Sharing but not Caring - Performance of TCP BBR and TCP CUBIC at the Network Bottleneck
Saahil Claypool · Digital WPI · 2019
Loss-based congestion control protocols such as TCP CUBIC can unnecessarily fill router buffers adding delays which degrade application performance. Newcomer TCP BBR uses estimates of the bottleneck bandwidth and round trip time (RTT) to try to operate at the theoretical optimum – just enough packets to fully utilize the network without excess queuing. We present detailed experimental results that show in practice, BBR can either over- or under-estimate 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.