Tuning Skype’s Redundancy Control Algorithm for User Satisfaction
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Transcript of Tuning Skype’s Redundancy Control Algorithm for User Satisfaction
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Te‐Yuan Huang, Kuan‐Ta Chen, Polly Huang
Network and Systems LaboratoryNational Taiwan University
Institute of Information ScienceAcademia Sinica, Taiwan
INFOCOM, 2009
Network and Systems Laboratorynslab.ee.ntu.edu.tw
MotivationVoice traffic is sensitive to network impairmentWhy VoIP sending rate is important?
Most important factors on user satisfactionSending Rate and its VariationHigh and Stable voice qualityg q y
Why adapting sending rate is difficult?Aggressively?Aggressively?Conservatively?
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Motivation – Cont.Skype – one of the most popular VoIP software
Q1: How Skype adapts its voice traffic?Q1: How Skype adapts its voice traffic?
Q2 I th i h i d h?Q2: Is their mechanism good enough?
Q3: How can Skype’s policy be improved?
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Related WorkSkype’s voice traffic is governed by: [Bonfiglio et al.]
Bit RateBit RateFraming TimeRedundant DataRedundant Data
PC‐PSTN callsG 729G.729
PC‐PC calls iSACiSAC
Only Redundant Data is controlled by SkypeOnly Redundant Data is controlled by Skype
Network and Systems Laboratorynslab.ee.ntu.edu.tw
OutlineMotivation
Related Work
How does Skype adapt the redundancy ratio?How does Skype adapt the redundancy ratio?
Is Skype’s mechanism good enough?
How can we do better?
ConclusionConclusion
Network and Systems Laboratorynslab.ee.ntu.edu.tw
OutlineMotivation
Related Work
How does Skype adapt its redundant data?How does Skype adapt its redundant data?
Is Skype’s mechanism good enough?
How can we do better?
ConclusionConclusion
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Experiment Setupp p
PC PSTN(G 729)PC‐PSTN(G.729)
PC‐PC(iSAC)
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Observation 10%
G.729 (PC‐PSTN) 8%9%
10%
Constant bit rate
Constant framing 6%7%
Constant framing time
3%4%
5%
2%1%
3%
0%1%
0%
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Redundancy RatioyDefinition
Th t f k t th t d d t i The percentage of packets that carry redundant voice data
1234
Redundancy Ratio = 2/4 = 0.5edu da cy at o / 0.5
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the latter is used in Taiwan and Hong Kong, and the former is used more often in Mainland
Estimate Redundancy Ratio of G.729 10%stimate Redundancy Ratio of G.7 9
8%9%
10%
G.729 (PC‐PSTN)
6%7%Constant bit rate
Constant framing
3%4%
5%Constant framing time
2%1%
3%
0%1%
0%
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Identify Redundancy Ratioy yRedundancy Ratio of G.729 (PC‐PSTN Calls)
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Identify Redundancy Ratioy yRedundancy Ratio of iSAC (PC‐PC Calls)
Network and Systems Laboratorynslab.ee.ntu.edu.tw
OutlineMotivation
Related Work
How does Skype adapt its redundancy ratio?How does Skype adapt its redundancy ratio?
Is Skype’s mechanism good enough?
How can we do better?
ConclusionConclusion
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Skype’s Redundancy Control AlgorithmSkype s Redundancy Control Algorithm
Adapt to network loss rateAdapt to network loss rate
Adapt to other factors?
Codec
N t k L B tiNetwork Loss Burstiness
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Effect of Codec
G.729
iSAC
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Effect of Network Loss BurstinessG.729 (PC‐PSTN)
BR=2
BR=1BR 1
BR=1.5
Network and Systems Laboratorynslab.ee.ntu.edu.tw
OutlineMotivation
Related Work
How does Skype adapt its redundancy ratio?How does Skype adapt its redundancy ratio?
Is Skype’s mechanism good enough?
How can we do better?
ConclusionConclusion
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Optimal Redundancy Control Policyp y yWhat’s the Optimal Policy?
Minimum amount of redundancy data we need to sustain the same audio qualityneed to sustain the same audio quality under different network conditions
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Emulation Flow
OptimalRedundancyRatio
G.729
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Skype vs. Optimal – G.729yp p
Skype
Burst Ratio = 1
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Optimal Redundancy for the Burst RatioOptimal Redundancy for the urst Ratio
BR=1.5BR=2BR=2
BR=1
Skype
G.729, MOS=3.5
Network and Systems Laboratorynslab.ee.ntu.edu.tw
Modeling Optimal Redundancy RatioModeling Optimal Redundancy RatioBased on the targeted voice quality
Take codec and burstiness into considerationconsideration
Optimal Policy for G.729, targeted MOS=3.5
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ConclusionExplore how Skype adapts its voice trafficRedundancy Ratio
Skype’s policy does not factor in the individualSkype s policy does not factor in the individual codec and loss patterns in to consideration
Propose a general model for optimal policyConsistent user satisfaction
Extensible to general VoIP software
Network and Systems Laboratorynslab.ee.ntu.edu.tw