CS 244 ’19: Reproducing Copa

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Sawyer Birnbaum, Nadin El-Yabroudi

Original paper: Venkat Arun and Hari Balakrishnan. 2018. Copa: Practical Delay-Based Congestion Control for the Internet. In Proceedings of the Applied Networking Research Workshop (ANRW ’18). ACM, New York, NY, USA, 19-19. DOI: https://doi.org/10.1145/3232755.3232783

We reproduce key findings from Copa: Practical Delay-Based Congestion Control, which presents a general purpose delay-based congestion control algorithm called Copa. In keeping with the original paper, we find that Copa achieves a higher flow-rate fairness than BBR, PCC, and Cubic. We also successfully reproduce the paper’s claim that on real-world wired and cellular links in February of 2018 Copa achieves nearly as much throughput and 2-10 times lower queuing delay as other congestion control schemes. However, our results show that in the last 2 months Copa achieves significantly lower throughput than most other schemes, and on in our fairness experiments we observe that a single Copa flow uses only about 85% of a link’s full capacity. Accordingly, our results indicate that further research is required to establish whether and in what conditions Copa provides better performance than other congestion control algorithms.

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