3. (20 Points) Random Access. Consider a slotted Aloha system. wi he time slot equals the fixed duration of each packet. Assu 3. (20 Points) Random Access. Consider a slotted Aloha system. wi he time slot equals the fixed duration of each packet. Assume that there are 4 stations A,B,C,D sharing the medium. (a) Stations A,B,C.D receive one packet each from higher layer imes 1.3, 1.5, 2.6, 5.7 respectively. Show which transmissions take place when, ading to the Slotted Aloha Protocol; describe all transmissions until all four packets ve been successful. If needed, each station has access to the following sequence of rau mumbers, provided by a random number generator and drawn uniformly between 0 nd 1: Station A draws numbers: 0.31, 0.27, 0.78, 0.9, 0.9, 0.11, 0.22 Station B draws numbers: 0.45, 0.28, 0.11, 0.83, 0.37, 0.22, 0.91.. Station C draws numbers: 0.1, 0.2. 0.3, 0.4, 0.5, .. Station D draws numbers: 0.36, 0.77, 0.9, 0.1, 0.1, 0.1, 0.1, 0.23.. (b) In slotted aloha, a station transmits in each time slot with a given probability. What probabilities would you assign to each of the four stations so as to: i. maximize the efficiency of the protocol? ii. maximize fairness among the four stations? (c) Will the efficiency increase or decrease if we modify slotted aloha as follows: i. Get rid of slots and allow stations to transmit immediately? ii. Implement carrier sensing? ii. Implement collision detection? iv. Implement collision avoidance?



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