Miroslav,
You don't need to read the code, just the documentation. The ntpdsim is
what the literature calls a probabilistic discrete event simulator
(PDES). It provides a virtual environment including multiple servers and
simulated network behavior within which the actual ntpd code runs.
Everything, including packet send and receive, is simulated independent
of operating system. It runs hundreds of times faster than the real
system. It is indent is to study the synchronization behavior under
low-probabiliy and long-baseline conditions. It is not a simple system;
it simulates the actual conditions in a real world, multiple server
environment and provides the same error reports, statistics reports and
synchronization data as the real system..
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.
Dave
Miroslav Lichvar wrote:
On Mon, Jun 28, 2010 at 05:35:34PM +0000, David L. Mills wrote:
How is your simulator different than the one included in the NTP
software distribution?
If I read the code correctly, ntpdsim simulates inside ntpd a
minimalistic NTP server (or multiple servers) with configured wander
and network delay, and an ideal local clock.
clknetsim simulates clocks and a network to which are connected
unmodified ntpd daemons. The simulation is transparent for them. With
symbol preloading (dynamic linker's LD_PRELOAD variable) they don't
use the real system calls like sendto(), recvfrom(), select(),
gettimeofday(), ntp_adjtime(), but they use the symbols provided by
clknetsim instead. The system calls are passed to the clknetsim
server, which synchronizes all events, adjusts the clocks, forwards
NTP packets and monitors the real time and frequency offsets of the
virtual clocks.
So, for a simulation similar to ntpdsim, at least two ntpd daemons
have to be connected to clknetsim, one configured as a server with
LOCAL clock (adding a refclock source is on my todo list) and a client
which will be the subject of testing.
The advantage of this approach is that it allows you to test pretty
much anything that can be tested in a real network, a chain of NTP
servers (few such tests are on the clknetsim webpage), server/peer
modes, broadcast modes, authentication, compatibility with older
versions or different NTP implementations, etc.
The disadvantage is that the simulation runs slower.
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