Methods, systems, and devices for wireless communication are described. A user equipment (UE) may prevent rejected attachment requests when connecting to a trusted wireless local area network (WLAN) and from a wireless wide area network (WWAN). For example, an attachment packet data network (PDN) connection may be maintained with the WWAN while connected to the trusted WLAN. In some cases, the connection used to maintain the attachment may be an internet protocol (IP) multimedia subsystem (IMS) connection. Alternatively, the UE may determine that the WLAN connection is a trusted connection and deactivate the WWAN connection. Should the WLAN become unavailable the UE may reactivate the connection with the WWAN.

Aspects of the disclosure can provide an apparatus and method for voice domain selection (VDS). A processing circuitry of user equipment (UE) is configured to receive an indication that an internet protocol (IP) multimedia core network subsystem (IMS) voice is unsupported over a 3GPP access, but is supported over a non-3GPP access in a first communication system. Then, the processing circuitry is configured to register to an IMS via the non-3GPP access in the first communication system and perform an IMS voice service over the non-3GPP access in the first communication system. The processing circuitry of the UE is further configured to switch to a second communication system when voice domain management (VDM) is set to the second communication system. After registering to the first communication system using a non-3GPP access, and registering to the IMS via the non-3GPP access in the first communication system, the processing circuitry of the UE can be configured to switch back to the first communication system from the second communication system.

A synchronization method for call supplementary service configuration includes: receiving an entered supplementary service configuration instruction, and obtaining a configuration parameter corresponding to the supplementary service configuration instruction; uploading the configuration parameter to a mobile switching center by using a circuit switched domain, so that the mobile switching center stores the configuration parameter as call supplementary service configuration of the circuit switched domain into a home location register; receiving returned configuration feedback information; and determining, according to the configuration feedback information, whether configuration succeeds, and storing the configuration parameter as on-terminal call supplementary service configuration if the configuration succeeds.

A method, an apparatus and a system for a handover to a circuit switched domain are disclosed. In an embodiment, a system includes a mobility management entity (MME) and at least two a mobile switching center (MSCs), wherein the at least two MSCs comprise a first MSC capable of supporting a circuit switched fallback (CSFB) and a single radio voice call continuity (SRVCC) and a second MSC not capable of supporting the SRVCC, and wherein the MME is configured to select the first MSC for a user equipment (UE) from the at least two MSCs in a combined tracking area update procedure of the UE when a location service of a circuit switched (CS) domain triggers an SRVCC procedure for the UE and when the UE has a Voice over Internet Protocol (VOIP) service in progress.

Apparatus and methods relating to enabling a wireless device to perform SRVCC when connected to a 3GPP specified gNB and a 5G core network that does not support SRVCC are disclosed. In some embodiments, a method of operation of a wireless device comprises providing an indication to the 5G core network that the UE support SRVCC in EPC mode and receiving instruction to connect to an eNB in EUTRAN and EPC that supports SRVCC to a circuit switched network. In this manner, the gNB and the 5G Core network is not required to support SRVCC. Related embodiments in gNB and a control plane entity in the G core network are also provided.

A method, apparatus and computer program product are provided to facilitate the handover from a packet switched network to a circuit switched network while an Internet protocol (IP) multimedia subsystem (IMS) session is ongoing. In the context of a method, a notification is received of the handover from a packet switched network to a circuit switched network while an IMS session is ongoing. The method also receives an indication that an emergency call service is active in the IMS session and determines that media resources in the circuit switched network are required to support the emergency call service, as supplemented by a minimum set of emergency related data, that is active in the IMS session. The method may further include causing the media resources to be reserved in the circuit switched network to support the emergency call service that is active in the IMS session.

Various communication systems may benefit from the transfer of sender or receiver communication parameters. For example, such transfer of sender communication parameters may be useful in connection with single radio voice call continuity (SRVCC) and reverse SRVCC. A method can include receiving, at an intermediate entity from a first entity, signaling including at least one parameter describing a user plane payload format that the first entity wants to receive and an encoding that the first entity wants to receive. The method can also include forwarding, by the intermediate entity, the at least one parameter in signaling to a second entity.

To provide a communication control means for establishing a session between a terminal apparatus and a network in a network-initiated manner and/or a connection control means for supporting service continuity and/or a session establishment control means for supporting service continuity and/or a communication control means for service continuity, and the like. These provide a communication control method for establishing an optimal session for service continuity through which service is continued by switching between sessions for communication, an optimal communication control method for service continuity, and the like.

A user equipment (UE) and an Internet Protocol (IP) Multimedia Subsystem (IMS) node may exchange fallback indicators in SIP signaling for purposes of controlling fallback procedures implemented by the UE. The SIP signaling may include a SIP request from the UE that includes first information. The IMS node can evaluate a criterion based on the first information, and, if the criterion is met, the IMS node may authorize (or prohibit) the use of a UE-supported fallback radio access technology (RAT) that corresponds to a fallback indicator also included in the SIP request. Based on the evaluation of the criterion, the IMS node may respond to the UE with a SIP response that includes second information indicating which of the supported Fallback RATs the UE is authorized to use (if any), and which of the supported Fallback RATs the UE is not authorized to use (if any).

A user equipment (UE) and an Internet Protocol (IP) Multimedia Subsystem (IMS) node may exchange fallback indicators in SIP signaling for purposes of controlling fallback procedures implemented by the UE. By sending fallback indicators to an IMS node in a SIP request, a UE is able to inform the IMS node of its capabilities in regards to particular fallback radio access technologies (RATs) that are supported by the UE. The IMS node may respond to the UE with a SIP response that includes information indicating which of the supported Fallback RATs the UE is authorized to use (if any), and which of the supported Fallback RATs the UE is not authorized to use (if any). In this way, the IMS node can control a fallback procedure at the UE by indicating which Fallback RATs are usable by the UE to reattempt communication sessions that cannot be established on an existing RAT.