GATE | GATE IT 2006 | Question 68

On a wireless link, the probability of packet error is 0.2. A stop-and-wait protocol is used to transfer data across the link. The channel condition is assumed to be independent from transmission to transmission. What is the average number of transmission attempts required to transfer 100 packets?
(A) 100
(B) 125
(C) 150
(D) 200

Answer: (B)
Explanation: Probability of success = 0.8
E = 0.8 * 1 + 0.8 * 1 +… n times = 100 {for 100 packets}
=> 0.8 * 1 * n = 100
=> n = 125
to receive 100 packets we have to transmit 125 packets
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