A Study on Performance of CUBIC TCP and TCP BBR in 5G Environment

5G (the fifth generation technology standard for cellular networks) is attracting attention as a new cellular network technology. This can achieve communication with lower latency and wider bandwidth comparing with 4G, which is the fourth generation. In addition, many of the current communications use TCP (Transmission Control Protocol), and it is expected that 5G’s these features have a large effect on the behaviors of TCP congestion control algorithms. In this paper, we focus on CUBIC TCP and TCP BBR, which are the most widely used congestion control algorithm and most getting attention one, and investigate the performance behaviors of these TCP algorithms in the 5G environment. First, we evaluate the change of throughputs of these algorithms over time in a practical 5G network using real 5G devices. We then show some unique behaviors. That is, their throughputs fluctuate in the long term, such as with a cycle of some minutes, CUBIC TCP outperforms TCP BBR most of the time, and their throughputs are sometimes extremely unfair, for example, their performance is more than 100 times different. Second, we investigate the change of the internal variables of both TCP algorithms, such as congestion window size and estimated bottleneck bandwidth, and reveal the reason of unique behaviors.