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Fault Tolerance Fundamentals

Fault Tolerance Fundamentals . ITV Model-based Analysis and Design of Embedded Software Techniques and methods for Critical Software Anders P. Ravn Aalborg University August 2011. Fault Tolerance. Means to isolate component faults. Prevents system failures.

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Fault Tolerance Fundamentals

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  1. Fault Tolerance Fundamentals ITV Model-based Analysis and Design of Embedded Software Techniques and methods for Critical Software Anders P. Ravn Aalborg University August 2011

  2. Fault Tolerance Means to isolate componentfaults Prevents systemfailures May increase systemdependability

  3. Dependability - attributes • Availability • Reliability • Safety • Confidentiality • Integrity • Maintainability

  4. Dependability - impairments • Faults • Errors • Failures

  5. System and Component

  6. Propagation among Components

  7. Error Classification (Fault  Error) • Effect • Extent • latent • effective • local • distributed

  8. Failure Classification (Fault  Error  Failure) • Consequence • benign • malign (a mishap)

  9. Fault Tolerance Means to isolate componentfaults ... And mask them Prevents systemfailures May increase systemdependability

  10. Fault Tolerance

  11. Full tolerance • Graceful Degradation • Fail safe FT - levels BW p. 107

  12. Retry ... ... Try Try Try FT basis: Redundancy • Time • Space Try Retry BW p. 109

  13. Fault Tolerance

  14. Basic Strategies

  15. Failure exception Interface exception Request/response Interface exception Failure exception Request/response The ideal FT-component Normal mode Exception Handler

  16. Model Design Procedure • Model the correct component and check that it has the desired properties. • Model relevant faults and introduce them as internal transitions to error states. Check that this fault-affected. • Introduce into the model the mechanisms for fault detection, error recovery and masking and check that the desired properties are valid for this design.

  17. Exercise • What is the purpose of a watchdog-timer? • How could it be used in a space based redundancy scheme? • - in a time based redundancy scheme?

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