[time-nuts] can of worms: time-of-day in a community radio station

[Fiorenzo Cattaneo]

Hi David, I don't particularly trust NTP servers from pool.ntp.org (I
assume that is what you mean by "pool"), and I use public stratum-1
servers chosen from a public list. Of course I make sure that my usage
complies with the policies and terms of use for each server (some
allow regional use only, some say do avoid using iburst keyword, some
require prior permission and/or notification).
I have found that using 3 to 5 public stratum-1 servers works very
well, and gives a time synchronization which is within 3 to 5
milliseconds when compared with a reference timing board with GPSDO.
This time offset discrepancy is actually due to the fact that my ISP
(comcast cable) has asymmetric send/receive delays. It disappears when
I tried this setup at my office, which has symmetrical fiber optic
connection to internet.

Your point about avoiding having all the internal machine hit
stratum-1 servers is a good one however. To avoid that in my setup I
designate 3 machines which serve as an internal stratum-2 pool for
internal distribution. Each of them has 3 to 5 external NTP stratum-1
servers and they all peer with each other. Then every other internal
machine uses these 3 machines. I have more details on my setup in my
reply to Eric.

Kind regards,

-- Fio Cattaneo

Universal AC, can Entropy be reversed? -- "THERE IS AS YET
INSUFFICIENT DATA FOR A MEANINGFUL ANSWER."

On Fri, Oct 18, 2019 at 11:08 PM David J Taylor via time-nuts
<time-nuts at lists.febo.com> wrote:
>
>    I fear that I am developing a reputation for bringing to the list rather
> oddball questions. In my rôle as agent provocateur, therefore, here is
> another such problem.
>
>    Questions for you are at the end. Thanks for your thoughts,.
>
> — Eric
> []
> ===============================================
>
> Eric,
>
> As others have mentioned, using the reference NTP should do the job with
> margin to spare!
>
> - Windows, use the Meinberg port.  I have some info here:
>   https://www.satsignal.eu/ntp/setup.html
>
> - Linux, NTP is usually installed by default, although it may be a release
> or two behind.  Usually this isn't important.  Use "ntpq -pn" to see whether
> you have it.
>
> - MAC, reference NTP is available (I believe), but you might need to compile
> it.
>
> - For your one stratum-1 server you can use a GPS source would with a
> Raspberry Pi, or even a Windows PC although that won't be quite as good, but
> adequate for 0.01 seconds accuracy.  Some notes here:
>   https://www.satsignal.eu/ntp/Raspberry-Pi-quickstart.html
>
> - For a wall-clock from the Raspberry Pi:
>   https://www.satsignal.eu/raspberry-pi/DigitalClock.html
>   I should really recompile this so that the RPi doesn't have to be rebooted
> when the clocks change, but the compiler/software I used
> (Lazarus/FreePascal) didn't have the required API call at the time.
>
> - using the pool servers for a few PCs is OK, I think, as all the PCs won't
> be hitting the same pool servers.  How many is "a few" - perhaps 20?  Don't
> use "stratum-1" public servers (e.g. time.nist.gov), as they are likely to
> be overloaded and therefore not as accurate as you might expect.  Using the
> "pool" command in NTP and pool servers is likely to be just as good, if not
> better.
>
> I hope that gives you a little more food for thought.
>
> Cheers,
> David
> --
> SatSignal Software - Quality software for you
> Web: http://www.satsignal.eu
> Email: david-taylor at blueyonder.co.uk
> Twitter: @gm8arv
>
>
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