PURPOSE:To give all terminal devices an even opportunity for making access to a transmission line by giving its own terminal device and other terminal devices positioned to lower ranks of the transmission line than its own terminal device priority for making access to the transmission line when traffic concentration is recognized at its own terminal device. CONSTITUTION:A transmission request controlling section 19 always compares the transmission request traffic from each terminal device at higher- and lower- rank positions of a transmission line A than this terminal device 11 with the transmission request traffic from the device 11 and, when the compared value exceeds both of a prefixed higher and lower thresholds, the section 19 randomly outputs virtual transmission requests to a transmission line interface section 11b at a fixed rate corresponding to the transmission request traffics of all terminals device at lower-rank position of the transmission line A by considering that transmission request traffics are concentrated to the device 11 so as to allow the terminal devices at lower-rank positions of the transmission line A than the device 11 to make access to the transmission line A earlier than the terminals device at higher-rank positions.
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