  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 measurement-assisted 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.
