Sharing but not Caring - Performance of TCP BBR and TCP CUBIC at the Network Bottleneck

摘要

Loss-based congestion control protocols, such as TCP CUBIC, can unnecessarily fill router buffers, adding delays that degrade application performance, particularly streaming video. Newcomer Transport Control Protocol (TCP) BBR (Bottleneck Bandwidth and Round-trip propagation time) uses estimates of the bottleneck bandwidth and Round-Trip Time (RTT) to try to operate at the theoretical optimum - just enough data to fully utilize the network without excess queuing. We present detailed experimental results showing that, in practice, BBR can misestimate the bottleneck bandwidth and RTT, causing high packet loss for shallow buffer routers and massive throughput variations when competing with TCP CUBIC flows. We suggest methods for improving BBR's estimation mechanisms to provide more stability and fairness.