KNet wireless CWLF 1 0 student guide vol 1 2006

Cisco Wireless LAN Fundamentals Course Goal Upon completing this course, you will be able to meet these objectives: Describe detailed modulation and spreading techniques and how it is

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Table of Contents

Volume 1

Course Introduction 1

Overview 1

Course Goal and Objectives 3

Course Flow 4

Additional References 5

Module 1: Cisco Aironet WLAN Overview

Lesson 1: Describing Wireless LAN Radio Technologies 1-3

Overview 1-3 Unlicensed Freuency Bands 1-4 Spread Spectrum RF Technology 1-16 2.4-GHz Antennas 1-22 IEEE 802.11a Characteristics 1-25 Lesson Self-Check 1-41 Summary 1-43

Lesson 2: Defining Antenna Concepts 1-45

Overview 1-45 Definition of Terms 1-46 Antenna Concepts 1-52 Various Antenna Types 1-55 EIRP Rules 1-59 Lesson Self-Check 1-66 Summary 1-68

Module 2: Cisco Aironet WLAN Products

Lesson 1: Describing Wireless LAN Access Points, Bridges Antennas and

Accessories 2-3

Overview 2-3 Platform Overview 2-4 Cisco Aironet Indoor Rugged Access Points 2-7

1500 Series Wireless Outdoor Mesh Access Points 2-9

1300 Series Access Point and Bridge 2-10 Cisco Aironet Access Point Comparisons 2-11

1400 Series Wireless Bridge 2-14 Powering Options for Access Points and Bridges 2-15 Power Injectors for Access Points 2-16 2.4-GHz Antennas 2-20 5-GHz Antennas 2-24 Lesson Self-Check 2-28 Summary 2-32

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Lesson 2: Describing WLAN Client Adapters 2-33

Overview 2-33Cisco Aironet 802.11a/b/g Client Adapter 2-34Cisco Wireless IP Phone7920 2-35Cisco Compatible Extensions Program 2-36Lesson Self-Check 2-42Summary 2-44

Lesson 3: Describing WLAN Network Management, Control, and Services 2-45

Overview 2-45Cisco’s Network Management 2-47Cisco WLAN Controllers 2-49CiscoWorks Wireless LAN Solution Engine 2-53CiscoWorks Wireless LAN Solution Engine Express 2-55Cisco Wireless Control System 2-57Cisco Wireless Location Appliance 2-59Integrated Services Routers 2-60Cisco 3200 Series Wireless and Mobile Routers 2-64Cisco Secure ACS Solution Engine 2-65Lesson Self-Check 2-67Summary 2-70

Lesson 4: Introducing Access Point Enterprise-Class Features 2-71

Overview 2-71Software Support 2-72Security 2-79Virtual LAN Support 2-80Quality of Service 2-81Lesson Self-Check 2-82Summary 2-84

Module 3: Wireless Bridges

Lesson 1: Using Wireless Bridges and Alternatives 3-3

Overview 3-3Wireless Bridges and Bridge Alternatives 3-4

1300 Series Wireless Bridge 3-10

1300 Series Outdoor Channels and Power Levels 3-14

1400 Series Access Point Bridge 3-19

1400 Series Outdoor Channels and Power Levels 3-24BR1410 an BR1310 Deployment Scenarios 3-25

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Comparing Access Points and Bridges 3-37Lesson Self-Check 3-51Summary 3-54

Lesson 3: Determining Bridge Path Information 3-55

Overview 3-55Installation Considerations 3-57Distance and Path Loss Considerations 3-61Bridge Distance Calculations 3-65Outdoor Path Considerations 3-67Antenna Considerations 3-77Common Deployment Questions 3-81Lesson Self-Check 3-85Summary 3-87

Module 4: Aironet Desktop Utility

Lesson 1: Describing Configuration Utilities 4-3

Overview 4-3Software Download 4-4Supported Operating Systems 4-5

PC Card LEDs 4-6Aironet Client Administrator Utility 4-7Lesson Self-Check 4-11Summary 4-13

