Tài liệu cwnaTMCertified Wireless Network AdministratorOfficial Study GuideEndorsed by the Wireless

Vendor-neutral wireless network

training and certification

Objective-by-Objective coverage

of the CWNA certification exam

Certified Wireless

Network Administrator

Official Study Guide

Exam PW0-100

Planet3 Wireless

cwnaTM Industry

Approved!

Endorsed by the

Wireless LAN

Association

CWNP™ Certification Program

The Certified Wireless Network Professional Training & Certification Program is

intended for individuals who administer, install, design, and support IEEE 802.11

compliant wireless networks. Because the CWNP program is vendor neutral, candidates

who achieve the different levels of CWNP Certification will be trained and qualified to

administer and support many different brands of wireless LAN hardware. Although there

are many manufacturers of wireless LAN hardware, the technologies behind the hardware

– Radio Frequency and Local Area Networking – are the same for each piece of gear.

Each manufacturer approaches these technologies in different ways.

The CWNP program consists of 4 levels of certification:

Administrator – Site survey, installation and management of 802.11 compliant wireless

LANs

Security Expert – Design and implementation of 802.11 security techniques, processes,

hardware, and software

Integrator – Advanced site survey, design, bridging and integration of 802.11 compliant

wireless LANs

Engineer – Lab intensive approach to design, implementation, troubleshooting & repair,

security and integration of 802.11 compliant wireless LANs

this publication may be stored in any retrieval system, transmitted, or reproduced in any way, including but not

limited to photocopying, photographing, magnetic, electronic, or other record, without the prior written agreement

and written permission of Planet3 Wireless, Inc.

ISBN: 0-9716057-2-6

Version: FAY534IR8E1

CNWP, CWNA, CWNI, CWSE, CWNE, CWAP, CWEC and their respective logos are registered marks of Planet3

Wireless, Inc. in the United States and/or other countries.

This study guide and reference manual are not sponsored by or affiliated with any wireless LAN manufacturer,

including those mentioned in the text and in the lab exercise notes.

TRADEMARKS: Planet3 Wireless, Inc. has attempted throughout this book to distinguish proprietary trademarks

from descriptive terms by following the capitalization style used by the manufacturers. The author and publisher

have made their best efforts to prepare this book, and the content is based upon final release software whenever

possible. Portions of the manuscript may be based on pre-release versions supplied by software manufactures. The

author and publisher make no representation or warranties of any kind with regard to the completeness or accuracy

of the contents herein and accept no liability of any kind including but not limited to performance, merchantability,

fitness for any particular purpose, or any losses or damages of any kind caused or alleged to be caused directly or

indirectly from this book.

Manufactured in the United States of America

LICENSE AGREEMENT

PLEASE READ THESE TERMS AND CONDITIONS CAREFULLY BEFORE USING THIS MANUAL

(“MATERIALS”). BY USING THE MATERIALS YOU AGREE TO BE BOUND BY THE TERMS AND

CONDITIONS OF THIS LICENSE.

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copyrights and other intellectual property rights in the Study Guide. These rights are protected by the national and

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treaty provisions, including without limitation the Universal Copyright Convention and the Berne Copyright

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PLANET3 WIRELESS, INC. Any other use of the Study Guide by any person or entity is strictly prohibited and a

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PLANET3 WIRELESS, INC. is granting you a limited, non-exclusive, non-transferable license to use the Study

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RESTRICTIONS ON TRANSFER

Reproduction or disclosure in whole or in part to parties other than the PLANET3 WIRELESS, INC. client that is

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Any purported sale, assignment, transfer or sublicense without the prior written consent of PLANET3 WIRELESS,

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LIMITED WARRANTY

THE INFORMATION CONTAINED IN THIS STUDY GUIDE IS BELIEVED TO BE RELIABLE BUT

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LICENSE FEE PAID BY YOU TO PLANET3 WIRELESS, INC.

We at Planet3 Wireless would like to dedicate this book to our Lord Jesus Christ. It is through Him that

we have had the talent, time, encouragement, and strength to work many long months in preparing this

text. Our goal through the creation of this book and through all things that He allows us to do going

forward is to glorify Him. We acknowledge His hand in every part of our company, our work, and our

friendships. We would also like to thank our families who have been amazingly supportive, our friends

who have encouraged us and everyone that contributed to this book in any way.

“I can do all things through Christ, who strengthens me.” – Philippians 4:13

Acknowledgements

Devin Akin

Kevin Sandlin

Scott Turner

Robert Nicholas

Josh McCord

Jeff Jones

Stan Brooks

Bill Waldo

Barry Oxford

Planet3 Wireless, Inc. would like to acknowledge and thank the following people for

their tireless contributions to this work:

Devin Akin, whose knowledge of wireless LANs, networking, and radio frequency

surprised even us. His talents to convey, teach, write, and edit were essential in making

this the most accurate and comprehensive writing on wireless LANs in today's market.

