[time-nuts] Time in a cave

[Harlan Stenn]

"Tucek, Joseph" writes:

> I do need time sync intra-cluster to be tight (sub millisecond, 100
> nano as a stretch goal).  UTC sync can comparatively be terrible; 10-1
> ms is fine, and I can live with "bad NTP, 100 ms" if I must.  From
> specs, */really/* good quartz is my limit and /good/ quartz is
> acceptable, so long as it doesn't mess with the intra-node PTP
> tightness.  I'm mostly looking at TCXO options. OCXO isn't out of the
> question, but rubidium doesn't seem to give $/value.

If you want intra-cluster at sub-millisecond, NTP is possible, and that
should be trivial with PTP.

I've been attending the ISPCS plugfests for the past few years' time and
I've been making sure that we can "take time" from upstream NTP or PTP,
and distribute that time via NTP or PTP.

>> Yes, the master will have a fairly low phase noise local oscillator
>> as it's internal reference. Everything will synch to that.  If all
>> you are doing is syncing the local cluster you don't even care about
>> time outside. This is true for most industrial applications that are
>> just syncing machinery.
> 
> Thanks for the info.  PTP isn't as well understood/documented as NTP,
> so I've not been as certain about my decisions. Of course, that is
> fair for a relatively new standard.

Network Time Foundation "includes" the NTP Project, Ntimed (and PHK
plans to at least look at PTP support sometime), and 2 PTP projects -
PTPd, which is designed to be portable and generally useful, and Linux
PTP, which is designed to be optimized for the latest Linux kernels.

> Currently, I think my two best options are: 1) CDMA enabled PTP
> appliance (set and forget), or 2) PTP appliance running as stratum 2
> from good NTP.

Either should be fine.

I saw you can't run an antenna wire from where you'll be, but perhaps a
lan cable?  That might go to either a GPS device or to a small NTP or
PTP device.

NTF is working to improve the products under its umbrella all the time,
and we're seriously resource-constrained.  OK, we're disturbingly
resource-constrained.  While the PTPd folks seem to have enough
developer resources and Richard Cochran has not complained about the
developer resources for Linux PTP, none of the projects have adequate
documentation writers.

Guess what I think would be a Swell Idea?
-- 
Harlan Stenn <stenn at ntp.org>
http://networktimefoundation.org - be a member!