apter 11. Telecommunication Networks Let us imagine targeting a 4 input OXC terminating WDM systems with 128 channels at a bit rate of 40 Gbit/s. In order to manage this huge capacity, a 512x512 optical switch fabric has to be realized. Imagining using a Clos architecture and that the bigger available crossbar switch is a 64 64 switch, we have 64, m = and n=8 (see Section 7.2.2), SO that the condition m>2n - 1 is realized and the switch fabric is strictly nonblocking. Using this design we need 64 switches 8x8 and 16 switches 64 X 64. Assuming that in a first approximation each crosspoint has a power consumption of 0.22 mW (700mW for a 56 56 switch as in Table 5.8), we can estimate a total switch fabric power consumption of 15 W. Adding the power consumption of the overall electronic control we achieve global power consumption around 20W, much smaller that the CMOS power consumption SO that, if CMOS footprint is determined by the need to dissipate the generated power, in the case of the optical switch, the footprint is determined by the physical dimensions of the switch. Even if the promise of a clear decrease in power consumption is realized by optical switches, other elements make the optical solution difficult to implement. The first is the footprint of the resulting switch fabric. Each 64x64 switch has an estimated dimension of 10x8x0.2cm (see Table 5.8). This means that one switch with its analog driver occupies in many platforms a whole card. Even in platforms with big cards, it is possible to estimate the need of more than 20 cards only to host the switch elements with their drivers. This is much more than the real estate needed for the equivalent electronic switch fabric. Perhaps even more important is the cost of optical switches, which is much higher than those of electronic switches. The use of optical switches can be made much more effective in terms of footprint and cost by observing that OXCs are characterized by the fact that they terminate DWDM systems, SO that it is possible to divide the optical 