Lesson 2: Installing and Configuring Aironet Desktop Utility 4-15

Overview 4-15Install the Aironet Desktop Utility 4-16Current Status Page 4-20ADU Profile Manager 4-22ADU Tools 4-25Lesson Self-Check 4-31Summary 4-33

Module 5: Core Access Point and Bridge Basic Configuration

Lesson 1: Describing Cisco Unified Wireless Network Core Products 5-3

Overview 5-3Introducing WLAN Management 5-4WLAN Core Products Overview 5-9Components and Protocols 5-11Management Benefits 5-14Security 5-15Roaming Concepts 5-20Lesson Self-Check 5-27Summary 5-30

Lesson 2: Setting up Autonomous Access Point Hardware 5-31

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Overview 5-31 Access Point Hardware 5-32 Initial Connect and Reset 5-45 Lesson Self-Check 5-50 Summary 5-52

Lesson 3: Configuring the Access Point 5-53

Overview 5-53 Access Point: Root Mode 5-55 Home Page 5-57 Express Setup 5-58 Express Security Setup 5-60 Network Interfaces 5-62 Cisco Services 5-75 VLAN Configuration 5-76 QoS Configuration 5-84 Simple Network Management Protocol Setup 5-89 Filtering 5-91 Access Point Cisco IOS CLI 5-96 Lesson Self-Check 5-107 Summary 5-110

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lightweight wireless networks

Learner Prerequisite Skills and Knowledge

This subtopic lists the skills and knowledge that learners must possess to benefit fully from the course The subtopic also includes recommended Cisco learning offerings that learners should first complete to benefit fully from this course

Learner Skills and Knowledge

• Basic Computer Literacy

• Knowledge of fundamental networking components and terminology

• Knowledge of the Open Systems Interconnection (OSI) reference model

• Knowledge of basic LAN components and functions

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Course Goal and Objectives

This topic describes the course goal and objectives

“To enable System Engineers and Field Engineers to offer their customers the most innovative and

comprehensive suite of WLAN solutions in the industry, spanning a wide range of customer sizes and needs”

Cisco Wireless LAN Fundamentals Course Goal

Upon completing this course, you will be able to meet these objectives:

Describe detailed modulation and spreading techniques and how it is used with various antennas

Describe detailed technical features, functions, and benefits of the WLAN product

offerings available from Cisco

Define concepts and describe considerations for deploying wireless bridges

Configure a Cisco client card with Cisco utilities

Configure the core access point and bridge

Configure an advanced featured WLAN using a Cisco wireless LAN controller

Implement a WLAN management solution available from Cisco

Perform an initial configuration of a WLAN

Secure a WLAN using security methods and products available from Cisco

Describe the requirement necessary for deployment and performing a site survey

Describe the steps, concepts, and tools available while performing a site survey

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Course Flow

This topic presents the suggested flow of the course materials

Course Flow

Cisco Aironet WLAN Products

Course Introduction

Lunch

A M

P M

Aironet Desktop Utility

Wireless Bridges

Advance Feature Set Product Administration

Cisco Wireless Mesh Network Installation

Site Survey Preparation

Manual Site Survey Tools and Utilities

Site Survey Preparation (Cont.) Security

WLAN Management Solutions

Advance Feature Set Product Administration (Cont.)

The schedule reflects the recommended structure for this course This structure allows enough time for the instructor to present the course information and for you to work through the lab activities The exact timing of the subject materials and labs depends on the pace of your specific class

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Additional References

This topic presents the Cisco icons and symbols that are used in this course, as well as

information on where to find additional technical references

Cisco Icons and Symbols

Router

CiscoWorks Workstation

Network Management Appliance

Workgroup Switch

Access Point

Laptop

File Server Line: Ethernet

Wireless Connectivity Wireless Bridge

Wireless Dual Mode Access Point

Network Cloud, White

BBFW Media

100BaseT Hub

Switch

Scanner

Tablet

Cisco 5500 Family

Cisco Icons and Symbols (Cont.)

