Systems, devices, and techniques described herein relate to use of an optimized security mode command (SMC) procedure for securing communications. When connecting to a different cellular network (e.g., from a 5.sup.th generation (5G) Radio Access Network (RAN)) to a different cellular network (e.g., a 4.sup.th generation (4G) RAN), a User Equipment (UE) performs the SMC procedure without processing subsequent commands until a period of time has elapsed. Instead of allowing the UE to process subsequent commands received close in time to receiving the SMC, the subsequent commands may be delayed/suspended so that the UE has time to perform the SMC procedure and establish secure communications with the 4G LTE network. According to some examples, the delay is set to a period of time (e.g., 1 ms, 10 ms, or some other value) such that the subsequent command does not interfere with performing the SMC procedure.

A method disclosed herein includes registering, by a User Equipment (UE), with a primary cell of a first Radio Access Technology (RAT) after terminating at least one communication service initiated in a second RAT, and initiating, by the UE, Inter-Radio Access Technology (IRAT) measurement of a secondary cell before receiving a reconfiguration message from the primary cell in response to the registering, the secondary cell being associated with the primary cell.

A method performed by an access and mobility node for interworking handover from an evolved packet system, EPS, to a fifth generation system, 5GS, in a radio access network is provided. The method includes receiving a relocation request from a mobility management node. The relocation request comprises an indication comprising a least one of that a user equipment, UE, supports a UP integrity protection mode over the radio access network connected to a fifth generation core, 5GC, and that the UE supports a UP integrity protection mode over the radio access network connected to the EPS. The method further includes sending a handover request to a radio access node. The handover request comprises the indication. Methods performed by a session management node, a mobility management node, a radio access node, a target radio access node, and computer products and computer programs are also provided.

A method includes receiving a request to initiate an emergency call, directing, the mobile device to initiate the emergency call using a cellular network, receiving a network not available indication that the emergency call cannot be completed using the cellular network, selecting location information of the mobile device and requesting the emergency call be initiated by a VoIP client on the mobile device using the location information obtained from the selecting step.

Methods and apparatuses are provided for controlling a voice call at a user equipment (UE) in a wireless network. A method includes transmitting, to a network entity, a tracking area update (TAU) service request for a subsystem (IMS) initiation; receiving, from the network entity, a TAU service reject message; and in response to the TAU service reject message, stopping a circuit switch (CS) fall back call in at least one legacy radio technology (RAT).

Various solutions for avoiding circuit-switched call drop with respect to user equipment and network apparatus in mobile communications are described. An apparatus transmits a non-access stratum (NAS) message in a NAS signaling connection. The apparatus receives a NAS response message. The apparatus initiates a timer to control the NAS signaling connection. The apparatus further receives a circuit-switched (CS) service notification. The apparatus then stops the timer and execute a CS service procedure.

A communication method and apparatus is provided for enhancing video telephony service quality by protecting against call setup failure or service quality degradation caused due to switching of the User Equipment (UE) to a network which does not fulfill the data rate required for video telephony in the video call setup process. The communication method of a terminal in a mobile communication system according to the present disclosure includes transmitting a video telephony call setup request message, receiving a switching command for Circuit Switched Fall Back (CSFB), and setting, if the switching command includes a target cell type set to the 2nd Generation (2G) cell and if a 3rd Generation (3G) cell to which the terminal can access exists, up the video telephony call by switching a connection to the 3G cell.

Embodiments of the present disclosure disclose a circuit switched fallback method, a network device, and a system. The method includes: determining, by the network device, that a serving cell handover process of UE is ended; determining, by the network device, that before the serving cell handover process of the UE is ended, it has been determined that the UE needs to be moved to a second network supporting a circuit switched service; and moving, by the network device, the UE to the second network. According to the foregoing method, when CSFB triggered by a CS service initiated by UE conflicts with a serving cell handover process of the UE, the CS service of the UE can continue to be performed after completing the serving cell handover process of the UE. In this way, a success rate of establishing the CS service is increased.

The disclosure generally relates to various methods to increase network coverage with respect to Voice-over-Internet Protocol (VoIP) sessions and/or other voice-based multimedia services. In particular, when establishing a voice session, two or more terminals may perform a codec negotiation to exchange information related to supported multimedia codecs and/or codec modes, jitter buffer management (JBM), and packet loss concealment (PLC) capabilities. Based on the exchanged information, a message may be sent to a base station to indicate the maximum packet loss rate (PLR) for each terminal. Additional techniques may ensure that the terminals use the most robust codecs or codec modes that are available when nearing the edge of coverage to help avoid unnecessary and/or excessive handovers to different radio access technologies.

A voice call method includes in a case that UE accesses a first network, receiving a registration reception message sent by a first network side device corresponding to a first network; based on the registration reception message, in a case that a predetermined condition is met, stopping using the first network and connecting to a second network; and sending a voice call request to a second network side device corresponding to the second network. The voice call request is used to request the second network side device to process a voice call service. The predetermined condition includes that the registration accept message carries a first identifier indicating that the UE does not support an IMS service; or the registration accept message carries a second identifier indicating that the UE supports an IMS service, and the UE confirms that registration of the IMS service to the first network side device fails.