[ns] Calculate err rate: track lost packets

Hi, Can some one please guide me how can we keep track of which packets are drops and how many were the total number of packets in one of the communication links. Need this information for formulating an error model for a certain type of traffic under certain network conditions over the WLA

[ns] Variable size packet

Hi, Can some one please guide me how can I implement the scenario of variable packet size in a communication link between two nodes. Actually, want to simulate video data that has packets of different lengths. Looking forward to get some helpful advice here. Regards Nasir Sa