Scott Turner, who constantly keeps us in line and focused on what is important. Scott's

work in formatting, framing, content organization, and graphics creation was

indispensable. Scott's eye for detail and his motivation for perfection in everything he

does keep us in awe.

Kevin Sandlin, for his intellect to make difficult concepts sound simple, his skill to write

and edit the most difficult material, and his ability to motivate every member of the team

to do their best and to keep their eyes on the sometimes moving target. His leadership

skills are second to none.

Robert Nicholas, for his ability to conceptualize and create difficult graphics and radio

frequency concepts, his savvy in presentation of difficult material, and his ability to find

the answer to even the most vague concepts through diligent research and study. His

effort in support of this book is greatly appreciated.

Jeff Jones and Josh McCord, who have been with Planet3 since the beginning of this

project. Their willingness to volunteer as much time and effort as was needed to make all

of it possible has been amazing. They have been an inspiration to the entire team. Their

relentless pursuit of perfection in support of Planet3's mission is recognized and greatly

appreciated.

Stan Brooks, Bill Waldo, and Barry Oxford, each of whom brought a unique set of

skills to the review and quality assurance process for this publication. Their time, effort

and eye for necessary changes were immeasurable, and helped to publish this book in a

timely manner.

vi Contents

Contents at a Glance

Introduction xvi

Chapter 1 Introduction to Wireless LANs 1

Chapter 2 Radio Frequency (RF) Fundamentals 17

Chapter 3 Spread Spectrum Technology 45

Chapter 4 Wireless LAN Infrastructure Devices 71

Chapter 5 Antennas and Accessories 103

Chapter 6 Wireless LAN Organizations and Standards 145

Chapter 7 802.11 Network Architecture 167

Chapter 8 MAC and Physical Layers 201

Chapter 9 Troubleshooting Wireless LAN Installations 223

Chapter 10 Wireless LAN Security 259

Chapter 11 Site Survey Fundamentals 295

Appendix A RF in Perspective 341

Glossary 347

Contents vii

Contents

Introduction xxiv

Chapter 1

Chapter 2

Chapter 3

Introduction to Wireless LANs 1

The Wireless LAN Market 2

Today’s Wireless LAN Standards 3

Applications of Wireless LANs 3

Access Role 4

Network Extension 5

Building-to-Building Connectivity 5

Last Mile Data Delivery 6

Mobility 7

Small Office-Home Office 8

Summary 10

Key Terms 11

Review Questions 12

Answers to Review Questions 15

Radio Frequency (RF) Fundamentals 17

Radio Frequency 18

RF Behaviors 19

Gain 19

Loss 19

Reflection 20

Refraction 21

Diffraction 22

Scattering 23

Voltage Standing Wave Ratio (VSWR) 23

VSWR Measurements 24

Effects of VSWR 24

Solutions to VSWR 25

Principles of Antennas 25

Line of Sight (LOS) 25

Fresnel Zone 26

Obstructions 27

Antenna Gain 27

Intentional Radiator 27

Equivalent Isotropically Radiated Power (EIRP) 28

Radio Frequency Mathematics 29

Units of Measure 30

Watts (W) 30

Milliwatt 30

Decibels 30

dBm 32

dBi 34

Accurate Measurements 35

Key Terms 37

Review Questions 38

Answers to Review Questions 43

Spread Spectrum Technology 45

viii Contents

Introducing Spread Spectrum 46

Chapter 4

Narrow Band Transmission 46

Spread Spectrum Technology 47

Uses of Spread Spectrum 48

Wireless Local Area Networks 48

Wireless Personal Area Networks 49

Wireless Metropolitan Area Networks 49

FCC Specifications 49

Frequency Hopping Spread Spectrum (FHSS) 50

How FHSS Works 50

Effects of Narrow Band Interference 51

Frequency Hopping Systems 51

Channels 51

Dwell Time 52

Hop Time 53

Dwell Time Limits 53

FCC Rules affecting FHSS 54

Direct Sequence Spread Spectrum (DSSS) 55

How DSSS Works 55

Direct Sequence Systems 55

Channels 56

Effects of Narrow Band Interference 58

FCC Rules affecting DSSS 58

Comparing FHSS and DSSS 58

Narrowband Interference 58

Cost 59

Co-location 59

Equipment compatibility and availability 60

Data rate & throughput 60

Security 61

Standards Support 61

Key Terms 62

Review Questions 63

Answers to Review Questions 68

Wireless LAN Infrastructure Devices 71

Access Points 72

Access Point Modes 73

Root Mode 74

Bridge Mode 74

Repeater Mode 75

Common Options 76

Fixed or Detachable Antennas 76

