802.11n MAC layer simulation802.11n MAC layer simulation

Submitted by:Submitted by:

Niv TokmanNiv Tokman

Aya MireAya Mire

Oren Gur-ArieOren Gur-Arie

Standard protocol transactionStandard protocol transaction

ST

A A

ctiv

ityP

HY

Tx

MA

C T

xA

P A

ctiv

ityP

HY

Tx

MA

C T

x

Bas

ic r

ate

non-

agg

IAC

MP

DU

(RT

S)

Bas

ic ra

te

non-

agg

RA

C M

PD

U

(CT

S)

ST

A A

ctiv

ityP

HY

Tx

MA

C T

xS

TA

Act

ivity

PH

Y R

xM

AC

Rx

Agg

P

PD

UD

ata

MP

DU

Dat

a M

PD

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ic r

ate

non-

agg

Dat

a M

PD

U

Bas

ic r

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non-

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IAC

MP

DU

(RT

S)

Bas

ic r

ate

non-

agg

Dat

a M

PD

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Bas

ic ra

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non-

agg

IAC

MP

DU

(R

TS

)

Bas

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non-

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Rec

eive

d da

ta

NAV

NAVNAV

NAV

Bas

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(CT

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NAV

NAV

DIFS

SIFS

1. Data arrives at Tx FIFO of STA A from VoIP data generator. IAC is sent.

2. AP receives IAC, wait SIFS and respond with RAC.

3. RAC received. STA A sends non-aggregated VoIP data

4. After DIFS, the operation is repeated by STA B5. Aggregation size is reached. AP send IAC followed by the aggregated data

6. Data is received by STA C

Simulation structure and flowSimulation structure and flowGUI

Simulation manager

STA

STA

STA

STA

STA

AP Network

Statistics

Simulation output files:- Analysis

- log

Main()

Packet Generator

Define “start conversation” events

Reached end of simulation time?

Handle next event

Last event in current time stamp?

NO

NO

Jump to next time stamp

YES

End Simulation

YES

Simulation assumptionsSimulation assumptions

There is no random noise in the simulation and error rate There is no random noise in the simulation and error rate is zero.is zero.All stations are 802.11n (no legacy devices)All stations are 802.11n (no legacy devices)Each station can be involved in one conversation at a Each station can be involved in one conversation at a timetimeAll conversations are between a local station and remote All conversations are between a local station and remote network (Through the AP)network (Through the AP)Only AP uses aggregated packagesOnly AP uses aggregated packagesThe destinations of conversations are distributed equally. The destinations of conversations are distributed equally. The length of conversations is distributed exponentially.The length of conversations is distributed exponentially.No Ack packages in MAC layer - the simulated network No Ack packages in MAC layer - the simulated network layerlayer

Network capacity calculationNetwork capacity calculation

The idea: to create a standard reference point to network The idea: to create a standard reference point to network capacity, regardless of aggregation size used.capacity, regardless of aggregation size used.The network capacity is the percentage of bandwidth The network capacity is the percentage of bandwidth actually used. Due to different timing scheme, the actually used. Due to different timing scheme, the percentage differs between regular station and AP.percentage differs between regular station and AP.Thus we calculate them independently and perform a Thus we calculate them independently and perform a weighted sum.weighted sum.This is a static calculation. A dynamic calculation taking This is a static calculation. A dynamic calculation taking actual collisions and transmissions into account provide actual collisions and transmissions into account provide different capacity per aggregation, which makes different capacity per aggregation, which makes comparison impossible.comparison impossible.The equations are in the next slide:The equations are in the next slide:

The AP has priority on the channel, thus STA can transmit only The AP has priority on the channel, thus STA can transmit only when AP is accumulating the aggregation. The weight is based on when AP is accumulating the aggregation. The weight is based on the AP portion of time:the AP portion of time:

Efficiency of STA/AP is the amount of actual data transmission out Efficiency of STA/AP is the amount of actual data transmission out of the total transmission period (including handshake and wait of the total transmission period (including handshake and wait times). Note that transmission of control messages is negligible:times). Note that transmission of control messages is negligible:

