How Networks Work

How Networks Work

by Les Freed, Frank J. Derfler Jr.
For those who need a solid introduction to networking concepts, there is no other book on the market that so clearly addresses their needs. This new edition of the original bestseller adds chapters on the Internet and the Web, ISDN, ATM, and more. The authors assume no prior knowledge of networking.


For those who need a solid introduction to networking concepts, there is no other book on the market that so clearly addresses their needs. This new edition of the original bestseller adds chapters on the Internet and the Web, ISDN, ATM, and more. The authors assume no prior knowledge of networking.

Editorial Reviews
The Barnes & Noble Review
How does a networking book sell 200,000 copies without telling you how to fix a broken network, or get a networking job, or earn a networking certification, or even how to avoid losing money on your telecom investments? By doing one thing better than anyone else: explaining how networks work, in plain English, so anyone can understand -- no matter how little technical background they have.

How Networks Work, Sixth Edition does precisely that. Of course, as good as the prose is, that’s only the beginning. This book brings network to life with stunning full-color, oversize 3-D graphics -- all completely revamped and updated for this edition.

If you’ve seen any of the other How It Works series books recently, you’re familiar with the attractive, incredibly lucid style of illustration this book now utilizes. You also realize just how powerful the illustrations are when it comes to understanding how complex devices (like networks) fit together.

We think this book ought to be in every school and every library. And if you’ve ever wondered how email gets from Timbuktu to you, or how the Internet keeps track of all those web addresses, or how your DSL line actually works, it ought to be in your library, too.

The authors are longtime PC Magazine networking editors Les Freed and Frank Derfler. (If you don’t read PC Magazine, you may still know them from their classic Get a Grip on Network Cabling, first published in 1993 but still used by instructors and professionals worldwide.)

Freed and Derfler begin in a time and place far, far away. You may, frankly, be surprised at where they start. We were, until we thought about it. To explain how networks communicate one bit of data at a time across vast distances, why not start with the first and simplest device ever to do that?

So Freed and Derfler start with Samuel Morse sitting at his desk in the Supreme Court chamber of the U.S. Capitol building in Washington, D.C., sending his famous “What hath God wrought” telegraph message up to Baltimore -- and launching Western Union, the world’s first telecommunications behemoth. “By itself,” Freed and Derfler note, “the telegraph can express only two states: on or off.” Sounds awfully digital to us.

Starting from these humble beginnings (and a discussion of Alexander Graham Bell’s equally primitive telephone), Freed and Derfler are able to simplify the fundamental principles of signaling and information packaging that apply in virtually all networks. And once that’s squared away, they can then illuminate everything from telephones and modems to Gigabit Ethernet, protocols to mainframe terminals, network servers to e-business and Internet infrastructure.

If you think you might work with network hardware someday -- or even if you just need to understand the house nerd -- you’ll appreciate how this book completely demystifies network interface cards, cabling, server-based and peer-to-peer LANs, routers, and switches. (This edition even adds a full chapter on IP, the Internet protocol.)

Speaking of wider connections, Freed and Derfler make sense of “metropolitan area networks”, circuit-switched networks like ISDN; and packet switched networks like frame relay -- and, best of all, today’s exciting broadband technologies, cable modems and DSL.

There’s even a full chapter on computer-telephony integration, covering everything from small-business PC-based systems that offer souped-up voice mail to industrial-strength outbound call centers designed to telemarket you into submission.

The book concludes with two entirely new sections: one on the networking technologies behind e-commerce, and another on “Intertainment.” Here, Freed and Derfler preview the finally-arriving convergence between networks and TV (TiVo, next-generation digital set-top boxes, and similar goodies).

If you’re going to live in a digital age, you ought to understand this stuff -- and with How Networks Work, Sixth Edition, you will. Bill Camarda

Bill Camarda is a consultant, writer, and web/multimedia content developer. His 15 books include Special Edition Using Word 2000 and Upgrading & Fixing Networks For Dummies®, Second Edition.

Reviews the history of the telegraph and modem, then overviews LANs and Internet connections for the average computer user. This edition expands coverage of the ways business computing works. Annotation c. Book News, Inc., Portland, OR (

Product Details

Ziff-Davis Press
Publication date:
How It Works Series
Edition description:
Product dimensions:
8.52(w) x 10.02(h) x 0.45(d)

Read an Excerpt

Part 3: Local Area Networks (LANs)

Until now, we've focused on how computers communicate-how they transmit and receive data. We looked at how they communicate with one another outside an office when the distance between them makes it practical to use a modem or a fax instead of a disk or a piece of paper. In this part of the book, we're going to focus on how computers interoperatehow they work together in a network to improve your ability to get things done.

