设计与部署Cisco Aironet无线网络指南：802.11基础知识

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"思科的无线网络基础资源——《802.11无线局域网基础》是一本由Pejman Roshan和Jonathan Leary合著的专业电子书，由Cisco Press出版于2003年12月23日。本书的ISBN为1-58705-077-3，共312页，旨在帮助读者深入理解和掌握设计、构建以及管理Cisco Aironet无线局域网（WLAN）的基本原理。《802.11无线局域网基础》以其浅显易懂的语言，全面涵盖了无线局域网的核心概念和技术架构。它首先从技术概述和WLAN架构的介绍开始，使读者对无线网络的工作原理有清晰的认识。书中进一步探讨了各种应用场景，包括垂直（如楼宇）、小型办公室/家庭办公室（SOHO）以及企业网络中的实施问题，使读者能够适应不同环境下的部署需求。作者提供了丰富的实例分析，通过实际案例让读者学习如何设计和解决无线网络中的常见问题，确保在实际项目中能灵活运用所学知识。本书的重点在于实用的设计指导和部署建议，帮助读者在面对WLAN的规划、安装、管理和故障排除时能够游刃有余。无线局域网的兴起，使得计算机网络可以通过无线信号而非传统的电话线或电缆进行连接，极大地提高了网络的灵活性和便捷性。无线网络的优势不仅体现在摆脱有线束缚，还体现在简化布线成本、增强移动性和可扩展性等方面。《802.11无线局域网基础》是IT工程师和专业人员必备的一本参考书，无论是初学者还是经验丰富的从业者，都能从中获取到设计、优化和维护无线网络的宝贵知识，从而提升其在无线网络领域的专业素养和实践能力。"

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Table of Contents

•

Index

802.11 Wireless LAN Fundamentals

Pejman Roshan

Jonathan Leary

Publisher

: Cisco Press

Pub Date

: December 23, 2003

ISBN

: 1-58705-077-3

Pages

: 312

Master the basics in designing, building, and managing a Cisco Aironet WLAN.

Master the basics of Wireless LANs with this concise design and deployment guide

Understand implementation issues for a variety of environments including vertical,

SOHO, and enterprise networks

Learn design and troubleshooting advice from real-world case studies

802.11 Wireless LAN Fundamentals

gives networking engineers and IT professionals the

knowledge they need to design, deploy, manage, and troubleshoot their own wireless local-

area networks (WLANs). Starting with an overview of the technology and architecture of

WLANs, the book goes on to explain services and advanced features that such applications

can provide. Most importantly, it provides practical design guidance and deployment

recommendations.

Wireless LANs connect computer networks via radio transmissions instead of traditional

phone lines or cables. Benefits to these systems go well beyond getting rid of all the cables

and wires. Campus networks can grow geographically larger while still retaining all their

efficiency and speed. Additionally, cost savings can be realized when third-party phone lines

are no longer necessary, saving the cost of line rental and equipment upkeep. Finally,

flexibility in campus network design increases significantly for the networking professional,

while the network accessibility and usefulness increases for the individual users.

802.11 Wireless LAN Fundamentals

helps networking professionals realize these benefits by

helping them understand how to design, build, and maintain these networks, as well as how

to justify their value within organizations.

Foreword

Wi-Fi is changing the world around us. It's changing the way we work, play, and interact with

each other. The economics of Wi-Fi are rapidly changing the landscape for the delivery of

high-speed wireless data services. It allows you to stay connected, compressing time by

allowing you to be productive no matter where you are. In fact, as I write this, I'm sitting in

the Tokyo airport waiting for a flight to Beijing connected to the local Wi-Fi network syncing

up e-mail from the long flight from the United States.

With humble beginnings in 1997 as a 1 Mbps and 2 Mbps wireless standard in the unlicensed

2.4 GHz band, data rates jumped to 11 Mbps in 1999 and, most recently, to 54 Mbps in both

the 2.4 GHz and 5 GHz frequency bands. It quickly became popular as a way for businesses

to make their employees more productive by allowing them to remain connected to the

network when they were away from the office. With multiple vendors building to a common

standard and an interoperability certification program provided by the Wi-Fi Alliance, the

performance of Wi-Fi equipment increased while the cost rapidly declined. Wi-Fi soon became

popular as a consumer technology and is now a standard feature on many laptop computers

and handheld devices. Today, readily available single PC cards can operate from 1 Mbps to

54 Mbps in both the 2.4 GHz and 5 GHz bands at a cost that's less than what most people

might pay for a cellular phone. Compare this speed, mobility, and cost to the $700 that one

might have paid for a 9600 Kbps modem about ten years ago, and you can see that Wi-Fi

technology is accelerating at a pace comparable to few technologies before it.

