Enhancing IEEE 802.11 MAC in congested environments Imad Aad, Qiang - - PowerPoint PPT Presentation

▶
enhancing ieee 802 11 mac in congested environments
SMART_READER_LITE
LIVE PREVIEW

Enhancing IEEE 802.11 MAC in congested environments Imad Aad, Qiang - - PowerPoint PPT Presentation

Nov 08, 2023 346 likes •795 views

Enhancing IEEE 802.11 MAC in congested environments Imad Aad, Qiang Ni, Chadi Barakat, Thierry Turletti ASWN, Boston-MA, USA August 9 th , 2004 Enh. 802.11 p.1 Outline IEEE 802.11 Very brief description Mathematical model description

slide-1
SLIDE 1

Enhancing IEEE 802.11 MAC in congested environments

Imad Aad, Qiang Ni, Chadi Barakat, Thierry Turletti

ASWN, Boston-MA, USA August 9th, 2004

  • Enh. 802.11 – p.1
slide-2
SLIDE 2

Outline

IEEE 802.11 Very brief description Mathematical model description Enhacement Related work Slow decrease (SD) Performance Evaluation

  • Enh. 802.11 – p.2
slide-3
SLIDE 3

MAC sub-layer

Source Destination Other DIFS Time (Tx) (Tx) Data ACK NAV Contention Window Backoff DIFS SIFS Defer access = NAV+DIFS CW

  • Enh. 802.11 – p.3
slide-4
SLIDE 4

MAC sub-layer

backoff = rand() × CW Collision → equal backoffs → too many nodes → Should increase CW !! at the ith retransmission: CW(i) = CWmin × 2i at a successful transmission: CW = CWmin

  • Enh. 802.11 – p.3
slide-5
SLIDE 5

MAC Throughput Model [Bianchi]

S = E[payload−information−transmitted−in−a−slot−time]

E[length−of−a−slot−time]

  • Enh. 802.11 – p.4
slide-6
SLIDE 6

MAC Throughput Model [Bianchi]

S = E[payload−information−transmitted−in−a−slot−time]

E[length−of−a−slot−time]

S =

PsPtrE[P] (1−Ptr)σ+PtrPsTs+Ptr(1−Ps)Tc

  • Enh. 802.11 – p.4
slide-7
SLIDE 7

MAC Throughput Model [Bianchi]

S = E[payload−information−transmitted−in−a−slot−time]

E[length−of−a−slot−time]

S =

PsPtrE[P] (1−Ptr)σ+PtrPsTs+Ptr(1−Ps)Tc

  • Enh. 802.11 – p.4
slide-8
SLIDE 8

MAC Throughput Model [Bianchi]

S = E[payload−information−transmitted−in−a−slot−time]

E[length−of−a−slot−time]

S =

PsPtrE[P] (1−Ptr)σ+PtrPsTs+Ptr(1−Ps)Tc

Ps = nτ(1−τ)n−1

Ptr

= nτ(1−τ)n−1

1−(1−τ)n

Ptr = 1 − (1 − τ)n

  • Enh. 802.11 – p.4
slide-9
SLIDE 9

MAC Throughput Model [Bianchi]

To find τ, 2 nonlinear equations to solve, 1: p = 1 − (1 − τ)n−1

  • Enh. 802.11 – p.4
slide-10
SLIDE 10

MAC Throughput Model [Bianchi]

To find τ, 2 nonlinear equations to solve, 2:

i,1 i,W −2 i,W −1

i i

i,2 0,1 0,W −2 0,W −1 0,2 m,1 m,W −2 m,W −1

m m

m,2 0,0 i−1,0 i,0 1 1 1 1 1 1 1 1 1 1 1 m,0 p/Wm

i

(1−p)/W0 p/W 1 p/Wi+1 p/Wm

  • Enh. 802.11 – p.4
slide-11
SLIDE 11

MAC Throughput Model [Bianchi]

To find τ, 2 nonlinear equations to solve: p = 1 − (1 − τ)n−1 τ =

2(1−2p) (1−2p)(W+1)+pW(1−(2p)m)

  • Enh. 802.11 – p.4
slide-12
SLIDE 12

MAC Throughput Model [Bianchi]

