Antonio M. Moreiras wrote: > The Cesium clock at observatorio nacional (ON) is UTC. In fact, the ON > is one of the metrology laboratories that colaborates with the Bureau > International des Poids et Measures (BIPM) in generating the UTC (as > NIST does in USA, for example). > > The Rubidium clocks are synchronized with the UTC at least one time per > year and the manufacturer says that the Rubidum reference has a monthly > aging less than 5e-11 and a yearly aging less than 5e-10. > > It gives us a 16ms maximum discrepancy from UTC (31,536,000,000 ms/year > * 5e-10 * 1 year = 15.765ms - is this correct?) > > After one year, with the discrepancy at 16ms it will be probabily of the > same order than the half round trip time for the majority of the clients. > > Given this, do you you think it will be necessary any modification? > > If so, what would be the maximum discrepancy allowed to not need any > modifications? As the primary servers are appliances from Symmetrycom or > Spectracom probabily it will be very difficult to get customized > firmware versions... Maybe we should study the possibility of > synchronize the Rubidium reference clocks more frequently with UTC. > > I don´t know if I correctly understood what this discrepancy can cause. > If a client is using other sources attached directly to GPSs, for > example, there is a risk that our servers being considered falsetickers. > Is it? Or is there other problems? > > A discrepancy of 16ms in a Internet NTP primary server is acceptable? > > In Brazil time stamps should be less than 100ms accurate to be legaly > valid (for financial or government institutions, for example). I think > it is the same in other parts of the world. Then, 16ms appears to > reasonable for an Internet service. > > The majority of the Internet NTP primary servers are GPS based. For > curiosity: what is the discrepancy of GPS time from UTC (without > considering the leap seconds)? >
Be aware that GPS is run by US satellites and their clocks are synchronized to US UTC provided by the US Government agency NIST. I have no idea how this may differ from that provided by the Braziian Government ot BIPM for that matter. Danny > []s > Antonio M. Moreiras. _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
