Bridging models, as the BSP, tend to abstract the characteristics of
the interconnection networks using a small set of parameters, by
dividing the computation in supersteps and organizing the
communication in global patterns called h-relations.

In this paper we evaluate, through experimental results conducted on a
wormhole-routed bi-dimensional torus and a quaternary fat-tree with
256 processing nodes, the execution time of three families of
h-relations with variable degree of imbalance. We also prove a strong
result that links the communication performance of the fat-tree with
the BSP abstraction of the interconnection network.  Given a generic
h-relation, we can provide a value of g that, in the worst case,
slightly overestimates the completion time and is very close to
optimality.