits of information on your
`
`hard disk and use that information to track you. It explains how the even’more controversial
`
`FBI system called Carnivore can in essence wiretap people’s use of the Internet to read their
`
`e—mail, watch their Web browsing, and more. This part also shows how firewalls work, how
`
`viruses can attack your computer, and how cryptosystems allow confidential information to
`
`be sent across the Internet. It delves into how hackers can attack Internet service providers
`
`(lSl’s) using so’called “smurf attacks,” and how they can attack your computer as well. And it
`
`covers the issue of pornography on the Internet and shows how parental’control software can
`
`prevent children from seeing objectionable material.
`
`80, come along and see how the vast Internet works. Even if you’re a cyberpro (and espe—
`
`cially if you’re not), you’ll find out a lot you never knew.
`
`13
`
`13
`
`

`

`PART I
`
`UNDERSTANDING THE INTERNET’S UNDERLYING ARCHITECTURE
`
`
`
`14
`
`14
`
`

`

`UNDERSTANDING
`
`THE INTERN ET’S
`
`UNDERLYING
`
`ARCHITECTURE
`
`Chapter 1: What Is the Internet?
`4
`
`Chapter 2: How Computer Networks Send Data Across
`the Internet
`8
`
`Chapter 3: How TCP/IP Works
`12
`
`Chapter 4: Understanding the Internet’s Software Structure
`16
`
`Chapter 5: How Internet Addresses and Domains Work
`20
`
`Chapter 6: How Routers Work
`28
`
`Chapter 7: How Internet File Types \‘Vork
`32
`
`15
`
`15
`
`

`

`
`
`
`
` I ' P Pl” the first time ever, the world is at your fingertips. From your computer, you can find
`
`information about anything you can name or even imagine. You can communicate with
`
`people on the other side of the world. You can set up a teleconference, tap into the resources
`
`of powerful computers anywhere on the globe, search through the world’s best libraries, and
`
`visit the world’s most amazing museums. You can watch videos, listen to music, and read sper
`
`cial multimedia magazines. You can shop for almost anything you can name. You can do all
`
`this by tapping into the largest computer network in the world—the Internet.
`
`The Internet isn’t a single network; it is a vast, globe—spanning network of networks. No
`
`single person, group, or organization runs the Internet. Instead, it’s the purest form of elec‘
`
`tronic democracy. The networks communicate with one another based on certain protocols,
`
`such as the Transmission Control Protocol (TCP) and the Internet Protocol (IP). More and
`
`more networks and computers are being hooked up to the Internet every day. Tens of thou;
`
`sands of these networks exist, ranging from university networks to corporate local area net;
`
`works to large online services such as America Online and CompuServe. Every time you tap
`
`int 3 the Internet, your own computer becomes an extension of that network.
`
`The first section of this book is spent defining the Internet. It also examines the architec—
`
`tures, protocols, and general concepts that make it all possible.
`
`Chapter I, “What Is the Internet?,” examines how the Internet runs. You’ll look at who
`
`pays for the high’speed data backbones that carry much of the Internet’s traffic and at the
`
`organizations that ensure that standards are set for networks to follow so the Internet can run
`
`smoothly. You’ll also look at the various types of networks connected to the Internet.
`
`Chapter 2, “How Computer Networks Send Data Across the Internet,” explains how
`
`information travels across the Internet and describes how hardware such as routers, repeaters,
`
`and bridges sends information among networks. It also shows how smaller networks are
`
`grouped into larger regional networks—and how those large regional networks communicate
`
`among themselves.
`
`Chapter 3, “How TCP/IP Works,” covers the Internet’s basic protocols for communica—
`
`tions. You’ll learn a little about basic Internet jargon, such as TCP/IP (short for Transmission
`
`Control Protocol and Internet Protocol). This chapter also explains how those protocols work
`
`and how special software such as Winsock enables personal computers to get onto a network
`
`originally designed for larger computers.
`
`Chapter 4, “Understanding the Internet’s Software Structure,” looks at the Internet’s
`
`client/server architecture. Sewers—also called hosts—are powerful computers that perform
`
`functions such as delivering information or Web pages, hosting databases, and handling
`
`email. A client is your own computer and the software that sits on it, such as a Web browser
`
`16
`
`16
`
`

