Thanks, it is used by Middle and high schools across the country, tech schools and many other businesses. The goal is to get kids excited about technology but we find a lot of people just want to know more about a technology that touches their everyday life. Glad you enjoyed it.
db > On Oct 31, 2020, at 5:24 PM, Bryan _ <bpl...@outlook.com> wrote: > > Great tutorial read on fiber in your website. > > -=Bryan=- > > ________________________________ > From: time-nuts <time-nuts-boun...@lists.febo.com> on behalf of The Fiber > Guru <fiber.g...@fiber.guru> > Sent: October 31, 2020 9:29 AM > To: Discussion of precise time and frequency measurement > <time-nuts@lists.febo.com> > Subject: Re: [time-nuts] Changes in commercial GPS clocks over the decades > > Yes, prior to use of GPS to discipline the Local oscillator, telecom timing > was a “trickle down” topology where a cesium source in Kansas City was > distributed across the continent. > > The cesium was the gold standard and as the timing signals cascaded to > distant geographical regions, it was obviously less pure, so if cesium was at > Stratum 1 (stability), the next element in line that mediated time of > downstream was at Stratum 2. As it arrived at your local telco central > office, it was at Stratum 4 (ok, but useless in today sadly networks). > > Enter GPS and instantly every local central office could achieve Stratum 1 > traceability, and if GPS was lost the best Rubidium's could holdover at > Stratum 2e (slightly better that Stratum 2). If the clock had OCXO, holdover > was Stratum 3 or 3e depending on the quality of the oscillator. > > Stratum levels are reported to most network elements by embedding the Stratum > value message in the Facility Data Link of an ESF T1 signal. The network > element would read the Stratum level from the incoming timing signal to > determine if it should lock to the signal, or fall back to its internal > clock, usually an ocxo at Stratum 3. > > If the master GPS clock suffered loss of GPS and the backup oscillator > deteriorated to a low stability, the clock would generate a message to the > connected elements that said “Don’t Use Me” (DUS). This method is called, > “Sync Status Messaging/SSM”, and also carry’s over to the latest packet > timing designs so that subtending elements always know the pedigree of a > timing/sync signals. > > It is notable that, while SSM provides a label as to the purported pedigree > (stableness) of the timing signal, it is no guarantee the signal is actually > as stable as reported, but generally it is truth. > > This has been my world for several decades so please let me know if this > information is not usef _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.
