node 23 wakes from the sleep mode to enter to a working status it transmits a request signal to the transferring node 28 a transmitting path 2 d is shown in fig4 the transferring node 28 determines whether the packet exists or not by checking the pending flag corresponding to the request signal when the transferring node 28 determines that the packet does not exist it will transmit an ending packet to the receiving node 23 a transmitting path 2 e for transmitting the ending packet is shown in fig5 then the receiving node 23 returns to the sleep mode when it receives the ending packet preferably the ending packet is a packet with zero length when the transferring node 28 determines that the packet exists the transferring node 28 transmits a retrieving command packet to the coordinator 20 after the coordinator 20 receives the retrieving command packet the coordinator 20 would check all packets which are corresponding to the retrieving command packet and transmit them to the receiving node 23 subsequently the coordinator 20 transmits an ending packet to the receiving node 23 similarly the receiving node 23 returns to the sleep mode corresponding to the ending packet and the ending packet is a packet with zero length in a preferred embodiment the second embodiment of the present invention.