Interriel Wteea
`the
`“How
`ehind‘this -wondertt
`lat
`love from
`one
`
`o
`
`THEINTERNET
`_WORKS
`
`GOOGLE 1005
`
`Illustrated by MICHAEL TROLLER
`
`GOOGLE 1005
`
`1
`
`

`

`ABOUT THE AUTHOR
`
`
`
`Preston Gralla is the award-winning 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, PC/Computing,
`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.
`Asa well-known expert on computers and the Internet, he has
`appeared frequently on numerous TV and radio shows and networks,
`including the CBS Early Show, CNN, National Public Radio’s All
`Things Considered, MSNBC, CNBC, TechTV, and CNetRadio.
`
`Hewas the founding managing editor of the well-known newspaper
`PC Week and a founding editor of PC/Computing. Underhis
`editorship, PC/Computing wasa finalist for General Excellence from
`the National 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 Internet Insider e-mail newsletter. To subscribe
`to it for free, send an e-mail to preston@gralla.com with the words
`SUBSCRIBE NETINSIDERonthe subjectline.
`
`2
`
`

`

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

`

`
`
`4
`
`

`

`How the
`internet
`Works
`
`1h Editios
`
`Preston Gralla
`
`ree
`
`Indianapolis, IN 46290
`
`5
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`

`

`6
`
`

`

`How the Internet Works, Sixth Edition
`Copyright © 2002 by Que
`
`Associate Publisher
`Acquisitions Editor
`Development Editor
`Managing Editor
`Project Editor
`Production Editors
`
`Indexer
`
`Technical Editor
`
`Illustrator
`
`Team Coordinator
`Page Layout
`
`Greg Wiegand
`Stephanie J. McComb
`NicholasJ. Goetz
`Thomas F. Hayes
`KarenS. 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. Noris anyliability
`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: 20-01087727
`Printed in the United States of America
`
`First Printing: September, 2001
`04
`03
`02 O|
`43 2
`
`)
`
`Trademarks
`All terms mentioned in this book that are known to be trademarks or service marks have been appropriately capitalized. Que
`cannotattest to the accuracy of this information. Use of a term in this book should not be regardedasaffecting the validity of
`any trademark or service mark.
`Warningand Disclaimer
`Every effort has been made to make this book as complete and as accurate as possible, but no warrantyorfitness is implied.
`The information provided is on an “as is” basis. The author and the publishershall have neither liability nor responsibility to any
`person or entity with respect to any loss or damagesarising from the information contained in this book.
`
`7
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`

`

`vi
`
`TABLE OF CONTENTS
`
`Introduction
`
`Part |: Understanding the
`Internet’s Underlying
`Architecture
`I
`
`Chapter |
`WhatIs 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
`Chapter6
`How Routers Work
`
`Chapter 7
`How Internet File Types Work
`
`4
`
`8
`
`12
`
`16
`
`20
`
`28
`
`32
`
`Chapter 13
`How You Connectto 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
`
`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
`
`122
`
`Chapter 8
`How Computers Connect to
`the Internet
`Chapter 9
`How a Modem Works
`Chapter 10
`How Internet/Television Connections
`Work
`Chapter 11
`How the Digital Subscriber Line (DSL)
`Works
`
`Chapter 12
`How ISDN Works
`
`40
`
`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 Mapsand Interactive
`Forms Work
`
`126
`
`134
`
`140
`
`148
`
`i352
`
`156
`
`8
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`

