[time-nuts] Time in a cave

[Bob Camp]

HI

Ok, some basics:

GNSS = GPS, they are the same thing with the same issues, GNSS lets you hit the Russian system as well as the US.

CDMA = your cell phone guy sets the clock. Many people have put *big* dollars into these systems only to find that the 
local cell phone guy(s) really don’t care what time it is. You can argue about that being right or wrong, we get to buy
lots of stuff on eBay because it’s often wrong. 

Time synch at the user level is a manual (!) setting on the basestation equipment. It’s independent of the CDMA. You would have 
to check the setup at your local tower to know what they have done. You are also dependent on them not changing that 
setting as soon as you leave. Good luck getting any real information along those lines. 

Probably your best bet is an atomic clock of some sort (cheap Rb through Hydrogen maser). The only question is the 
budget being $200 or $200,000 (or something in-between). 

Bob

> On May 12, 2015, at 7:00 PM, Tucek, Joseph <joseph.tucek at hp.com> wrote:
> 
> I'm looking for information on non-GPS time sources.
> 
> For background, I need to provide PTP to a cluster where we don't have line of sight to the sky, and are unlikely to get roof-rights without a fight.  There are CDMA solutions that would work (e.g. Endrun Technologies), but I was wondering if there were any other options.  I either need an indoor capable PTP, or an indoor capable PPS.  Microsemi claims to have an indoor capable "GNSS" system, but I've yet to find a sales rep to talk about it; if anyone has a link to one who can, I'd love to find out the problems^W^W^W^W talk to them about it.
> 
> For an example of something that almost but doesn't quite work, Beagle Software has a CDMA NTP server, but they do neither PTP nor PPS in the CDMA version.  Similarly, Meinberg will sell a PTP unit that freeruns (if you override the config), but they have no solution to discipline via CDMA.
> 
> I'm also curious if anyone has any idea about non-GPS time sync after CDMA gets turned off (can I get time from 4G?).
> 
> My endgame worst case is to just do PPS from a stratum 2 NTP (or even a freerunning oscillator) and lie to my PTP server; hard sync to UTC is a secondary concern so long as the cluster agrees with itself.  Endrun is looking pretty good, but I'd really like to have a second option to compare against.
> 
> -Joe
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