On Tue, Jun 29, 2010 at 06:31:01PM +0000, David L. Mills wrote: > From your description your simulator is designed to do something > else, but what else is not clear from your messages. It might help > to describe an experiment using your simulator and show what results > it produces.
It's designed to test NTP implementations, but it uses a more general approach. Ntpdsim tests ntpd as an NTP client with simulated NTP servers in a simulated network. Clknetsim doesn't simulate NTP servers, it simulates only a network to which are connected real NTP clients and servers. The difference is that ntpdsim tests one NTP client and clknetsim tests whole NTP network. Say we want to test how does the Linux SHIFT_PLL change affect an NTP network. There is a chain of seven ntpd daemons configured, all using poll 6. Strata 1, 3, 5, 7 have SHIFT_PLL 2 and strata 2, 4, 6 have SHIFT_PLL 4. Stratum 1 has clock with zero wander and frequency offset and is using the LOCAL driver, the rest have clocks with 1ppb/s wander. Between all nodes is network delay with exponential distribution and a constant jitter. The simulations are repeated with jitter starting from 10 microseconds and increased to 0.1 second in 28 steps. Each simulation is 4000000 seconds long and the result is a list of RMS offsets, one for each stratum. After finishing all iterations, we'll make an RMS offset/jitter plot: http://fedorapeople.org/~mlichvar/clknetsim/test5_ntp2.png And the same experiment with all strata using SHIFT_PLL 4: http://fedorapeople.org/~mlichvar/clknetsim/test5_ntp.png You probably know what to expect here, but I was surprised to see that with high jitter the SHIFT_PLL 4 strata are actually better than their SHIFT_PLL 2 sources. -- Miroslav Lichvar _______________________________________________ questions mailing list [email protected] http://lists.ntp.org/listinfo/questions
