Download - slides
Georgia Institute of Technology 1
Performance Monitoring Interfacefor the 802.11b Networks
Yusun ChangAkshay Dayal
Robert Liu
CS6255 Project Background Presentation
Georgia Institute of Technology 2
Contents
I. Introduction
II. 802.11b Protocol Operation
III. System Overview & Design
IV. Existing Tool Support
V. Future Works
Georgia Institute of Technology 3
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
Georgia Institute of Technology 4
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
Georgia Institute of Technology 5
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)
Georgia Institute of Technology 6
Contents
I. Introduction
II. 802.11b Protocol Operation
III. System Overview & Design
IV. Existing Tool Support
V. Future Works
Georgia Institute of Technology 7
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)
Georgia Institute of Technology 8
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]
Georgia Institute of Technology 9
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]
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
Georgia Institute of Technology 11
I. Introduction
II. 802.11b Protocol Operation
III. System Overview & Design
IV. Existing Tool Support
V. Future Works
Georgia Institute of Technology 12
System Overview
Maximize Throughput
Minimize Power Usage
Minimize Packet Loss
Georgia Institute of Technology 13
Packet Loss
• Packet Errors
• Packet Collisions
Obstructions
Interference
Low signal strength for distance
Georgia Institute of Technology 14
Packet Loss
• Packet Errors
• Packet Collisions
Few users experiencing problems
Many users experiencing problems
Boost signal strength
Adjust data rates, other parameters
Georgia Institute of Technology 15
MIBs
Tables:
dot11PhyTxPower
SupportedDataRatesTx
SupportedDataRatesRx
Objects:
dot11EDThreshold (from dot11PhyDSSSEntry TABLE)
dot11BeaconPeriod (from SMT Station Config TABLE)
dot11OperationalRateSet (from SMT Station Config TABLE)
Georgia Institute of Technology 16
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
Georgia Institute of Technology 17
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
Georgia Institute of Technology 18
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
Georgia Institute of Technology 19
I. Introduction
II. 802.11b Protocol Operation
III. System Design Overview
IV. Existing Tool Support
V. Future Works
Georgia Institute of Technology 20
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
Georgia Institute of Technology 21
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
Georgia Institute of Technology 22
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.
Georgia Institute of Technology 23
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.
Georgia Institute of Technology 24
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
Georgia Institute of Technology 25
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.
Georgia Institute of Technology 26
I. Introduction
II. 802.11b Protocol Operation
III. System Design Overview
IV. Existing Tool Support
V. Future Works
Georgia Institute of Technology 27
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
Georgia Institute of Technology 28
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