Inside a dedicated parallel computer the communication times were generally modeled in the same way, independently of which processors communicate. In a network where the links among the computers are heterogeneous, or in hierarchical clusters, this might not be true anymore. Computers that have faster links, or are closer to each other should be able to exchange messages faster. These differences on communication times should be considered, not only for attributing tasks to the processors but also in global synchronization/communication. The goal of this paper is to study irregular all-to-all communications in a network of dedicated clusters.