PURPOSE: To vary the number of times of retransmission at transmission fault in response to the state and traffic of a transmission line by providing a transmission fault cause detection means detecting the cause to fault at each fault and a number of times of retransmission setting means setting the number of times of retransmission in response to the transmission fault cause.
CONSTITUTION: A power line carrier module (9) detects collision or transmisison data error as a transmission fault cause, and when the cause to transmission fault is collision, it is judged that the traffic on the transmission line is large and the number of times of retransmission is set to four times which is a small value so as not to increase the traffic more. In contrast, when th cause to transmission fault is transmission error, the number of time of retransmission is set to 8 times, which is a large value to improve the sure transmission performance. A power line carrier module (8) sends data again and when the transmission is successful or the retransmission counter is '0', the transmission processing is finished. In other cases, the retransmission counter is decremented, the step is restored to the transmission control section and the retransmission is repeated until the set number of times of retransmission.
KUSHIRO NORIYUKI
MARUYAMA KAZUHIRO