`

`Chapter 27
`How Web HostServers Work
`
`Chapter 28
`How WebSites Work with Databases
`Chapter 29
`HowInternet-Based Software Works
`
`160
`
`164
`
`168
`
`Part 5: Using Common
`Internet Tools
`
`172
`
`Chapter 30
`How Tenet Works
`
`Chapter31
`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
`Chapter 7..
`How Napster and File Sharing Work
`Chapter 38
`How Video on the Internet Works
`
`Chapter 39
`How Multicast IP and the MBone
`Work
`
`ztz
`
`220
`
`224
`
`gaz
`
`Chapter 40
`How Virtual Reality Works
`Chapter 41
`Animation on the Web
`
`236
`
`240
`
`Part 7: Shopping and Doing
`Business on the
`Internet
`
`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
`HowInternet Sites Can Invade
`Your Privacy
`Chapter 48
`Cryptography, Privacy, and Digital
`Certificates
`
`Chapter 49
`Howthe FBI’s “Carnivore” Program
`Works
`Chapter30"
`Parental Controls on the Internet
`
`Glossary
`Index
`
`BIZ
`
`280
`
`286
`
`292
`
`302
`
`308
`
`312
`
`316
`326
`
`9
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`
`
`#40: book,like the Internet, is a collaborative work. My name might be on the cover, but I am far
`from the only person involvedin its creation.
`Development editor Nick Goetz managcd to pull togetherall the elements of a complex project,all
`the while keeping a cool head, improvingthe illustrations, and offering editorial insight and help. And
`acquisitions editor Stephanie McComb was instrumentalin getting the book off the ground, andasal-
`ways, was a pleasure to work with.
`Theillustrator for the book, Michael Troller, deserves much thanks. Not only did he create new il-
`lustrationsfrom scratch specifically for this book, he redidall the ones from past books and madethis
`edition a more coherent, richer, more visually pleasing experience.
`Thanksalso go to illustrators of past editions: Mina Reimer, Sarah Ishida, Shelly Norris, and Stephen
`Adams. And many thanksto the entire team at Que who produced the book, including Karen Shields,
`Megan Wade, AmyJay, Gloria Schurick, and Erika Millen.
`Thanksalso 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, SurfWatch Software, WebTV, Accrue, VDONet Corporation, America
`Online, Yahoo!, Hilgraeve, Fairmarket, eWallet, and Nuborn Technologies are only a few of the folks
`who gavetheir time to help me understand the nitty-gritty of how various Internet technologies work.
`Tim Smith frum ZDNet offered mevital 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 anonymousauthors of those documents, whoeverthey 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 occasional glassy-eyed looks
`that were replies to simple questions like,‘Did you leave your keys in the refrigerator again?” Shealso
`endured my extreme absent-mindedness while I wasfiguring out ways to explain how firewalls, ISDN, or
`Web robots work when I should have been concentrating on more immediate matters.
`
`10
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`

`

`rE
`
`EMISeeSseAecSETSa2eryeeee
`
`Tell Us What You Think!
`/\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-
`lish 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, e-mail, 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 problemsrelated to the topic of this book, and
`that due to the high volumeof mail ] receive, I 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
`phoneor fax number.I will carefully review your comments and share them with the authorandeditors
`who worked on the book.
`
`Fax:
`
`E-mail:
`Mail:
`
`317-581-4666
`
`feedback@quepublishing.com
`Greg Wiegand
`Associate Publisher
`Que
`201 West 103rd Street
`Indianapolis, IN 46290 USA
`
`11
`
`

`

`
`
`Introduction
`
`'|\) the course of cruising the World Wide Web andclicking 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 youfirst.
`heard about technologies such as spam, cookies, and firewalls. Maybe you’ve wondered how
`a message sent from your computertravels through the vastness of cyberspace and ends up
`in the right e-mail 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? How can youlisten to music and view animations while surfing the
`Web?
`
`This book is designed for everyoneinterested in the Internet.Its guiding principleis this:
`No matter how muchof a cyberpro you are—or how muchof 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
`madehis living with companies involved with the Internet for many years. He’s a complete
`cyberpro wholives and breathes the Internet. One day, he almost whispered to me, “I don’t
`like to admit this, but I don’t know whata proxyserver is. How does it work, anyway?”
`
`He’s not alone. The Internet changes so quickly and the technology advancesso rapidly
`that it can seem almost impossible to keep up withall 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 underly-
`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 theclient/server architecture underpinsvirtually 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 ofthe followingtopics:
`how a cable modem,a digital subscriber line (DSL), or ISDN works; how online services con-
`nect to the Internet; how you can connecthysatellite 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 e-mail and newsgroups work, how IRC chat works, what e-mail “spam”is
`and what you can do to preventit, how instant messaging works, and how you can use the
`Internet to make telephonecalls anywhere in the world.
`
`12
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`12
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`

`

`
`
`Part 4, “Using the World Wide Web,” covers what has becomeby 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 thatis likely to be of interest to you.
`
`Part 5, “Using Common Internet Tools,” takes a close look at common Internettools.
`Here’s the place to learn aboutbasic 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, howJavaScript works, howagents can silently do your hidding for
`you, and howthe Common GatewayInterface (CGT) works, whichis a little-known butvital
`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
`(ISPs) using so-called “smurf attacks,” and how they can attack your computeras well. Andit
`covers the issue of pornography on the Internet and shows how parental-control software can
`prevent children from seeing objectionable material.
`
`So, 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 |
`
`UNDERSTANDING THE INTERNET’S UNDERLYING ARCHITECTURE
`
`
`
`14
`
`

`

`UNDERSTANDING
`THE INTERNET’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 Work
`32
`
`15
`
`

