|Documents Home :: 4.2.8p2 :: ntpdsim.html
All in a row.
Last update: 11-Sep-2010 05:55 UTC
The ntpdsim program is an adaptation of the ntpd operating system daemon. The program operates as a discrete time simulator using specified systematic and random driving sources. It includes all the mitigation and discipline algorithms of the actual daemon, but with the packet I/O and system clock algorithms driven by simulation. Most functions of the real ntpd remain intact, including the monitoring, statistics recording, trace and host name resolution features. Further information on the simulator is on the NTP Discrete Event Simulator page.
The simulator is most useful to study NTP behavior in response to time and/or frequency transients under specific conditions of network jitter and oscillator wander. For this purpose the daemon can be driven by pseudorandom jitter and wander sample sequences characteristic of real networks and oscillators. The jitter generator produces samples from a Poisson distribution, while the wander generator produces samples from a Guassian distribution.
The easiest way to use this program is to create a ntpstats directory, configuration file ntp.conf and frequency file ntp.drift and test shell test.sh in the base directory. The ntp.drift file and ntpstats directory can be empty to start. The test.sh script can contain something like
rm ./ntpstats/* ntpdsim -O 0.1 -C .001 -T 400 -W 1 -c ./ntp.conf,
which starts the simulator with a time offset 100 ms, network jitter 1 ms, frequency offset 400 PPM and oscillator wander 1 PPM/s. These parameters represent typical conditions with modern workstations on a Ethernet LAN. The ntp.conf file should contain something like
disable kernel server pogo driftfile ./ntp.drift statsdir ./ntpstats/ filegen loopstats type day enable filegen peerstats type day enable