IEEE 802.11, or Wi-Fi, has expanded from its vertical application roots of warehousing,

inventory management, and linking cash registers together to a horizontal application used

by many of us at home and at work. Today, Wi-Fi is primarily used as a high-speed wireless

extension of the Ethernet network that is all around us, connecting us effortlessly and

conveniently to the Internet and our office applications, wherever we might be—in the office,

at an airport, at home, at our favorite coffee shop, or at the park down the street.

Wi-Fi will continue to mushroom into applications that its inventors surely never envisioned.

New extensions to the standard are being developed that will improve security, provide

quality of service (QoS) support, improve manageability, and take data rates well beyond

100 Mbps. These new extensions will not only improve the performance of Wi-Fi in today's

applications, but will allow new applications like toll quality calls using Voice over Wi-Fi to

streaming video from consumer electronics devices to a display panel on your wall. Many of

these applications are already here and more are still to come as Wi-Fi becomes a part of our

everyday lives. And with the continued convergence between computers and consumer

electronics comes a desire to connect these devices effortlessly. You might one day be able to

go to your favorite electronics store and buy a new AV receiver that will wirelessly hook to

your home network stream video content to a flat panel display located in another part of

your home.

New standards extensions, client mobility, and rapid evolving equipment all create the

potential for confusion. What do the alphabet soup of 802.11 standards mean and which ones

should you be interested in? How many access points will you need, and where should you

deploy them? What about user mobility and its impact on legacy applications? Should any

special considerations be given for your particular business? We are still early in the adoption

and growth of Wi-Fi technology, and many exciting things lie ahead. This book helps you

grasp the fundamentals of Wi-Fi networking and prepares you for the best that's yet to come.

Dennis Eaton

Chairman, Wi-Fi Alliance

www.wi-fi.org

•

Table of Contents

•

Index

802.11 Wireless LAN Fundamentals

Pejman Roshan

Jonathan Leary

Publisher

: Cisco Press

Pub Date

: December 23, 2003

ISBN

: 1-58705-077-3

Pages

: 312

Master the basics in designing, building, and managing a Cisco Aironet WLAN.

Master the basics of Wireless LANs with this concise design and deployment guide

Understand implementation issues for a variety of environments including vertical,

SOHO, and enterprise networks

Learn design and troubleshooting advice from real-world case studies

802.11 Wireless LAN Fundamentals

gives networking engineers and IT professionals the

knowledge they need to design, deploy, manage, and troubleshoot their own wireless local-

area networks (WLANs). Starting with an overview of the technology and architecture of

WLANs, the book goes on to explain services and advanced features that such applications

can provide. Most importantly, it provides practical design guidance and deployment

recommendations.

Wireless LANs connect computer networks via radio transmissions instead of traditional

phone lines or cables. Benefits to these systems go well beyond getting rid of all the cables

and wires. Campus networks can grow geographically larger while still retaining all their

efficiency and speed. Additionally, cost savings can be realized when third-party phone lines

are no longer necessary, saving the cost of line rental and equipment upkeep. Finally,

flexibility in campus network design increases significantly for the networking professional,

while the network accessibility and usefulness increases for the individual users.

802.11 Wireless LAN Fundamentals

helps networking professionals realize these benefits by

helping them understand how to design, build, and maintain these networks, as well as how

to justify their value within organizations.

Introduction

How many times have you needed network or Internet access at home and wished you could

work in a different room, or even outside, without having to run a long Ethernet cable? How

many times have you been in a public spot, such as an airport or hotel, and realized you

needed to send a quick e-mail? How many hours have you wasted sitting in conference rooms

between meetings while your e-mails pile up?

If you are like thousands of other corporate network users, telecommuters, business

travelers, and home users, the answer is more than once. Network users take heed: 802.11-

based WLANs hold the answer for you. 802.11-based networks provide the much sought-after

mobility and bandwidth that network users have been asking for.

