A voice call method applied to a terminal including a first subscriber module and a second subscriber module, including: monitoring a network quality of the first subscriber module while performing an Internet protocol Multimedia Subsystem (IMS) session; and in response to determining that the network quality of the first subscriber module while performing the IMS session does not satisfy a preset network quality condition, and the second subscriber module satisfies a predetermined switching condition, switching to the second subscriber module to continue the IMS session.

A method and system in which upon occurrence of a P-CSCF failure, a network sends an IMS reregistration request message to a UE. An S-CSCF or an AS monitors a P-CSCF to detect occurrence of a failure in the P-CSCF. Upon detecting the occurrence of a P-CSCF failure, the S-CSCF or the AS sends a request message for IMS reregistration to the UEs being served by the failed P-CSCF. In this manner, the UE can continuously receive the service even though a failure occurs in the P-CSCF.

A method and system in which upon occurrence of a P-CSCF failure, a network sends an IMS reregistration request message to a UE. An S-CSCF or an AS monitors a P-CSCF to detect occurrence of a failure in the P-CSCF. Upon detecting the occurrence of a P-CSCF failure, the S-CSCF or the AS sends a request message for IMS reregistration to the UEs being served by the failed P-CSCF. In this manner, the UE can continuously receive the service even though a failure occurs in the P-CSCF.

The disclosure relates to an apparatus and method for providing a call function in an electronic device. The electronic device includes first communication circuitry supporting new radio (NR) communication and/or long term evolution (LTE) communication, second communication circuitry supporting wireless local area network (LAN) communication, and at least one processor operatively connected to the first communication circuitry and the second communication circuitry. The processor may be configured to resister the electronic device with a network using the NR communication through the first communication circuitry, connect communication with an evolved packet data gateway (ePDG) based on a protocol data unit (PDU) session being identified as being connected over a network using wireless LAN communication in a state in which the electronic device has registered with the network using the NR communication, obtain information related to a call function of the network using the NR communication based on the communication connection with the ePDG, connect the PDU session over the network using the wireless LAN communication, and control the connection with the network using the NR communication based on the information related to the call function of the network using the NR communication.

Techniques for call recovery for multiple call failures are described and may be implemented via a wireless device to adapt to a variety of different wireless scenarios. For instance, when multiple call failures for a call occur over a particular set of radio access technologies, an IP-based call and/or a direct device-to-device call can be implemented to complete the call.

Various embodiments of the present disclosure provide a method for call setup. The method which may be performed by a session management node comprises receiving an evolved packet system (EPS) fallback indicator from a mobility management node. In an embodiment, the EPS fallback indicator may indicate that a fallback to an EPS for an Internet protocol multimedia subsystem (IMS) voice service is ongoing. The method further comprises reporting an EPS fallback event to a policy charging node, according to the EPS fallback indicator.

A method for enhanced call control using User Equipment (UE)-triggered fallback procedure is provided. A UE starts a guard timer in response to initiating or receiving an Internet Protocol (IP) Multimedia Subsystem (IMS) call in a mobile communication network which utilizes a first Radio Access Technology (RAT). The UE determines whether a condition for call continuation in the mobile communication network is met when the guard timer expires. The UE triggers a fallback from the first RAT to a second RAT in response to the condition for call continuation in the mobile communication network not being met.

A method for changing a communication network for video communication is provided. The method includes performing, by a user equipment (UE), video communication through a mobile communication network; searching for whether there is a wireless local area network (WLAN) accessible by the UE; displaying, if a WLAN accessible by the UE is found, the accessible WLAN; and when the displayed WLAN is selected by a user, changing a communication network for the video communication to perform the video communication through the selected WLAN.

An improved core network that allows a UE to still initiate and/or receive communications via a native SIM line even if the registration of a virtual line fails is described herein. For example, the UE may include embedded virtual line settings that, when enabled, cause the UE to transmit a virtual line registration request to the core network. The core network can determine whether the UE is authorized to register a virtual line. If the UE is authorized, the core network can register a native SIM line, register the virtual line, and transmit a single message to the UE indicating that the native SIM and virtual lines are registered. If the UE is not authorized, the core network still registers the native SIM line and transmits a single message to the UE indicating that the native SIM line is registered.

Techniques for call recovery for call failure are described and may be implemented via a wireless device to adapt to a variety of different wireless scenarios. For instance, when multiple call failures for a call occur over a particular set of radio access technologies, an IP-based call and/or a direct device-to-device call can be implemented to complete the call.