Patent ID: 7136368

Claim:
A communication system, comprising: a mobile terminal device capable of accessing both a mobile communication network and a local network simultaneously; and a gateway device provided between a fixed communication network and the local network; the mobile terminal device having, an inquiry message transmission unit configured to transmit an inquiry message to the gateway device for inquiring information regarding a location on networks of a correspondent of packet communications to be carried out, through the local network; the gateway device having, a lookup unit configured to carry out a lookup processing to determine whether the location of the correspondent on networks is on the local network, or within same management domain on the fixed communication network as the mobile terminal device and outside the local network, or outside the same management domain on the fixed communication network, upon receiving the inquiry message from the mobile terminal device through the local network, and a transmission unit configured to transmit the location of the correspondent on networks as a result of the lookup processing obtained by the lookup unit as a response message to the mobile terminal device through the local network; and the mobile terminal device also having, an address assignment unit configured to receive the response message from the gateway device through the local network, acquire an address of the correspondent to be used by the mobile terminal device in the packet communications with the correspondent according to the response message, and assign the address to a communication interface for the local network.