Questionnaire guidelines:
Typically, you just have to spend an hour skimming through the first paper on
the list. Spend a few minutes thinking about the problem/approach/contributions
of the paper and then answer the questionnaire briefly. This is mainly testing
your ability to think critically about the problem at hand. A response of
around 100 words is fine, although longer responses are also welcome. 


Question: 
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Fault Tolerance in Coherence Protocols

Transient faults do not render a device permanently faulty -- they momentarily
disrupt a value (flip a bit). By altering a value, various errors in a cache
coherence protocol can be caused:
(i) a message arrives with a corrupted value,
(ii) a network message gets dropped,
(iii) the cache controller makes an incorrect decision,
(iv) a cache block is stored in an incorrect state, etc.

Present at least 5 different concrete examples of how a directory-based cache
coherence protocol's behavior can be disrupted because of transient faults.
(For example: an invalidation acknowledgement message is dropped and the
writer node stalls forever.)