Virtual Gate Test Series: Computer Networks - Bandwidth

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.

$(A) 2\%$

$(B) 98\%$

$(C) 97\%$

$(D) 3\%$

Answer 1

Think about 100 frames. 2% lost = 2 lost

1 frame overhead = 20bits  

Overhead for 100 frames = 100*20  =2000

2 frames needs to be retransmitted

Overhead = 2 * (2000  + 20=NAC) =4040

Total Overhead= 2000 + 4040  = 6040

Actual Data = 100 * 1980 =198000

Bandwidth Wasted =  (6040 *100 ) /198000 =3.05 %

Comments

for this I think we should compare with net total that is 2000*100 +2*2000 +40