Networks are for sharing. Sharing such things as word processing and spreadsheet files, printers, communication links to distant computers and networks, and electronic mail systems is the function of a network. Every sharing activity, from car pools to bank lines, has its own rules. In networking, we call these rules standards and protocols. Standards describe how things should be; typically they set a minimum performance level. Protocols are sets of rules and agreements; they describe how elements interact. The key to understanding networking is understanding the standards and protocols that make it possible to interoperate without losing or abusing the shared files and devices.

In this section, we'll talk about standards, protocols, and sharing. First, let's spend a little time learning how many of these standards and protocols came about; then we'll talk more about sharing. Although the standards and protocols for computer communications go back to the work of Morse and Bell at the beginning of the 1900s, the standards and protocols for computer interoperation did not emerge until the early 1980s. Three streams fed the computer networking flood: IBM, the U.S. Department of Defense (DoD), and the Xerox Corporation's Palo Alto Research Center. Later, other industry and professional organizations, particularly the Institute of Electrical and Electronic Engineers (the IEEE, pronounced i-triple-e) played an important part in developing standards, but the story starts with a computer system called SAGE.

The Semi-Automatic Ground Environment (SAGE) was developed by IBM for the DoD in the 1960s. SAGE, an air-defense system that operated until the mid-1980s, used vacuumtube computers with memory banks so large that two people could stand inside them. The computers were installed in pairs in blockhouse buildings, and the filaments from the tubes in a pair of SAGE computers supplied all the winter heat for large three-story buildings in places such as Great Falls, Montana, and Duluth, Minnesota. The SAGE program involved the efforts of all the best U.S. communications and computer scientists in the 1960s and resulted in a network of interoperating computers that stretched across the United States. The program was the equivalent of the Golden Spike that linked the railroads in 1869. SAGE proved the practicality of interoperating computer systems and stimulated development efforts, particularly by IBM and the federal government.

In the 1970s, the DoD-faced with an inventory of different computers that could not intemperate-pioneered the development of network software protocols that work on more than one make and model of computer. The major set of protocols established by the DoD is the Transmission Control Protocol/Internet Protocol (TCP/IP). As the name implies, these protocols are agreements on how transmission takes place across networks. Companies, particularly those that want the federal government's business, write software that conforms to those protocols.

At about the same time in the 1970s, IBM began making public the standards and protocols it used for its proprietary computer systems. The standards included detailed descriptions of cabling, and the protocols were designed to ensure accurate communications under heavy loads. This work led others to emulate IBM's techniques and raised the quality of network development in the entire industry. It also led to an uprising by other computer companies that objected to IBM's total control of the most widely used standards and protocols. Eventually, this uprising led to the flexibility and interoperability we enjoy today.

Computer interoperation involves moving a lot of data, but it's difficult to move a lot of anything, including data, over a long distance. So, computer interoperation usually begins with computers in the same office or the same building connected to a local network. The term local area network, or LAN (rhymes with pan), describes a group of computers typically connected by no more than 1,000 feet of cable, which interoperate and allow people to share resources.

In the 1970s, IBM and Digital Equipment Corporation developed ways for a few large computers to intemperate over local networks, but the most important work on LANs for a large number of computers was done at the Xerox Corporation's Palo Alto Research Center (PARC) in the late 1970s and early 1980s. At PARC, an important set of standards and protocols called Ethernet was conceived and developed to the point of becoming a commercial product. At about the same time, people working independently at Datapoint Corporation developed a standard called ARCnet, but Datapoint kept ARCnet as a proprietary set of specifications, so it didn't have the commercial success of Ethernet. Later, IBM developed the third major networking technology we use today, Token-Ring.

The early local area network architectures, such as Ethernet and ARCnet, combined inflexible hardware specifications with strict protocol descriptions. Specific types of copper cable, specific cable connectors, one physical configuration, and certain software functions were bundled together in each LAN definition...

Meet the Author

Frank J. Derfler, Jr., has had multiple careers in radio and computer systems, procurement, education, and publishing. He was one of the very earliest columnists and reviewers in computer publishing and, in 1986, Frank opened the PC Magazine LAN Labs. Today, as the senior networking editor of PC Magazine, Frank continues to use his great skill to explain what is important about products and technology. His understanding of both the technology and the human side of the computer equation allows him to express the important ideas in networking without getting lost in technobabble. That's the beauty of How Networks Work, Millennium Edition.

Les Freed has been involved in the PC industry right from the start. During his previous career with CBS News, Les discovered that computers and telephones were made for each other, and he left CBS to develop Crosstalk, one of the first communications programs for the PC. Since leaving Crosstalk, Les has returned to journalism, working as a contributing editor at PC Magazine. He has authored or co-authored (with Frank Derfler) a dozen books on computers, networking, and electronic communications.

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