01071nas a2200145   4500000000100000008004100001260005000042100002400092700001200116700001200128700001800140245009500158300001200253520066000265       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.