Correct Answer - Option 1 : Receive clock should go back by 3 milliseconds
The correct answer is “option 1”.
CONCEPT:
Original timestamp: Original timestamp is the time at which the sender sent the packet.
Receiving timestamp: Receiving timestamp is the time at which the receiver receives the packet.
Transmit Timestamp: Transmit timestamp is the timestamp at which the receiver of the message sent the reply packet.
Returned timestamp: Returned timestamp is the timestamp at which the sender of the message receives the reply packet.
Formulas related to timestamp are:
Sending time = Receiving time – Original time
Receiving time = Returned time – transmit time
Round trip time = sending time + receiving time
One-way time = \(\frac{RTT}{2}\)
CALCULATION:
Original timestamp: 46
Receiving timestamp: 59
Transmit timestamp: 60
Returned timestamp: 67
Sending time = 59ms - 46ms
= 13 ms
Receiving time = 67 ms - 60 ms
= 7 ms
RTT = 13 ms + 7 ms
= 20 ms
One-way time = \(\frac{20}{2}\)
= 10 ms
Time difference = Receive timestamp – (original timestamp + one-way time)
= 59 ms - (46 ms + 10 ms)
= 59 - 56
= 3 ms
Hence, the receiver should go back by 3 ms.
