Paper review: Adaptive Playout Mechanisms for Packetized Audio Application in Wide-Area Networks

Reviewer: Mike Liu

  1. State the problem the paper is trying to solve.
  2. The main problem the paper is trying to solve is how to develop and evaluate 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.
  3. 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? 
  4. The main contribution of this paper is that the authors investigated and evaluated the performance of four different algorithms for adaptively adjusting the playout delay for audio packets in the face of varying network delays. This is a new analysis because adaptively adjusting to delay distribution by adjusting the playout delay is relatively new technique and much work had not been down to evaluate the performance of different algorithms of this type. This evaluation is an improvement over just presenting a single algorithm that has this new feature because by comparing several algorithms of this type, more knowledge is gained regarding which algorithm should be implemented. The problem will continue to be important as the Internet welcomes more and more real-time, interactive multimedia applications.
  5. Summarize the (at most) 3 key main ideas (each in 1 sentence.) 
  6. The three 3 key main ideas are: (1) An approach to dealing with the unknown nature of the delay distribution is to estimate these delays and adaptively respond to their change by dynamically adjusting the playout delay. (2) Four algorithms of this type were tested and evaluated using the experimentally-obtained delay measurements of audio traffic between several different Internet sites. (3) In comparing the algorithms, the results indicated that an adaptive algorithm which explicitly adjust to the sharp, spike-like increases in packet delay which were observed in traces can achieve a lower rate of lost packets for both a given average playout delay and a given maximum buffer size.
  7. Critique the main contribution
  8. What lessons should researchers and builders take away from this work. What (if any) questions does this work leave open?
  9. The lessons that researchers should take away from this work are that an adaptive algorithm which explicitly adjusts to the sharp, spike-like increases in packet delay can achieve a lower rate of lost packets for both a given average playout delay and a given maximum buffer size. The questions the work leaves open are what are the timed trial results and average packet losses on the real Internet like for these four algorithms and are the results the same. Also, another area for investigation are the possibilities for quantifying the distortion which occurs when silence periods are artifically contracted or expanded, and how can the different algorithms be compared based on these factors. Finally, additional research is needed in formalizing and arriving at a better understanding of the dynamics of network delays.