f the switch, the real estate and espe- cially the dissipated power if it is used for dynamic switching growth with the squared number of input ports. 7.2.2 Clos Switch Fabric Clos switch fabrics are characterized by three stages of architecture [13]: Switching Systems: Architecture and Performances FIGURE 7.7 Block scheme of a Clos switch fabric. 1. The ingress stage 2. The middle stage 3. The egress stage Each stage is composed by a set of crossbar switches. The switches of a stage are connected with those of the following stage but not among them. All the characteristics of a Clos switch fabric are defined by three integers n, m, and r as shown in Figure 7.7 representing the general scheme of a Clos switch fabric. The first stage of the switch is composed by r crossbar with n inputs and m outputs, SO that the overall number of input lines of the switch fabric is N = rn. The middle stage is composed by m crossbar switches with r input and r output ports. Thus, it can be done with exactly one connection between each output of the first stage and each input of the second. Similar to the first, the third stage is composed by crossbar with m inputs and n outputs SO that each output of the middle stage is connected to one input of the egress stage. The connection between the first and the second stage is realized by connecting the m ports of the first switch of the first stage to the first ports of all the switches of the second stage, the m ports of the second switch of the first stage with all the second ports of the switches of the second stage, and SO on. In general, the ports of the kth switch of the first stage are connected with all the kth ports of the switches of the second stage (compare Figure 7.7). The relative values of m and n define the blocking characteristics of the Clos network [4], while the switch fabric dimension is fixed by r, once the dimensions of the crossbar has been chosen. 7.2.2.1 Strictly Nonblocking Clos Networks If m 2n - 1, the Clos network is strictly nonblocking. Assume that there i