[ntp:questions] Re: NTP Protocol Characterization

David L. Mills mills at udel.edu
Tue Aug 12 17:35:51 UTC 2003


Emmanuel,

The NTP simulator is in the latest version. You need to configure with a
--enable-simulator option. The command line flags are listed in the
documentation. The network noise generators simulate network jitter
(exponential) and oscillator wander (random walk). But, the simulator
does only one server and no packet loss or misordering.

You can open the clock discipline feedback loop with an "disable ntp"
command in the configuration file. See the miscellaneous options page
for more kinky things.

In the very latest version the noselect option on the peer/server
command line has been fixed. With that option on the test machine,
configure the GPS driver and the other PC with the GPS driver as well.
Do not use the "disable ntp" command. The test machine will synchronize
to the other PC and log the peerstats for that machine as well as the
GPS derver for comparison, but the GPS driver will not affect the system
clock.

Dave 

Emmanuel Tychon wrote:
> 
> Folks,
> 
> I am looking for a way to analyse NTP's performance under various
> network conditions like jitter, latency, packet loss, misordering,
> and so on.
> 
> I have two different ideas in mind:
> 
>   - I have seen on ntp.org a reference to a tool called 'ntpdsim'.
>     However, I can't find this tool in the distribution. Then, this
>     lead to the other solution ....
> 
>   - Using two PCs, each of them synchronized with GPS clock. Between
>     those PCs, I also run NTP through a network impairement generator
>     like PacketStorm. Then I compare the NTP-time with the GPS-time.
>     How can I compare my GPS-time and NTP-time? Is is possible to
>     have ntpd running without touching the system clock?
> 
> Thanks for your attention,
> Emmanuel



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