FAST TCP: Some queueing models and stability

We analyse the stability of FAST TCP, a new proposal for TCP, in three limiting regimes. When the queue is modelled as an integrator, the fluid model may lose local stability as the feedback delay varies. Loss of local stability is shown to occur via a Hopf bifurcation, and we analytically characterise the asymptotic orbital stability of the bifurcating limit cycles. In an intermediate and a small buffer regime, larger thresholds for dropping packets can lead to a locally unstable regime. Packet-level simulations complement some of the analytical insights.