nd correct switching of the connection destina- tion node. This is a specific role of the E-NNI-compatible protocols that have to do that without allowing one domain to know hidden information from the other domain. In conclusion, the functions carried out by the E-NNI are as follows: Connection request and creation Connection parameters change Connection delete Client identity change Data transit Protection/restoration management Domain A Domain B E-NNI E-NNI FIGURE 8.6 Inter-domain path protection via the E-NNI interface. Telecommunication Networks The third standard interface is the I-NNI (internal Network to Network Interface) that is designed to connect network equipments belonging to the same administrative domain. All control plane protocols transiting through the I-NNI interface have the role to exchange information. While the O-UNI and the E-NNI are objects of a great standard work within ITU-T and OIF, since they assure the cross-compatibility of any specific con- trol plane implementation and its ability to interwork with its clients, the I-NNI is specific to any control plane implementation and has not been standardized in detail. The functionalities of the I-NNI are strictly related to the functionalities of the control plane and it can be said that the best I-NNI definition is that it has to be able to convey all the protocols constituting the control plane. 8.2.3 ASON Control Plane Functionalities The ASON architecture, besides the general structure of the ASN network and the inter- faces between different network entities, define the functionalities the protocol suite com- posing the control plane has to carry out. In general, ASON does not assume that vertical interoperability will exist between dif- ferent implementations of the control plane, since the internetworking is guaranteed by the possibility of assigning to any technology its own administrative domain and to con- nect them via the O-UNI, but if different implementations of the protocols are ASON- compatible, they have to provide the sa