Reliable Multicast Mechanism in WLAN with Extended Implicit MAC Acknowledgment

In this paper, we study reliable multicast at the MAC layer for IEEE 802.11 wireless LANs. In IEEE 802.11, multicast protocol is based on the basic access procedure of carrier sense multiple access with collision avoidance (CSMA/CA). This protocol does not provide any recovery mechanism for multicast frames. As a result, transmitted multicast frames may be lost due to collisions or errors. Recently, several reliable multicast protocols at MAC layer have been proposed for 802.11, and they can be classified into two categories: one is based on negative feedback (NFB-based) and the other is based on positive feedback (PFB-based). We first analyze the problems with existing reliable multicast MAC protocols and then propose a novel PFB-based scheme: "Extended Implicit MAC Acknowledgment (EIA)". With EIA, ACK packets are eliminated and collisions of CTS frames are avoided. Since ACK packets account for nearly one-third of the total control overhead, we argue that such a scheme can be beneficial. Simulation results, using the OPNET, confirm that the improvements are encouraging.