WLANs are not a new concept. They have been around for decades. The 802.11 standard was

ratified in 1997, so why is it that WLANs are really starting to take off now? The answers are

bandwidth and cost. Early wireless networks, such as Aloha, ARDIS, and Ricochet, offered

data rates of less than 1 Mbps. The 802.11 standard offers vendor interoperable rates as high

as 2 Mbps. The ratification of 802.11b in 1999 raised the bar to 11 Mbps, competing against

wired 10 Mbps Ethernet rates. The 802.11a and 802.11g standards offer data rates as high

as 54 Mbps, giving wired Fast Ethernet a run for its money.

As early implementers of WLANs, vertical industries such as retail stores, healthcare

providers, and manufacturers see the value that WLANs and wireless applications bring.

Many of these industries rely on WLANs as core components of their business. As a result,

vendors are rising to meet the challenge of delivering cost-effective WLAN solutions for these

customers. Vendors can increase their manufacturing volumes and lower their costs and as a

result their prices, making WLAN hardware available to consumer and enterprise customers

at reasonable prices.

Although 802.11 networks are a LAN topology, they present new challenges to network

administrators who are accustomed to a world of wires and wired-based network

technologies such as 802.3 Ethernet networks. Issues like site surveys, security, QoS, and

network-device mobility require attention that a network administrator might not have the

experience to give.

The premise to this book is to discuss the aspects of 802.11 in terms that IT and network

engineers can relate to. This book is a reference guide to operating and troubleshooting

802.11 networks and also serves as the first stepping stone to bridge the gap between wired

and wireless networks.

•

Table of Contents

•

Index

802.11 Wireless LAN Fundamentals

Pejman Roshan

Jonathan Leary

Publisher

: Cisco Press

Pub Date

: December 23, 2003

ISBN

: 1-58705-077-3

Pages

: 312

Master the basics in designing, building, and managing a Cisco Aironet WLAN.

Master the basics of Wireless LANs with this concise design and deployment guide

Understand implementation issues for a variety of environments including vertical,

SOHO, and enterprise networks

Learn design and troubleshooting advice from real-world case studies

802.11 Wireless LAN Fundamentals

gives networking engineers and IT professionals the

knowledge they need to design, deploy, manage, and troubleshoot their own wireless local-

area networks (WLANs). Starting with an overview of the technology and architecture of

WLANs, the book goes on to explain services and advanced features that such applications

can provide. Most importantly, it provides practical design guidance and deployment

recommendations.

Wireless LANs connect computer networks via radio transmissions instead of traditional

phone lines or cables. Benefits to these systems go well beyond getting rid of all the cables

and wires. Campus networks can grow geographically larger while still retaining all their

efficiency and speed. Additionally, cost savings can be realized when third-party phone lines

are no longer necessary, saving the cost of line rental and equipment upkeep. Finally,

flexibility in campus network design increases significantly for the networking professional,

while the network accessibility and usefulness increases for the individual users.

802.11 Wireless LAN Fundamentals

helps networking professionals realize these benefits by

helping them understand how to design, build, and maintain these networks, as well as how

to justify their value within organizations.

How This Book Is Organized

Beginning in

Chapter 1

, "Ethernet Technologies," we cover the different flavors of Ethernet

networks, from 10 Mbps Ethernet to Gigabit Ethernet. This chapter provides a review of

Ethernet as a point of contrast for you as you continue with this book. Examining a simple yet

mature technology should give you some perspective on the challenges of deploying and

planning 802.11 WLANs.

Chapter 2

, "802.11 Wireless LANs," provides an overview of the technology in the frame of

reference of Ethernet. It provides an overview of the 802.11 wireless Media Access Control

(MAC) layer while detailing the basic functions that it performs.

Chapter 3

, "802.11 Physical Layer Technologies," overviews the physical layer (PHY)

technologies used to create the 802.11, 802.11b, 802.11a, and 802.11g physical layers. They

are reviewed in the context of the basic building blocks of radios. We also present the specific

interface between the MAC and the PHY that has allowed the easy expansion of newer PHYs.

