edouard funke wrote: > Hi, > > I am running several (less than 30) servers on LAN with these restrictions : > - no Internet > - Windows XP/2003 > - no GPS possible > - I need less than a millisecond accuracy. >
Submillisecond requires a refclock at a minimum. On a network even with a refclock it's hard to achieve. If you can't get outside information such as from GPS then you may have to go for an atomic clock onsite. That's all very expensive. If you have this as a requirement for whatever it is that you are doing then you need to have the kind of money to spend on doing it. Nothing is free. The tighter your requirements the more you need to spend to achieve them. For Windows you will need to use ntpd and not w32ts since that cannot discipline the clock like ntpd. > 5 of them are on the same switch and two in an other building. Latency > between buildings is less than 20ms. There _might_ be an internal NTP > server synchronised to a server on internet but let say i dont have to > count on it. > You should be setting up multiple ntpd servers in each building so you are not too dependent on the network between. You assume that the latency is enough but network congestion between the buildings and just within the building will cause delays that will show up in the received packets. ntpd is good at dealing with these kinds of issues but it will reduce the perceived precision of the results. > If : > - i choose one "good" server as my time reference (local clock) and > synchronised all the other clients to it > > - i put all servers in peer mode > > - i put a pci card that uses a TCXO to replace the hardware clock (any > known vendors ? i dont care about GPS sync) > > - limit maxpoll (what is the impact ?) > > - change OS (again what is the impact ?) > Do you need everything to be in relative agreement with each other? You certainly should have more than one server involved in this, in this case at least 4 so that if one drops out for any reason (reboot, maintenance, hardware problems, etc.) you still have 3 left for ntpd to make a decision on which peer is giving the best information. Do NOT modify maxpoll or minpool, it will cause more problems than you expect since the algorithms use them do discipline the clock in a way that provides the best convergence and keeps down overshoot. You really need to understand how the algorithms work and your environment before you mess with the polling intervals. > is the accuracy of a millisecond "achievable" in those conditions ? If > not, what can i do to achieve it ? Under those conditions, no. Not with a multi-LAN network. You would need to set up multiple ntpd servers in each location to get something close to what you need. Danny _______________________________________________ questions mailing list [email protected] https://lists.ntp.isc.org/mailman/listinfo/questions
