Traffic studies is an important subject to evaluate the performance of the switching elements in an ATM environment. The main reason is that ATM cell stream have a variable birate where the maximum peak birate can be several times the mean birate. Furthermore, the lenght of the bursts is a key parameter to be taken into account. In the papaer we present a study of the switching blocs behavious with bursty cell streams, We characterize the bursty cell stream by the mean duration of the bursts (high activity periods), its mean traffic intensity, the mean interval of time between bursts, and the mean traffic intensity of these low activity periods. A bursty cell stream source is developed for this study so taht we can evaluate the switching bloc varying the burst length and its traffic intensity. This is an alternative measurement method to the one based on the mean traffic intensity at the input port of the switching bloc. From the results obtained, some interesting design considerations for the switching bloc architectures follow.