Abundant content, data type and diverse members' interests naturally lead to preference heterogeneity within a multicast session requiring frequent communication within subgroups of members sharing common interests/requirements. In this paper, we propose a topology-sensitive subgroup communication (TSC) mechanism to support efficient subgroup communications in large-scale multicast applications. Our mechanism takes an end-to-end approach which can completely eliminate additional creation of multicast groups. Our TSC mechanism exploits the spatial locality of members within a given subgroup, and enables members to autonomously build a TSC forwarding structure consisting of multiple unicast and scoped multicast connections. Through simulations, we observe that TSC mechanisms perform well for diverse densities and distributions of nodes in a subgroup. Categories and Subject Descriptors C.2 [Computer Systems Organization]: Computer Communication Networks General Terms Performance Key...