A communication scheme for supporting data transfer to a visited site of a mobile terminal which moves across a private network operated by a private address system and an Internet operated by a global address system is disclosed. When the mobile terminal has moved from the first network to the second network, packets destined to an original home address of the mobile terminal on the first subnet are transferred from the first router device in the first subnet by setting an address of the first interface of a packet relay device as a care-of address of the mobile terminal. Then, the packets received by the packet relay device from the first router device at the first interface are transferred to the second router device in the second subnet through the second interface of the packet relay device, and the packets received by the second router device from the packet relay device are transferred to a current location address of the mobile terminal.