system integration of a wireless local area network -...

System Integration of a WirelessLocal Area Network

By: Jonathan Jump, Jason Lister, Geoff Mikosz

Advisor: Dr. Brian Huggins

May 15, 2001

System Integration of a Wireless Local Area Network Jump Jump, Lister, Mikosz

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Abstract

The purpose of this project is to design and implement a wireless LAN system for

the Bradley University Electrical Engineering Department. The system is made up of an

access point (AP) which connects the wired LAN with wireless peripherals. Wireless

peripherals include laptops, desktops and embedded systems. The project consists of five

phases: research, design and development, purchasing, implementation and testing.


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Table of Contents

INTRODUCTION ............................................................................................................ 4

SYSTEM DESCRIPTION ............................................................................................... 4

MODES OF OPERATION .............................................................................................. 7

WIRELESS LAN STANDARDS AND PROTOCOL................................................... 9

PROJECT TIMELINE..................................................................................................13

CHOOSING A PRODUCT:...........................................................................................14

TESTS AND MEASUREMENTS .................................................................................14

TRANSMISSION POWER ...........................................................................................16

PERFORMANCE MAPPING.......................................................................................17

ANALYSIS OF RESULTS.............................................................................................17

CONCLUSIONS .............................................................................................................19

REFERENCES...............................................................................................................21

APPENDIX A: DATA....................................................................................................23

APPENDIX B: TESTING UTILITIES..........................................................................29

APPENDIX C: SUPPLEMENTARY DATA................................................................33

APPENDIX D: ALGORITHMS FOR FUTURE TESTING.......................................34


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Introduction

The task of this project is to implement a wireless local area network into the Bradley

University Electrical and Computer Engineering department. Specifications for the

network are based on the needs of the customer, the Electrical and Computer Engineering

department. The department would like to be able to use this network for three major

purposes: allowing network connections to portable computers, networking computers

which are far away form wired ethernet jacks, and networking wireless embedded

projects.

The project encompasses the following tasks:

1. Obtain information on the technology of wireless LANs, including standards.

2. Establish functional requirements and specifications of the system.

3. Identify vendors of wireless LANs, and establish criterion for selection of a

vendor's product.

4. Select a vendor(s) by application of the criterion.

5. Implement the design of the wireless system.

6. Design methods to thoroughly test the system.

System Description

The wireless local area network (WLAN) is made up of several different

subsystems. A block diagram of the system is shown in Fig.1. The inputs to the system

will be desktop computers, laptop computers, and embedded systems (fixed and mobile).

Each client has a wireless network card that can communicate with an access point (AP).


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The AP manages WLAN traffic and physically connects the wireless system to the wired

local area network (LAN). The wired LAN will then send the requested information

back to the access points, which will relay it to the appropriate client.


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Fig. 1 : Block Diagram of a Wireless LAN


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Modes of Operation

The system has three modes of operation:

Op-Mode: This is the standard operating mode for system operation. The mode consists

of interaction between clients and one or more server. The clients are wireless devices

such as laptops, desktops and telerobtics platforms. Servers are access points that

connect the clients to a wired network. Quality of communication between the clients

and server depends on distance, obstructions, RF noise level and network traffic.

Manage Mode: This mode is accessible to system administrators. It consists of software,

which allows administrators to maintain and modify system settings. The software is

located on the access point and accessed either by a web browser.

Test Mode: This mode contains the diagnostic programming that examines the

performance of the overall network, along with the separate components (i.e. the AP and

network card). The test mode includes measurements such as signal quality, signal

strength and network load as well as instructions on how to find and troubble shoot

common problems.There are five main subsystems in the system and three modes of

operation. The subsystems are the client, manager, RF network card, access point and

wired network. The modes of operation are op-mode, manage mode and test mode.

Table 1 lists the different subsystems and how they operate under each control mode.


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Table 1: Subsystem OperationsSubsystem Op-mode Manage Mode Test ModeClient The client computer

exchanges data withits RF network card.

The systemadministrator hasaccess to aconfiguration toolusing a web browser.The client can alsocontrol the localsettings of its RFnetwork card.

Client's computers arecapable of running aseries of tests todiagnose networkproblems anddetermine bestplacement and datarate of the clientcomputers and APs.

