Methods for Large-Scale Time-Triggered Network Scheduling

Francisco Pozo,Hans Hansson,Guillermo Rodriguez-Navas

doi:10.3390/electronics8070738

Abstract

Future cyber–physical systems may extend over broad geographical areas, like cities or regions, thus, requiring the deployment of large real-time networks. A strategy to guarantee predictable communication over such networks is to synthesize an offline time-triggered communication schedule. However, this synthesis problem is computationally hard (NP-complete), and existing approaches do not scale satisfactorily to the required network sizes. This article presents a segmented offline synthesis method which substantially reduces this limitation, being able to generate time-triggered schedules for large hybrid (wired and wireless) networks. We also present a series of algorithms and optimizations that increase the performance and compactness of the obtained schedules while solving some of the problems inherent to segmented approaches. We evaluate our approach on a set of realistic large-size multi-hop networks, significantly larger than those considered in the existing literature. The results show that our segmentation reduces the synthesis time by up to two orders of magnitude.

Highlights

The time-triggered (TT) communication paradigm, which originated with the time-triggered protocol (TTP) [1], has been advocated fornetworks that require low transmission latency and high reliability
It is essential that when scheduling the segment, we handle the offsets of the frames with relaxed constraints in our segment preprocessing algorithm, adding the offsets of frames that the solver scheduled in the segment. The scope of this evaluation is to find the upper bound on the number of frames that the segmented approach can schedule in a reasonable time for different network sizes and traffic configurations
According to our industrial contacts, less than 5 hours is reasonable for scheduling a large network, we will use that figure as a reference

Summary

Introduction

The time-triggered (TT) communication paradigm, which originated with the time-triggered protocol (TTP) [1], has been advocated fornetworks that require low transmission latency and high reliability. For networks of larger sizes, where the use of switches becomes necessary, implementations over Ethernet like TTEthernet [6] and IEEE 802.1Qbv [7], have been proposed. These networks are expected to meet the predictability and reliability requirements of next-generation real-time multi-hop networks, which will be found, for instance, in smart cities [8] and mega factories [9]. The application of different transmission media and different medium access control (MAC) mechanisms further adds an extra layer of complexity for scheduling hybrid wired/wireless networks, which to our best knowledge has not been investigated

Objectives

Results

Conclusion