This paper generalizes the classical Jacobaeus method for evaluating call blocking probabilities in multistage interconnection networks in the context of ATM type traffic. The aim of this generalization is twofold, first the results are extended to capture the heterogeneous, multirate and multiclass nature of the traffic; second it takes into account a path hunting algorithm inside the interconnection network. Sequential routing is chosen. The kernel of the method is computing occupancy probabilities of interstage links. An aggregation method is used for this computation. The accuracy of the method is shown by comparing with simulation. In addition to call blocking evaluation, the method may easily be extended to include other hunting algorithms.