WLAN Controller

Access point

Wireless Router

Rooftop or poletop access point Wi-Fi Tag Wireless Dual

Mode Access Point

Integrated Service Router

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Cisco Glossary of Terms

For additional information on Cisco terminology, refer to the Cisco Internetworking Terms and

Acronyms glossary of terms at http://www.cisco.com/univercd/cc/td/doc/cisintwk/ita/index.htm

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Describe the basic concepts of modulation and spreading techniques used in WLAN applications

Describe antenna basics

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Lesson 1

Describing Wireless LAN

(WLAN) Radio Technologies

Describe the 2.4- and 5-GHz bands

Discuss theories and processes of using spread spectrum technology to send data over a RF signal

Describe the various 2.4-GHz antennas available from Cisco

Describe the modulation technique used by 802.11a

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Unlicensed Frequency Bands

This topic describes the 2.4- and 5-GHz bands Cisco Aironet products use these bands and adhere to the 802.11a, 802.11b, and 802.11g standards

Extremely Low Very Low Low Medium High Very High Infrared Visible Light Ultra- violet X Ray

Audio

AM Broadcast

Shortwave Radio FM Broadcast

Television Infrared Wireless LAN Cellular (840 MHz)

NPCS (1.9 GHz)

902-928 MHz

26 MHz

5 GHz 802.11a Frequencies Vary with Countries

2.4 – 2.4835 GHz 83.5 MHz 802.11b and 802.11g

Ultra High Super High

Unlicensed Frequency Bands

There are three unlicensed bands: 900 MHz, 2.4 GHz, and 5.7 GHz The 900-MHz and GHz bands are referred to as the Industrial, Scientific, and Medical (ISM) bands, and the 5-GHz band is commonly referred to as the Unlicensed National Information Infrastructure (UNII) band

2.4-Frequencies for these bands are as follows:

5-GHz band: 5.150 to 5.350 MHz, 5.725 to 5.825 MHz, with some countries supporting middle bands between 5.350 and 5.825 MHz The number of countries that permit 802.11a and the available spectrum varies widely, and the list change quickly

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Three Wireless Technologies

The Laws of Radio Dynamics:

Higher data rate = Shorter transmission range Higher power output = Increased range, but lower battery life Higher-frequency radios = High data rates, shorter ranges Note: Different modulation schemes may change some of these dynamics

Cordless phones, Microwave ovens, Wireless video, and, Bluetooth devices

HyperLAN devices, Maritime and satellite systems

Cordless phones, Microwave ovens, Wireless video, and, Bluetooth devices

Other Services (Interference)

54 Mbps

11 Mbps Maximum Data

Rate

Worldwide Limited

(Growing) Worldwide

Availability

2.4 GHz

5 GHz 2.4 GHz

Frequency Band

802.11 g 802.11 a

802.11 b

2.4 GHz (802.11b)

The 802.11b standard, the most widely deployed wireless standard, operates in the 2.4-GHz unlicensed radio band and delivers a maximum data rate of 11 Mbps The 802.11b standard has been widely adopted by vendors and customers who find its 11-Mbps data rate more than adequate for most applications Interoperability between many of the products on the market is ensured through the Wi-Fi Alliance™ certification program Therefore, if your network

requirements include supporting a wide variety of devices from different vendors, 802.11b is probably your best choice

5 GHz (802.11a)

The IEEE also ratified the 802.11a standard in 1999, but the first 802.11a-compliant products did not begin appearing on the market until December 2001 The 802.11a standard delivers a maximum data rate of 54 Mbps and twelve nonoverlapping frequency channels—resulting in increased network capacity, improved scalability, and the ability to create microcellular

deployments without interference from adjacent cells Operating in the unlicensed portion of the 5 GHz-radio band, 802.11a is also immune to interference from devices that operate in the 2.4-GHz band, such as microwave ovens, cordless phones, and Bluetooth devices (a short-range, low-speed, point-to-point, personal area network [PAN] wireless standard)

