Patent ID: 7403518

Claim:
A packet communication system, comprising: a master station configured to transmit a downstream packet signal including identification information for identifying transmission permission without receiving a transmission request; and a slave station configured to receive the downstream packet signal transmitted from the master station and judge if transmission is permitted based on the identification information in the received downstream packet signal, wherein the slave station is configured to transmit an upstream packet signal to the master station when the slave station judges that transmission is permitted, the master station includes a first timer configured to measure a limit time when the master station can judge if the upstream packet signal has been transmitted from the slave station to which transmission is permitted, the master station is configured to judge if the upstream packet signal transmitted from the slave station is received within the limit time measured by the first timer, stops the first timer when the master station has received the upstream packet signal, and updates the identification information for identifying transmission permission when the master station has not received the upstream packet signal, the master station includes a second timer configured to measure limit time when the master station can continuously receive the upstream packet signal transmitted from the slave station to which transmission has been permitted, and the master station judges if receipt of the upstream packet signal transmitted from the slave station has ended within the limit time measured by the second timer, stops the second timer when the receipt has ended, and updates the identification information for identifying transmission permission when the receipt has not ended.