A multipoint-to-multipoint multi-cast architecture in an IPATM network is significantly simpler and scales better than existing proposals because it does not require any address resolution architecture and requires substantially fewer resources in terms of virtual circuits (VC), CPU power and memory storage. The architecture includes having both sender and receivers reside on the same delivery tree and only one Virtual Circuit (VC) is used to send data over that tree. The delivery tree is a spanning tree and packets are replicated only on the branches where they are needed. An included algorithm has switches that keep track of the branches of the tree where there are group members. The interleaving of ATM cells is prevented by a VC merging mechanism. A core selection mechanism is provided which optimizes the shape of the tree structure.