Patent ID: 7519363

Claim:
In data communication in a WLAN and/or a cellular network using a mobile IP system, a roaming method between the WLAN and the cellular network, comprising: a first step wherein a packet data serving node of the cellular network which detects the current location of a specific mobile terminal provides a con-inform message to an access point managing means associated with an access point of the WLAN located in a current service area of the mobile terminal, the con-inform message including information on a current access state of the mobile terminal, wherein the access point managing means is notified of information on a current access state of the mobile terminal prior to the mobile terminal accessing the access point; a second step wherein the access point managing means associated with the access point which the mobile terminal newly accesses requests address renewal to replace an address of the packet data serving node by its address, allocates an IP address to the mobile terminal according to the renewal result, and provides a con-notify message to the packet data serving node the con-notify message including the IP address; and a third step wherein the packet data serving node which receives the con-notify message from the access point managing means transmits data obtained during the roaming due to the movement to the access point managing means of the WLAN from the packet data serving node of the cellular network, whereby the roaming is performed from the cellular network to the WLAN.