me basic set of functionalities. 8.2.3.1 Discovery The discovery function can be divided into three different subfunctions: 1. Neighbor discovery 2. Resource discovery 3. Service discovery The neighbor discovery is responsible for determining the state of local links connecting to all neighbors. This kind of discovery is used to detect and maintain node adjacencies; without it, it would be necessary to manually configure the interconnection information in management systems or network elements. The neighbor discovery usually requires some manual initial configuration and auto- mated procedures running between adjacent nodes when the nodes are in operation. Three instances of neighbor discovery are defined in ASON, that is 1. Physical media adjacency discovery 2. Data plane layer entities adjacency discovery 3. Control entities logical adjacency discovery Physical media discovery has to be done first to verify the physical connectivity between two ports. Generally this verification is carried out through an exchange of messages between adjacent network entities that verify both the network entities and the connecting link functionality. The layer adjacency discovery is used for building the layer specific network topology (see Figure 8.3) that has to be stored into the local CC to support routing. Convergent Network Management and Control Plane As a matter of fact, logical adjacencies between both data and control entities are created by layer adjacency discovery. Moreover, layer adjacency discovery, fixing the topology of the layer, also identifies link connection endpoints that are needed to describe connections through the cascade of links composing them, to manage such connections in correspon- dence to client request changes and to assure proper network working when a failure happens. Discovery processes involve exchange of messages containing identity attributes. Relevant protocols may operate in either an acknowledged or unacknowledged mode. In the first case, the discovery messages can contain the near-end