Thus the total network efficiency is the weight sum:Thus the total network efficiency is the weight sum:

Network capacity equationsNetwork capacity equations

1

AP

STA AP

DIFS agg Tx timeW

DIFS agg Tx time agg accumulation time

W W

2

AP

STA

agg Tx timeS

agg Tx time DIFS

messageTx timeS

messageTx time DIFS SIFS

network AP AP STA STAS S W S W

Packets reaching dst. before 1ms

0

20

40

60

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15 23.75 32.5 41.25 50

Network capacity (MB/s)

Pa

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ets

(%

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agg 100agg 200agg 300agg 400agg 500agg 600agg 700

Packets reaching dst. before 5ms

0

20

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15 23.75 32.5 41.25 50

Network capacity (MB/s)

Pac

kets

(%

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agg 100

agg 200

agg 300

agg 400

agg 500

agg 600

agg 700

Packets reaching dst. before 10ms

0

20

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15 23.75 32.5 41.25 50Network capacity (MB/s)

Pa

ck

ets

(%

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agg 100

agg 200

agg 300

agg 400

agg 500

agg 600

agg 700

Simulation analysisSimulation analysis

We can see that at lower network capacity, we get better We can see that at lower network capacity, we get better results for the higher aggregation sizes, while at higher results for the higher aggregation sizes, while at higher network capacities we get better performance for middle network capacities we get better performance for middle range of aggregation sizerange of aggregation sizeIn the current simulation configuration, the aggregated In the current simulation configuration, the aggregated AP has priority over the regular stations. When network AP has priority over the regular stations. When network capacity is low, it takes time to accumulate an capacity is low, it takes time to accumulate an aggregation, which gives equal opportunity to the aggregation, which gives equal opportunity to the stations to transmit their messages.stations to transmit their messages.When the network capacity is high, aggregations are When the network capacity is high, aggregations are accumulated in no time, and the AP starves the other accumulated in no time, and the AP starves the other stations, thus their messages expire and the success stations, thus their messages expire and the success rate is falling.rate is falling.

Simulation analysis (cont.)Simulation analysis (cont.)

Aggregation of 100 is like almost no Aggregation of 100 is like almost no aggregation at all. Success rate is poor at aggregation at all. Success rate is poor at lower network capacities, while at higher lower network capacities, while at higher rates the success rate is similar to higher rates the success rate is similar to higher aggregation sizes.aggregation sizes.

It can be seen that the trends are kept as It can be seen that the trends are kept as margin is raised.margin is raised.

Success rate relative to agg size (for different network capacities)

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agg 100 agg 200 agg 300 agg 400 agg 500 agg 600 agg 700

Su

cces

sfu

l p

acke

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%)

15

23.75

32.5

41.25

50

Network capacity (MB/s)

Success rate analysisSuccess rate analysis

It can be seen that for low-mid range It can be seen that for low-mid range network capacity, the largest aggregation network capacity, the largest aggregation is the best.is the best.

At higher network capacities, the larger At higher network capacities, the larger aggregations causes regular stations aggregations causes regular stations starvation, thus success rates are slightly starvation, thus success rates are slightly lower than at smaller aggregation sizes.lower than at smaller aggregation sizes.

ConclusionsConclusions

At all simulated network capacities, the larger At all simulated network capacities, the larger aggregations provide better results than smaller aggregations provide better results than smaller aggregation sizes. The only exception is at the highest aggregation sizes. The only exception is at the highest network capacities, at which a slight degradation can be network capacities, at which a slight degradation can be observed.observed.Higher aggregation size is better for almost all Higher aggregation size is better for almost all network capacities, even at a network were not all network capacities, even at a network were not all devices aggregate.devices aggregate.The degradation at higher network capacities is probably The degradation at higher network capacities is probably simulation dependent. In networks with better balance simulation dependent. In networks with better balance between AP and stations priorities (such as QoS), one between AP and stations priorities (such as QoS), one can assume that there will be no degradation.can assume that there will be no degradation.

Thank youThank you

Niv, Oren & AyaNiv, Oren & Aya