Fault-tolerant systems

Article By:

Meyer, John F. Computing Research Laboratory, Department of Electrical Engineering and Computer Science, College of Engineering, University of Michigan, Ann Arbor, Michigan.

Last reviewed:January 2020

DOI:https://doi.org/10.1036/1097-8542.251650

Systems, predominantly computing systems, communication systems, and other computer-based systems, which tolerate undesired changes in their internal structure, internal state, or external environment. Such changes, generally referred to as faults, may occur at various times during the lifetime of a system, beginning with its specification and proceeding through its use. Faults can be classified in a variety of ways according to when, where, why, and how they occur. For example, in the taxonomy of faults reported by A. Avizienis and colleagues in January 2004, elementary fault classes are defined according to eight basic dichotomies. Specifically, faults that occur during specification, design, implementation, or maintenance of a system are development faults, while those that occur during use (by users of services delivered by the system) are operational faults. Some other basic distinctions include where a fault occurs (internal or external, relative to some designated boundary between the system and its use environment), its phenomenological cause (natural or human-made), the objective of its cause (malicious or nonmalicious), the intent of its cause (deliberate or nondeliberate), and how long it persists (permanent or transient). Membership in a given elementary fault class may exclude membership in another; for example, a development fault cannot be external because the use environment is nonexistent during the periods of development. Operational faults, on the other hand, can be either internal or external and either natural or human-made. Examples include physical component failures (internal, natural), temperature and radiation stress (external, natural), mistakes by human operators who are integral parts of the system (internal, human-made), and malicious denial-of-service attacks (external, human-made).

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