[time-nuts] Time in a cave

Tucek, Joseph joseph.tucek at hp.com
Wed May 13 17:44:44 EDT 2015


In response to Oz-in-DFW

> Given your description here, I'm guessing a millisecond or ten 
> will do that as long as local cluster relative accuracy is maintained.

Spot on; I hope I'd made it clear earlier, but perhaps I've been communicating poorly.  My goals w.r.t. to sync to UTC and w.r.t. holdover are very loose.

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.

> 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.  

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.

Thanks to everybody for the feedback.

-joe


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