offset > .5 second. What does this mean? - NTP

This is a discussion on offset > .5 second. What does this mean? - NTP ; What does "Time set (offset > .5 second)" mean? Does it mean more than 0.5sec but less than 1sec? If the time was out by 30seconds, would it still error "Time set (offset > .5 second)" ?? Initially I got ...

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  1. offset > .5 second. What does this mean?

    What does "Time set (offset > .5 second)" mean?
    Does it mean more than 0.5sec but less than 1sec?
    If the time was out by 30seconds, would it still error "Time set
    (offset > .5 second)" ??

    Initially I got "Time service corrected the clock error by 63 seconds"
    in the event log.

    SBS2000, NTP using w32time.
    Thanks
    Nick


  2. Re: offset > .5 second. What does this mean?

    nicough@gmail.com wrote:
    > What does "Time set (offset > .5 second)" mean?
    > Does it mean more than 0.5sec but less than 1sec?
    > If the time was out by 30seconds, would it still error "Time set
    > (offset > .5 second)" ??
    >
    > Initially I got "Time service corrected the clock error by 63 seconds"
    > in the event log.
    >
    > SBS2000, NTP using w32time.
    > Thanks
    > Nick
    >


    We are just guessing here because W32TIME is a Microsoft product. It
    may make a difference which version of Windows you are using as well.

    My guess is that it meant what it said; the clock was set rather than
    corrected by "slewing" and that this was done because the offset was
    greater than 0.5 seconds! Smaller errors would be corrected by speeding
    up or slowing down the clock (slewing) until the offset became zero.
    The larger offset requires a "bigger hammer". Slewing is limited, on
    most systems, to speeding up or slowing down by 500 parts per million or
    one half millisecond per second. Correcting a large error at this rate
    could take days!





  3. Re: offset > .5 second. What does this mean?

    The application in use will fail if the time is out by >2 seconds.

    Does anyone know if "Time set (offset > .5 second)" could potentially
    mean that my clock is out by 3 (or more) seconds?
    On SBS2000 (Windows 2000 Server SP4)

    Nick


  4. Re: offset > .5 second. What does this mean?

    nicough@gmail.com wrote:
    > The application in use will fail if the time is out by >2 seconds.
    >
    > Does anyone know if "Time set (offset > .5 second)" could potentially
    > mean that my clock is out by 3 (or more) seconds?
    > On SBS2000 (Windows 2000 Server SP4)
    >
    > Nick


    Nick,

    Did you read this Microsoft article?

    http://support.microsoft.com/?kbid=232209

    It mentions a "Time set (offset < .5 second)" message.

    If your application is as critical as you say, I /strongly/ urge you to
    look at NTP instead of w32time. In Windows 2000, w32time may well step
    the clock, which could confuse your application even more, and might even
    step the clock back. At least with NTP you can control that type of
    behaviour.

    David



  5. Re: offset > .5 second. What does this mean?

    Can someone clarify for me whether "offset" in the NTP world, is
    talking about:

    (a) The difference in time between the incorrect time on a local
    server, and the correct time on a correct NTP server.
    or
    (b) The time delay (caused by latency etc) to receive the correct time
    from an NTP server. Ie By the time the local server receives the
    "correct time", this "correct time" value is now slightly old.

    Remembering that eventlog regularly says "Time set (offset > .5
    second)"
    and initially (once) said "Time service corrected the clock error by 63
    seconds".

