On design and formal verification of SNSP: a novel real-time communication protocol for safety-critical applications
The correct operation of time-triggered protocols highly depends on the well-synchronized clocks of the system. To maintain the global time, one strict constraint must be exerted on communication activities (e.g. temporal padding and sparse time base etc.), which not only increases complexity of the protocol design but also incurs a penalty in the network utilization. While for event-triggered protocols, it is difficult to achieve the real-time requirement and determinism. Therefore, it is necessary to explore the combination of the advantages of these two categories of protocol for applications in different scenarios. This paper proposes the Safe Node Sequence Protocol (SNSP), which is a variant of full time-triggered protocol TTP/C. In SNSP, a strict node sequence is defined and the order of communication events is established by this pre-configured order without binding to global time, so the protocol changes communication activities and error detection to an event-triggered model. Therefore, SNSP possesses the characteristics of both time-triggered and event-triggered model. Also, the potential impact of global time, such as byzantine clock failure, on the protocol is eliminated. At the same time, the formal verification of SNSP is much easier in the absence of global time. Moreover, we model the protocol and use formal checker SPIN to validate the basic fault-tolerant requirement of SNSP. The simulation results show the protocol enables better resource utilization and is more effective.
formal verification event-triggered protocol safe node sequence protocol fault-tolerance safety