In reply to cuonghl:
You should ALWAYS be able to predict what the response of your DUT will be to the stimulus sent to it. This is what the design specification is for. If you DUT has an input of packets A, B and C, then you predict that it will output packets X, Y, and Z. There should never be any point where you have to decide if the packet received should be X or Y or Z. If you have to make these decisions, then your predictor model for the DUT isn’t detailed enough.