 sion systems. As already discussed, in the United States, frequently the traffic managed by metro net- works, especially in big cities, is not pure hub traffic, but has a hub component plus a compo- nent (called mesh component) constituted by direct connections between metro nodes [11]. Moreover, when the planning of the broadband evolution was done, the main RBOCs were not in charge of the core network. Long haul transmission was carried out by leasing capacity by the long haul carriers. In order to reduce the leasing cost, the main regional bell operating companies (RBOCs) (first of all Verizon) designed a network that was able to avoid transit through long haul nodes as far as possible. Starting from the two-level ring architecture, the solution is to directly connect different metro core rings to implement all metro-to-metro connections without network blocking and without transit through core machines. This interconnected ring architecture is also characterized by high survivability, if a suitable mechanism is implemented to protect the ring interconnection [12]. The core network that is in charge of covering very long distances is characterized by a few specific elements: All the network nodes are similar (there is no hierarchy as in the metro network). Network nodes perform signal processing in terms of Consolidation (grooming and multiplexing) Routing Rerouting to assure survivability Every network node can add-drop capacity to-from the core network. A set of logical connections between couples of network nodes exists (pure mesh traffic). Distances between nodes are big (sometimes several thousand kilometers) requir- ing long haul transmission. Telecommunication Networks The core topology, as a consequence, is a mesh of connections between couples of nodes (see as an example Figure 3.2). 3.2 Network Functional Architecture 3.2.1 Core Network Vertical Architecture The core network has a complex set of functionalities, ranging from transmission through thousands of kilometers, optimization of the resources