Enhanced Loss-Recovery Mechanism for BBR to Improve Inter-protocol Fairness

Abstract

In 2016, Google proposed a new congestion control algorithm called bottleneck bandwidth round-trip propagation time (BBR). While existing loss-based congestion control algorithms tend to fill the bottleneck buffer, TCP BBR determines the amount of delivered data based on Bottleneck Delay Product (bdp) consisting of available maximum and minimum round-trip time avoiding creation of excess queues. However, when it competes with loss-based congestion control algorithm, BBR encounters problems caused by its incorrect RTT min estimation, in particular the imbalance in the share of the bottleneck bandwidth for each flow, and excessive packet loss occurrence. In this paper, we propose a new loss recovery mechanism for BBR so that BBR shares the bottleneck link with loss-based congestion control algorithm flows without excessive packet losses. We focused on searching for the appropriate minimum RTT to allow BBR and CUBIC to coexist on a bottleneck link. Finally, we constructed a simple testbed topology in order to evaluate the performance of the proposed BBR loss recovery mechanism. We confirmed that the proposed BBR approach allows it to fairly share a bottleneck link with CUBIC while reducing the packet loss caused by the overestimation of bdp.