Manager The manager is aclient but alsomonitors variousfunctions such as RFnetwork traffic.

The systemadministrator can runsoftware on his/hercomputer to access anetwork configurationtool that manages theRF network.

The administrator canrun a series of tests toevaluate the networkand determine bestplacement and datarate of the clientcomputers and APs.

RF Network Card Exchanges databetween client and theAP via 802.11b DSSSformat.

Exchanges databetween client and theAP via 802.11b DSSSformat.

Exchanges databetween client and theAP via 802.11b DSSSformat.

Access Point Allows the RF LANto access the wiredLAN. It receives datafrom the LAN andrelays it to theappropriate clientradio through RFDSSS signals. It alsochecks for data fromclients to relay to theLAN.

Contains networkmanagement softwarethat can be accessedby a systemadministrator from aweb browser orcommercial software.

Serves as a gatewaybetween the wiredEthernet and the RFnetwork cards.

Wired Network Allows the wirelessLAN access to theInternet and the wiredLAN.

Allows the wirelessLAN access to theInternet and the wiredLAN.

Allows the wirelessLAN access to theInternet and the wiredLAN.


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Wireless LAN Standards and Protocol

Wireless LAN's have been used for years in vertical markets such as academia,

warehousing, retail and health care. It has just recently been realized as a general-purpose

connectivity alternative for a broad range of business. The first wireless LAN was created

in 1971 as a research project at the University of Hawaii called ALOHNET. The system

used seven computers deployed over four islands to communicate in a bi-directional star

topology with a central computer on Oahu. There are three major wireless LAN

standards that were considered are IEEE 802.11(b), Blue Tooth, and IEEE 802.11a

(HiperLAN2).

IEEE 802.11

For Wireless LAN's to be widely accepted there needed to be an industry standard

to ensure compatibility and reliability among the various manufactures. The original

802.11 standard was ratified by Institute of Electrical and Electronics Engineers (IEEE)

in 1997 as the standard for wireless LAN's. It provides for data rates of 1 Mbps and 2

Mbps and a set of fundamental signaling methods and other services. The specifications

of IEEE 802.11 define two layers: the physical layer and the Media access control

(MAC) layer. These are described below.


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Physical Layer

The physical layer (PHY) specifies which modulation scheme to use and the

signaling characteristics for the transmission through the radio frequencies. The 802.11

standard defines two different RF transmission methods. Both are types of spread

spectrum technology designed by the Military for reliability, integrity and security. The

trade off is bandwidth efficiency. The two techniques are Direct Sequence Spread

Spectrum (DSSS) and Frequency Hopping Spread Spectrum (FHSS).

Frequency Hopping Spread Spectrum

In FHSS, the available band is split into several channels. The carrier changes

frequency in a sequence known by both the transmitter and receiver. The modulation

scheme defined for FHSS is 2-4 level Gaussian Frequency Shift Keying (GFSK). The

main concept behind GFSK is to vary the carrier frequency to represent different binary

symbols. The transmitted data is shifted above or below the center frequency by the

comdulator.5 One advantage is that FHSS enables coexistence of multiple networks. The

equipment is also inexpensive compared to the DSSS equipment. Also, GFSK reduces

the potential for interference since noise will tend to affect the amplitude of the signal but

not the frequency. 5

Direct Sequence Spread Spectrum

In DSSS a single pseudo-random binary string, sometimes referred to as a

chipping signal, is used to modulate the transmitted signal. (Generates a redundant bit


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pattern, length of eleven bits, which then multiplies each data bit to be transmitted. The

bit pattern is also often referred to a chipping code.) The 802.11 standards for modulation

in this mode are Differential Bi and Quadrature Phase Shift Keying (DBPSK and

DQPSK). DBPSK is a modulation scheme where a spread digital signal is converted to a

Differential Binary Phase Shift Keyed signal. If a logic one is found in the transmitted

packet, the phase of the carrier is altered. Since only detection of transitions occur,

DBPSK provides freqeuncy independence. 14 DSSS is better where throughput is needed

and interference is not a problem.

