#251: Add fudge option to server config (was: Tracker bugs and our release process)
Stromeko at nexgo.de
Mon Aug 14 16:24:16 UTC 2017
Eric S. Raymond via devel writes:
> #251: Add fudge option to server config
> Gary and Daniel are having an argument over whether this is a good
The general idea of allowing NTP to compensate for asymmetric network
delays is sound, I think. Attaching that information to the server
config is one way to do that and the only sane way of compensating for
asymmetries that are introduced by both the local and remote end.
> Me, I'd rather not do it. Just to keep life simple. But they
> understand the terrain in ways I don't.
I'd leave that out for 1.0, especially as it's almost impossible to
figure out what those asymmetries really are without having a few
known-good stratum-1 sources at various points in the network topology.
I've ran at around 1.5…2.0ms excess upstream delay for the last few
years (VDSL2) and had to shift the GPS chimers accordingly in order to
allow reasonably smooth client fallback from internal to external sync.
But that asymmetry is actually variable and goes to over 30ms when you
load the downstream to capacity. I've got switched to VDSL2 w/ full
vectoring last week and the asymmetry went to below 300µs best I can
tell, so I've removed the fudge completely for now. I can't fully load
the downstream anymore as I'm currently synced at ~105MBit but get
capped at 50MBit via QOS by the provider, but I've seen delay spikes to
around 10ms so far.
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