2014版《以太网权威指南》详解

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"《以太网：权威指南》（Ethernet: The Definitive Guide, Second Edition）由Charles E. Surgeon和Joann Zimmerman共同撰写，于2014年3月发布。作为一本详尽介绍以太网技术发展历程、标准规范以及实践应用的经典著作，该书对于希望深入了解这一通信网络技术的专业人士来说，具有很高的参考价值。作者在书中详细阐述了以太网自其诞生以来，从最初的IEEE 802.3标准到后续的多个版本，如快速以太网（Fast Ethernet）、千兆以太网（Gigabit Ethernet）直至更高级别的技术，如10 Gigabit Ethernet和今天的Wi-Fi技术背后的原理和实现。读者可以在这本指南中找到关于帧结构、介质访问控制（MAC）协议、物理层规范、以及不同速率和协议标准（如TCP/IP、IPv4/IPv6）如何与以太网协作的深入剖析。此外，书中还涵盖了以太网在网络工程、数据中心设计、网络安全和无线局域网（WLAN）等领域的实际应用案例，帮助读者理解技术在实际场景中的作用和优化策略。第二版的修订历史记录了2014年3月11日首次发行后的更新内容，确保了信息的时效性和准确性。该书不仅适合从事网络技术的工程师和技术人员阅读，也对教育机构、企业和销售人员提供有价值的参考资料。在线版本也为持续学习者提供了便利，可通过O'Reilly Media网站获取。《以太网：权威指南》是一本全面且实用的参考书籍，无论你是入门者还是经验丰富的专业人士，都能从中收获关于以太网技术的深厚理解和实践经验。通过深入研究本书，读者将能更好地应对日益变化的网络环境，并在日常工作中做出明智的技术决策。"

Ethernet Is Everywhere

Ethernet is the most widely used networking technology, and Ethernet networks are

everywhere. There are a number of factors that have helped Ethernet to become so

popular. Among these factors are cost, scalability, reliability, and widely available man‐

agement tools.

Cost

The rapid evolution of new capabilities in Ethernet has been accompanied by an equally

rapid decrease in the cost of Ethernet equipment. The widespread adoption of Ethernet

technology created a large and fiercely competitive Ethernet marketplace, which serves

to drive down the cost of networking components. The consumer wins out in the pro‐

cess, with the marketplace providing a wide range of competitively priced Ethernet

components to choose from.

Scalability

The first industry-wide Ethernet standard was published over 30 years ago, in 1980.

This standard defined a 10 megabits per second (Mb/s) system, which was very fast for

the time. The development of the 100 Mb/s Fast Ethernet system in 1995 provided a

tenfold increase in speed. Following on that success came the development of twisted-

pair Gigabit Ethernet in 1999. Network interfaces that can automatically support 10,

100, and 1000 Mb/s operation of twisted-pair media systems are widely available, mak‐

ing the support of high-performance networking easy to accomplish.

Applications tend to grow to fill all available bandwidth. To manage the constant in‐

crease in network usage, the 10 Gigabit Ethernet standard was developed in 2002, and

most recently the 40 and 100 Gigabit systems were standardized in 2010. All of this

progress in Ethernet capabilities makes it possible for a network manager to provide

high-speed backbone systems and connections to high-performance servers.

Desktop machines can be connected to an Ethernet link that can operate at 10 Mb/s

Ethernet, 100 Mb/s Fast Ethernet, or Gigabit Ethernet speeds, as required. Network

routers and switches can use 10 Gigabit and 40 or 100 Gigabit links for network back‐

bones, and data centers can connect to high-performance servers at 10, 40, or even 100

gigabits per second (Gb/s).

Reliability

Ethernet is simple and robust and reliably delivers data day in and day out at sites all

over the world. Ethernet based on twisted-pair media was introduced in 1987, making

it possible to provide Ethernet signals over a structured cabling system.

xvi | Preface

Structured cabling provides a data delivery system for a building that is modeled on

high-reliability cabling practices originally developed for the telephone system. This

makes it possible to install a standards-based cabling system for Ethernet that is highly

reliable and easy to manage.