The 802.11a standard is not, however, compatible with existing 802.11b-compliant wireless devices Organizations with 802.11b equipment that want the extra channels and network speed supported by 802.11a technology must upgrade to a product that supports the technology Some product support dual-band operation, and it is important to note that 2.4- and 5-GHz equipment can operate in the same physical environment without interference

2.4 GHz (802.11g)

The 802.11g standard was ratified in June 2003 The 802.11g standard delivers the same Mbps maximum data rate as 802.11a, yet it offers an additional and compelling advantage— backward compatibility with 802.11b equipment This means that 802.11b client cards will work with 802.11g access points and that 802.11g client cards will work with 802.11b access

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54-points Because 802.11g and 802.11b operate in the same 2.4-GHz unlicensed band, migrating

to 802.11g is an affordable choice for organizations with existing 802.11b wireless

infrastructures Note that 802.11b products cannot be “software upgraded” to 802.11g This limitation is due to the fact that 802.11g radios use a different chipset in order to deliver the higher data rate However, much like Ethernet and Fast Ethernet, 802.11g products can be commingled with 802.11b products in the same network Both 802.11g and 802.11b operate in the same unlicensed band As a result, they share the same three channels that can limit

wireless capacity and scalability

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IEEE 802.11 Standard

• Became a standard in July 1997

• Two radio frequency (RF) technologies were first defined:

–Frequency Hopping Spread Spectrum (FHSS)—1 Mbps and 2 Mbps

–Direct Sequence Spread Spectrum (DSSS)—2-Mbps and

11 Mbps

• Defines the performance of radios

• Provides specifications for vendor interoperability (over the air)

• Defines security used over the air and authentication types

When an IEEE committee works on a standard, the members ask to have engineers from all appropriate companies in the field participate in the development of the specification The 802.11 committee is no different Engineers from many different wireless data companies (and some wired LAN companies) together developed a standard that they believe is a high-quality, high-performance standard

For this reason an 802.11 radio will be a better product than any of the older proprietary

products The 802.11 standard defines such things as receiver sensitivity, MAC layer

performance, data rates, security, and so on

Radio engineers put the 802.11 specification together from wireless companies such as Cisco Systems (Aironet), Harris Corporation (Intersil), and Lucent Technologies (Agere), as well as network engineers from companies such as Bay Networks, 3Com Corporation, and Microsoft Corporation

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WI-Fi Certification

• Wi-Fi Alliance certifies interoperability between products

–Products include 802.11a, 802.11b, 802.11g, dual band products, and security testing

–Provides assurance to customers of migration and integration options

• Cisco is a founding member of Wi-Fi Alliance

• Certified products can be found at http://www.wi-fi.com

The Wi-Fi Alliance offers certification for interoperability among 802.11 products offered by various vendors This certification provides a comfort zone for the users purchasing the

products It also helps market the WLAN technology, by promoting interoperability between vendors Certification includes all three 802.11 RF technologies, as well as Wi-Fi Protected Access (WPA), a security model that follows the 802.11i security task group work

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IEEE 802.11 Standard Activities

* Denotes Ratified standard, otherwise in draft

802.11a* —5 GHz, ratified in 1999

802.11b* —11 Mbps 2.4 GHz, ratified in 1999

802.11d* —World Mode

802.11e* —Quality of service

802.11F* —Inter-Access Point Protocol (IAPP)

802.11g* —Higher data rate (>20 Mbps) 2.4 Mbps

802.11h* —Dynamic Frequency Selection and Transmit Power Control mechanisms

802.11i* —Authentication and security

802.11j* —Additional Japanese frequencies

802.11k —Radio Resource Management

The 802.11a, b, and g specifications all relate to WLAN physical layer standards

Cisco Aironet access points in this release support the 802.11d standard for world mode World mode enables the access point to inform an 802.11d client device which radio setting the device should use to conform to local regulations

