Protecting voice calls from the background traffic in a mixed

Protecting voice calls from the background traffic

in a mixed voice/data transmission over wireless LANs

Communications Network Research InstituteDublin Institute of Technology

[email protected]

Miroslaw Narbutt

ETSI Workshop 17-19 June 2008 , Prague, Czech Republic “Effect of transmission performance on Multimedia Quality of Service”

Outline

� Introduction

� Predicting voice transmission quality (ITU-T Rec. 109/App I)

� Traffic prioritization at L2/MAC (IEEE 802.11e/WMM)

Experimental results

Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs

� Experimental results

� Conclusions

� Future work - the EQUAL project

Introduction

� transmission impairments (delay, loss, jitter) affect conversational speech

� mechanisms in various communication layers can greatly mitigate their effect

� adaptive voice prioritization at L2/MAC in response to changing network load conditions is necessary due to limited and shared bandwidth


� tuning of L2/MAC parameters should be done from the perspective of end user (maximizing end-to-end voice transmission quality and user satisfaction)

Predicting transmission quality ITU-T Rec. G.109/Appendix I


R-value 94.15 -90 90-80 80-70 70-60 60-50

Speech transmission

quality

Best High Medium Low Poor

User satisfaction very satisfied

satisfied some very dissatisfied

many very dissatisfied

almost all dissatisfied

Predicting transmission quality (cont.)ITU-T Rec. G.109/Appendix I

� ITU-T Rec. G.109/App I, “The E-model-based quality contours for predicting speech transmission quality and user satisfaction from time-varying transmission impairments”

“Quality contours can be used in cross-layer optimization of various communications layers

(e.g., adaptive playout scheduling at the application layer, traffic differentiation at the MAC layer)”


“…useful in the process of parameter tuning when a trade-off exists between packet delays and

loss and efforts are focused on finding the operating point where conversational quality is maximized.”

� Real-time implementation of the quality predictor for cross-layer optimization is currently under development:

http://www.cnri.dit.ie/research.equal.html

Voice prioritization at L2/MAC (IEEE 802.11e/WMM)

Voice Video Best effort Background

Network layer802.11e/W

MM station

MAC layer

12034567


Backoff:AIFSN[AC_BK]CWmin[AC_BK]CWmax[AC_BK]Tx oportunity:

TXOP[AC_BK]

Backoff:AIFSN[AC_BE]CWmin[AC_BE]CWmax[AC_BE]Tx oportunity:

TXOP[AC_BE]

Backoff:AIFSN[AC_VI]CWmin[AC_VI]CWmax[AC_VI]Tx oportunity:

TXOP[AC_VI]

Backoff:AIFSN[AC_VO]CWmin[AC_VO]CWmax[AC_VO]Tx oportunity:

TXOP[AC_VO]

contend to transmit

Physical layer

802.11e/W

MM station

Medium

Voice prioritization at L2/MAC (IEEE 802.11e) cont.

� Hindering the ability of the background traffic (AC_BK queue) to win transmission opportunities by increasing its defferal time (AIFSN) and its back-off time (CWmin)

AIFS[AC_BK] Background

CWmin[AC_BK]


� Allowing the voice traffic (AC_VO queue) to seize more bandwidth per one transmission opportunity by increasing its transmission opportunity limit (TXOP)

ACK

DIFS

AIFS[AC_VO]

Voice

t

CWmin[AC_VO]

Experimental test-bed

� 16 VoIP stations (Madwifi drivers with 802.11e/WMM ) + 1 BK station

� Bi-directional VoIP traffic (wired/wireless scenario)� Encoding scheme: G.711

� Packetization scheme: 10ms, modulated CBR (ON/OFF) according to ITU-T Rec. P.59

� Background traffic (BK)

Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 8

� Traffic type: Poisson

� Traffic load: 256Bytes 512Bytes 1024Bytes 1500Bytes (IP packet size)

� 1Mbps 488pps 244pps 122pps 83pps



� parameters tuning at L2/MAC� AIFSN: 2,3,…,14,15 for AC_BK queue

� CWmin:7,15,31,…,511,1023 for AC_BK queue

� TXOP: 0,512, 1024, 2016,4000,8192us for AC_VO queue

tuning the AIFSN [AC_BK] parameter


Network layer802.11e station

MAC layer

12034567



TXOP[AC_BK]


TXOP[AC_BE]


TXOP[AC_VI]


TXOP[AC_VO]

contend to transmit

Physical layer

802.11e station

Medium

AIFSN[AC_BK]=2,3,….,15AIFSN[AC_VO]=2

BK: 1Mbps, AIFSN [AC_VO] =2, AIFSN [AC_BK] =2


User satisfaction: av. R=6.0










tuning the CWmin [AC_BK] parameter



MAC layer

12034567



TXOP[AC_BK]


TXOP[AC_BE]


TXOP[AC_VI]


TXOP[AC_VO]

contend to transmit

Physical layer

802.11e station

Medium

CWmin[AC_BK]=7,15, 31, …, 1023CWmin[AC_VO]=7

TXOP[AC_BK]

BK: 1Mbps, CWmin[AC_VO] =7, CWmin[AC_BK]=7



BK: 1Mbps, CWmin[AC_VO] =7, Cwmin[AC_BK]=31



BK: 1Mbps, CWmin[AC_VO] =7, CWmin[AC_BK] =127



BK: 1Mbps, CWmin[AC_VO] =7, CWmin[AC_BK] =1023



tuning theTXOP [AC_VO] parameter



MAC layer

12034567



TXOP[AC_BK]