`

`
`
` PORthefirst 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 otherside 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 spe-
`cial multimedia magazines. You can shop for almost anything you can name. You candoall
`this by tapping into the largest computer network in the world—the Internet.
`
`TheInternet 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-
`worksto large online services such as America Online and CompuServe. Every time you tap
`into the Internet, your own computer becomesan 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 makeit all possible.
`
`Chapter 1, “What Is the Internet?,” examines how the Internet runs. You’ll look at who
`pays for the high-speed data backbones that carry muchof 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 connectedto 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 learnalittle 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 howspecial 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. Servers—also called hosts—are powerful computers that perform
`functions such as delivering information or Web pages, hosting databases, and handling
`e-mail. A client is your own computer andthe software that sits on it, such as a Web browser
`
`16
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`16
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`

`

`
`
`or piece of e-mail 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
`domainservers are capable of keeping track of all the locations on the Internet and translat-
`ing addresses such as ww. 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 connectto the Internet.
`
`Chapter 6, “How Routers Work,” details how the most basic piece of hardware on the
`Internet—a router—works. Routers are combinations of hardware and software that perform
`the job of ensuring that all data is sent to the properdestination. Thinkof routers as traffic
`cops of the Internet. They use the IP addresses the nameservers 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 datais finally delivered. They use routing tables to determine
`how to route thetraffic, and they can also adjust the routes as the traffic on the Internet
`changes, thus ensuring that the data is routed in the mostefficient way possible.
`
`Chapter 7, “How Internet File Types Work,” gives you an understanding of the most com-
`montypes offiles you’ll come across when you browse the Net. Compressedfiles, videofiles,
`graphics files—you’ll learn about almost every type offile you might encounter.
`
`Whether you’re a newbie or cyberpro, this section teaches you the basics of the Internet.
`
`17
`
`17
`
`

`

`cHarTe® What Is the
`Internet?
`
`
`
`18
`
`

`

`
`
`ONEof the most frequently asked questions about the Internet is: Whorunsit? Thetruth is that no cen-
`tralized managementofthe 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 othernet-
`worksto direct Internettraffic so that information can pass among them. Together, these networks and orga-
`nizations makeup 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 standardsarelaid 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 helpingto establish standards and by educating people
`on the proper way.to use the Internet. Perhaps the most importantis the Internet Society, a private, non-
`profit group. The Internet Society supports the work of the Internet Activities Roard (TAR), which handles
`muchofthe 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 aboutthe
`IETE, go to www. ietf.org.(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.org). 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 www. zdnet .com or
`www. quepublishing.com. These companies,called registrars, all must cooperate with one anotherto
`ensure that only one person or company can owna particular domain andthatall the domains work prop-
`erly. The registrars compete with one anotheras wellin 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.
`Althoughall 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,
`governmentagencies, and onlineservices. They are funded separately from each other andin a variety of
`manners, suchas 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 wantto access
`the Internet pay ISPs a monthly connection rate, so in that sense, everyone whouses the Internet helps pay
`forit.
`
`The networks are connected in a variety of ways. Forefficiency’s sake, local networks join in consortiums
`knownasregional networks. A variety of leased lines connect regional and local networks. The leased lines
`that connect networks can beas simple as a single telephoneline or as complex as a fiber-optic cable with
`microwavelinks and satellite transmissions.
`
`Private companies who make moneybyselling access to their lines build backbones, which are very high-
`capacity lines that carry enormous amountsofInternet 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
`
`

