Integrating end-system frame scheduling for more accurate AFDX timing analysis

Avionics systems distributed on AFDX networks are subject to stringent real-time constraints that require guaranteeing the Worst-Case Traversal Time (WCTT) on the network for each of the data flows. Over the last 10 years, since the initial use of Network Calculus in certification, important progresses have been made in AFDX timing verification. The maximum pessimism for the latencies is now known to range from 10 to 25% on realistic systems. Further progresses towards more accurate timing analysis can still be made by considering additional temporal information. In this paper, we show that integrating the knowledge of the scheduling of the frames that is done within an end-system in the timing analysis enables to dramatically reduce the WCTT bounds computed by Network Calculus. Indeed, in our experiments performed on a realistic configuration provided by Thales Avionics, this technique reduces the WCTT upper bound by 40% on average over all flows. The reason is that the scheduling of the frames shapes the outgoing traffic, reducing thus peaks of load on the outgoing traffic , which can be accounted for in the timing analysis. Importantly, because the scheduling of the frames within the end-systems is in the scope of the network supplier, unlike the scheduling of tasks done at the application level, the approach presented here does not imply major changes in the design process.