TXOP[AC_BE]


TXOP[AC_VI]


TXOP[AC_VO]

contend to transmit

Physical layer

802.11e station

Medium

TXOP[AC_VO]=0,512, 1024, 2016,4000,8192us TXOP[AC_BK]=0us

BK:1Mbps,TXOP [X] = 0µs (1 frame/access opportunity)



BK:1Mbps, TXOP[AC_VO]=512µs, TXOP[AC_BK]=0µs



BK:1Mbps,TXOP[AC_VO]=1024µs, TXOP[AC_BK]=0µs



BK:1Mbps,TXOP[AC_VO]=2016µs, TXOP[AC_BK]=0µs



Results summary for BK traffic 1Mbps

2 4 6 8 10 12 14 160

50

100 quality at wireless side (BK traffic 1Mbps) R

2 4 6 8 10 12 14 160

50

100 quality at wired side (BK traffic 1Mbps)

R

2 4 6 8 10 12 14 160

0.5

1 goodput (BK traffic 1Mbps)

Goo

dput

[Mbp

s]

1500Bpp@83pps1024Bpp@122pps512Bpp@244pps256Bpp@488pps

tuning AIFSN [AC_BK] tuning CWmin [AC_BK]

7 15 31 63 127 255 511 10230

50

100quality at wireless side (BK traffic 1Mbps)

R

7 15 31 63 127 255 511 10230

50


R

7 15 31 63 127 255 511 10230

0.5


Goo

dput

[Mbp

s]


R=70 R=70


Guidelines for setting L2/MAC param.

� ∆ AIFSN > 4 slots

� ∆ Cwmin > 120 slots

� tuning TXOP is ineffective for voice traffic

2 4 6 8 10 12 14 160G

oodp

ut [M

bps]

AIFSN[AC__BK]

tuning TXOP [AC_VO]

7 15 31 63 127 255 511 10230

CWmin[AC__BK]

0 512 1024 2016 4000 81920

50

100 quality at wireless side (BK traffic 1Mbps)

R

0 512 1024 2016 4000 81920

50

100quality at wired side (BK traffic 1Mbps)

R

0 512 1024 2016 4000 81920

0.5

1goodput (BK traffic 1Mbps)

Goo

dput

[Mbp

s]

TXOP[AC__VO]


R=70


2 4 6 8 10 12 14 160

50

100 quality at wireless side (BK traffic 2Mbps) R

2 4 6 8 10 12 14 160

50


R

2 4 6 8 10 12 14 160

1


Goo

dput

[Mbp

s]


7 15 31 63 127 255 511 10230

50


R

7 15 31 63 127 255 511 10230

50


R

7 15 31 63 127 255 511 10230

1


Goo

dput

[Mbp

s]



R=70 R=70


0 512 1024 2016 4000 81920

50

100 quality at wireless side (BK traffic 2Mbps)

R

0 512 1024 2016 4000 81920

50


R

0 512 1024 2016 4000 81920

1


Goo

dput

[Mbp

s]

TXOP[AC__VO]


2 4 6 8 10 12 14 160G

oodp

ut [M

bps]

AIFSN[AC__BK]7 15 31 63 127 255 511 1023

0Goo

dput

[Mbp

s]

CWmin[AC__BK]

tuning TXOP [AC_VO]

R=70






7 15 31 63 127 255 511 10230

50


R

7 15 31 63 127 255 511 10230

50


R

7 15 31 63 127 255 511 10230

2


Goo

dput

[Mbp

s]


2 4 6 8 10 12 14 160

50


R

2 4 6 8 10 12 14 160

50


R

2 4 6 8 10 12 14 160

2

4goodput (BK traffic 4Mbps)

Goo

dput

[Mbp

s]



R=70 R=70


0 512 1024 2016 4000 81920

50


R

0 512 1024 2016 4000 81920

50


R

0 512 1024 2016 4000 81920

2


Goo

dput

[Mbp

s]

TXOP[AC__VO]


7 15 31 63 127 255 511 10230

CWmin[AC__BK]2 4 6 8 10 12 14 16

0Goo

dput

[Mbp

s]

AIFSN[AC__BK]

tuning TXOP [AC_VO]

R=70





Conclusions

� In principle it is possible to protect VoIP from heavy background traffic through prioritization at L2/MAC (802.11e/WMM)

Guidelines for setting L2/MAC parameters: � AIFSN difference between AC_VO and AC_BK greater than 6

� CWmin difference between AC_VO and AC_BK greater than 120

NOT A


� tuning TXOP [AC_VO] parameter is ineffective for voice traffic

� AIFSN tuning works better thanCWmin tuning (only voice traffic compete and access the wireless medium during the protected time slots)

� One has to be aware of a substantial reduction of the background traffic

� Since network load conditions change continuously, adaptive tuning of L2/MAC parameters is essential

� Strategy of cross-layer optimization is required!

A GENERAL

RULE

Future work

� Goal – to improve VoIP transmission quality in wireless environment

� Strategy – adaptive cross-layer optimization

� Objective – automatically tune parameters in various communication layers

� Achievements to date


� Achievements to date

� The EQUAL real-time implementation of the ITU-T G.109/AppI� Adaptive playout buffer in a real VoIP terminal controlled by the EQUAL tool

� Future work� Cross-layer optimization of the VoIP protocol stack controlled by the EQUAL tool

the EQUAL project: http://www.cnri.dit.ie/research.equal.html

Thank you.

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Protecting voice calls from the background traffic in a mixed