Fast automatic restoration

Fast automatic restoration (FASTAR) is an automated fast response system developed and deployed by American Telephone & Telegraph (AT&T) in 1992 for the centralized restoration of its digital transport network. FASTAR automatically reroutes circuits over a spare protection capacity when a fiber-optic cable failure is detected, hence increasing service availability and reducing the impact of the outages in the network. Similar in operation is real-time restoration (RTR), developed and deployed by MCI and used in the MCI network to minimize the effects of a fiber cut.

It is a recovery technique used in computer networks and telecommunication networks such as mesh optical networks, where the backup path (the alternate path that affected traffic takes after a failure condition) and backup channel are computed in real time after the occurrence of a failure. This technique can be broadly classified into two: centralized restoration and distributed restoration.

This technique utilizes a central controller which has access to complete up-to-date and accurate information about the network, the available resources, resources utilized, the physical topology of the network, the service demands etc. When failure is detected in any part of the network through some failure detection, identification and notification scheme, the central controller calculates a new re-route path around the failure based on the information in its database about the current state of the network. After this new route (backup path) is calculated, the central controller sends out commands to all the affected digital cross-connects to make appropriate reconfigurations to their switching elements in order to implement this new path. FASTAR and RTR restoration systems are examples of systems that utilize this restoration technique.

In this restoration technique, no central controller is used, hence no up-to-date database of the state of the network is needed. In this scheme, all nodes in the network utilize local controllers that have only local information about how a particular node is connected to its neighboring nodes, available and spare capacity on the links used to connect to neighbors, and the state of their switching elements. When a failure occurs in any part of the network, the local controllers handle the computation and re-routing of the affected traffic. An example of an approach where this technique is utilized is the Self-Healing Networks(SHN).

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