Widely Available Management Tools

The widespread acceptance of Ethernet brings with it the wide availability of Ethernet

management and troubleshooting tools. Management tools based on standards such as

the Simple Network Management Protocol (SNMP) make it possible for network ad‐

ministrators to keep track of an entire campus full of Ethernet equipment from a central

location. Management capabilities embedded in Ethernet switches and computer in‐

terfaces provide powerful network monitoring and troubleshooting capabilities.

Design for Reliability

A major goal of this book is to help you design and implement reliable networks, because

network reliability is of paramount importance to users and organizations. Access to

the Internet and information sharing between networked computers is an essential fea‐

ture of today’s world, and if the network fails, everything comes to a halt. This book

shows you how to design reliable networks, how to monitor them and keep them work‐

ing reliably, and how to fix them should something fail.

The wide range of Ethernet components and cabling systems available today provides

enormous flexibility, making it possible to build an Ethernet to fit just about any cir‐

cumstance. However, all this flexibility does have a price. The many varieties of Ethernet

each have their own components and their own configuration rules, which can make

the life of a network designer complex. Designing and implementing a reliable Ethernet

system requires that you understand how all the bits and pieces fit together, and that

you follow the official guidelines for the configuration of the media systems. To help

you with that task, this book provides the configuration guidelines for the widely used

media systems.

Downtime is Expensive

Avoiding network downtime is important for a number of reasons, not least of which

is the cost of a network outage. Some quick “back of the envelope” calculations can show

how expensive network downtime can be. Let’s assume that there are 1,000 network

users at the Amalgamated Widget Company, and that their average annual salary in‐

cluding all overhead (benefits, etc.) is $100,000. That comes to $100 million a year in

employee costs.

Let’s further assume that everyone in the company depends on the network to get their

work done, and that the network is used 40 hours a week, for about 50 weeks of the year.

Preface | xvii

That’s 2,000 hours of network operation. Dividing the annual employee cost by the hours

of network operation shows that the network is supporting $50,000 per hour of em‐

ployee cost during the year.

Let’s further assume that when we total up all of the network outages over the period of

a year in our hypothetical corporation, we find that the network was down just 1% of

the time (99% uptime, or “two nines”). That sounds like really good uptime, but that

small fraction of 2,000 hours represents a total of 20 hours of network outage. Twenty

hours of network downtime at $50,000/hour is $1,000,000 in lost productivity due to

network outage.

Obviously, our example is very “quick and dirty.” We didn’t bother to calculate the impact

of network outages during times when no one is around but when the network is still

nevertheless supporting critically important servers. Also, we’re assuming that a net‐

work failure brings all operations to a halt, instead of trying to factor in the varying

effects of localized failures that cause outages on only a portion of the network system.

Nor do we try to estimate how much other work people could get done while the network

is down, which would tend to lessen the impact.

However, the main point is clear: even relatively small amounts of network downtime

can cost quite a lot in lost productivity. That’s why it’s worth investing extra time, effort,

and money to create the most reliable network system you can afford.

How to Use This Book

The goal of this book is to provide the information needed for you to understand and

operate any Ethernet system. For example, if you are a newcomer to Ethernet and you

need to know how twisted-pair Ethernet systems work, then you can start with Part I.

After reading those chapters, you can go to the twisted-pair media chapters in Part II,

as well as the twisted-pair cabling information in Part III. Twisted-pair cables are con‐

nected together to form a network using switches, and these are described in Part IV.

Experts in Ethernet can use the book as a reference guide and jump directly to those

chapters that contain the information they need.

Organization of This Book

The purpose of this book is to provide a comprehensive and practical guide to the

Ethernet system and the Ethernet devices and components commonly used in office

and building networks. The emphasis is on practical issues, with minimal theory and

jargon. Chapters are kept as self-contained as possible, and many examples and illus‐

trations are provided. The book is organized into six parts to make it easier to find the

specific information you need.

xviii | Preface

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