Stations Alpha and Zeta are the transmitting on an Ethernet. Both Alpha and…
Stations Alpha and Zeta are the transmitting on an Ethernet. Both Alpha and Zeta attempt to transmit a frame but they collide and Zeta wins the first backoff race. With what probability, Zeta wins the first backoff race?
Answer: A. 0.25 — A) 0.25 At every attempt to transmit a frame, both Alpha and Zeta chooses value of ‘K’ randomly. Based on the value of ‘K’ we will decide by looking at the…
- A.
0.25
- B.
0.625
- C.
0.125
- D.
0.375
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Correct answer: A
A) 0.25
At every attempt to transmit a frame, both Alpha and Zeta chooses value of ‘K’ randomly. Based on the value of ‘K’ we will decide by looking at the backoff time who will win the race. We know that the station having smaller backoff time will win and it will send the frames earlier.
Attempt 1: Value of K is 0 <= K <= 2x-1 (x is the attempt number). Since Zeta won the race that means Zeta must have chosen the smaller number. Now K can be 0 or 1. So Zeta chose 0 and Alpha chose 1.
Total possibilities are (0,0), (0,1), (1,0), (1,1).
Probability = Favorable Outcome / Total outcome.
Favorable Outcome = (1,0)
P = 1 / 4 = 0.25