A Study on Cyclic Performance Fluctuation of CUBIC TCP and TCP BBR Considering Estimated RTT and Bandwidth

Previous works showed that the throughputs of TCP BBR and CUBIC TCP fluctuated in a condition wherein they communicate concurrently. In this paper, we discuss the reason of this fluctuation. TCP BBR estimates the bottleneck link bandwidth (BtlBw) and the round-trip propagation delay time (RTprop) during communication. This then its congestion window size to the product of BtlBw and RTprop. We discuss the relationship between Btlbw, RTprop, and performance fluctuation. We evaluate performance fluctuation with constant Btlbw and RTprop and show that the fluctuation is relieved by constant RTprop.