rvivability to implement and consequently the service availability and cost. In our model for QoS-driven multilayer survivability we will start mainly from Ref. [27], where a similar model was introduced and detailed. The main differences are that we will exploit multilayer structure of the network to benefit, when needed, to the possibility of layer 2 to manage reduced granularity LSPs with respect to the high capacity optical GLSPs and that we will assume that the network is designed and optimized for the specific level of traffic. Even if in real networks, every LSPs has a specific bandwidth request, SO that different classes of LSPs exist with respect to the capacity, we will continue to model the network as having a single type of LSP having fixed capacity. This assumption simplifies greatly the model and does not impact essentially results on survivability. We will imagine, on the contrary, that when the layer 3 makes the request of a new LSP to layer 2 through the UNI interface, this request is characterized not only by the indication of the two end nodes, but also by the request of a certain QoS that, for what is our interest in this section, consists in the request of one of the available survivability classes. In order to maintain a better control on the use of network resources, the network man- ager is imagined to force a constraint on the control plane, forcing not to allow the traffic allocated into a certain service class to go over a fixed percentage of the maximum traffic that the network can accept. Only the class one traffic, which does not require spare capac- ity, is allowed to grow as much as possible. Telecommunication Networks We will image that the network will offer to the client layer five possible classes of sur- vivability, whose description is given in the following. 1. Service Class 0: Low Priority Traffic This is constituted by unprotected LSPs that are routed using exclusively spare capacity that is planned to be used for shared protection or for restoration. When a failure occurs