This paper describes the design principles of a fluid-based, discrete-event
simulator and its application to the characterization of losses in ATM net
works. This simulation technique allows us to obtain performance measures t
hat either cannot be found using known analytical methods or for which a co
nventional simulation is too expensive; notably, fluid-model simulation mak
es it feasible to characterize for a given buffer its occupation, duration
of congestion periods, frequency of loss bursts and loss-burst volume in fa
irly complex networks. Several numerical examples illustrate the proposed s
imulation method.