1 define($OUTPUT "This is a default value for OUTPUT");

     2 define($UNDEFINED "UNDEFINED is an undefined variable");

     3 

     4 // It is mandatory to use an IPRouteTable element with ns-3-click

     5 rt :: LinearIPLookup ();

     6 Idle -> rt;

     7 

     8 output :: Message($OUTPUT);

     9 undefined :: Message($UNDEFINED);