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The Internet Book: Everything You Need to Know About Computer Networking and How the Internet Works, Fourth Edition

by Douglas E. Comer - Cisco Systems San Jose, CA and Department of Computer Sciences Purdue University

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Copyright, iv
About The Author, vii
Preface, xxv
Other Books By Douglas Comer, xxxi
1. The Internet Has Arrived, 1
The World Has Changed, 1
Numbers Do Not Tell The Story, 2
Learning About The Internet, 3
Understanding The Big Picture, 3
Terminology And Technology, 4
Growth And Adaptability, 4
The Impact Of The Internet, 4
Organization Of The Book, 5
A Personal Note, 5
2. Getting Started: Hands-On Experience, 7
Introduction, 7
The Web: Sites And Pages, 8
Web Browsers and Browsing, 8
Using A Browser, 9
Examples Of Web Sites And Services, 9
Internet Search, 12
Summary, 12
I. Introduction To Networking, 13
3. Telephones Everywhere, 15
Introduction, 15
A Communication Service, 15
Selling Communication, 15
Limited Access, 16
High Cost, 17
The Difficult Transition, 17
Ubiquitous Access, 18
Relevance To The Internet, 19
4. The World Was Once Analog, 21
Introduction, 21
Sound, Vibrations, And Analog Recording, 21
Analog Electronic Devices, 22
Many Electronic Devices Are Analog, 23
The First Analog Communication, 23
Analog Is Simple But Inaccurate, 23
Sending An Analog Signal Across A Wire, 24
Digital Music, 25
The Digital Revolution, 25
Computers Are Digital, 26
Digital Recording, 26
Using Digital To Recreate Analog, 27
Why Digital Music?, 28
Summary, 28
5. The Once And Future Digital Network, 31
Introduction, 31
The World Was Previously Digital, 31
A Telegraph Is Digital, 32
Morse Code, 32
Letters And Digits In Morse Code, 33
Users Did Not Encounter Morse Code, 34
Virtually Instant Communication, 34
Speed Is Relative, 34
The Telephone Became Digital, 35
Relevance To The Internet, 36
Binary Encoding Of Data On The Internet, 36
Why Use Two Symbols?, 36
Summary, 36
6. Basic Communication, 39
Introduction, 39
Communication Using Electricity, 39
Signals On Wires, 40
Information Coding, 40
Modems Allow Two-Way Traffic, 41
A Character Code For Digital Information, 42
Detecting Errors, 43
Summary, 45
7. The Local Area Network Arrives, 47
Introduction, 47
Motivation, 47
Interchangeable Media, 48
A Computer Consists Of Circuit Boards, 48
Circuit Boards Plug Into A Computer, 48
Connecting One Computer To Another, 49
LAN Technologies, 50
Connecting A Computer To A LAN, 51
The Importance Of LAN Technology, 52
Relationship To The Internet, 53
II. A Brief History Of The Internet, 55
8. Internet: The Early Years, 57
Many Independent Networks, 57
The Proliferation Of LANs, 57
Facts About LANs, 58
LANs Are Incompatible, 59
Wide Area Technologies Exist, 59
Few WANs, Many LANs, 60
WANs and LANs Are Incompatible, 61
The Desirability Of A Single Network, 61
The Department Of Defense Had Multiple Networks, 62
Connecting Disconnected Machines, 62
The Internet Emerges, 62
The ARPANET Backbone, 63
Internet Software, 63
The Name Is TCP/IP, 64
The Shock Of An Open System, 64
Open Systems Are Necessary, 65
TCP/IP Documentation Is Online, 65
The Military Adopts TCP/IP, 67
Summary, 67
A Personal Note, 67
9. Two Decades Of Incredible Growth, 69
Introduction, 69
Disseminating The Software, 69
Meanwhile, Back In Computer Science, 70
The Internet Meets UNIX, 70
The U.S. Military Makes A Commitment, 71
The Internet Doubles In Size In One Year, 71
Every Computer Science Department, 72
Graduate Students Volunteer Their Time, 73
The IAB evolves, 73
The IETF, 74
Doubling Again In A Year, 74
The Internet Improves Science, 75
