Queuing models are important tools for studying the
performance of complex systems, but despite the
substantial queuing theory literature, it is often necessary
to use approximations in the case the system is nonmarkovian.
Phase type distribution is by now
indispensable tool in creation of queuing system models.
The purpose of this paper is to suggest a method and
software for evaluating queuing approximations. A
numerical queuing model with priorities is used to
explore the behaviour of exponential phase-type
approximation of service-time distribution. The
performance of queuing systems described in the event
language is used for generating the set of states and
transition matrix between them. Two examples of
numerical models are presented – a queuing system
model with priorities and a queuing system model with