owing equations: nr=N and m 2n - 1. Working with the limit values, it results in n=r= JN, m = 2VN. Starting from these figures, the overall number C(N) of crosspoints of an NxN Clos network is C(N) = 6NVN (7.7) It results that, for a number of input/output ports greater than 36, a strictly nonblock- ing Clos switch fabric has less crosspoints than a crossbar switch of the same dimension. This difference becomes greater and greater while N increases, and for big fabrics it often makes the difference between a practical solution and an unpractical one. For example, let us consider a dynamic switch fabric with input signals at 5 Gbit/s and realized with electronics crosspoints having a power consumption of 1 pJ/bit (i.e., a realis- tic number for 22 nm CMOS crosspoints). Let us also imagine that connection between crosspoints are active elements (that again reflects the characteristics of CMOS technology) that have a power consumption of 0.5 pJ/bit. Moreover, let us assume that the traffic load is q=0.5, SO that the average percentage of active connections among crosspoints is 50%. Last, but not least, in order to make a realistic calculation of the overall power dissipated by the switch fabric, the power dissipated by the controller has also to be evaluated. It can be divided into two terms: the power dissipated by the processor, that is almost constant and we assume equal to 50W, and the power dissipated by the unit commanding the Telecommunication Networks Crossbar FIGURE 7.9 Power dissipated by a Clos switch fabric versus the power dissipated by a crossbar switch fabric with the same number of ports. Number of input/output ports fabric, that is proportional to the sum of the number of crosspoints and the number of active connections through a coefficient of 0.2 pJ/bit. In Figure 7.9, the power dissipated by a Clos switch fabric is compared with that dissi- pated by a crossbar switch fabric with the same number of ports. Due to the different number of crosspoint of the two switch fabrics, the difference in dissip