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Alternative backoff: Achieving low latency and high throughput with ECN and AQM
Conference paper

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

N. Khademi, G. Armitage, M. Welzl, S. Zander, G. Fairhurst and D. Ros
2017 IFIP Networking Conference (IFIP Networking) and Workshops
2017 IFIP Networking Conference (IFIP Networking) and Workshops (Stockholm, Sweden, 12/06/2017–16/06/2017)
2017
DOI: https://doi.org/10.23919/IFIPNetworking.2017.8264863
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Abstract

A number of recently proposed Active Queue Management (AQM) mechanisms instantiate shallow buffers with burst tolerance to minimise the time that packets spend enqueued at a bottleneck. However, shallow buffering causes noticeable TCP performance degradation as a path's underlying round trip time (RTT) heads above typical intra-country levels. Using less-aggressive multiplicative backoffs in TCP can compensate for shallow bottleneck buffering. AQM mechanisms may either drop packets or mark them using Explicit Congestion Notification (ECN), depending on whether the sender marked packets as ECN-capable. While a drop may therefore stem from any type of queue, an ECN-mark indicates that an AQM mechanism has done its job, and therefore the queue is likely to be shallow. We propose ABE: “Alternative Backoff with ECN”, which consists of enabling ECN and letting individual TCP senders back off less aggressively in reaction to ECN-marks from AQM-enabled bottlenecks. Using controlled testbed experiments with standard NewReno and CUBIC flows, we show significant performance gains in lightly-multiplexed scenarios, without losing the delay-reduction benefits of deploying AQM. ABE is a sender-side-only modification that can be deployed across networks incrementally (requiring no flag-day) and offers a compelling reason to deploy and enable ECN across the Internet.

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