r Ethernet version that can be deployed in public networks. The basic functions that are necessary include the following [33]: Continuous connectivity check (CC), that is, the ability to monitor continuously the existence of connectivity along the links that are present in the network topology Tunnels loopback (LB), that is, the ability to monitor Ethernet tunnels (i.e., con- nections transiting through higher level machines like routers without being processed at higher layer, but simply passing through) Trace route (TR), that is, the ability to trace and report to the central management the route of individual Ethernet frames or of all the frames belonging to a higher layer connection Alarms filtering and suppression, that is, the capacity of discerning the origin of a failure when it generates alarms from a great number of different network entities due to its consequences, for example, lack of signal Telecommunication Networks Equipment discovery Performance monitoring Survivability The first three functions are needed to assure a correct reporting of the network status at the central management system. In order to implement them, new protocols are needed that are not included in LAN Ethernet. These protocols have been introduced in MEF recommendation Y1731 and, in line with the Ethernet frame use, are based on the transmission of suitable control frames that are used both to monitor the existence of the connectivity also when no frame is transmitted between a certain couple of nodes and to realize the loopback of the connections. As far as the trace or the frame routes is concerned, the passage of these control frames is registered into the switches with the frame identifiers. When the route of a certain set of frames have to be reconstructed, it is sufficient to interrogate the switches and to detect those having in memory the right route identifier. 3.2.4.2 QoS and Resilience The key idea to reach this specification is the use of the virtual (V)LAN technology to sepa- rate data streams relative to differen