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Alternative Backoff: Achieving low latency andhigh throughput with ECN and AQM
Conference paper

Alternative Backoff: Achieving low latency andhigh throughput with ECN and AQM

N. Khademi, M. Welzl, G. Armitage, C. Kulatunga, D. Ros, G. Fairhurst, S. Gjessing and S. Zander
IFIP Networking Conference (IFIP Networking) AND WORKSHOPS
IFIP Network Conference (IFIP Networking) and Workshops (Toulouse, Framce, 20/05/2015–22/05/2015)
2015
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Abstract

CoDel and PIE are recently proposed Active Queue Management (AQM) mechanisms that minimize the time packets spend enqueued at a bottleneck, instantiating shallow, 5 ms to 20 ms buffers with short-term packet burst tolerance. However, shallow buffering causes noticeable TCP performance degradation when a path’s underlying round trip time (RTT) heads above 60 ms to 80 ms (not uncommon with cross-continental and inter-continental traffic). Using less-aggressive multiplicative backoffs is known to compensate for shallow bottleneck buffering. We propose ABE: “Alternative Backoff with ECN”, which consists of enabling Explicit Congestion Notification (ECN) and letting individual TCP senders use a larger multiplicative decrease factor in reaction to ECN-marks from AQMenabled bottlenecks. Using a mix of experiments, theory and simulations with standard NewReno and CUBIC flows, we show significant performance gains in lightlymultiplexed scenarios, without losing the delay-reduction benefits of deploying CoDel or PIE. ABE is a senderside- only modification that can be deployed incrementally (requiring no flag-day) and offers a compelling reason to deploy and enable ECN across the Internet.

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