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 ) **************************************** * Environment Test Configuration * **************************************** GPS || \/ Derived PPS on a cable conneted to the serial port of Stratum 1 pc || \/ Stratum 1 PC with ntpd running || \/ Ethernet Cable || \/ Stratum 2 PC with ntpd running || \/ Output PPS signal passing by parallel port pin || \/ Measure Instrument with GPS Ref. Clock ************************************************************** Thanks in advance, Best Regards, Elio _______________________________________________ questions mailing list [email protected] https://lists.ntp.org/mailman/listinfo/questions
