  Although recent works try to improve collective communication in grid systems
by separating intra and inter-cluster communication, the optimisation of
communications focus only on inter-cluster communications. We believe, instead,
that the overall performance of the application may be improved if
intra-cluster collective communications performance is known in advance. Hence,
it is important to have an accurate model of the intra-cluster collective
communications, which provides the necessary evidences to tune and to predict
their performance correctly. In this paper we present our experience on
modelling such communication strategies. We describe and compare different
implementation strategies with their communication models, evaluating the
models' accuracy and describing the practical challenges that can be found when
modelling collective communications.
