Re-evaluating Event-Triggered and Time-Triggered Systems

Industrial control system design is increasingly adopting object oriented (OO) approaches. These approaches use an event-triggered communication model where communication is triggered by the occurrence of a significant event. Traditional low-level control systems for safety-critical applications use a different approach, namely time-triggered. The truth is that both event-triggered and time-triggered protocols have their advantages. Time-triggered protocols are dependable and event-triggered protocols are more responsive. Safety-critical systems demand dependability and as a result, time-triggered protocols have been used to date. Promising new findings indicate that an event-triggered protocol can be both responsive and dependable: a first in safety-critical control systems. This paper contrasts the two existing protocol paradigms and evaluation methodologies. A new protocol and new evaluation methodology are suggested that meet the stringent requirements of a safety-critical system. Initial findings are reported that indicate this to be a promising new direction.