ith the group to which the link under analysis belongs. 8.4.2.2.6 Restoration at Optical Layer In case of use of restoration at the optical layer, the OXC manages the restoration procedure in such a way that the MPLS layer does not detect the failure if possible. Different types of restoration exists, depending on when the restoration resources are assigned to the LSPs affected by a certain failure event. Among them we will consider three cases: 1. Type 1. Restoration resources are reserved and the connection is set up after the failure. In other words, the optical GLSPs affected by the failure are rerouted in the network as if they were new requests of connection delivered directly at the optical layer. If new connection requests arrive during the restoring phase, they go in competition with the GLSPs to be restored. 2. Type 2. Reservation is made before the failure (but without a links with a specific failure event) and the path setup is performed after the failure. If new connection requests arrive during the restoring phase, no competition with the GLSPs to be restored happens due to the assignment of the restoration resources to survivabil- ity only. 3. Type 3. Resources are reserved to survivability and a certain number of restoration paths are set-up. When a failure occurs, the affected paths are rerouted using the prepared restoration paths. This is the most rapid restoration, based on the setup of a certain number of prereserved paths. Naturally it is also the most resource- hungry restoration technique. Telecommunication Networks When restoration is used, an effective way to operate is similar to that of shared protection, but for the fact that in Type 1 restoration even the parts of the working GLSP that are not affected by failure are considered available as restoration paths. In order to take into account this strategy, the following algorithm can be used to design the restoration capacity: for each link in the topology graph, the link is elimi- nated and the GLSPs involved are determined. These GLSP