Selfish Routing on the Internet

In large-scale communication networks, like the Internet, it is usually impossible to globally manage network traffic. In the absence of global control it is typically assumed in traffic modeling that network users follow the most rational approach, that is, they behave selfishly to optimize their own individual welfare. This motivates the analysis of network traffic using models from Game Theory in which each player is aware of the situation facing all other players and tries to minimize its cost. Under these assumptions, the routing process should arrive into a so-called Nash equilibrium in which no network user has an incentive to change its strategy. It is well known (and easy to see) that Nash equilibria do not always optimize the overall performance of the system. In this survey we investigate the relation between these two notions for traffic routing: network performance in the Nash equilibria and the optimal performance of the system. Our main focus is on the analysis of the coordination ratio, which is the ratio between the worst possible Nash equilibrium and the overall optimum. In other words, this analysis seeks the price of uncoordinated selfish decisions (“the price of anarchy”). ∗Research supported in part by NSF grant CCR-0105701.