Modelling Synchronization in TCP Networks Using Weakly-Coupled Oscillators

In this paper, we consider a fluid model of a TCP network consisting of many edge routers directing traffic through a common core link equipped with a small buffer. We are interested in how packet loss at this core router can dynamically couple, and potentially synchronize, the edge traffic. By using concepts from weakly-coupled oscillator theory, we show that synchronization occurs when a so-called coupling strength exceeds a critical value. This coupling strength is a property of the network, and can be expressed in terms of network parameters such as the core link’s utilization and its router’s buffer size. Avoiding synchronization requires a tradeoff between these two. That is, to avoid synchronization, small buffers should be accompanied by a commensurate reduction in link utilization. For example, in the paper, we will estimate that a 20-packet core buffer should have its link under-utilized by more that 35% to avoid synchronization.