Stability analysis of compound TCP with adaptive virtual queues

Compound TCP (C-TCP) is currently the default transport layer protocol in the Windows operating system. We study a non-linear fluid model of Compound along with Virtual Queue (VQ) management schemes in network routers. One can implement virtual queue policies either non-adaptively or adaptively. The Adaptive Virtual Queue (AVQ), in particular, has the objective of driving the link utilisation to a desired level. The stability analysis of non-adaptive virtual queues reveals that smaller virtual buffer sizing rules help stability. Small virtual buffers would quite naturally reduce queueing delays in routers. Some guidelines for Compound and network parameters to ensure local stability are outlined. Analysis of the AVQ policy shows that the system is prone to losing local stability with large feedback delays, high link capacities, and with variations in the AVQ damping factor. We further show that the loss of local stability would occur via a Hopf bifurcation. Based on the analysis, our recommendation is that a virtual queue, with small buffer sizes, could be an attractive queue management scheme.