with respect to the cost of a simple C-MOS TSI, SO that up to the moment in which volumes 81 Monolithic InP WI External External demux coupler 81 Monolithic InP WI 81 Monolithic InP WI 81 Monolithic InP WI FIGURE 7.25 Functional scheme of a wavelength interchanger based on monolithically integrated subelements. Telecommunication Networks of the InP technology will be SO high to justify a cost at least two orders of magnitude smaller, such a WI is feasible but not practical. Another possible way to realize a WI is to realize it electronically. This is the most eco- nomic design and has the advantage of offering also signal regeneration. However, the final system is much more complex and expensive with respect to a similar time domain switch. At the end, we can conclude that with present day's technology, switching in the wave- length domain using WI is theoretically interesting, but not practically applicable. On the other hand, it is not easy to devise a wavelength domain system that is the equiv- alent of a TDM bus SO to devise a wavelength domain dynamic switch. Generally, the architectures proposed for wavelength domain dynamic switches are completely different and they will analyzed in more detail in Chapter 10. 7.5 Hardware Platforms for Switching Network Elements At a first glance, the hardware platform of a switching network element is not SO different from what has been described in the case of transmission systems in Chapter 6. However, a more detailed analysis reveals a few key points that differentiate clearly a hardware platform for a transmission system from an hardware platform for a switching system. The general architecture of a switching system platform is based on the same elements we found in the case of transmission systems: racks, sub-racks, and cards. Naturally, stan- dards relative to racks and sub-racks are the same and, to specify with an example, an ATCA rack can be used in principle to host both a transmission and a switching system [87] (ATCA is a complete standard both for mechanical 