different administrative domain whose topology is not known to node (A, A). Domain A Domain B E-NNI FIGURE 8.5 Example of inter-domain routing in an ASON network. Convergent Network Management and Control Plane Node (A, A) has a routing table knowing that the external network to network (E-NNI) interface toward administrative domain B is between node (C, A) and (A, B) SO node (A, A) sets up a link to node (C, A) that forwards the link through the interdomain interface to node (A, B). Now Node (A, B) knows that a connection between node (*, A) is to set up with node (B, B) starting from the connection that was set up through the interdomain interface with domain A. Node (A, B) knows exactly from the routing table the position within domain B of the node (B, B) and set up the second part of the connection, represented in the figure by the dotted line. Besides the separation of information belonging to competitor carriers, in our example the administrative domain separation cause every node to store a topology made of six nodes: five in the same domain and one is a virtual node that is the connection with the other domain. If all the information was shared among all the network nodes, every node should store a topology of 11 nodes. The concept of administrative domain is also a powerful instru- ment for the gradual introduction of the ASON architecture in carrier networks. As a mat- ter of fact, an abrupt introduction of a new architecture in a big network like that of an incumbent carrier is not feasible. The new technology is in general introduced gradually in pace with CAPEX expenditure and market request. Thus during the introduction of the ASON control plane, for a long time there will be parts of the carrier network that will include subsets of ASON features, possibly dif- ferent subsets depending on the circumstances and on the kind of equipment the car- rier has installed in that part of the network, and parts of the network that are not yet migrated. The network has to work in this hybrid situation without 