Cover image for How the Internet works
How the Internet works
Gralla, Preston.
Personal Author:
Seventh edition.
Publication Information:
Indianapolis, Ind. : Que, [2004]

Physical Description:
xiii, 354 pages : color illustrations ; 26 cm
General Note:
Includes index.

Previous ed.: 2002.
Subject Term:
Format :


Call Number
Material Type
Home Location
Item Holds
TK5105.875.I57 G72 2004 Adult Non-Fiction Open Shelf

On Order



Intended for various courses on the Internet and/or World Wide Web, or as a supplement to computer literacy courses covering the Internet. This is a full-color, visual guide to the Internet that explains its various facets. Students discover how the Internet fits together, and how individual computers can be connected to it.

Author Notes

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 columnist 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 computer magazine.

As a 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 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/Computing was a 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 email newsletter. To subscribe to it for free, send an email to with the words SUBSCRIBE NETINSIDER on the subject line.



Chapter One The Wired World of the Internet ONE of the most frequently asked questions about the Internet is: Who runs it? The truth is that no centralized 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 networks to direct Internet traffic so that information can pass among them. Together, these networks and organizations 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 RFCs (requests for comment) agreed upon 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 way to use the Internet. Perhaps the most important is the Internet Society, a private, nonprofit 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 IAB's Internet Engineering Task Force is responsible for overseeing how the Internet's TCP/IP protocols evolve. (See Chapter 3, "How TCP/IP Works" for details on protocols.)     The World Wide Web Consortium (W3C) develops standards for the evolution of the fastest-growing part of the Internet, the World Wide Web. The W3C is an industry consortium run by the Laboratory for Computer Science at the Massachusetts Institute of Technology (MIT).     Private companies, such as, oversee the registering of Internet domains. These companies are overseen by boards made up of people from business, the government, and individual Internet users.     Although these organizations are important as a kind of glue 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. How the Internet Runs 1 Because the Internet is a loose organization of networks, no single group runs it and pays for it. Instead, many private organizations, universities, and government agencies pay for and run parts of it. They all work together in a democratic, loosely organized alliance. Private organizations range from small, homegrown networks to commercial online services, such as America Online and CompuServe, and private Internet service providers (ISPs) that sell access to the Internet. 2 Through agencies such as the National Science Foundation, the federal government pays for some high-speed backbones that carry Internet traffic across the country and the world. The extremely high-speed vBNS (very high-speed Backbone Network Services), for example, provides a high-speed infrastructure for the research and education community by linking together supercomputer centers. The government is also building an even faster backbone, which will transmit data at 9.6 billion bits per second (bps). Often, a large corporation or organization such as NASA will provide backbones to link sites across the country or the world. 3 Regional networks provide and maintain Internet access within a geographic area. Regional nets may consist of smaller networks and organizations within the area that have banded together to provide better service. 4 Private companies called Internet Registrars are responsible for registering Internet domains, such as, to people and businesses. Until recently, a quasi-public company called the InterNIC had sole responsibility for doing this, but other registrars are being allowed to register domains as well. Internet Registrars are over-seen by boards made up of people from private and public institutions. 5 Internet Registries are responsible for maintaining the domains registered through registries. They track the connections between Internet addresses, such as, and domain names, such as Until recently, the InterNIC had sole responsibility for this. Each major domain, such as .com, has its own separate registry. 6 The Internet Society is a private nonprofit organization that makes technological and architectural recommendations that pertain to the Internet, such as how TCP/IP and other Internet protocols should work. This body guides the direction of the Internet and its growth. 7 ISPs sell people monthly connections to the Internet. They run their own segments of the Internet and may also supply long-distance connections called backbones. Telephone companies are another source of long-distance connections for the Internet. Chapter Two How Information Travels Across the Internet YOU may 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) first breaks it up into packets. 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 destination, which may 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 communicate 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 kind 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 make sure 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 needed 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 destination. They take into account the volume of activity on the Internet, and they send the packets to another router--one that is closer to the packet's final destination.     Midlevel networks hook 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 kind 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 the packets to their proper destination. However, if the destination lies outside the midlevel network, the packets are sent to a NAP (Network Access Point), where they are 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 (millions of bits) per second (Mbps). Even faster backbones are being built that will transmit data at an astonishing 9.6 billion bits per second. Linking Networks to the Internet 1 The Internet comprises networks that are attached to one another via pathways that facilitate the exchange of information, data, and files. Being connected to the Internet means having access to these pathways. Your computer can send packets of data over these pathways to any other computer connected to the Internet. 2 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 connected to the Internet via an online service or a dial-in Internet service provider (ISP), or you can use another kind of Internet service, such as a cable modem. Ethernet networks and token-ring networks are two kinds 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 configuration. In Ethernet networks, the data goes from a server to a computer on the network. 3 Routers, which connect networks, perform most of the work of directing traffic on the Internet. Routers examine the packets of data that travel across the Internet to see where the data is headed. Based on the data's destination, the packet is routed in the most efficient way--generally to another router, which in turn sends the packet to the next router, and so on. 4 Networks are connected in different ways. Dedicated telephone lines can transmit data at 56Kbps (kilobits per second). An increasing number of T1 leased telephone lines exist that carry data between networks. A T1 link can carry data at 1.544Mbps. Higher-speed T3 links, which can carry data at 44.746Mbps, are being used as well. If you dial into an ISP from home, you might connect at a lower speed than at your office, where you might have higher-speed connections such as a T1 or 56Kbps line. However, a variety of high-speed options are available for connecting to the Internet at home, such as cable modems or high-speed Digital Subscriber Line (DSL) connections. 5 Satellites can also link networks, as can fiber-optic cables, special ISDN (Integrated Services Digital Network) telephone lines, or high-speed DSL connections. 6 The networks in a particular geographic area are connected into a large regional network. Routers pass information within that area from network to network. 7 Regional networks are connected to one another via high-speed backbones--connections that can send data at extremely high speeds. When data is sent from one regional network to another, it is first sent to a Network Access Point (NAP). The NAP then routes the data to high-speed backbones, such as vBNS, which can transmit data at 165Mbps, The data is then sent along the backbone to another regional network. Finally, it is passed to a specific network and computer within that regional network. Copyright © 1998 Que Corporation. All rights reserved.

