[EMAIL PROTECTED] wrote: > Hi , > > On 8 Ott, 22:06, "David L. Mills" <[EMAIL PROTECTED]> wrote: > >>The performance with ntpd running in a rusting Pentium hulk with several >>hundred clients and PPS is surprisingly good. Our rackety.udel.edu runs >>FreeBSD 6.1 with PPS via the parallel port. It usually shows residual >>offset and jitter in the order of a few microseconds. It is good enough >>that the daily variations in the air-conditioned machine room >>temperature can be measured accurately. >> >>Measuring the PPS offset within a few hundred nanoseconds is brilliant; >>however, the measured latency to read the system clock from an >>application is in the order of a microsecond and this polluted by >>context switches, cache misses, timer interrupts, etc. > > > I work for a big international telecom Company (Number 1 in Mobile) > and I think that I have to give you more details of our Company > project that could use NTP technology. > In this moment we're making our tests with NTP on a test pc, but our > aim is to run NTP on our telecom blades which have onboard their own > processor and an embedded linux OS. > These blades will get a PPS signal derived from a GPS and, thanks to > ntpd daemon, will synchronize their local time. > These "Stratum 1" blades will send to other (Stratum 2) blades NTP > messages, so the question is: > > - is the precision of these "messages" (or timestemps) affected by the > stability of the local oscillator ? > > The application will run in a MAN corporate network where packet > delays should be small compared to the Internet delays. So it could be > worth to enhance the accuracy of the timestemps provided by the ntp > stratum1 server; than the second question is: > > - which kind of accuracy can we reach enhancing the stability of the > oscillator ? (nanoseconds? ) > (note that we already use high stability oscillator inside the > equipment, that could also feed the processor clock) > > The same question at client side is: > > - which accuracy of local clock can we expect using high stability > oscillators? (we have measured around 60 microseconds peak-to-peak, > using standard crystal in *environment test* configuration- see > below ) <snip>
The accuracy on the clients depends on, more than anything else, the network connection between them and the server. With a 100 MB LAN the delay and, therefore, the uncertainty should be on the order of 1 millisecond. The stability of the oscillator has very little to do with it; NTP disciplines the local clock and will compensate for any drift in the oscillator. If you really need synchronization to less than 1 millisecond between clients, you need to consider something like a PPS signal sent to each client and compensating for speed of light delays in each length of cable! _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
