In this paper a modeling approach to performance evaluation of a shared buffer switching element is described, based on the well-known fluid model of producers and consumers (PC fluid model). A procedure is outlined that leads to a suitable characterization of some typical parameters of the producer and consumer fluid model, making it representative of the shared buffer switch. Simulation analysis is used to investigate the relationships between the behaviour of the shared buffer switching element and of the PC fluid model. In the paper it is shown that by means of a suitable fitting of one parameter characterizing the PC fluid model, it is possible to make it representative of the shared buffer in the region of interest for ATM applications. This in spite of the actual operating differences between the real system and the PC fluid model. Numerical results regarding cell loss probability performance and dimensioning of 4x4 and 8x8 switches are presented and suitably discussed.