We study, from the competitive analysis perspective, the trade off between communication cost and delay cost (or simply the sendor-wait dilemma) on a hierarchy (rooted tree). The problem is an abstraction of the message aggregation problem on communication networks and the organizational problem in network hierarchies. We consider the most natural variant of the problem, the distributed asynchronous regime, and give tight (within an additive constant) upper and lower bounds of the competitive ratio. We also consider the centralized version of the problem, where we combine the natural rent-to-buy strategy with prediction techniques to achieve the first constant competitive ratio algorithm for any non-trivial class of network topologies.