Integration of SMT-based Scheduling with RC Network Calculus Analysis in TTEthernet Networks

In mixed-criticality Ethernet-based time-triggered networks, like TTEthernet, time-triggered communication (TT) coexists with rate-constrained (RC) and best-effort (BE) traffic. A global communication scheme, i.e., a schedule, establishes contention-free transmission times for TT flows ensuring guaranteed low latency and minimal jitter. Current approaches use Satisfiability Modulo Theories (SMT) to formulate the scheduling constraints and solve the resulting problem. However, these approaches do not take into consideration the impact of the TT schedule on RC traffic. Hence, the resulting TT schedule may cause the worst-case latency requirements of RC traffic not to be fulfilled anymore.In this paper, we present a novel method for including an RC analysis in state-of-the-art SMT-based schedule synthesis algorithms via a feedback loop in order to maintain the optimality properties of the SMT-based approaches while also being able to improve the RC traffic delays. Our method is designed in such a way that it can be readily integrated into existing SMT- or MiP-based solutions. We evaluate our approach using variants derived from a realistic use-case and present methods to further improve the efficiency of our feedback-based approach.

I. Introduction

For certain application domains, critical communication flows need to be proven correct in terms of their temporal behavior. For example, in the aerospace domain, but also in emerging industrial automation systems, authorities require the proof of correctness as part of the certification process with respect to critical traffic fulfilling end-to-end latency requirements. These requirements have been guaranteed through analysis methods like Network Calculus [1] , [2] , [3] or the more recent Compositional Performance Analysis [4] , for technologies like Avionics Full DupleX (AFDX) [5] . The Network Calculus method [1] is a well-known mathematical framework based on min-plus algebra that is widely used in the certification process to derive worst-case end-to-end latency bounds for individual asynchronous communication flows.