Hi, thanks a lot for the explanation, will transmitting a follow up message late will introduce an offset? or it does not matter since the slave will sync his clock with the timestamp from the follow up message or it does matter? and we need to send follow up very fast
This is the very simplified version since the role of the announce message is missed. The ptp announce message is very important since contains the PTP priority ( the Port with the lower priority value become the master!).
How does it work if propagation is not the same in both directions? So when delay in one direction is not round-trip/2 ? That is not unrealistic - even in direct P2P links (though would be smaller than in NTP sync of a workstation over some dial up link or a antique broad band where downstream was via cable tv signal but upstream via dial up phone. This did happen in the early years where older cable networks where not return capable
Hi Dr David, That was one of the well-made, neat and smooth PhD presentations that I ever seen. Even though my work is not in your exact specialty but I could understand much concepts (hopefully I can apply one of your presentation techniques in my upcoming PhD defense, that is in computer science as well). Thank you for the share! I wish you the best for your current and future activities. Kind regards,
Great Video for sure ! Question: why the Master could not embed the directly its transmission timestamps inside the first Sync message ? the Slave being capable to embed the transmission timestamp directly inside the delay_request message , I'm wondering why the Master would not be able to act similarly ? ( I would suspect here that add the timestamps inside the message would be done right before being sent on the wire, by the Network Interface itself) , thanks for your response !
What is the rate of the messages (the bandwidth) between the Master and Slave ? and how does the message looks like, how long is each message ? is it possible to obtain the precision using RF link instead of fiber ? I would like to ask more questions if it is possible to contact you in someway it would be great. Thank you very much for the great videos
What determines which side is passive on the link between C and D or are both sides passive? Is there some sort of messaging that's occurring on the link to keep one/both ports passive?
In the final delay request sent by the slave clock, you have chosen 208s, an even number. What if you had chosen 209s, yielding a difference of 3 seconds instead of 4? This would give us 1.5 second transmission delay - what happens then?
If the slave had sent its delay request at 209 seconds then the master would have received it at (according to its clock) a timestamp of 213. When the slave receives 213 in the delay response, it would subtract 209 from 213 = 4. So the propagation delay is still 4/2 = 2 seconds. However, if the network had a propagation of only 1.5 seconds instead of 2, the calculations are still exactly the same - you would simply add 1.5 seconds to the slave's clock.
It seems there is an error here. The annouce messages are used to change the state of the PTP ports, not the sync messages. And the announce message contain 2 parametes clockClass and ClockAccuracy to determine which is the best clock
Same question asked by George in previous comment: "I understand why there needs to be compensation for the processing/encapsulating delay in the master's first message, but why isn't there a similar one for the slave's delay request time stamp? Wouldn't there be a delay between reading its own clock and transmitting as well?"
The Delay Request message does *not* contain a timestamp in the message. The slave reads the timestamp from hardware after the Delay Request message is sent.
because only the slave needs this timestamp, and master doesn't need it. Slave can read it's hardware timestamp after it sends out the Delay Request message.
I understand why there needs to be compensation for the processing/encapsulating delay in the master's first message, but why isn't there a similar one for the slave's delay request time stamp? Wouldn't there be a delay between reading its own clock and transmitting as well?
Hi George, the difference between the first master message (SYNC) and the first slave message (DELAY_REQ) is that the timestamp inside the message of DELAY_REQ isn't that important. The important value in this case is the time the packet left the port, which can be determined with high precision right away. I hope this helps.