The IEEE 802.11e standard is being developed to enhance the current 802.11 MAC to expand support for applications with quality of service (QoS) requirements and improve the

capabilities and efficiency of the protocol This standard will assist with voice, video, and other time-sensitive applications In March 2005, the IEEE will submit this standard to the Executive Committee for approval

The IEEE 802.11F standard is a recommended practice guideline, defining a protocol for intercommunication between access points, to assist in roaming, and handoff of traffic Most vendors have implemented their own proprietary Inter-Access Point Protocol (IAPP) for use with their access points

The IEEE 802.11h standard is supplementary to the MAC layer to comply with European regulations for 5-GHz WLANs Most European radio regulations for the 5-GHz band require products to have transmission power control (TPC) and dynamic frequency selection (DFS) TPC limits the transmitted power to the minimum needed to reach the farthest user DFS selects the radio channel at the access point to minimize interference with other systems, particularly radar

The IEEE 802.11i standard is intended to enhance the current 802.11 MAC to provide

improvements in security

The IEEE 802.11j standard is intended to enhance the 802.11 standard and amendments, to add channel selection for 4.9 GHz and 5 GHz in Japan to conform to Japanese rules on operational mode, operational rate, radiated power, spurious emissions, and channel sense

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The IEEE 802.11k task group was developed to define and expose radio and network

information as well as facilitate the management and maintenance of a wireless and mobile LAN It is also expected to enable new applications based on this radio information—for

example, location-enabled services

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802.11a

Ratified as standard in September 1999 Provides similar technology to HyperLAN 2.0 Data rates to 54 Mbps defined

Provides eight indoor WLAN channels today

• More channels forthcoming

Regulations differ extensively across countries

The Cisco Aironet 1000 Series consists of three access points each featuring dual 2.4- and GHz radios supporting IEEE 802.11a, 802.11b and 802.11g In addition it is available with a single 2.4 GHz radio that supports 802.11g and 802.11b, for installations where 5 GHz is not allowed due to regulatory restrictions All interoperate with Cisco Wireless LAN Controllers and the Wireless Control System (WCS) management tool Each is optimized for different application scenarios:

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802.11a Issues

Twelve channels (UNII-1, UNII-2 and UNII-3 combined)

• Avoid the use of adjacent channels in adjacent cells due to sidebands

Antenna limitations

• UNII-1–Indoor usage The requirement for permanently attached antennas in the U.S was removed in June, 2004

• UNII-2–Indoor/outdoor and may use external antennas

• UNII-3–Can be used indoors

Not qualified in many countries

• Transmit (Tx) power control and dynamic frequency selection required (802.11h)

The 5-GHz band is divided into several sections The lower eight channels cover the two

sections known as UNII-1 and UNII-2 Each of these sections includes 100 MHz of spectrum,

in which there are four channels The UNII-1 band has limitations in the United States (and some other countries) that require it to be used indoors UNII-2 is permitted for both indoor and outdoor usage, and permits external antennas UNII-3 can be used indoors or outdoors

There are rule changes under way With the adoption of 802.11h, the new rules will provide up

to an additional 11 channels in many countries, as well as providing the UNII-3 band for

WLAN usage This change will increase the number of WLAN channels from eight to as many

as 24

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• Virtually approved for worldwide use

The 802.11b standard was ratified in 1999 Products were actually introduced into the market before the standard was ratified; 802.11b became the de facto standard for wireless, and

adoption grew rapidly There are 11 channels available in the United States However, only three of these channels are nonoverlapping In the European Telecommunications Standards Institute (ETSI) domains, there are 13 available channels, but again there are only three

nonoverlapping channels In Japan, there is an additional channel located at the top end of the band It is possible to use this along with three other channels for a total of four nonoverlapping channels

