A method includes receiving, by a mobility management network element in a first network, first information from an access network device in the first network, where the first information indicates a handover of a terminal device from the first network to a second network, and sending, by the mobility management network element in the first network, second information to a mobility management network element in a third network based on the first information, where the second information instructs the mobility management network element in the third network to send a handover request to a mobile switching network element in the second network, and the handover request requests to hand over a voice service of the terminal device to the second network.

A method includes receiving, by a mobility management network element in a first network, first information from an access network device in the first network, where the first information indicates a handover of a terminal device from the first network to a second network, and sending, by the mobility management network element in the first network, second information to a mobility management network element in a third network based on the first information, where the second information instructs the mobility management network element in the third network to send a handover request to a mobile switching network element in the second network, and the handover request requests to hand over a voice service of the terminal device to the second network.

Embodiments include methods for a target node to establish a connection with a user equipment (UE) operating in dual connectivity (DC) with a PCell utilizing a first radio access technology (RAT) and with a PSCell utilizing a second RAT. Embodiments include receiving, from the UE, a re-establishment request message comprising parameters associated with the PSCell, a first message authentication code (MAC), and an indication of the UE's selection of a target cell served by the target node as a replacement for the PCell. The target cell utilizes the second RAT. Embodiments include verifying the message integrity based on the first MAC, and determining a full UE context based on the plurality of parameters associated with the PSCell and on a successful verification of the message integrity. Embodiments include establishing a connection with the UE based on the full UE context, whereby the target cell serves as a PCell for DC.

Embodiments include methods for a target node to establish a connection with a user equipment (UE) operating in dual connectivity (DC) with a PCell utilizing a first radio access technology (RAT) and with a PSCell utilizing a second RAT. Embodiments include receiving, from the UE, a re-establishment request message comprising parameters associated with the PSCell, a first message authentication code (MAC), and an indication of the UE's selection of a target cell served by the target node as a replacement for the PCell. The target cell utilizes the second RAT. Embodiments include verifying the message integrity based on the first MAC, and determining a full UE context based on the plurality of parameters associated with the PSCell and on a successful verification of the message integrity. Embodiments include establishing a connection with the UE based on the full UE context, whereby the target cell serves as a PCell for DC.

The present disclosure aims to enable communication to be performed with stable quality even when a user uses a terminal while moving. In the wireless communication system according to the present disclose, a switching control unit 15 sets switching illuminance p.sub.th for maintaining illuminance of an optical signal received by a terminal 91 at requested illuminance corresponding to throughput or higher during the time until connection switching between the communication with an optical wireless access point 92 and the communication with an RF wireless access point 93 is completed, and when the received illuminance p becomes lower than the switching illuminance p.sub.th during connection with the optical wireless access point 92, the switching control unit 15 performs connection switching from the optical wireless communication to the RF wireless communication.

This application provides a communication method, a network element, a terminal apparatus, and a system. The communication method includes: receiving, by a first network element, first indication information from a second network element, where the first indication information is used to indicate that a current condition supports establishment of a session of a first network for a terminal apparatus; obtaining, by the first network element, first quality of service QoS control information of a first session of the terminal apparatus after receiving the first indication information, where the first session is a session established by the terminal apparatus by using a second network; and sending, by the first network element, the first QoS control information to the second network element. The communication method in the embodiments of this application can improve communication efficiency.

The present disclosure relates to a communication method and system for converging a 5.sup.th-Generation (5G) communication system for supporting higher data rates beyond a 4.sup.th-Generation (4G) system with a technology for Internet of Things (IoT). The present disclosure may be applied to intelligent services based on the 5G communication technology and the IoT-related technology, such as smart home, smart building, smart city, smart car, connected car, health care, digital education, smart retail, security and safety services.

A communication apparatus receives a signal that is transmitted from a partner apparatus using a first communication scheme, and establishes, on the basis that the signal received includes information indicating that parameter exchange processing is to be executed, a connection with the partner apparatus using a second communication scheme, wherein the second communication scheme has a higher communication rate and consumes more power than the first communication scheme. In addition, the communication apparatus exchanges, by using the second communication scheme, information to be used in communication for the parameter exchange processing with the partner apparatus, and executes the parameter exchange processing using the information by using the second communication unit scheme.

A communication terminal (10) according to the present disclosure includes: a control unit (12) configured to, in a case of a movement from a communication area formed by the 5GS to a communication area formed by the EPS or a movement from a communication area formed by the EPS to a communication area formed by the 5GS, determine whether or not a communication system forming a communication area at a movement destination can satisfy requirements of services; and a communication unit (11) configured to, when it is determined that the communication system forming the communication area at the movement destination can satisfy the requirements of the services, send a connection request message to the communication system forming the communication area at the movement destination.

A communication terminal (10) according to the present disclosure includes: a control unit (12) configured to, in a case of a movement from a communication area formed by the 5GS to a communication area formed by the EPS or a movement from a communication area formed by the EPS to a communication area formed by the 5GS, determine whether or not a communication system forming a communication area at a movement destination can satisfy requirements of services; and a communication unit (11) configured to, when it is determined that the communication system forming the communication area at the movement destination can satisfy the requirements of the services, send a connection request message to the communication system forming the communication area at the movement destination.