Patent ID: 7586939

Claim:
A packet relay device in a network system supporting a mobile computer that is capable of carrying out communications while moving over a plurality of interconnected networks, for relaying packets having an address of the mobile computer as a destination or source, the packet relay device comprising: a packet receiving unit configured to receive a packet in a first format using a global address which is transmitted by the mobile computer for a location registration at a home network from a visited site managed by a global address system which is valid throughout the interconnected networks, the packet being transmitted by using a global address of the packet relay device, and to check a content of the packet; and a packet transfer unit configured to transfer the packet in a second format using a private address, to a correspondent computer in the home network of the mobile computer managed by a private address system which is valid only within the home network according to the content of the packet, the packet being transferred by using a private address of the correspondent computer which is different from the packet relay device identified by the global address of the packet received by the packet receiving unit; wherein the packet receiving unit decrypts the packet received from the mobile computer at the visited site using a key corresponding to the mobile computer, and the packet transfer unit re-encrypts a decrypted packet using a key corresponding to the correspondent computer, encapsulates an encrypted packet by attaching a header having a private address of the packet relay device as a source and a private address of the correspondent computer as a destination, and transfers an encapsulated packet to the correspondent computer.