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Once upon a time, back in the early Packetozoic, Ethernet was simple and easy to configure. There was only one media system, based on a heavy-duty "thick" coaxial cable, and the configuration rules for that system could be listed in a couple of sentences. As Ethernet caught on and became steadily more popular, clever engineers extended the capabilities of Ethernet again and again. They invented thin coaxial Ethernet, and twisted-pair Ethernet, and fiber optic Ethernet. Not content with that, they invented the 100 megabit per second variety of Ethernet.
This wide range of media systems provides enormous flexibility and make it possible to design an Ethernet LAN to fit virtually every circumstance. However, all this flexibility does have a price: the varieties of Ethernet media each have their own bits and pieces of equipment and their own configuration rules, which makes the system a lot more complex than things were in the old days. This guide helps deal with the complexity by listing the official configuration rules in a set of self-contained chapters that are designed as quick reference guides to the territory.
The rules in this book can all be found in the Ethernet standards for each media system. However, the formal standards are not usually stocked in bookstores. To help make things simpler, this book collects the configuration rules in one place, which means that you don't have to pay high prices to buy the standards documents and then wade through the formal standards language trying to extract all of the rules yourself.
The intent of this guide is to answer typical questions about Ethernet configuration, including the maximum segment length for a given media type, and the rules for linking segments together. This is not a general guide on how to use Ethernet equipment or how to design networks, nor does it explain how to build cables and media systems. While there is a small amount of tutorial information included, most of what you will find here is page after page of Ethernet configuration rules, including all those three-letter acronyms that the computer industry seems to thrive on.
This book describes the configuration rules for seven media varieties from the official IEEE Ethernet standard. For the original 10-Mbps system, this includes the following media varieties:
· 10BASE5 thick coax
· 10BASE2 thin coax
· 10BASE-T twisted-pair
· 10BASE-FL fiber optic
For the 100-Mbps Fast Ethernet system, this includes the following varieties:
· 100BASE-TX twisted-pair
· 100BASE-T4 twisted-pair
· 100BASE-FX fiber optic
A few standard and non-standard media varieties have been developed over the years that have not seen wide usage. They are not covered in this guide. The varieties from the IEEE standard that are not covered include the broadband cable variety (10BROAD36), which was designed for use over cable TV systems, and the 1-Mbps twistedpair variety (1BASE5), which is a slower twisted-pair system that never became widely used.
There have also been a number of vendor-specific innovations developed over the years that are not part of the official standard and that operate at various speeds. Examples of vendor-specific systems include 5-Mbps broadband cable segments as well as several wireless channels. These vendor-specific systems are not covered in this guide because they are not part of the formal specifications, and are therefore not described in the official configuration guidelines.
If you know which variety of media segment you're interested in, you can jump right to the chapter that describes the configuration rules for it. Also, Appendix A provides a summary of the 10-Mbps segment rules, and Appendix B provides a summary of the 100-Mbps segment rules.
The book begins with a brief Ethernet tutorial which describes the basic operation of the Ethernet system, and those features of the system that are common to all media varieties. Following the tutorial are two sets of chapters, one covering the 10-Mbps and the other covering the 100-Mbps media varieties.
The chapters on the 10-Mbps media segments begin with a chapter which introduces the 10-Mbps media system, describing the features that are common to all 10-Mbps media segments. Similarly, the chapters on 100-Mbps Fast Ethernet segments begin with a chapter which introduces the 100-Mbps media system, and that describes the features common to all 100-Mbps media segments.
The chapters on individual media segments follow these introductory chapters. Each variety of 10-Mbps and 100-Mbps Ethernet media segment is briefly described in a separate chapter, including the configuration guidelines for a single segment of the media type being described. At the end of the individual media segment chapters are chapters on the multi-segment configuration guidelines for the 10- Mbps and 100-Mbps systems. These chapters describe how multiple segments that operate at a given speed may be combined to form larger Ethernet systems. The media segment chapters and the multisegment configuration chapters are designed as self-contained references. For that reason, some small portions of text are repeated in these chapters.
If you want to link Ethernet segments that operate at different speeds you must use a bridge or switching hub, therefore Chapter 15 briefly describes how bridges and switching hubs work.
I would like to thank Bob Metcalfe and his fellow researchers at Xerox PARC for inventing Ethernet in the first place. The acumen that underlies the original design for Ethernet is reflected in its remarkable success. I would also like to thank the scores of engineers who have voluntarily given their time in countless IEEE standards meetings over the years to help extend the Ethernet system and to write the specifications.
I also thank William C. Bard, manager of the Networking Services group at the Computation Center of the University of Texas at Austin, for supporting my writing efforts. I especially thank William Green and Rich Seifert for critically reading the manuscript and for providing a number of useful suggestions.
Most importantly, I would like to thank my wife, Joann Zimmerman, for enduring yet another book project, and for her patience, her support, and her editing skills. Without her, this book would not have been possible.
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