Virtual Gate Test Series: Computer Networks - Acknowledgment

Question

Consider data frames consisting of $20$ header and $1980$ data bits. Assume headers and retransmissions are overhead, ACK frames are negligible and NAK frames are $20$ bits. The error rate for data frames is $2$ percent and the error rate for NAK frames is negligible. Compute the fraction of the bandwidth that is wasted on overhead.

$(A) 2\%$

$(B) 98\%$

$(C) 97\%$

$(D) 3\%$

 
My Solution:

Case $1 :$ When Error Does Happen So:

Hence For sending $1980$ data bits total $2220 $ bits are transmitted ($20$ bit NACK)

So throughput $= \frac{2000}{2220} = 90.09\%$

So waste$= 9.9099\%$

Error Probabitlity is $2\% =  2%$  of  $10.81% =  0.1981%$

Case $2:$ If Error doesnt occur then Normal Header Overhead is there:-

So Waste is $ = 100 - (\frac{1980}{2000})\times100 = 1%$

So total $= 1+0.1981 = 1.1981\%$

Io i chose $A$ option and its correct

My approach was right?

Comments

Hence For sending 1980 data bits total 2220 bits are transmitted (20bit NACK), where's 2220 coming from ? Isn't it 2020 ?
 

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i am getting answer as 2.9 percent