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3 votes
3 votes

Assume the following information.

  • Original timestamp value $= 46$
  • Receive  timestamp value $= 59$
  • Transmit timestamp value $= 60$
  • Timestamp at arrival of packet $= 69$

​Which of the following statements is correct?

  1. Receive clock should go back by $3$ milliseconds
  2. Transmit and Receive clocks are synchronized
  3. Transmit clock should go back by $3$ milliseconds
  4. Receive clock should go ahead by $1$ milliseconds
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2 Answers

Best answer
5 votes
5 votes
Ans a.

This topic is from ICMP and I dont think its in GATE syllabus anymore. Still it goes like this :

Note : TS -> Timestamp

assume there is a sender and a reciever.

Original TS : Time at which sender sent packet acc to its own clock.

Recieving TS : Time at which reciever recieves that packet acc to its own clock.

Transmit TS : Time at which reciever sent a reply of that packet acc to its own clock.

Returned TS : Time at which sender of recieves the reply acc to its own clock.

=> Sending time = Recieving time - Original time

=> Recieving time = Return time - Transmit time

=> RTT = Sending Time + Recieving time (Think why ?)

=> One way time should be $\frac{RTT}{2}$ => 10ms

=> Sender sent the packet at 46 and reciever should have recieved it at 56 , but its recieving it at 59, => its 3 ms ahead. So it should set its clock 3 ms behind to sync with sender.
5 votes
5 votes

Given the following information:

Value of original timestamp: 46

Value of receive timestamp: 59

Value of transmit timestamp: 60

Time the packet arrived: 67

We can calculate:

Sending time = 59 − 46 = 13 milliseconds

Receiving time = 67 − 60 = 7 milliseconds

Round-trip tim e = 13 + 7 = 20 milliseconds

Time difference = receive timestamp − ( original timestamp field + one-way time duration)

Time difference = 59 − (46 + 10) = 3

So,answer is (A)

Answer:

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