AMF selection method for inter-PLMN handover, apparatus, device and medium

Abstract

The present invention belongs to the technical field of communications. Provided are an access and mobility management function (AMF) selection method for inter-PLMN handover, an apparatus, an electronic device and a computer-readable storage medium. The method comprises: determining whether a user terminal undergoes inter-PLMN handover; in response to the user terminal undergoing inter-PLMN handover, acquiring NSSAI of a target PLMN; sending to a network element service repository function (NRF) an AMF instance query request, such that the NRF selects a target AMF according to the NSSAI of the target PLMN and a target tracking area identity (TAI); and receiving the target AMF fed back by the NRF and performing AMF handover. Thus, the present invention at least solves the problem in the prior art that a target AMF having inaccurate slice capability is possibly selected during inter-PLMN handover, and therefore the handover may be interrupted and then UE service experience is affected, thus being suitable for scenarios such as international roaming and shared network roaming.

Description

Method, device, equipment and medium for selecting AMF for inter-PLMN handover

[0001] The present invention claims priority to a Chinese patent application with an application date of June 30, 2023, application number 202310798005.2, and name “AMF selection method, device, equipment and medium for inter-PLMN switching”. Technical Field

[0002] The present invention relates to the field of communication technology, and in particular to a method, device, electronic device, and computer-readable storage medium for selecting an access and mobility management function (AMF) for handover across a public land mobile network (PLMN). Background Art

[0003] Currently, during the handover process across public land mobile networks (PLMNs), the target AMF selection is triggered by the source access and mobility management function (AMF). The network element service storage function (NRF) query mechanism is used in the selection process. The query request sent by the source AMF to the NRF carries the target PLMN ID, source PLMN ID, slice instance identifier (ie, NSI ID), single network slice selection auxiliary information S-NSSAI, and network function service setting identifier (NF service set ID). If the initiator is the source AMF, the query request will carry the AMF region, AMF set, GUMAI, and target tracking area identifier TAI. However, during network deployment, if there are both target AMF ToB (industry users subscribe to NSSAI 1) and target AMF ToC (public users subscribe to NSSAI 2), when the slice capabilities of NSSAI 1 and NSSAI 2 are different, the NRF query mechanism is inaccurate in selecting the target AMF.

[0004] For example, AMF ToB (with NSSAI 1) and AMF ToC (with NSSAI 2) belong to the same target PLMN ID, while the AMF region, AMF set, and GUMAI of the cross-PLMN are invisible to the visited public land mobile network VPLMN. However, AMF ToB (with NSSAI 1) and AMF ToC (with NSSAI 2) are both linked to the 5G radio access network NG-RAN (Next Generation Radio Access Network, i.e., 5G radio access network) to which the target TAI belongs, and it is impossible to accurately distinguish whether to select AMF ToB (with NSSAI 1) or AMF ToC (with NSSAI 2). Therefore, during the cross-PLMN handover process, the target AMF with inaccurate slicing capabilities may be selected. If the target AMF can only meet some of the connected service capabilities of the user terminal UE, the handover may be interrupted, affecting the UE's service experience.

[0005] Summary of the Invention

[0006] The technical problem to be solved by the present invention is to address the above-mentioned deficiencies in the prior art and provide a method, device, electronic device and computer-readable storage medium for selecting an AMF for PLMN switching, so as to at least solve the problem in the related art that an inaccurate target AMF with inaccurate slicing capabilities may be selected during cross-PLMN switching. For example, if the target AMF can only meet part of the connected service capabilities of the user terminal UE, the switching may be interrupted, affecting the UE's service experience.

[0007] In the first aspect, the present invention provides a method for selecting an access and mobility management function AMF for switching across public land mobile networks (PLMNs), which is applied to a source AMF and includes: determining whether a user terminal is switching across PLMNs; obtaining network slice selection auxiliary information NSSAI of a target PLMN in response to the user terminal switching across PLMNs; sending an AMF instance query request to a network element service storage function (NRF), wherein the AMF instance query request includes the NSSAI of the target PLMN and the target tracking area identifier (TAI), so that the NRF selects a target AMF based on the NSSAI and target TAI of the target PLMN; receiving the target AMF fed back by the NRF and performing AMF switching to support service continuity of user terminals switching across PLMNs.

