); SAEximRunCond expanded to false Errors-To: [EMAIL PROTECTED] RETRY From: John Ackermann N8UR <[EMAIL PROTECTED]> Subject: Re: [time-nuts] Basic Stratum 1 question Date: Thu, 02 Aug 2007 11:56:51 -0400 Message-ID: <[EMAIL PROTECTED]>
> ); SAEximRunCond expanded to false > Errors-To: [EMAIL PROTECTED] RETRY > > Jared Morrisen wrote: > > ); SAEximRunCond expanded to false > > Errors-To: [EMAIL PROTECTED] RETRY > > > > Hi, > > > > I am having a debate with our CIO. He wrote in a memo about timing: > > > > *Local hardware is to be considered Stratum 1, since it get time from its > > own CMOS.* > > > > > > > > I told him that absurd and that it can't be considered stratum 1. > > Hi Jared -- > > I don't want to get in the middle of that argument! > > However, note that there are two different definitions of "Stratum 1" > floating around. ... at least, and within the synchronisation community. The stratum as such only significance a hierarchial order. > In the NTP sense, it is nearness to a reference clock that > (theoretically) provides time traceable to a national institute. So an > NTP "stratum 1" server is one that is directly connected to a reference > clock. (Check the NTP website; I'm sure you'll be able to find a more > formal version of that definition somewhere there.) The NTP Stratum meaning is really a hop-count measure, a metric. > But in the telecom industry, "Stratum 1" signifies a certain level of > timing performance, and I suppose that some computer system somewhere in > the world might be able to meet that standard for some period of time. > Someone else will be able to tell you just what the definition of > Stratum 1 is. The SONET Stratum numbers indicate the level of clocks being interconnected: Stratum 1 - Primary Reference Clock (i.e. Cesium, Hydrogen or GPS) +/- 1E-11 in frequency relative UTC Stratum 2 - Station clock (i.e. high quality OCXO or Rb-cells) Stratum 3 - Equipment clock (i.e. good OCXO or very good TCXO) +/- 4.6E-6 in frequency Stratum 4 - Line clocks +/- 20E-6 in frequency You always (in the ideal) try to hold-over from the lowest stratum, i.e. the highest stability. A lower Stratum clock does not listen to a higher stratum clocks holdover, but it will certainly listen to it when it is locked directly or indirectly to a clock of same or lower stratum number. These Stratum concepts are quite different and it is unfortunate that they coexist and help confusing the issues. An NTP Statum 1 clock can be either a very high quality one or one of very low quality. The NTP Stratum number says nothing as such about stability and correctness in tracking relative UTC. > So the real question is which of those definitions is your CIO using? > Based on that, you should be able to answer that either (a) local CMOS > isn't a reference clock traceable to a national institute, or (b) that > the CMOS clock isn't certified to meet telecom Stratus 1 standards. > > Of course, if his point is that one local free-running clock is the > "master" and that he cares only about synchronization, not accuracy, > across the network, then he might be making sense. But he's not using > the terminology correctly. Indeed. For some purposes all you need is to have the same time scale, regardless if that matches the surrounding world or not. Cheers, Magnus _______________________________________________ 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.
