CSE 322: Software Reliability Engineering

Topics covered:Dependability concepts Dependability models

Dependability tree

Dependability

Attributes

Means

Impairments

AvailabilityReliabilitySafetyConfidentialityIntegrityMaintainability

Fault preventionFault removalFault toleranceFailure forecasting

FaultsErrorsFailures

Impairments

Fault:

Impairments (contd..)

Errors:

Impairments (contd..)

Failure:

Impairments (contd..)

Example of the fault pathology:

Classification of faults

Physical faults:

Design faults:

Interaction faults:

Design and interaction faults are human-made. Can be further classified as:

Classification of faults (contd..)

Intentional, non malicious design faults:

Intentional, malicious interaction faults:

Classification of faults (contd..)

Intentional, malicious design faults:

Intentional, malicious interaction faults:

Dependability tree

Dependability

Attributes

Means

Impairments

AvailabilityReliabilitySafetyConfidentialityIntegrityMaintainability

Fault preventionFault removalFault toleranceFailure forecasting

FaultsErrorsFailures

Attributes

Dependability:

Service:

Availability:

Reliability:

Safety:

Confidentiality:

Attributes (contd..)

Integrity:

Maintainability:

Security:

Performability:

Relative significance of dependability attributes:

Dependability tree

Dependability

Attributes

Means

Impairments

AvailabilityReliabilitySafetyConfidentialityIntegrityMaintainability

Fault preventionFault removalFault toleranceFailure forecasting

FaultsErrorsFailures

Means

Fault prevention:

Means (contd..)

Fault removal:

Means (contd..)

Fault tolerance:

Means (contd..)

Fault/failure forecasting:

Dependability models

Measures of interest: Reliability Availability

Dependability evaluation:

Dependability models:

Dependability models

Combinatorial models:

State-space models:

Reliability block diagrams

Basics

Reliability block diagrams (contd..)

Series system:

Parallel system:

k-of-n system:

Reliability block diagrams (contd..)

Combination of series, parallel and k-of-n in one model

Fault trees

Basics:

Fault trees (contd..)

AND gate:

OR gate:

k-of-n gate:

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 Rp, and the reliability of the memory unit be denoted Rm. 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.

Combinatorial models: Example

Reliability Block Diagram

Combinatorial models: Example

Fault Tree

Combinatorial models (contd..)

Advantages:

Drawbacks: