RU2776778C2 - Method and equipment for establishing session - Google Patents

Abstract

FIELD: wireless communication.

SUBSTANCE: during the establishment of a package data transmission network (hereinafter – PDN) connection in 4G network, a terminal receives single network slice selection assistance information (hereinafter – S-NSSAI) corresponding to the established PDN connection, and a public land mobile network ID (hereinafter – PLMN ID), which indicates that received S-NSSAI is S-NSSAI of a home PLMN. When the terminal makes a decision to transfer the established PDN connection to 5G network, the terminal can use S-NSSAI of a guest PLMN corresponding to PDN connection, which is converted from received S-NSSAI.

EFFECT: providing successful transfer of established PDN connection in 4G network to 5G network in a roaming scenario with home routing.

56 cl, 6 dwg, 5 tbl

Description

Technical field

[0001] This application relates to the field of communication technologies and, in particular, to a method and equipment for establishing a session.

State of the art

[0002] With the rapid development of wireless communication technologies, fifth generation (5G) mobile communication technology is emerging. At the initial stage of network deployment, since the coverage of the 5G network is insufficient, when the location of the User Equipment (UE) changes, the UE can switch between the 5G network and the fourth generation network (4G).

[0003] A network segment (network slice, network slice) is a logically isolated network used to support certain network capabilities and network functions, and may include the entire network in an end-to-end (E2E) manner, or some network functions may shared across multiple network segments. Network segmentation is a key technology to meet differentiated network requirements in 5G mobile communication technology.

[0004] A network segment can be specifically represented by network slice selection assistance information (NSSAI). When a terminal accesses a 5G core network (5GC), the terminal provides the requested NSSAI and the network selects the appropriate network segment for the terminal based on the NSSAI. In addition, the network determines, based on the requested NSSAI of the terminal, the NSSAI of the network segment to which the terminal is allowed to access, namely, the allowed NSSAI.

[0005] However, in a 4G network, there is no concept of a network segment. In 4G, each packet data network (PDN) connection corresponds to an access point name (APN). A data network name (DNN) and a single NSSAI (single NSSAI, S-NSSAI) are required to create a packet data unit (PDU) session on a network segment. In the existing protocol, although the APN may be equivalent to the DNN when the terminal is transferred from the 4G network to the 5GC that supports network slicing, there is currently no appropriate solution to determine the S-NSSAI of the network segment corresponding to the PDN connection established by the terminal in the 4G network in order to set up a PDU session on the 5GC network segment based on the defined S-NSSAI.

The essence of the invention

[0006] Embodiments of this application provide a session establishment method and equipment so that an established PDN connection can be transferred to a network segment in a 5G network during terminal inter-system mobility.

[0007] To solve the above problem, embodiments of this application provide the following technical solutions:

[0008] According to a first aspect, a method for establishing a session is provided, the method including: receiving by the terminal, from the control plane functional entity, corresponding network segment information used for transmitting an established PDN connection of a packet data network to a 5G network, where the corresponding network segment information, used for transferring the established PDN connection to the 5G network, includes the corresponding unit information S-NSSAI of network segment selection assistance used for transferring the established PDN connection to the 5G network; and sending a session establishment request of the packet data PDU, where the PDU session establishment request includes the corresponding network segment S-NSSAI used to transfer the first PDN connection to the 5G network and the corresponding data network DNN used to transfer the first PDN connection to the 5G network and the first PDN connection is any of the established PDN connections. The terminal establishes one or more PDN connections in the 4G network using one or more control plane functional entities.

[0009] When the terminal is in a non-roaming scenario or in a Local Breakout (LBO) roaming scenario, the corresponding network segment S-NSSAI used to transfer the first PDN connection to the 5G network is the network segment S-NSSAI, received by the terminal from the control plane functional entity.

[0010] When the terminal is in a home routed scenario, the corresponding network segment S-NSSAI used to forward the first PDN connection to the 5G network is the network segment S-NSAI of the visited PLMN. Specifically, before sending the PDU session establishment request, the method further includes: converting, to the S-NSSAI of the network segment of the visited PLMN by the terminal, based on the mapping relation between the S-NSSAI of the network segment of the home PLMN and the S-NSSAI of the network segment of the visited PLMN corresponding to the network information segment which is received from the control plane functional entity and which is used to transfer the first PDN connection to the 5G network.

[0011] The control plane functional entity sends to the terminal the corresponding network segment information used to transfer the established PDN connection to the 5G network, so that when transferring the established PDN connection to the 5G network, the terminal can establish a PDU session in the 5G network segment based on the corresponding network segment information.

[0012] In an exemplary implementation, the corresponding network segment information used to convey the established packet data PDN connection to the 5G network is carried in the protocol configuration option PCO message. The control plane functional entity sends to the terminal, via a PCO message, the appropriate network segment information used to transfer the established PDN connection to the 5G network. In particular, the PCO message may be sent to the terminal via a Mobility Management Entity (MME) and a base station in a 4G network. The corresponding network segment information used to transfer the established packet data PDN connection to the 5G network is sent using the PCO message, so that the MME can only transmit the message transparently, but does not require the message to be stored.

[0013] In an exemplary implementation, the terminal further receives indication information from the control plane functional entity, where the indication information is used to indicate that the network segment information received from the control plane functional entity is home PLMN network segment information. Before sending a session establishment request PDU to the network, the terminal first converts, based on the mapping between the S-NSSAI of the home PLMN network segment and the S-NSSAI of the visited PLMN network segment, the corresponding S-NSSAI of the home PLMN network segment used to transmit the 5G PDN connection, which the terminal wants to send, to the corresponding S-NSSAI of the network segment of the visited PLMN used to send in the 5G PDN connection that the terminal wants to send; and then adds, to the session establishment request PDU, the corresponding S-NSSAI of the network segment of the visited PLMN used to transmit in 5G the PDN connection that the terminal wants to transmit in order to initiate the network to establish the PDU session.

[0014] In an exemplary implementation, the corresponding network segment information used to transfer the established PDN connection to the 5G network further includes the corresponding NSI-ID of the network segment instance used to transfer the established PDN connection to the 5G network. When more than one network segment instance is deployed for one S-NSSAI fragment in the network, the corresponding network segment information that is sent by the control plane functional entity to the terminal is used to transfer the PDN connection to the 5G network, further includes the corresponding network segment instance identifier, so thereby ensuring session continuity after the transfer of the PDN connection.

[0015] In an exemplary implementation, before the terminal receives from the control plane functional entity the corresponding network segment information used to transfer the established packet data PDN connection to the 5G network, the method further includes: sending, by the terminal, a capability indication to the control plane functional entity, where the capability indication is used to indicate that the terminal can be handed over to the 5G network. In a specific implementation, after PDN connections are established in the 4G network, not all terminals need to receive the corresponding network segment information used to transfer the established PDN connections to the 5G network. For example, a terminal not capable of communication in a 5G network cannot be transferred to the 5G network using the information even if the terminal receives the information.

[0016] Optionally, sometimes not all PDN connections can be transferred to the 5G network. For PDN connections that cannot be forwarded to the 5G network, session establishment eventually fails even if the terminal sends a session establishment request PDU. To avoid unnecessary signaling waste, before sending the session establishment request of the packet data PDU, the method further includes: determining by the terminal a PDN connection that is in the established PDN connections and that can be transferred to the 5G network, where the first PDN connection is any PDN connection, which can be transferred to the 5G network. The determination by the terminal of the PDN connection that is in the established PDN connection and that can be transferred to the 5G network specifically includes: sending the registration request by the terminal, where the registration request includes the corresponding network segment information used for transferring the PDN connection to the 5G network, which the terminal wants to transfer, and the PDN connection that the terminal wants to transfer is some or all of the established PDN connections; receiving a registration response, where the registration response includes the S-NSSAI of the network segment to which the terminal is allowed to access; and determining a PDN connection that can be transferred to the 5G network based on the corresponding S-NSSAI used to transfer to the 5G network the PDN connection that the terminal wants to transfer and the S-NSSAI of the network segment that the terminal is allowed to access.

[0017] It should be noted that when the terminal is in a non-roaming scenario or in a roaming scenario with Local Breakout (LBO) request processing, the corresponding network segment information used to transfer to the 5G network the PDN connection that the terminal wants to transfer, is the network segment information received by the terminal from the control plane functional entity.

[0018] When the terminal is in the Home routed scenario, the corresponding network segment information used to transmit the PDN connection to the 5G network that the terminal wants to transmit is the network segment information of the visited PLMN. Specifically, before sending the PDU session establishment request, the method further includes: mapping, by the terminal, based on a mapping relationship between the home PLMN network segment S-NSSAI and the guest PLMN network segment S-NSSAI, the network segment information sent by the control plane functional entity, in the network segment information of the visited PLMN.

[0019] According to a second aspect, a session establishment method is provided, the method including: sending, by the control plane functional entity, to the terminal, using the MME, the corresponding network segment information used to transfer the established PDN connection of the packet data network to the 5G network, where the corresponding network information the segment used to transfer the established PDN connection to the 5G network includes a single network segment selection assistance information S-NSSAI corresponding to the established PDN connection; and receiving a session establishment request of a packet data PDU that is sent using AMF by the terminal, wherein the session establishment request PDU includes a network segment S-NSSAI corresponding to the first PDN connection and a corresponding data network DNN used to transmit the first PDN connection. to the 5G network, and the first PDN connection is any of the established PDN connections. The control plane functional entity sends to the terminal the corresponding network segment information used to transfer the established PDN connection to the 5G network, so that when handover to the 5G network, the terminal can establish a PDU session in the 5G network segment based on the corresponding network segment information.

[0020] In an exemplary implementation, the corresponding network segment information used to transfer the established packet data PDN connection to the 5G network is carried in the protocol configuration option PCO message. The control plane functional entity sends to the terminal, via a PCO message, the appropriate network segment information used to transfer the established PDN connection to the 5G network. In particular, the PCO message may be sent to the terminal by a Mobility Management Entity (MME) and a base station in a 4G network. The corresponding network segment information used to transfer the established packet data PDN connection to the 5G network is sent using the PCO message, so that the MME can only transmit the message transparently, but does not require the message to be stored.

[0021] In an exemplary implementation, the control plane functional entity may specifically determine, based on the APN of the access point corresponding to the established PDN connection, the corresponding network segment information used to transfer the established PDN connection to the 5G network.

[0022] In a possible implementation in the home routing scenario, the control plane functional entity further sends indication information to the terminal, where the indication information is used to indicate that the network segment information sent by the control plane functional entity is the home PLMN network segment information, so that after receiving the indication information, the terminal converted the home PLMN network segment information received from the control plane functional entity into the guest PLMN network segment information.

