Right buffer sizing matters: Stability, queuing delay and traffic burstiness in compound TCP

Motivated by recent concerns that queuing delays in the Internet are on the rise, we conduct a performance evaluation of Compound TCP in two topologies. The first topology consists of a single bottleneck, and the second consists of two distinct sets of flows, regulated by two edge routers, feeding into a core router. We consider long-lived flows, and a combination of long and short flows. For these models, we derive necessary and sufficient conditions for stability and prove that the dynamical system undergoes a Hopf bifurcation as the stability condition gets violated. Using a combination of analysis and packet-level simulations, we emphasise that larger buffers, in addition to increasing delay, are prone to inducing limit cycles. These limit cycles in turn induce synchronisation among TCP flows and tend to make the downstream traffic bursty.