Performance analysis of reliable MAC-layer multicast for IEEE 802.11 Wireless LANs

In this paper, we study reliable multicast at the MAC layer for IEEE 802.11 Wireless LANs. In IEEE 802.11, multicast transmissions are unreliable in the sense that multicast frames are transmitted from the access point (AP) without an ACK being returned from each receiver as in unicast transmissions. As a result, transmitted multicast frames may be lost due to collisions or errors. There are two types of reliable multicast at the MAC layer proposed for 802.11 in the literature: one is ACK-based and the other is a leader-based mechanism. For the ACK-based mechanism, the AP monitors the frame reception progress of all receivers and retransmits frames whenever no ACK is received from any receiver; for leader-based mechanism, the AP retransmits frames only when no ACK frame is received from the selected leader. We analyze their performance in terms of frame holding time at the AP, and conduct simulation to validate our analytical model. We also propose a new channel acquisition and multicast notification mechanism called RTS/CTS/SEQ to improve the performance of existing work for reliable multicast in IEEE 802.11 WLANs.