[ntp:questions] Getting precision when server side only offers seconds... Ideas?
unruh-spam at physics.ubc.ca
Tue Feb 26 12:33:49 UTC 2008
sgb1010 at hotmail.com writes:
>I didn't know exactly where I could post this, but hovering around I
>found this group
>which I think could perhaps throw some ideas into my problem.
>My issue is that I need to time sync two machines. My first idea was
>to use NTP,
Do you want to sync the two machines or do you want the two machines to
also have the "right" time? In the former case just use your most stable
machine as the server, and the ohter as the client and they wilol sync to
each other to Usec precision They may not have the right time but they have
the same time.
If you really wnat the right time as well, buy yourself a Garmin 18LVC wire
it up and you will have usec precision as well.
($70+1/2 hour time +a DB9 and USB connectors)
>of course. But the problem is that the hardware I have to implement it
>in (the "server"
>side, so to speak), which has the "right" time, doesn't offer me even
>precision. I only have seconds available.
>Explaining it better, it is a kind of network switch for which I don't
>have total access,
>and can only talk through a protocol, that offers me a date in format
>YYYY-MM-DD hh:mm:ss. Period.
>On the "client", though, I have total hardware access to do what I
>want (normal PC, linux, etc).
>That being said, I immediately thought: I will have a maximum possible
>error of 0.999... seconds:
>09:40:22:0000 (would see as 09:40:22 - Error: 0.0000)
>09:40:22:9999 (would see as 09:40:22 - Error: 0.9999)
>The precision I need is a MAXIMUM of 1.0001 seconds error. Given the
>worst case scenario,
>this leaves me with a remainder of only (1.0001 - 0.9999 = ) 0.0002s
>remainder to "play" with.
>Given the network delay (the switch is over a satellite connection, so
>the difference between the
>several takes for the round trip time would have to be less then
>that), this just seems like
>not possible at all.
>Am I right and is it impossible to get the desired precision or does
>any idea of how could I accomplish this? Is it possible to perhaps
>millisecond "behind" the seconds I receive? The satellite delay is
>the order of 700-1200 ms.
>Thank you for any ideas regarding this issue,
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