Mixed-triggered communication with limited elastic slot boundaries

Abstract

Time-triggered systems provide dependable and deterministic communication based on strict time boundaries for tasks and messages. On the other hand, event-triggered communication is less strict on requirements and more flexible, but it is difficult to provide fault isolation. Thus, the combination of time-triggered and event-triggered communication is desirably extending a time-triggered communication system by a dynamic property. This paper improves a novel mixed-triggered communication approach based on ESBs which adds limited delay tolerance to an otherwise strict real-time communication. The presented approach overcomes the problem of delayed respectively missing messages by adding fail-operational behavior to the ESB-based communication. This is achieved by extending the basic mechanism using additional fault-tolerant features. The presented mechanism allows the system to stay operable even when messages occasionally violate their planned slot boundaries and provides fault isolation for timing violations beyond a predefined tolerance budget. The introduced fault-tolerant features are analyzed via Monte-Carlo simulations where the resulting data throughput is compared to two straightforward hard real-time communication approaches. As our results show, the proposed guards enable the system to handle extended message reception delays while, compared to strictly bounded communication, having a better performance of successfully transmitted messages.