Table of Contents

I Understanding The Internet's Underlying Architecture
1 What Is the Internet?
2 How Computer Networks Send Data Across the Internet
3 How TCP/IP Works
4 Understanding the Internet's Software Structure
5 How Internet Addresses and Domains Work
6 How Routers Work
II Connecting To The Internet
7 How Computers Connect to the Internet
8 How a Modem Works
9 How Internet/Television Connections Work
10 How the Digital Subscriber Line (DSL) Works
11 How You Connect to the Internet from Online Services
12 How Wireless and Palmtop Connections Work
13 How Home Networks Work
III Communicating On The Internet
14 How Email Works
15 How Email Spam Works
16 How Newsgroups Work
17 How Internet Chat and Instant Messaging Work
18 How Internet Phone Calls Work
IV Using The World Wide WeB
19 How Web Pages Work
20 How Web Browsers Work
21 How Markup Languages Work
22 How Hypertext Works
23 How URLs Work
24 How Image Maps and Interactive Forms Work
25 How Web Host Servers Work
26 How Web Sites Work with Databases
27 How .NET and Web Services Work
28 How Grid Computing Works
V Using Common Internet Tools
29 How Telnet Works
30 How FTP Works
31 How Internet Searching Works
32 How Agents Work
33 How Java, ActiveX, and JavaScript Work
34 How CGI Scripting Works
VI Enjoying Entertainment And Multimedia On The Internet
35 How Music and Audio Work on the Internet
36 How Music Sharing and File Sharing Work
37 How Video on the Internet Works
38 How Multicast IP and the MBone Work
39 How Virtual Reality Works
40 How Animation on the Web Works
VII Shopping And Doing Business On The Internet
41 How Intranets Work
42 Shopping on the Internet
VIII Protecting Yourself On The Internet
43 How Firewalls Work
44 How Hackers Can Cripple the Internet and Attack Your PC
45 How Viruses Work
46 How Internet Sites and Software Can Invade Your Privacy
47 Cryptography, Privacy, and Digital Certificates
48 How FBI and Workplace Surveillance Work
49 Parental Controls on the Internet