1. 1 Mm3 Fault-Tolerance related to your projects 2 x 45 min. of Discussions

2. 2 Strategies towards Fault-Tolerance Goals: What do we want to obtain by our strategy towards fault-tolerance? What failures should be covered – and to what extend? (identification of threaths to the sytem) How critical is the system? (what price/performance ratio are we heading for?) Different classes of failures Arbitrary failures – no assumptions Fail-silence / Crash Weak Fail-silence / omissive “Loud” failures? Recovery? Timing failures – synchronous / asynchronous models What can be assumed about the communication systems?

3. 3 HW/SW Fault-Tolerance HW based Fault Tolerance FT embedded in HW Low-level mechanisms, e.g. self-checking Hot or cold stand-by (states) Triple-Modular Redundancy and N-Modular Redundancy SW based HW Fault Tolerance SW Fault Tolerance What kinds of SW faults can occur? And how can they be prevented? Fault-Tolerant Communication Failure characteristics?

4. 4 The strategies Fault-Tolerance vs Fault Avoidance Quantity vs. quality Handling Design Faults Non-stop operations Reconfigurable operations (restoration vs. protection in networks) Recoverable configuraions Fail-safe or Fail-Operational?

5. 5 Remote Operations Client failures Network failures Server failures Exactly-once – Desirable but impossible? Alternatively: At-least-once or At-most-once

6. 6 Remote Operations

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8. 8 Remote operations

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10. 10 Remote operations Do they play a role in your projects? How to make them reliable?