To find τ, 2 nonlinear equations to solve: p = 1 − (1 − τ)n−1 τ =

2(1−2p) (1−2p)(W+1)+pW(1−(2p)m)

→ Matlab → very close to simulations

  • Enh. 802.11 – p.4
slide-13
SLIDE 13

MAC Throughput Model [Bianchi]

600 650 700 750 800 850 5 10 15 20 25 30 35 40 45 50 Total throughput (KBytes/s) Number of contending flows, n 802.11, simul 802.11, model SD, δ = 0.5, model SD, δ = 0.5, simul SD, δ = 0.25, model SD, δ = 0.25, simul

  • Enh. 802.11 – p.4
slide-14
SLIDE 14

Outline

  • Enh. 802.11 – p.5
slide-15
SLIDE 15

CW slow decrease

After each collision, CSMA/CA increases CW Upon a successful transmission, reset CW BUT! congestion did not “reset”!

  • Enh. 802.11 – p.6
slide-16
SLIDE 16

CW slow decrease

To reset or not to reset, that is the question!

  • Enh. 802.11 – p.7
slide-17
SLIDE 17

Related work

In 1994, Bharghavan et al. proposed MACAW: MILD: Multiplicative Increase (CW = CW × 1.5) Linear Decrease (CW = CW − 1)

  • Enh. 802.11 – p.8
slide-18
SLIDE 18

Related work

In 1994, Bharghavan et al. proposed MACAW:

  • Enh. 802.11 – p.9
slide-19
SLIDE 19

Related work

In 1994, Bharghavan et al. proposed MACAW:

  • Enh. 802.11 – p.10
slide-20
SLIDE 20

Our approach

We propose a slow CW decrease mechanism (SD), e.g. CW = 0.9 × CW

  • Enh. 802.11 – p.11
slide-21
SLIDE 21

Simulation scenario

50 100 200 150

Simulation time (sec): 42

  • Enh. 802.11 – p.12
slide-22
SLIDE 22

Simulation scenario

50 100 200 150

Simulation time (sec): 44

  • Enh. 802.11 – p.12
slide-23
SLIDE 23

Simulation scenario

50 100 200 150

Simulation time (sec): 50

  • Enh. 802.11 – p.12
slide-24
SLIDE 24

Simulation scenario

50 100 200 150

Simulation time (sec): 100

  • Enh. 802.11 – p.12
slide-25
SLIDE 25

Simulation scenario

50 100 200 150

Simulation time (sec): 140

  • Enh. 802.11 – p.12
slide-26
SLIDE 26

Simulation scenario

50 100 200 150

Simulation time (sec): 150

  • Enh. 802.11 – p.12
slide-27
SLIDE 27

Throughput vs. n

50 100 150 200 250 50 100 150 200 250 300 Throughput (KBytes/s) Time (s) SD, basic, qlen = 2 802.11, basic, qlen = 2 No decrease, basic, qlen = 2

  • Enh. 802.11 – p.13
slide-28
SLIDE 28

Settling time vs. δ

0.2 0.4 0.6 0.8 1 1.2 0.2 0.4 0.6 0.8 1 Settling time, Tl, (s) Multiplicative factor, δ

  • Eq. (8), pkt-size = 1050

Simul, λ=1, pkt-size = 1050

  • Enh. 802.11 – p.14
slide-29
SLIDE 29

Delays vs. n

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 50 100 150 200 250 300 Packet delay (s) Time (s) "delays_09_comm_noRTS_qlen2.dat" "delays_noenh_comm_noRTS_qlen2.dat"

  • Enh. 802.11 – p.15
slide-30
SLIDE 30

Throughput gain vs. δ

0.95 1 1.05 1.1 1.15 1.2 1.25 1.3 1.35 1.4 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Throughput gain, G Multiplicative factor, δ Basic, λ = 1, pkt-size = 1050 RTS/CTS, λ = 1, pkt-size = 1050 Basic, λ = 0.1, pkt-size = 105

