 the volumes of optical components due to the growth of the telecommunication market and on the spare due to the elimination of intermediate optical-electrical-optical interfaces. This hypoth- esis implies that a market price of optical equipment would rapidly decrease [6,8]. In front of these expected advantages, the transparent optical network also presented important problems [9]: Management: If the signal travels transparently through all the networks, it is impos- sible to read its header at a switch input and output; thus, in the most radical imple- mentation, switching errors are detected only at the network edge by the electronics edge equipment; for this reason, they are quite difficult to identify and to insulate [10]. Transmission characteristics: Wavelength routing has to take into account trans- mission characteristics not to route a wavelength on a path that for some reason (length, number of nodes, and SO on) does not allow correct transmission [11]. Sub-wavelength grooming is impossible. Moreover, as we have seen in Chapter 7, the OXC of Figure 10.10, as all the architectures suggested for transparent operation, has a certain blocking probability. Next Generation Networking: Enabling Technologies, Architectures, and Performances FIGURE 10.11 Example of network blocking due to the need of wavelength continuity. The figure is discussed in detail in the text. It is a consequence of the fact that transparency implies wavelength continuity also in the passage through an OXC. This means that the transparent network appears as the super- imposition of a number of independent networks equal to the number of wavelengths in the DWDM transmission systems. In this situation, blocking occurs where a path characterized by a physical wavelength continuity connecting two designated edge ports of the network does not exist, but it would exist if the wavelength continuity were not required. An example of this blocking situation is reported in Figure 10.11. In the figure, it is supposed that the WDM systems have two