cing-yu chu 2012.08.06 infocom 2012. outline introduction measurement measurement results ...
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PROFILING SKYPE VIDEO CALLS: RATE
CONTROL AND VIDEO QUALITY
CING-YU CHU
2012.08.06
INFOCOM 2012
Outline
Introduction Measurement Measurement Results Modeling Skype Behaviors Analysis on TCP-friendly
Motivation
Skype VoIP service is well studied while video service is not
Skype video service consumes more bandwidthUp to 950 kbps
Imperative for network providers and network researchers
Key Questions
Q1: How does a Skype video call adapt its sending rate, video rate and quality under different network conditions?
Q2: Are Skype video calls friendly to TCP flows when they compete for network resources?
Methodology Measurement
Black-box approachDifferent network setting with
○ configurable packet loss,○ propagation delay○ available bandwidth
Aim to measure○ sending rate○ throughput○ RTT○ video bit rate○ frame rate
Methodology
ModelingRate control modelFEC modelVideo quality model
AnalysisUser back-off
○ User-level rate control schemeTCP-friendliness
Contribution
Measures Skype’s stationary behaviors of video callsSending rate is insensitive to packet loss
when PLR < 10%Utilization of the available bandwidth is
around 80%Overly aggressive FEC scheme, 4.5 times
the PLR
Contribution
Derive various models to verifyUser back-offs react fast to congestionSkype video calls are TCP-friendly
○ Due to quality-driven user back-offs
Measurement Test-bed
Experiment Design
TV news video sequence “Akiyo”From Joint Video Team (JVT)Head and shoulder movements
Virtual video camera tool Data collection
TCP-dumpSkype technical reports
Skype Video Call
On2 video codecVideo quantization stepVideo resolutionNumber of frames per seconds (FPS)
Measurements Results
Impact ofPacket LossAvailable BandwidthPropagation Delay
Impact of Packet Loss
PLR varies from 0% to 12% Propagation delay: 50ms 3 available bandwidth settings
250 kbps750 kbps1000 kbps
Impact of Packet Loss
Forward Error Correction Two states
PLR < 10% => NORM statePLR >= 10% => CONS state
Different from TCP congestion control scheme
Impact of Available bandwidth
Available Bandwidth varies from 50 kbps to 1000kbps
Two PLRs: 2% and 10% Propagation delay: 50ms
Impact of Propagation Delay Propagation delay varies from 50ms to
2000ms Available bandwidth: 500 kbps PLR: 0%
Modeling
Sending rate Video rate Video Quality
Sending Rate Model
NORM and CONS states
25 scenarios withPLR: 0% to 12%Available bandwidth: 50 kbps to 1000 kbps
γ = 0.77, μ = -10.8 and δ = 21
Video Rate Model
FEC ratio
FEC ratio model
Ψ = 0.15 and ω = 4.5
Video Quality Model
ITU-T Recommendation G.1070
frame rate
video rate
Video Quality Model
Frame rate model
Video Quality Model
a = 1.431, b = 0.02228, c = 3.759, d = 184.1, e = 1.161, h = 1.446 and g = 0.03881
Model Validation
Co-current UDP traffic (from iPerf)0 kbps to 600 kbps
Link capacity: 700 kbps Propagation delay: 50ms Available bandwidth for Skype
Model Validation
Pearson Correlation Coefficient
Sending rate Video rate Frame rate
0.9898 0.9831 0.9545
Analysis
Q1: How Skype video call users respond to quality degradation resulted from network impairments? How effective user back-offs are as a user-level rate control scheme?
Q2: What is the performance of a Skype video call when it competes with other Skype calls and TCP flows? Is Skype video call TCP-friendly?
Network Model
LTE wireless networkMultiple TCP and Skype usersM/M/1/K queue using drop-tailDownlink: 100 Mbps, uplink: 50 Mbps
TCP Model
Reacts to packet loss and RTT
p = pq + pc
t = tq + tc
User-level Rate Control
Video drop-off probability
Number of active users
Effective traffic generated by all users
User-level Rate Control
Average traffic of each user
Expected Skype sending rate
Responsiveness to Loss
Responsiveness to Delay
Competition with TCP
pc = 2% and tc = 50ms
NT = # of TCP users, NS = # of Skype users
Aggregate traffic
For each Skype user
Competition with TCP
Scale-up factor: k
Conclusion
Measures Skype video trafficShows that Skype is robust against mild
packet loss and propagation delaySkype can efficiently utilize available
bandwidth Models Skype video behaviors Shows that Skype video is indeed TCP-
friendlyBased on user back-off rate control scheme
Q & A