IP multicast is an effective technology to distribute identical data simultaneously to multiple users. However, for technical and administrative reasons, IP multicast has not been globally deployed on the Internet. Another approach to multicast is
(ALM). In ALM, multicast related features, such as group membership management, multicast routing and packet replication, are implemented at end-hosts instead of routers. Multicast delivery tree is constructed in the application layer, so all nodes in this tree are end-hosts. Packet transmission between end-hosts uses conventional IP unicast service. Therefore, ALM is a promising alternative to IP multicast. However, application-level multicast relying on end-hosts is more fragile than IP multicast relying on routers. Especially, when a mobile host forwards packets to downstream hosts, a handover causes performance degradations on downstream hosts. In this paper, to alleviate the impact of a handover, we propose a new tree building protocol which locates mobile hosts on leaves of multicast tree. A handover of the mobile host on a leaf does not affect other end-hosts. To investigate performance of our protocol, it is compared with existing application-level multicast protocols. Our simulation results show that our protocol outperforms existing protocols from the viewpoints of loss probability, throughput and delay performance.