[ntp:questions] Tighter regulation?

Mischanko, Edward T Edward.Mischanko at arcelormittal.com
Sun May 26 04:35:47 UTC 2013

> -----Original Message-----
> From: questions-bounces+edward.mischanko=arcelormittal.com at lists.ntp.org
> [mailto:questions-
> bounces+edward.mischanko=arcelormittal.com at lists.ntp.org] On Behalf Of
> Brian Utterback
> Sent: Saturday, May 25, 2013 12:15 PM
> To: questions at lists.ntp.org
> Subject: Re: [ntp:questions] Tighter regulation?
> On 5/25/2013 5:55 AM, Mischanko, Edward T wrote:
> > [Mischanko, Edward T]
> >
> > I would modify the current algorithm with an exception that if offsets
> >   exceed 1 millisecond for more than one polling cycle, then, polling
> will be
> >   reduced by one interval, else, continue normal operation.
[Mischanko, Edward T] 

I chose 1 millisecond because it appears to be achievable.  I don't have
 that specific requirement; I don't have any requirements.  What is the
 expectation, though?

> What if 1 millisecond doesn't happen to by the tolerance that some
> particular system needs? Ten years ago, I was thrilled if my customers
> reported off sets in the 10-20ms range and sub-10ms was rare. Not to
> mention that what should be expected in the way of maximum offset is a
> function to the polling period and the frequency measurement accuracy,
> the latter of which is probably large and unknown when the clock system
> starts.
> The current algorithm is supposed to use the amount of jitter and the
> increase in the offset between polls to determine when to increase the
> polling period. If the noise in the samples is greater than the amount
> of offset between polls, then there is no way to increase the accuracy
> of the clock at the current polling rate. So, if you are seeing large
> offsets at a particular poll rate, then that would indicate that your
> jitter is too high to prevent it. However, conditions change, and I
> believe that the algorithm for reducing the poll rate again is known to
> be too "stiff".
[Mischanko, Edward T] 

Brian, I see the latter.
> So, are you seeing offsets that are large immediately after the poll
> rate is increased, or does it cruise along fine for awhile and then you
> see increasing offsets? The former would indicate too much jitter, the
> latter woudl indicate an actual failure of NTP to respond quickly to
> change in clock frequency.
> Brian Utterback
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