NSF Takes A Leadership Role, 75
Target: All Of Science And Engineering, 75
NSF’s Approach, 76
The NSFNET Backbone, 76
The ANS Backbone, 77
Exponential Growth, 78
A Commercial Assessment, 79
The End Of Growth, 80
10. The Global Internet, 81
Introduction, 81
Early ARPA Networks, 81
Electronic Mail Among Computers, 81
BITNET And FIDONET, 82
Networks In Europe, 82
EBONE: The Internet In Europe, 84
Backbones And Internet Hierarchy, 84
Internet On All Continents, 86
The World Of Internet after 1998, 87
A Personal Note, 87
11. A Global Information Infrastructure, 89
Introduction, 89
Existing Infrastructure, 89
Communication Infrastructure, 90
The Internet Infrastructure, 92
The Internet Offers Diverse Information Services, 92
TCP/IP Provides Communication Facilities, 92
A Personal Note, 93
III. How The Internet Works, 95
12. Packet Switching, 97
Introduction, 97
Sharing Saves Money, 97
Sharing Introduces Delays, 98
Sharing Wires, 98
Selectable Channels, 98
Sharing By Taking Turns, 99
Packet Switching Avoids Delays, 100
Each Packet Must Be Labeled, 100
Computers Have Addresses, 100
Packets Are Not All The Same Size, 101
Packet Transmission Seems Instantaneous, 101
Sharing Is Automatic, 102
Network Hardware Handles Sharing, 102
Many Devices Can Use Packet Switching, 102
Relevance To The Internet, 103
Summary, 103
13. Internet: A Network Of Networks, 105
Introduction, 105
Network Technologies Are Incompatible, 105
Coping With Incompatibility, 106
Two Fundamental Concepts, 106
Using A Computer To Interconnect Networks, 108
Interconnecting Computers Pass Packets, 109
Interconnecting Computers Are Called Routers, 110
Routers Are The Building Blocks Of The Internet, 110
The Internet Includes Multiple Types Of Networks, 111
Routers Can Interconnect WANs And LANs, 111
The Hierarchical Structure Of The Internet, 113
Where Packets Travel, 114
Interconnecting Networks Was Revolutionary, 114
Summary, 115
14. ISPs: Broadband And Wireless Access, 117
Introduction, 117
Internet Service Providers And Fees, 117
Customer Connections Form The Last Mile, 118
Leased Circuits Are Expensive, 118
Dial-up Access Is Inexpensive, But Slow, 119
Broadband Connections Offer High Speed, 120
The Important Concept Of Continuous Connectivity, 120
Instantaneous Access Changes Use, 121
Modern Technologies Offer Inexpensive Dedicated Access, 121
Wireless Access Is Available, 124
Wi-Fi And 3G Wireless Technologies, 124
A Personal Note, 125
15. IP: Software To Create A Virtual Network, 127
Introduction, 127
Protocol: An Agreement For Communication, 127
Basic Functionality: The Internet Protocol, 128
IP Software On Every Machine, 128
Internet Packets Are Called Datagrams, 128
The Illusion Of A Giant Network, 129
The Internet’s Internal Structure, 130
Datagrams Travel In Packets, 131
Every Computer Is Assigned A Unique Address, 132
Internet Addresses, 132
An Odd IP Address Syntax, 132
IP Addresses Are Not Random, 133
A Trip Through An Example Internet, 133
How Fast Is Your Connection?, 134
Summary, 135
16. TCP: Software For Reliable Communication, 137
Introduction, 137
A Packet Switching System Can Be Overrun, 137
TCP Helps IP Guarantee Delivery, 139
TCP Provides A Connection Between Computer Programs, 140
The Magic Of Recovering Lost Datagrams, 140
TCP Retransmission Is Automatic, 141
TCP And IP Work Together, 141
Summary, 142
17. Clients + Servers = Distributed Computing, 143
Introduction, 143
Large Computers Use Networks For Input And Output, 143
Small Computers Use Networks To Interact, 144
Distributed Computing On The Internet, 144
A Single Paradigm Explains All Distributed Computing, 145
Communicating Programs Are Clients Or Servers, 146
