To guarantee the reliability in multicast transmission, researches providing reliability through hierarchical control tree which is independent on data channel tree are known to provide high scalability. However, the logical control tree in transport layer constructed without topology information of the corresponding network layer tree may inefficiently use the network resources because the logical control tree is not closely related to the tree topology of the network layer. A router assisted control tree mechanism presented in this paper would improve the efficiency of the link as well as it would remove the replicated data. In addition, it requires to a router a small change which examines the message type of the control tree.