`

`high-speed Backbone NetworkServices), for'example, provides
`a high-speedinfrastructure for theresearch and education
`community bylinking together supercomputercenters.
`_ Often, a large corporation or organization such as
`NASAprovides backbonestolink sites across the
`TS country or the world. The government has
`' also funded theInternet2, a super-fast net-
`““§ _ workthat can-transfer data at an
`oeF.“Se Fonisebyuniversities.Anumberofuni-
`astounding2.4 aeabits per second,
`versities already arc connectedto it. When
`Finished in 2008,it will link 140 universities.
`_ Eventually, theentire Internet might run at its speed.
`
`»
`
`oe
`
`\
`
`
`
`—
`
`;
`
`.
`
`_=
`
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`
`.
`
`.
`
`; yr
`
`“
`
`—— fy
`
`=
`
`&
`
`6
`
`PART | UNDERSTANDING THE INTERNET’S UNDERLYING ARCHITECTURE
`
`F
`
`=
`
`How the Internet Cames Together
`
`©
`
`Organization of networks Becausethe Internet is a loose organization of-networks, no single group
`runsit or paysfor it all. instead, many private organizations, universities, and government agencies pay
`for and run parts of it.
`|hey all work together in a democratic, lodsely organized alliance. Private organi-
`zations range from small, homagrown networks to. commercial online services, such as'‘America Online
`and CompuServe,andprivate Internet sérvite providers {ISPs) that sell accessto the Internet.
`a
`.
`Funding Naat Through agencies such as the National Science|
`Foundation, the federal governmentpaysfor some high-speed.backbones that
`carryinternet traffic across the country and the world. The high-speed vBNS(very
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`Regional networks
`Regional networks provide
`and maintain Internet access
`within @.geographic area.
`Regional nets can consist of
`smaller networks and organi-
`zations within the area that
`have bandedtogetherto
`provide better service.
`
`_
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`~
`
`\ %
`Private companiescalled
`_ Registrars
`Internet registrars are responsible for
`_
`registeringInternet domains, such as
`iw. zdnet.com, to pedple and.businesses.
`Until recently,|a quasi:publiccompany
`called the InterNIC had’sole 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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`Internet sorting.provide.
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`
`connections to the internet.
`
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`ments oftheInternet and
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`also mightsupply long-
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`called backbones
`ferdee
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`Internet
`Society
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`Internet Society The Internet
`Society is a private nonprofit organiza- noe
`
`tion that makes technoladical and
`architectural recommendations that
`pertain to the Internet, such as how
`TCP/IP and otherInternet protocols
`should work. This body guides the
`direction of the Internet and
`its growth.
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`=~ InterNIC TheInterNIC is responsible for
`maintaining the domains registered through
`._ registries.It tracks the connections
`_™ between Internet addresses, suchas
`Ds.. 126\34.24.21, and domain names,
`~~. such as gga,com,
`>
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`
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`
`21
`
`21
`
`

`

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

`

`ieeeieieeeace
`
`VOU might take for granted that when yousend 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 onlineservice.
`From there, the packets travel through manylevels of networks, computers, and communicationslines
`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 muchof the glue that holds the Internet together. Five of the
`mast 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.
`Whendata travels across the Internet, it often crosses great distances, which can be a problem because
`the signal sending the data can weaken overthe distance. To solve the problem, repeaters amplify the data at
`intervals so the signal doesn’t weaken.
`Routers play a key role in managing Internettraffic. Their job is to ensure the packets alwaysarrive 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 handleits internal traffic. Routers come into play when
`the data is sent between twodifferent networks. Routers examine packets to determinetheir destinations.
`They take into account the volumeof 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
`Work.”
`
`All this hardware connects the many networks that make up the Internet. At the mostlocal level of net-
`works are corporate local area networks. Midlevel networks hook these LANstogether using high-speed
`telephonelines, ethernet, and microwavelinks. A regional network is a midlevel network in a geographic
`area. A wide area network (W/AN)is another type of midlevel network. A WANconsists of an organization
`with many networkedsites linked together.
`Whena packettravels from a computer on a LAN in a midlevel network to a computer somewhereelse
`on the midlevel network, a router (ura series of routers) sends the packctto its proper destination. However,
`if the destination lies outside the midlevel network, the packet is sent to a network access point (NAP),
`whereit is sent across the country or the world on a backbone. High-speed backbonessuch 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 backbonesare being built that will transmit data at an astonish-
`ing 9.6 billion bits per second.
`
`23
`
`23
`
`

`

`10
`
`
`aa
`~<—
`m
`all 2
`|
`UNDERSTANDINGTHEINTERNET’S UNDERLYING ARCHITECTURE
`
`
`PARTI
`
`
`
`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
`
`dial-in Internet service provider (ISP), or you can
`
`use another typeof Internet service, such as a
`
`cable modem. Ethernet networks and token-ring
`
`networksare twotypesof networksthat
`
`can be connectedto the Internet. Token-
`
`ring networks pass data in tokens from
`
`computer to computer in a ring or star
`
`Satellite
`configuration. In Ethernet networks,
`Link
`the data goes from a server
`
`{uv a cornputer on the
`
`network.
`
`&
`
`Token-Ring Network
`
`Nines
`-_
`
`
`
`
`
`
`Ethernet Network [7
`
`
`2 After you're connected
`
`
`and you wantto
`dor
`
`
`
`
`receive information,
`r
`
`requests and data are
`
`handled by routers on the
`Internet. Routers perform
` Server
`most of the workof direct-
`ing traffic on the Internet.
`They examine the packets of data that travel across the Internet to
`see wherethe data is headed. Based on the data’s destination, the
`packetis routed in the mostefficient way—generally to another
`router, which in turn sends the packet to the next router, and so on.
`Routers also connect networks to each other.
`
`
`
`Server
`
`
`
`
`
`
`
`
`3 The data can be transferred between networks in a numberof ways. Dedicated telephonelines can transmit
`data at 56Kbps (kilobits per second). An increasing number of T1 leased telephone lines carry data between
`networks. AT7 link can carry data at 1.544Mbps.