A Server Must Always Run, 147
Summary, 147
18. Names For Computers, 149
Introduction, 149
People Prefer Names To Numbers, 149
Naming A Computer Can Be Challenging Or Fun, 150
Computer Names Must Be Unique, 151
Suffixes On Computer Names, 151
Names With Many Parts, 152
Domain Names Outside The US, 153
Translating A Name To An Equivalent IP Address, 154
Domain Name System Works Like Directory Assistance, 154
Computer Name Lookup Is Automatic, 155
IP Addresses And Domain Names Are Unrelated, 156
Summary, 157
19. NAT: Sharing An Internet Connection, 159
Introduction, 159
High Capacity And Multiple Computers, 159
It Is Possible To Share A Single IP Address, 160
A Device For Connection Sharing Is Called A NAT Box, 160
A NAT Box Acts Like A Miniature ISP, 161
NAT Changes The Address In Each Datagram, 162
Computer Software Can Perform The NAT Function, 162
NAT Can Use A Wireless Network, 163
Summary, 164
20. Why The Internet Works Well, 165
Introduction, 165
The Internet Works Well, 165
IP Provides Flexibility, 166
TCP Provides Reliability, 167
TCP/IP Software Was Engineered For Efficiency, 167
TCP/IP Research Emphasized Practical Results, 168
The Formula For Success, 168
Summary, 169
IV. Services Available On The Internet, 171
21. Electronic Mail, 173
Introduction, 173
Description Of Functionality, 173
The Best Of All Worlds, 174
Each User Has A Mailbox For Email, 174
Sending An Email Message, 174
Notification That Email Has Arrived, 175
Reading An Email Message, 175
A Browser Can Be Used To Send And Receive Email, 175
Email Messages Look Like Interoffice Memos, 176
Email Software Fills In Header Information, 177
How Email Works, 177
Using Email From A Personal Computer, 178
Mailbox Address Format, 179
Abbreviations Make Email Friendly, 180
Aliases Permit Arbitrary Abbreviations, 180
Aliases Shared By All Users Of A Computer System, 181
Sending To Multiple Recipients, 181
Public Mailing Lists And Mail Exploders, 183
Exchanging Email With Non-Internet Sites, 183
Access To Services Via Email, 184
Speed, Reliability, And Expectations, 184
Impact And Significance Of Electronic Mail, 185
A Convention For Joining A Mailing List, 186
22. Bulletin Board Service (Newsgroups), 187
Introduction, 187
Description Of Functionality, 187
Many Bulletin Boards With Diverse Topics, 188
Network News, 189
Categories, 189
Obtaining Network News And The Software To Read Articles, 190
How Network News Appears To A User, 191
Checking For News Articles, 191
Reading Network News, 192
Submission Of An Article, 192
Moderated Newsgroups, 193
Size Of Network News, 193
Impact And Significance Of Newsgroups And Mailing Lists, 193
Hints And Conventions For Participating In Discussions, 194
Summary, 195
23. Browsing The World Wide Web, 197
Introduction, 197
Description Of Functionality, 197
Browsing Vs. Information Retrieval, 198
Early Browsing Services Used Menus, 198
A Menu Item Can Point To Another Computer, 199
How A Browser Works, 200
An Example Point-And-Click Interface, 201
Combining Menu Items With Text, 202
The Importance Of Integrated Links, 204
Embedded Links In Text Are Called Hypertext, 205
Multimedia, 206
Video And Audio References Can Be Embedded In Text, 207
The World Wide Web, 208
Browser Software Used To Access The Web, 209
An Example Hypermedia Display, 209
Control Of A Browser, 212
External References, 212
Recording The Location Of Information, 213
Bookmarks Or Favorites, 215
How The World Wide Web Works, 216
A URL Tells A Browser Which Computer To Contact, 216
A URL Tells A Browser Which Server To Contact, 216
Use Of The Name www In URLs, 217
A Browser Provides Access To Multiple Services, 218
Inside A Browser Program, 218