`

`
`
`or piece of email software. Clients request information from servers, which do the heavy—
`
`duty processing and then send the information back to the client, which displays the infor—
`mation.
`
`Chapter 5, “How Internet Addresses and Domains Work,” takes the mystery out of the
`
`Internet’s often confusing addressing scheme. You’ll learn about Internet domains and
`
`addresses and will even be able to make sense of them. More than that, you’ll learn how
`
`domain servers are capable of keeping track of all the locations on the Internet and translat—
`
`ing addresses such as w. zdnet . com into Internet IP addresses such as 134 .54 . 56 . 120.
`
`You’ll also learn how some computers are assigned new IP addresses by special servers every
`
`time they connect to the Internet.
`
`Chapter 6, “How Routers Work,” details how the most basic piece of hardware on the
`
`Internet—a router—works. RouLe'rs are combinations of hardware and software that perform
`
`the job of ensuring that all data is sent to the proper destination. Think of routers as traffic
`
`cops of the Internet. They use the IP addresses the name servers have translated to route the
`data. Routers look at the addresses and then send the data to the next—closest router to the
`
`destination and so on, until the data is finally delivered. They use routing tables to determine
`
`how to route the traffic, and they can also adjust the routes as the traffic on the Internet
`
`changes, thus ensuring that the data is routed in the most efficient way possible.
`
`Chapter 7, “How Internet File Types Work,” gives you an understanding of the most com—
`
`mon types of files you’ll come across when you browse the Net. Compressed files, video files,
`
`graphics files—you’ll learn about almost every type of file you might encounter.
`
`Whether you’re a newbie or cyberpro, this section teaches you the basics of the Internet.
`
`17
`
`17
`
`

`

`”APT” What Is the
`
`Internet?
`
`
`
`18
`
`

`

`
`
`GN E of the most frequently asked questions about the Internet is: Who runs it? The truth is that no cen—
`tralized management of the Internet exists. Instead, it is a collection of thousands of individual networks
`
`and organizations, each of which is run and paid for on its own. Each network cooperates with other net,
`
`works to direct Internet traffic so that information can pass among them. Together, these networks and orga—
`nizations make up the wired world of the Internet. For networks and computers to cooperate in this way,
`however, a general agreement must take place about things such as Internet procedures and standards for
`
`protocols. These procedures and standards are laid out in requests for comment (RFCs) that are agreed on by
`Internet users and organizations.
`
`A variety of groups guide the Internet’s growth by helping to establish standards and by educating people
`on the proper wayto use the Internet. Perhaps the most important is the Internet Society, a private, non—
`profit group. The Internet Society supports the work of the Internet Activities Board (IAB), which handles
`
`much of the Internet’s behind—the»scenes and architectural issues. The Internet Engineering Task Force
`(IETF) is responsible for overseeing how the Internet’s TCP/IP protocols evolve. For information about the
`IETF, go to www. ietf . or‘g.(See Chapter 3, “How TCP/IP Works,” for details on TCP/IP protocols.)
`
`The World Wide Web Consortium (W3C) develops standards for the evolution of the fastest—growing
`
`part of the Internet, the World Wide Web (find it at www.w3 . or‘g). The W3C is an industry consortium run
`by the Laboratory for Computer Science at the Massachusetts Institute of Technology (MIT).
`
`Private companies oversee the registering of Internet domains, such as w. zdnet . com or
`
`www. quepublishing . com. These companies, called registrars, all must cooperate with one another to
`
`ensure that only one person or company can own a particular domain and that all the domains work prop—
`erly. The registrars compete with one another as well in allowing people and businesses to register domains.
`Registering a domain costs money, and the registrars compete on cost and on giving extra services to those
`
`who buy domains.
`
`Although all these types of organizations are important for holding together the Internet, at the heart of
`
`the Internet are individual local networks. These networks can be found in private companies, universities,
`government agencies, and online services. They are funded separately from each other and in a variety of
`manners, such as fees from users, corporate support, taxes, and grants. Many Internet service providers
`(ISPs), which provide Internet access for individuals, have networks as well. Individuals who want to access
`
`the Internet pay ISPs a monthly connection rate, so in that sense, everyone who uses the Internet helps pay
`for it.
`
`The networks are connected in a variety of ways. For efficiency’s sake, local networks join in consortiums
`known as regional networks. A variety of leased lines connect regional and local networks. The leased lines
`
`that connect networks can be as simple as a single telephone line or as complex as a fiber—optic cable with
`microwave links and satellite transmissions.
`
`Private companies who make money by selling access to their lines build backbones, which are very high
`capacity lines that carry enormous amounts of Internet traffic. Government agencies, such as NASA, and
`
`large private corporations pay for some of these backbones. The National Science Foundation also pays for
`some backbones.
`
`19
`
`19
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`

