Patent ID: 7551561

Claim:
A packet communication terminal for use in a network system, wherein the network system includes a plurality of communication terminals connected to a single transmission medium, a packet to be sent out on the transmission medium for communication between the communication terminals contains priority information about a priority for sending the packet, and said packet communication terminal comprises: a priority information acquisition section for acquiring priority information contained in a currently transmitting packet being sent out on the transmission medium to a first communication terminal; a first priority determination section for determining which one of a to-be-sent packet and the currently transmitting packet is to be given priority based on priority information contained in the to-be-sent packet which is to be sent to a second communication terminal from said packet communication terminal and the priority information acquired by said priority information acquisition section; an elapsed time measurement section, which has information pertinent to a predetermined time indicating a time during which sending of the to-be-sent packet is given priority over sending of the currently transmitting packet, for measuring an elapsed time starting from when the currently transmitting packet is sent out on the transmission medium and for determining whether or not the elapsed time exceeds the predetermined time; a second priority determination section for determining that the currently transmitting packet is given priority if the first priority determination section determines that the to-be-sent packet is given priority and if the elapsed time measurement section determines that the elapsed time exceeds the predetermined time; a jam signal generation section for generating a jam signal for causing a packet collision on the transmission medium if the first and second priority determination sections determine that the to-be-sent packet is given priority; and a packet sending out section for, if the first and second priority determination sections determine that the to-be-sent packet is given priority, sending out the to-be-sent packet on the transmission medium after the jam signal stops and before the currently transmitting packet is sent out again, and for, if the first and second priority determination sections determine that the currently transmitting packet is given priority, sending out the to-be-sent packet after completing sending of the currently transmitting packet.