  Datacenter applications frequently cause incast congestion, which degrades
both flow completion times of short flows and throughput of long flows. Without
isolating incast, existing congestion control schemes (e.g., DCTCP) rely on
existing ECN signal to react to general congestion, and they lose performance
due to their slow, cautious, and inaccurate reaction to incast. We propose to
isolate incast using Explicit Incast Notifications (EIN) that are generated by
switches, similar to ECN. Our incast detection is fast and accurate. Further,
we present our congestion control scheme, called Pulser, which drastically
backs off during incast based on EIN, but restores sending rate once incast
ends. Our real experiments and ns-3 simulations show that Pulser outperforms
prior schemes, DCTCP and ICTCP, in both flow completion times and throughput.
