Enhanced BBR Congestion Control Algorithm for Improving RTT Fairness

Abstract

Google has proposed the Bottleneck Bandwidth and Round-trip propagation time (BBR) as a new congestion control algorithm. The difference between it and the existing congestion control algorithm is that it is derived from actual congestions. BBR measures the bottleneck bandwidth and round-trip propagation time sequentially and sends data based on bandwidth delay product (BDP). The mere dependence on the BDP unfairly allocates a larger part of the bandwidth to a flow with long RTT than a short RTT flow. This nature of the BBR entirely conflicts with the trend of traditional TCP where a short RTT flow is more vibrant than long RTT flow. To solve this problem, we previously proposed the bottleneck queue buildup suppression method and verified that through NS-3. However, during the testbed experiments, we found that the previous method was unstable and led to unexpected results. Therefore, in this paper, we propose an improved version of the previously proposed algorithm. We confirmed through extensive testbed experiments that our proposed BBR-E improves fairness between the flows with different RTTs and ensures better throughput.