at if an LSP of the MPLS layer is routed through the hth node of the optical layer while it is merged in an optical channel, but it is not sent to the local LSR, we will have 1p ijkhv = 1, but 2p ijkhv = 0 since it does not travel through the node in the MPLS layer, but only in the optical layer. This shows as in the multilayer representation of routing the grooming is automatically comprised. The matrix [A] is a 1N X 1N matrix and Nij represents the number of wavelength connect- ing node i with node j to route the LSPs. The wavelength channels connecting OXCs and transporting LSPs that travel only at the optical layer without being extracted by the wave- length up to their destination can be considered GLSPs in the optical layer. The elements of the matrixes [s]R], [A] are the design parameters and the solution of any optimized design has to provide values for these elements. However, this determines also the number of variables of our ILP problem and from this point of view, this is clearly quite a big number. Thus frequently simplifications are introduced to decrease the number of variables. We will discuss a few ways to simplify the problem when we will have a com- plete algorithm formulation. Considering the cost model, we will use a generalization of what we have assumed in our example in the last section. Every equipment has a cost constituted by two terms: a platform and an interfaces term. DWDM systems cost is given by where l is the system length and W is the number of wavelengths, while Xwo Xw1 are constants typical of the system. M is the number of wavelengths supported by a single system and [x] indicates the smaller integer greater than X. We will also call W the normalized capacity of one wavelength in term of LSPs (maintaining for definition equal to one the capacity of each LSP). The cost of OXC is given by where q is the number of bidirectional line ports of the OXC, Ma is the number of bidirectional line ports supported by a single platform unit (e.g., a single rack), and [x] indicates the smal