A system for, and method of operation of, estimating a blocking probability for at least a portion of a network and a model of the same are provided. The blocking probability represents a likelihood that a transmitted signal will arrive at least at the portion of the network. The system includes an estimator controller and a processing controller. The estimator controller derives both a direct and an indirect estimator. The direct controller is derived as a function of a number of losses and arrivals occurring with respect to at least the portion of the network during a period of time, and the indirect estimator is derived as a function of an offered load with respect to at least the portion of the network during the period of time. The processing controller, that is associated with the estimator controller, applies a weighting factor to the direct and indirect estimators to derive the blocking probability. The weighting factor minimizes variance of combined estimates.