Paper review: Quality Adaptation for Congestion Controlled Video Playback over the Internet

Reviewer: Mike Liu

1. State the problem the paper is trying to solve.
The main problem the paper is trying to solve is the creation of an effective congestion control for streaming video and audio applications on the Internet.
2. State the main contribution of the paper: solving a new problem, proposing a new algorithm, or presenting a new evaluation (analysis). If a new problem, why was the problem important? Is the problem still important today? Will the problem be important tomorrow?  If a new algorithm or new evaluation (analysis), what are the improvements over previous algorithms or evaluations? How do they come up with the new algorithm or evaluation? 
The main contribution of the paper is that the authors present a mechanism for using layered video in the context of unicast congestion control. The problem the paper addresses is still relevant today in that an efficient mechanism for large amounts of audio and video applications on the Internet has yet to be released and implemented. The problem will continue to be important as we seek to used the Internet for more and more multimedia, interactive applications.
3. Summarize the (at most) 3 key main ideas (each in 1 sentence.) 
The three 3 key main ideas are: (1) The paper presents a quality adaptation mechanism using layered video, which adds and drops layers of the video stream to perform long-term coarse-grain adaptation, while using a TCP-friendly congestion control mechanism to react to congestion on very short timescales. (2) The mismatches between the two timescales are absorbed using buffering at the receiver and a smoothing parameter for the distribution of buffering among the active layers to trade short-term improvement for long-term smoothing of quality were introduced. (3) They simulated the results of their simulation by obtaining bandwidth traces using their Rate Adaptation Protocol (RAP) in the ns2 simulator and using real Internet Experiments.
4. Critique the main contribution
   • Rate the significance of the paper on a scale of 5 (breakthrough), 4 (significant contribution), 3 (modest contribution), 2 (incremental contribution), 1 (no contribution or negative contribution). Explain your rating in a sentence or two.
   I give this paper a rating of 4 because it provides method for incrementally incorporating audio and video into the current Internet. The method of using incremental layers that only improve quality but do not prevent minimal transmission is a novel idea.
   • Rate how convincing the methodology is: how do the authors justify the solution approach or evaluation? Do the authors use arguments, analyses, experiments, simulations, or a combination of them? Do the claims and conclusions follow from the arguments, analyses or experiments? Are the assumptions realistic (at the time of the research)? Are the assumptions still valid today? Are the experiments well designed? Are there different experiments that would be more convincing? Are there other alternatives the authors should have considered? (And, of course, is the paper free of methodological errors.)
   Their methodology was somewhat convincing. They used a number of bandwidth traces to show that their protocol worked as they had proposed. This experimental evidence does convince the reader that the system does works as intended but it does not prove that the protocol is valid enough or will be successful enough in widespread distribution and implementation. What would be more convincing is if they could somehow show actual video that was displayed using the protocol and gave examples of how quality degraded as traffic increased. Perhaps quantitative numbers of how many frames were dropped given high traffic conditions would alse be helpful. Finally, for its widespread adoption, the protocol should be deployed to a large number of test users who should rate their satisfaction with the system for video and audio applications. Only in this way would the system have a chance of forecasting its deployability against or in conjunction withestablished systems such as RealVideo, Window Media Player, and Quicktime. Only if this protocol makes a noticeable improvement in performance will it become viable as a standard.
   • What is the most important limitation of the approach?
   The most important limitation of their experimental approach was that it was simulated and so it may have been a little less realistic than possible but this was done on purpose because they did not want to disrupt real Web traffic with their experiments. Another limitation is it would have been nice if they included more application oriented results since their project is so geared towards improving the performance of a specific class of applications.
5. What lessons should researchers and builders take away from this work. What (if any) questions does this work leave open?
The lessons researchers should take away from this work are that layered video and audio and its related system of buffering may work as a system for compensating for the bandwidth changes, especially due to congestion control, that may hinder using the Internet for large-scale video and audio applications. The questions the work leaves open are the application of quality adaptation schemes to other congestion control schemes that employ AIMD algorithm, quality adaption with a non-linear distribution of bandwidth among layers, a measurement-based approach of quality adaptation that adjusts Kmax on-the-fly based on the recent history, and the opportunity of proxy caching of multimedia streams.