 sessions, call admission control, and maintenance of the call state. The connection control is responsible for the overall control of individual connections, including setup and release procedures and the maintenance of the state of the connections. 8.2.3.5 Survivability As detailed in Chapter 2, survivability can be attained by either protection or restoration mechanisms, or both in some cases, where protection is based on the replacement of a failed resource with a preassigned standby resource, while restoration, is based on rerout- ing using available but not preprovisioned spare capacity. Since the ASON architecture is intrinsically a multilayer architecture, protection or restoration may be applied at different layers allowing very high availability levels to be achieved, but also requiring appropriate layers coordination. In the ASON architecture, protection management is in general terms a responsibility of the management plane. The management plane performs protection configuration and failure identification and reporting after that the protection mechanism has assured service continuity. However, the control plane is not out from the protection management activity. First, the manage- ment plane should inform the control plane about all failures of transport resources as well as their additions or removals. Unsuccessful transport plane protection actions may trigger restoration supported by the control plane. Moreover, the control plane supports the protection switching by suitable control plane protocols that are used in any case to advertise all the network entities in the data plane of the performed protection and, in some cases, necessary to coordinate protection switching itself. Telecommunication Networks Path 1 Path 1 ||||||| 11111 Path 1 Path 1 Path 2 Path 2 Path 3 Path 2 Path 3 Path 2 FIGURE 8.7 Protection mechanism in an OCh-SPRing. Just to do an example, let us image to have an optical channel shared protection ring (OCh-SPRing detailed in Chapter 3). The OCH-SPRing mechanism is shown in Figur