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If the bandwidth f the line is 1.5 Mbps, RTT is 45ms and packet size is 1KB, then find link utilization stop and wait protocol.

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--> Utilization = transmission time / ( transmission time + RTT )

--> Transmission time = Length of packet / Bandwidth

                                   = 1KB / 1.5 Mbps = 1*10^(3)*8 / 1.5*10^(6) =  5.33 msec.

--> Utilization = 5.33 / (5.33 + 45) = 0.1059 = 10.59% .              [ Rtt = 45 msec(given) ]

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Take upto 4 places of decimal or approximate to 8.24 its giving right answer...

1/(1 + 8.2397)=0.12136

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Link utillization which means how much we are useing th channel

usefull time/totaltime

what is usefull time = transmission time is known as useful time remaing time we are not using the channel

total time = total time untill ack comes back as it is stop and wait

total time = TT+2*PD

now here we neglect the tt at the reciever (by default it is )

so link utillization is TT/total time

to find tt we have formula message size/bandwidth

(10^3  * 8) / (1.5* 10^6)  == 5.33 milisec

5.33/45+5.33 === 0.1057

so option C is most appropriate
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Link Utilization  = efficiency = Useful Time / Total Time

Transmission Time = L / B  = ($2^{10}$ * 8) / (1.5 *$10^{6}$) =  5.46*$10^{-3}$ s

Propogation Time = RTT/2 = 45*$10^{-3}$ / 2 = 22.5*$10^{-3}$ s

 Useful Time = Transmission Time 

Total Time = Transmission Time + Propogation Time  + Propogation Time(ACK) 

=  5.46 * $10^{-3}$ + 45*$10^{-3}$ = 50.46*$10^{-3}$ s

Link Utilization  = efficiency = Useful Time / Total Time = 5.46*$10^{-3}$ / 50.46*$10^{-3}$ = 0.108


but, as you can see that no option matches .

This question is not clear or ambiguous . i think they forget to mention that RTT = Transmission Time + 2*Propogation Time 

but in almost all cases we assume that RTT = ransmission Time + Propogation Time 

Let's assume RTT = Transmission Time + 2*Propogation Time 

then , Link Utilization = Transmission Time / RTT                 // here total time is itself RTT

Link Utilization = 5.46*$10^{-3}$ / 45*$10^{-3}$ = 0.121

but again this question is not proper . Gate will not ask you this type of question . data  given in gate will always proper 

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