the wavelength of the conflicting backup path to comply with the condi- tions of sharing. As usual, assume the most economic solution. It is to be observed that this algorithm is much more trial and error with respect to those presented for networks with nodes completely equipped with WCs. However, the effec- tiveness of this algorithm in going near the rigorous optimum network is very good. It is to take into account, that if no WC is present, the network is de facto divided into planes. A wavelength path is completely contained in a single plan. In these conditions, the problem is in a first approximation divided into one problem for each wavelength situation in which a trial and error algorithm works well. 10.3.5.3 Partial Wavelength Conversion Cyclic Algorithm This is the case in which the OXC accommodates only a small number of WCs, in general proportional to the number of wavelengths of a WDM system. In this case, the so-called global arrangement algorithm is used, and which is described in [47]. This strategy makes use of the approach used in the case of the absence of WCs in a recur- sive manner. First of all, the strategy used without WCs is adopted, and the links with the max- imum number of unused wavelength channels are individuated: these are the inefficient links. For each inefficient link, a certain number of WCs is introduced, SO as to fill, as much as possible, the wavelength channels on the used transmission fibers. For each WC placed in the network, the new wavelength to be assigned to the converted path is determined by once again adopting the WP algorithm on a suitable subnetwork. In this way, some fibers in the network remain completely unused and can be eliminated, thereby reducing network costs. This algorithm is run several times, up to the moment in which the final results are stabilized. A similar procedure is applied for the backup capacity. Telecommunication Networks 10.3.5.4 Cost Model and Transmission Feasibility in Cyclic Algorithms Up to now, we have not specified the target that 