protecting voice calls from the background traffic in a mixed
TRANSCRIPT
Protecting voice calls from the background traffic
in a mixed voice/data transmission over wireless LANs
Communications Network Research InstituteDublin Institute of Technology
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
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs
� 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
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs
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)”
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs
“…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
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs
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]
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs
� 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
� 2Mbps 976pps 488pps 244pps 167pps
� 4Mbps 1952pps 977pps 488pps 333pps
� 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
Voice Video Best effort Background
Network layer802.11e station
MAC layer
12034567
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs
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 station
Medium
AIFSN[AC_BK]=2,3,….,15AIFSN[AC_VO]=2
BK: 1Mbps, AIFSN [AC_VO] =2, AIFSN [AC_BK] =2
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 10
User satisfaction: av. R=6.0
BK: 1Mbps, AIFSN [AC_VO] =2, AIFSN [AC_BK] =4
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 11
User satisfaction: av. R=45.2
BK: 1Mbps, AIFSN [AC_VO] =2, AIFSN [AC_BK] =6
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 12
User satisfaction: av. R=87.6
BK: 1Mbps, AIFSN [AC_VO] =2, AIFSN [AC_BK] =10
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 13
User satisfaction: av. R=88.4
tuning the CWmin [AC_BK] parameter
Voice Video Best effort Background
Network layer802.11e station
MAC layer
12034567
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs
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 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
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 15
User satisfaction: av. R=3.34
BK: 1Mbps, CWmin[AC_VO] =7, Cwmin[AC_BK]=31
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 16
User satisfaction: av. R=56.6
BK: 1Mbps, CWmin[AC_VO] =7, CWmin[AC_BK] =127
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 17
User satisfaction: av. R=85.0
BK: 1Mbps, CWmin[AC_VO] =7, CWmin[AC_BK] =1023
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 18
User satisfaction: av. R=84.1
tuning theTXOP [AC_VO] parameter
Voice Video Best effort Background
Network layer802.11e station
MAC layer
12034567
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs
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 station
Medium
TXOP[AC_VO]=0,512, 1024, 2016,4000,8192us TXOP[AC_BK]=0us
BK:1Mbps,TXOP [X] = 0µs (1 frame/access opportunity)
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 20
User satisfaction: av. R=35.1
BK:1Mbps, TXOP[AC_VO]=512µs, TXOP[AC_BK]=0µs
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 21
User satisfaction: av. R=50.0
BK:1Mbps,TXOP[AC_VO]=1024µs, TXOP[AC_BK]=0µs
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 22
User satisfaction: av. R=57.6
BK:1Mbps,TXOP[AC_VO]=2016µs, TXOP[AC_BK]=0µs
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 23
User satisfaction: av. R=58.6
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
100 quality at wired side (BK traffic 1Mbps)
R
7 15 31 63 127 255 511 10230
0.5
1 goodput (BK traffic 1Mbps)
Goo
dput
[Mbp
s]
1500Bpp@83pps1024Bpp@122pps512Bpp@244pps256Bpp@488pps
R=70 R=70
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 24
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]
1500Bpp@83pps1024Bpp@122pps512Bpp@244pps256Bpp@488pps
R=70
Results summary for BK traffic 2Mbps
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
100quality at wired side (BK traffic 2Mbps)
R
2 4 6 8 10 12 14 160
1
2 goodput (BK traffic 2Mbps)
Goo
dput
[Mbp
s]
1500Bpp@167pps1024Bpp@244pps512Bpp@488pps256Bpp@977pps
7 15 31 63 127 255 511 10230
50
100quality at wireless side (BK traffic 2Mbps)
R
7 15 31 63 127 255 511 10230
50
100 quality at wired side (BK traffic 2Mbps)
R
7 15 31 63 127 255 511 10230
1
2 goodput (BK traffic 2Mbps)
Goo
dput
[Mbp
s]
1500Bpp@167pps1024Bpp@244pps512Bpp@488pps256Bpp@977pps
tuning AIFSN [AC_BK] tuning CWmin [AC_BK]
R=70 R=70
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 25
0 512 1024 2016 4000 81920
50
100 quality at wireless side (BK traffic 2Mbps)
R
0 512 1024 2016 4000 81920
50
100quality at wired side (BK traffic 2Mbps)
R
0 512 1024 2016 4000 81920
1
2 goodput (BK traffic 2Mbps)
Goo
dput
[Mbp
s]
TXOP[AC__VO]
1500Bpp@167pps1024Bpp@244pps512Bpp@488pps256Bpp@977pps
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
Guidelines for setting L2/MAC param.
� ∆ AIFSN > 5 slots
� ∆ Cwmin > 120 slots
� tuning TXOP is ineffective for voice traffic
Results summary for BK traffic 4Mbps
7 15 31 63 127 255 511 10230
50
100quality at wireless side (BK traffic 4Mbps)
R
7 15 31 63 127 255 511 10230
50
100 quality at wired side (BK traffic 4Mbps)
R
7 15 31 63 127 255 511 10230
2
4 goodput (BK traffic 4Mbps)
Goo
dput
[Mbp
s]
1500Bpp@336pps1024Bpp@488pps512Bpp@977pps256Bpp@1954pps
2 4 6 8 10 12 14 160
50
100quality at wireless side (BK traffic 4Mbps)
R
2 4 6 8 10 12 14 160
50
100quality at wired side (BK traffic 4Mbps)
R
2 4 6 8 10 12 14 160
2
4goodput (BK traffic 4Mbps)
Goo
dput
[Mbp
s]
1500Bpp@336pps1024Bpp@488pps512Bpp@977pps256Bpp@1954pps
tuning AIFSN [AC_BK] tuning CWmin [AC_BK]
R=70 R=70
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 26
0 512 1024 2016 4000 81920
50
100quality at wireless side (BK traffic 4Mbps)
R
0 512 1024 2016 4000 81920
50
100 quality at wired side (BK traffic 4Mbps)
R
0 512 1024 2016 4000 81920
2
4 goodput (BK traffic 4Mbps)
Goo
dput
[Mbp
s]
TXOP[AC__VO]
1500Bpp@336pps1024Bpp@488pps512Bpp@977pps256Bpp@1954pps
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
Guidelines for setting L2/MAC param.
� ∆ AIFSN > 6 slots
� ∆ Cwmin > 120 slots
� tuning TXOP is ineffective for voice traffic
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
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 27
� 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
Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs 28
� 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.
Questions?