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802.11g

Standard for higher-rate (20+ Mbps) extensions in the 2.4- GHz band

• Provides data rates up to 54 Mbps at 2.4 GHz

• Same speeds as 802.11a

• Backward compatible with

The 802.11g standard was ratified in June 2003 Products were actually being shipped before the standard was ratified The speeds of 802.11g promised to be similar to those of 802.11a, and 802.11g uses the same frequencies as 802.11b As a result, 802.11g has full backward compatibility with 802.11b

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802.11g Transmit Power

The power must be backed off for OFDM to handle peaks

of modulation

• Complementary Code Keying (CCK):

–100 milliwatt (mW) (20-decibels compared to 1 mW [dBm])

802.11g Transmit Power (Cont.)

• Maximum power setting will vary according to individual country regulations.

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Spread Spectrum RF Technology

This topic discusses theories and processes of using spread spectrum technology to send data over a RF signal

What is WLAN RF Technology?

Data sent over the air waves Two-way radio communications (half-duplex) Same radio frequency for sending and receiving (transceiver)

No licensing required for Cisco Aironet wireless products (in most countries)

Transmitting a signal using 802.11 specifications is a two-way communication, using the same frequency for both transmit and receive (often called half-duplex or simplex) The 802.11 specification was developed so that there would be no licensing required in most countries, and the user could install and operate without any license or operating fees

Spread spectrum is a type of emission designed to be somewhat immune to interference,

difficult to detect, and hard to intercept

U.S Actress Hedy Lamarr and music composer George Antheil patented the concept of spread spectrum in 1942 The idea was to provide a method for guiding a torpedo without interference from a jamming signal

In 1986, the U.S Federal Communications Commission (FCC) agreed to allow the use of spread spectrum in the commercial market under the ISM bands

Just as the radio in your car has amplitude modulation (AM) and frequency modulation (FM) bands, other radios use different bands and types of modulation

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When you are transmitting a signal in data format, three questions must be addressed:

How fast: What data rate can be achieved?

How far: How far apart can the units be that are transmitting or receiving and still get the

maximum data rate?

unacceptable level? The 2.4-GHz and 5-GHz products operate as a shared medium and have the same scalability and utilization issues as a wired Ethernet segment

These factors all relate to the ability to receive a good signal as far away as possible Increasing the amount of data requires the use of more frequency spectrum or a different method of

placing the data on the RF signal (modulation technique)

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More information means more frequency

spectrum is used.

3K 175K 4500K Bandwidth in kHz

TV Signal

FM Radio Signal

CB Radio SignalFrequency Bandwidth

As more information is placed on a radio signal, more frequency spectrum (or bandwidth) is used A brief comparison is a follows:

A citizens band (CB) signal has very low-quality audio and requires about 3 kHz of

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Signal Strength Strong Medium Weak Low Medium High Noise Level

Modulation

Complex modulation

• Better signal strength

• Less coverage area

Complex modulation schemes compress data Better (quieter) phone line needed for higher speed More noise, less speed

Years ago, a modem was able to communicate at 300 baud Today, a 56-kbps modem gets much higher speeds over the same wire as the 300-baud modem This increase in speed is due

to the modem compressing the data into a smaller space and using the same bandwidth of the phone line that the 300-baud modem used

One problem that may arise is that if there is noise on the phone line, the modem speed will be reduced As the data is further compressed, it requires a stronger signal as compared to the noise level More noise means slower speed for the data to be received correctly

The same is true in radio As a receiver moves farther from a transmitter, the signal gets

weaker, and the difference between the signal and noise decreases At some point, the signal cannot be distinguished from the noise, and loss of communication occurs The amount of compression (or modulation type) at which the signal is transmitted determines the amount of signal necessary to be clearly received through the noise

As transmission or modulation schemes (compression) become more complex and data rate goes up, immunity to noise decreases, and coverage goes down

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The 802.11b specification uses different modulation techniques, including the following:

another to represent a binary 0 for a total of two bits of binary data This technique is used

to transmit data at 1 Mbps

changes in phase and can thus represent four binary bits of data This technique is used to transmit data at 2 Mbps

complementary codes to send more data One of the advantages of CCK over similar modulation techniques is that it suffers less from multipath distortion This technique is used to transmit data at 5.5 and 11 Mbps

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802.11b Direct Sequence Modulation

Each data bit becomes a string of chips (chipping sequence) transmitted in parallel across a wide frequency range.