[0023] In an exemplary implementation, if the established PDN connection is established in a home routing scenario, the control plane functional entity may determine the corresponding home PLMN network segment information used to forward the established PDN connection to the 5G network; then convert the corresponding network segment information of the home PLMN used to transfer the established PDN connection to the 5G network into the network segment information of the visited PLMN; and send to the terminal, as the corresponding network segment information used to transfer the established PDN connection to the 5G network, the corresponding network segment information of the visited PLMN used to transfer the established PDN connection to the 5G network. Thus, all the network segment information received by the terminal can be used directly, and the terminal does not need to configure the associated local lookup table, and it is no longer necessary to determine whether the current situation is a home routing scenario when establishing a PDU session.

[0024] In an exemplary implementation, the corresponding network segment information used to transfer the established PDN connection to the 5G network further includes the corresponding NSI-ID of the network segment instance used to transfer the established PDN connection to the 5G network. When more than one network segment instance is deployed for one S-NSSAI fragment in the network, the corresponding network segment information, which is sent by the control plane functional entity to the terminal and used to transfer the PDN connection to the 5G network, further includes the corresponding network segment instance identifier, so thereby ensuring session continuity after the transfer of the PDN connection.

[0025] In an exemplary implementation, before the control plane functional entity sends to the terminal the corresponding network segment information used to transfer the established packet data PDN connection to the 5G network, the method includes: receiving, by the control plane functional entity, a capability indication from the terminal, where the capability indication is used to indicate that the terminal can be handed over to the 5G network. The control plane functional entity may establish PDN connections for different terminals at the same time. However, for PDN connections corresponding to terminals that do not have 5G communication capability or do not need to transfer to the 5G network, the control plane functional entity does not need to send to the terminals the corresponding network segment information used to transfer PDN connections to the 5G network.

[0026] According to a third aspect, a terminal is provided, wherein the terminal has a function of implementing the method in the first aspect. The function may be implemented in hardware, or may be implemented in hardware running corresponding software. The hardware or software includes one or more modules corresponding to the above function.

[0027] According to a fourth aspect, an equipment is provided, including a processor and a memory, where the memory is configured to store a computer-executable instruction, and when the equipment is operated, the processor executes the computer-executable instruction stored in the memory, so that the equipment executes a session establishment method. in accordance with any of the first aspect or implementations of the first aspect. In particular, the equipment may be a terminal in a session establishment method according to any of the first aspect or implementations of the first aspect, or a chip in the terminal.

[0028] According to a fifth aspect, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores an instruction, and when the instruction is executed on a computer, the computer can perform a session establishment method according to any of the first aspect or implementations of the first aspect.

[0029] According to a sixth aspect, a computer program product is provided including an instruction, wherein when the computer program product is running on the computer, the computer can perform a session establishment method according to any of the first aspect or implementations of the first aspect.

[0030] The technical effect introduced in any constructive manner in the third to sixth aspects is related to the technical effects introduced in the different constructive manner in the first aspect. Details are not described here again.

[0031] According to a seventh aspect, a control plane functional entity is provided, wherein the control plane functional entity has a method implementation function in the second aspect. The function may be implemented in hardware, or may be implemented in hardware running corresponding software. The hardware or software includes one or more modules corresponding to the above function.

[0032] According to an eighth aspect, an equipment is provided, including a processor and a memory, where the memory is configured to store a computer-executable instruction, and when the device is operated, the processor executes the computer-executable instruction stored in the memory, so that the device performs a session establishment method according to with any of the second aspect or implementations of the second aspect.

[0033] According to a ninth aspect, a computer-readable storage medium is provided, wherein the computer-readable storage medium stores an instruction, and when the instruction is executed on a computer, the computer can perform a session establishment method according to any of the second aspect or implementations of the second aspect.

[0034] According to a tenth aspect, a computer program product is provided including an instruction, wherein when the computer program product is running on the computer, the computer can perform a session establishment method according to any one of the second aspect or implementations of the second aspect.

[0035] These aspects or other aspects of this application are clearer and easier to understand in the descriptions of the following embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0036] FIG. 1 is a schematic diagram of an architecture for interworking between a 4G network and a 5G network;

[0037] FIG. 2 is a schematic diagram of a hardware structure of a communication device according to an embodiment of this application;

[0038] FIG. 3 is a schematic flowchart 1 of a session establishment method according to an embodiment of this application;

[0039] FIG. 4 is a flowchart 2 of a session establishment method according to an embodiment of this application;

[0040] FIG. 5 is a schematic structural diagram of equipment according to an embodiment of this application; and

[0041] FIG. 6 is a block diagram of a control plane functional entity according to an embodiment of this application.

Description of Embodiments

[0042] For ease of understanding of the technical solutions in the embodiments of this application, below, the technologies associated with this application are first briefly described.

[0043] NSSAI:

[0044] NSSAI includes many parts of S-NSSAI. S-NSSAI includes a slice/service type (SST) and a segment differentiator (SD). SST and SD can be defined in the standard or customized by the operator. SD is optional information that complements SST to distinguish between multiple network segments of the same segment/service type, eg SD can be used to represent ownership of a network segment. The NSSAI types and functions defined in 3GPP TS 23.501 are shown in Table 1.

Table 1

Type of Function Description Configured NSSAI (configured NSSAI) NSSAI pre-configured on the terminal S-NSSAI Used to identify a specific network segment Permitted NSSAI (allowed NSSAI) NSSAI provided for the current registration area by the service network, the network segment to which the terminal is allowed to access

[0045] The network architecture and service scenario that are described in the embodiments of the present disclosure are intended to more clearly describe the technical solutions in the embodiments of the present disclosure and do not limit the technical solutions provided in the embodiments of the present disclosure. One of skill in the art may be aware that with the evolution of network architecture and the advent of new service scenarios, the technical solutions provided in the embodiments of the present disclosure are also applicable to similar technical problems.

[0046] An embodiment of the present disclosure provides a mobility management method that can be applied to architecture 100 for interworking between a 4G network and a 5G network, as shown in FIG. 1. As shown in FIG. 1, the architecture 100 includes the following entities that are shared between the 4G network and the 5G network: user plane function (UPF) entity + PDN gateway user plane function (PGW-U) entity, session management function (SMF) + PDN gateway control plane function (PGW-C) object, policy control function (PCF) object + policy and charging rules object (policy and charging rules function (PCRF) and home subscriber server (HSS) + unified data management (UDM) object. The "+" symbol in this document represents a combination. UPF is a 5G network user plane feature. PGW-U is a gateway user plane function corresponding to UPF, 4G network. SMF is a 5G network session management function. PGW-C is a function of the gateway control plane corresponding to the SMF of the 4G network. PCF is a 5G network policy management function. PCRF is a policy and charging rule function corresponding to PCF, 4G network. "Combination" in this document means that one device has the functions of two objects. In this embodiment of this application, for ease of description, the HSS + UDM entity is referred to as a user data management entity, and the PGW-C entity + SMF entity is referred to as a control plane functional entity. A uniform description is made here, and the details are not described below again. Of course, another name may alternatively be used for the network device obtained by the above combination. This embodiment of the present application does not place particular restrictions on it.

[0047] In addition, as shown in FIG. 1, an architecture for interworking between a 4G network and a 5G network may further include an MME, a Serving Gateway (SGW) and an Access and Mobility Management Function (AMF) in the 5G network.

[0048] The terminal accesses the 4G network using the evolved universal terrestrial radio access network (E-UTRAN) device, and the terminal accesses the 5G network using the next generation radio access network device , NG-RAN) device. The E-UTRAN device communicates with the MME via the S1-MME interface. The E-UTRAN device communicates with the SGW via the S1-U interface. The MME communicates with the SGW via the S11 interface. The MME communicates with the user data management entity via the S6a interface. The MME communicates with the AMF entity via the N26 interface. The SGW communicates with the PGW-U entity + the UPF entity via the S5-U interface. The SGW communicates with the PGW-C entity + SMF entity via the S5-C interface. The PGW-U entity + the UPF entity communicate with the NG-RAN device via the N3 interface. The PGW-U entity + UPF entity communicate with the PGW-C entity + SMF entity via the N4 interface. The PGW-C entity + SMF entity communicate with the PCRF entity + PCF entity via the N7 interface. The HSS + UDM entity communicates with the PGW-C entity + SMF entity via the N10 interface. The HSS + UDM object communicates with the AMF object via the N8 interface. The PCRF entity + the PCF entity communicate with the AMF entity via the N15 interface. The PGW-C entity + SMF entity communicate with the AMF entity via the N11 interface. The AMF entity communicates with the NG-RAN device through the N2 interface. The AMF object communicates with the terminal via the N1 interface.

[0049] It should be noted that the names of interfaces between network elements in FIG. 1 are just examples, and interface names may be different names in a particular implementation. This embodiment of the present application does not impose particular restrictions on it.

[0050] It should be noted that an NG-RAN device in a 5G network may also be referred to as an access device. The access device is a device that accesses the core network, for example, it can be a base station, a broadband network gateway (BNG), an aggregation switch, or a non-3GPP access device. The base station may be a base station in various forms, such as a macro base station, a micro base station (also called a small cell), a relay station, or an access point. This embodiment of the present application does not impose particular restrictions on it.

[0051] Of course, there may be other network elements in the 4G network and the 5G network. For example, the 4G network may further include a general packet radio system (GPRS) serving node (serving GPRS support node, SGSN) and the like; and the 5G network may further include an authentication server function (AUSF) object, a network slice selection function (NSSF) object, and the like. This embodiment of the present application does not impose particular restrictions on it.

[0052] Since the PDN connection in the 4G network is served by the combined PGW-C/SMF (namely, the control plane functional entity) and the combined PGW-U/UPF, when the terminal is transferred from the 4G network to the 5G network, the PDU session is still served by the PGW- C/SMF and PGW-U/UPF. In other words, the session service binding remains the same before and after the transfer, so the session IP address remains the same. In this embodiment of this application, when a UE accesses a 4G network and establishes a PDN connection, the control plane functional entity sends to the terminal the corresponding network segment information used to transfer the PDN connection established by the terminal to the 5G network. When the terminal subsequently moves to the 5G coverage area, the terminal adds to the registration request to be sent to the 5G network the corresponding network segment information used to transfer the established PDN connection to the 5G network. Based on the network segment information corresponding to the established PDN connection, the 5G network determines the AMF serving the UE and the allowed NSSAI, and sends the allowed NSSAI to the terminal. The terminal can determine, based on the allowed NSSAI and the corresponding network segment information used to transfer the PDN connection established by the terminal in the 4G network to the 5G network, those established PDN connections that can be transferred to the 5G network. For a PDN connection that can be handed over to a 5G network, the terminal initiates a PDU session establishment to complete the handover of the session between networks.

