Integrated and Modular Systems for Commercial ... - Nonstop Systems

Redundancy
• Attributes:
� form (physical, temporal, performance, data,
analytical)
� similarity/diversity*
� level of replication
� physical distribution within a/c
� allocation along end-to-end path
� configuration (grouping & interconnects)
� redundancy management concept (static, dynamic)
- more resources that required for fault-free single-thread operation -
* Notes:
- dissimilarity’s power is based on assumption that it makes simultaneous common-mode (generic) faults extremely improbable
- dissimilarity does not reduce the probability of simultaneous random faults
- dissimilarity provides little advantage against common-mode environmental faults (EMI, temp/vibe, power)
- dissimilarity allows shift away from proving absence of generic faults, to demonstrating ability to survive them (cert. level!)
- dissimilarity of design drives source of faults back to (common) requirements and system architecture
- dissimilarity is fault avoidance tool, as long as independence is not compromised when fixing ambiguities or divergence
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©1995-1997 F.M.G. Dörenberg