    Thanks
    Nick


  6. Re: offset > .5 second. What does this mean?

    nicough@gmail.com wrote:
    > Can someone clarify for me whether "offset" in the NTP world, is
    > talking about:
    >
    > (a) The difference in time between the incorrect time on a local
    > server, and the correct time on a correct NTP server.
    > or
    > (b) The time delay (caused by latency etc) to receive the correct time
    > from an NTP server. Ie By the time the local server receives the
    > "correct time", this "correct time" value is now slightly old.
    >
    > Remembering that eventlog regularly says "Time set (offset > .5
    > second)"
    > and initially (once) said "Time service corrected the clock error by
    > 63 seconds".
    >
    > Thanks
    > Nick


    Nick,

    Please be aware that w32time in Windows 2000 DOES NOT use NTP! It uses
    SNTP. SNTP is a single query/response mechanism for getting a time
    estimate, but NTP involves software which queries multiple servers (to
    eliminate bad servers), and queries them continuously (with an adaptive
    interval) as part of a controlled time and frequency locking loop.

    In NTP, offset refers to the time by which the OS time differs from the
    best current estimate of UTC (at least, that's what I would say, but the
    gurus will correct me). In NTP, the delay to and from the server is
    measured and removed as an error source (although this is not perfect if
    the path to and from the server does not have the same time delay).

    Also, once started, NTP will change the clock rate slightly to keep it in
    sync rather than stepping the clock. I don't believe that the Windows
    2000 version of w32time does that - it uses the much cruder time steps.

    David



  7. Re: offset > .5 second. What does this mean?

    nicough@gmail.com wrote:

    > The application in use will fail if the time is out by >2 seconds.
    >
    > Does anyone know if "Time set (offset > .5 second)" could potentially
    > mean that my clock is out by 3 (or more) seconds?
    > On SBS2000 (Windows 2000 Server SP4)
    >
    > Nick
    >


    I think I've mentioned before that you need to ask Microsoft! W32TIME
    is a Microsoft product. Microsoft supports it, to whatever extent it is
    supported. We don't!

    "Time set (offset > .5 second)" undoubtedly means that your time is off
    by more than 0.5 seconds. The message does not say how much more and I
    would not attempt to guess!!!!

    If it's important, I would strongly suggest a more capable tool than
    W32TIME.

  8. Re: offset > .5 second. What does this mean?

    nicough@gmail.com wrote:

    > Can someone clarify for me whether "offset" in the NTP world, is
    > talking about:
    >
    > (a) The difference in time between the incorrect time on a local
    > server, and the correct time on a correct NTP server.
    > or
    > (b) The time delay (caused by latency etc) to receive the correct time
    > from an NTP server. Ie By the time the local server receives the
    > "correct time", this "correct time" value is now slightly old.
    >
    > Remembering that eventlog regularly says "Time set (offset > .5
    > second)"
    > and initially (once) said "Time service corrected the clock error by 63
    > seconds".
    >
    > Thanks
    > Nick
    >


    Offset refers to the difference between the local clock and the server's
    clock.

  9. Re: offset > .5 second. What does this mean?

    Richard B. Gilbert wrote:
    []
    > Offset refers to the difference between the local clock and the
    > server's clock.


    Thanks for that correction, Richard. I had mistakenly thought that the
    offset value reported by ntpq -c rv was between the local clock and UTC.
    I have amended my Web page accordingly.

    David



  10. Re: offset > .5 second. What does this mean?

    Ok. So I should run NTP rather than W32TIME/SNTP.
    Can Server 2003 natively do NTP, or is 3rd party software required?

    Thank you all for your advice. Far more helpful than Microsoft.
    Nick


  11. Re: offset > .5 second. What does this mean?

    nicough@gmail.com wrote:

    > Ok. So I should run NTP rather than W32TIME/SNTP.
    > Can Server 2003 natively do NTP, or is 3rd party software required?
    >
    > Thank you all for your advice. Far more helpful than Microsoft.
    > Nick
    >


    Third party software required! If you have Windoze development tools,
    you may be able to build it from source. If not, there are two Windows
    builds available for download.

    This page has links to the Windows builds. . . .
    http://ntp.isc.org/bin/view/Main/Ext...rosoft_Windows

  12. Re: offset > .5 second. What does this mean?

    In article <1162197598.557296.181620@m73g2000cwd.googlegroups. com>,
    nicough@gmail.com wrote:

    > (a) The difference in time between the incorrect time on a local
    > server, and the correct time on a correct NTP server.
    > or


    It's closer to this one, but it is not this one. In the peers output,
    it is the difference between the estimated value of the software clock on
    the local machine and estimated value of the software clock on the
    server in question, allowing for round trip delay, but not for past
    history.

