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

David J Taylor david-taylor at blueyonder.co.uk
Sat Aug 2 07:20:40 UTC 2003


> 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.
> Congratulations.
> It is beyond my scope for the time being.
>
> Thanks for trying,

Christopher, you are almost there - don't give up!

If you think about it, there is no way in which the packet from server to
client can know when it will be received by the client, so the packet on
the wire cannot carry the T4 value!  The contents of the packet are made
up at the server in the ways described, and the packet is then put on the
wire.  At some point later, the packet is received by your client, and one
of the first things your client should to do is to note the time of
reception.  This will be the T4 value used in the formula.  The client
will also have already noted the time of sending (T1) to allow it to make
up the packet in the first place.  It will put that sending time in the
Originate field of the packet, and that field should not be altered by the
server.  The values for T2 and T3 for the formula come from the Receive
and Transmit fields of the received packet, as filled in by the server.

Cheers,
David





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