Media Access Control Layer

The Media Access Control (MAC) layer defines a way of accessing the physical

layer as well as services related to the radio resource and the mobility management. It is

similar to the Ethernet standard 802.3. However, the two standards deal with collisions

differently. Ethernet uses Carrier Sense Multiple Access with Collision Detection

(CSMA/CD). However, 802.11 uses Carrier Sense Multiple Access with Collision

Avoidance (CSMA/CA) because it is difficult to detect collisions in wireless systems.

IEEE 802.11b

Throughput is a critical issue that is affecting the Wireless LAN demand. The

IEEE 802.11b recognized the need to support higher data-transmission rates. The

802.11b standard can transmit up to 11Mbps making it able to achieve wireless

performance and throughput comparable to wired Ethernet. The physical layer uses


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Direct Sequence Spread Spectrum and Complementary Code Keying as the modulation

scheme. Complementary Code Keying (CCK) modulation puts more bits into each

symbol that is being transmitted. 8 This results in more bits per second being transmitted,

even though the overall number of symbols being transmitted may not change. It can

also implement Packet Binary Coding Modulation, but systems that implement this must

also be able to support CCK.

Blue Tooth

Another standard that has become popular is Bluetooth. Bluetooth is designed for

low power consumption and, therefore, has limited range. It was not created specifically

for wireless LAN technology but with the right software it can be used as one. One

problem with Bluetooth is that it only has a throughput of 800kbps, makes it doubtful that

it will replace wireless LAN equipment. It also has no procedure for handing off from

one AP to another.

HiperLAN2

The next significant improvement to wireless LAN’s is HiperLAN2 which is the

IEEE 802.11a standard. This system operates at 5GHz with a maximum throughput of

54Mbps and provides freedom from interference. HiperLAN2 is an emerging technology

and will take 2-3 years before equipment to be available. HiperLAN2 does have it's

problems though. Higher frequency and data rate will mean greater power consumption

and more limited range.


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Project Timeline

The project is divided into several phases. These phases include research, design

and development, purchasing, implementation, and testing.

Phase I: Research

In this phase product vendors were researched, specifications and protocols were

analyzed, and price was compared with product quality. A vendor was then selected to

best fit the Electrical Engineering Department's needs. The team also determined the

needs of the client and where the best number and placement of access points would be in

the Engineering building.

Phase II: Design and Development

Once the vendor and product has been selected the team will devise a wireless

local area network plan. This plan will take into consideration the locations where the

client wants to access the network, the structure of the building, and the number of users.

Phase III: Purchasing

The team will present the proposed system to the project advisor and Lab Director

for purchasing approval.

Phase IV: System Implementation

Once the equipment has arrived the system will be integrated in accordance with

the previously developed plan.


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Phase V: Test and Measurements

A series of tests and measurements will be executed to test the performance of the

wireless system. The system will be pushed to extremes to test its limitations. During

this phase, all network troubleshooting should be done.

Choosing a product:

The product chosen was the Cisco Aironet 340. It was choosen because it had

execellent preformance4, best all round value, and was compatable with Bradley

Computing Services wireless LAN.

a) b)

Fig 2 : a) Aironet wireless LAN clients b) Aironet 340 Access Points

Tests and Measurements

The dependent variables tested in the system were throughput and signal strength.

Throughput is the amount of data transmitted per unit time. In our tests, throughput was

measured as mega-bits per second (Mbps). In order to measure throughput, the WS_FTP

utility was used. The WS_FTP utility is File Transfer Protocol (FTP) program that


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enables users to transfer files from one computer to another over a TCP/IP connection.

WS_FTP was chosen mainly because it is easy to transfer files with and it provides

throughput and transfer time measurements. Fig.11 depicts a screenshot of the WS_FTP

interface (refer to Appendix B). The “Transfer Status” window that is present over the

actual WS_FTP interface indicates that a file transfer is in progress. In can be seen in this

window that the program displays throughput and transmit time measurements. The

timing of the file transfer is both initiated and ended based on replies from the receiving

machine. For every FTP command there is a “handshake” from the receiving machine to

verify the command. When FTP initiates a file transfer, the timer starts when the

receiving machine replies that it is ready to receive the file. Once the receiving machine

receives the entire file, it sends a reply back to the sender that the file transfer is complete

and the timer is stopped. Signal strength was measured using the Link Status Utility

(Fig.15) provided by Cisco Systems. Signal strength was measured as a percentage of

maximum power.