[0053] The terminal in this embodiment of this application may be various devices having a wireless communication function, such as a portable device, an automotive device, a wearable device, a computing device, or other processing device connected to a wireless modem; or may be a subscriber unit, a cellular phone, a smart phone, a wireless data card, a personal digital assistant (PDA), a tablet computer, a wireless modem (modem), a portable (handheld ) device, laptop computer, cordless phone or wireless local loop (WLL) station, machine type communication terminal (MTC), user equipment (user equipment, UE) , mobile station (mobile station, MS), terminal device (terminal device) or the like. For ease of description in this application, the above devices are collectively referred to as terminals.

[0054] The following describes the technical solutions in the embodiments of this application with reference to the accompanying drawings in the embodiments of this application. In the description of this application, "multiple" means at least two, unless otherwise indicated. In addition, in order to clearly describe the technical solutions in the embodiments of this application, terms such as "first" and "second" are used in the embodiments of this application to distinguish between the same elements or similar elements that have basically the same function and purpose. One skilled in the art can understand that terms such as "first" and "second" are not intended to limit the number and sequence of execution; and terms such as "first" and "second" do not indicate a definite difference.

[0055] As shown in FIG. 2 nodes shown in Fig. 1, such as terminal, MME, AMF, SMF entity + PGW-C entity, E-UTRAN device, or NG-RAN device, may be implemented by the communication device (or system) in FIG. 2.

[0056] FIG. 2 is a schematic diagram of a hardware structure of a communication device according to an embodiment of this application. The communication device 200 includes at least one processor 201, a communication line 202, a memory 203, and at least one communication interface 204.

[0057] The processor 201 may be a central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits capable of controlling the execution of programs from the solutions of this application. .

[0058] Link 202 may include a channel used to transfer information between the above components.

[0059] The communication interface 204 is configured to communicate using any equipment, such as a transceiver, with another device or communication network, such as Ethernet, a radio access network (RAN) or a wireless local area network (wireless local area network, WLAN ).

[0060] The memory 203 may be read-only memory (ROM), another type of static storage device that can store static information and instructions, random access memory (RAM), or another type of dynamic storage device. which can store information and instructions; or may be electrically erasable programmable read-only memory (EEPROM), compact disc read-only memory (CD-ROM), or other optical disk storage device, optical disk storage device (including compact optical disc, laser disc, optical disc, digital versatile disc, Blu-ray disc, etc.), magnetic disk storage device or other magnetic storage device, or any other medium that can be transferred or storing the expected program code in the form of an instruction or data structure that is accessible to the computer. However, this is not a limitation. The memory may exist independently and be connected to the processor using link 202 . Alternatively, the memory may be integrated with the processor.

[0061] The memory 203 is configured to store a computer executable instruction for executing the solutions of this application, and the processor 201 controls the execution of the computer executable instruction. The processor 201 is configured to execute a computer-executable instruction stored in the memory 203 to implement the session establishment method provided in the following embodiment of this application.

[0062] Optionally, a computer-executable instruction in this embodiment of this application may also be referred to as an application program code. This embodiment of the present application does not impose particular restrictions on it.

[0063] In a specific implementation, in an embodiment, processor 201 may include one or more CPUs, such as CPU 0 and CPU 1 in FIG. 2.

[0064] In a specific implementation in an embodiment, communication device 200 may include a plurality of processors, such as processor 201 and processor 208 in FIG. 2. Each of the processors may be a single-core (single-CPU) processor or may be a multi-core (multi-CPU) processor. A processor, as used herein, may be one or more devices, circuitry, and/or a processing core configured to process data (eg, a computer program instruction).

[0065] In a specific implementation in the embodiment, the communication device 200 may further include an output device 205 and an input device 206. An output device 205 communicates with the processor 201 and can display information in a variety of ways. For example, the output device 205 may be a liquid crystal display (LCD), a light emitting diode (LED) display device, a cathode ray tube (CRT) display device, or a projector. Input device 206 communicates with processor 201 and can receive user input in a variety of ways. For example, input device 206 may be a mouse, keyboard, touch screen device, or touch device.

[0066] Communication device 200 may be a general purpose device or a dedicated device. In a specific implementation, communication device 200 may be a desktop computer, a laptop computer, a network server, a personal digital assistant (PDA), a mobile phone, a tablet computer, a wireless terminal device, an embedded device, or a device having a structure similar to that of FIG. . 2. The type of communication device 200 is not limited in this embodiment of this application.

[0067] The following describes in detail the session establishment method provided in the embodiment of this application with reference to FIG. 1 and FIG. 2.

[0068] FIG. 3 shows a session establishment method provided in an embodiment of this application. In this embodiment, the terminal first accesses the 4G network using the E-UTRAN device and establishes a PDN connection in the 4G network. Subsequently, since the terminal transitions to the 5G service band, the terminal accesses the 5G network using the NG-RAN device. This embodiment of this application is applicable to a non-roaming scenario or an LBO roaming scenario. The method includes the following steps.

[0069] Step 301: The terminal establishes a PDN connection in the 4G network.

[0070] The PDN connection may be established during the attachment process, or the PDN connection establishment may be initiated by the terminal after the attachment. For the process of establishing a PDN connection, refer to the existing protocol. Details are not described here again.

[0071] Optionally, when the terminal establishes a PDN connection, the terminal determines that the terminal can subsequently be migrated to the 5G network, for example, determines that the terminal is capable of supporting the 5G network, the terminal sends a capability indication to the control plane functional entity. The capability indication is used to indicate that the terminal can subsequently be transferred to the 5G network. The capability indication may be capability information indicating that the terminal supports 5G (eg, indicating that the terminal supports 5G NAS). Sending by the terminal a capability indication to the control plane functional entity specifically includes: sending by the terminal a capability indication to the MME when the terminal is connected to the 4G network, so that in the PDN connection establishment process, the MME sends the capability indication to the control plane functional entity using the SGW; or the terminal sending a protocol configuration option (PCO) message to the control plane functional entity, where the PCO message carries an indication of capabilities.

[0072] It should be noted that a terminal may establish one or more PDN connections in a 4G network, and one or more PDN connections may be served by one or more control plane functional entities. This embodiment of the present application does not impose any restrictions on it. For ease of description, this embodiment of this application uses an example in which a terminal establishes one or more PDN connections using only one control plane functional entity.

[0073] Step 302: The control plane functional entity obtains the corresponding network segment information used to transfer the established PDN connection to the 5G network, and sends the network segment information to the terminal, so that the terminal receives the corresponding network segment information used to transfer the established PDN connection to the 5G network.

[0074] An established PDN connection includes one or more PDN connections. In actual deployment, all PDU sessions in a 5G network are associated with network segment instances. One network slice instance may be indicated by a network slice instance ID (NSI-ID). One network segment identified by S-NSSAI may have multiple network segment instances (eg, different network segment instances may be used to implement load balancing). In addition, one instance of a network segment can support one or more data networks. The data network can be identified by the name of the data network (Data Network Name, DNN).

[0075] Therefore, based on the network deployment state, in order to transfer the PDN connection established by the terminal in the 4G network to the session PDU in the network segment instance in the 5G network, the corresponding network segment information which is used to transfer the PDN connection to the 5G network, and which sent by the control plane functional entity to the terminal, may include various content. Since the control plane functional entity resides in a network segment instance, when the control plane functional entity supports multiple network segments, the control plane functional entity can obtain the S-NSSAI corresponding to the different network segment instances supported by the control plane functional entity, the NSI-IDs of the network segment instance and the name or names of one or more data networks supported by the network segment instances. The corresponding network segment information used to transfer the established PDN connection to the 5G network includes the corresponding network segment S-NSSAI used to transfer the established PDN connection to the 5G network, and optionally further includes the corresponding NSI-ID of the network instance. segment used to transfer the established PDN connection to the 5G network. When the DNN used to handoff the terminal to the 5G network is different from the APN in the 4G network, optionally, the control plane functional entity also needs to obtain the DNN used to handoff the terminal to the 5G network and send the DNN to the terminal. Details are described below.

[0076] In an exemplary implementation based on the network deployment state, the mapping between the PDN connection and the S-NSSAI is pre-configured in the control plane functional entity. The acquisition by the control plane functional entity of the corresponding network segment information used to transfer the established PDN connection to the 5G network includes: acquisition by the control plane functional entity based on the established PDN connection information and the preconfigured mapping between the PDN connection and S-NSSAI, S -NSSAI of the network segment corresponding to the established PDN connection. For this network deployment, the DNN used to forward the PDN connection to the 5G network is the same as the APN in the 4G network, and only one network segment instance is deployed per S-NSSAI fragment.

[0077] For example, it is assumed that a preconfigured mapping between a PDN connection and an S-NSSAI is shown in Table 2.

table 2

PDN connection information S-NSSAI PDN connection 1 S-NSSAI 1 PDN connection 2 S-NSSAI 2 PDN connection 3 S-NSSAI 3 … …

[0078] In another possible implementation, based on the network deployment state, the mapping between the PDN connection and the S-NSSAI/DNN is pre-configured in the control plane functional entity. The acquisition by the control plane functional entity of the relevant network segment information used to transfer the established PDN connection to the 5G network includes: acquisition by the control plane functional entity based on the established PDN connection information and the preconfigured mapping between the PDN connection and the S-NSSAI/DNN , corresponding to the S-NSSAI of the network segment used to carry the established PDN connection to the 5G network, and the DNN used to carry the established PDN connection to the 5G network. For this network deployment, the DNN used to forward the PDN connection to the 5G network may be different from the APN in the 4G network, and only one network segment instance is deployed per S-NSSAI fragment.

[0079] For example, it is assumed that a preconfigured mapping between a PDN connection and an S-NSSAI/DNN is shown in Table 3.

Table 3

PDN connection information S-NSSAI DNN PDN connection 1 S-NSSAI 1 DNN 1 PDN connection 2 S-NSSAI 2 DNN 2 … … …

[0080] In another possible implementation, based on the network deployment state, the mapping between the PDN connection and the S-NSSAI/DNN/NSI-ID is preconfigured in the control plane functional entity. The acquisition by the control plane functional entity of the relevant network segment information used to transfer the established PDN connection to the 5G network includes: acquisition by the control plane functional entity based on the established PDN connection information and the preconfigured mapping between the PDN connection and the S-NSSAI/DNN /NSI-ID corresponding to the S-NSSAI of the network segment used to carry the established PDN connection to the 5G network, the DNN used to carry the established PDN connection to the 5G network, and the corresponding NSI-ID of the network segment instance used to carry the established PDN connection to the 5G network. For this network deployment, the DNN used to carry the PDN connection in 5G may be different from the APN in 4G, and more than one network segment instance may be deployed for each S-NSSAI fragment.

