Reg: NTP accuracy - NTP

This is a discussion on Reg: NTP accuracy - NTP ; HI, Need following clarification. Our Application needs to have two individual hardware (with DSP processor) to have same crystal clock freqency. Though individual boards are alike, due to environmental factors there might be drift after long run. As the two ...

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Thread: Reg: NTP accuracy

  1. Reg: NTP accuracy

    HI,
    Need following clarification.

    Our Application needs to have two individual hardware (with DSP processor)
    to have same crystal clock freqency. Though individual boards are alike, due
    to environmental factors there might be drift after long run.

    As the two boards are connected to local LAN through ethernet, we feel by
    comparing time at regular intervals can determine any drift in clock.
    (assuming one board as server and another as client).

    We run 'ntpd' in server and ntpdate in the client and after every 5 seconds,
    if we query the client (ntpdate -q) we find there is millisecond difference.
    As both of them are connected through the same LAN and both are running the
    same time( ofcourse same clock freq) we are suppose to get 'zero' time
    difference.

    Can anyone explain why there is millisecond delay and how to reduce it?

  2. Re: Reg: NTP accuracy

    In article ,
    linux.newbie79@gmail.com (linux newbie) writes:
    >HI,
    >Need following clarification.
    >
    >Our Application needs to have two individual hardware (with DSP processor)
    >to have same crystal clock freqency. Though individual boards are alike, due
    >to environmental factors there might be drift after long run.
    >
    >As the two boards are connected to local LAN through ethernet, we feel by
    >comparing time at regular intervals can determine any drift in clock.
    >(assuming one board as server and another as client).


    >We run 'ntpd' in server and ntpdate in the client and after every 5 seconds,
    >if we query the client (ntpdate -q) we find there is millisecond difference.
    >As both of them are connected through the same LAN and both are running the
    >same time( ofcourse same clock freq) we are suppose to get 'zero' time
    >difference.


    >Can anyone explain why there is millisecond delay and how to reduce it?


    1 ms is a small number. Try waiting longer.

    ntpd tries to keep your local clock in sync with UTC.
    One of the important things it does is figure out how
    far off your local crystal is. Look in your drift file.

    If you run ntpd (rather than ntpdate) on the client side,
    it will also figure out the drift on that machine.

    --
    These are my opinions, not necessarily my employer's. I hate spam.


  3. Re: Reg: NTP accuracy

    linux newbie wrote:
    > HI,
    > Need following clarification.
    >
    > Our Application needs to have two individual hardware (with DSP processor)
    > to have same crystal clock freqency. Though individual boards are alike, due
    > to environmental factors there might be drift after long run.


    This suggests that you need frequency synchronisation, not time-of-day
    synchronisation. Frequency synchronisation is used a lot in
    telecommunications networks (e.g. SDH/SONET).

    > As the two boards are connected to local LAN through ethernet, we feel by
    > comparing time at regular intervals can determine any drift in clock.
    > (assuming one board as server and another as client).


    As telecommunications networks evolve from TDM to packet, there is also
    an increased need to transport synchronisation information across packet
    networks.

    Work is ongoing in the IETF (e.g. TICTOC) and elsewhere (e.g. IEEE
    1588). But before choosing a solution, you need to be clear on what
    problem you are trying to solve.

    Cheers, Jan

  4. Re: Reg: NTP accuracy

    >>> In article <475459d4$0$29258$ba620e4c@news.skynet.be>, Jan Ceuleers writes:

    Jan> Work is ongoing in the IETF (e.g. TICTOC) and elsewhere (e.g. IEEE
    Jan> 1588). But before choosing a solution, you need to be clear on what
    Jan> problem you are trying to solve.

    I gather TICTOC is only a BOF at this time. And I have heard it is heavily
    slanted toward IEEE 1588 (and its problem/solution space), and I would love
    to know if folks who are familiar with NTP's problem/solution space are
    doing anything at the TICTOC BOF.

    H
    --
    http://ntpforum.isc.org - be a member!

  5. Re: Reg: NTP accuracy

    >>> In article , linux.newbie79@gmail.com (linux newbie) writes:

    linux> We run 'ntpd' in server and ntpdate in the client and after every 5
    linux> seconds, if we query the client (ntpdate -q) we find there is
    linux> millisecond difference. As both of them are connected through the
    linux> same LAN and both are running the same time( ofcourse same clock
    linux> freq) we are suppose to get 'zero' time difference.

    Run ntpd on both systems for a bit, then take a look. As others have said,
    you may be using the wrong tool for this job. If you want better sync, you
    may want to run a PPS signal to both boxes and let them each sync to that as
    well as to each other.

    H
    --
    http://ntpforum.isc.org - be a member!

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