Patent ID: 6954654

Claim:
A method for registering a mobile unit with a communication system including a serving system, a home IP Multimedia Subsystem (IMS), a mobile switching center (MSC), and an interworking MSC (IMSC), the IMSC including at least one Media Gateway (MGW) that is controlled by the iMSC, the method comprising: performing a location update procedure by the mobile unit; processing by the serving system the registration by authenticating the mobile unit and informing the Home Subscriber Server (HSS) of the location of the current serving system; determining if the serving system can process the mobile unit as an iMSC; and if the serving system can process the mobile unit as an iMSC: performing SIP registration procedures by the IMSC with the home IMS on behalf of the mobile unit; delivering phone calls destined for the mobile unit to the serving system; utilizing a Domain Name System (DNS) by the iMSC to determine if there is an I-CSCF address associated with the mobile unit; sending a SIP registration message to the I-CSCF in the home IMS on behalf of the mobile unit; communicating by the I-CSCF with the HSS to complete the IMS registration procedure; and sending subscriber profile information to a Serving Call State Control Function (S-CSCF).