Circuit-switched and multimedia subsystem voice continuity

摘要

The present invention moves service control, including call control, for a user element from a cellular network to a multimedia subsystem (MS), such as the Internet Protocol (IP) Multimedia Subsystem (IMS). Call control is provided by the MS irrespective of whether the user element is using cellular or WLAN access for the call. Call control for originating and terminating calls in the CS or MS as well as transferring calls between a circuit-switched subsystem (CS) and MS is anchored at a continuity control function (CCF) in the MS. All call signaling for the call is passed through the CCF. The CCF is a service provided in the user element's home MS and anchors the user element's active CS calls and MS sessions to enable active roaming across the CS and MS.

主权项

1. A method of providing a continuity control function comprising:
providing a signaling anchor point in a multimedia subsystem for a first access signaling leg and a remote access signaling leg that initially form a signaling path for a call between a user element and a remote endpoint, the first access signaling leg being connected to the user element via a transferring-out subsystem; establishing a second access signaling leg toward a user element via a transferring-in subsystem; replacing the first access signaling leg with the second access signaling leg to update the signaling path, such that the second leg is anchored at the signaling anchor point; providing call signaling via the signaling path to transfer at least a portion of a bearer path used for the call between the user element and the remote endpoint, from a first network to a second network while maintaining continuity of the call, wherein the transferring-out subsystem is circuit-switched subsystem or the multimedia subsystem, and the transferring-in subsystem is the multimedia system or the circuit-switched subsystem, respectively, thereby the method transferring calls from the circuit-switched subsystem to the multimedia subsystem and transferring calls from the multimedia subsystem to the circuit-switched subsystem; receiving a request intended for the continuity control function to originate the call from the user element to the remote endpoint; terminating the first access signaling leg; identifying an address or number associated with the remote endpoint; and establishing the remote signaling leg for the call toward the remote endpoint using the address or number; wherein the user element will initiate a call to the continuity control function;wherein the address or number for the remote endpoint is identified from a message separate from the request and wherein the message is sent via a Unstructed Supplementary Service Data (USSD) channel.