ection and the cost of restoration is completely dependent on the particular topology and traffic, thus can be quite different from network to network. In any case, a qualitative idea is given by the network sharing degree, that is, the average number of working path that share a certain protection wavelength on a protection link in the shared channel protection. It is intuitive that this parameter impacts also the quantity of spare capacity needed for restoration and in general higher the sharing degree, higher the cost advantage that restoration has on shared protection (even if counterexample can be found with a suitable choice of the topology and the traffic). In out example, the sharing degree is 1.3, quite low, thus shared protection and restoration are not SO different in cost and in survivability degree. It exist even a value of Z above it shared protection is cheaper than restoration. Both are however quite cheaper with respect to dedicated protection. 8.4.1.2.6 Design in Condition of Uncertain Traffic A last step in the design of our example network before generalizing our considerations to provide design tools that are valid for every network: what happens when the traffic is not known? If the traffic is completely unknown, no design can be done, different from placing a tentative capacity on each link and see what happen. However generally traffic estimation exists, but it is not sufficiently accurate to allow an optimum design to be realized. In this case the design has to leverage the statistical description of the traffic fixing maximum acceptable block probability (that is, the probability that an GLSP setup request has to be rejected) and designing the network to assure a blocking probability at most equal to the maximum acceptable. We will detail much better this problem dealing with general design methods, for now the discussion about our small example can be considered ended. It allowed us to intro- duce a set of fundamental concepts for the network design: Convergent Network Management and Co