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.
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About 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.
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...
Table of ContentsIntroduction.
I. Communicating by Wire.1. How Telegraphs Work.
2. How Telephones Work.
II. Mixing Computers and Telephones.3. How Early Networks Worked.
4. How Early Communications Terminals Worked.
5. Alphabet Soup: Morse, Baudot, ASCII, and EBCDIC.
6. How Modems Work.
7. How Remote Terminals Work.
8. How Serial Communications Works.
9. The PC As a Terminal.
10. How Broadband Works.
11. How Computer Telephony Integration Works.
III. Local Area Networks (LANs).12. How Local Area Networks Work.
13. How Networking Operating Systems Work.
14. How Network Interface Cards Work .
15. How Network Cables Works .
16. How IP Works.
17. How Server-Based LANs Work.
18. How Peer-to-Peer Networks Work.
19. How Enterprise Network Systems Work.
20. How LAN-to-LAN Connections Work.
IV. Links Between LANs.21. How Bridges, Routers, and Switches Work.
22. How Metropolitan Area Networks Work.
23. How Circuit-Switched Digital Networks Work.
24. How Packet-Switched Networks Work.
V. The Internet.25. How Internet Connections Work.
26. Network Security.
VI. Networks for e-Business.27. e-Business Infrastructure.
VII. Intertainment.28. Convergence and Telematics.
Computer networking didn't just emerge as a unique and independent technology. Networking depends on many things you've seen or are familiar with already. In fact, modern networks have roots in the early telegraph and telephone systems. In this book, we take advantage of those historical ties to explain and illustrate the underlying technology of networks in a simple graphic format.
Then, we move into modern networking and explain the relationships between the hardware and software in networks. Our illustrations detail packets, network interface cards, servers, routers, management software, and many other aspects of networking. Our constant goal is to provide useful information in an easily understood manner.
The information in this book isn't specific to any particular type of computer or network operating system. We illustrate models of operation and tell you how some popular products fit into the models. Whether your computer is an IBM PC, DEC VAX, or anApple Macintosh; whether your network operating system is NetWare, LANtastic, or UNIX; and whether your cabling is copper or fiber-optic, the information in this book applies to your network.