On 5/12/2015 6:00 PM, Tucek, Joseph 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 LTE and WCDMA both provide time, but it's a function of how carefully the operators actually maintain it. That's less of a problem today, but there are no absolute /guarantees/, even with IS-95 CDMA. The only guarantee is that the basestations in the system will track within a few microseconds of each other.
What you don't say is how much accuracy you need. Is a hundred milliseconds enough, or do you need sub-microsecond absolute accuracy? How much holdover accuracy do you need? These are considerably different probelms. You indicate that you need to provide PTP to a 'cluster.' Is relative accuracy within the cluster all that's important, or do you need to coordinate with the outside? If so, there are a host of other considerations. Too many applications grossly over specify some requirements in the name of safety and miss critical performance needs. More information might let the group a more complete answer. -- mailto:[email protected] Oz POB 93167 Southlake, TX 76092 (Near DFW Airport) _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
