s Since the OXC does not decompose the optical wavelength channel, both line and client interfaces have the capacity of a wavelength. The client interfaces are generally "gray" interfaces, but for the case in which another WDM system is connected to the client lines, for example, a metro ring or a coarse wave- length division multiplexing (CWDM). Line interfaces can be either gray, wavelength interfaces or WDM interfaces, that is, interfaces with the wavelength stability suitable for WDM transmission. In the first case, that is schematically represented in Figure 7.31, the OXC is connected on the line side with the client input/output ports of a WDM system line terminal. Multiplexing and demultiplexing are performed by the WDM that also terminate the OTS-OH and the OMS-OH. Since, in general, it is the OXC that hosts the control plane controller, there must be a way in which the WDM passes OTS and OMS information to the OXC controller. Switch fabric interfaces interfaces FIGURE 7.31 Client ports Block scheme of an OXC connected on the line side WDM line WDM line with the client input/output ports of a WDM system terminal OXC gray OXC gray terminal line terminal. interfaces interfaces Switching Systems: Architecture and Performances Switch fabric interfaces FIGURE 7.32 Block scheme of an OXC incorporating into its platform the line termi- Client ports nals of the input/output DWDM systems. The other solution is schematically represented in Figure 7.32: the OXC has WDM qual- ity line interfaces and, from a control point of view, the multiplexer and the demultiplexer, like the booster amplifier and the preamplifier, belong to the OXC. From a pure cost point of view, the analysis of this solution is similar to the analysis presented as an example at the end of Section 7.6 and the cost aspect of the two solutions depends critically on the complexity of the OXC platform. The main difference is that OXC line cards have not the complexity of router line cards, being essentially transponders; thus, the relation among the i