 the carriers. In particular, almost all the carriers have injected, following different technology visions, a huge amount of packet functionalities in the transport network. At present, it can be asserted that major carriers have completed the evolution of the long distance network and have almost completed that of the metropolitan and regional network. Unified IP processing and WDM transmission are diffused in long distance while different approaches have been adopted to inject packet-switching capabilities in the metro and regional networks, always relying on WDM optical systems for data transmission. Drivers for Telecommunication Network Evolution As far as the access network is concerned, while in Asia and the United States there is a mixed situation, where relevant fiber-based access networks coexist with more traditional ADSL-based areas, in Europe fiber-based access is almost absent. At this point, it should be clear if the great technology evolution that has transformed the old telephone-based network into today's data-based network has achieved or not its goal. The answer is that the target to diffuse broadband and to lower sensibly the prices of wideband services while taking under control carriers OPEX and CAPEX has been reached, but the market has not started to grow again. On the contrary, the risk of stagnation is always present, a strong push to consolidation and selection in all the market segments is still at work, and the customers go on asking for much more bandwidth at a much lower cost. Since no new service is going to be introduced that is able to relevantly increase the ARPU, the only possible solution is to envision a further deep change in the network that will drive lower OPEX with a reasonable amount of CAPEX. This new technology should bring about the so-called next generation network (NGN). Considering the technologies involved in the vision of NGN, there are a lot of different ideas and there is no consensus around a single solution or even around the fact that one of the proposed s