ion methods less computationally complex than the ILP and capable of incorporating fiber nonlinearities. We will present only one class of these methods, and we will use it to make a study on the problem of WC placing. 10.3.5 Cyclic-Based Design Algorithms and Wavelength Converters Placement As the ILP optimization is aimed at producing a real network optimization, cyclic-based algorithms aim at producing suboptimum acceptable results with a relatively low compu- tation complexity [45]. Besides the adoption of heuristic procedures to determine the network design, these algorithms also perform the design of the optical layer alone, SO that interlayer coordina- tion for protection, grooming at the client layer, and all the other interlayer functionalities cannot be included in the design. Moreover, design for survivability is performed in any case in two stages where similar algorithms are used: first the working capacity is obtained in an optimized way, then a new separated optimization allows the spare capacity to be determined. On the other hand, these algorithms are suitable for the incorporation of complex trans- mission models. The name "Cyclic" is based on the fact that this algorithm cycles more and more times on the set of paths to be routed (i.e., the traffic matrix) to perform various operations. We will present a particular form of cyclic algorithms; several possible variations exist, some of them suited to adapt the algorithm better to a certain type of network. All the algorithms of this class are composed of two steps, except for the design of a network completely equipped with WCs for which the first step is sufficient because wave- length continuity is not required. 10.3.5.1 Full Wavelength Conversion Cyclic Algorithm The first algorithm of this group is that suited for networks where WCs are present on each OXC port SO that OXCs are strictly nonblocking. This algorithm will also be the first part of the more complex algorithms for the cases in which WCs are either absent or present in small number