Varying Offset Values - NTP

This is a discussion on Varying Offset Values - NTP ; Hi, I have been observing the values that a stratum 2 server has for its clock offset from multiple stratum 1 GPS based time servers using ntpq -p. Two of the three time servers show an offset agreement in the ...

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Thread: Varying Offset Values

  1. Varying Offset Values

    Hi,



    I have been observing the values that a stratum 2 server has for its clock
    offset from multiple stratum 1 GPS based time servers using ntpq -p.



    Two of the three time servers show an offset agreement in the 50-200
    microsecond range. But the offset for third, which is at the same site as
    one of the first two, has been off as much as 10 milliseconds from the other
    two but now is down to 800 microseconds.



    The first two timer servers are installed at different sites and the third
    is installed on an adjacent subnet to one of the servers in the first group.
    I am showing a consistent offset for two stratum 1 servers at different
    sites but a significant difference between two stratum 1 servers that have a
    nearly identical path to/from the stratum 2 server.



    It seems to me that the data is telling me that the third stratum 1 server
    is drifting all over the place and should be taken out of service and fixed.



    My question is: if I had three stratum 1 servers installed side by side that
    were perfect time keepers, shouldn't my stratum 2's clock offset from the
    each of stratum 1 servers be nearly the same?





    Thanks,



    David







    Note: The information contained in this message may be privileged and confidential and protected from disclosure. If the reader of this message is not the intended recipient, or an employee or agent responsible for delivering this message to the intended recipient, you are hereby notified that any dissemination, distribution or copying of this communication is strictly prohibited. If you have received this communication in error, please notify us immediately by replying to the message and deleting it from your computer. Thank you. ThruPoint, Inc.
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  2. Re: Varying Offset Values

    David Russell wrote:

    > Hi,
    >
    >
    >
    > I have been observing the values that a stratum 2 server has for its clock
    > offset from multiple stratum 1 GPS based time servers using ntpq -p.
    >
    >
    >
    > Two of the three time servers show an offset agreement in the 50-200
    > microsecond range. But the offset for third, which is at the same site as
    > one of the first two, has been off as much as 10 milliseconds from the other
    > two but now is down to 800 microseconds.
    >
    >
    >
    > The first two timer servers are installed at different sites and the third
    > is installed on an adjacent subnet to one of the servers in the first group.
    > I am showing a consistent offset for two stratum 1 servers at different
    > sites but a significant difference between two stratum 1 servers that have a
    > nearly identical path to/from the stratum 2 server.
    >
    >
    >
    > It seems to me that the data is telling me that the third stratum 1 server
    > is drifting all over the place and should be taken out of service and fixed.
    >
    >
    >
    > My question is: if I had three stratum 1 servers installed side by side that
    > were perfect time keepers, shouldn't my stratum 2's clock offset from the
    > each of stratum 1 servers be nearly the same?
    >


    I wouldn't worry about it! A stratum of 1 does not say anything about
    the accuracy, actual or potential! It only says that the server is one
    hop away from a reference clock of some sort. If the reference clock
    happens to be an HF or VLF receiver getting a signal from WWV or WWVB,
    it could be off by considerably more than ten milliseconds.

    I have a WWV receiver that I have used as a reference clock. It's a
    PST/Traconex Model 1030 that selects the best signal from the 2.5, 5.0,
    10.0 , 15.0 or 20 MHz broadcasts. Depending on the current radio
    propagation conditions it could deviate from my GPS receiver by anywhere
    from a few microseconds to a few HUNDRED milliseconds. (When it's good,
    it's really good and when it's bad it's really bad!) Just to make
    things REALLY fun, WWVH in Hawaii broadcasts on the same frequencies as
    WWV and I sometimes get a better signal from Hawaii (I'm in New Jersey)
    than I do from Colorado!

    Ntpd should be able to figure out who has the right time if you've
    configured it properly! That's why it's recommended that you configure
    four or more servers; ntpd can then just say "poor old xxxx has had a
    little too much to drink; we'll just ignore him till he sobers up!"





  3. Re: Varying Offset Values

    David Russell wrote:
    > Hi,
    >
    > I have been observing the values that a stratum 2 server has for its
    > clock offset from multiple stratum 1 GPS based time servers using
    > ntpq -p.
    >
    > Two of the three time servers show an offset agreement in the 50-200
    > microsecond range. But the offset for third, which is at the same
    > site as one of the first two, has been off as much as 10 milliseconds
    > from the other two but now is down to 800 microseconds.
    >
    > The first two timer servers are installed at different sites and the
    > third is installed on an adjacent subnet to one of the servers in the
    > first group. I am showing a consistent offset for two stratum 1
    > servers at different sites but a significant difference between two
    > stratum 1 servers that have a nearly identical path to/from the
    > stratum 2 server.
    >
    > It seems to me that the data is telling me that the third stratum 1
    > server is drifting all over the place and should be taken out of
    > service and fixed.
    >
    > My question is: if I had three stratum 1 servers installed side by
    > side that were perfect time keepers, shouldn't my stratum 2's clock
    > offset from the each of stratum 1 servers be nearly the same?
    >


    I'd add several additional stratum 1 servers and see what falls out. If
    the additional servers confirm that it's bad, either take it out of
    service and get it fixed if you own it or just drop it and use different
    ones.

    > Thanks,
    >
    > David
    >
    > Note: The information contained in this message may be privileged and
    > confidential and protected from disclosure. If the reader of this
    > message is not the intended recipient, or an employee or agent
    > responsible for delivering this message to the intended recipient,
    > you are hereby notified that any dissemination, distribution or
    > copying of this communication is strictly prohibited. If you have
    > received this communication in error, please notify us immediately by
    > replying to the message and deleting it from your computer. Thank
    > you. ThruPoint, Inc.


    No, the information here is no longer privileged or confidential and is
    no longer protected from disclosure. Anyone may now read it disseminate
    it or do anything they want within the limitations of copyright law.
    There is nothing that can be strictly prohibited by any known law. You
    published it by posting it here.

    Danny
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