Patent ID: 8130718

Claim:
A method for use in a wireless transmit/receive unit (WTRU), the method comprising: obtaining the address of a packet data gateway (PDG) using Domain Name Service (DNS); registering with a Third Generation Partnership Project (3GPP) IP multimedia subsystem (IMS) via a Wireless Local Area Network (WLAN) using Session Initiation Protocol (SIP); invoking an IP session for a user service from the IMS; receiving the user service from the IMS via the WLAN and a tunnel between the PDG and the WTRU; initiating a handover from the WLAN to a cellular network; and performing the handover from the WLAN to the cellular network, wherein the performing the handover includes: maintaining a connection to the WLAN while simultaneously maintaining a connection to the cellular network; and continuously receiving the user service from the IMS.