Improving DCTCP/Prague Congestion Control Responsiveness

01/19/2021

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by   Bob Briscoe, et al.

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This report explains how DCTCP introduces 1–2 rounds of unnecessary lag, due to the way it processes congestion feedback. To solve this, a per-ACK moving average is proposed. It always cuts out 1 RTT of this lag and, paradoxically, it cuts out most of the rest of the lag by spreading the congestion response over a round. The EWMA still averages out variations in the feedback signal over the same set number of round trips, even though it is clocked per-ACK. This version of the report is released prior to full evaluation, in order to elicit early feedback on the design.