Summary, 219
An Observation About Hypermedia Browsing, 220
24. World Wide Web Documents (HTML), 221
Introduction, 221
Display Hardware Varies, 221
A Browser Translates And Displays A Web Document, 222
A Consequence Of The Web Approach, 223
HTML, The Language Used For Web Documents, 223
Instructions In A Web Page Control The Output, 224
A Web Page Is Divided Into Two Main Sections, 225
Indentation Can Make HTML Readable, 225
The Body Of A Web Page Can Contain Text, 226
Indentation Can Make Paragraphs Easier To Find, 227
A Web Page Can Link To Another Page, 228
HTML Allows Numbered And Unnumbered Lists, 229
Images On A Web Page Are Digital, 230
HTML Allows A Web Page To Include An Image, 232
Text Can Appear Adjacent To An Image, 233
Images Can Link To Another Web Page, 234
Some Browsers Can Stretch Or Shrink Images, 235
The Background Can Be Controlled, 235
Other Features Of HTML, 235
Importance Of HTML, 236
GUI Tools Help With Web Page Creation, 236
Summary, 237
25. Advanced Web Technologies (Forms, Frames, Plugins, Java, JavaScript, Flash), 239
Introduction, 239
Conventional Web Pages Are Static, 239
How A Server Stores Static Web Pages, 240
Fetching Items One At A Time, 242
Conventional Web Pages Use The Entire Screen, 242
A Web Page Can Change Part Of the Screen, 243
The Web, Advertising, And Frames, 245
Pop-Ups And Pop-Up Blockers, 246
Static Documents Have Disadvantages, 246
Controlling How A Browser Processes Data, 247
Plugins Allow Variety, 248
A Server Can Compute A Web Page On Demand, 249
How Server-Side Scripting Works, 250
Professional Programmers Build Server Scripts, 251
Personalized Web Pages, 252
Personalized Advertisements, 253
Web Pages Can Interact, 253
Shopping Carts, 253
Cookies, 254
Should You Accept Cookies?, 255
A Web Page Can Display Simple Animations, 255
Active Documents Are More Powerful, 256
Java Is An Active Document Technology, 258
JavaScript Is An Active Document Technology, 258
Flash And Real Technologies, 259
The Importance Of Advanced Web Technologies, 259
26. Group And Personal Web Pages (Wikis And Blogs), 261
Introduction, 261
The Disadvantage Of A Bulletin Board System, 261
Shared Pages, 262
Shared Pages Are Called Wikis, 263
Sharing And Consensus Building, 263
The Disadvantage Of Wikis, 263
Wikipedia Is An Experiment, 264
Should You Trust Wikipedia?, 264
Publication Of A Personal Diary, 265
A Personal Note, 265
27. Automated Web Search (Search Engines), 267
Introduction, 267
Description Of Functionality, 267
Browsing Vs. Automated Searching, 268
A Search Engine Helps Users Get Started, 268
A Search Tool Can Help Recover From Loss, 269
How An Automated Search Service Operates, 269
Gathering Information In Advance, 270
Modern Systems Search Web Page Contents, 271
How A Web Search Appears To A User, 272
How A Search Engine Returns Results, 273
Automated Search Services Use String Matching, 274
The Advantages And Disadvantages Of String Matching, 274
Automated Search Programs That Use Multiple Keys, 275
Advanced Services Offer More Sophisticated Matching, 276
Personalized Search Results, 277
More Details About How Content Searching Works, 277
Searches Are Restricted, 278
Advertising Pays For Searching, 279
Examples Of Automated Search Services, 279
Significance Of Automated Web Search, 280
28. Text, Audio, And Video Communication (IM, VoIP), 281
Introduction, 281
Instant Messaging Provides Textual Communication, 281
Audio And Video Functionality, 282
Audio And Video Require Special Facilities, 283
An Audio Clip Resembles An Audio CD, 283
Real-Time Means No Delay, 284
Internet Audio In Real-Time, 284
Radio Programs On The Internet, 285
Real-Time Audio Transmission Is Called Webcasting, 285
