01084nas a2200157   4500000000100000000000100001008004100002260005000043100002400093700001200117700001200129700001800141245009500159300001200254520066000266       2014                            d  bSpringer International Publishing Switzerland1 aTadeusz Czachórski1 aM. Nycz1 aT. Nycz1 aV. Vishnevsky00aModelling Transient States in Queueing Models of Computer Networks: A Few Practical Issues  a58–723 aThe article summarises author`s experience in two problems related to the use of queueing models in performance evaluation of computer networks: modelling transient states of queues and computations for queueing network models having large number of nodes. Both issues are not well represented in classical queuing theory, yet important to applications, because the observed traffic is time dependant and network topologies that should be considered become larger and larger. The article discusses two approaches: diffusion approximation and fluid-flow approximation that can cope with much larger models that are attainable with the use of Markov chains.