[0081] For example, it is assumed that the preconfigured mapping between the PDN connection and the S-NSSAI/DNN/NSI-ID is shown in Table 4.

Table 4

PDN connection information S-NSSAI NSI ID DNN PDN connection 1 S-NSSAI 1 NSI-ID 1 DNN 1 PDN connection 2 S-NSSAI 2 NSI ID 2 DNN 2 ... ... ... ...

[0082] A PDN connection may be represented by an APN corresponding to the PDN connection. In other words, the established PDN connection information may specifically include an APN corresponding to the established PDN connection. Optionally, the PDN connection may be represented by an APN corresponding to the PDN connection and the corresponding subscription information. The specific form of the PDN connection information is not limited in this embodiment of this application.

[0083] In a particular implementation, in a PDN connection establishment response or a terminal attach response, the control plane functional entity may send to the terminal, via a PCO message, appropriate network segment information used to convey the established PDN connection to the 5G network. Optionally, the PCO message sent by the control plane functional entity to the terminal further includes a DNN used to transfer the established PDN connection to the 5G network.

[0084] Step 303: When the terminal moves to a 5G network coverage area, the terminal initiates a registration request, and the registration request includes the corresponding network segment information used to transfer to the 5G network the PDN connection that the terminal needs to transfer, the registration request is sent to the AMF using an access device (eg, a base station), so that the AMF receives the registration request and the PDN connection to be sent to the terminal is some or all of the established PDN connections.

[0085] In particular, after receiving from the control plane functional entity the corresponding network segment information used to transmit the established PDN connection in 5G in step 302, the terminal determines, according to the requirement of the terminal policy, the PDN connection that the terminal needs to transmit and the corresponding network information. segment used to transfer to the 5G network the PDN connection that the terminal needs to transfer. For example, the user initiates the establishment of PDN connection 1 and PDN connection 2, respectively, using APP 1 and APP 2 installed on the terminal. The control plane functional entity returns to the terminal the corresponding network segment information used to transfer the 1 PDN connection to the 5G network and the corresponding network segment information used to transfer the 2 PDN connection to the 5G network. In this case, if the terminal detects that a transfer policy (which may be set by the user or may be inherent in the APP) has been set for APP 1 and APP 2, for example, APP 1 is prohibited from transferring to the 5G network, and APP 2 is preferably transferred to the network 5G, when there is 5G coverage, the terminal determines that the 2 PDN connection is the PDN connection that the terminal needs to transfer, and the corresponding network segment information used to transfer the 2 PDN connection to the 5G network is the corresponding network segment information used to transfer to the network 5G PDN connection that the terminal needs to transmit.

[0086] Specifically, when a terminal initiates a registration request in a 5G network, if the registration request carries an S-NSSAI, the access device selects an AMF based on the S-NSSAI carried in the registration request. In this embodiment of this application, the terminal adds to the registration request the corresponding network segment S-NSSAI used to transfer to the 5G network the PDN connection that the terminal needs to transfer. Optionally, the registration request may further carry another S-NSSAI requested by the terminal. The access device selects the AMF based on the corresponding S-NSSAI of the network segment used to send the PDN connection to the 5G network that the terminal needs to send and the other S-NSSAI requested by the terminal; and forwards the registration request to the selected AMF, so that the AMF receives the registration request sent by the terminal.

[0087] In particular, the terminal may add to the "requested NSSAI" both the corresponding network segment S-NSSAI used to transmit the PDN connection to the 5G network that the terminal needs to transmit, and the other S-NSSAI requested by the terminal; and send "requested NSSAI" to AMF. In addition, the terminal notifies the AMF of the S-NSSAI in the "requested NSSAI" corresponding to the established PDN connection. Alternatively, the terminal puts the other requested S-NSSAI in the "requested NSSAI" and puts, in the other independent NSSAI, the corresponding network segment S-NSSAI used to send to the 5G network the PDN connection that the terminal needs to send; and sends another independent NSSAI to the AMF. The method of sending by the terminal with the AMF registration request of the corresponding S-NSSAI of the network segment used for the transmission in 5G of the PDN connection that the terminal needs to transmit is not limited in this embodiment of this application.

[0088] Optionally, the registration request further includes a terminal identifier. After receiving the registration request from the terminal, the AMF may perform a process such as authentication on the terminal and finally obtain a permanent identifier (SUPI, Subscription Permanent Identifier) of the terminal. Please refer to the relevant standard protocol for details. The details are not described again in this embodiment of this application.

[0089] Step 304: The AMF obtains the terminal subscription data, where the terminal subscription data includes the terminal's network segment subscription data and the correspondence between the APN corresponding to the PDN connection to be transmitted by the terminal and the control plane functional entity identifier.

[0090] In particular, the AMF obtains the terminal's subscription data based on the terminal identifier (or SUPI) in the registration request. The AMF preferably obtains the terminal's subscription data locally. If there is no local terminal subscription data, the AMF obtains the terminal subscription data from the user data management entity. Optionally, the AMF further stores the subscription data of the terminal in a context appropriate for the terminal.

[0091] The network segment subscription data of the terminal includes an S-NSSAI corresponding to the subscribed network segment, and optionally further includes information such as a DNN corresponding to the subscribed network segment.

[0092] Step 305: The AMF obtains the S-NSSAI (namely, NSSAI allowed) corresponding to the network segment that the terminal is allowed to access.

[0093] In particular, the AMF can obtain the authorized NSSAI based on information such as the corresponding network segment information used to transmit to the 5G network the PDN connection that the terminal needs to transmit, and the subscription data of the terminal.

[0094] In an exemplary implementation, the AMF determines the allowed NSSAI based on information such as the corresponding network segment information used to transmit to the 5G network the PDN connection that the terminal needs to transmit and the terminal's subscription data. Optionally, the AMF may alternatively determine the allowed NSSAI based on another S-NSSAI requested by the terminal.

[0095] For example, when the corresponding network segment information used to transmit to the 5G network the PDN connection that the terminal needs to transmit includes the corresponding network segment S-NSSAI used to transmit to the 5G network the PDN connection that the terminal needs to transmit, AMF obtains a union of the S-NSSAI of the network segment corresponding to the PDN connection that the terminal needs to transmit and another S-NSSAI requested by the terminal; and then obtains the intersection of the union, the S-NSSAI corresponding to the network segment subscribed to by the terminal, and the S-NSSAI corresponding to the network segment supported by the AMF to determine the allowed NSSAI. When the corresponding network segment information used to transmit to the 5G network the PDN connection that the terminal needs to transmit includes the network segment S-NSSAI corresponding to the PDN connection that the terminal needs to transmit, and the corresponding network segment instance NSI-ID used for 5G transmission of the PDN connection that the terminal needs to transmit, in addition to the above definition, the AMF further resolves, based on the NSI-ID of the network segment instance used to transmit to the 5G network of the PDN connection that the terminal needs to transmit, the PDN connection corresponding to the network instance segment that AMF cannot serve.

[0096] For example, the S-NSSAI of the network segment corresponding to the PDN connection that the terminal needs to transmit includes S-NSSAI 1 and S-NSSAI 2; the other S-NSSAI requested by the terminal includes S-NSSAI 3 and S-NSSAI 4; The S-NSSAI corresponding to the network segment subscribed by the terminal includes S-NSSAI 1, S-NSSAI 3, and S-NSSAI 5; and the S-NSSAI corresponding to the network segment supported by the AMF includes S-NSSAI 1, S-NSSAI 12, S-NSSAI 13, S-NSSAI 14 and S-NSSAI 15. The AMF then obtains the S-NSSAI association of the network segment, corresponding to the PDN connection that the terminal needs to send and the other S-NSSAI requested by the terminal: S-NSSAI 1, S-NSSAI 2, S-NSSAI 3 and S-NSSAI 4; and then obtains the intersection of the union, the S-NSSAI corresponding to the network segment subscribed to by the terminal, and the S-NSSAI corresponding to the network segment supported by the AMF: S-NSSAI 1 and S-NSSAI 3, thereby determining that the allowed NSSAI includes in yourself S-NSSAI 1 and S-NSSAI 3.

[0097] In another possible implementation, the AMF queries a network slice selection function (NSSF) object to determine the allowed NSSAI for the terminal. Specifically, the AMF sends a segment selection request to the NSSF. The segment selection request includes the corresponding network segment information used to transmit to the 5G network the PDN connection that the terminal needs to transmit and the terminal's subscription data, and optionally further includes another S-NSSAI requested by the terminal. The NSSF determines the allowed NSSAI and the target AMF set corresponding to the allowed NSSAI based on the corresponding network segment information used to send to the 5G network the PDN connection that the terminal needs to send and the terminal's subscription data, and optionally further based on another S-NSSAI, requested by the terminal. Specifically, when the corresponding network segment information used for forwarding to the 5G network of the PDN connection that the terminal needs to transmit includes the corresponding network segment S-NSSAI used to forward to the 5G network of the PDN connection that the terminal needs to transmit, the NSSF obtains the merge. the corresponding S-NSSAI of the network segment used to transmit the PDN connection to the 5G network that the terminal needs to transmit, and the other S-NSSAI requested by the terminal; then obtains the intersection of the union and the S-NSSAI corresponding to the network segment to which the terminal has subscribed; and then, based on information such as the location of the terminal and the AMF deployment state in the network, determines the allowed NSSAI and the target AMF set corresponding to the allowed NSSAI. An authorized NSSAI is part or all of the first NSSAI. Any AMF in the target AMF set may serve any network segment that complies with the allowed NSSAI. Optionally, the NSSF may select a target AMF from a target AMF set.

[0098] The NSSF sends the allowed NSSAI and the target AMF set (or the target AMF selected from the target AMF set) to the AMF. In this embodiment of this application, the AMF and NSSF may alternatively determine the allowed NSSAI using a different method. The method of determining the allowed NSSAI by AMF and NSSF is not limited in this embodiment of this application.

[0099] The AMF determines, based on the target AMF set or the target AMF returned by the NSSF, whether the terminal needs to be redirected to another AMF for processing. If the terminal needs to be redirected to another AMF, the AMF redirects the terminal to another AMF. The method of redirection is well known. The details are not described again in this embodiment of this application. In this embodiment of this notice, the AMF is considered by default to be included in the target AMF set, ie the AMF does not need to redirect the terminal to another AMF for processing.

