6. Dependability

It is said that Nobel Laureate Hannes Alfven once remarked that in Technology Paradise no acts of God can be permitted and everything happens according to the blueprints. The real world is no technology paradise – components can fail and blueprints (software) can contain design errors. This is the subject of this chapter. The chapter introduces the notions of fault, error, and failure and discusses the important concept of a fault-containment unit. It then proceeds to investigate the topic of security and argues that a security breach can compromise the safety of a safety-critical embedded system. The direct connection of many embedded systems to the Internet – the Internet of Things (IoT) – makes it possible for a distant attacker to search for vulnerabilities, and, if the intrusion is successful, to exercise remote control over the physical environment. Security is thus becoming a prime concern in the design of embedded systems that are connected to the Internet. The following section deals with the topic of anomaly detection. An anomaly is an out-of-norm behavior that indicates that some exceptional scenario is evolving. Anomaly detection can help to detect the early effects of a random failure or the activities of an intruder that tries to exploit system vulnerabilities. Whereas an anomaly lies in the grey zone between correct behavior and failure, an error is an incorrect state that requires immediate action to mitigate the consequences of the error.