Paper review: < Adaptive Playout Mechanisms for Packetized Audio Applications in Wide-Area Networks [RKTS94] >

Reviewer: <Ryan Gehl>

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

The purpose of this paper is to investigate the performance of four different algorithms for adaptively adjusting the playout delay of audio packets in an interactive packet-audio terminal application in the face of varying network delays.

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 that adaptive algorithms which adjust rapidly to changing delays can achieve a lower rate of packet loss for both a given average playout delay and a given maximum buffer size.

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

(1) The authors present four algorithms which perform delay estimation and dynamic playout delay adaptation.
(2) An adaptive algorithm which explicitly adjusts to the sharp, spike-like increases in packet delay which were observed in the authors' traces can achieve a lower rate of packet loss for both a given average packet delay and a given maximum buffer size.


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 3 because this paper does present a modest contribution in terms of an adaptive algorithm to deal with audio applications. I feel that this paper will be increasingly more important as additional applications, such as IP telephony, are created.

   • 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.)

   In justifying their results, the authors wrote a simulator which takes the received packet trace file generated by running NeVoT and simulates the behavior of the playout algorithms. By addressing an observed problem, the delay spike, I felt that the authors effectively addressed a previously untouched area of this problem.

   • What is the most important limitation of the approach?

   One limitation of this approach is that I'm not sure how applications without frequent "talkspurts" perform using algorithm 4.

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 dynamic algorithms can often improve upon static algorithms.