Abstract: The traditional congestion control algorithm based on packet loss can’t meet the requirements of many applications for network performance because of its high packet loss rate and buffer expansion. The BBR (bottleneck bandwidth and round trip) algorithm proposed by Google has attracted extensive attention and research because of its characteristics of anti packet loss, high bandwidth utilization and low delay. However, BBR still has some problems, such as high queuing delay, poor performance in a small RTT (round trip time) environment, untimely bandwidth detection, etc. This paper analyzes the queuing delay and convergence of BBR, and then puts forward an improved method: Limit inflight data, and reduce the congestion window size timely according to the network feedback to reduce the delay; In small RTT environment, the bandwidth estimation before the probe RTT stage is retained to after probe RTT; Set the maximum holding time of steady state, exit the steady cycle in time and enter the detection cycle. The simulation results in NS3 show that the improved BBR reduces the RTT and its jitter, and improves the convergence speed of the algorithm; The bandwidth can be efficiently used in the environment with small RTT; The improved BBR can significantly improve the bandwidth probe frequency of long RTT streams.

Key words: congestion control algorithm, BBR optimization, low latency, BBR fairness, bandwidth probe