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Georgia Institute of Tech nology 1 Performance Monitoring Interface for the 802.11b Networks Yusun Chang Akshay Dayal Robert Liu CS6255 Project Background Presentation
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Georgia Institute of Technology 1

Performance Monitoring Interfacefor the 802.11b Networks

Yusun ChangAkshay Dayal

Robert Liu

CS6255 Project Background Presentation

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Contents

I. Introduction

II. 802.11b Protocol Operation

III. System Overview & Design

IV. Existing Tool Support

V. Future Works

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Introduction

Goal of the Project

Design and implementation of an NMS

Monitoring IEEE 802.11b AP & local user

Performing effective management job

NMS

802.11b Access Point

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Wireless environment Power Loss Long Propagation Delay Fading Interference Random & Burst Errors

Introduction(cont’d)

Transmitters Receivers

Signal Processing

Signal Processing

PacketScheduler

PacketScheduler

User SignalMultiplexer

SignalMultiplexer ReceiverReceiver User

time

Signal strength Signal strength

time

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Wireless Communication

Packet basedPacket based

Wireless LANsWireless LANs802.11802.11

HiperLAN/2HiperLAN/2BluetoothBluetooth

Cellular circuit basedCellular circuit based

CDMACDMAIS-95 (2.5G)IS-95 (2.5G)

CDMA-2000 (3G)CDMA-2000 (3G)UMTS (3G)UMTS (3G)

WCDMA (3G)WCDMA (3G)

GSMGSMGPRS (2.5G)GPRS (2.5G)EDGE (3GEDGE (3G))

Large coverage areaLarge coverage area

Users are actually mobileUsers are actually mobile

Low data ratesLow data rates

Limited coverage areaLimited coverage area

No mobility supportNo mobility support

High data ratesHigh data rates

Introduction(cont’d)

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Contents

I. Introduction

II. 802.11b Protocol Operation

III. System Overview & Design

IV. Existing Tool Support

V. Future Works

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Physical layer Radio DSSS(Direct Sequence Spread spectrum)

Most frequently used radio Data rate

- 1Mbps/DBPSK(Differential Binary Phase Shift Keying)

- 2Mbps/QDBPSK

- 5.5Mbps, 11Mbps/ CCK (Complementary Code Keying) 2.4GHz ISM Band

FHSS(Frequency Hoping Spread Spectrum)

IR(Infra Red)

802.11b Protocol operation(Physical Layer)

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The PCF Protocol AP polls mobile stations one after another by sending polling

message Slot time: signal propagation and processing delay (20 s) SIFS (10 s) : the shortest interval PIFS (30 s) : 1 SIFS + slot time

802.11b Protocol operation(MAC)

[4]

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The DCF Protocol Employs the CSMA/CA mechanism for contention based access

SIFS (10 s)

DIFS (50 s) : 1 SIFS + 2 slot times

Access mechanism

- Select time slot(CW:Contention Window) randomly [0~31]

- Decrement when medium is idle more than DIFS

- When CW expires, access the channel

- If medium is busy, back off CW exponentially

802.11b Protocol operation(MAC)

[4]

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Georgia Institute of Technology 10RTS/CTS/DATA/ACK and NAV[4]

802.11b Protocol operation(MAC)

Initial attempt Previous frame DIFS

31 slots

time

1st retransmission Previous frame DIFS

63 slots

time

6th retransmission Previous frame DIFStime

1023 slots

DSSS CW size

Slots

Station

Initial 5 slot times

TX/

RX

Next

Stage

10 Slot

times

A 5 0 Busy 23 13

B 15 10 10 10 0

Frozen CW in DCF

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I. Introduction

II. 802.11b Protocol Operation

III. System Overview & Design

IV. Existing Tool Support

V. Future Works

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System Overview

Maximize Throughput

Minimize Power Usage

Minimize Packet Loss

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Packet Loss

• Packet Errors

• Packet Collisions

Obstructions

Interference

Low signal strength for distance

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Packet Loss

• Packet Errors

• Packet Collisions

Few users experiencing problems

Many users experiencing problems

Boost signal strength

Adjust data rates, other parameters

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MIBs

Tables:

dot11PhyTxPower

SupportedDataRatesTx

SupportedDataRatesRx

Objects:

dot11EDThreshold (from dot11PhyDSSSEntry TABLE)

dot11BeaconPeriod (from SMT Station Config TABLE)

dot11OperationalRateSet (from SMT Station Config TABLE)

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For correcting packet loss due to packet errors the system will adjust the power levels using the dot11PhyTxPower Table.

For correcting packet loss due to packet collision the system will adjust the beacon period. If the beacon period is too small then the beacon packets will contribute to the traffic.

