As the transmission network develops, the survivability of the network becomes a key factor in the design, operation and maintenance of the network. An ASON network must have effective and flexible protection and restoration schemes.
Generally, protection involves the capacity pre-allocated among NEs. Protection only involves NEs and does not involve the management system. The protection switching time is short and is generally not more than 50 ms. The backup resources, however, cannot be shared in the network.
Generally, restoration involves the usage of any usable capacity among NEs. Even the extra capacity of low priority can be used for restoration. When a service trail fails, the network automatically searches for a new route and switches the services from the faulty route. The algorithm that restores is the same as the algorithm that selects the trail. Restoration requires spare resources in the network for service rerouting. Service rerouting involves the computation of routes. The service restoration takes a relatively long time, which is always in seconds.
The traditional protection schemes can still be applied in an ASON network. When a fault occurs, the protection switching is performed by the transport plane. In this case, the protection switching does not involve the control plane.
In the case of an ASON network, the rerouting scheme is applied to restore services. When an LSP fails, the source node computes the best trail for service restoration and then uses signaling to create an LSP. Then, the new trail carries the services. For the non-revertive services, the original LSP is deleted after the new LSP is created, however, for the revertive services, the original LSP would not be deleted.
The network restoring schemes can be classified into the centralized restoring scheme and distributed restoring scheme according to the control mechanism. Huawei OptiX GCP applies the distributed restoring scheme.
If the centralized restoring scheme is applied, a central control system is required to control the entire network in a comprehensive manner. The central control system contains a large network database, which stores all the information about all nodes, links and spare resources. When a link or a node fails, the fault information is reported to the central control system along other routes. The central control system then computes a route to replace the faulty route according to the information stored in the database. The central control system then issues control commands to each node. A route is created to restore the services.
The distributed restoring scheme does not require any central control system. When a link fails, the nodes at both ends of the faulty link detect the fault and flood this information to the entire network. When a node fails, the adjacent nodes detect the fault and flood this information to the entire network. All LSPs that are involved with the faulty link or node then reroute and new LSPs are created to restore services.
In a WDM ASON network, when a fiber cut occurs, the WDM ASON OCh trail, WDM ASON ODU2 trail, and WDM ASON ODU1 trail can restore separately. You can set the delay time for the trail recovery. There is, however, no delay by default.