Circuit-switched and multimedia subsystem voice continuity with bearer path interruption

A network node for performing voice continuity, wherein the network node comprises:

• a communication interface;
• and
• a control system to facilitate communications via the communication interface, wherein the control system is configured to:
• receive, via a call session control function (CSCF) at a continuity control function (CCF) of the network node, a first message from a client of a first subsystem, the first message including at least one transition indication indicating transition of an ongoing session from the first subsystem to a second subsystem, wherein the CCF anchors active circuit-switched subsystem (CS) calls and home multimedia subsystem (MS) sessions;
• in response to receiving the first message, send a first response from the CCF;
• receive, from a client of the second subsystem at the CCF, a second message via a target access leg, the second message comprising a CCF public service identities (PSI);
• and
• send, from the CCF, a session initiation protocol (SIP) 200 OK message to perform voice continuity such that the ongoing session is maintained while transferring the ongoing session from the first subsystem to the second subsystem,
• wherein the ongoing session is anchored at the CCF in an MS, and wherein the network node is configured to invoke the CCF when a bearer path interruption occurs while transferring the ongoing session between a CS and the MS to maintain the ongoing session during the transfer.

A method of performing voice continuity in a user equipment, the method comprising:

• sending, to a continuity control function (CCF) and via an interface on the user equipment, a first message including at least one transition indication corresponding to an ongoing session with the user equipment, wherein the CCF anchors active circuit-switched subsystem (CS) calls and home multimedia subsystem (MS) sessions;
• receiving, via the interface, a first response acknowledging receipt of the first message;
• and
• sending, via the interface, a second message in response to receipt of said first response to perform voice continuity such that the ongoing session is maintained while the user equipment transitions from a first subsystem to a second subsystem,
• wherein the first message is sent from an MS client on the user equipment in response to the user equipment detecting a need to transition from the first subsystem to the second subsystem,
• wherein the second message contains a CCF public service identities (PSI), wherein the CCF PSI enables initiating session transfers between the first and second subsystems, and
• wherein the SETUP message is sent from a CS client on the user equipment to transfer the ongoing session from a multimedia subsystem to a CS subsystem, and wherein the CCF is invoked to maintain the ongoing session when a bearer path interruption occurs during the transfer.

A user equipment for performing voice continuity, the user equipment configured to:

• send, to a continuity control function (CCF), a first message including at least one transition indication corresponding to an ongoing session with the user equipment, wherein the CCF anchors active circuit-switched subsystem (CS) calls and home multimedia subsystem (MS) sessions;
• receive a first response acknowledging receipt of said first message;
• and
• send a second message in response to receipt of said first response to perform voice continuity such that the ongoing session is maintained while the user equipment transitions from a first subsystem to a second subsystem,
• wherein the first message is sent from an MS client on the user equipment in response to the user equipment detecting a need to transition from the first subsystem to the second subsystem,
• wherein the second message contains a CCF public service identities (PSI), wherein the CCF PSI enables initiating session transfers between the first and second subsystems, and
• wherein the CCF is invoked to maintain the ongoing session when a bearer path interruption occurs during the transfer.