chitectures versus the normalized traffic level. The architectures assume a mesh physical topology. The normalized traffic, evaluated considering only 10 Gbit/s channels in the network, corresponds at the physical layer to an average number of wavelength per DWDM link equal to 4 (traffic = 1), 16 (traffic=4), and 32 (traffic = 8), respectively. The corresponding average DWDM utilizations are 6% (40 Gbit/s), 25% (160 Gbit/s), and 50% (320 Gbit/s), respectively. In the limit of very high traffic, the DXC manages paths that are concatenated 10 Gbit/s SO that grooming is no more possible and the DXC architecture is useless. The partition of the CAPEX among the different network elements is also interesting and it is reported in Figure 3.58 for the same architectures of Figure 3.57. The first factor that results is the huge CAPEX that is used for pure transmission (fiber cables, optical amplifiers, and regenerators essentially). This is due to the great distances covered by the considered network that spans all North America: several links are near or beyond 1000 km and the transmission has to be suitably assisted. If a similar evaluation is done with the Italian network and the German one, the contribution of the pure transmis- sion goes down to below 40%. TX/RX Tran. Tran. Tran. IP over IP over IP over sonet Normalized traffic equal to 12.5 (see Figure 3.50) FIGURE 3.58 Relative cost of the different network elements in the same cases of Figure 3.50. Tran, DWDM transmission systems; TX/RX, DWDM transponders; LSR, MPLS routers (both LR and LER are included). Networks Fundamentals and Present Architectures Looking at the cost of the routers (indicated as LSR, but also LERs are included), it is obviously more important in the case of the absence of a real intelligent physical layer, while it is substituted partially by the cost of OXCs and DXCs in the case in which these equipment are present. In order to compare networks with mesh and the multiring physical architecture, some topology parameters can be usefully introd