HIMAC: High Throughput MAC Layer Multicasting in Wireless Networks

Efficient, scalable and robust multicasting support from the MAC layer is needed for meeting the demands of multicast based applications over WiFi and mesh networks. However, the IEEE 802.11 protocol has no specific mechanism for multicasting. It implements multicasting using broadcasting at the base transmission rate. We identify two fundamental reasons for performance limitations of this approach: (a) Channel-state indifference: irrespective of the current quality of the channel to the receivers, the transmission always uses the base transmission rate; (b) Demand ignorance: packets are transmitted by a node even if children in the multicast tree have received those packets by virtue of overhearing. We propose a solution for MAC layer multicasting called HIMAC that uses the following two mechanisms: unary channel feedback (UCF) and unary negative feedback (UNF) to respectively address the shortcomings of 802.11. Our study is supported by measurements in a testbed, and simulations. We observe that the end-to-end throughput of multicast sessions using MAODV can be increased by up to 74% while reducing the end-to-end latency by up to a factor of 56