Why simple timeout strategies work perfectly in practice?

In all kinds of dynamic power management (DPM) policies, the time-out policy works perfectly in practice, but this could not be elucidated in the traditional queuing theory. With the pareto distribution, the drawback of the exponential distribution was overcome, and this phenomena was explained well. The conclusion provided the theoretical basis for the simplification of DPM algorithm. In this paper, a simple DPM algorithm was described when the length of idle time follows the Pareto distribution. The simulation result testified the conclusion above.