Scheduling MPEG-4 Video Streams Through the 802.11e Enhanced Distributed Channel Access

The upcoming IEEE 802.11e standard for Wireless LAN has gained a lot of popularity, recently. It improves the Medium Access Control (MAC) of the legacy 802.11 with regard to Quality of Service (QoS) by introducing the Enhanced Distributed Channel Access (EDCA) and the HCF Controlled Channel Access (HCCA). In contrast to the legacy DistributedCoordinationFunction (DCF), EDCAachievesQoS by providing independent transmit queues andMAC parameters for each traffic class, and hence higher prioritized traffic has a higher probability for transmission. Crucial to the success of such a strategy is a scheduler that assigns the data traffic to the respective transmit queues. This is all the more essential in cases where priorities cannot be assigned statically before run-time, but rather require dynamic and adaptable priority assignment as this is the case for manymultimedia applications, e.g. MPEG-4 video streaming. This paper develops and accommodates a new scheduler for EDCA into the MPEG-4 Delivery Framework. The scheduler dynamically determines MPEG frame priorities and assigns data packets to the EDCA transmit queues accordingly. We use the NS-2 network simulator to show that we are able to increase the amount of timely transmitted frames significantly and hence improve the QoS percepted by the user. To the best of our knowledge this is one of very few scheduling approaches that considers MPEG-4 related traffic priorization in EDCA.