[ntp:questions] Re: NTP and DCF77 leap logs

Serge Bets serge.bets at NOSPAM.laposte.invalid
Thu Jan 5 12:15:15 UTC 2006

 On Tuesday, January 3, 2006 at 13:03:26 +0100, Serge Bets wrote:

> But what happened 2 hours before is much less clear.

Update after some more log crossing, and a pair of replay experiments:
The bad frequency I saw on Windows was entirely due to a perturbating
source 2 hours before the leap. Now, the fact that this initial
perturbation was not at all stabilised and even aggravating 22 hours
later is really annoying.

The Windows ntpd specific new super-fast slewing works very well, as 2
replays in normal conditions have shown me a very clean post-leap
behaviour. Stable frequency and offset. Bravo Martin.

In contrast, I replayed a leap with older code: False time during
10 minutes, time reset -1.000938 s at 0:10:46, and frequency explosion
-629 followed by a long period of instability. Many other time resets.
I can imagine what would happen if Murphy makes sources unreachable at
this moment... Wander of 3 centuries per minute.

Conclusion: The inclusion in the daemon of code doing the leap on
platforms where the kernel does not itself leap should be reevaluated.
Bug 508 discussion shows it's not easy to do universaly right, but the
Win prototype from Meinberg nicely proves it's possible.

While at it, I also simulated a negative leap deletion: Step +1 and
frequency explosion exceeding +500 PPM unfortunately.

Serge point Bets arobase laposte point net

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