Flexible Reliable Timing - Real-Time vs. Reliability

The design of safety-critical real-time systems has to provide for demands on predictability, flexibility, and reliability. A number of systems have been developed, whose paradigms focus on one of these requirements: Time triggered real-time systems provide verifiable timing behavior and allow distribution, complex application structures, and general requirements. Their benefits are, however, limited in changing environments and for applications with not completely known characteristics. In these scenarios, event triggered systems provide appropriate mechanisms and better efficiency. Fault tolerance methods provide for reliability requirements, but are often in conflict with temporal constraints. Many standard practices confront designers with an exclusive choice of one paradigm over the other, and consequently between temporal determinism or flexibility and reliability, instead of allowing a customized selection.In this talk, we will discuss relations between determinism, flexibility, and reliability and identify tradeoffs. We will show how event triggered methods can be combined with time triggered systems to enhance flexibility and enable adaptive fault tolerance. With the discussion of a number of issues for interaction between fault tolerance and real-time methods, we will demonstrate the combination of seemingly adverse methods, to lay a basis for flexible, reliable real-time systems.