Abstract
Time-triggered Ethernet (TTE) is designed as a deterministic real-time network for mixed-critical real-time systems, such as industrial automation, aerospace, and aviation. Due to asynchrony between tasks and the network in end systems (ESes), time-triggered (TT) messages have to spend uncertain time in waiting for being scheduled after they are generated. The waiting time uncertainly increases end to end delays for TT messages and will degrade the real-time and determinacy of TT messages sequentially. The contribution of this paper is to present a new architecture SDTTE to minimize the end to end delays, so as to enhance real-time and determinacy of TT messages. More specifically, a frame-based network model is built to describe distributed network resources. Under the network model, the end to end delay model with asynchrony between tasks and the network is analyzed. To match the generated time with the triggered time for TT messages, the triggered mechanism of the TT traffic in ESes is regarded as event strategy to detect the generated time of TT messages automatically. Based on this, the software defined TTE (SDTTE) is presented to optimize TT schedule online in switches. Furthermore, a simplified algorithm based on Satisfiability Modulo Theories (SMT) is proposed to satisfy real-time computing requirements. Finally, experiments with three network sizes verify the availability of SDTTE and analyze its performance. The results show that end to end delays for TT messages in SDTTE are decreased by about 95% compared with those in TTE. And the delays for rate-constrained and best-effort messages in SDTTE are almost as well as those in TTE. The processing time is less than 10s. In general, SDTTE provides a method to optimize end to end delays for TT messages in TTE, thus SDTTE has more determinacy and real-time than TTE. Meanwhile, SDTTE makes dynamic reconfiguration possible in practice.
Highlights
CONTRIBUTIONS To solve the above three problems, we propose the software defined time-triggered ethernet (SDTTE) framework which decreases the end to end delay and jitter for TT messages caused by asynchrony between tasks and the network and can increase real-time and determinacy of the TT traffic
The results show that the end to end delays for TT messages in software defined TTE (SDTTE) are far less than those in TTE
The synchronization between tasks and the network is a critical prerequisite for the TT traffic to ensure real-time and determinacy requirement
Summary
Thereafter, Craciunas transformed the taskand network-level schedule co-synthesis into a Mixed Integer Programming (MIP) problem with different objectives [12] He found that the MIP spends too much time to perform calculating online, and the processing time of the optimized SMT-based method is still too long. C. CONTRIBUTIONS To solve the above three problems, we propose the software defined time-triggered ethernet (SDTTE) framework which decreases the end to end delay and jitter for TT messages caused by asynchrony between tasks and the network and can increase real-time and determinacy of the TT traffic. 1) A triggered mechanism of the TT traffic, which makes the generated time of each TT message indirectly detectable, is presented to ease asynchrony between tasks and the network in end systems (ESes).
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