Unruh wrote: > Andy Yates <[email protected]> writes: > >> Hal Murray wrote: >>> In article <[email protected]>, >>> Andy Yates <[email protected]> writes: >>>> Does anybody have any figures that shows the effect on accuracy of an >>>> NTP v3 client using a stratum 1 server rather than a stratum 2 or 3 >>>> server? It's all in a GE LAN based scenario, commercial stratum 1 >>>> servers connected to GPS and stratum 2 and 3 servers are typically >>>> dedicated Linux boxes. >>>> However I'm been pressed to supply an SLA for accuracy. My argument is >>>> that although you can get your stratum one server to synchronize to >>>> microseconds of UTP, as soon as the client uses NTP v3 over the LAN, >>>> even a GE LAN, then the accuracy degrades and putting well designed well >>>> specified stratum between the boxes is not going to decrease accuracy >>>> sufficiently to warrant purchasing many stratum one appliances. >>> What sort of accuracy are you interested in? 1 ms? 10 ms? 100 ms? > >> Hi Hal > >> Its up to us to specify what we think the SLA should be - the guide is >> "as accurate as possible"! > > That is of course completely idiotic. They do NOT want it as accurate as > possible. That would cost them millions of dollars and is not in fact > needed. What are they using the time for? what kind of machines are they > ( Windows, linux, BSD, special home grown OS?) > > >>> How stable is your temperature? (Both the room and the CPU load.) > > ntp is terrible if anything varies ( absurdly long settling times). > > >> Temperature will be very stable, the DC is the very well specified and >> scrupulously engineered - no cables blocking air flow etc. Generally >> speaking the CPU is over specified. > >>> What is the load on the LAN between the clients and servers? >>> (Delay is not a problem. Variation in delay is a problem.) >> The NTP will be on a separate management LAN to the production traffic >> so not subject to the variances that application load has on the network. >>> >>> I suggest you measure it. Start with your current system. >>> >>> Setup a box as a ntpd system and tell it to use several target boxes >>> as servers and turn on logging. peerstats will tell you the difference >>> between your local clock and the target system. >>> >> I'll look at the current NTP infrastructure however its completely >> different to the new. The old has 3 geographically diverse GPS receivers >> plus a GPS and radio source on the roof of the data centre and we use >> network components to provide the intermediate strata between stratum >> one and client - and have not really had many issues after almost 10 >> years of use. However, requirements are changing and we will probably be >> using dedicated stratum 2/3 servers as required. > > Does teh GPS have PPS ( puse per second) or are they just using the nmea > time signal? Radio about as bad as GPS with just NMEA for timing. > > Hi Unruh
it uses IRIG-B but can use PPS amongst others - However I should have said "as accurate as possible using a well designed NTP system". Our stratum zero sources and stratum 1 sources will be v.accurate - its the distribution via NTP that were trying to get our heads around. Regards Andy _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