RTS Threshold – If throughput is slow, decrease RTS threshold

Fragmentation Threshold – Tricky to balance, small size vs number of packets, large size vs transmission time

Retry Limits – Lower retry limits

MIBs

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Simple State Diagram

Packet Loss occurring

Figure out cause

Increase PowerAdjust data rates & beacon

period

No Packet Loss

Monitor Network

Lower power & adjust data rates/beacon

period

Packet Collisions Packet Errors

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Access Point

For implementation and testing we will be using a Linksys WAP11:

It is easy to setup and supports 802.11b

It can transfer data at the rate of 11 Mbps

It supports roaming

Compatible with all major O/Ss

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I. Introduction

II. 802.11b Protocol Operation

III. System Design Overview

IV. Existing Tool Support

V. Future Works

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Existing Tool Support (1)

WAP11 Unix Configuration Utility

•LinkSys does not provide Linux SNMP client

•The use of this tool fills the gap of initial setup and configuration on our Linux working environment

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Existing Tool Support (2)

Wireless Access Point utilities for Unix (ap-utils-1.4.1)

•Provides a set of utilities to configure and monitor wireless AP using SNMP protocols

•Supports LinkSys WAP 11 hardware and its private mib – AT76C510.MIB.

•Three utilities ~

•ap-config: to config and get stats from Atmel-MIB based APs

•ap-mrtg: to get stat from AP and return it in MRTG parsable format

•ap-trapd: to receive, parse and log trap messages from AP

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Existing Tool Support (2, continued)

Wireless Access Point utilities for Unix (ap-utils-1.4.1)

•ap-config:

•Configure and get stats from AP that supports MIB-II, IEEE 802.11 MIB and NWN DOT11EXT MIB, in addition to the private MIB.

•Set bridging and wireless options, radio signal power.

•Get information about AP software and hardware:

Dynamically updated wireless port statistics

Latest events and errors

List of current associated stations with information about signal quality and station activity.

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Existing Tool Support (2, continued)

Wireless Access Point utilities for Unix (ap-utils-1.4.1)

•ap-mrtg:

•Get stat from AP and return it in MRTG (Multi Router Traffic Grapher) parseable format.

•Get Ethernet statistics in bytes, wireless statistics in packets, associated stations number and Link Quality/Signal Strength stats from AP in client mode.

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Existing Tool Support (2, continued)

Wireless Access Point utilities for Unix (ap-utils-1.4.1)

•ap-trapd:

•A SNMP trap processing daemon that accepts traps, parse them and store useful data using syslog, at logging LEVEL0.

•Generic traps:

•ColdStart / WarmStart

•LinkDown / LinkUp

•Specific traps:

•Reset / Startup

•APClientAssociating / APClientConnected

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Existing Tool Support (3)

Cricket

•Tool that supports traffic data collection which can be visualized (real-time trending) over the web.

•A configuration, polling, and data-display engine wrapped around the Round Robin Database (RRD) tool.

•Main components in Cricket:

•Collector – runs from cron (e.g. every 5 mins) and fetches data from devices according to the info in the config tree.

•Grapher – CGI application that allows user traversal of the config tree and the recorded data from a web browser.

•Threshold Monitors – alert mechanism for sending traps.

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I. Introduction

II. 802.11b Protocol Operation

III. System Design Overview

IV. Existing Tool Support

V. Future Works

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Future Works

Thank you !!

•Setup the working environment for the experiment:

•LinkSys WAP11 and the wireless network

•Laptop running Linux (client user)

•NMS Workstation

•Gather relevant data on the performance-related MIB objects

•Analyze the data for feasibility studies

•Design and Implement performance monitoring and optimization interface (NMS) for AP and local users

•System evaluation

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References

[1] David Kotz, Kobby Essien, Analysis of a campus-wide wireless network, Proceedings of the 8th annual international

conference on Mobile computing and networking, September 23-28, 2002, Atlanta, Georgia, USA [2] Diane Tang, Mary Baker, Analysis of a local-area wireless network, Proceedings of the 6th annual international conference on Mobile computing and networking, p.1-10, August 06-11, 2000, Boston, Massachusetts, United

States [3] Hutchins, R.; Zegura, E.W, Measurements from a campus wireless network, Communications, 2002. ICC 2002.

IEEE International Conference on , Volume: 5, 28, April-2 May 2002, Pages:3161 - 3167 vol.5 [4] IEEE Standard for Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specification, P802.11,

1999. [5] WAP11 Unix Configuration Utility: http://wap11gui.sourceforge.net/ [6] Wireless Access Utilities for Unix: http://ap-utils.polesye.net/ [7] Multi Router Traffic Grapher: http://people.ee.ethz.ch/~oetiker/webtools/mrtg/ [8] Cricket: http://cricket.sourceforge.net/ [9] RRD Tool: http://people.ee.ethz.ch/~oetiker/webtools/rrdtool/ [10] Net-SNMP: http://www.net-snmp.org/ [11] Linksys: http://www.linksys.com/products/product.asp?prid=157&scid=7 [12] 802.11 presentation:http://www.umiacs.umd.edu/partnerships/ltsdocs2004/Agrawala_talk.pdf