Patent ID: 7391754

Claim:
A method for performing handoff of user equipment (UE) connected to a wireless local area network (WLAN) to a mobile communication network in an interworking system between the WLAN and the mobile communication network including a gateway General Packet Radio Service (GPRS) support node (GGSN) and a serving GPRS support node (SGSN), the method comprising: receiving, by the SGSN, a pre-registration request message including a home IP address and an international mobile station identifier (IMSI) of the UE from the UE via the WLAN when the UE determines handoff in response to a link layer trigger while it communicates with the WLAN using a first temporary Internet protocol (IP) address; performing, between the UE and the SGSN, authentication vector generation, authentication for the UE, and encryption key distribution processes based on the IMSI; generating, by the GGSN, a second temporary IP address to be used by the UE in the mobile communication network, and transmitting a first message for requesting registration of the second temporary IP address to a home agent (HA) of the UE; receiving, by the GGSN, a second message indicating registration of the second temporary IP address from the HA of the UE, and transmitting a third message to the UE via the WLAN indicating completion of pre-authentication for the UE and registration of the second temporary IP address; and transmitting, by the UE, a fourth message indicating completion of pre-registration handoff for the UE to the HA of the UE when the handoff of the UE to the mobile communication network is completed.