    As one normally expects to be able to read the local clock more accurately
    than the server clock (NB this does not apply to W2003 latest service
    pack W32Time as a client to the reference implementation on Windows or
    many Unix(like) boxes), the normal state will be that the local time is a
    better estimate of true time than the server time. The local time will
    only be the more "incorrect" time during initial convergence (and even
    then there was a big debate, about a couple of weeks ago, as to whether
    ntpd could actually avoid this situation in cases where it knew it to
    be true). (Actually, it could be wrong in phase due to assymmetric
    delays, as well, but those would not be visible in the reported offset.)

    The offset actually used for the disciplining the local clock is, a
    weighted average of the, assumed, best value from several of the
    servers.

    > (b) The time delay (caused by latency etc) to receive the correct time
    > from an NTP server. Ie By the time the local server receives the
    > "correct time", this "correct time" value is now slightly old.


    Noting the above caveat about the local time being likely to be the more
    correct, the delay parameter gives half the maximum error due to this,
    give or take the clock reading precisions.

    (Noting that W32Time on anything except the current SP of W2K3 does not
    implement NTP, the reason that the W32Time implementation of NTP may be
    less correct than the server is that it only reads the software clock to
    a one tick resolution, whereas the reference implementation interpolates,
    using the cycle counter on the CPU.)

  13. Re: offset > .5 second. What does this mean?

    Environment. 2 PC's, both running W2K. (no server).
    PointOfSale and Video requires time within 2 seconds, so that video
    lines up with PointOfSale time stamps.

    They want it locked down so that PC-B cannot access the internet at
    all.
    So PC-A should sync time with an internet NTP server, and PC-B should
    sync time from PC-A.

    I've disabled w32time on both machines, and installed "NTP Time Server
    Monitor".
    By default, this application will synchronise the close to an internet
    NTP server I specify.
    How can I set the NTP Time Server Monitor program to act as a "server"
    to provide NTP time to my PC-B machine?

    Thanks
    Nick


  14. Re: offset > .5 second. What does this mean?

    On 2006-10-30, Richard B. Gilbert wrote:

    > This page has links to the Windows builds. . . .
    > http://ntp.isc.org/bin/view/Main/Ext...rosoft_Windows


    http://ntp.isc.org/links is the short URL for the links topic.

    All of the shortcuts are listed at http://ntp.isc.org/short

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

  15. Re: offset > .5 second. What does this mean?

    nicough@gmail.com wrote:
    > Environment. 2 PC's, both running W2K. (no server).
    > PointOfSale and Video requires time within 2 seconds, so that video
    > lines up with PointOfSale time stamps.
    >
    > They want it locked down so that PC-B cannot access the internet at
    > all.
    > So PC-A should sync time with an internet NTP server, and PC-B should
    > sync time from PC-A.
    >
    > I've disabled w32time on both machines, and installed "NTP Time Server
    > Monitor".
    > By default, this application will synchronise the close to an internet
    > NTP server I specify.
    > How can I set the NTP Time Server Monitor program to act as a "server"
    > to provide NTP time to my PC-B machine?
    >
    > Thanks
    > Nick


    You need to install and configure the NTP software (which runs as a
    service) on both PCs. The NTP Time Server Monitor is just a diagnostic
    tool.

    http://www.meinberg.de/english/sw/ntp.htm

    Cheers,
    David



  16. Re: offset > .5 second. What does this mean?

    I have installed this NTP software, and it is working well. It gives
    far more detailed logging. Highly recommended, and can run as an NTP
    server too.

    http://www.meinberg.de/english/sw/ntp.htm

    Thanks everyone
    Nick


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