Patent ID: 8576729

Claim:
A communication method for a point-to-multipoint communication system including: a main transmission apparatus; a pair of bidirectional lines connected to the main transmission apparatus; and a plurality of subsidiary transmission apparatuses connected to the bidirectional lines, said communication method comprising: on a respective subsidiary transmission apparatus of the plurality of subsidiary transmission apparatuses, transmitting a response request signal, being received by the respective subsidiary transmission apparatus from a downstream subsidiary transmission apparatus, to the main transmission apparatus through an upstream line of the bidirectional lines when a transmission request by the respective subsidiary transmission apparatus to the main transmission apparatus is absent during the receiving of the response request signal by the respective subsidiary transmission apparatus from the downstream subsidiary transmission apparatus, and halting the transmission of the response request signal when a transmission request to the main transmission apparatus is generated by the respective subsidiary transmission apparatus during the receiving of the response request signal by the respective subsidiary transmission apparatus from the downstream subsidiary transmission apparatus, on the main transmission apparatus, sending, while receiving the response request signal through the upstream line, a specified notification signal, which is to be sent out in response to the reception of the response request signal, to a downstream line of the bidirectional lines, and halting, when no longer receiving the response request signal, the sending of the specified notification signal, and on each of the plurality of subsidiary transmission apparatuses, determining, based on the presence or absence of reception of the specified notification signal from the downstream line, whether another subsidiary transmission apparatus uses the upstream line.