Advanced Filtering Capabilities 76

Removable (Modular) Radio Cards 77

Variable Output Power 77

Varied Types of Wired Connectivity 77

Configuration and Management 78

Wireless Bridges 79

Wireless Bridge Modes 80

Root Mode 80

Non-root Mode 81

Contents ix

Access Point Mode 81

Chapter 5

Repeater Mode 81

Common Options 82

Fixed or Detachable Antennas 82

Advanced Filtering Capabilities 83

Removable (Modular) Radio Cards 83

Variable Output Power 83

Varied Types of Wired Connectivity 83

Configuration and Management 84

Wireless Workgroup Bridges 84

Common Options 85

Configuration and Management 85

Wireless LAN Client Devices 86

PCMCIA & Compact Flash Cards 86

Wireless Ethernet & Serial Converters 87

USB Adapters 88

PCI & ISA Adapters 88

Configuration and Management 89

Driver Installation 89

Manufacturer Utilities 89

Wireless Residential Gateways 90

Common Options 91

Configuration and Management 92

Enterprise Wireless Gateways 92

Configuration and Management 94

Key Terms 95

Review Questions 96

Answers to Review Questions 100

Antennas and Accessories 103

RF Antennas 105

Omni-directional (Dipole) Antennas 105

Usage 107

Semi-directional Antennas 108

Usage 109

Highly-directional Antennas 110

Usage 110

RF Antenna Concepts 111

Polarization 111

Gain 113

Beamwidth 113

Free Space Path Loss 114

The 6dB Rule 115

Antenna Installation 115

Placement 115

Mounting 116

Appropriate Use 116

Orientation 116

Alignment 117

Safety 117

Maintenance 118

Power over Ethernet (PoE) Devices 118

x Contents

Common PoE Options 119

Chapter 6

Single-port DC Voltage Injectors 120

Multi-port DC Voltage Injectors 120

Active Ethernet Switches 121

PoE Compatibility 121

Types of Injectors 121

Types of Picker / Taps 122

Voltage and Pinout Standards 122

Fault Protection 122

Wireless LAN Accessories 123

RF Amplifiers 123

Common Options 124

Configuration & Management 125

RF Attenuators 125

Common Options 126

Configuration and Management 127

Lightning Arrestors 127

Common Options 128

Configuration & Maintenance 130

RF Splitters 130

Choosing an RF Splitter 131

RF Connectors 133

Choosing an RF Connector 134

RF Cables 134

RF “Pigtail” Adapter Cable 136

Key Terms 137

Review Questions 138

Answers to Review Questions 142

Wireless LAN Organizations and 145

Standards 145

Federal Communications Commission 146

ISM and UNII Bands 146

Advantages and Disadvantages of License-Free Bands 147

Industrial Scientific Medical (ISM) Bands 147

900 MHz ISM Band 148

2.4 GHz ISM Band 148

5.8 GHz ISM Band 148

Unlicensed National Information Infrastructure (UNII) Bands 148

Lower Band 149

Middle Band 149

Upper Band 149

Power Output Rules 149

Point-to-Multipoint (PtMP) 149

Point-to-Point (PtP) 150

Institute of Electrical and Electronics Engineers 151

IEEE 802.11 152

IEEE 802.11b 152

IEEE 802.11a 153

IEEE 802.11g 153

Major Organizations 154

Wireless Ethernet Compatibility Alliance 154

Contents xi

European Telecommunications Standards Institute 154

Chapter 7

Wireless LAN Association 155

Competing Technologies 155

HomeRF 156

Bluetooth 156

Infrared Data Association (IrDA) 157

Infrared 157

Wireless LAN Interoperability Forum (WLIF) 158

Key Terms 159

Review Questions 160

Answers to Review Questions 164

802.11 Network Architecture 167

Locating a Wireless LAN 168

Service Set Identifier 168

Beacons 168

Time Synchronization 169

FH or DS Parameter Sets 169

SSID Information 169

Traffic Indication Map (TIM) 169

Supported Rates 169

Passive Scanning 169

Active Scanning 171

Authentication & Association 171

Authentication 172

Association 172

States of Authentication & Association 172

Unauthenticated and Unassociated 173

Authenticated and Unassociated 173

Authenticated and Associated 173

Authentication Methods 174

Open System Authentication 174

Shared Key Authentication 175

Authentication Security 176

Shared Secrets & Certificates 176

Emerging Authentication Protocols 177

Service Sets 181

Basic Service Set (BSS) 181

Extended Service Set (ESS) 182

Independent Basic Service Set (IBSS) 182

Roaming 183

Standards 184

Connectivity 185

Reassociation 185

VPN Use 186

Layer 2 & 3 Boundaries 187

Load Balancing 189

Power Management Features 190

Continuous Aware Mode 190

Power Save Polling 191

PSP Mode in a Basic Service Set 191

