ealized using wave- channels channels length converters. Besides the base schemes we have shown, several other architectures have been pro- posed for transparent OXCs, targeting different equipment performances[30-32]. A great majority of them are based on a space division switch fabric, but a few proposals based on wavelength division switch fabric have also been done [31]. Since an OXC is complex equipment, it is not easy to make a synthesis of its perfor- mances in few numbers. 11 Switch 12 Switch 13 Switch Local Local channels channel FIGURE 10.18 Transparent OXC architecture allowing the deployment of a limited number of WCs, but preserving full WC accessibility for each incoming channel. Next Generation Networking: Enabling Technologies, Architectures, and Performances A first group of OXC performance indicators is constituted by its transmission charac- teristics: its loss in case of passive equipment or its gain and ASE power in the case of an active one, the equivalent filter that represents the spectral effect of the OXC crossing on a wavelength, and possible polarization-dependent loss and dispersion. In particular, losses or noise and filtering effect are quite important, since if not suitably controlled, they could drastically reduce the transmission reach through the network. Another physical effect that is peculiar of transparent OXCs is the introduction of cross- talk among channels traveling in different directions [33]. The transit of a set of channel through a transparent OXC (or another transparent equip- ment, like an OADM) causes two types of crosstalk: in-band and out-of-band (InB, OutB) crosstalk [34]. OutB crosstalk is the same phenomenon that is present in simple DWDM systems, con- sisting in the fact that due to the infinite spectra tail that characterizes both the chan- nels spectra and the optical filters, every time a DWDM comb is demodulated to divide the component wavelength channels, every channel is affected by the interference of the nearby channel power that is captured by the 