Summary
This paper presents an evaluation of several schemes to improve the performance of TCP over lossy links, such as wireless. The authors classify the schemes into the following 3 categories:
1. end-to-end protocols: have the sender detect and handle losses using techniques such as SACKs and ELN
2. link-layer protocols: hide link-layer losses from the transport layer and handle them in the link-layer instead using techniques such as local retransmissions and forward error correction.
3. split-connection protocols: terminate the TCP connection at the station so that the sender is not aware of the wireless link at the end. Use a different protocol from the station to the receiver that deals with losses.
After evaluating the various schemes they got the following results: the enhanced link-layer scheme that has knowledge of the TCP protocol and uses SACKs works much better than a simple link-layer retransmission scheme. Out of the various end-to-end protocols, selective acknowledgements was found to be better than partial acknowledgements or ELN, but not better than the enhanced link-layer scheme. The split-connection protocol is worse than the two schemes above, and shows that a split-connection is not necessary to get optimal performance.
Overall, the link-layer scheme that was TCP aware and uses SACKs was found to be the best scheme.
Criticism & Questions
I would be very interested in finding out which schemes, if any, are currently used in lossy networks. They touch on this a little, but I would like to learn more about the practicality of each of the schemes and have that be one of the criteria considered when choosing the optimal scheme.
Feedback
I enjoyed reading this paper. It was great to learn about the various schemes available to improve performance in lossy links. I think the authors did a great job at explaining each of the schemes and why one was better than the other. I vote to keep this paper in the syllabus.
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