High-precision synchronization between two computers - NTP

This is a discussion on High-precision synchronization between two computers - NTP ; Hello everybody. For a little project, I have two computers which need to be as best synchronized as they could be. I tried to use ntp for that. I defined the first one as a time server. The second one ...

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Thread: High-precision synchronization between two computers

  1. High-precision synchronization between two computers

    Hello everybody.

    For a little project, I have two computers which need to be as best
    synchronized as they could be. I tried to use ntp for that. I defined the
    first one as a time server. The second one use the first one as unique
    time server (I know that several time servers is recommended, but I don't
    need perfect time, only perfect synchronization). When I run ntpdate on
    the client, all work fery well. To achieve best synchronization, I run it
    several time and it gives me precision up to 0.000001 seconds (which is
    very very well). The problem is that I don't want to run ntpdate from a
    cron job since I cannot have any steps (unless at run time). So I use
    ntpd, but it seems not to work since the difference between the two clocks
    becomes bigger and bigger.

    What can be the problem? How could I solve this?

    I still have to add that the two hosts have a 100Mb ethernet connection
    just for them, so traffic load is not really a problem for me...

    Thanks a lot for your answers.

    Bruno
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  2. Re: High-precision synchronization between two computers

    On 2007-08-28, Bruno.OBSOMER@thalesaleniaspace.com wrote:

    > For a little project, I have two computers which need to be as best
    > synchronized as they could be. I tried to use ntp for that. I defined the
    > first one as a time server. The second one use the first one as unique
    > time server (I know that several time servers is recommended, but I don't
    > need perfect time, only perfect synchronization).


    If you want "perfect synchronization" then you want your server to be
    synchronized to a high quality time base (e.g UTC acquired via GPS) so
    that the clients will not be chasing a moving target.

    > When I run ntpdate on the client, all work fery well. To achieve best
    > synchronization, I run it several time and it gives me precision
    > up to 0.000001 seconds (which is very very well). The problem is
    > that I don't want to run ntpdate from a cron job since I cannot have
    > any steps (unless at run time). So I use ntpd, but it seems not to
    > work since the difference between the two clocks becomes bigger and
    > bigger.


    There are a number of possible issues here. Please post the ntp.conf
    files from both systems omitting the comment lines.

    --
    Steve Kostecke
    NTP Public Services Project - http://support.ntp.org/

  3. Re: High-precision synchronization between twocomputers

    > For a little project, I have two computers which need to be as best
    > synchronized as they could be. I tried to use ntp for that. I defined the
    > first one as a time server. The second one use the first one as unique
    > time server (I know that several time servers is recommended, but I don't
    > need perfect time, only perfect synchronization). When I run ntpdate on
    > the client, all work fery well. To achieve best synchronization, I run it
    > several time and it gives me precision up to 0.000001 seconds (which is
    > very very well). The problem is that I don't want to run ntpdate from a
    > cron job since I cannot have any steps (unless at run time). So I use
    > ntpd, but it seems not to work since the difference between the two clocks


    > becomes bigger and bigger.
    >
    > What can be the problem? How could I solve this?


    As Steve said, there could be a number of problems...

    The first issue is that the PC clock is not all that accurate. So if your
    server drifts a lot, the client will have to adjust to drift at the same
    rate. It would probably be advisable to have the first PC run NTP with other
    servers for a while so that it can create a reasonable drift value. Then you
    can disconnect it from those and have it only use the local clock, then have
    your client use that server. That is probably as good as you are going to
    get.

    If you want better synchronization then you could use a stable external 1PPS
    source (i.e. ovenized crystal oscillator, rubidium oscillator , GPS, etc)
    and have the output going to the serial port on both machines. This will
    yield you better numbers than over ethernet.

    Jason

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  4. Re: High-precision synchronization between two computers

    hi all !

    i know this is an old thread so maybe nobody will see my post ... but i keep on !

    i'm very interested on knowing how did it finally worked this ...
    i'm trying to achieve similar stuff but with more then 2 computers.

    my first approach was to stablish one of the computers as "master" who will send time data to all the other in order to all share the same clock as precise as possible to display multimedia content based on timeline.

    The last post of this thread says very usefull information for me as a newbie in NTP ...

    * computer clocks always drift so having a computer master without an accuracy source could not be useful
    * to get better synch, use an external accurate source as (i.e. ovenized crystal oscillator, rubidium oscillator ) ...

    i'm interested on this last option as (maybe it's cheaper then a GPS clock signal?)
    does anybody has some references on "cheap" ovenized crystal oscillator, rubidium oscillator to be used as a stable clock source ?
    i've been asking for GPS clock servers and they are arround 2000$ ... too much for my project budget and also they need to have at least visibility with 4 satelites to get good results?

    any link where i can find more info about this setup with oscillators as clocks ?
    are they cheaper ?

    any information much much appreciated ...

    e*

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