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

Khademi, N., Welzl, M., Armitage, G., Kulatunga, C., Ros, D., Fairhurst, G., Gjessing, S. and Zander, S. (2015) Alternative Backoff: Achieving low latency and high throughput with ECN and AQM. In: IFIP Network Conference (IFIP Networking) and Workshops, 20 - 22 May 2015, Toulouse, Framce


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.

Item Type: Conference Paper
Murdoch Affiliation: School of Engineering and Information Technology
Conference Website:
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