 of attaining a larger fabric is to use the same algorithm used for crossbars, since from a functional point of view, a Clos nonblocking switch is exactly equivalent to a crossbar switch. Switching Systems: Architecture and Performances FIGURE 7.10 Four NxN Clos switches combined to obtain a 2Nx2 nonblocking switch fabric. 4x4 Clos switch FIGURE 7.11 Example of the recursive way to extend a rearrangeable nonblocking Clos fabric building a rearrangeable non- blocking Benes fabric. Thus, four NxN Clos switches can be combined as shown in Figure 7.10 to obtain a 2Nx2N nonblocking switch. This technique, however, generates a quadratic growth rate of the switch crosspoints with the number of ports, gradually attenuating the advantage of the Clos fabric on the crossbar. Another recursive way to extend a rearrangeable nonblocking Clos fabric is shown in Figure 7.11 for the case n = 2, r=2, m = =2; what is obtained in the case is not another Clos fabric, but a rearrangeable nonblocking Benes fabric [17]. 7.2.3 Banyan Switch Fabric We have studied the Clos architecture in detail since this is widely used in practical switch- ing equipment both for static and for dynamic applications. We have also seen that, even if the number of crosspoints is smaller than that character- izing the crossbar switch, it is still on the order of N3/2, increasing rapidly with the number of input/output ports N. Telecommunication Networks Moreover, the fact that the crosspoints have to be independently operated to create the required routes inside the switch requires the presence of a routing processing in order to satisfy connection requests across the switch. The presence of a processor allows different priority strategies to be implemented and gives flexibility at the switch fabric, but also implies slower operation with respect to embedded function coded somehow in the hardware itself. A structure that does not have these two limitations is that of Banyan switch [17]. The Banyan switch is based on the concept of perfect shuffle permutation