Breaking One-RTT Barrier: Ultra-Precise and Efficient Congestion Control in Datacenter Networks

Congestion control is crucial to the overall performance of datacenter networks and still faces great challenges, especially when network traffic exhibits complicated and time-varying patterns, from long-running flows to burst short-lived flows. Recently congestion control techniques based on in-network-telemetry (INT) are emerging as the promising approach to enable precise flow control. Existing INT-based method mainly relies on receiver ACK packets to transfer INT data and acquire link load information. Their control precision in term of response time, however, is still beyond one round-trip time (RTT), since the receiver ACK feedback needs at least one RTT and the sender cannot obtain INT data of one flow within the first RTT. In this paper, we make the first attempt to explore INT-based techniques and break the one-RTT barrier efficiently. We come up with an ultra-precise and efficient congestion control algorithm, called UECC. UECC utilizes both switch-based and host-based INT simultaneously, and realizes accurate, timely and low-overhead flow control. We tackle the challenging issues of cooperation between the two types of INT and the additional overhead introduced by confirmation packets, and conduct extensive experiments to evaluate the performance of our design. The results show that UECC achieves 42% reduction in average queue length compared to the state-of-the-art INT-based method, and 5% reduction in 95th-percentile flow completion time.