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`PART I UNDERSTANDING THE INTERNET’S UNDERLYING ARCHITECTURE
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`How the Internet Cemes Together-
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`Organization of networks Because the Internet is a loose organization'of—networks, no single groUp
`runs it or pays for it all. Instead, many private organizations, universities, and government agencies pay
`for and run parts of It. Ihey all work together In a democratic, IoCIsely organized alliance. Private organi—
`zations range from small, homegrown networksto commercial online services, such as‘America Online
`and CompuServe, and private Internet serVICe prbIQders (ISPs) that sell access to the Internet.
`\
`.
`Funding thUlntemet Through agencies such as the National Science ,
`
`Foundation, the federal government pays for some high-speed backbones that
`carry‘lmernet traffic across the oeuntry and the world. The high-speed vBNS (very
`, “
`high-speed Backbone Network Services), forexample, proVides
`@ a high-speed infrastructure for the, research and education
`_
`community by linking together supercomputer centers.
`,5
`, Often, a large corporation or organization such as
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`NASA provides backbones to link sites acrOss the
`country or the world. The government has
`‘ also funded the Internet2, a super-fast net—
`, work that canr’t/ransfer data at an
`I astounding 2.4 grgaabits per second,
`@ vereities already are connected to it. When
`for use by universiti s. A number of uni-
`Eventually, therentire Internet might run at its speed.
`
`finished in 2003, it will link 140 universities.
`
`Regional Network
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`Regional networks
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`RegIonaI networks prOVIde
`and marntam '"te’F‘et access
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`have. banded ‘09 her to
`prQVIde better serVI e.
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`Private companiescalled
`,7 Registrars
`Internet registrars are responsible for
`registeringInternet domains, such as
`7
`WWW.zdnet.com, to people andbusinesses.
`Until Fe\entlv,ia quasI-public Company
`called the InterNIC hadsole responsibility
`for doing this, but other registrars can
`now register'domains as well-
`‘.
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`
`20
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`20
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`registries. It tracks the connections
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`betw en Internet addresses, suchas
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`perta'n to the Internet, such as how
`TCP/I and other Internet protocols
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`21
`
`21
`
`

`

`
`
`CHAPTER How Computer
`2
`Networks Send
`Data Across
`
`the Internet
`
`
`
`22
`
`22
`
`

`

`_
`
`YOU might take for granted that when you send a piece of information across the Internet, it will always
`reach its intended destination. However, the process of sending that information is remarkably complex.
`
`When you send information across the Internet, the Transmission Control Protocol (TCP)—the language
`
`computers use when communicating over the Internet—first breaks the information up into packets, smaller
`
`blocks of information that also contain a variety of data that helps the packets travel across the Internet.
`
`Your computer sends those packets to your local network, Internet service provider (ISP), or online service.
`
`From there, the packets travel through many levels of networks, computers, and communications lines
`
`before they reach their final destinations, which might be across town or around the world. A variety of
`
`hardware processes those packets and routes them to their proper destinations. This hardware is designed to
`transmit data between networks and makes up much of the glue that holds the Internet together. Five of the
`
`most important pieces of hardware are hubs, bridges, gateways, repeaters, and routers.
`
`Hubs are important because they link groups of computers to one another and let computers communi«
`cate with each other. Bridges link local area networks (LANs) with one another. They enable data destined
`
`for another LAN to be sent there, while keeping local data inside its own network. Gateways are similar to
`
`bridges, but they also translate data from one type of network to another.
`
`When data travels across the Internet, it often crosses great distances, which can be a problem because
`
`the signal sending the data can weaken over the distance. To solve the problem, repeaters amplify the data at
`
`intervals so the signal doesn’t weaken.
`
`Routers play a key role in managing Internet traffic. Their job is to ensure the packets always arrive at
`
`the proper destination. If data is being transferred among computers that are on the same LAN, routers
`often aren’t necessary because the network itself can handle its internal traffic. Routers come into play when
`
`the data is sent between two different networks. Routers examine packets to determine their destinations.
`
`They take into account the volume of activity on the Internet, and they send the packet to another router
`
`that is closer to the packet’s final destination. For more information on routers see Chapter 6, “How Routers
`Wor .”
`
`All this hardware connects the many networks that make up the Internet. At the most local level of net;
`
`works are corporate local area networks. Midlevel networks hook these LANs together using high’speed
`
`telephone lines, ethernet, and microwave links. A regional network is a midlevel network in a geographic
`
`area. A wide area network (WAN) is another type of midlevel network. A WAN consists of an organization
`
`with many networked sites linked together.
`
`When a packet travels from a computer on a LAN in a midlevel network to a computer somewhere else
`on the midlevel network, a router (or a series of routers) sends thc packet to its proper destination. However,
`
`if the destination lies outside the midlevel network, the packet is sent to a network access point (NAP),
`
`where it is sent across the country or the world on a backbone. High—speed backbones such as the VBNS
`
`(very high/speed Backbone Network Services) can transmit enormous amounts of data—155 megabits (mil—
`lions of bits) per second (Mbps). Even faster backbones are being built that will transmit data at an astonish»
`
`ing 9.6 billion bits per second.
`
`23
`
`23
`
`

`

` ‘ . n! ear”
`
`to
`IPA-RT I unnausfl-uumsfmelittle-tiers UNfifikLYING ARCHITECTURE *
`
`
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`Dial Up
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`1
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`Server
`
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`“k"
`
`You get onto the Internet through a LAN at
`your home or place of business in one of two
`ways. You can dial into a large computer con—
`
`
`nected to the Internet via an online service or a
`
`’
`
`Token-Ring Network
`
`{mm ,
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`
`s
`
`
`
`dial-in Internet service provider (ISP), or you can
`
`use another type of Internet service, such as a
`
`cable modem. Ethernet networks and token—ring
`
`networks are two types of networks that
`
`
`can be connected to the Internet. Token-
`ring networks pass data in tokens from
`
`computer to computer in a ring or star
`Satelfite
`
`configuration. In Ethernet networks,
`Link
`the data goes from a server
`
`to a co