  A growing body of literature in networked systems research relies on game
theory and mechanism design to model and address the potential lack of
cooperation between self-interested users. Most game-theoretic models applied
to system research only describe competitive equilibria in terms of pure Nash
equilibria, that is, a situation where the strategy of each user is
deterministic, and is her best response to the strategies of all the other
users. However, the assumptions necessary for a pure Nash equilibrium to hold
may be too stringent for practical systems. Using three case studies on
computer security, TCP congestion control, and network formation, we outline
the limits of game-theoretic models relying on Nash equilibria, and we argue
that considering competitive equilibria of a more general form may help
reconcile predictions from game-theoretic models with empirically observed
behavior.
