In unstructured peer-to-peer systems, significant improvements on search results can be provided
by the adoption of particular search strategies. Compare and contrast expanded ring search and
random walk strategies, highlighting when each approach is likely to be effective.
What will be an ideal response?
An expanded ring search is a variant of a flooding based strategy whereby flood messages are sent out with
increasing time-to-live values until a particular item is found. The approach is therefore quite heavyweight in
terms of the message traffic generated but can be very effective if items are found locally, for example with
popular items which are likely to be heavily replicated. A random walk strategy is one where a walker is set
out on a random path until an item is found. This can greatly decrease the number of messages generated but
at the expense of significant increases in the average time to find an item. This can be reduced by having
multiple walkers (changing the the granularity of coverage).
In summary, expanded ring search can be used when minimizing delay is more important than the
number of messages generated and can be very effective if items are likely to be local. Random walk strategies
can be used when the number of messages should be kept under control and this can be fine-tuned in multiple
walker variants.
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