be applied in this area also if scaling is considered a main requirement. On the other hand, the fact that both next generation SONET and carrier class Ethernet present a direct Ethernet interface is quite important. As a matter of fact, another scaling operation that can be done in the metro area (and has less meaning in the core network) is the move of some service sources from core nodes to metro nodes. Telecommunication Networks This network evolution can happen for services that requires a great number of content servers, like VoD. At the beginning of the service penetration, it is possible that the servers are placed in core nodes where, for example, the BRAS are placed. However, if the service has really a great diffusion, the number of servers becomes huge and their installation in an area nearer to the end customer becomes advantageous. Since almost all the content servers have Ethernet interfaces, having native Ethernet interfaces in the metro transport equipment facilitates a lot the installation of content serv- ers in this area. 3.4.1.4 Network Survivability All the proposed architectures implement fast protection at the physical layer. If no physi- cal layer switching is possible since LSR and LER are directly connected via DWDM sys- items, only link-by-link protection will be possible, either 1+1 or 1:1 if low-priority traffic exists. This kind of protection requires a duplication of all the DWDM systems with quite an increase in the cost of the transmission infrastructure. Protection at the physical layer can be eliminated, relying only on MPLS fast restoration to prevent service interruption when a failure occurs. MPLS can contemporarily manage fast protection (i.e., realized by provisioning two disjoined tunnels when answering to the request of a new connection) and restoration (realized considering the tunnels hit by the failure as it were new connection requests and routing them through the network from which the failed element has been eliminated) [67,68]. When SONET or OTN exists at the phys