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 streams have varible bitrate where the maximun peak bitrate can be several times the mean bitrate. Furthermore, the length of the bursts is a key parameter to be taken into account. In this paper we present a study of the switching blocs beahavior with bursty cell streams. We characterize the bursty cell streams by means duration of the bursts (high activity periods), its mean traffic intensity of these low activity periods. A bursty cell stream source is developed for this study so that we can evaluate the switching bloc variying the burst lenght 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.