Flow-aware explicit congestion notification for datacenter networks

Explicit congestion notification (ECN) has been widely adopted by recent proposals to build up high-throughput and low-latency datacenter network transport. In these ECN-based proposals, when the queue length of a switch exceeds a pre-defined threshold, the switch would mark all arriving packets with ECN to explicitly notify their senders to slow down the rates. Such a design enables the network to eliminate congestions quickly. However, it marks packets without considering the flow state, which may overkill flows, especially those only send a few packets, thus resulting in significant throughput loss and long flow completion times. In this paper, we propose a novel flow-aware ECN marking approach (FECN), which can improve the throughput and flow completion time by taking flow states into consideration. By selectively marking packets respecting to their flow rates, FECN enables the network to precisely slow down the high-speed flows to avoid congestions without killing low-speed short flows. Moreover, FECN does not require switches to maintain per-flow state, which yields low overhead and thus makes FECN to be easily implemented and deployed in commodity switches. Simulations show that FECN can shorten the flow completion time by up to 44.7% and reduce the throughput loss by up to 40.3%, compared with prior flow-agnostic ECN marking approach.