owner is 0 this allows the third terminal that is a non owner to transmit the first non owner frame because it is determined that there is no frame to be transmitted by the slot owners in the first slot when the contention window value becomes 0 assuming that the second non owner frame non owner frame 2 that will be transmitted by the fifth terminal that is a non owner of the second slot and the third owner frame owner frame 3 that will be transmitted by a fourth terminal that is a slot owner are sequentially generated while the first non owner frame is transmitted through the first slot and the second slot the fourth terminal and the fifth terminal that will transmit the two frames perform contention for ensuring a channel and each sets a contention window in this process since the fourth terminal that is a slot owner of the second slot selects a contention window value that is smaller than that of the fifth terminal that is a non owner it can preferentially transmit a frame even if the third owner frame that will be transmitted by the fourth terminal is generated later than the second non owner frame accordingly the third owner frame that will be transmitted by the fourth terminal is firstly transmitted further the fifth terminal that is.