1 / 28

Dependability

Dependability. TSW 10 Anders P. Ravn Aalborg University November 2009. Characteristics of a RTS. Timing Constraints Dependability Requirements Concurrent control of separate components Facilities to interact with special purpose hardware. . Fault. Error. Failure. Fault.

landry
Download Presentation

Dependability

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Dependability TSW 10 Anders P. Ravn Aalborg University November 2009

  2. Characteristics of a RTS • Timing Constraints • Dependability Requirements • Concurrent control of separate components • Facilities to interact with special purpose hardware

  3. ... Fault Error Failure Fault Dependability - impediments • Faults • Errors • Failures BW Ch 2, ...

  4. System and Component

  5. Dependability - attributes • Availability • Reliability • Safety • Confidentiality • Integrity • Maintainability BW Ch 2

  6. Dependability - means • Fault prevention • Fault tolerance • Error Removal • Failure Forecasting BW Ch 2

  7. byzantine Fault classification • physical (internal/external) • logical (design/interaction) • Origin • Kind • Property • omission • value • timing • duration (permanent, transient) • consistency (determinate, nondeterminate) • autonomy (spontaneous, event-dependent)

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

  9. Failure Classification • (Fault  Failure) • Consequence • benign • malign (a mishap) BW (Failure modes) Ch 2

  10. Dependability - means • Fault prevention • Fault tolerance • Error Removal • Failure Forecasting

  11. Fault Prevention • process (procedures) • notations • tools • Careful Design • Conservative Design • robust functionality • testability • tracability

  12. Dependability - means • Fault prevention • Fault tolerance • Error Removal • Failure Forecasting

  13. Error Removal • Verification (analysis of design) • Test (analysis of implementation)

  14. Dependability - means • Fault prevention • Fault tolerance • Error Removal • Failure Forecasting

  15. Failure Forecasting • Calculation – analysis of design • Simulation – measurement on design • Test -- measurement on implementation

  16. Dependability - means • Fault prevention • Fault tolerance • Error Removal • Failure Forecasting BW Ch 2

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

  18. Fault Tolerance

  19. Full tolerance • Graceful Degradation • Fail safe FT - levels BW Ch 2

  20. Retry ... ... Try Try Try FT basis: Redundancy • Time • Space Try Retry BW Ch 2

  21. N-version programming V1 V3 V2 Comparison vectors (votes) Driver (comporator) Comparison status indicators Comparison points BW Ch 2

  22. byzantine Fault classification (scope of N-VP) + + (+) ++ (+) + / (+) + / + + / + • physical (internal/external) • logical (design/interaction) • Origin • Kind • Property • omission • value • timing • duration (permanent, transient) • consistency (determinate, nondeterminate) • autonomy (spontaneous, event-dependent)

  23. Dynamic Redundancy • Error detection • Damage confinement and assessment • Error recovery • Fault treatment and continued service BW Ch 2

  24. D Error Detection f: State x Input  State x Output • Environment (exception) • Application • Assertion: • precondition (input) • postcondition (input, output) • invariant(state, state’) • Timing: • WCET(f, input) • Deadline (f,input) BW Ch 2

  25. object I object I Damage Confinement • Static structure • Dynamic structure BW Ch 2

  26. Error Recovery • Forward • Backward Repair the state – if you can ! • define recovery points • checkpoint state at r. p. • roll back • retry Domino effect BW Ch 2

  27. Recovery blocks ENSURE acceptance_test BY { module_1 } ELSE BY { module_2 } ... ELSE BY { module_m } ELSE ERROR BW Ch 2

  28. Failure exception Interface exception Request/response Interface exception Failure exception Request/response The ideal FT-component Normal mode Exception Handler BW Ch 2

More Related