Chapter 4

, "802.11 Wireless LAN Security," provides a primer on security, including

authentication and encryption. This information is a prelude to examining security as defined

in the 1997 802.11 standard and its associated vulnerabilities. This chapter also provides

details on the 802.11i draft standard for wireless security and a look at WiFi Protected Access

(WPA) and interim vendor-interoperable WLAN security specifications.

Chapter 5

, "Mobility," describes the mobility of 802.11 client devices, with specific focus on

how wireless applications directly impact access point (AP) deployment. Client mobility

impacts the 802.11 MAC protocol but also has an impact on IP-based networks, so a brief

discussion of mobile IP is also included.

Chapter 6

, "QoS for 802.11 Wireless LANs—802.11e," discusses the challenges of deploying

wireless applications that require low-latency network connectivity, such as Voice over IP

(VoIP). This chapter provides an overview by examining the 802.11 protocol and taking a

sneak peak at the forthcoming 802.11e 802.11 QoS standard.

Chapter 7

, "Radio Frequency Essentials," overviews the essentials of radio technology as it

applies to WLANs. Topics include antennas, receivers, and radio system performance. We

discuss different unlicensed frequencies used throughout the world. The intent of this chapter

is to provide you with the knowledge to evaluate the physical layer performance of different

vendors radios.

Chapter 8

, "Deploying Wireless LANs," considers the deployment aspects of a wireless

network from the physical layer through the application layer. First considering the

applications to be used, it derives the requirements for the lower layers while providing

specific network-setting suggestions. We discuss coverage- and capacity-oriented WLANs.

This chapter outlines several different approaches to the site survey process while indicating

the necessary tools for a successful survey. We detail the deployment aspects of your WLAN

security policy and the tools for managing your network.

Chapter 9

, "The Future of Wireless LANs," provides a glimpse at technology trends. The

specific technologies considered are Bluetooth, Ultra Wide Band, Free Space Optics, and

future higher-speed 802.11 technologies.

Chapter 10

, "WLAN Design Considerations," steps through several WLAN application areas

while providing insight into their unique requirements. The application areas are retail stores,

healthcare organizations, branch offices, and education organizations. Also considered are

scenarios that are likely to use client devices from multiple vendors. We detail the specific

potential pitfalls of WLANs for remote locations. We delineate design considerations for public

access networks and the unique requirements of WLANs for public-safety entities.

One thing to note: The WLAN industry is moving at an exponential pace. With each passing

•

Table of Contents

•

Index

802.11 Wireless LAN Fundamentals

Pejman Roshan

Jonathan Leary

Publisher

: Cisco Press

Pub Date

: December 23, 2003

ISBN

: 1-58705-077-3

Pages

: 312

Master the basics in designing, building, and managing a Cisco Aironet WLAN.

Master the basics of Wireless LANs with this concise design and deployment guide

Understand implementation issues for a variety of environments including vertical,

SOHO, and enterprise networks

Learn design and troubleshooting advice from real-world case studies

802.11 Wireless LAN Fundamentals

gives networking engineers and IT professionals the

knowledge they need to design, deploy, manage, and troubleshoot their own wireless local-

area networks (WLANs). Starting with an overview of the technology and architecture of

WLANs, the book goes on to explain services and advanced features that such applications

can provide. Most importantly, it provides practical design guidance and deployment

recommendations.

Wireless LANs connect computer networks via radio transmissions instead of traditional

phone lines or cables. Benefits to these systems go well beyond getting rid of all the cables

and wires. Campus networks can grow geographically larger while still retaining all their

efficiency and speed. Additionally, cost savings can be realized when third-party phone lines

are no longer necessary, saving the cost of line rental and equipment upkeep. Finally,

flexibility in campus network design increases significantly for the networking professional,

while the network accessibility and usefulness increases for the individual users.

802.11 Wireless LAN Fundamentals

helps networking professionals realize these benefits by

helping them understand how to design, build, and maintain these networks, as well as how

to justify their value within organizations.

day, new innovations from vendors are making WLANs more secure; easier to deploy and

manage; and, most importantly, more cost-effective. This book is not designed to be a finite

description of WLANs. Its goal is to provide the fundamental foundations necessary for you,

the network administrator, to understand how to plan, deploy, and operate a WLAN. We

chose the topics and examples from real-world problems we have encountered in internal

product development at Cisco Systems and from the many companies that are evaluating or

actively deploying WLANs.

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