Improving RTT Fairness on CUBIC TCP

Tomoki Kozu, Yuria Akiyama, Saneyasu Yamaguchi


CUBIC TPC is a congestion control algorithm for TCP. It is the current default TCP algorithm in Linux. Because many Internet servers, such as web servers, are running on Linux operating system, keeping throughput obtained with this TCP enough is quite important. Then, many performance studies have been published. However, most of these studies have been based on network simulators. Thus, evaluations using an actual TCP implementation and actual network elements are important in addition to these existing studies. In this paper, we focus on RTT (round trip time) fairness on CUBIC TCP, which is performance fairness among CUBIC TCP connections with different network delay times. Firstly, we present RTT fairness evaluation using actual TCP implementations and actual network elements and show that the fairness is not enough. Secondly, we discuss the cause of the unfairness based on CUBIC TCP behaviors. Thirdly, we propose a method for improving RTT fairness of CUBIC TCP. Unlike an existing work, the proposed method is not based on heuristic optimization. Finally, we present evaluation results and demonstrate that the proposed method provides better fairness than original CUBIC TCP implementation. 


TCP; congestion control algorithm; CUBIC TCP; RTT fairness

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