Patent ID: 7596136

Claim:
A data communication apparatus in a first local network, the data communication apparatus comprising: a communication unit configured to carry out data communication with a first other data communication apparatus in the first local network and with a second other data communication apparatus in a second local network, the communication unit configured to carry out data communication using a local network address for allowing communication with the first other data communication apparatus in the first local network and carry out data communication using a global network address for allowing communication with the first other data communication apparatus in the first local network and the second other data communication apparatus in the second local network; a detection unit configured to detect a connection request from another data communication apparatus; a control unit configured to control the communication unit to carry out data communication with the another data communication apparatus using a local network address when the another data communication apparatus sending the connection request detected by the detection unit employs a global network address and is located in the first local network; an address change requesting unit configured to request the another data communication apparatus to employ a local network address when the another data communication apparatus sending the connection request detected by the detection unit is located in the first local network and sends the connection request using a global network address; and a network address acquiring unit configured to acquire the first local network address of the another data communication apparatus based on a response from the another communication apparatus to the request from the address change requesting unit; wherein, when the network address acquiring unit acquires the local network address of the another communication apparatus, the control unit is configured to carry out control to disconnect a connection between the communication unit and the another data communication apparatus using a global network address and to establish connection again between the communication unit and the another data communication apparatus using the local network address so as to resume communication.