经典瓶颈链路带宽和往返传播时延(bottleneck bandwidth and round-trip propagation time，BBR)拥塞控制算法在链路拥塞时无法及时调整发送行为及发包数量，容易导致链路拥塞程度加剧，从而产生较大时延。分析发现，BBR拥塞检测的滞后性是这一问题的主要根源。为解决该问题，提出了BBR拥塞预测及避免(BBR congestion prediction and avoidance，BBR-CPA)算法，该算法从BBR的传输时延(round-trip time，RTT)更新机制入手，通过动态检测瓶颈路径，根据传输时延(round-trip time，RTT)数据实现对链路拥塞状态的预判，提前减少发包数量，从而排空链路中可能存在的拥塞。运行过程中记录瓶颈路径带宽数据并对带宽估值进行均值处理，加快链路向最优状态收敛。实验结果表明，与经典BBR算法和最新的BBR-S、BBR-ACD算法相比，BBR-CPA的平均时延分别降低了56%、44%、8%，有效消除了链路拥塞并降低了由此带来的时延。
BBR congestion prevention and control algorithm based on RTT updating mechanism
The classic BBR congestion control algorithm lacks timely adjustment of sending behavior and packet quantity during link congestion,which can easily exacerbate the degree of congestion and result in significant delays.Through analysis,the main root cause of this issue is the hysteresis in BBR congestion detection.To address this problem,the BBR congestion prediction and avoidance(BBR-CPA)algorithm was proposed.This algorithm started from the round-trip time update mechanism of BBR,dynamically detected the bottleneck path,and predicted the congestion state of the link based on RTT data,thus reduced the packet quantity in advance to alleviate potential congestion in the link.Dur-ing operation,it records the bottleneck path's bandwidth data and performed mean processing on band-width estimation,accelerated the convergence of the link to the optimal state.Experimental results show that compared to the classic BBR algorithm and the latest BBR-S and BBR-ACD algorithms,BBR-CPA achieve an average delay reduction of 56%,44%,and 8%.It effectively eliminates link con-gestion and reduces the resulting delays.
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