Improvement of RTT Fairness Problem in BBR Congestion Control Algorithm by Gamma Correction

Xiaofeng Li,Haibo Tan,Jinlin Xu,Xiru Li,Wansu Pan

doi:10.3390/s21124128

Abstract

Google proposed the bottleneck bandwidth and round-trip propagation time (BBR), which is a new congestion control algorithm. BBR creates a network path model by measuring the available bottleneck bandwidth and the minimum round-trip time (RTT) to maximize delivery rate and minimize latency. However, some studies have shown that there are serious RTT fairness problems in the BBR algorithm. The flow with longer RTT will consume more bandwidth and the flows with shorter RTT will be severely squeezed or even starved to death. Moreover, these studies pointed out that even small RTT differences will lead to the throughput of BBR flows being unfair. In order to solve the problem of RTT fairness, an improved algorithm BBR-gamma correction (BBR-GC) is proposed. BBR-GC algorithm takes RTT as feedback information, and then uses the gamma correction function to fit the adaptive pacing gain. This approach can make different RTT flows compete for bandwidth more fairly, thus alleviating the RTT fairness issue. The simulation results of Network Simulator 3 (NS3) show that that BBR-GC algorithm cannot only ensure the channel utilization, but also alleviate the RTT fairness problem of BBR flow in different periods. Through the BBR-GC algorithm, RTT fairness is improved by 50% and the retransmission rate is reduced by more than 26%, compared with that of the original BBR in different buffer sizes.

Highlights

This study proposes an optimized algorithm based on the original bottleneck bandwidth and round-trip propagation time (BBR), named BBR-gamma correction (BBR-GC), to improve the round-trip time (RTT) fairness of BBR without affecting the bandwidth utilization of the network
In order to evaluate the performance of BBR-GC, the original BBR algorithm, the BBQ algorithm and the BBR-ACW algorithm are introduced as the benchmark
We use Network Simulator 3 (NS3) to do a lot of simulation experiments, and compare the fairness between BBR, BBQ, BBR-ACW and BBR-GC

Summary

Introduction

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Methods

Results

Conclusion