Quality Adaptation for Congestion Controlled Video Playback over the
- 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
- 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.
- 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
- 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
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.
- 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