Improving DCTCP/Prague Congestion Control Responsiveness

Bob Briscoe

This report motivates and defines an improvement to the responsiveness of the Data Center TCP (DCTCP) algorithm. It explains how DCTCP introduces unnecessary lag equivalent to 1.5--2 RTTs, due to the way it processes congestion feedback. A per-ACK moving average is proposed that cuts out 1 RTT of this lag. Paradoxically, the rest of the lag is reduced by spreading the congestion response over a round. The EWMA is designed to still smooth over the same set number of round trips, even though it is clocked per-ACK. This version is released prior to full evaluation in order to elicit early feedback on the design.

Knowledge Graph



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