Question

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. What is the average number of transmission attempts required to transfer 100 packets?

• A. 100
• B. 125
• C. 200
• D. 150

Answer 1

The correct option is B 125

In sliding window protocol (stop and wait):
Average number of transmission of single packet
$=\frac{1}{1-P}$
(where P = probability of packet for).
So for 100 packets
$=100\times \left(\frac{1}{1-0.2}\right)$
$=100\times \frac{1}{0.8}=125$