[ns] Use of "switch-treetype" under some conditions

[Andrea Josi <cmoncharlie@tiscalinet.it>]

Hi everybody,
i  have a very poor experience in writing tcl scripts, therefore i need
to put  a question about the centralized multicast routing protocol
implemented in NS , version 2.1b7:
is it possible to make the switch from shared tree to source specific
happen under certain conditions?
for instance, i would like such a transition to happen when the rate of
a given source exceeds a certain
threshold;
I wish that this is something that can be done with Tcl!
Thanks in advance,
                                   Andrea.