This monograph is devoted to the study of the insensitivity property of the stationary characteristics of queueing systems using analytical methods and simulation models. For systems with rejections, consisting of heterogeneous channels, we examine the insensitivity of the stationary characteristics with respect to the form of the service-time distributions. We consider three ways of distribution of customers by channels of the queueing system: equiprobable distribution by free channels, equiprobable distribution by all channels, and ordered distribution. For systems with waiting we define...