On the Interactions Between Layered Quality Adaptation and Congestion Control for Streaming Video 11 th International Packet Video Workshop Nick Feamster Deepak Bansal Hari Balakrishnan MIT Laboratory for Computer Science http: //nms. lcs. mit. edu/projects/videocm/ April 30, 2001 MIT Laboratory for Computer Science
Not Like Watching TV! April 30, 2001 MIT Laboratory for Computer Science 2
Why Is This Happening? • The Internet poses several problems for the delivery of data – Variable Bandwidth – Variable Delay – Packet Loss • Very detrimental to interactive video delivery • How do we transmit video on the Internet in the face of varying bandwidth? April 30, 2001 MIT Laboratory for Computer Science 3
System Context Request for Video Streaming Video Loss/Latency Feedback Video Server Video Client • This talk is about bandwidth adaptation • Conclusion: The combination of smooth congestion control and clever receiver buffering can overcome the evils of bandwidth variation! April 30, 2001 MIT Laboratory for Computer Science 4
Bandwidth Adaptation • Available bandwidth varies with time • Servers should adapt to varying bandwidth – Congestion Control: Transmission rate must • correspond to available bandwidth • be TCP-friendly – Quality Adaptation: Quality of video should correspond to transmission rate • Limited capacity for buffering! April 30, 2001 MIT Laboratory for Computer Science 5
Layered Video • Simulcast: Each layer is independent • Hierarchical: Higher depends on lower – Base/Enhancement layers – Linear granularity (C bits/layer) Simulcast Layering April 30, 2001 Hierarchical Layering MIT Laboratory for Computer Science 6
Binomial Congestion Control w(t) n Expo ff acko l. B entia AIMD t AIMD Increase Decrease Binomial a bw a / w. K b w. L • Trade-off between increase aggressiveness and decrease magnitude • K+L=1 implies TCP-friendly [Bansal, INFOCOM 2001] • SQRT has a modest backoff (~R 1/2) => attractive for streaming media April 30, 2001 MIT Laboratory for Computer Science 7
Reduced Oscillations In many cases, AIMD drops multiple layers in one backoff! This is not the case with SQRT. Rate oscillations in SQRT are much less pronounced than in AIMD. SQRT Bitrate AIMD April 30, 2001 MIT Laboratory for Computer Science 8
Layered Quality Adaptation • Tailor video to available bandwidth! • Can be immediate or receiver-buffered – Rejaie et al. , SIGCOMM ‘ 99 April 30, 2001 MIT Laboratory for Computer Science 9
Receiver Buffering R illing er F Buff Consumption Rate (na+1)C C Optimal L 0 buffering Buffer Drainin g R/2 • Allocate more buffer space to lower layers • Add a layer when the following conditions are met: – Enough bandwidth is available – Enough video is buffered to sustain a backoff and continue playing all of the layers (including the new layer) April 30, 2001 MIT Laboratory for Computer Science 10
Interaction of SQRT and QA: We Win! R Consumption Rate (na+1)C C R– b. R 1/2 Total buffering to add an additional layer is O(R 3/2) rather than O(R 2) • With SQRT: – Smaller Oscillations – Less buffering required for quality adaptation April 30, 2001 MIT Laboratory for Computer Science 11
Reduced Buffering 56% less buffering to add 4 layers SQRT requires less buffering to add layers! April 30, 2001 MIT Laboratory for Computer Science 12
Conclusion • Combination of SQRT congestion control with receiver quality adaptation enables smooth video delivery – Reduces rate oscillations – Reduces buffering/Increases interactivity • Software is available – Includes selective reliability for packet loss – http: //nms. lcs. mit. edu/software/videocm/ April 30, 2001 MIT Laboratory for Computer Science 13
Extra Slides April 30, 2001 MIT Laboratory for Computer Science 14
Outline • Problem Overview • Background – Bandwidth Variation – Quality Adaptation – Binomial Congestion Control • Approach • Results • Conclusion April 30, 2001 MIT Laboratory for Computer Science 15
The Goal • TCP-friendly congestion control • Reduce rate oscillations: – Limit size of playout buffer – Smooth perceptual quality • Limit receiver buffering for QA – Reach acceptable playout rate faster – More interactivity in certain cases (i. e. , if RTT and RTT jitter are small) April 30, 2001 MIT Laboratory for Computer Science 16
Results of SQRT • Tested on emulated network conditions with Dummynet and SURGE toolkit • SQRT reduces rate oscillations for: – Immediate adaptation – Receiver-buffered QA • Also reduces buffering: – – Less jitter due to rate oscillations Backoffs less severe => less QA buffering Can play out at higher layers more quickly More interactivity April 30, 2001 MIT Laboratory for Computer Science 17
RTSP MPEG Server loss/RTT callbacks data MPEG Client loss/RTT/requests data loss/RTT/requests Internet CM April 30, 2001 RTP/RTCP SR-RTP MIT Laboratory for Computer Science RTP/RTCP 18
System Architecture RTSP MPEG Server data Layering callbacks MPEG Client Internet loss/RTT/requests SR-RTP RTP/RTCP loss/RTT/requests RTP/RTCP callbacks CM April 30, 2001 data Band widt h Ad apta tion MIT Laboratory for Computer Science 19
Reduced Oscillations In many cases, AIMD drops multiple layers in one backoff! This is not the case with SQRT. Rate oscillations in SQRT are much less pronounced than in AIMD. Layers Dropped SQRT Bitrate AIMD April 30, 2001 MIT Laboratory for Computer Science 20
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