445 views
A $20$ kbps satellite link has propagation delay of $300$ ms , transmitter use Go Back $10$ ARQ scheme, if each frame is $50$ bytes long then the maximum data rate is ________  kbps

rajesh170293   and @kavita_joshi

Go back N used where n value is 10

Transmission time  = 50 * 8 bits /  20 kbps =  20 ms

Propagation Time = 300 ms

Efficiency = Window Size*Transmission Time/(Transmission Time + 2*Propagation Time)

= (10 * 20 ) / ( 20 + 2 * 300 )

= 200 / 620

= 0.322580

so Maximum Data Rate  or throughput is ( efficiency * bandwidth )

=( 0.322580 * 20 ) kbps  [ bandwidth 20 kbps given ]

= 6.45 kbps

thanks boss
i have given answer as 6.451 asuming till 3 decimal places and got it as a wrong answer.how to know whether to give till 2 or 3 decimal places as it is not mentioned in the question?

Go back N used where n value is 10

Transmission time  = 50 * 8 bits /  20 kbps =  20 ms

Propagation Time = 300 ms
Efficiency = Window Size*Transmission Time/(Transmission Time + 2*Propagation Time)

= (10 * 20 ) / ( 20 + 2 * 300 )

= 200 / 620

= 0.322580

Maximum Data Rate = 0.322580 * 20 kbps = 6.45
by

Tt is 20ms and RTT is 60ms
you can't send more than 3 packets in 1 RTT though here the size of windos is 10.
hence throughout should be:

in 60ms we are sending 3packets or 3*50 = 150Bytes or 150*8 = 1200 bits
1 ms = 1200/60 = 20bits bits
1 sec =  20,000 bits = 20kbps
Throughput = 20Kbps should be answer
edited by

@manu00x

No,

maximum data rate or throughput is asked, throughput is efficiency * bandwidth .

Bandwidth 20 kbps is given .

you can see above comments ..they also got 6.45 as throughput.

see this for reference  https://gateoverflow.in/15759/throughput-calculation

Please Update the range in GO Tests, or at least mention in question (up to two decimal places.)

Given Bandwidth = 20 kbps, Tp = 300 ms, Frame Size = 50 Bytes = 50 * 8 bits,

N = 10

Now, Tt = $\frac{Frame Size}{Bandwidth}$ = $\frac{50 * 8 b}{20 * 10^{3} bps}$ = 20 ms

We know Throughput = Efficiency * Bandwidth = $\frac{N}{1+2*\frac{Tp}{Tt}}* Bandwidth$

=$\frac{10}{1+2*\frac{300}{20}} * 20 kbps$ = 6.45 kbps

1 vote
1
241 views
1 vote