PSP in an Independent Basic Service Set 192

xii Contents

Key Terms 194

Chapter 8

Chapter 9

Review Questions 195

Answers to Review Questions 199

MAC and Physical Layers 201

How Wireless LANs Communicate 202

Wireless LAN Frames vs. Ethernet Frames 202

Collision Handling 203

Fragmentation 204

Dynamic Rate Shifting (DRS) 205

Distributed Coordination Function 206

Point Coordination Function 206

The PCF Process 206

Interframe Spacing 207

Three Types of Spacing 207

Short Interframe Space (SIFS) 208

Point Coordination Function Interframe Space (PIFS) 208

Distributed Coordination Function Interframe Space (DIFS) 208

Slot Times 209

The Communications Process 209

Request to Send/Clear to Send (RTS/CTS) 212

Configuring RTS/CTS 213

Modulation 214

Key Terms 216

Review Questions 217

Answers to Review Questions 221

Troubleshooting Wireless LAN 223

Installations 223

Multipath 224

Effects of Multipath 225

Decreased Signal Amplitude 225

Corruption 225

Nulling 226

Increased Signal Amplitude 227

Troubleshooting Multipath 228

Solutions for Multipath 229

Hidden Node 230

Troubleshooting Hidden Node 231

Solutions for Hidden Node 232

Use RTS/CTS 232

Increase Power to the Nodes 233

Remove Obstacles 233

Move the Node 233

Near/Far 233

Troubleshooting Near/Far 234

Solutions for Near/Far 235

System Throughput 235

Co-location Throughput (Theory vs. Reality) 236

Theory: What Should Happen 237

Reality: What Does Happen 238

Solutions for Co-location Throughput Problems 239

Use Two Access Points 239

Contents xiii

Use 802.11a Equipment 240

Chapter 10

Summary 240

Types of Interference 241

Narrowband 241

All-band Interference 243

Weather 244

Wind 244

Stratification 245

Lightning 245

Adjacent Channel and Co-Channel Interference 245

Adjacent Channel Interference 246

Co-channel Interference 247

Range Considerations 248

Transmission Power 249

Antenna Type 249

Environment 249

Key Terms 250

Review Questions 251

Answers to Review Questions 255

Wireless LAN Security 259

Wired Equivalent Privacy 260

Why WEP Was Chosen 261

WEP Keys 262

Static WEP Keys 263

Centralized Encryption Key Servers 264

WEP Usage 265

Advanced Encryption Standard 266

Filtering 266

SSID Filtering 266

MAC Address Filtering 268

Protocol Filtering 269

Attacks on Wireless LANs 270

Passive Attacks 270

Active Attacks 271

Jamming 272

Man-in-the-middle Attacks 274

Emerging Security Solutions 275

WEP Key Management 275

Wireless VPNs 275

Key Hopping Technologies 276

Temporal Key Integrity Protocol (TKIP) 277

AES Based Solutions 277

Wireless Gateways 277

802.1x and Extensible Authentication Protocol 278

Corporate Security Policy 280

Keep Sensitive Information Private 280

Physical Security 281

Wireless LAN Equipment Inventory & Security Audits 281

Using Advanced Security Solutions 282

Public Wireless Networks 282

Limited and Tracked Access 282

xiv Contents

Security Recommendations 283

Chapter 11

WEP 283

Cell Sizing 283

User Authentication 284

Security Needs 284

Use Additional Security Tools 285

Monitoring for Rogue Hardware 285

Switches, not hubs 285

Wireless DMZ 285

Firmware & Software Updates 286

Key Terms 287

Review Questions 288

Answers to Review Questions 293

Site Survey Fundamentals 295

What is a Site Survey? 296

Preparing for a Site Survey 297

Facility Analysis 298

Existing Networks 299

Area Usage & Towers 301

Purpose & Business Requirements 302

Bandwidth & Roaming Requirements 303

Available Resources 305

Security Requirements 306

Preparation Exercises 307

Preparation Checklist 307

Site Survey Equipment 308

Access Point 308

PC Card and Utilities 309

Laptops & PDAs 311

Paper 311

Outdoor Surveys 312

Spectrum Analyzer 312

Network Analyzer (a.k.a. "Sniffer") 313

Site Survey Kit Checklist 314

Conducting a Site Survey 316

Indoor Surveys 316

Outdoor Surveys 317

Before You Begin 317

RF Information Gathering 318

Range and Coverage Patterns 319

Data Rate Boundaries 321

Documentation 321

Throughput Tests & Capacity Planning 322

Interference Sources 322

Wired Data Connectivity & AC Power Requirements 325

Outdoor Antenna Placement 326

Spot Checks 327

Site Survey Reporting 327

Report Format 327

Purpose and Business Requirements 328

Methodology 328

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