e for a fixed capacity, an MPLS router is a much more complex and thus a more expensive machine with respect to an OXC that simply switches wavelengths and also with respect to a DXC, at least as far as the traffic is not huge. Thus, using smaller LERs and smaller and perhaps less LSR by managing the pass- through traffic through a physical layer switch like a DXC or an OXC is generally advantageous. Naturally, this is also due to the fact that in our model the router has optical grey inter- faces (i.e., interfaces that are not suitable to enter directly into a DWDM system due to the poor wavelength stability) and it is connected to the DWDM systems via transponders (see Chapter 5). Directly mounting the DWDM interfaces in the router chassis for sure causes a CAPEX decrease, but not as much as expected. We do not carry out in detail this discus- sion here since the router and the DWDM architectures have to be detailed; we will go through this point in Chapter 8. Networks Fundamentals and Present Architectures Bolzano Milano Trieste Verona Torino Venezia (mestre) Genova Bologna Firenze Ancona Perugia Pescara Napoli Potenza Cagliari Catanzaro Palermo Catania FIGURE 3.56 Topology of the Italian long haul network used in some examples of network cost evaluation. For a low traffic volume, SDH mesh is advantageous with respect to OTN mesh. This result also is quite intuitive: if the traffic to process is not huge, the DXC core does not cost SO much more with respect to an OXC core. On the other hand, for low traffic, the DXC is much more effective due to the ability to perform grooming at much lower capacity (the OXC operates on the wavelengths as a whole). Increasing traffic changes the situation, and the OTN version of the network gains more and more advantages with the need of the DXC to groom at greater and greater capacity level, SO as not to grow to an impractical dimension. Telecommunication Networks Normalized CAPEX Normalized traffic MPLS/DWDM SONET/DWDM MPLS/OTN FIGURE 3.57 Normalized cost of three network ar