To enable a terminal device to detect communication failure between a communication control apparatus and an object device, and make it possible to achieve failure detection with high communication efficiency.
A monitor device 15, a VPN server 35 and a first center device 13a correspond to a terminal device, a communication control apparatus and an object device, respectively. The communication control apparatus transmits/receives a first communication acknowledgement signal to/from the terminal device, and a second communication acknowledgement signal to/from the object device. The communication control apparatus achieves addition of failure information to the first communication acknowledgement signal transmitted from the communication control apparatus to the terminal device when it does not receive the second communication acknowledgment signal from the object device. The terminal device can detect communication failure between the communication control apparatus and the object device from the failure information added to the received first communication acknowledgement signal.
COPYRIGHT: (C)2011,JPO&INPIT
Masayuki Fujisawa
Tatsuo Yoshida
Kazuo Tsunemine
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