1. 11. Practical fault-tolerant system design Reliable System Design 2005 by: Amir M. Rahmani

2. matlab1.ir Past and Future So far, we have studied: - Some techniques for designing FT systems - Some techniques of redundancy - Some techniques for measuring FT parameters - Some techniques for evaluating FT systems Now, we learn - The complete process of designing FT systems - How to apply the previous learned knowledge to design a FT systems

3. matlab1.ir Design of fault-tolerant system Trade-off Old computer vs. New computer Fault tolerant techniques Fault avoidance techniques System evaluations

4. matlab1.ir Design Process 1- Problem definition Completely understand the problems 2- System requirements Reliability Availability Coverage & latency Speed Power consumption Cost Weight Size Etc. Ex1: a computer with reliability of 0.99999 which controlling a motor with reliability of 0.9 ? Ex2: fault coverage of 0.99 ? for which fault?

5. matlab1.ir Design Process (cont.) 3- System partitioning Partitioning system into manageable subsystems Partitioning system based on Reliability Availability Critically Example: Reliability of aircraft subsystems Flight-critical functions ; R(t) =0.99999 –Fly-by-wire (flap) Mission-critical functions ; R(t) =0.995 –Telecommunication Convenience functions ; R(t) =0.95 –“No smoking” lamp

6. matlab1.ir Design Process (cont.) 4- Candidate designs - TMR vs. duplication - Advantages of one approach will uncover disadvantages of another approach 5- High level analysis - Basic analysis based on Reliability estimation Cost estimation Size estimation Complexity estimation Weight estimation Etc. - Omitting some designs Ex: Omitting TMR approach (good reliability but high weight)

7. matlab1.ir Design Process (cont.) 6- Hardware & Software specifications - The specifications for the hardware & software must be developed 7- Hardware & Software design Analysis - Commercial aircraft control problem - NASA solutions FTMP (Fault-Tolerant Multi-Processor) SIFT (Software Implemented Fault-Tolerant)

8. matlab1.ir Design Process (cont.) 8- Testing - An extremely part of design process Design mistake Implementation mistake Component defects 9- System integration - Combining the hardware & software working together correctly 10- Final testing 11- Documentation Example in Johnson’s book: Aircraft computer system

9. matlab1.ir Some concepts Fault prevention - How to prevent, through construction, the occurrence, or introduction of faults Examples: Design methodologies Selecting high quality components Design reviews Fault tolerance - How to provide, through redundancy a service up to fulfilling the system function in spite of faults Examples: Redundant HW/SW Voting Reconfiguration

10. matlab1.ir Some concepts (cont.) Fault removal - How to reduce, through verification, diagnosis, and correction the presence of faults Examples: Inspection or walk-thorough Data flow analysis Proof of correctness System behavior analysis (petri net) Fault forecasting - How to estimate, by evaluation, the presence, creation & consequences of failures Examples: Failure Mode and Affect Analysis Markov chain Reliability block diagram Fault trees

11. matlab1.ir Using fault avoidance in the design process Fault avoidance - How to produce a fault-free systems Fault avoidance = Fault prevention + Fault removal Fault avoidance against - Design mistake, implementation mistake, … Fault avoidance approaches - Various design reviews Documentation is very important when team work is used - Adherence to design rules - Shielding against external disturbance - Quality control check