Paper review: A Comparison of Mechanism for Improving TCP Performance over Wireless Links

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 classify, compare, and evaluate different mechanisms for improving TCP performance over wireless links.
  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 the paper is that it provides a framework for evaluating new mechanisms for improving TCP performance over wireless links and shows how improvements to each of the improvements to each scheme can maximize performance. Prior to this, different schemes were proposed but no one had determined a way to classify them or measure their performance. In addition, improvement under each class of mechanisms were made to seek out the most optimal performance in each class. This framework is still rather relevant today because wireless technologies for the internet are still developing and it is yet to be decided which will be dominant scheme before it is widely implemented amongst the general publi.
  5. Summarize the (at most) 3 key main ideas (each in 1 sentence.) 
  6. The three 3 key main ideas are: (1) The three basic groups of schemes for improve TCP performance over Wireless Link are: end-to-end proposals, split-connection protocols, and link-layer proposals, with the last of the three having the best performance overall. (2) Other discoveries amongst each of the three groups are: it is important for link-layer schemes to be aware of TCP algorithms in order to achieve high end-to-end throughput; using a SMART-based selective acknowledgement scheme for the wireless hops yields higher throughput in a split-connection approach, though the throughput is still slightly less than a well-tuned link-layer scheme, indicating that splitting the end-to-end connections is a requirement of good performance; end-to-end schemes, while not as effective as local techniques in handling wireless losses, can use explicit loss notification to acheive an improvement in throughput and are promising since significant performance gains can be achieved without any extensive support from intermediate nodes in the network. (3) The SMART-based selective acknowledgement scheme is quite efective in dealing with a high packet loss rate, when employed over the wireless hop or by a sender in a LAN environment while a SACK scheme based on the IETF Draft resulted in significantly improved end-to-end performance in a WAN environment.
  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. Researchers and builders should take away from this work the fact that well-tuned link-layer schemes that are TCP aware and use a SMART-based selective acknowledgement scheme are currently the most optimal scheme to be used for maximizing performance in wireless environments. The questions that the work leaves open are that are there perhaps even better or more implementations of the link-layer scheme or also, are there other schemes in the other two classes, end-to-end and split-connection, that may acheive better performance but were not considered in this paper. Finally, further work can also be done to evaluate the performance of different protocols under the influence of wireless losses in different network topologies.