DCTCP Data Center TCP
A TCP congestion control variant built for data centers, presented by Microsoft Research in 2010. It uses ECN marks to measure how much queue has built up, not merely whether there is any.
Ordinary TCP halves the window on every congestion signal, producing sawtooth behaviour and large buffers. DCTCP instead counts the fraction of ECN-marked ACKs and reduces the window proportionally to that fraction. The result is short queues, low latency and high throughput at the same time — exactly what mixed traffic with both large flows and small latency-sensitive requests needs. It also addresses incast, where a hundred servers answer simultaneously and fill a switch port. Requires ECN support in the switches and a single administrative domain; it does not work across the internet, where CUBIC and BBR rule.