An adaptive protocol for reliable multicast in mobile multi-hop radio networks

In this paper we propose a new protocol for reliable multicast in a multi-hop mobile radio network. The protocol is reliable, i.e., it guarantees message delivery to all multicast nodes even when the topology of the network changes during multicasting. The proposed protocol uses a core based shared tree. The multicast tree may get fragmented due to node movements. A notion of forwarding region is introduced which is used to glue together fragments of a multicast trees. The gluing process involves flooding of the forwarding region of the nodes which witness topology change due to node movements. Delivery of multicast messages to mobile nodes is expedited through (i) pushing of the message by witness nodes in their forwarding regions and (ii) pulling of messages by a mobile node during the (re)joining process. Hence, the protocol conserves network bandwidth by using a combination of the push-pull approach and limiting network flooding to only minimal parts of the network that is affected by topology change. The protocol adapts to both topology change and the distribution of the multicast group members to minimize the use of system resources.