Minimum chip rate per the FCC is 10 chips for 1 and 2 Mbps (BPSK/QPSK) and 8 chips for 11 Mbps (CCK) data rates

IEEE 802.11b uses 11 chips.

If the data bit was: 1001 Chipping code is : 1=00110011011 0=11001100100 Transmitted data would be:

00110011011 11001100100 11001100100 00110011011

1 0 0 1

If the data bit was: 1001 Chipping code is : 1=00110011011 0=11001100100 Transmitted data would be:

00110011011 11001100100 11001100100 00110011011

1 0 0 1

A feature of these codes is that the receiver could actually miss several bits and the software would still be able to identify that the code was intended to be a 1 or a 0 If there were an interfering signal, the unit would still be able to get the data through without loss of data or reduction in throughput or performance

Note A bit received that was a 01111011011 would, when compared to a 1, be two bits different

Compared to a 0, it would be 9 bits different Therefore, that received bit should represent a

1 More than 5 data bits would have to be inverted to change the value, which means that more than half the signal would have to be lost before the original message would be impossible to reconstruct

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2.4-GHz Antennas

This topic describes the various 2.4-GHz antennas available from Cisco

2.4-GHz Channel Sets (Cont.)

North American

• 11 channels – each channel 22 MHz wide

• Three nonoverlapping channels

ETSI

• 13 channels – each channel 22 MHz wide

–Still only three nonoverlapping channels

• Three access points can occupy same area

With 802.11b and 802.11g products, the energy is spread over a wide area of the band With 802.11b or 802.11g products, the channels have a bandwidth of 22 MHz This bandwidth will allow three nonoverlapping, noninterfering channels to be used in the same area

If there is severe signal interference in one area, it is possible to change to another channel and totally avoid the interference Normally, changing channels does not happen automatically in DSSS and must be done with reconfiguration to the access point Cisco firmware will allow an access point to search for the least congested channel

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802.11b Access Point Coverage

1-Mbps DSSS

5.5-Mbps DSSS 11-Mbps DSSS 2-Mbps DSSS

All Cisco 802.11 WLAN products have the ability to data rate shift while moving This allows the person operating at 11 Mbps to shift to 5.5 Mbps, 2 Mbps, and finally still communicate at the outside ring at 1 Mbps This rate shifting happens without losing connection and without any interaction from the user Rate shifting also happens on a transmission-by-transmission basis Therefore, the access point has the ability to support multiple clients at multiple speeds depending upon the location of each client

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combined) data rate for an 802.11b system is 33 Mbps for a given cell area

Using the ability to scale throughput and add access points in the same cell area increases the overall available bandwidth of any cell

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IEEE 802.11a Characteristics

This topic describes the modulation technique used by 802.11a

Comparing the Technologies 802.11a Data Rates

54 1125

64-QAM

48 1000

64-QAM

36 750

16-QAM

24 500

16-QAM

18 375

QPSK

12 250

QPSK

9 187.5

BPSK

6 125

Modulation with Sub-channels

OFDM is the modulation technique used by 802.11a and 802.11g OFDM works by breaking one high-speed data carrier into several lower-speed sub-carriers, which are then transmitted in parallel Each high-speed carrier is 20 MHz wide and is broken up into 52 subchannels, each approximately 300 kHz wide OFDM uses 48 of these subchannels for data, while the

remaining four are used for error correction Coded Orthogonal Frequency Division

Multiplexing (COFDM) delivers higher data rates and a high degree of multipath reflection recovery, thanks to its encoding scheme and error correction

