Downstream Bandwidth estimation in the absence of RTS/CTS

The total delay incurred by a data frame from an AP in the absence of $RTS/CTS$ handshake is given by: the contention and transmission delay of the data frame plus the respective $ACK$ delay.

$$T = T_{D} + T_{A}$$ (1)

$T_{D}$ in turn can be estimated from the beacon delay $T_{B}$, estimated as in Section 3.2, and the transmission delay of the frame², and is given by:

$$T_{D} = T_{B} + \frac{DATA}{R}$$ (2)

Upon receiving the data frame, the receiver sends an $ACK$ frame after a delay of $SIFS$. $ACK$ frames are fixed in length and are typically sent at the same rate as the data frame. Hence, knowing the sender rate, $T_{A}$ can be easily determined as:

$$T_{A} = SIFS + \frac{ACK}{R}$$ (3)

The potential bandwidth $B$ from the $AP$ to the end-host is then given by:

$$B = \frac{DATA}{T}$$ (4)