Internet Telephone Service Is Possible, 286
Internet Telephone Service Is Known As VoIP, 286
Audio Teleconferencing, 287
A Cooperative Document Markup Service, 287
Marking A Document, 289
The Participants Discuss And Mark A Document, 290
Video Teleconferencing, 290
Video Teleconference Among Groups Of People, 292
A Combined Audio, Video, Whiteboard, And IM Service, 292
Summary, 293
A Personal Note, 293
29. Faxes, File Transfer, And File Sharing (FTP), 295
Introduction, 295
Sending A Fax, 295
The Internet Can Be Used To Copy Files, 296
Data Stored In Files, 296
Copying A File, 296
FTP Is Invoked From A Browser, 297
FTP Allows A User To View Directory Contents, 297
FTP Allows A User To Upload Files, 298
FTP Transfers Must Be Authorized, 298
How FTP Works, 299
Impact And Significance Of FTP, 300
Peer-To-Peer File Sharing, 300
Summary, 301
30. Remote Login And Remote Desktops (TELNET), 303
Introduction, 303
Early Computers Used Textual Interfaces, 303
A Timesharing System Requires User Identification, 304
Remote Login Resembles Conventional Login, 304
How Remote Login Works, 305
Escaping From Remote Login, 305
The Internet Remote Login Standard Is TELNET, 306
Remote Access Can Display A Desktop, 306
How Remote Desktops Operate, 307
Assessment Of Remote Login And Desktops, 308
Generality Makes Remote Login And Desktops Powerful, 308
Remote Access Accommodates Multiple Types Of Computers, 309
Unexpected Results From Remote Access, 309
Summary, 310
31. Facilities For Secure Communication, 311
Introduction, 311
The Internet Is Unsecure, 311
Lack Of Security Can Be Important, 312
Authentication And Privacy Are Primary Problems, 312
Data Can Be Changed, 313
Encoding Keeps Messages Private, 313
Computer Encryption Uses Mathematics, 314
No Network Is Absolutely Secure, 314
Encryption Makes Email Private, 315
Encryption Software Needs A Key, 315
Two Keys Means Never Having To Trust Anyone, 316
Secure Email In Practice, 317
Secure Wireless Networks, 318
Firewalls Protect Networks From Unwanted Packets, 318
A Firewall Filters Packets, 319
Firewalls Guard Against Trojan Horses, 320
Residential And Individual Firewalls, 320
Systems Exist To Detect Intrusion, 321
Service Can Be Denied, 321
Summary, 322
32. Secure Access From A Distance (VPNs), 323
Introduction, 323
Organizations Grant Employees Special Privileges, 323
Traveling Employees Lose Privilege, 324
Telecommuters Do Not Have Privilege, 324
Dedicated Leased Circuits Allow Secure Telecommuting, 325
Standard Internet Connections Are Low-Cost, 326
Can A Technology Combine Advantages?, 326
A Virtual Private Network Solves The Problem, 326
How A VPN Works, 327
The Illusion Of A Direct Connection, 327
Significance Of VPNs, 329
33. Internet Economics And Electronic Commerce, 331
Introduction, 331
Who Pays For The Internet?, 331
E-commerce Is Big Business, 332
Security Technology Made E-commerce Possible, 333
Secure Sockets, 333
Public Key Encryption Provides Authenticity, 334
Digital Signatures, 335
Certificates Contain Public Keys, 335
What Is Digital Money?, 336
Digital Cash Is Not Widely Available, 336
Business And E-commerce, 337
The Controversies Over Taxation And Net Neutrality, 338
34. The Global Digital Library, 339
Introduction, 339
A Cornucopia Of Services, 339
New Services Appear Regularly, 340
Flexibility Permits Change, 340
A Digital Library, 341
Card Catalogs And Search Tools, 341
Internet Services Can Be Integrated, 341
Mr. Dewey, Where Are You?, 342
Information In The Digital Library, 343
What Is The Internet?, 343
A Personal Note, 344
1. Glossary Of Internet Terms, 345
Index, I-1-1

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