fares,
In order to connect to the pc you must have an external address to connect to (in the world of ip at least) so if the internal ip address is one of the private ones (192.168.x.x for class c which is pretty typical) you MUST have an "outside" address/port to connect to that is then mapped to the internal address/port. Everyones answers thus far have been on the mark - perhaps you may need to rephrase the question
/JD