RT-WLAN: A Soft Real-Time Extension to the ORiNOCO Linux Device Driver

Abslrucl-The current IEEE 802.11 Wireless LAN (WLAN) systems are unable to support real-time applications because the underlying contention-based MAC (Medium Access Control) protocol causes unpredictable delays. I n this paper, we present the implementation details of a new RT-WLAN device driver module, which extends t h e original Linux device driver for the popular Agere ORiNOCO cards to support soft real-time communications. To o u r best knowledge, this is the first effort i n providing real-time support in t h e WLAN environment at the device driver level. By shifting the design focus from the MAC layer, which is normally hard-coded in the NIC (Network Interface Card), to the device driver level, which is between the system kernel and the MAC layer, our scheme has a clear advantage. Users can simply replace the original ORiNOCO driver w i t h RT-WLAN, and then enjoy the benefits of real-time communications without having to change the NIC firmware or re-compile the Linur kernel. RT-WLAN uses two separate queues for real-time and non-realtime traffic. The real-time queue is served according to the EDF (Earliest-Deadline-First) policy, while the non-real-time queue is served in a FIFO (First-In-First-Out) manner. Besides, an adaptive traffic smoother is implemented in RT-WLAN to regulate bursty non-real-time traffic before they are injected into the network, thus giving higher priority to in-progress real-time transmissions. Experimental results show that the desired real-time support and service .-differentiation among multiple real-time sessions are achieved by using RT-WLAN. -~ --