[00100] Step 306: The AMF sends a registration response to the terminal, so that the terminal receives a registration response, where the registration response includes an S-NSSAI corresponding to the network segment that the terminal is allowed to access, namely, the allowed NSSAI.

[00101] Step 307: The terminal determines a PDN connection that can be transferred to the 5G network.

[00102] In particular, the terminal determines a PDN connection that can be transferred to the 5G network based on the S-NSSAI corresponding to the network segment that the terminal is allowed to access and the corresponding network segment information used to transfer to the 5G PDN connection, which the terminal needs to be sent. For example, the S-NSSAI corresponding to the network segment that the terminal is allowed to access includes S-NSSAI 1 and S-NSSAI 3, and the network segment S-NSSAI corresponding to the PDN connection that the terminal needs to transmit includes: S -NSSAI 1 and S-NSSAI 2. The terminal then determines that the PDN connection corresponding to the network segment whose S-NSSAI is S-NSSAI 1 can be transferred to the 5G network.

[00103] The following steps are performed for each PDN connection that can be transferred to the 5G network to transfer the PDN connection to a PDU session in the 5G network.

[00104] Step 308: The terminal sends a PDU session establishment request to the AMF, so that the AMF receives the PDU session establishment request sent by the terminal, the PDU session establishment request includes a network segment S-NSSAI corresponding to the first PDN connection, and the DNN is used for transfer of the first PDN connection in 5G, and the first PDN connection is any PDN connection that can be transferred.

[00105] In particular, if the control plane functional entity does not send to the terminal the DNN used to transfer the established 5G PDN connection in step 302, the default terminal considers that the DNN used to transfer the established 5G PDN connection is the same as APN in 4G. Therefore, the DNN used to carry the first PDN connection in 5G is the same as the APN corresponding to the first PDN connection.

[00106] If the control plane functional entity sends to the terminal the DNN used to transfer the established connection of the PDN in 5G in step 302, the terminal by default considers that the DNN used to transfer the established connection of the PDN in 5G is different from the APN in 4G. Therefore, the session establishment request PDU further includes an APN corresponding to the first PDN connection.

[00107] It should be noted that after the PDN connection is established, the terminal stores the APN corresponding to the established PDN connection.

[00108] Step 309: The AMF determines the control plane functional entity and forwards the session establishment request PDU to said determined control plane functional entity such that the control plane functional entity receives the session establishment request PDU.

[00109] The AMF determines the control plane functional entity based on the APN corresponding to the first PDN connection and the correspondence between the APN and the control plane functional entity identifier.

[00110] Specifically, when the session establishment request PDU received by the AMF includes the network segment S-NSSAI corresponding to the first PDN connection and the DNN used to carry the first PDN connection in 5G, the AMF determines that the APN corresponding to the first connection The PDN is the same as the DNN used to carry the first PDN connection in 5G, and determines the control plane function object based on the APN corresponding to the first PDN connection and the correspondence between the APN and the control plane function object identifier. When the PDU session establishment request received by the AMF includes the network segment S-NSSAI corresponding to the first PDN connection, the DNN used to carry the first PDN connection in 5G, and the APN corresponding to the first PDN connection, the AMF determines the control plane functional entity based on the APN corresponding to the first PDN connection and the mapping between the APN and the control plane functional entity identifier.

[00111] Step 310: Establish a PDU session on the network segment instance corresponding to the PDN connection.

[00112] The subsequent PDU session establishment process is the same as in the existing protocol. Details are not described here.

[00113] In this embodiment of this application, when a UE has established a PDN connection in a 4G network, the control plane functional entity determines the corresponding network segment information used to convey the established PDN connection in 5G, and sends the network segment information to the UE via the PCO. When the UE subsequently registers with the 5GC, the UE adds the network segment information to the request. This helps the 5GC select the appropriate 5G network segment that supports the established PDN connection and ensures that the session IP address remains the same.

[00114] FIG. 4 shows another session establishment method provided in an embodiment of this application. In this embodiment, the terminal first accesses the 4G network using the E-UTRAN device and establishes a PDN connection in the 4G network. Subsequently, since the terminal transitions to the 5G service band, the terminal accesses the 5G network using the NG-RAN device. This embodiment of this application is applicable to the roaming scenario (with home routing) HPLMN (Home public land mobile operator network). In this embodiment of this application, the home control plane functional entity is located in the HPLMN. The method includes the following steps.

[00115] Step 401: The terminal establishes a PDN connection in the 4G network.

[00116] Step 402: The home control plane functional entity obtains the corresponding network segment information used to transmit the established PDN connection to the 5G network, and sends the network segment information to the terminal, so that the terminal receives the corresponding network segment information used to transmit the established PDN connection to the 5G network.

[00117] Step 401 is the same as step 301, and step 402 is the same as step 302. For related descriptions, refer to the related steps in the above embodiment. Details are not described here again. It should be noted that, in the implementation, the corresponding network segment information that is sent by the home control plane functional entity to the terminal and that is used to transfer the PDN connection in 5G is the home PLMN network segment information (eg, S-NSSAI). If the network segment information sent by the home control plane functional entity to the UE is home PLMN network segment information, the home control plane functional entity sends indication information to the UE indicating that the PDN connection is home routable. The indication information is used to indicate that the network segment information received from the home control plane functional entity is the home PLMN network segment information, so that the UE maps the home PLMN S-NSSAI to the visited PLMN S-NSSAI based on the home PLMN ID, S- the NSSAI of the home PLMN and the mapping relationship that is configured by the UE and which is the relationship between the S-NSSAI of the home PLMN and the S-NSSAI of the visited PLMN. The home routing indication information may be a home PLMN ID or a home routing tag.

[00118] In another implementation, the corresponding network segment information that is sent by the home control plane functional entity to the terminal and that is used to transfer the PDN connection in 5G is the Visited PLMN S-NSSAI. In this case, the home control plane functional entity converts the corresponding home PLMN network segment information used to transfer the PDN connection in 5G to the guest PLMN network segment information. In particular, the home control plane functional entity first determines, according to the method of step 302, the corresponding home PLMN network segment information used to transfer the PDN connection in 5G; and then converts the corresponding network segment information of the home PLMN used to transfer the PDN connection in 5G to the network segment information of the visited PLMN. The home control plane functional entity obtains from the MME the PLMN ID for the visited PLMN currently being accessed by the terminal; and then converts the home PLMN network segment information to the guest PLMN network segment information based on the mapping relationship configured by the home control plane functional entity, which is the relationship between the S-NSSAI of the visited PLMN and the S-NSSAI of the home PLMN, as shown in the following table.

Home PLMN ID S-NSSAI Home PLMN Guest PLMN ID S-NSSAI Guest PLMN PLMN ID 1 S-NSSAI 1 PLMN ID 2 S-NSSAI 12 PLMN ID 1 S-NSSAI 2 PLMN ID 2 S-NSSAI 22 PLMN ID 1 S-NSSAI 1 PLMN ID 3 S-NSSAI 13

[00119] Optionally, the home control plane functional entity may alternatively request the NSSF to map the S-NSSAI of the home PLMN to the S-NSSAI of the visited PLMN. In particular, the control plane functional entity sends the home PLMN ID, the home PLMN S-NSSAI, and the guest PLMN ID to the NSSF. The NSSF returns the S-NSSAI of the visited PLMN to the control plane functional entity.

[00120] Step 403: When the terminal moves to a 5G network coverage area, the terminal initiates a registration request, wherein the registration request includes the corresponding network segment information used to transfer to 5G the PDN connection that the terminal wants to transfer, and the registration request is sent to the AMF using an access device (eg, a base station), so that the AMF receives the registration request. If the terminal receives the home routing indication information in step 402, the terminal converts the received home PLMN network segment information to the visited PLMN network segment information. The terminal maps the home PLMN network segment information to the visited PLMN network segment information based on the home PLMN network segment information, the home PLMN ID, and a mapping relationship that is configured by the UE, which is a relationship between the home PLMN network segment information and the visited PLMN network segment information. The PDN connection that the terminal wants to send is some or all of the established PDN connection.

[00121] Step 404: The AMF obtains the terminal's subscription data, the terminal's subscription data including the terminal's network segment subscription data and the correspondence between the APN corresponding to the PDN connection that the terminal wants to transmit and the control plane functional entity identifier.

[00122] Step 404 is the same as step 304. For related descriptions, refer to the related step in the preceding embodiment. Details are not described here again.

[00123] Step 405: The AMF obtains the S-NSSAI (namely, NSSAI allowed) corresponding to the network segment that the terminal is allowed to access.

[00124] In an exemplary implementation, the specific implementation of step 403 is the same as the implementation of step 303, except that the AMF in step 403 is a guest AMF, but the AMF in step 303 is a home AMF. In this case, in step 405, based on the mapping between the S-NSSAI of the home PLMN network segment and the S-NSSAI of the visited PLMN network segment, the AMF converts the corresponding network segment S-NSSAI used to carry the established 5G PDN connection into an S-NSSAI network segment of the visited PLMN, and converts the S-NSSAI of the network segment to which the user has subscribed to the S-NSSAI of the network segment of the visited PLMN; and then determines the S-NSSAI corresponding to the network segment of the visited PLMN to which the terminal is allowed to access. The specific determination method is the same as in step 305. Details are not described here again.

[00125] In another exemplary implementation, the corresponding network segment information used to transmit the 5G PDN connection that the terminal wants to transmit in step 403 is obtained by the terminal by converting, based on the mapping between the home PLMN network segment S-NSSAI and the network S-NSSAI of the visited PLMN segment corresponding to the S-NSSAI of the network segment used to carry the 5G PDN connection that the terminal wants to send to the corresponding S-NSSAI of the visited PLMN network segment used to send the 5G PDN connection that the terminal wants to send. To be specific, compared to step 302, after determining the PDN connection that the terminal wants to transmit, the terminal further needs to translate, based on the mapping between the S-NSSAI of the home PLMN network segment and the S-NSSAI of the visited PLMN network segment, the corresponding S-NSSAI of the network segment used for 5G transfer of the PDN connection that the terminal wants to transfer to the corresponding S-NSSAI of the visited PLMN network segment used for 5G transfer of the PDN connection that the terminal wants to transfer. Thus, in step 405, based on the mapping between the S-NSSAI of the home PLMN network segment and the S-NSSAI of the visited PLMN network segment, the AMF also maps the S-NSSAI of the network segment that the user has subscribed to into the S-NSSAI of the visited PLMN network segment; and then determines the S-NSSAI corresponding to the network segment of the visited PLMN that the terminal is allowed to access based on the S-NSSAI of the network segment of the visited PLMN corresponding to the S-NSSAI of the network segment to which the user has subscribed and based on the corresponding S-NSSAI of the network segment the visited PLMN used to carry the 5G PDN connection that the terminal wants to send. The specific determination method is the same as in step 305. Details are not described here again.

