Paper review: < Quality Adaptation for Congestion Controlled Video Playback over the Internet [RHE99] >

Reviewer: <Ryan Gehl>

1. State the problem the paper is trying to solve.

The purpose of this paper is to present a mechanism for using layered video in the context of unicast congestion control.

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 this paper is to describe a method known as quality adaptation to adjust the quality of the playback stream so that the perceived quality is as high as the available network bandwidth will permit.

3. Summarize the (at most) 3 key main ideas (each in 1 sentence.) 

(1) Quality adaptation allows the server to adjust the quality of the playback stream so that the perceived quality is as high as the available network bandwidth will permit. This is done using a layered scheme.
(2) With a small amount of buffering, the mechanism can efficiently cope with short-term changes in bandwidth due to AIMD congestion control.


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 would rate this paper as a 4 because it not only provides as effective, _deployable_ solution to a growing problem on the internet, it also raises several questions for future areas of research.

   • 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.)

   By presenting an algebraic justification and a simulation for their technique, I found their approach to be convincing. I felt like a strength of the authors approach was that they did not make any assumptions about loss patterns or available bandwidth.

   • What is the most important limitation of the approach?

   One limitation of the approach is that it is unclear to me why users would opt for a non-greedy strategy when they could receive a higher quality transmission with a slight delay (the paper assumes that a large delay is unacceptable).

5. What lessons should researchers and builders take away from this work. What (if any) questions does this work leave open?

One lesson to take away from this work is that smoothness can be achieved in an inherently bursty environment by setting up a producer/consumer model where times of excess bandwidth fill the buffer and times of sparce bandwidth drain it. Maybe this line of thinking can be applied to other smoothness problems.