tly like the working one in the successive routing operations, to reflect the 1 + 1 protection. On the other hand, if shared protection has to be planned, the algorithm is similar, but the protection capacity is considered free for use in successive routing of protection optical paths with a procedure similar to that adopted for shared protection in the section dealing with ILP. A great number of routing policies has been proposed as basis of the network design. We will introduce and comment few of them [15] limiting the comment to the design of Telecommunication Networks the working capacity and of the optical layer only. Extension to a multilayer network is immediate. 8.4.3.1 OSPF Protocol This is the simpler choice, suggested by the fact that is one of the most diffused routing protocols. Moreover, it is possible to shape the working of the protocol by tagging the network links with a suitable tag and, in case, tagging also the crossing through a node. The algorithm corresponding to pure OSPF for the routing, as it is generally used in dimensioning tools, remembering that in this case infinite resources are assumed, can be described as follows: Evaluate the shortest path between source and destination with the given graph metrics. If on every link there is an incomplete DWDM system with available wavelengths, route the GLSP and go to END. If there is no wavelength available on one or more links, route the GLSP on the shortest path by opening new DWDM systems where needed. The operation of opening new DWDM systems is generally an expensive operation since it requires the deployment of new equipment in the central office and the deployment in the field of optical amplifier places. Thus sometimes effort is paid to avoid the aperture of a new DWDM system by explor- ing the possibility of routing the new GLSP on a second shortest path. In this case the algorithm is the following (we will call it M-OSPF: Modified OSPF): Evaluate the shortest path between source and destination with the given graph metrics. If on eve