yer. Assuming, for example, that all the tributaries would be VC12 (2Mbit/s payload) the DXC should manage up to 1.6 million channels, which is an impossible task. Of course, the situation gets better and better if the tributary channel speed increases. For exam- ple, working with VC3 tributaries, the number of paths to manage decreases up to about 66,000; that is a huge number but completely of another order of magnitude. On the other hand, increasing the tributary speed, the efficiency in the exploitation of the transmission lines decreases as far as the grooming effectiveness is decreasing SO that the choice of using DXCs is less and less justified. On the survivability side, using DXCs changes completely the scenario since fast ring survivability is no more possible. Thus, either link is protected one by one using, for example, 1+1 DMSP or only restoration is adopted leveraging on DXCs rerouting capabilities. In the first case, the number of DWDM systems has to be doubled with a clear CAPEX problem, in the second, there is no more a fast protection procedure and real-time services could experiment problems in case of a failure. Thus, sooner or later IP over SDH/SONET over WDM architecture has to be evolved in order to face carriers CAPEX problems in pace with the required network evolution. On one side, there is a certain number of carriers, especially in North America, that push for the evolution of SDH/SONET toward the so-called next generation SONET starting from the generalized introduction of GFP. On the other side, other carriers simply call for the elimination of the SDH/SONET layer to build the packet virtual network directly on the optical layer. Of course, this means that layer 2 functionalities have to be demanded to the packet network, and the most immediate solution is to design an MPLS-based packet network to directly put over the optical transmission layer. This solution requires some adaptation function that matches the MPLS packets with the TDM frame at the optical level. This is not a diffic