[ntp:questions] Re: Question about RFC-2030 SNTP Version4

Christopher J. Holland msnews at microsoft.com
Fri Aug 1 22:30:52 UTC 2003


I give up. I really don't want to get too deep into understand the theory
behind the formulas.
I would just like to calculate the answers, so they look like the NTP Client
Program does.
I thought I could just plug in the Received Packet Values and come up with
Delta and
Round trip. Unfortunately, it isn't working out that way. So, maybe someday
I will come back
and understand it.

This is as far as I got.....
Originate Timestamp     T1   time request sent by client
Receive Timestamp       T2   time request received by server
Transmit Timestamp      T3   time reply sent by server
Destination Timestamp   T4   time reply received by client

d = (T4 - T1) - (T3 - T2)     t = ((T2 - T1) + (T3 - T4)) / 2.

Originate Timestamp corresponds to the Packet's Originate Timestamp.
Receive Timestamp corresponds to the Packet's Recieve Timestamp.
Transmit Timestamp corresponds to the Packet's Transmit Timestamp.

There is no "Destination Timestamp" in the receive Packet, Just the
Reference TimeStamp.
So, what is meant by Destination Timestamp. I am not sure.
Perhaps T4 it is the Reference Timestamp,  but that aint working.
If you can plug in the values and come up with a correct answer.
It is beyond my scope for the time being.

Thanks for trying,
"David J Taylor" <david-taylor at blueyonder.co.uk> wrote in message
news:FqzWa.201$6M2.2658466 at news-text.cableinet.net...
> > No matter what Values I plug in for T1,T2,T3 & T4, they
> > don't come out to the expect values.
> Sorry, I was wrong.  You better check the RFCs.
> As I now read it, in the packet T1 is completed by the server as the
> reference time.
> T2 is what the client filled in when it sent the packet, and T3 and T4 are
> completed by the server on receipt of the client packet, and sending of
> the return packet.
> On your client, you should note the time at which the packet is sent (TA),
> and the time at which the reply is received (TB).  The client could use T2
> to check that the packet it got back was in response to its own request
> (i.e. T2 = TA), and it could use T1 for server sanity checks.  It is
> actually T3, T4, TA and TB that are used in the delay and offset
> calculations.
> I hope this is now correct!
> Cheers,
> David

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