Abstract: A communications method, apparatus, and system to implement handover between session management network elements, where a target session management network element sends a first message to a source session management network element based on the information about the source session management network element received. After receiving the first message from the target intermediate session management network element, the source session management network element indicates, based on the first message, a source intermediate user plane network element to establish a forwarding tunnel. As such, the forwarding tunnel between the source intermediate user plane network element and a target intermediate user plane network element is established, and the source intermediate user plane network element can forward data to the target intermediate user plane network element through the forwarding tunnel.

Abstract: A subscription update method, device, and system, where the method is performed by a first event notification network element and includes: determining that a notification condition of a first subscription event of a first terminal is met; obtaining first callback address information of a target subscription network element; and sending a first message to the target subscription network element based on the first callback address information, where the first message carries an identifier of the first terminal and a first event notification of the first subscription event, and the identifier of the first terminal is used to correlate the first event notification with the first terminal.

Abstract: A service subscription method for reporting service change in a communications system is provided. In the method, a first network function network element sends a first message to a second network function network element to subscribe a first service on behalf of a third network function network element. The first service is provided by the second network function network element and the first message includes a first address of the first network function network element. When the second network function network element is changed to a fourth network function network element, the fourth network function network element sends a third message to the first network function network element according to the first address to notify the first network function network element that a subscription of the first service has changed.

Abstract: Optionally, when the apparatus 1200 is a chip or a circuit, the functions/implementation processes of the receiving unit 1201 and the sending unit 1202 may be alternatively implemented by a pin, a circuit, or the like. Optionally, when the apparatus 1200 is a chip, the memory 1103 may be a storage unit in the chip, for example, a register or a cache. Certainly, when the apparatus 1200 is a mobility management network element, the memory 1103 may be a storage unit that is in the mobility management network element and that is outside a chip. This is not specifically limited in this embodiment of this application.

Abstract: A subscription update method includes receiving, by a second mobility management network element (MMNE), event subscription information of a first terminal from a first MMNE, where the event subscription information includes information about a first subscription to a first event, the information about the first subscription includes group subscription identification information, the first terminal belongs to a first user group, and the first event is an event subscribed to by a unified data management (UDM) for the first user group, allocating a second subscription correlation identifier if the second MMNE has no subscription to the first event, and sending a first message to the UDM, including the second subscription correlation identifier and the group subscription identification information.

Abstract: A policy control method includes receiving, by a policy control network element, an update request message carrying information about a first mobility management network element from the first mobility management network element, updating, by the policy control network element according to the update request message, information about a second mobility management network element in information of a policy association corresponding to a terminal that is stored in the policy control network element to information about the first mobility management network element. The policy control network updates the information about the second mobility management network element in the information of the policy association to the information about the first mobility management network element instead of deleting the policy association and re-establishing a policy association with the first mobility management network element.

Abstract: This application provides a method and an apparatus for determining a protocol data unit session service network element, so as to help control an AMBR. The method includes: receiving, by a control plane function network element, a request for establishing a first PDU session from a mobility management device, where the request for establishing the first PDU session includes a first data network name DNN; determining, by the control plane function network element, that a same control plane function network element and a same user plane function network element need to be selected for a PDU session corresponding to the first DNN; and sending, by the control plane function network element, first indication information to the mobility management device, where the first indication information is used to indicate that a same control plane function network element needs to be selected for the PDU session corresponding to the first DNN.

Abstract: This application provides a handover method and apparatus. The method includes: determining, by a first control plane function network element, at least one bearer that needs to be established when a protocol data unit PDU session of a terminal in a first network is to be switched to a packet data network PDN connection in a second network; and obtaining, by the first control plane function network element, tunnel information of the PDN connection, where the tunnel information of the PDN connection includes user plane tunnel information corresponding to each of the at least one bearer.

Abstract: An address management method, system, and device to avoid a problem that a same Internet Protocol (IP) address is assigned to different packet data unit (PDU) sessions and to effectively use IP addresses in an address pool. The method includes: obtaining, by a session management network element, an identifier of a user plane function network element serving a terminal and session information of the terminal; determining, by the session management network element based on the identifier of the user plane function network element and the session information, an address pool identifier corresponding to the session; sending, by the session management network element, the address pool identifier to a server, where the address pool identifier is used to assign an IP address to the session; and receiving, by the session management network element from the server, the IP address corresponding to the session.