To investigate throughput and signal strength, several independent variables were

introduced. These variables are file size, distance, and transmit power.

File Size

The file size test was used to investigate how file size affected throughput.

WS_FTP was used to FTP files of vaious sizes from CEGT201 to the wireless client

(laptop). The file sizes were: 1kB, 10kB, 100kB, 500kB, 1MB, 10MB, 50MB, and

100MB. File size, transmit time, and throughput were recorded for each file transfer.

The results can be seen if Fig. 3 and Fig. 4 (refer to Appendix A).


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Distance

The distance test was used to show the relationship between distance, throughput,

and signal strength. As before WS_FTP was used, but this time only a 1Mb file was

transferred. The starting point for the test was directly underneath the AP and was

designated as 0ft. The 1Mb file was FTP’ed from CEGT201 to the wireless client

(laptop) and the distance, throughput, and signal strength were all recorded. The same

1Mb file was FTP’ed again at a distance of 5ft away from the previous position. Each

time a trial was run, the distance increased by 5ft and distance, throughput, and signal

strength were recorded. The maximum distance used was 62ft. There was no magical

reasoning for this number. The test was performed repeatedly as described until the end

of the hallway was reached. This distance happened to be 62ft. The results of this

experiment can be found in Fig. 5.

Transmission Power

The power testing was split in to two tests. The first test measured throughput

and signal strenght at a range of power levels from 1mW, 10mW, and 30mW. To change

the transmit power on the AP, the browser based management software was used.

Various screen shots of the software are dipicted fig. 12, 13, 14. Fig. 13, the AP Radio

Hardware screen, shows a pull down menu where the transmit power can be changed. At

each power level the distance test was repeated. The second test measured throughput

and signal strengh using three different power modes on the radio card settings. These

power modes Constant Awake Mode (CAM), Fast Power Save Mode (Fast PSM),

Maximim Power Save Mode (Max. PSP). CAM is the default mode where the power is

constantly on. Fast PSP switches between CAM and sleep mode. When there is traffic it


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operates in CAM and then jumps into sleep mode during other times. Max. PSP is in

sleep mode most of the time. It will periodicly check with the AP to see if there is a large

amount of data buffered then receives it when a certan size of data is buffered. The

power mode settings are set on the client software. The distance test was repeated for

each power mode and distance, throughput, and signal strength was recorded.

Performance Mapping

The purpose of performance mapping was to get an idea of how well the system

will preform in different parts of the ECE department. The Cisco Link Status utility (Fig.

15) was used to determine the performance based on signal strength and signal quality.

Ratings of excellent, good, fair, and poor were given by the utility based on the following

signal properties3 :

Excellent - both values (signal strength & quality) >75%

Good - both values greater than 40%, but one or both are less than 75%

Fair - both values are greater than 20%, but one or both are less than 40%

Poor - one or both values are less than 20%

Blueprints of the three floors of the North end of Jobst were obtained for this test.

Readings were taken throughout each floor and recorded on copies of the blueprints.

Fig 8, 9, & 10 show the coverage area as determined by the experiment.

Analysis of Results

In discussion of throughput, our team thought that, in theory, the throughput

would increase with the increase of file size. In actual testing, the throughput peaks at a


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certain point that is x feet from the AP (see Fig. 3). This is due to reflections from

doorways, metal in the walls and floors, etc. The time taken to FTP a file from cegt201

to our client versus its file size matched our theoretical thinking. The graph of these two

variables shows a perfectly linear increase of time as file size increases (see Fig. 4).

In the three power modes tested, throughput was the greatest when the system was set to

30mW of operational power, with the next greatest to be 15mW, followed by 1mW as the

least greatest (see Fig. 5). In power save testing, the results varied slightly from theory.

In actual results, the best throughput and signal strength came from the Fast PSP (or

power save mode). Throughput versus distance was not very stable for Max PSP

(maximum power save mode). CAM (Continuously Active Mode) gave the system

stable throughput versus distance, but the throughput was not quite as high as throughput

in Fast PSP mode (Fast PSP) throughput peaked at 6.7Mbps and CAM throughput peaked

at 6Mbps) (see Fig. 6). The signal strength of our system in CAM decreased steadily

with distance through the whole testing distance (62 ft.). Signal strength in Fast PSP

decreased steadily as well, but began to significantly drop off at 50 ft. Signal strength of

Max PSP was not as steady and began to drop off at 42 ft (see Fig. 7).