  • Enh. 802.11 – p.16
slide-31
SLIDE 31

802.11 throughput model

i,1 i,W −2 i,W −1

i i

i,2 0,1 0,W −2 0,W −1 0,2 m,1 m,W −2 m,W −1

m m

m,2 0,0 i−1,0 i,0 1 1 1 1 1 1 1 1 1 1 1 m,0 p/Wm

i

(1−p)/W0 p/W 1 p/Wi+1 p/Wm

  • Enh. 802.11 – p.17
slide-32
SLIDE 32

SD throughput model

i,1 i,W −2 i,W −1

i i

i,2 0,1 0,W −2 0,W −1 0,2 m,1 m,W −2 m,W −1

m m

m,2 0,0 i−1,0 i,0 1 1 1 1 1 1 1 1 1 1 1 p/Wm

i

(1−p)/W0 p/W 1 p/Wi+1 p/Wm m,0

  • Enh. 802.11 – p.18
slide-33
SLIDE 33

Throughput vs n

600 650 700 750 800 850 5 10 15 20 25 30 35 40 45 50 Total throughput (KBytes/s) Number of contending flows, n 802.11, simul 802.11, model SD, δ = 0.5, model SD, δ = 0.5, simul SD, δ = 0.25, model SD, δ = 0.25, simul

  • Enh. 802.11 – p.19
slide-34
SLIDE 34

Throughput Gain vs. CWmin

0.95 1 1.05 1.1 1.15 1.2 1.25 1.3 20 40 60 80 100 120 140 Throughput gain of SD CWmin simul, n=5 model, n=5 simul, n=20 model, n=20 simul, n=50 model, n=50

  • Enh. 802.11 – p.20
slide-35
SLIDE 35

802.11 Fairness, varying CWmin

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 500 1000 1500 2000 Average Jain fairness index Window size 10 flows, CWmin = 32 10 flows, CWmin = 63 10 flows, CWmin = 127

  • Enh. 802.11 – p.21
slide-36
SLIDE 36

802.11 Fairness, varying n

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Average Jain fairness index Window size 10 flows 25 flows 50 flows 80 flows

  • Enh. 802.11 – p.22
slide-37
SLIDE 37

SD Fairness, varying n

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 Average Jain fairness index Window size SD, 10 flows SD, 15 flows SD, 20 flows SD, 40 flows SD, 50 flows SD, 80 flows

  • Enh. 802.11 – p.23
slide-38
SLIDE 38

Fairness comparison

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 1000 2000 3000 4000 5000 6000 7000 8000 9000 10000 Average Jain fairness index Window size 802.11, 10 flows SD, 10 flows 802.11, 80 flows SD, 80 flows

  • Enh. 802.11 – p.24
slide-39
SLIDE 39

Coexisting SD and 802.11

5 10 15 20 25 30 0.2 0.4 0.6 0.8 1 Throughput/node (KBytes/s) Proportion of 802.11 nodes 10 flows, 802.11, simul 10 flows, SD λ = 0.5, simul 20 flows, 802.11, simul 20 flows, SD λ = 0.5 , simul 10 flows, 802.11, model 10 flows, SD λ = 0.5, model 20 flows, 802.11, model 20 flows, SD λ = 0.5, model

  • Enh. 802.11 – p.25
slide-40
SLIDE 40

Energy consumption

1 2 3 4 5 6 7 8 9 10 11 5 10 15 20 25 30 Energy/Bit (x10e-6 Joules) Number of contending flows 802.11, Tx SD, Tx 802.11, Rx SD, Rx

  • Enh. 802.11 – p.26
slide-41
SLIDE 41

On the application layer, FTP

50 100 150 200 250 300 5 10 15 20 25 30 FTP duration (s) Number of contending flows 802.11 SD

  • Enh. 802.11 – p.27
slide-42
SLIDE 42

Noisy channel

0.4 0.5 0.6 0.7 0.8 0.9 1 1.1 1.2 1.3 1.4 0.02 0.04 0.06 0.08 0.1 Throughput gain of SD Packet Error Rate (PER) 1 flow 4 flows 15 flows 25 flows 40 flows 50 flows

  • Enh. 802.11 – p.28
slide-43
SLIDE 43

Conclusion

Deep analysis of simple Slow Decrease (SD) functions SD outperforms 802.11 in: throughput delay fairness (if congested) battery consumption etc. 802.11 outperforms SD if channel is severely noisy

  • Enh. 802.11 – p.29
slide-44
SLIDE 44

The End

Thank you! ... questions ?

imad.aad@epfl.ch

  • Enh. 802.11 – p.30