Protecting voice calls from the background traffic in a mixed voice/data transmission over wireless LANs Communications Network Research Institute Dublin 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”
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Protecting voice calls from the background traffic in a mixed
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Protecting voice calls from the background traffic
in a mixed voice/data transmission over wireless LANs
Communications Network Research InstituteDublin Institute of Technology
� 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
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