A method used in a network device for outputting data to a bus with a data bus width at each cycle includes: using a packet generator for generating idle data after an end of packet for a packet at a cycle and generating a start of packet for a next packet at a different cycle; and using an inter-packet gap (IPG) generator for receiving data transmitted from the packet generator, dynamically writing the received data into the buffer, and inserting a gap of idle data between the end of packet and the start of packet according to the end of packet and the idle data generated by the packet generator.