[0008] Preferably, the inter-PLMN handover includes one of the following: national roaming, shared network roaming, different network roaming, and core network roaming.

[0009] Preferably, before determining whether the user terminal is switched across PLMNs, the method further includes: receiving a switching request sent by a source 5G wireless access network NG-RAN, wherein the switching request includes a result identifier of the source NG-RAN determining whether the user terminal is switched across PLMNs.

[0010] Preferably, the determining whether the user terminal is inter-PLMN handover specifically includes: obtaining the target TAI, cell identifier, and global RAN node identifier in the handover request; determining whether the PLMN of the target TAI or cell identifier is the same as the PLMN of the global RAN node identifier; in response to the determination result being different, determining that the user terminal is inter-PLMN handover; and in response to the determination result being the same, determining that the user terminal is intra-system handover.

[0011] Preferably, the obtaining of the network slice selection auxiliary information NSSAI of the target PLMN specifically includes: obtaining the NSSAI of the target PLMN based on an NRF query or based on a network slice selection function NSSF query.

[0012] Preferably, the obtaining of the NSSAI of the target PLMN based on NRF query or network slice selection function NSSF query specifically includes: determining whether the slice type of the NSSAI of the source PLMN is greater than a preset threshold; in response to a negative determination, obtaining the NSSAI of the target PLMN based on NRF query; in response to a positive determination, obtaining the NSSAI of the target PLMN based on NSSF query.

[0013] Preferably, the obtaining of the NSSAI of the target PLMN based on the NRF query specifically includes: obtaining the target PLMN in the switching request; sending a first query request to the source NRF, the first query request including the source PLMN+NSSAI and the target PLMN, so that the source NRF is routed to the target NRF according to the target PLMN, and the target NRF queries the S-NSSAI of the source PLMN and the corresponding S-NSSAI mapping relationship of the target PLMN according to the source PLMN, and finds the S-NSSAI matching the target PLMN according to the mapping relationship, and returns the S-NSSAI matching the target PLMN to the source NRF; receiving the S-NSSAI matching the target PLMN returned by the source NRF to obtain the NSSAI of the target PLMN.

[0014] Preferably, before sending the first query request to the source NRF, the method further comprises: configuring a corresponding S-NSSAI mapping relationship between the source PLMN's S-NSSAI and the target PLMN in the source NRF or the target NRF.

[0015] Preferably, the obtaining of the NSSAI of the target PLMN based on the NSSF query specifically includes: sending a second query request to the NSSF, the second query request including the source PLMN+NSSAI, the target PLMN and an indicator bit, the indicator bit representing the query of the target network switching information during the PDU switching process in the home roaming scenario, so that the NSSF queries the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI according to the source PLMN+NSSAI and the target PLMN, wherein the target NSSF stores the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI; receiving the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI returned by the NSSF according to the indicator bit to obtain the NSSAI of the target PLMN.

[0016] In the second aspect, the present invention also provides an AMF selection method for cross-PLMN switching, which is applied to NRF, including: receiving an AMF instance query request sent by a source AMF, wherein the AMF instance query request includes the NSSAI and target TAI of the target PLMN. Before the source AMF sends the AMF instance query request, the source AMF determines whether the user terminal is switched across PLMNs. In response to the user terminal being switched across PLMNs, the source AMF obtains the NSSAI of the target PLMN; selects the target AMF according to the NSSAI and target TAI of the target PLMN; and feeds back the target AMF to the source AMF so that the source AMF performs AMF switching to support service continuity of user terminals switched across PLMNs.

[0017] Preferably, the inter-PLMN handover includes one of the following: national roaming, shared network roaming, different network roaming, and core network roaming.

[0018] Preferably, the NRF selects the target AMF according to the NSSAI and target TAI of the target PLMN, specifically including: the NRF finds a matching target AMF set according to the NSSAI of the target PLMN; the NRF selects the target AMF from the target AMF set according to the target TAI.

[0019] In a third aspect, the present invention also provides an AMF selection device for inter-PLMN switching, which is applied to the source AMF and includes: a judgment module, which is used to judge whether the user terminal is switched across PLMNs. An acquisition module, connected to the judgment module, is used to obtain the NSSAI of the target PLMN in response to the user terminal being switched across PLMNs. A sending module, connected to the acquisition module, is used to send an AMF instance query request to the network element service storage function NRF, wherein the AMF instance query request includes the NSSAI and target TAI of the target PLMN, so that the NRF selects the target AMF according to the NSSAI and target TAI of the target PLMN. A first receiving module is used to receive the target AMF fed back by the NRF and perform AMF switching to support service continuity of user terminals switched across PLMNs.

