A new design of the IEEE 802.11 MAC layer to enhance the scalability of the DMS service

Abstract

The Directed Multicast Service (DMS) is defined within the IEEE 802.11v amendment to enhance the reliability of the multicast transport over the WLAN networks by converting a multicast traffic into unicast. Therefore DMS guarantees the same unicast reliability degree to multicast traffic at the cost of the bandwidth. While DMS can be used to deliver a standard multicast stream to a limited number of receivers, it does not scale well for high throughput traffic like High Definition (HD) TV streams. In this paper we study the DMS scalability and we evaluate the transmission queue behavior using both constant and variable bit rate traffic. We show that in the case of a real time video streaming, losses caused by queue rejections may exceed the packet loss rate of the legacy multicast, limiting therefore the reliability of the DMS service. We propose a scalable version of DMS called S-DMS which executes the DMS service on the base layer and switches between DMS and the legacy multicast for the enhancement layer of a video traffic to avoid queue rejections. We show that S-DMS is able to increase considerably the number of admitted multicast members and protects the essential packets from both queuing rejections and channel losses.