Understanding TCP Cubic Performance in the Cloud: a Mean-field Approach

Cloud networking typically leads to scenarii where a large number of TCP connections share a common bottleneck link. In this paper, we focus on the case of TCP Cubic, which is the default TCP version in the Linux kernel. TCP Cubic is designed to better utilize high bandwidth-delay product path in an IP network. To do so, Cubic modifies the linear window growth function of legacy TCP standards, e.g., New Reno, to be a cubic function. Our objective in this work is to assess the performance of TCP Cubic in a cloud setting with a large number of long-lived TCP flows. We rely on a mean-field approach leading to a fluid model to analyze the performance of Cubic. After a careful validation of the model through comparisons with ns-2, we evaluate the efficiency and fairness of Cubic as compared to that of New Reno for a set of typical cloud networking scenarii.