Patent ID: 8374604

Claim:
A method for performing multiple registrations across different radio access technologies (RATs) by a multimode mobile device, the method comprising: registering the mobile device with a primary RAT; and pre-registering the mobile device with at least one non-primary RAT different from the primary RAT, wherein the pre-registration includes: setting up a radio session context with the non-primary RAT using non-primary RAT air interface; setting up a packet data network (PDN) context with the non-primary RAT; setting up a pseudo-binding with an external PDN gateway and obtaining a binding state information for the mobile device from the PDN gateway without transferring binding state from the primary RAT to the non-primary RAT; and adding the obtained binding state information to the PDN context; and determining whether a full PDN context or partial PDN context is preset on the non-primary RAT; when a full PDN context is preset on the non-primary RAT, performing handoff from primary RAT to non-primary RAT using preset PDN context; and when a partial PDN context is preset on the non-primary RAT, (i) completing the PDN context with the missing parameters obtained from the mobile device, primary RAT or external PDN gateway, and (ii) performing handoff from primary RAT to non-primary RAT using the completed PDN context.