On the Efficiency and Fairness of Transmission Control Loops: A Case for Exogenous Losses

We postulate that exogenous losses–which are typically regarded as introducing undesirable “noise” that needs to be filtered out or hidden from end points–can be surprisingly beneficial. In this paper we evaluate the effects of exogenous losses on transmission control loops, focusing primarily on efficiency and convergence to fairness properties. By analytically capturing the effects of exogenous losses, we are able to characterize the transient behavior of TCP. Our numerical results suggest that “noise” resulting from exogenous losses should not be filtered out blindly, and that a careful examination of the parameter space leads to better strategies regarding the treatment of exogenous losses inside the network. Specifically, we show that while high levels of exogenous losses lead to inefficient network utilization, lower levels of losses do help connections converge to their fair share. This observation suggests that the beneficial value of exogenous losses should be leveraged inside the network in favor of TCP connections. To that end, we propose an eXogenous-loss aware Queue Management (XQM) that actively accounts for exogenous losses to improve efficiency and fairness. Our proposed approach is based on classifying the effects of exogenous losses into long-term and short-term effects. Such classification informs the extent to which we control exogenous losses, so as to operate in an efficient and fair region. We validate our results through simulations.