Hi Chih-Yuan Lee, The TIME which user provides using -t option is not the Timeout. It goes like this. 1) Read the Amout of data coming in/going out, Let it be X 2) Wait for TIME watever the user specified using -t option. 3) Again repeat the Step (1), Let it be Y Then calculate the Bandwidth using X and Y. Hope this helps.. ~Regards Ujwal Trivedi