Abstract

A cell loss ratio calculating method is a method of calculating a cell loss ratio of a buffer for storing call cells from a plurality of traffic sources and comprises a distribution expressing step, a number-of-average-arrivals expressing step, an average path calculating step and a cell loss ratio calculating step. In the distribution expressing step, a distribution of the number of cells accumulated within a time for which the cell passes the buffer is expressed by use of a Poisson distribution on an assured side. In the number-of-average-arrivals expressing step, the number-of-cells distribution is expressed with parameters representing a number of average arrivals of the Poisson distribution. In average path calculating step, an average path is calculated with respect to time-variations of a cell arrival ratio and a distribution of the cell arrival ratio. In the cell loss ratio calculating step, the cell loss ratio of the buffer is calculated by using a result of the calculation in the average path calculating step as well as by using a table for storing a precalculated value of a number-of-lost-cells expected value corresponding to each number of average arrivals.