uced. The different topologies can be classified on the ground of these parameters to group topologies that are similar from some point of view. This approach follows completely [67]. A first possible parameter is the network connectivity a that is defined as follows: (3.1) where M is the number of network links N is the number of nodes This is a well-known parameter, obtained from the ratio between the number of links of the considered network and the number of links for a full meshed network with the same number of nodes. Networks with the same connectivity are really "topologically similar" if they have almost the same number of nodes. However, the connectivity is not useful to compare networks with quite different number of nodes. To introduce a network classification that is independent from the number of nodes, a new topological parameter has been introduced: the average connection degree X. The connection degree is defined as follows: (3.2) where X1, is the number of disjoined paths between the kth and the jth node. Thus, Xm represents the average number of disjoint paths between two network nodes. The connection degree is always greater than 2 in the considered networks, due to the fact that the minimum number of links cuts that divide the network into two unconnected parts is two. Moreover, in realistic networks, it is normally smaller than 2.5. For this rea- son, it is convenient to introduce a normalized connection degree Cm = 100 (Xm - 2). In Figure 3.59, the normalized CAPEX is reported versus the normalized connection degree for the different architectures at a normalized traffic level of 12.5. The traffic level is quite high, reporting it to normal measuring units and looking at the network dimensioning it means that an average occupation of the DWDM link equals to about 50 wavelength at 10 Gbit/s per link. The fact that the solutions based on SONET are not quite competitive is due to this high traffic level; at a lower traffic the difference decreases up to a threshold. Below the threshold, IP ove