Generation of fault-tolerant state-based communication schedules for real-time systems

Akramul Azim

doi:10.1186/s13639-017-0082-x

Abstract

State-based schedules use a time division multiple access (TDMA) mechanism that supports executing conditional semantics and making on-the-fly decisions at runtime in each communication cycle. Until now, state-based schedules are unable to tolerate transient faults due to the assumption that stations make the on-the-fly decision on which message to execute next. Stations may make a faulty decision at run time in an unreliable communication environment such as wireless medium due to the presence of transient faults. This faulty decision causes state inconsistency among the stations in the system.In this work, we extend state-based schedules to tolerate faulty decisions in environments where transient faults can occur at the communication layer. Our proposed approach generates fault-tolerant state-based schedules using an integer linear programming optimization model after reducing the possibility of state inconsistency through using a clock and a sampling rate synchronization mechanism. The optimization model maximizes the use of time slots to place checkpoints for fault tolerance and resolving state inconsistency.

Highlights

The popularity of wireless networks is increasing every day because of their easy and affordable deployment characteristics
Wired networks in general are more reliable than wireless networks due to the transmission characteristics such as low channel interference and high bandwidth
We have shown that triple modular redundancy (TMR), a commonly used fault-tolerance technique, can be efficiently implemented using state-based schedules, may still suffer from state inconsistency due to making incorrect decisions at run time

Summary

Introduction

The popularity of wireless networks is increasing every day because of their easy and affordable deployment characteristics. It is possible to reduce the number of faulty decisions when using clock and sampling rate synchronization Existing approaches such as C-State-based approach or history of recent transmissions can be used to detect state inconsistency. In state-based scheduling, participating stations in the communication use dedicated slots to send their messages. In the state-based schedule of TMR, a faulty decision may occur after the transmission of the first two samples to decide whether to transmit the third sample in the time slot. We address the challenge of generating fault-tolerant state-based TDMA schedules using a number of constraints that are specific to messages requirements and to the characteristics (i.e., non-preemptive). To generate fault-tolerant state-based schedules, we formulate a number of constraints that are specific to message requirements and characteristics (i.e., nonpreemptive). The number of faulty decisions that lead to state inconsistency varies with the number of stations (see Fig. 8)

10.1 State-based TDMA scheduling vs static TDMA scheduling

Findings

11 Discussion

13 Conclusions