Reliable multicast MAC protocol for wireless LANs

Reliable multicast in wireless applications is gaining importance with the development in technology. Applications like multicast file transfer, distributed computing, chat and whiteboard applications need reliability. However, due to mobility and wireless channel characteristics, obtaining reliability in data transfer is a difficult and challenging task. IEEE 802.11 does not support reliable multicast due to its inability to exchange RTS/CTS and ACKS with multiple recipients. However, several MAC layer protocols have been proposed that provide reliable multicast. For example, [1] have proposed the Leader-Based, Probability-Based and Delay-Based Protocols. These protocols work around the problem of multiple CTSs/ACKs colliding by providing ways to have only one of the multicast recipient nodes respond with a CTS or an ACK. These protocols perform well in low mobility wireless LANs but the performance degenerates as the mobility of nodes increases. In this paper, we discuss the inherent drawbacks of these protocols and provide an alternative approach. We present an extension to the IEEE 802.11 MAC layer protocol to provide link level reliability to both unicast as well as multicast data communications. The extension is NAK based and uses tones, instead of conventional packets, to signal a NAK. We also incorporate Dual Tones, proposed by [2], to prevent an incoming mobile node from interrupting an ongoing transmission. Simulation results suggest that our MAC performs better than those proposed by [1] in terms of both data throughput as well as reliability.