1. Software Fault Tolerance – The big Picture mMIC-SFT September 2003 Anders P. Ravn Aalborg University

2. Fault Tolerance Means to isolate component faults Prevents system failures May increase system dependability

3. Dependability - attributes Availability Reliability Safety Confidentiality Integrity Maintainability BW p. 139

4. Dependability - means Fault prevention Fault tolerance Error Removal Failure Forecasting BW p. 106,...

5. Dependability - impediments Faults Errors Failures BW p. 103,... FaultErrorFailure... Fault

6. System and Component

7. Fault classification Origin Kind Property physical (internal/external) logical (design/interaction) omission value timing byzantine 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) p. 105

10. Fault Avoidance Careful Design Conservative Design process (procedures) notations tools robust functionality testability tracability

11. Error Removal Verification (analysis of design) Test (analysis of implementation)

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