Software-implemented fault-tolerance and separate recovery strategies enhance maintainability [substation automation]

This paper describes a novel approach to software-implemented fault tolerance for distributed applications. This new approach can be used to enhance the flexibility and maintainability of the target applications in a cost-effective way. This is reached through a framework-approach including: (1) a library of fault tolerance functions; (2) a middleware application coordinating these functions; and (3) a language for the expression of nonfunctional services, including configuration, error recovery and fault injection. This framework-approach increases the availability and reliability of the application at a justifiable cost, also thanks to the re-usability of the components in different target systems. This framework-approach further increases the maintainability due to the separation of the functional behavior from the recovery strategies that are executed when an error is detected, because the modifications to functional and nonfunctional behavior are, to some extent, independent, and hence less complex to deal with. The resulting tool matches well, e.g., with current industrial requirements for embedded distributed systems, calling for adaptable and reusable software components. The "integration of this approach in an automation system of a substation for electricity distribution" reports this experience. This case study shows in particular the ability of the configuration-and-recovery language ARIEL to allow adaptability to changes in the environment. This framework-approach is also useful in the context of distributed automation systems that are interconnected via a nondedicated network.