[ns] From where Connector::drop_ is initialized .?

Dear all,

We know in function Connector::drop(Packet* p, const char *s), if
*drop_* iszero then it will pass the packet to the object using
*drop_*->recv(p,s).
I want to know *where* and *when* it was *initialized*?

Hoping for the best help asap.

*p.s.* : It is clear to me that when we set up a simple simulation, we do
not write for the initialization of the drop_. Although it is initialized.
So I am asking about the insight.

-- Pathik Shah