1. CSE 322: Software Reliability Engineering Topics covered: Dependability concepts Dependability models

2. Dependability tree Dependability Attributes Means Impairments Availability Reliability Safety Confidentiality Integrity Maintainability Fault prevention Fault removal Fault tolerance Failure forecasting Faults Errors Failures

3. Impairments  Fault:

4. Impairments (contd..)  Errors:

5. Impairments (contd..)  Failure:

6. Impairments (contd..)  Example of the fault pathology:

7. Classification of faults  Physical faults:  Design faults:  Interaction faults:  Design and interaction faults are human-made. Can be further classified as:

8. Classification of faults (contd..)  Intentional, non malicious design faults:  Intentional, malicious interaction faults:

9. Classification of faults (contd..)  Intentional, malicious design faults:  Intentional, malicious interaction faults:

10. Dependability tree Dependability Attributes Means Impairments Availability Reliability Safety Confidentiality Integrity Maintainability Fault prevention Fault removal Fault tolerance Failure forecasting Faults Errors Failures

11. Attributes  Dependability:  Service:  Availability:  Reliability:  Safety:  Confidentiality:

12. Attributes (contd..)  Integrity:  Maintainability:  Security:  Performability:  Relative significance of dependability attributes:

13. Dependability tree Dependability Attributes Means Impairments Availability Reliability Safety Confidentiality Integrity Maintainability Fault prevention Fault removal Fault tolerance Failure forecasting Faults Errors Failures

14. Means  Fault prevention:

15. Means (contd..)  Fault removal:

16. Means (contd..)  Fault tolerance:

17. Means (contd..)  Fault/failure forecasting:

18. Dependability models  Measures of interest:  Reliability  Availability  Dependability evaluation:  Dependability models:

19. Dependability models  Combinatorial models:  State-space models:

20. Reliability block diagrams  Basics

21. Reliability block diagrams (contd..) Series system: Parallel system: k-of-n system:

22. Reliability block diagrams (contd..) Combination of series, parallel and k-of-n in one model

23. Fault trees  Basics:

24. Fault trees (contd..) AND gate: OR gate: k-of-n gate:

25. Combinatorial models: Example  Consider a multiprocessor system consisting of two processors and two memory units. For the system to be functioning, at least one processor and one memory unit should be up, else the system fails. Let the reliability of the processor be denoted R p, and the reliability of the memory unit be denoted R m. Construct a reliability block diagram and a fault tree model to evaluate the reliability of the multiprocessor system. Derive an expression for system reliability in both these cases.

26. Combinatorial models: Example Reliability Block Diagram

27. Combinatorial models: Example Fault Tree

28. Combinatorial models (contd..)  Advantages:  Drawbacks: