Beacon delays in contention-free environments

In a contention-free environment and when the AP has no load, the mean beacon delay can be expressed as: Mean Beacon Delay = $DIFS + E[CW_{min}] \times SLOT + PLCP,$ where $DIFS$ is the duration for which an AP senses the channel before transmitting a beacon frame; $E[CW_{min}] \times SLOT$ is the back-off delay once the AP has sensed the channel to be idle for a duration $DIFS$; and $PLCP$ is the Physical Layer Convergence Protocol overhead associated with every transmitted frame. The IEEE 802.11b standard specifies the various parameter values as follows: $DIFS = 50\mu s,$ $SLOT = 20 \mu s,$ $CW_{min} = 31,$ $PLCP = 192 \mu s$. From these values, we obtain the mean beacon delay to be 552 $\mu s$.

Figure 2: Beacon Delays when the AP has no load

We conduct a number of experiments to estimate the beacon delays using the methodology described in Section 3. Figure 2 shows that the mean estimated beacon delay value is $547 \mu s$, which is close to the expected value of $552 \mu s$. We next perform experiments to determine whether the bandwidth estimated through the beacon delay measurements closely approximates the actual bandwidth obtained by the end-host upon affiliation with the AP.