[00126] Step 406: The AMF sends a registration response to the terminal so that the terminal receives a registration response, the registration response including an S-NSSAI corresponding to the network segment of the visited PLMN that the terminal is allowed to access, namely the NSSAI allowed.

[00127] Step 407: The terminal determines a PDN connection that can be transferred to the 5G network.

[00128] Referring to step 307, the difference from step 307 is: If the corresponding network segment information which is received by the terminal and which is used to transmit the PDN connection in 5G is the S-NSSAI of the home PLMN, the terminal converts, based on the correspondence between the S-NSSAI of the home PLMN network segment and the S-NSSAI of the visited PLMN network segment, the network segment S-NSSAI corresponding to the PDN connection that the terminal wants to transmit to the corresponding S-NSSAI of the guest PLMN network segment used to transmit in 5G the PDN connection that the terminal wants to send; and then determines a PDN connection that can be transferred to the 5G network with the reference to the S-NSSAI, which is received at step 406 and which corresponds to the network segment of the visited PLMN to which the terminal is allowed to access.

[00129] The following steps are performed for each PDN connection that can be transferred to the 5G network to transfer the PDN connection to a PDU session in the 5G network.

[00130] Step 408: The terminal sends a session establishment request PDU to the AMF, so that the AMF receives the session establishment request PDU sent by the terminal, the session establishment request PDU includes the corresponding S-NSSAI of the visited PLMN network segment used to transfer the first PDN connection to the 5G network, and the DNN used to transfer the first PDN connection to 5G, and the first PDN connection is any PDN connection that can be transferred.

[00131] Specifically, in step 402, if the home control plane functional entity does not send to the terminal the DNN used to transmit the established PDN connection in 5G, the default terminal considers that the DNN used to transmit the established PDN connection in 5G is the same as like APN in 4G. Therefore, the DNN used to carry the first PDN connection in 5G is the same as the APN corresponding to the first PDN connection.

[00132] If the home control plane functional entity sends to the terminal the DNN used to transmit the established PDN connection in 5G in step 402, the terminal by default considers that the DNN used to transmit the established PDN connection in 5G is different from the APN in 4G. Therefore, the session establishment request PDU further includes an APN corresponding to the first PDN connection.

[00133] It should be noted that after the PDN connection is established, the terminal stores the APN corresponding to the established PDN connection.

[00134] Optionally, if the UE receives the home PLMN network segment instance ID in step 402, the UE sends home PLMN network segment instance ID information to the AMF.

[00135] Step 409: The AMF determines the guest control plane functional entity and the home control plane functional entity, and forwards a PDU session establishment request to said determined guest control plane functional entity such that the guest control plane functional entity receives the PDU session establishment request.

[00136] Specifically, determining by the AMF the home control plane functional entity includes: obtaining by the AMF the PDN connection context information of the terminal from the user data management entity, where the PDN connection context information includes a correspondence between the APN corresponding to the PDN connection, and a functional entity identifier of the home control plane. When the PDU session establishment request received by the AMF includes the S-NSSAI of the visited PLMN network segment corresponding to the first PDN connection and the DNN used to carry the first PDN connection in 5G, the AMF determines that the APN corresponding to the first PDN connection is the same as the DNN used to carry the first PDN connection in 5G, and determines the home control plane function object based on the APN corresponding to the first PDN connection and the correspondence between the APN and the functional object identifier of the home control plane function. When the PDU session establishment request received by the AMF includes the S-NSSAI of the visited PLMN network segment corresponding to the first PDN connection, the DNN used to carry the first PDN connection in 5G, and the APN corresponding to the first PDN connection, the AMF determines the home plane functional entity control based on the APN corresponding to the first PDN connection and the correspondence between the APN and the home control plane functional entity identifier.

[00137] Determining the guest control plane functional entity by the AMF specifically includes: determining, by the AMF, the guest control plane functional entity based on the S-NSSAI of the network segment of the guest PLMN corresponding to the first PDN connection and the DNN used for transmission the first PDN connection in 5G. In particular, the AMF may determine the guest control plane functional object based on local configuration or by querying the network function repository function (NRF) function object. For a specific determination process, refer to the existing protocol. Details are not described here again. If the AMF receives the Home PLMN Network Segment Instance ID from the UE in step 408, the AMF selects the Guest Control Plane Functional Entity further based on the Home PLMN Network Segment Instance ID. The selected guest control plane functional entity may be compatible with the home PLMN network segment instance.

[00138] Step 410: The AMF forwards the session establishment request PDU and the identifier of the home control plane functional entity to the guest control plane functional entity.

[00139] Step 411: The guest control plane functional entity sends a PDU session establishment request to the home control plane functional entity based on the identifier of the home control plane functional entity.

[00140] Step 412: Establish a PDU session on the network segment instance corresponding to the PDN connection.

[00141] The subsequent PDU session establishment process is the same as in the existing protocol. Details are not described here.

[00142] In this embodiment of this application, when a UE has established a PDN connection in a 4G network, the home control plane functional entity determines the corresponding network segment information used to convey the established PDN connection in 5G, and sends the network segment information to the UE via the PCO. When the UE subsequently registers with the 5GC, the UE adds to the request the network segment information of the visited PLMN into which the above network segment information has been mapped. This helps the 5GC select the appropriate 5G network segment that supports the established PDN connection and ensures that the session IP address remains the same.

[00143] The actions of network elements (eg, terminal and control plane functional entity) in the embodiments of FIG. 3 and FIG. 4 may be executed by the processor 201 of the communication device 200 shown in FIG. 2 by executing the application program code stored in the memory 203. This embodiment of the present application does not impose any restrictions on it.

[00144] The solution provided in the embodiments of this application has been described above, mainly in terms of interaction between network elements. It can be understood that in order to implement the above functions, devices such as a terminal, an AMF, and a control plane functional entity include respective hardware structures and/or software modules to perform the functions. One skilled in the art will readily appreciate that with reference to the examples described in the embodiments disclosed in this specification, the blocks and steps of an algorithm may be implemented by hardware or a combination of hardware and computer software in this application. Whether the function is performed by hardware or by hardware controlled by computer software depends on particular applications and design constraints. A person skilled in the art can use various methods to implement the described functions for each particular application, but such an implementation should not be considered to be outside the scope of this application.

[00145] In embodiments of this application, functional modules of devices such as a terminal and a control plane functional entity may be separated in accordance with the above method examples. For example, functional modules may be separated based on functions, or two or more functions may be integrated into one processing module. An integrated module may be implemented in hardware or may be implemented in a software function module. It should be noted that the separation of modules in the embodiments of this application is an example and is simply a logical separation of functions, and there may be other ways of separation in actual implementation.

[00146] For example, FIG. 5 is a schematic block diagram of equipment 500 when functional modules are separated by an integration method. Equipment 500 may be a terminal in the above embodiments, or may be a chip in a terminal. This embodiment of the present application does not impose particular restrictions on it. As shown in FIG. 5, the equipment includes a receiving unit 501 and a sending unit 502. The receiving unit 501 is configured to receive, from the control plane functional entity, corresponding network segment information used to transmit the established packet data PDN connection to the 5G network, wherein the corresponding network segment information used to transmit the established packet data PDN connection to the 5G network includes the corresponding unit information S-NSSAI of network segment selection assistance used to transfer the established PDN connection to the 5G network. The sending module 502 is configured to send a session establishment request PDU of the packet data unit, wherein the session establishment request PDU includes the corresponding network segment S-NSSAI used to transfer the first PDN connection to the 5G network and the corresponding data network DNN used to transferring the first PDN connection to the 5G network, and the first PDN connection is any of the established PDN connection.

[00147] Optionally, the corresponding network segment information used to transfer the established packet data PDN connection to the 5G network is carried in the protocol configuration option PCO message.

[00148] Optionally, the receiving unit 501 is further configured to receive indication information from the control plane functional entity, where the indication information is used to indicate that the network segment information received from the control plane functional entity is home PLMN network segment information.

[00149] The terminal further includes a conversion module. The conversion module is configured to convert, based on the correspondence between the S-NSSAI of the home PLMN network segment and the S-NSSAI of the guest PLMN network segment, the S-NSSAI of the home PLMN network segment used for 5G transmission of the PDN connection that the terminal wants to transfer to the corresponding S-NSSAI of the network segment of the visited PLMN used to carry the 5G PDN connection that the terminal wants to send.

[00150] Optionally, the corresponding network segment information used to transfer the established PDN connection to the 5G network further includes the corresponding network segment instance NSI-ID used to transfer the established PDN connection to the 5G network.

[00151] In an exemplary implementation, send module 502 is further configured to send a capability indication to the control plane functional entity, where the capability indication is used to indicate that the terminal can be handed over to the 5G network.

[00152] The equipment further includes a determination module 503. The determining unit 503 is configured to determine the PDN connection that is in the established PDN connection and that can be transferred to the 5G network. The first PDN connection is any PDN connection that can be passed in 5G. In an exemplary implementation, the determining module 503 is specifically configured to: send a registration request, wherein the registration request includes the corresponding network segment information used to transfer to the 5G network the PDN connection that the terminal wants to transfer, and the PDN connection that the terminal wants to transfer is some or all established PDN connections; receiving a registration response, where the registration response includes the S-NSSAI of the network segment to which the terminal is allowed to access; and determining a PDN connection that can be transferred to the 5G network based on the corresponding S-NSSAI used to transfer to the 5G network the PDN connection that the terminal wants to transfer and the S-NSSAI of the network segment that the terminal is allowed to access.

[00153] Optionally, the PCO message further includes a corresponding DNN used to transfer the first PDN connection to the 5G network, and the PDU session establishment request further includes an access point APN corresponding to the first PDN connection.

[00154] For a description of the functions of the respective functional modules, refer to all related contents of the steps included in the above method embodiments. Details are not described here again.

[00155] In this embodiment, the equipment 500 is represented by dividing the functional modules in the integration mode. Here, a "module" may be an application-specific integrated circuit (ASIC), a circuit, a processor that executes one or more software or firmware programs, and a memory, integrated logic circuit, and/or other device that can provide the aforementioned features. In a simple embodiment, one of ordinary skill in the art can recognize that equipment 500 may take the form shown in FIG. 2.

