On performance limitations of congestion control

Fundamental performance limitations on congestion control is discussed in relation to the information that is available in the controller. Three control architectures that all use bottle-neck buffer delay information of various form as inputs and sending rate as outputs are considered. It is shown that feedback delays from buffer to senders set limits on the achievable performance measured through fairness, efficiency and stability. We apply our findings to TCP FAST and can make some new interesting control theoretic interpretations of that protocol.