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The bandwidth in a Stop n Wait ARQ is $1$ Gbps and $1$ bit delay to make round trip time $30$ microseconds, if data frames are $2000$ bits in length then the link is utilized in __________  percentage.

At the same time avoid silly mistakes. Best of luck.

Now i understand what actually happened here ..

many thanks @papesh :)

yes  @ dhruvkc123   you provided value is 6.67 is correct but you put that like this 6. 67 with a gap between decimal point and 6 so exam interface is not taking it  :)

Hope you understand now..

i think you are right..there is space..!!  :(

The bandwidth is 1 Gbps or 109 bits ,

1 bit = 1/ 109 sec = 1/ 103 microsecond

RTT = 30  microsecond

1/ 103 microsec for 1 bit , 1 microsec for  103 bits

30 microsec 30, 000 bit

data frme size 2000 bit

link utilization = (2,000 / 32,000) * 100 = 2/32 = 0.0625 * 100 = 6.25

in this question

1 bit delay to make round trip time 30 microseconds

means

Transmission delay for 1 bit t = 1/(109)  = 1/ 103 microsecond .

we calculate RTT by using  RTT= 2 * Tp + Tt ..

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Another way of solving :

the efficiency formula for Stop&Wait ,

1/1+2a   .... (i)

a = Tp / Tt

Tp = 15 Microseconds and Tt = 2 microseconds

now put them in (i)  , a = 15/2 , 2a = 15 .

1/1+15 = 1/16 = 0.0625

0.0625 * 100 = 6.25 %

we get link utilization or efficiency is  0.0625 or 6.25%

by

what is wrong with the following solution

utilization  = Transmission Dealy (TD) / Transmission Delay (TD) + 2 * Propagation Delay (TP)

TD = 2000/10^9 = 2 Micro Seconds

2 * TP = RTT = 30 Micro Seconds

So, utilization = 2/(2+30) = 6.25 %
edited by
yes, you are correct.

Transmission delay for 1 bit ,  t = 1/(10^9)  = 1/ 10^3 microsecond .

calculate RTT by using only RTT= 2 * Tp + Tt
Isn’t the bandwith utilization formula is L/TD+2TP?

tusharhigh Yes right but that is Bandwidth utilization formula in exact value, to find percentage you would again have to divide answer by bandwidth and multiply by 100 which is nothing but

utilization in percentage  =100 * Transmission Delay (TD) / Transmission Delay (TD) + 2 * Propagation Delay (TP)

utilization in value = L/TD+2TP

utilization in percentage =100 * utilization in value / Band width

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