EXPLORING THE QUEUING BEHAVIOR OF ATM SWITCHES

In this paper we describe methods which we have used to verify queuein g models of two ATM switches, namely the Fairisle ATM switch developed at Cambridge University Computer Laboratory and an AT&T Globeview 200 0 switch installed in the experimental test-bed at Telia Research Labo ratories. Our approach relies on methods from large deviation theory, which we believe provides an appropriate scale on which agreement may be expected between a simple model and an actual ATM switch. We found that for the purpose of estimating delays the single-server queue prov ides an adequate model, at the large deviation scale, of both switches under the conditions investigated. However it does not reproduce the output behaviour of the Globeview switch at high loads, The model was evaluated using both analytic techniques and simulation. We emphasize that the model is not exact, indicating that very complex models may b e required in order to obtain results more detailed than those afforde d by large deviation theory. This calls into question the common pract ice of using detailed models of network traffic in conjunction with si mplified models of the network itself.