how to use $ns create-trace type file src dst op

Hi all,

Can anyone help me in using this command?

Suppose my topology is
s0
\
r1==r2==d0
//
s1

I don’t know where I should put this command in my script.

If I want to get statistics of drops btw link s0 and d0, should I do things like:

set ns [new Simulator]
$ns create-trace Drop file s0 d0

and then the creating nodes, links, sources part?

I think I missed something… also, what should the “file” be?

Thanks for any advice!