To get a better feel for the relationship between throughput and packet errors, the

team FTP’ed a 1MB file to the laptop and recorded forwarded packets and number of

retries at several different link qualities, as defined by the Cisco site survey utility. The

results, which are shown in Table 2 (see Appendix C), clearly show that as throughput

dimishes the number of retries increases. The results somewhat conflict with the signal


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quality meter found in Cisco’s Site Survey utility. The utility consistently depicts the

signal quality as being between 75-100% even when the signal strength is extremely low

and overall link quality is low. A possible explaination for this is that the packets sent by

the AP to determine link quality and, consequently, signal quality could be relatively

small in comparision to the 1MB file we sent. Smaller packet sizes have a reduced

probability of error whereas the opposite is true for larger packets sizes. If the packets

the AP sends to determine link quality are small, the probability of error is low and,

consequently, the quality of the signal is relatively good. Also, the signal strength could

still be lowered since a smaller packet would require less energy to tunnel through

barriers. With a larger file such as the 1MB file we tested with, the probability of error is

larger. Hence the increse in the number of retries and the drop in throughput.

Conclusions

Our overall system was successful in achieving our goal of operation for the

CEGT department. The coverage area received by our system was not quite what we

wanted it to be, but there are ways of improving this, which will be discussed shortly.

The second floor of Jobst gave our system the best coverage area, followed by the third

floor, and then the first floor giving the worst coverage area (see Fig. 8-10). Throughput

and signal strength varied from our theoretical understanding, in that both variables took

on almost an oscillatory behavior in many graphed results. This was due to reflections in

the metal components of the building's barriers. Power save results were desirable to a

point. It is favorable to the operation of the system in the sense that our best mode is the

Fast PSP mode, but Max PSP left less than desired results. Another thing to consider


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with power save mode is the tradeoff between throughput and power saving: the higher

the power save mode is, the less throughput the system will acquire. Ways on improving

the system include adding a second AP, which will broaden the coverage area, and

performing several more tests. These tests include encryption, network loading, handoff

capabilities between AP’s (if a second AP is purchased), and interoperability between

vendor. Algorithms for these tests are included in Appendix D.


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References

1. Cisco 340 Aironet Series Base Station. Cisco Systems, Inchttp://www.cisco.com/warp/public/cc/pd/witc/ao340ap/prodlit/bstn_ds.htm

2. Cisco Aironet 340 Series Client Adapters and Access Points. Cisco Systems, Inc.http://www.cisco.com/warp/public/cc/pd/witc/ao340ap/prodlit/airoi_ds.htm

3. Cisco Systems, Inc. "Using the Cisco Aironet 340 Series PC Card Client Adapters"Cisco Systems, Inc March 27, 2000.

4. Conover, Joel. "Wireless LANs Work Their Magic." Network Computing July 2000.http://www.networkcomputing.com/1113/1113f2.html

5. Cueva, Vincent, Kim, Samson, Hossain, Shahroz. The Modulation Scheme Used byDECT is GFSK. http://www-ug.eecg.utoronto.ca/~hossain/dect_gfsk.htm

6. Enterasys Networks, Inc. "Roamabout R2 Wireless Access Platform Data Sheet"Enterasys Networks, Inc.

7. Files, Patrick. "Using the Cisco Aironet 340 Series Access Point" Cisco Systems, IncMarch 3, 2000.

8. Frank, Alan. Wireless LAN’s Up-Shift to 11Mbps.http://www.networkmagazine.com/article/DCM20000426S0002

9. Intermec Technologies. "Enterprise Wireless LAN 2101" Intermec Technologies.November 7, 2000.

10. Leon-Garcia, Alberto and Indra Widjaja. Communication Networks: FundamentalConcetps and Key Architechtures. New York: McGraw-Hill Professional BookGroup, 2000.

