| 摘要 |
PROBLEM TO BE SOLVED: To enable a receiving side user to grasp that communication is not established in data communication between radio communication terminal devices. SOLUTION: A portable terminal 30 located outside a vehicle exchanges data composed of packets with a car navigator 10 having a communication unit 11 loaded on a vehicle VL. When receiving of data from the portable terminal 30 is started, the car navigator 10 monitors a receiving state for each packet and when the communication is cut off in the middle of the packet or when the communication is cut off without receiving the final packet in the packets comprising the data, the signal of data receiving error is transmitted to a display device 12 of the car navigator and the portable terminal 30. By displaying such a caution, the user can immediately improve a communication environment on the receiving side by changing the position of the vehicle or can transmit data again on the transmitting side.
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