A discrete-time G/G/1 (General arrivals/General service times/single server) queueing model is considered, useful for performance evaluation of asynchronous communication systems, in particular ATM (Asynchronous Transfer Mode) systems. The attention is focused on the unfinished work tail probability. In fact it is equivalent to the overflow probability, and hence closely related to the Cell Loss Probability, one of the most important performance parameter in ATM networks. In this paper a non-parametric estimate and related asymptotic confidence intervals of an approximation of the equilibrium unfinished work tail probability is first proposed. Opposite to the usual assumptions, a general correlation function (including Long Range Dependence...