An efficient multicasting scheme using prejoin technology in mobile computing environments

As multimedia services in mobile computing environments are growing today, more investigations on multicasting for mobile computing environments are in progress. When the multicasting is performed on wireless networks, some serious problems, that do not occur in the traditional fixed networks, can occur. One problem is that, when a mobile host (MH) enters a new cell, if there is no member belonging to the same multicast group as the mobile host in the new cell, the mobile support station (MSS) of the new cell must join the multicast group. In this process, the MH may encounter the group join delays and the graft delays. Also, the frequent acknowledgements and the packet re-transmissions caused by the transmission media with low bandwidth and high error rate can generate some extra heavy traffic. This paper presents a prejoin method that lets the new MSS join the multicast group ahead for reducing the join delay and the graft delay. Additionally, we propose a multi-level ACKs strategy that separately confirms the ACKs exchanged between a data sender and a MSS and between a MSS and a MH. It is shown that our scheme shows more performance improvements as more adjacent cells have not joined the multicast group and each MH has lower mobility rate.