any service disruption: this can be achieved by defining every area of the network where there is a different ASON- compatible technology as a different administrative domain, and interface these adminis- trative domains with those parts of the network where ASON is not yet implemented by suitable interfaces. Besides the administrative domains, the ASON standard defines another horizon- tal entity: the routing area. The routing area is generally a subpart of an administrative domain that has the characteristic to be represented by other routing areas like a single virtual node. Thus, exactly like for the administrative domain, when a node external to the rout- ing area wants to set up a connection with a node inside the routing area it sends the connection setup protocol to the virtual node representing all the routing area that physically corresponds to the point of contact of the destination routing area with the origination one. Only when the connection setup protocol arrives at the gateway of the routing area it completes the connection setup inside the area. Differently from the administrative domain, routing areas are not insulated under an administrative point of view and the internal information is not completely hidden. This is due to the different destination of the routing areas with respect to the adminis- trative domains: routing areas are used inside a big administrative domain to reduce the complexity of the address tables of the routing entities by introducing a routing hierarchy while the administrative domain serves mainly to divide parts of the network that have to be administrated independently either because they are owned by different carriers or because they are built on different technologies. Telecommunication Networks 8.2.2 ASON Standard Interfaces In correspondence to the structure of the network in administrative domains, the ASON standard defines a set of interfaces that are conceived for compatibility between different equipments and different particular implementations of the contro