Given the escalating need for greater bandwidth, there is a growing interest in implementing mechanisms that ensure reliable and optimal service levels for specific traffic classes, especially during periods of heavy network traffic. One such mechanism is the prioritization mechanism, where certain portions of resources are exclusively allocated to predefined services. In the context of contemporary flexible WDM networks that employ advanced data transmission techniques, efforts have been made to create a simulation program capable of assessing the traffic characteristics of nodes within flexible WDM networks. This article presents a simulator of flexible WDM nodes with an implemented mechanism for prioritizing call classes. The simulator allows us to determine the loss probability for individual traffic classes in a switching network with point-to-point selection. In the simulator, the Clos structure was adopted as the structure of the flexible WDM network node due to its popularity in many studies and applications.