Abstract: A session establishment method and an apparatus, such that an established packet data network (PDN) connection is transferred to a network slice in a fifth generation (5G) network during inter-system mobility of a terminal. The method includes receiving, by a terminal from a control plane function entity, corresponding network slice information used for transferring an established PDN connection to a 5G network, where the corresponding network slice information includes corresponding single network slice selection assistance information (S-NSSAI). The method further includes sending a packet data unit (PDU) session establishment request, where the PDU session establishment request includes corresponding S-NSSAI used for transferring a first PDN connection to the 5G network and a corresponding data network name (DNN) used for transferring the first PDN connection to the 5G network, and the first PDN connection is any one of one or more established PDN connections.

Abstract: A communication method and a communications apparatus, wherein the communication method includes: receiving, by a network repository network element, a first request message from a mobility management network element, where the first request message carries a data network name of a session that a terminal device requests to establish; determining, by the network repository network element based on the first request message, at least one target session management network element from session management network elements that support the data network name; and sending, by the network repository network element, an identifier of the at least one target session management network element to the mobility management network element, such that a session management network element can be selected to provide a service for a terminal device.

Abstract: A service subscription method for reporting service change in a communications system is provided. In the method, a first network function network element sends a first message to a second network function network element to subscribe a first service on behalf of a third network function network element. The first service is provided by the second network function network element and the first message includes a first address of the first network function network element. When the second network function network element is changed to a fourth network function network element, the fourth network function network element sends a third message to the first network function network element according to the first address to notify the first network function network element that a subscription of the first service has changed.

Abstract: A communication method applicable to different scenarios of interworking between communications systems includes determining, by a session management network element, a first data channel in a first system, where the first data channel is a data channel to be synchronized with a terminal device; and synchronizing, by the session management network element in an interworking procedure for the terminal device from the first system to a second system, at least one of the first data channel or a second data channel that is in the second system and that corresponds to the first data channel.

Abstract: The present disclosure relates to session establishment methods, systems, and devices. One example method includes obtaining, by a first mobility management entity, information about a packet data network (PDN) connection that has been established when a terminal accesses an evolved packet core (EPC) network, and obtaining, by the first mobility management entity, single network slice selection assistance information (S-NSSAI) of a network slice corresponding to the PDN connection.

Abstract: A subscription update method, device, and system, where the method is performed by a first event notification network element and includes: determining that a notification condition of a first subscription event of a first terminal is met; obtaining first callback address information of a target subscription network element; and sending a first message to the target subscription network element based on the first callback address information, where the first message carries an identifier of the first terminal and a first event notification of the first subscription event, and the identifier of the first terminal is used to correlate the first event notification with the first terminal.

Abstract: Embodiments of the present disclosure disclose a mobility management method, apparatus, and system, and pertain to the field of wireless communications technologies. The method includes: determining, by a first mobility management entity based on information about a Packet Data Network (PDN) connection established by user equipment in a 4G network, a network slice corresponding to the PDN connection, and then determining, with reference to a subscribed network slice of the user equipment, a network slice allowed for the user equipment.

Abstract: A method for detecting quality of service of a service includes obtaining, by a packet sending device, detection indication information, where the detection indication information is used to instruct the packet sending device to detect quality of service of a service; and sending, by the packet sending device, a detection packet to a packet receiving device based on the detection indication information, where the detection packet is used to detect the quality of service of the service.

Abstract: A subscription update method, device, and system, where the method is performed by a first event notification network element and includes: determining that a notification condition of a first subscription event of a first terminal is met; obtaining first callback address information of a target subscription network element; and sending a first message to the target subscription network element based on the first callback address information, where the first message carries an identifier of the first terminal and a first event notification of the first subscription event, and the identifier of the first terminal is used to correlate the first event notification with the first terminal.

Abstract: A communication method, a communications device, and a communications system to avoid, when an access and mobility management function (AMF) entity fails, a case in which a re-registration process of a terminal that is being served is triggered because a context of the terminal is lost. The method includes: obtaining, by a communications device, a first group identifier of a terminal group to which a first terminal served by a first mobility management entity belongs; and sending, by the communications device, a message related to the first terminal to a second mobility management entity based on the first group identifier when an exception occurs in the first mobility management entity, where the second mobility management entity is a mobility management entity in which a context of the first terminal exists.

Abstract: A service subscription method and an apparatus for reporting a service change, where the method includes a first network function network element sending the address of the first network function network element to a second network function network element. Therefore, when a first service changes, the first network function network element can receive a notification.