Information transmitting method and information transmitting system

A master station comprising:

• a transmitting unit for transmitting information to slave stations;
• a receiving unit for receiving information from the slave stations;
• and
• a control unit that controls information transmission to the slave stations,
• wherein the control unit:
• determines, on the basis of a packet error rate from the master station to the slave stations, a number of times of multicast transmission in accordance with an expected value of a number of slave stations that transmit retransmission requests, an expected value of a number of retransmitted packets responding to the retransmission requests, or a probability that the slave stations receive all packets forming information,
• notifies the determined number of times of multicast transmission to the slave stations via the transmitting unit,
• transmits same information formed of plural packets to plural slave stations via the transmitting unit in multicast, the determined times of multicast transmission,
• connects unicast connection to a slave station that identifies a lacking packet after receiving information, the notified number of times of multicast transmission,
• receives, from the slave station that receives information in multicast, a retransmission request including an identifier of the lacking packet among packets forming the information by the unicast connection via the receiving unit;
• and
• retransmits a packet corresponding to the identifier of the packet to the slave station by the unicast connection.