11. Lucent Technologies. "Orinoco AP-500 Access Point" Lucent Technologies.September 20, 2000.

12. Lucent Technologies. "Orinoco AP-1000 Access Point" Lucent Technologies.August 21, 2000.

13. Lucent Technologies. "Orinoco PC Card" Lucent Technologies.September 1, 2000.

14. Megarity, Mark, Drazek, Pawel, Chung, Yee. Wireless Spread SpectrumCommunications. http://www.ee.unb.ca/thesis97/ee4000k/report/report10.html


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15. No Wires Needed. "11Mbps Wireless Enterprise Access Point" No Wires Needed.December 8, 2000.

16. No Wires Needed. "11Mbps Wireless LAN PC Card" No Wires Needed. December8, 2000.

17. Postel, J., Reynolds, J. RFC959: File Transfer Protocol (FTP).ftp://nic.merit.edu/documents/rfc/rfc0959.txt

18. 3 Com corporation. "Airconnect 11Mpbs Wireless LAN Solution" 3 Comcorporation. September 15, 2000.

19. What is a Wireless LAN? Proxim.http://www.proxim.com/wireless/whiteppr/whatwlan.shtml

20. Wi-Fi Certified Products. Wireless Ethernet Compatibility Alliance.http://www.wirelessethernet.org/certified_products.asp


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Appendix A: Data

Fig. 3

Fig. 4

1 2 3 4 5 6 7 8 9 10

x 104

0

1

2

3

4

5

6

7Throughput vs. File Size

File Size (KB)

Thr

ough

put (

Mbp

s) Power Lab Outside parts room

1 2 3 4 5 6 7 8 9 10

x 104

0

1

2

3

4

5

6

7Throughput vs. File Size

File Size (KB)

Thr

ough

put (

Mbp

s) Power Lab Outside parts room


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Fig. 5

Fig. 6

0 1 0 2 0 3 0 4 0 5 0 6 00

1

2

3

4

5

6

7T h r o u g h p u t v s . D i s t a n c e

D i s t a n c e ( f t )

Thro

ughp

ut (

Mbp

s) 3 0 m W F a s t P S P5 m W F a s t P S P 1 5 m W F a s t P S P

0 1 0 2 0 30 4 0 5 0 6 00

1

2

3

4

5

6

7T h r o u g h p u t v s . D i s t a n c e


Thro

ughp

ut (

Mbp

s)

3 0 m W C A M 3 0 m W F a s t P S P3 0 m W M a x P S P


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Fig. 7

0 1 0 2 0 30 40 50 600

1 0

2 0

3 0

4 0

5 0

6 0

7 0

8 0

9 0

1 0 0S i g n a l S t r e n g t h v s . D i s t a n c e


Sig

nal S

treng

th (

%po

wer

)

3 0 m W C A M 3 0 m W F a s t P S P3 0 m W M a x P S P


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Fig. 8


27

Fig. 9


28

Fig. 10


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Appendix B: Testing Utilities

Fig. 11: FTP Window

Fig. 12: Main Page of AP Management Software


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Fig. 13: AP Radio Management Utility

Fig. 14: AP Radio Statistics Page


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Fig. 15: Cisco Link Status Utility

Fig. 16: Cisco Site Survey Utility


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Fig. 17: Cisco System Status Utility


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Appendix C: Supplementary Data

Table 2: Link Status vs Number of Resent Packets

Location Data Rate(Mbps)

ForwardedPackets

Retries Signal Type

EELounge

5.3 1063 113 Fair

GradLab

1.7 903 677 Poor

Jobst243

5.78 880 53 Good

UnderAP

5.72 868 62 Excellent

Sr. Lab 5.52 848 74 Fair


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Appendix D: Algorithms For Future Testing

Encryption

-Set the encryption of the client radio to no encryption.

-Using FTP, send a 1MB file to CEGT201.

-Record throughput, transmit time, and signal strength.

-Repeat with 40-bit and 128-bit encryption.

Network Load

-Using FTP, send a 1MB file to CEGT201.

-Record throughput, transmit time, and signal strength.

-Repeat with multiple clients using large files, ftping at the same time.

Handoff Capabilities

-On a mobile client, walk from one AP to another.

-Record signal strength, distance, and throughput.

-Note where AP handoff occurs.

Interoperability

-Install wireless LAN equipment from different vendors on several machines.

-Repeat Network Load and Handoff Capability tests.

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