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Mathematical cell delay modelling and performance comparison of four iterative scheduling algorithms for ATM input-queued switches are carried out. The iterative round robin with multiple classes (IRRM-MC) algorithm is compared to iterative round robin with slip (iSLIP), parallel iterative matching (PIM) and simplified PIM (SPIM) algorithms. By using Bernoulli arrivals a mathematical cell delay model is proposed for the algorithms. The developed model is compared to the simulation to verify the extension of the model fitness. The algorithms are compared according to cell delay and throughput performances. The comparison is also carried out using on-off types of arrivals. The algorithms are severely degraded by this type of source but it is shown that the use of service class priority is a good scheduling policy to satisfy cell delay constraints while keeping high throughput, even when the switch is submitted to bursty traffic. The comparison shows that an input switch based on the IRRM-MC algorithm is a flexible one and suited to easily satisfying the QoS of each class of service.