 a carrier in the framework on a national multicarrier network. The concept of administrative domain is needed to allow the network to hide its own internal data to the overall network and to encapsulate all the internal addressing into a global network address SO that they cannot be seen by other administrative domains. This hiding and encapsulating strategy has a twofold function: it is needed in order to allow carriers to hide data relative to their network to competitors even if roaming among dif- ferent carriers have to be provided by the control plane, but it is also needed to reduce the dimension of the routing tables in the network routing elements. As a matter of fact, when the network is divided into administrative domains, every switching element stores the complete topology of its own domain and a metatopology relative to the connections with different domains. The partition of the ASON network is shown in Figure 8.4. Telecommunication Networks Corporate Client geographic device network O-UNI O-UNI O-UNI E-NNI Carrier A Carrier B single domain multi domain Domain A Domain B E-NNI I-NNI I-NNI FIGURE 8.4 Domain partition of the ASON network model. When a connection has to be set-up with a node in a different domain, the precise node address is encapsulated into the global domain address. The switch that has to set up the connection simply send a connection set-up protocol to the point of contact with the destination domain and it will be this node that is inside the domain of the connection end point to complete the connection setup establishing the path into the destination domain. This procedure is shown in Figure 8.5, where the logical working of encapsula- tion is shown. Let us image that the address of every node is a couple of letters, SO that node A of domain A has an address (A, A). Let us image that a connection has to be established from (A, A) to (B, B). The node (A, A) receives the instruction to open a connection to (*, B). The exact destination node address is hidden since it belongs to a 