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ISRO CSE 2014 | Question: 45

• edited by
12,137 views
13 13 votes

Consider a $50$ kbps satellite channel with a $500$ milliseconds round trip propagation delay. If the sender wants to transmit $1000$ bit frames, how much time will it take for the receiver to receive the frame?

  1. $250$ milliseconds
  2. $20$ milliseconds
  3. $520$ milliseconds
  4. $270$ milliseconds

6 Answers

Best answer
20 20 votes

Round trip time = 2 * Propagation time ===>Propagation time =500/2= 250 ms

Transmission time = Message size / bandwidth ===>1000 bits / 50 kbps = 20 ms

Time to receive the frame by the receiver ===> 250 + 20 = 270 ms

• edited by
5 5 votes

receiver to receive frame=transmission time + propagation time from sender to receiver

transmission time=L/B=1000b/50Kb

                                 =20ms

RTT=2*PD

=>PD=RTT/2=250 ms

so total time for receiver to receive frame=250+20 ms=270ms

ans=D

3 3 votes
Option D
RTT = 500 ms ==> one way propagation time is 250 ms
Bandwidth is 50 kbps ==> per sec it transmits 50k bits
So for 1k bits  it will take 20ms
So the total time it taken is 250 + 20 ms= 270 ms
1 1 vote

=> RTT = 4 * Tp

=> 500 * 10-3 = 4 * Tp

=> Tp = 125 * 10-3

=> Tt = 103 / 50 * 103

=> Tt = 20 * 10-2

Time for a frame to reach receiver from sender = Tt + 2 * Tp

=> 2 * 10-2 + 2 * 125 * 10-3

=> 20 * 10-3 + 250 * 10-3

=> 270 * 10-3

 

Cross Check and point out mistakes if any ?

0 0 votes

Given:

  • RTT = 500 ms
  • Packet size = 1000 bits
  • Bandwidth = 50 kbps

Calculating Propagation Delay (Tp)     

      Tp = RTT / 2 = 500 / 2 = 250 ms

Calculating Transmission Delay (Td)

      Td = Packet size / Bandwidth

      Td = 1000 / 50000 = 0.02 sec = 20 ms

Calculating Total Time

     Total time = Tp + Td = 250 + 20 = 270 ms

 




 
0 0 votes

Here Round trip propagation delay means :
(Sender)--------(Satellite)--------(Receiver)--------(Satellite)--------(Sender) delay

Therefore, for  (Sender)--------(Satellite)--------(Receiver) path :
Tp = 500/2 = 250 ms

 

Most academic problems treat satellite as a simple mirror rather than a store and forward device, therefore :

Tt = 1000/50,000 = 20 ms (Considered only for sender and not satellite)

Total delay (sender-to-receiver) = Tp + Td = 250 + 20 = 270 ms

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