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F IG . 34. Number of passes ( Bottom Up Retrieval Scheme ).
F IG . 35. Number of broadcast passes ( Top Down Retrieval Scheme ).
conflicts first. However, it is not likely that a query of public data would involve a
substantial percentage of the total data available, hence it can be concluded that in
general, the bottom up retrieval scheme reduces the number of passes.
The Top down Retrieval scheme sacrifices the response time and the number of
passes, for lower power consumption. Experiences showed that the number of passes
increases greatly for a small number of requests and reaches a maximum where the
number of passes equals the number of channels. This is mainly due to the intelli-
gence of the least-cost path method that only expands the path that has the smallest
number of channel switches. As the number of user requests increases, the algorithm
generates the access patterns according to the Row Scan method ( Fig. 35 ).
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