[00156] For example, processor 201 in FIG. 2 can execute the computer-executable instruction stored in the memory 203 so that the equipment 500 executes the session establishment methods in the above method embodiments.

[00157] In particular, the functions and processes for implementing the receive module 501, the send module 502, and the determine module 503 in FIG. 5 may be implemented by processor 201 in FIG. 2 by executing the computer-executable instruction stored in the memory 203.

[00158] Optionally, when the equipment 500 is a chip, the functions and processes for implementing the receive unit 501, send unit 502, and determine unit 503 may be implemented by output, circuit, or the like. Optionally, when hardware 500 is a chip, memory 203 may be an on-chip storage device such as a register or cache. Of course, when the equipment 500 is a terminal, the memory 203 may be a storage unit that resides in the terminal and is off-chip. This embodiment of the present application does not impose particular restrictions on it.

[00159] The equipment provided in this embodiment of this application may be configured to perform the above session establishment methods. Therefore, for the technical effect that can be achieved by the equipment, refer to the above method embodiments. Details are not described here again.

[00160] FIG. 6 is a block diagram of a control plane functional object 600. The control plane functional entity 600 includes a sending module 601 and a receiving module 602 . The sending unit 601 is configured to send corresponding network segment information used to transmit the established packet data PDN connection to the 5G network, where the corresponding network segment information used to transmit the established PDN connection to the 5G network includes single information S- NSSAI to facilitate selection of the network segment corresponding to the established PDN connection. The receiving module 602 is configured to receive a packet data PDU session establishment request, where the PDU session establishment request includes a network segment S-NSSAI corresponding to the first PDN connection and a corresponding data network DNN used to transfer the first PDN connection to the network. 5G, and the first PDN connection is any of the established PDN connection.

[00161] Optionally, the corresponding network segment information used to convey the established packet data PDN connection to the 5G network is carried in the PCO message of the protocol configuration option, and the PCO message further includes the corresponding DNN used to convey the established PDN connection to the 5G network.

[00162] Optionally, the control plane functional entity further includes a definition module. The determination module is configured to determine, based on the APN of the access point corresponding to the established PDN connection, the corresponding network segment information used to transfer the established PDN connection to the 5G network.

[00163] In an exemplary implementation, the sending module 502 is further configured to send indication information, where the indication information is used to indicate that the network segment information sent by the control plane functional entity is the home PLMN network segment information.

[00164] If the established PDN is set in a home routing scenario, the sending module 502 is specifically configured to: determine the corresponding home PLMN network segment information used to convey the established PDN connection in 5G; converting corresponding network segment information of the home PLMN used for transferring the established PDN connection in 5G to network segment information of the visited PLMN; and sending to the terminal, as the corresponding network segment information used for transmitting the established PDN connection in 5G, the corresponding network segment information of the visited PLMN used for transmitting the established PDN connection in 5G.

[00165] Optionally, the corresponding network segment information used to transfer the established PDN connection to the 5G network further includes the corresponding network segment instance NSI-ID used to transfer the established PDN connection to the 5G network.

[00166] In an exemplary implementation, the receiving module 602 is further configured to receive a capability indication from the terminal, where the capability indication is used to indicate that the terminal can be transferred to the 5G network.

[00167] For a description of the functions of the respective functional modules, refer to all related contents of the steps included in the above method embodiments. Details are not described here again.

[00168] The control plane functional entity 600 may be implemented on an integrated circuit, an RF integrated circuit, a printed circuit board, or the like. Furthermore, the control plane functional entity 600 may be an independent device or may be part of a relatively large device. In this embodiment, the control plane functional entity 600 is represented by dividing the functional modules in an integration manner. Here, a "module" may be a specific ASIC, a circuit, a processor that executes one or more software or firmware programs, and a memory, an integrated logic circuit, and/or other device that can provide the aforementioned functions.

[00169] In a simple embodiment, one skilled in the art can recognize that the control plane functional entity 600 may have the form shown in FIG. 2. For example, processor 201 in FIG. 2 can call a computer-executable instruction stored in the memory 203 so that the control plane functional entity 600 executes the session establishment methods in the above method embodiments.

[00170] All or some of the above embodiments may be implemented in software, hardware, firmware, or any combination thereof. When software is used to implement the embodiments, the embodiments may be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When computer program instructions are downloaded and executed on a computer, all or some of the procedures or functions are generated in accordance with embodiments of the present application. The computer may be a general purpose computer, a dedicated computer, a computer network, or other programmable equipment. The computer instructions may be stored on a computer-readable storage medium or may be transferred from a computer-readable storage medium to another computer-readable storage medium. For example, computer instructions may be transmitted from a website, computer, server, or data center to another website, computer, server, or data center by wire (such as coaxial cable, optical fiber, or digital subscriber line (DSL) ) or wirelessly (eg infrared, radio or microwave). A computer-readable storage medium may be any usable medium accessible to a computer, or a data storage device, such as a server or data center, that combines one or more usable media. The medium used may be a magnetic medium (eg, floppy disk, hard disk, or magnetic tape), an optical medium (eg, DVD), a semiconductor medium (eg, a solid state disk (SSD)) or the like.

[00171] While this application has been described with reference to the embodiments, in the course of implementing this application that seeks protection, one skilled in the art can understand and implement another variation of the disclosed embodiments by viewing the accompanying drawings, the disclosure, and the accompanying claims. In the claims, the term "comprising" (comprising) does not exclude another component or another step, and the indication of the singular does not exclude the case of a plurality. One processor or other unit may implement several of the functions listed in the claims. Some measures are reflected in dependent claims that differ from each other, but this does not mean that these measures cannot be combined to obtain a better effect.

[00172] Although this application has been described with reference to specific features and their embodiments, it is obvious that various modifications and combinations can be made to this application without deviating from the scope of this application. Accordingly, the description and accompanying drawings are merely exemplary descriptions of this application as defined by the appended claims, and are construed as any and all modifications, variations, combinations or equivalents that fall within the scope of this application. Obviously, a person skilled in the art can make various modifications and changes to this application without departing from the scope of this application. This application is intended to cover these modifications and variations of this application, provided that they fall within the protection scope defined by the following claims and their equivalent technologies.

Claims (91)

