Revisiting Congestion Detection in Lossless Networks

Congestion detection is the cornerstone of end-to-end congestion control. Through in-depth observations and understandings, we reveal that existing congestion detection mechanisms in mainstream lossless networks (i.e., Converged Enhanced Ethernet and InfiniBand) are improper, due to failing to cognize the interaction between hop-by-hop flow controls and congestion detection behaviors in switches. We define the ternary states of switch ports and present Ternary Congestion Detection (TCD) for mainstream lossless networks. TCD utilizes the ON-OFF sending pattern and the feature of queue length evolutions to detect the transitions among ternary states. We also enable TCD under the practical multiple queues scenario by TCD-MQ. Testbed and extensive simulations demonstrate that TCD can detect congestion ports accurately and identify flows contributing to congestion as well as flows only affected by hop-by-hop flow controls. Meanwhile, we shed light on how to incorporate TCD with rate control. Case studies show that existing congestion control algorithms can achieve $3.3\times $ and $2.0\times $ better median and 99th-percentile FCT slowdown by combining with TCD.