1. Consider a CSMA/CA IEEE 802.11 wireless network with two Stations A and B, and an Access Point (AP). The parameters for this network are as follows. (15 points)

• Slot time = 1 time unit
• DIFS = 2 slot times
• SIFS = 1 slot time
• ACK size = 1 slot time
• Timeout period (measured from the end of frame transmission) = 2 slot times. For simplicity, assume that a DIFS can overlap with a timeout period.
• Assume that there is no hidden node problem in the network and that the RTS/CTS mechanism is not used.

Consider that at time t = 0, Station A has one data frame (of size 5 slot times) to be transmitted to the AP. At the same time t = 0, Station B also has one data frame (of size 5 slot times) to be transmitted to the AP. Suppose that the two data frames collided once and that the data frame from Station B was received by the AP after the data frame from Station A was received. Suppose that the random backoffs chosen by Station A for the first and second transmission attempt of its frame are denoted by rA(1) and rA(2), respectively. Similarly, suppose that the random backoffs chosen by Station B for the first and second transmission attempt of its frame are denoted by rB(1) and rB(2), respectively. Find all possible values of rA(1), rA(2), rB(1) and rB(2) as well as the probability of achieving the aforementioned communication behavior of the two frames. Also, out of the various possible scenarios that result in the aforementioned communication behavior of the two frames, draw a diagram for the one that requires the least amount of time to complete all transmissions.