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DOI: 10.4230/LIPIcs.ECRTS.2019.9

From Iteration to System Failure: Characterizing the FITness of Periodic Weakly-Hard Systems

Authors: Arpan Gujarati, Mitra Nasri, Rupak Majumdar, and Björn B. Brandenburg

Published in: LIPIcs, Volume 133, 31st Euromicro Conference on Real-Time Systems (ECRTS 2019)

Abstract

Estimating metrics such as the Mean Time To Failure (MTTF) or its inverse, the Failures-In-Time (FIT), is a central problem in reliability estimation of safety-critical systems. To this end, prior work in the real-time and embedded systems community has focused on bounding the probability of failures in a single iteration of the control loop, resulting in, for example, the worst-case probability of a message transmission error due to electromagnetic interference, or an upper bound on the probability of a skipped or an incorrect actuation. However, periodic systems, which can be found at the core of most safety-critical real-time systems, are routinely designed to be robust to a single fault or to occasional failures (case in point, control applications are usually robust to a few skipped or misbehaving control loop iterations). Thus, obtaining long-run reliability metrics like MTTF and FIT from single iteration estimates by calculating the time to first fault can be quite pessimistic. Instead, overall system failures for such systems are better characterized using multi-state models such as weakly-hard constraints. In this paper, we describe and empirically evaluate three orthogonal approaches, PMC, Mart, and SAp, for the sound estimation of system’s MTTF, starting from a periodic stochastic model characterizing the failure in a single iteration of a periodic system, and using weakly-hard constraints as a measure of system robustness. PMC and Mart are exact analyses based on Markov chain analysis and martingale theory, respectively, whereas SAp is a sound approximation based on numerical analysis. We evaluate these techniques empirically in terms of their accuracy and numerical precision, their expressiveness for different definitions of weakly-hard constraints, and their space and time complexities, which affect their scalability and applicability in different regions of the space of weakly-hard constraints.

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Arpan Gujarati, Mitra Nasri, Rupak Majumdar, and Björn B. Brandenburg. From Iteration to System Failure: Characterizing the FITness of Periodic Weakly-Hard Systems. In 31st Euromicro Conference on Real-Time Systems (ECRTS 2019). Leibniz International Proceedings in Informatics (LIPIcs), Volume 133, pp. 9:1-9:23, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2019)

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@InProceedings{gujarati_et_al:LIPIcs.ECRTS.2019.9,
  author =	{Gujarati, Arpan and Nasri, Mitra and Majumdar, Rupak and Brandenburg, Bj\"{o}rn B.},
  title =	{{From Iteration to System Failure: Characterizing the FITness of Periodic Weakly-Hard Systems}},
  booktitle =	{31st Euromicro Conference on Real-Time Systems (ECRTS 2019)},
  pages =	{9:1--9:23},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-110-8},
  ISSN =	{1868-8969},
  year =	{2019},
  volume =	{133},
  editor =	{Quinton, Sophie},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2019.9},
  URN =		{urn:nbn:de:0030-drops-107468},
  doi =		{10.4230/LIPIcs.ECRTS.2019.9},
  annote =	{Keywords: reliability analysis, MTTF/FIT analysis, weakly-hard constraints}
}

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DOI: 10.4230/LIPIcs.ECRTS.2018.16

Quantifying the Resiliency of Fail-Operational Real-Time Networked Control Systems

Authors: Arpan Gujarati, Mitra Nasri, and Björn B. Brandenburg

Published in: LIPIcs, Volume 106, 30th Euromicro Conference on Real-Time Systems (ECRTS 2018)

Abstract

In time-sensitive, safety-critical systems that must be fail-operational, active replication is commonly used to mitigate transient faults that arise due to electromagnetic interference (EMI). However, designing an effective and well-performing active replication scheme is challenging since replication conflicts with the size, weight, power, and cost constraints of embedded applications. To enable a systematic and rigorous exploration of the resulting tradeoffs, we present an analysis to quantify the resiliency of fail-operational networked control systems against EMI-induced memory corruption, host crashes, and retransmission delays. Since control systems are typically robust to a few failed iterations, e.g., one missed actuation does not crash an inverted pendulum, traditional solutions based on hard real-time assumptions are often too pessimistic. Our analysis reduces this pessimism by modeling a control system's inherent robustness as an (m,k)-firm specification. A case study with an active suspension workload indicates that the analytical bounds closely predict the failure rate estimates obtained through simulation, thereby enabling a meaningful design-space exploration, and also demonstrates the utility of the analysis in identifying non-trivial and non-obvious reliability tradeoffs.

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Arpan Gujarati, Mitra Nasri, and Björn B. Brandenburg. Quantifying the Resiliency of Fail-Operational Real-Time Networked Control Systems. In 30th Euromicro Conference on Real-Time Systems (ECRTS 2018). Leibniz International Proceedings in Informatics (LIPIcs), Volume 106, pp. 16:1-16:24, Schloss Dagstuhl – Leibniz-Zentrum für Informatik (2018)

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@InProceedings{gujarati_et_al:LIPIcs.ECRTS.2018.16,
  author =	{Gujarati, Arpan and Nasri, Mitra and Brandenburg, Bj\"{o}rn B.},
  title =	{{Quantifying the Resiliency of Fail-Operational Real-Time Networked Control Systems}},
  booktitle =	{30th Euromicro Conference on Real-Time Systems (ECRTS 2018)},
  pages =	{16:1--16:24},
  series =	{Leibniz International Proceedings in Informatics (LIPIcs)},
  ISBN =	{978-3-95977-075-0},
  ISSN =	{1868-8969},
  year =	{2018},
  volume =	{106},
  editor =	{Altmeyer, Sebastian},
  publisher =	{Schloss Dagstuhl -- Leibniz-Zentrum f{\"u}r Informatik},
  address =	{Dagstuhl, Germany},
  URL =		{https://drops.dagstuhl.de/entities/document/10.4230/LIPIcs.ECRTS.2018.16},
  URN =		{urn:nbn:de:0030-drops-89884},
  doi =		{10.4230/LIPIcs.ECRTS.2018.16},
  annote =	{Keywords: probabilistic analysis, reliability analysis, networked control systems}
}

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From Iteration to System Failure: Characterizing the FITness of Periodic Weakly-Hard Systems

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Quantifying the Resiliency of Fail-Operational Real-Time Networked Control Systems

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