[time-nuts] Typical NTP performance? Monitoring multiple NTP servers?

Chris Albertson albertson.chris at gmail.com
Wed Jul 31 12:55:22 EDT 2013


Your time logging method likely introduces a large error.  Larger then any
problems in the things you are trying to measure.   A good NTP system
generally works at the "few microseconds" level.

As for running multiple "NTP Clients",  First off there is not such
distintion between a client and a server.  You simply run "ntpd" and it
looks at it's config file to find reference clocks.  ntpd will accept any
number of clocks and will serve time to any computer that asks

If you want to monitor multiple ntpd running on several computers just set
up one of them to use the uothers as reference clocks and the have 'ntpq"
print a "billboard" and you will see the reletive performance.

On Fri, Jul 26, 2013 at 12:21 AM, Anders Wallin <anders.e.e.wallin at gmail.com
> wrote:

> Hi all, I have two NTP-related questions:
>
> 1.
> We are setting up a White-Rabbit[1] network for time-distribution. We
> 'seed' the WR-network with 10MHz and PPS signals form atomic clocks. This
> means on each computer in the network there's a very accurate PTP-server
> running on the WR-card, as well as the normal system time on the computer.
> For fun I logged both the system-time (kept on time using NTP) as well as
> the PTP time and plotted the error:
>
> http://www.anderswallin.net/wp-content/uploads/2013/07/NTP_time_2013jul26.png
> I was wondering if this plot is typical for a (good?) NTP-disciplined
> computer clock?
> Without NTP the free-running clock shows >40 ppm error:
>
> http://www.anderswallin.net/wp-content/uploads/2013/07/freerunning_vs_ntp_2013jul26.png
>
> The -16ms offset in this graph is probably due to my naive program where we
> first call a simple function that asks the NTP time, and then over a serial
> link ask for the PTP time. In reality the two time-stamps might be better
> synchronized - I don't know. The slow variation I see should be real
> however and completely due to drift in the NTP time, since the WR-time is
> much more accurate.
>
> 2.
> Is it possible to run several NTP-clients on one machine? That means I'd
> have multiple "system-times" each synchronized to its own NTP server.
> If this is possible I'd like to monitor several NTP-servers at once and log
> their time-stamps against our WR-time which is known to be good.
>
> thanks,
>
> Anders
> [1] http://en.wikipedia.org/wiki/The_White_Rabbit_Project
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-- 

Chris Albertson
Redondo Beach, California


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