Abstract: In order to solve the problem of delay oscillation and empty window caused by the bottleneck bandwidth and round-trip time(BBR) congestion control algorithm in the STARTUP phase due to not receiving the acknowledge character(ACK) in the campus network,the BBR unilateral adaptation algorithm is proposed.The algorithm only runs on the sender,and it is not restricted by network protocols and upper-layer applications.By improving the weighting coefficient of the delay estimator,we design the instantaneous average deviation estimator of the delay and use the estimation result as the oscillation smoothing factor of the delay estimator to improve the ability of the delay estimator to deal with severe delay jitter.To solve the inevitable empty window problem and sequence number wraparound as much as possible,a flow state machine and a STARTUP state machine are designed at the sending end to maintain a high link throughput.According to the specific transmission situation,the traffic is divided into 6 states:new,blocked,waiting,time_waiting,running,terminated,and according to the traffic feedback,the transmission performance of the STARTUP stage is divided into 3 states:GOOD,NORMAL,BAD.Experimental results show that the improved BBR has better transmission performance in the STARTUP phase than the original BBR algorithm and is better than the passive congestion control algorithm (Reno,CUBIC) currently.

Key words: Flow state machine, Instantaneous average deviation, Oscillation smoothing factor, STARTUP state machine, Time delay estimator