PROBLEM TO BE SOLVED: To alleviate a load of transmission on a terminal while securing reliability when data packets having the same contents are transmitted to a plurality of terminals.;SOLUTION: A first terminal holds a reception confirmation check list comprising a plurality of second terminals as entries, holds a data packet as an original packet and makes a timer start clocking when transmitting the data packet, sets the respective entries of the reception confirmation list to a non-reception-confirmation state, updates a corresponding entry of the reception confirmation list to a reception-confirmation state when receiving a reception confirmation packet from a second terminal, and retransmits the original packet only to a terminal that the reception confirmation check list indicates as a terminal in the non-reception-confirmation state and makes the timer clock again when the clocking result of the timer indicates that a predetermined time passes. The first terminal discards the original packet and stops the timer from clocking when all the entries are in the reception-confirmation state.;COPYRIGHT: (C)2008,JPO&INPIT
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