802.11 wlan mac layer modeling · team 2: 802.11 wlan mac layer modeling mentor: radu v. balan...
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TEAM 2: 802.11 WLAN MAC layer modeling
Mentor: Radu V. Balan
802.11 WLAN MAC Layer Modeling
Lisa Driskell Yejun Gong Xueying HuPurdue University Michigan Technological
UniversityUniversity of Michigan
Rashi Jain Mechie NkenglaNew Jersey Institute of
TechnologyUniversity of Illinois-Chicago
August 17, 2007
TEAM 2: 802.11 WLAN MAC layer modeling
Outline
v Objectivev Overviewv ns-2v Results (.nam)v Results (.tr)v Conclusionsv Future Objectives
TEAM 2: 802.11 WLAN MAC layer modeling
Project Objective: Analyze the relationships of the parameters for a modified EO Markov model and validate the model under certain assumptions with (ns2) network simulations.
Objective
TEAM 2: 802.11 WLAN MAC layer modeling
Overview
MAC MAC
Packets Generated
IFQ
Agent/UDP Transmission
Agent/NullFinal
Destination
System Layout
TEAM 2: 802.11 WLAN MAC layer modeling
p
Overview
TEAM 2: 802.11 WLAN MAC layer modeling
Prob (packet dropped due to collision) =
Avg # of retries = )p1(p1
p L−−
1Lp +
pL(1-p) + pLp
…pb(1-p)…p2(1-p)p(1-p)1-pProbability
L…b…210Exact # retries
Previous Analysis of Markov Model
Overview
TEAM 2: 802.11 WLAN MAC layer modeling
• Analyzed Markov model• Compared analytical results with computed
results to verify the analysis.• Use analytical results compared with network
simulations to determine whether the system can indeed be modeled with a Markov chain.
Outline
Overview
TEAM 2: 802.11 WLAN MAC layer modeling
Ns-2
Ns-2 simulator
Ns-2 SimulatorInput
.tcl file
.tr file
Output Trace File
.nam file
TEAM 2: 802.11 WLAN MAC layer modeling
Ns-2
Ns-2 simulator
• Closely relates to real world.
• A packet-based event-driven simulation.
• Can incorporate the wireless mechanism
• Allows for mobile stations
• Provides animations
TEAM 2: 802.11 WLAN MAC layer modeling
Ns-2
Example of a ns2 simulation
TEAM 2: 802.11 WLAN MAC layer modeling
Nam Trace
Nam Trace Format<type> -t <time> -s <source id> -d <destination id> -p <pkt-type> -e <extent> -c <conv> -a <packet attribute> -i <id> -k <trace level>
0~#pkts
i
AGT, MAC
k
cbr,ACK
0~NSTA
0~simTime
h, r, d, +, -
psttype
TEAM 2: 802.11 WLAN MAC layer modeling
Nam Trace : Medium Busy Time
The packet is on the air from t, if at ttype=‘h’ AND k=‘MAC‘ (Hop)
The medium is busy in[t, t+pktTransTime]
The medium is busy in collision case.
TxFrame 1
TxFrame 2
BusyCollision
TEAM 2: 802.11 WLAN MAC layer modeling
Nam Trace : Medium Busy Time
Medium Busy Time ? , if NSTA ? < critical numberMedium Busy Time ? , if NSTA ? > critical number
TEAM 2: 802.11 WLAN MAC layer modeling
1-Hop# cket)Retries(pa# with
ThisNodepktsSendTo#
packet thisof Retries#(node)AvgRetries hisNodepktSendToT
=
=∑Numerical:
Theoretical:
But how to find p?
retries. #max theis L andy probabilitcollision theis p where
)p1(*p-1
p(node)AvgRetries L−=
TEAM 2: 802.11 WLAN MAC layer modeling
1LcpktTransSuColpktDropDue
ColpktDropDuep +
+=
pktSend=
pktDropDueCol+
pktDropDueQueue+
pktDropDueEnd+
pktTransSuc
Type=‘h’ AND k=‘AGT’ AND p=‘cbr’
Type=‘d’ AND k=‘IFQ’ AND p=‘cbr’
LastHopTime+pktTransTime>sucTime
Type=‘r’ AND k=‘AGT’ AND p=‘ACK’
TEAM 2: 802.11 WLAN MAC layer modeling
Results (.nam)
Average number of retries
TEAM 2: 802.11 WLAN MAC layer modeling
Results (.nam)
Average number of retries
TEAM 2: 802.11 WLAN MAC layer modeling
Example of a .tr output
TEAM 2: 802.11 WLAN MAC layer modeling
Results (.tr)
Average number of retriesFrom simulation
From calculation
TEAM 2: 802.11 WLAN MAC layer modeling
Results (.tr)
Average number of retries for AP with varying packet period and offset
TEAM 2: 802.11 WLAN MAC layer modeling
Average number of retries with varying packet period and offset
5 Stations
TEAM 2: 802.11 WLAN MAC layer modeling
Results (.tr)
Comparison between of the average number of retries from calculation and simulation
TEAM 2: 802.11 WLAN MAC layer modeling
Conclusions
Conclusions
• Estimated parameter ‘p’• Determined the saturation value• Established validity of the Markov model• Established importance of assumption of
synchronicity
TEAM 2: 802.11 WLAN MAC layer modeling
Future Objectives
• Use the .nam and .tr files to extract information about– Average service time – Average wait time
• Use the above times to find relationships between parameters
• Compare computed results and simulated results for different packet arrival configurations
• Compute the throughput/delay
• Create a deterministic model
(Someone Else’s) Future Objectives
TEAM 2: 802.11 WLAN MAC layer modeling
Questions
Questions?
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