A Reliable and Efficient MAC Layer Multicast Protocol in 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. 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). After analyzing the problems with existing reliable multicast MAC protocols, we propose a novel PFB-based multicast protocol, namely DPMM (Double Piggyback Mode Multicast). The protocol piggybacks the ACK in the CTS frame and piggybacks the priority information in the DATA frames. With DPMM, ACK packets are eliminated and collisions of control frames are avoided. A grouping algorithm using RSS (Received signal strength) measurement is also developed to further improve upon DPMM. Simulation results, using the OPNET, confirm that the improvements are encouraging.