 simple expression of the number of OXC ports. The number of wavelengths has to be evaluated link by link, since we have assumed electrical core OXCs, thus the wavelength is physically discontinued pass- ing through an OXC and could also change. With the assumption w >> Max(th,k), we have one wavelength for each direction on all the equipped link. Thus the final expression of the network cost C is (8.1) where Eh,k is the link functional tag that is equal to one if a WDM system is equipped on that link and equal to 0 if no transmission system is equipped on the link; Whik is the number of wavelengths routed along the link h-k; Equation 8.1 is specific of the case we are studying and of the simple cost models we have chosen. However, if the integer part is neglected with the idea of taking the greatest integer at the end, it presents itself as a linear combination of the elements representing the chosen routing, Th,kr and Eh,kr whose coefficient depends on the cost coefficients (the Xj parameters) and on the traffic matrix and on the link matrix elements (that are the number describing the physical topology). This is a quite general property and with a suitable definition of the elements represent- ing routing, topology, traffic, and cost, a similar linear relationship can be obtained also with more complex networks and more realistic cost models. This property, to which we will return in the next section, is the basic of a network design method that is applicable when a traffic forecast is available. Convergent Network Management and Control Plane 8.4.1.1.2 Link Cost Minimization In order to minimize the link cost, we have to minimize the link length and the number of wavelength. This can be done by modifying the routing used in the previous example as follows. The paths from node 1 to node 3 are always routed through node 4 to minimize the route length, but arriving at node 4, they are sent to the LSR that is resident in node 4 that sent it back together with the other GLSPs, which have to travel from node 4 to n