[0020] Preferably, the inter-PLMN handover includes one of the following: national roaming, shared network roaming, inter-network roaming, and core network roaming.

[0021] Preferably, the device further includes a second receiving module.

[0022] The second receiving module is connected to the judgment module and is used to receive a handover request sent by the source 5G wireless access network NG-RAN, wherein the handover request includes a result identifier of the source NG-RAN judging whether the user terminal is an inter-PLMN handover.

[0023] Preferably, the judgment module includes a first acquisition unit and a first judgment unit.

[0024] The first acquiring unit is configured to acquire a target TAI, a cell identifier, and a global RAN node identifier in a handover request.

[0025] The first judgment unit is connected to the first acquisition unit, and is used to determine whether the PLMN identified by the target TAI or cell is the same as the PLMN identified by the global RAN node, and is used to determine that the user terminal is switched across PLMNs in response to the judgment result being different, and is used to determine that the user terminal is switched within the system in response to the judgment result being the same.

[0026] Preferably, the acquisition module is used to acquire the NSSAI of the target PLMN based on an NRF query or an NSSF query.

[0027] Preferably, the acquisition module includes a second judgment unit, a second acquisition unit and a third acquisition unit.

[0028] The second judgment unit is used to determine whether the slice type of the NSSAI of the source PLMN is greater than a preset threshold.

[0029] The second acquiring unit is connected to the second judging unit and is configured to acquire the NSSAI of the target PLMN based on the NRF query in response to a negative judgment result.

[0030] The third acquiring unit is connected to the second judging unit and is configured to acquire the NSSAI of the target PLMN based on the NSSF query in response to a yes judgment result.

[0031] Preferably, the second acquisition unit is used to obtain the target PLMN in the switching request and send a first query request to the source NRF, the first query request including the source PLMN+NSSAI and the target PLMN, so that the source NRF is routed to the target NRF according to the target PLMN, and the target NRF queries the S-NSSAI of the source PLMN and the corresponding S-NSSAI mapping relationship of the target PLMN according to the source PLMN, and finds the S-NSSAI matching the target PLMN according to the mapping relationship, returns the S-NSSAI matching the target PLMN to the source NRF, and receives the S-NSSAI matching the target PLMN returned by the source NRF to obtain the NSSAI of the target PLMN.

[0032] Preferably, the device further comprises a configuration module.

[0033] The configuration module is used to configure the mapping relationship between the S-NSSAI of the source PLMN and the corresponding S-NSSAI of the target PLMN in the source NRF or the target NRF.

[0034] Preferably, the third acquisition unit is used to send a second query request to NSSF, the second query request includes the source PLMN+NSSAI, the target PLMN and an indicator bit, the indicator bit represents the query of the target network switching information in the PDU switching process in the home roaming scenario, so that the NSSF queries the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI according to the source PLMN+NSSAI and the target PLMN, wherein the target NSSF stores the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI, and is used to receive the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI returned by the NSSF according to the indicator bit to obtain the NSSAI of the target PLMN.

[0035] In a fourth aspect, the present invention also provides an AMF selection device for cross-PLMN handover, which is applied to NRF and includes: a third receiving module, which is used to receive an AMF instance query request sent by a source AMF, wherein the AMF instance query request includes the NSSAI and target TAI of the target PLMN. Before the source AMF sends the AMF instance query request, the source AMF determines whether the user terminal is switching across PLMNs. In response to the user terminal switching across PLMNs, the source AMF obtains the network slice selection auxiliary information NSSAI of the target PLMN. A feedback module, connected to the third receiving module, is used to select a target AMF based on the NSSAI and target TAI of the target PLMN, and is used to feed back the target AMF to the source AMF so that the source AMF performs AMF handover and supports service continuity for user terminals switching across PLMNs.

[0036] Preferably, the feedback module includes a selection unit, which is used to find a matching target AMF set according to the NSSAI of the target PLMN, and to select a target AMF from the target AMF set according to the target TAI.

