AbstractThis paper is concerned with information dissemination in a tree. It is assumed that a vertex can either transmit or receive a message and an informed vertex can transmit it to only one of its neighbors at a time. Under a minisum criterion, a necessary and sufficient condition for an optimal call sequence at each vertex is established. Based on this, anO(NlogN) algorithm is designed to find optimal call sequences at all vertices and to determine the broadcast center of a tree—the set of all vertices from which minisum broadcasting can be accomplished. ©1993 John Wiley&Sons, I