nterface prices is a bit differ- ent from the case in the example. Moreover, it is to be considered also the situation in which the transmission elements are located in their own sub-rack, receiving the signal on the front via a well-dimensioned fiber patch-cord routing system, SO to be divided as a platform, but integrated as far as control is concerned. Since the OXC switch fabric is huge and, in its typical configuration, occupies several sub-racks, this is many times a convenient solution from an economic point of view. However in this case, as in other similar cases, there is another important consider- ation that often brings mainly incumbent carriers to choose the solution adopting gray interfaces. Even if ITU-T has done a certain amount of work for the standardization of internal interfaces of WDM systems, the design of long-haul systems is SO complex and sensible to small variations in the design parameters, that it is, in practice, impossible to generate a WDM channel with a WDM interface of a vendor and propagate it through the line (ampli- fiers and optical equalizers like flattening filters and dispersion compensating fiber [DCF] modules) designed by another vendor, unless a large underperformance of the system is accepted. For this reason, if the integrated solution is selected, selecting the same vendor for the OXC and the WDM is almost mandatory, both for the first installation and for the succes- sive upgrades. This solution can be good for a competitive carrier, since it gives the network almost completely in the hands of a big vendor maintaining in this way a light cost structure that an independent research lab or a large network design department cannot sustain. On the contrary, the incumbent carriers have advantage in leveraging on the market competition among the main equipment vendors and would see as a strong limitation to their autonomy installing a network architecture that right from the installation has to be sustained by single vendor. Telecommunication Networks At the end, the advan