Each sub-channel in the OFDM implementation is about 300 kHz wide At the low end of the speed gradient, BPSK is used to encode 125 kbps of data per channel, resulting in a 6000-kbps,

or 6-Mbps, data rate Using QPSK, you can double the amount of data encoded to 250 kbps per channel, yielding a 12-Mbps data rate And by using 16-state quadrature amplitude modulation (16-QAM) encoding 4 bits per cycle, you can achieve a data rate of 24 Mbps The 802.11a standard specifies that all 802.11a-compliant products must support these basic data rates The standard also lets the vendor extend the modulation scheme beyond 24 Mbps Data rates of 54 Mbps are achieved by using 64-state quadrature amplitude modulation (64-QAM), which yields

8 bits per cycle or 10 bits per cycle, for a total of up to 1.125 Mbps per 300-kHz channel With

48 channels, this results in a 54-Mbps data rate Remember, the more bits per cycle (hertz) that are encoded, the more susceptible the signal is to interference, and ultimately the shorter the range, unless power output is increased

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Channel sampled at 20 MHz

• 64-sample (3.2 microsecond) symbols

• 16-sample (0.8 microsecond) cyclic prefix/guard interval

• 250 symbols per second

Of 64 subcarriers:

• 12 zero subcarriers (In black) on sides and center

– Side is frequency guard band leaving 16.5 MHz occupied bandwidth

– Center subcarrier is zero for DC offset/carrier leak rejection

• 48 data subcarriers ( in green ) per symbol

• 4 pilot subcarriers ( in red ) per symbol for synchronization/tracking

OFDM (52 of 64 subcarriers used)

20 MHz

802.11a Uses OFDM Modulation

The OFDM encoding scheme works by splitting the 20-MHz radio channel into 52 smaller subcarriers, 48 of which are used to transmit data The remaining four subcarriers are used as pilot carriers for monitoring path shifts and intercarrier interference (ICI) These subcarriers are then transmitted simultaneously at different frequencies to the receiver

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802.11a 5-GHz Frequency Bands

5150 Lower Band Edge 5180 5200 5220 5320

20 MHz

5240 5260 5280 5300 5350

Upper Band Edge

High-Speed Physical Layer in the 5-GHz Band Lower and Middle U-NII Bands: Eight Carriers in 200-MHz/20-MHZ Spacing

Upper U-NII Bands: Four Carriers in 100-MHz/20-MHZ Spacing

20 MHz

Lower Band Edge 5725 5745 5765 5785 5805 Upper Band Edge 5825

Std 802.11a-1999

The figure shows the center frequency of the channels The frequency of the channel is 10 MHz

on either side of the dotted line and there is 5 MHz of separation between channels

The 802.11a standard has twelve channels without overlap of frequency; 802.11b has 11

channels with only three channels that do not overlap in frequency UNII-1 uses the first four channels and UNII-2 uses the second four channels and UNII-3 uses the upper 4 channels The lower and middle UNII U.S channels included the following:

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For more information see:

http://www.cisco.co m/go/aironet/compli ance

Cisco UNII-1 and UNII-2 802.11a Channel Sets

If a 6-dBi antenna is used then the radiated power is as follows:

UNII- 1: 50 mW in the United States and Japan, 200 mW in Europe, 4 channels (5.15 to

5.25), indoor access, fixed antenna

UNII- 2: 250 mW in United States, four channels (5.25 to 5.35), indoor and outdoor use,

flexible antenna

UNII- 3: 1 W in the United States, four channels (5.725 to 5.825), indoor and outdoor use,

flexible antenna

HiperLAN: 200 mW in Europe, eight channels (5.25 to 5.35), indoor use only

HiperLAN II: 1 W in Europe, 11 channels (5.470 to 5.725), indoor and outdoor use,

flexible antenna

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