[ns] with wired and wireless links on, sending data on own desired link for over layered application routing protocol

I am working on overlayered application layer routing protocol,with
wired as well as wireless links (interfaces) working between them.but data is
sent on both interfaces at same time, i want that a parameter should
be passed within cc code not from tcl script that could control all
this process.how to switch between these two interfaces, so that i
could send on my own desire,i-e on which argument it should forward
this traffic onwards
thanks