tomer, but also among customers themselves not to repeat the same VID causing unwanted confusions in the public network. This coordination cannot be done, also because it violates the principle of customers' signals isolation; thus, the problem was solved another way. IEEE introduced the 801.ad standard [31] separating the public VID from the private VID. Following this standard, when a frame enters the public network, a new header field is added by the edge switch containing the public VID that refers to the so-called service VLAN. In this way, the carriers VLAN can be distinguished from the "customer VLAN" whose VID is coded in the inner frame header. The frame is switched in the public network using the service VID, at the destina- tion edge switch, the service VID is removed and the frame is sent again to the private network. This mechanism is generally called provider bridge (PB) since it allows the service pro- vider to separate customers' signals and to uniquely identify service VLANs and custom- ers VLANs. Although the introduction of PB solves the problem of isolating service VLANs from private VLANs, this still does not guarantee a real Carrier Ethernet Scalability. As a matter of fact, MAC addresses have to be learned and used by the carrier even if they belong to the customers LAN. The problem is similar to those arising with IP addresses when a customer private network uses the TCP/IP stack as the public Internet. While however IP domains can be separated by routers using the NAT principle, noth- ing similar exists in Ethernet since switches cannot perform MAC translations and MAC domains does not exist. Moreover, if the number of MAC addresses increases too much, switches forwarding tables become difficult to manage and private switches cannot be asked to have suitable dimensions. On top of the MAC proliferation and the consequent copenetration of public and private networks, another problem also arose from the definition of service VLANs. Following standard VID definition, the maximum number of ser