Performance of Quantized Congestion Notification in TCP Incast Scenarios of Data Centers

This paper analyzes the performance of Ethernet layer congestion control mechanism Quantized Congestion Notification (QCN) during data access from clustered servers in data centers. We analyze the reasons why QCN does not perform adequately in these situations and propose several modifications to the protocol to improve its performance in these scenarios. We trace the causes of QCN performance degradation to flow rate variability, and show that adaptive sampling at the switch and adaptive self-increase of flow rates at the rate limiter improve performance in a TCP In cast setup significantly. We compare the performance of QCN against TCP modifications in a heterogeneous environment, and show that modifications to QCN yield better performance.