This report addresses the problem of constructing multicast trees with reservation of resources. The main features of the approach described are that it tolerates asymmetric traffic loads on network links and algorithmically locates data distribution centers for every multiparticipant interaction. A fast and scalable algorithm for locating distribution centers based on the network load and a priori knowledge of participant's locations and resource requirements is given. To explicitly handle cases of disjoint send and receive paths between two nodes, a protocol to build separate send-trees and receive-trees around the centers located in the manner above is given. Simulation results on various topologies are presented showing that, with the above center location mechanism, center-specific trees yield lower tree cost than source-specific trees for many concurrent senders without increasing the average path length significantly. The use of distribution centers, a priori information, and sensitivity to load asymmetry permit effective combination of center-specific and source-specific trees for an interaction and eliminate the need for symmetry checks during resource reservation. Multicast trees, Scalable, Quality of service, Wide area networks.