1. A method for establishing a session, comprising the steps of: receiving, by the terminal, from the control plane functional entity at the time of setting up a packet data network, PDN, connection in a 4G network, a single network segment selection assistance information, S-NSSAI, corresponding to the PDN connection, and a home public land mobile network ID, PLMN, wherein the home PLMN ID indicates that the S-NSSAI corresponding to the PDN connection received from the control plane functional entity is the home PLMN S-NSSAI; converting, by the terminal, the S-NSSAI of the home PLMN corresponding to the PDN connection to the S-NSSAI of the visited PLMN corresponding to the PDN connection; and sending, by the terminal, a session establishment request when handing over the PDN connection to the fifth generation network, 5G, wherein the session establishment request contains a Visited PLMN S-NSSAI corresponding to the PDN connection. 2. The method of claim 1, wherein the home S-NSSAI corresponding to the PDN connection is included in the protocol configuration option, PCO. 3. The method according to claim 1 or 2, wherein converting the S-NSSAI of the home PLMN corresponding to the PDN connection to the S-NSSAI of the visited PLMN corresponding to the PDN connection comprises: converting, by the terminal, based on the mapping between the S-NSSAI of the home PLMN and the S-NSSAI of the visited PLMN, the S-NSSAI of the home PLMN corresponding to the PDN connection to the S-NSSAI of the visited PLMN corresponding to the PDN connection. 4. The method according to any one of claims 1 to 3, further comprising the step of: sending, by the terminal, a capability indication to the control plane functional entity, wherein the capability indication is used to indicate that the terminal can be handed over to the 5G network. 5. The method of claim 4, wherein sending the capability indication to the control plane functional entity comprises: sending, by the terminal, with the protocol configuration option, PCO, a capability indication to the control plane functional entity. 6. The method according to any one of claims 1 to 5, further comprising the steps of: sending, by the terminal, a registration request to the base station, the registration request containing a visited S-NSSAI corresponding to the PDN connection; receiving, by the terminal, a registration response, wherein the registration response contains the allowed NSSAI of the terminal. 7. The method of claim 6, wherein the visited S-NSSAI corresponding to the PDN connection is carried in the NSSAI Requested field of the registration request. 8. The method according to claim 6 or 7, further comprising selecting, by the base station, an access and mobility control function in accordance with the visited S-NSSAI corresponding to the PDN connection. 9. The method according to any one of claims 1 to 8, wherein the session establishment request further comprises a corresponding data network name, DNN. 10. The method according to any one of claims 1 to 9, wherein the control plane functional entity is a PGW-C+SMF (PDN Gateway Control Plane Functions + Session Management Functions) object. 11. A communication terminal containing a receiving module, a sending module and a conversion module, wherein: the receiving module is configured to receive from the control plane functional entity at the time of setting up a packet data network connection, PDN, in a 4G network, a single network segment selection assistance information, S-NSSAI, corresponding to the PDN connection, and a home public land mobile network ID, PLMN, wherein the home PLMN ID indicates that the S-NSSAI corresponding to the PDN connection received from the control plane functional entity is the home PLMN S-NSSAI; the conversion module is configured to convert the S-NSSAI of the home PLMN corresponding to the PDN connection to the S-NSSAI of the visited PLMN corresponding to the PDN connection; and the sending module is configured to send a session establishment request when handing over the PDN connection to the fifth generation network, 5G, wherein the session establishment request contains the S-NSSAI of the visited PLMN corresponding to the PDN connection. 12. The communication terminal of claim 11, wherein the home S-NSSAI corresponding to the PDN connection is included in the protocol configuration option, PCO. 13. The communication terminal according to claim 11 or 12, wherein the conversion module is configured to convert the S-NSSAI of the home PLMN corresponding to the PDN connection to the S-NSSAI of the visited PLMN corresponding to the PDN connection, which is: converting, based on the mapping between the S-NSSAI of the home PLMN and the S-NSSAI of the visited PLMN, the S-NSSAI of the home PLMN corresponding to the PDN connection to the S-NSSAI of the visited PLMN corresponding to the PDN connection. 14. The communication terminal according to any one of claims 11-13, wherein the sending module (502) is further configured to send a capability indication to the control plane functional entity, wherein the capability indication is used to indicate that the communication terminal can be transferred to the 5G network. 15. The communications terminal of claim 14, wherein the sending module is further configured to send the capability indication to the control plane functional entity, which is: sending, using the protocol configuration option, PCO, a capability indication to the control plane functional entity. 16. The communication terminal according to any one of claims 11 to 15, wherein the sending module is further configured to send a registration request to a base station, the registration request comprising a Visited S-NSSAI corresponding to the PDN connection; and the receiving module is further configured to receive a registration response, wherein the registration response contains the allowed NSSAI of the communication terminal. 17. The communication terminal of claim 16, wherein the visited S-NSSAI corresponding to the PDN connection is transferred to the NSSAI Requested field of the registration request. 18. The communication terminal according to any one of claims 11-17, wherein the session establishment request further comprises a corresponding data network name, DNN. 19. The communication terminal according to any one of claims 11-18, wherein the control plane functional entity is a PGW-C+SMF entity. 20. A method for establishing a session, comprising the steps of: sending, by means of the control plane functional entity, to the terminal at the time of setting up a packet data network, PDN, connection in a 4G network, a single network segment selection assistance information, S-NSSAI, corresponding to the PDN connection, and a home public land mobile network ID, PLMN, wherein the home PLMN ID indicates that the S-NSSAI corresponding to the PDN connection received from the control plane functional entity is the home PLMN S-NSSAI; and receive, by the control plane functional entity, a session establishment request when transferring the PDN connection to the fifth generation network, 5G, wherein the session establishment request contains the S-NSSAI of the visited PLMN corresponding to the PDN connection, and the S-NSSAI of the visited PLMN corresponding to the PDN connection is mapped from the S-NSSAI of the home PLMN corresponding to the PDN connection via the terminal. 21. The method of claim 20, wherein the home S-NSSAI corresponding to the PDN connection is included in the protocol configuration option, PCO. 22. The method of claim 20 or 21, further comprising receiving, via the control plane functional entity, a capability indication from the terminal, the capability indication being used to indicate that the terminal can be handed over to the 5G network. 23. The method of claim 22, wherein receiving a capability indication from the terminal comprises: receiving, via the control plane functional entity, with the protocol configuration option, PCO, a capability indication from the terminal. 24. The method of any one of claims 20-23, wherein the control plane functional entity is a PGW-C+SMF entity. 25. A control plane functional entity comprising a send module and a receive module, wherein the sending module is configured to send to the terminal, at the time of setting up a connection of a packet data network, PDN, in a 4G network, a unit network segment selection assistance information, S-NSSAI, corresponding to the PDN connection and a home public land mobile network ID, PLMN, wherein the ID the home PLMN indicates that the S-NSSAI corresponding to the PDN connection received from the control plane functional entity is the S-NSSAI of the home PLMN; and the receiving module is configured to receive the session establishment request when transferring the PDN connection to the fifth generation network, 5G, wherein the session establishment request contains the S-NSSAI of the visited PLMN corresponding to the PDN connection, wherein the S-NSSAI of the visited PLMN corresponding to the PDN connection is converted from S -NSSAI of the home PLMN corresponding to the PDN connection by the terminal. 26. The control plane functional entity of claim 25, wherein the home S-NSSAI corresponding to the PDN connection is included in the protocol configuration option, PCO. 27. The control plane functional entity of claim 25 or 26, wherein the receiving module is further configured to receive a capability indication from the terminal, where the capability indication is used to indicate that the terminal can be handed over to the 5G network. 28. The control plane functional entity of claim 27, wherein the receiving module is further configured to receive a capability indication from the terminal, which is: receiving with the protocol configuration option, PCO, indication of capabilities from the terminal. 29. A control plane functional entity as in any one of claims 25-28, wherein the control plane functional entity is a PGW-C+SMF entity. 30. A communication terminal, the communication terminal comprising at least one processor and a memory coupled to at least one processor; and the memory is configured to store a computer-executable instruction, and when the communication terminal is running, at least one processor executes the computer-executable instruction stored in the memory, so that the communication terminal performs the session establishment method of any one of claims 1 to 10. 31. The communication terminal of claim 30, comprising a terminal or a chip in the terminal. 32. A control plane functional entity, the control plane functional entity comprising at least one processor and a memory coupled to the at least one processor; and the memory is configured to store a computer-executable instruction, and when the communication terminal is running, at least one processor executes the computer-executable instruction stored in the memory, so that the communication terminal performs the session establishment method according to any one of claims 20 to 24. 33. A computer storage medium containing an instruction, wherein when the instruction is executed on the computer, the computer is directed to perform the method of any one of claims 1-10. 34. A computer storage medium containing an instruction, wherein when the instruction is executed on the computer, the computer is directed to perform the method of any one of claims 20-24. 35. A session establishment system comprising a communication terminal according to any one of claims 11-19 and a control plane functional entity according to any one of claims 25-29. 36. A method for establishing a session, comprising the steps of: receiving, by the terminal, from the control plane functional entity at the time of setting up a packet data network, PDN, connection in a 4G network, a single network segment selection assistance information, S-NSSAI, for the network segment corresponding to the PDN connection, and a home public land mobile ID network, PLMN, wherein the home PLMN ID indicates that the S-NSSAI corresponding to the PDN connection received from the control plane functional entity is the home PLMN S-NSSAI; sending, by the terminal, a registration request to the 5G access and mobility control function when the terminal moves to the coverage area of the 5G network, the registration request contains a Visited S-NSSAI corresponding to the PDN connection, and the Visited S-NSSAI corresponding to the PDN connection is transformed by the terminal based on the home S-NSSAI corresponding to the PDN connection, and receiving, by means of the terminal, a registration response from the access and mobility control function, wherein the registration response contains a visited S-NSSAI corresponding to the network segment to which said terminal is allowed to access. 37. The method of claim 36, wherein the home S-NSSAI corresponding to the PDN connection is contained in the protocol configuration option, PCO. 38. The method of claim 36 or 37, wherein the method further comprises: converting, by the terminal, based on the mapping between the S-NSSAI of the home PLMN and the S-NSSAI of the visited PLMN, the S-NSSAI of the home PLMN corresponding to the PDN connection to the S-NSSAI of the visited PLMN corresponding to the PDN connection. 39. The method according to any one of claims 36 to 38, wherein the S-NSSAI corresponding to the network segment to which said terminal is allowed to access is determined by intersecting the visited S-NSSAI corresponding to the PDN connection, the S-NSSAI to which the terminal is subscribed, and S-NSSAI supported by the access and mobility control function. 40. The method according to any one of claims 36-39, wherein the method further comprises the step of: indicate, by the terminal, to the control plane functional entity that the terminal supports the ability to transmit subsequently to the 5G network. 41. The method according to any one of claims 36-40, wherein the method further comprises the step of: sending, by the terminal, a session establishment request when transferring the PDN connection to the 5G network, wherein the session establishment request contains a visited PLMN S-NSSAI corresponding to the PDN connection. 42. The method of claim 41, wherein prior to sending the session establishment request, the method further comprises: determining, by the terminal, that the PDN connection can be transferred to the 5G network. 43. The method of claim 42, wherein determining, by the terminal, that the PDN connection can be transferred to the 5G network comprises: determining, by the terminal, based on the S-NSSAI of the visited PLMN corresponding to the PDN connection and the visited S-NSSAI corresponding to the network segment to which said terminal is allowed to access, that the PDN connection can be transferred to the 5G network. 44. The method of any one of claims 36-43, wherein the visited S-NSSAI corresponding to the PDN connection is carried in the NSSAI Requested field of the registration request. 45. A communication terminal, wherein the communication terminal includes a receiving module, a sending module, and a conversion module, wherein the receiving module is configured to receive from the control plane functional entity at the time of setting up a packet data network connection, PDN, in the 4G network, a single network segment selection assistance information, S-NSSAI, for the network segment corresponding to the PDN connection, and a home ID. a public land mobile network, PLMN, wherein the home PLMN ID indicates that the S-NSSAI corresponding to the PDN connection received from the control plane functional entity is the home PLMN S-NSSAI; the sending module is configured to send a registration request to a 5G network access and mobility control function when the terminal moves to a 5G network coverage area, the registration request contains a visited S-NSSAI corresponding to the PDN connection, and the visited S-NSSAI corresponding to the PDN connection, translated by the communication terminal based on the home S-NSSAI corresponding to the PDN connection; and the receiving module is further configured to receive a registration response from the access and mobility control function, wherein the registration response contains a visited S-NSSAI corresponding to the network segment to which said terminal is allowed to access. 46. The communication terminal of claim 45, wherein the home S-NSSAI corresponding to the PDN connection is contained in the protocol configuration option, PCO. 47. The communication terminal according to claim 45 or 46, wherein the communication terminal further comprises a determination module, and the determination module is configured to convert based on the mapping between the S-NSSAI of the home PLMN and the S-NSSAI of the visited PLMN, the S-NSSAI of the home PLMN corresponding to the PDN connection to the S-NSSAI of the visited PLMN corresponding to the PDN connection. 48. The communication terminal according to any one of claims 45 to 47, wherein the S-NSSAI corresponding to the network segment to which said terminal is allowed to access is determined by intersecting the Visited S-NSSAI corresponding to the PDN connection, the S-NSSAI to which the terminal is subscribed. , and S-NSSAI supported by the access and mobility control function. 49. The communication terminal according to any one of claims 45 to 48, wherein the sending module is further configured to indicate to the control plane functional entity that the communication terminal supports the ability to transmit subsequently to the 5G network. 50. The communication terminal according to any one of claims 45 to 49, wherein the sender is further configured to send a session establishment request when handing over the PDN connection to the 5G network, the session establishment request comprising a Visited PLMN S-NSSAI corresponding to the PDN connection. 51. The communication terminal of claim 50, wherein the communication terminal further comprises a determination module, and the determining module is configured to determine that the PDN connection can be transferred to the 5G network. 52. The communication terminal of claim 51, wherein the determining module is further configured to determine, based on the S-NSSAI of the visited PLMN corresponding to the PDN connection and the visited S-NSSAI corresponding to the network segment to which said terminal is allowed to access, that the PDN connection can be transferred to the 5G network. 53. The communication terminal according to any one of claims 45 to 52, wherein the visited S-NSSAI corresponding to the PDN connection is carried in the NSSAI Requested field of the registration request. 54. A communication terminal according to any one of claims 45 to 53, wherein the communication terminal comprises a terminal or a chip in the terminal. 55. The communication terminal according to any one of claims 45 to 53, wherein the control plane functional entity is a PGW-C+SMF entity. 56. A computer-readable storage medium, wherein the computer-readable storage medium stores instructions and, when the instructions are executed at the communication terminal, the communication terminal is capable of performing the method of any one of claims 36-44.

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