Journal of Networking Technology Elena Ivanova, Rostislav Raev and Dimitar Radev 14 4 2023 https://doi.org/10.6025/jnt/2023/14/4/93-100 https://www.dline.info/jnt/fulltext/v14n4/jntv14n4_1.pdf This paper studies the computer simulation event probability using Quality of Service parameters. The reference model is built with a single server queuing system when the service disciplines are FIFO and LIFO. Simulation results for the queuing systems [X]/M/1/N M/[X]/1/N and [X]/[X]/1/ N are presented at the end.