  In this paper, we study contention resolution protocols from a game-theoretic
perspective. We focus on \emph{acknowledgment-based} protocols, where a user
gets feedback from the channel only when she attempts transmission. In this
case she will learn whether her transmission was successful or not. Users that
do not transmit will not receive any feedback. We are interested in equilibrium
protocols, where no player has an incentive to deviate.
  The limited feedback makes the design of equilibrium protocols a hard task as
best response policies usually have to be modeled as Partially Observable
Markov Decision Processes, which are hard to analyze. Nevertheless, we show how
to circumvent this for the case of two players and present an equilibrium
protocol. For many players, we give impossibility results for a large class of
acknowledgment-based protocols, namely \emph{age-based} and \emph{backoff}
protocols with finite expected finishing time. Finally, we provide an age-based
equilibrium protocol, which has infinite expected finishing time, but every
player finishes in linear time with high probability.
