delay in stats - NTP

This is a discussion on delay in stats - NTP ; Hi, I am running some tests on the NTP protocol for my company : I need to achieve (if possible) in LAN a precision (for clients) of about 1 millisecond (or less :-)) 1. the following properties are studied : ...

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Thread: delay in stats

  1. delay in stats

    Hi,

    I am running some tests on the NTP protocol for my company : I need to
    achieve (if possible) in LAN a precision (for clients) of about 1
    millisecond (or less :-))

    1. the following properties are studied :

    - the time for a client to "calibrate" its clock
    o with/without iburst mode
    o with/without drift file
    o with fixed drift
    o with different values for max polling

    - the maximum precision achievable for clients :
    o with different values for max polling
    o with huff n'puff filter
    o with all clients in peer mode or at least some of them

    the NTP server clock reference will be :
    o undisciplined local clock
    o internet stratum 1 or 2
    o GPS (i have a meinberg lantime M300 and PCI card + GPS receiver on loan)

    I am trying to know here which configuration parameters can improve
    the "calibration" speed and maximum precision of clients clock.
    I am not trying to have the exact time on clients but rather, that all
    clients have the same time.

    I must run NTP daemon on Windows Server 2003 SP1 and it almost sure
    that, in the end, NTP servers wont be able to have internet connection
    or even GPS : they are included in tests because i want to determine
    the impact of the server precision on the client precision.

    For the GPS, i know there is some hardware solution that can run in
    free-run mode after 24h calibration (meinberg).

    I am sure it is a commun problem but i couldn't find any good reports
    on it : if you have some that might interest me, that would be great
    :-))

    2. I just checked the ntpd 4.2.4 changelog : is the windows multimedia
    timer enabled by default ? Where can i find some informations on it ?

    3. I would like to know if there is a way to display the delay in ms
    in loopstats stats ? I am actually talking about the delay column in
    ntpq -p.

    Ok, i am stopping there :-) I know i am asking a lot ! I just need
    some infos about how to proceed for my tests to be as accurate as
    possible

    Thanks,
    Edouard
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  2. Re: delay in stats

    On 2007-03-01, edouard funke wrote:

    > I am not trying to have the exact time on clients but rather, that all
    > clients have the same time.


    NTP synchronizes a group of computer clocks to a common timebase; the
    most commonly used timebase is UTC traceable to NIST.

    A good timebase allows you to achieve better synchronization between
    systems because the clients will not be chasing a drifing master clock.
    An accurate timebase also ensures that one second is consistantly one
    second.

    > I must run NTP daemon on Windows Server 2003 SP1 and it almost sure
    > that, in the end, NTP servers wont be able to have internet connection
    > or even GPS


    Clock stability is affected by many interrelated factors including the
    host OS and application software, hardware, system load, and ambient
    temperature. Some combinations of factors produce better results than
    others.

    One important question you need to answer is what clock accuracy,
    precision, and stability, are needed for your application. Without
    a clear set of requirements you won't have a valid metric to use in
    evaluating the test results.

    Your tests should include running ntpd with the Windows Server in its
    production configuration so that you can determine if that server will
    fulfill your requirements.

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

  3. Re: delay in stats

    edouard funke wrote:
    > Hi,
    >
    > I am running some tests on the NTP protocol for my company : I need to
    > achieve (if possible) in LAN a precision (for clients) of about 1
    > millisecond (or less :-))


    To get that kind of precision you need to have the system directly
    connected to a refclock. You'll rarely get that kind of precision over a
    network.

    >
    > 1. the following properties are studied :
    >
    > - the time for a client to "calibrate" its clock
    > o with/without iburst mode
    > o with/without drift file
    > o with fixed drift


    There is no such think.

    > o with different values for max polling
    >


    It will calibrate without ever reaching maxpoll.

    > - the maximum precision achievable for clients :
    > o with different values for max polling


    You will get surprising results if you change maxpoll. The algorithms
    are designed to give you the best results without touching maxpoll. You
    really need to understand the engineering and algorithms used before you
    can draw any conclusions on the best value for maxpoll.

    > o with huff n'puff filter


    Are you expecting asymmetric paths?

    > o with all clients in peer mode or at least some of them
    >
    > the NTP server clock reference will be :
    > o undisciplined local clock


    Then forget precision here.

    > o internet stratum 1 or 2
    > o GPS (i have a meinberg lantime M300 and PCI card + GPS receiver on loan)
    >
    > I am trying to know here which configuration parameters can improve
    > the "calibration" speed and maximum precision of clients clock.
    > I am not trying to have the exact time on clients but rather, that all
    > clients have the same time.
    >

    You are better of reading Dave's research reports on how all of this
    works and his analyses of the data.

    > I must run NTP daemon on Windows Server 2003 SP1 and it almost sure
    > that, in the end, NTP servers wont be able to have internet connection
    > or even GPS : they are included in tests because i want to determine
    > the impact of the server precision on the client precision.
    >


    Well in such a case your server has no precision since it's not
    connected to anything and is just drifting.

    > For the GPS, i know there is some hardware solution that can run in
    > free-run mode after 24h calibration (meinberg).
    >
    > I am sure it is a commun problem but i couldn't find any good reports
    > on it : if you have some that might interest me, that would be great
    > :-))
    >


    Did you try http://www.eecis.udel.edu/~mills/ntp.html

    > 2. I just checked the ntpd 4.2.4 changelog : is the windows multimedia
    > timer enabled by default ? Where can i find some informations on it ?
    >


    You need to add -M to the command line or the service to enable it. It's
    not enabled by default.

    Danny
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  4. Re: delay in stats

    Steve Kostecke wrote:

    > Your tests should include running ntpd with the Windows Server in its
    > production configuration so that you can determine if that server will
    > fulfill your requirements.
    >


    And environment of course, since things like air conditioning,
    temperature, diurnal variations affect the clock.

    Danny
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