Understanding CHOKe

A recently proposed active queue management, CHOKe, is stateless, simple to implement, yet surprisingly effective in protecting TCP from UDP flows. As UDP rate increases, even though the number of UDP packets in the queue rises, its bandwidth share eventually drops to zero, in stark contrast to the behavior of a regular FIFO buffer. We derive a detailed model of CHOKe that accurately predicts this, and other behaviors of CHOKe, and validate the model with simulations. Its key features are the incorporation of the feedback equilibrium of TCP with dropping probability and the spatial characteristics of the queueing process. CHOKe produces a "leaky buffer" where packets can be dropped as they move toward the head of the queue. This leads to a spatially nonuniform distribution of packets and their velocity, and makes it possible for a flow to simultaneously maintain a large number of packets in the queue and receive a vanishingly small bandwidth share. This is the main mechanism through which CHOKe protects TCP from UDP flows.