An autonomous distributed admission control scheme for IEEE 802.11 DCF

Abstract

Admission control as a mechanism for providing QoS requires an accurate description of the requested flow as well as already admitted flows. Since 802.11 WLAN capacity is shared between flows belonging to all stations, admission control requires knowledge of all flows in the WLAN. Further, estimation of the load-dependent WLAN capacity through analytical model requires inputs about channel data rate, payload size and the number of stations. These factors combined point to a centralized admission control whereas for 802.11 DCF it is ideally performed in a distributed manner. The use of measurements from the channel avoids explicit inputs about the state of the channel described above. BUFFET, a model based measurementassisted distributed admission control scheme for DCF proposed in this paper relies on measurements to derive model inputs and predict WLAN saturation, thereby maintaining average delay within acceptable limits. Being measurement based, it adapts to a combination of data rates and payload sizes, making it completely autonomous and distributed. Performance analysis using OPNET simulations suggests that BUFFET is able to ensure average delay under 7ms at a near-optimal throughput.

Feedback based distributed admission control in 802.11 WLANs

“…T data depends on packet size and channel data rate for all frame transmissions on the WLAN. Similar to BUFFET [4], T data is measured from the wireless channel.…”

“…An example of feed-forward approach is the use of an analytical model [4] to compute the advisable load from model inputs (average packet size, data rate and number of stations), requiring detailed knowledge of the system being controlled. Alternatively, feedback from the WLAN about performance measures such as delay, queue length or collision rate can be used to tune the threshold.…”