M3: Practical and reliable multi-layer video multicast over multi-rate Wi-Fi network

IEEE 802.11-based wireless LAN, commonly referred to as Wi-Fi, has become a universal solution for the last-hop network access. In large and public assembly places, people may use their mobile devices to view the video of the same popular events via the same wireless access points (APs). However, current 802.11 APs transmit the same video stream multiple times via separate unicast sessions due to the well-known poor reliability and low data rate of the legacy Wi-Fi multicast. Besides, in traditional single-layer-coded video streams, all clients have to settle with the lowest video bitrate limited by the client with the worst channel quality. To address these problems, we propose M3, a practical and reliable multi-layer video multicast solution over multi-rate Wi-Fi networks. The aims of our system are, in the premise of no change to APs, not only to ensure that all clients can smoothly watch the video at least with the lowest quality, but also to maximize the overall video quality received by all clients. To meet these design goals, the video server selects certain clients as unicast receivers to transmit different SVC video layers, and other clients listen for the packets in the promiscuous mode. It is challenging to select specific unicast receivers and allocate different SVC layers to fully utilize the available bandwidth because of dynamic network conditions. To overcome this challenge, we use a periodical feedback mechanism to collect necessary statistics from clients, and use them to derive an optimal SVC-layer allocation strategy to maximize the video quality. We implemented a prototype in a real Wi-Fi testbed consisting of one AP and one M3 server and 8 clients. Compared with the single-layer video multicast, our M3 system can improve the total received video rate by up to 200%