Mobile system, terminal and interface, as well as methods for providing backward compatibility to first and second generation mobile systems

Abstract

Application-layer signaling of a packet data network, such as the Session Initiation Protocol (SIP), is used to communicate with an interworking interface between the packet data network and a circuit-switched network, particularly a public land mobile network (PLMN), wherein the interface converts the application-layer signaling of the packet data network to a control protocol utilized in the PLMN, wherein a private user identification is carried, for example, by means of a Session Description Protocol (SDP) within the application-layer signaling between the packet data network terminal and the interface, and wherein standardization of lower layers of the packet data network protocol stack is not required beyond that which is already defined. The interface between the packet data network and the circuit-switched network provides the private user identification to the circuit-switched network in the manner in which the circuit-switched network is accustomed.