the management network that connects all the entities of the management plane. The central network management entity is connected to an OCC in control plane via the network management interface for ASON control plane (NMI-A) and to one of the switches via network management interface for the transport network (NMI-T). Using these interfaces, the management plane can access to all the control plane entities via the control plane connectivity to perform control plane management and to all the data plane entities to perform reporting of data plane status and those functionalities that are responsibility of the management plane. The management structure of the ASON network is illustrated in Figure 8.1. The network model on which the ASON standard is based is a multilayer model in which a single control plane coordinates the activity of all the layers. This vertical struc- ture is reproduced in Figure 8.2, where there is evidence to show that all the layers define specific physical or virtual connection, SO that in its whole we can talk about a virtual connection-oriented network. Connectionless layer can be clients of an ASON network, but cannot be managed by an ASON control plane. The ASON network is intrinsically a multilayer network and dif- ferent network topologies can be defined at each layer. Let us refer just for an example to Figure 8.3 where a three layer network is represented. At the base physical layer, there is the set of fiber cables represented by gray bold lines and the set of buildings that are the carrier points of presence in the area. In all the buildings there is an optical cross connect (OXC), but not all the cables are equipped with WDM systems, quite a realistic situation due to the fact that cables are gen- erally deployed with long-term plans that are completely independent of the network that will be realized on the cable infrastructure. The WDM layer has probably different clients, one of that is an MPLS layer composed by a set of label-switched routers (LSRs). Not in all the nodes there 