An active handoff system and method of a dual mode terminal capable of
connecting to a wireless network, such as wireless local area network
(LAN), and a mobile communication system are provided. The handoff method
includes the steps of assigning, at a packet data service node of the
mobile communication system, an IP address to the dual mode terminal
connected to the service network, establishing, at the packet data
service node, a tunneling path to the wireless LAN when the dual mode
terminal moves from the mobile communication network to the wireless LAN,
and disconnecting, at the packet data service node, the tunneling path to
the wireless LAN, and establishing a tunneling path to another packet
data service node whose Internet Protocol (IP) address has been
established by the packet data service node, when the dual mode terminal
moves from the wireless LAN to the mobile communication system. A dual
mode terminal that moves from a 3G mobile communication system to a
wireless network in an active state maintains an existing IP address
assigned from an active 3G mobile communication system so that the dual
mode terminal can maintain an upper layer session and transmit an IP
packet to a terminal located in a 3G mobile communication system.