[0037] In a fifth aspect, the present invention also provides an electronic device comprising a memory and a processor, wherein the memory stores a computer program, and the processor is configured to run the computer program to implement the AMF selection method for cross-PLMN switching as described in the first aspect or the second aspect.

[0038] In a sixth aspect, the present invention also provides a computer-readable storage medium having a computer program stored thereon, and when the computer program is executed by a processor, the method for selecting an AMF for cross-PLMN switching as described in the first aspect or the second aspect is implemented.

[0039] The present invention provides an AMF selection method, device, electronic device and computer-readable storage medium for inter-PLMN switching. When a user terminal switches across PLMNs, the method obtains the network slice selection auxiliary information NSSAI of the target PLMN and sends an AMF instance query request to the NRF, so that the NRF selects the target AMF according to the NSSAI and target tracking area identifier TAI of the target PLMN in the AMF instance query request, thereby continuing the connection state service of the user terminal and avoiding service interruption due to inaccurate selection of the target AMF and failure to meet the service capabilities of the user terminal. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] FIG1 is a schematic flow chart of a method for selecting an AMF for inter-PLMN handover according to Embodiment 1 of the present invention;

[0041] FIG2 is a schematic structural diagram of an apparatus for selecting an AMF for inter-PLMN handover according to embodiment 3 of the present invention;

[0042] FIG3 is a schematic structural diagram of an apparatus for selecting an AMF for inter-PLMN handover according to embodiment 4 of the present invention;

[0043] FIG4 is a schematic structural diagram of an electronic device according to Embodiment 5 of the present invention. DETAILED DESCRIPTION

[0044] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0045] It should be understood that the specific embodiments and drawings described herein are only used to explain the present invention rather than to limit the present invention.

[0046] It is understood that, in the absence of conflict, the various embodiments of the present invention and the various features in the embodiments may be combined with each other.

[0047] It can be understood that, for the convenience of description, the drawings of the present invention only show parts related to the present invention, while parts unrelated to the present invention are not shown in the drawings.

[0048] It can be understood that each unit and module involved in the embodiments of the present invention may correspond to only one physical structure, or may be composed of multiple physical structures, or multiple units and modules may be integrated into one physical structure.

[0049] It will be understood that, without conflict, the functions and steps marked in the flowcharts and block diagrams of the present invention may occur in an order different from that marked in the drawings.

[0050] It is understood that the flowcharts and block diagrams of the present invention illustrate the possible architectures, functions, and operations of the systems, devices, equipment, and methods according to various embodiments of the present invention. Each box in the flowchart or block diagram may represent a unit, module, program segment, or code, which contains executable instructions for implementing the specified functions. Moreover, each box or combination of boxes in the block diagram and flowchart may be implemented using a hardware-based system that implements the specified functions, or may be implemented using a combination of hardware and computer instructions.

[0051] It can be understood that the units and modules involved in the embodiments of the present invention can be implemented by software or hardware. For example, the units and modules can be located in a processor.

[0052] Example 1:

[0053] This embodiment provides a method for selecting an access and mobility management function (AMF) for handover across public land mobile networks (PLMNs). The method supports more accurate AMF selection in user connection-state service handover from a local public land mobile network (HPLMN) to a visited public land mobile network (VPMN), and also supports more accurate AMF selection in user connection-state service handover from a VPLMN to an HPMN. Connection-state services include data services and / or voice services. The selection method is applicable to various cross-PLMN handover scenarios, such as national roaming, shared network, inter-network roaming, and core network roaming. For example, participating operators and hosted access network (RAN) operators provide services for user terminals (UEs) moving between their service areas. The services provided are based on the user subscription and billing requirements of the participating operators, including service logic provided by the participating operators and hosted RAN operators, such as UE voice, short message service (SMS), and data communications.

[0054] Application scenarios include user terminals registered in the HPLMN, that is, they can log in to the 5G system through the HPLMN's NG-RAN and AMF. There is an intercommunication interface between the HPLMN and the VPLMN to transmit messages between network elements. In addition, a cooperation agreement has been signed between the HPLMN and the VPLMN, allowing terminals to switch between PLMNs to ensure business continuity.

[0055] As shown in Figure 1, this embodiment provides a method for selecting an access and mobility management function (AMF) for handover across public land mobile networks (PLMNs), which is applied to a source AMF and includes:

[0056] Step 101: Determine whether the user terminal is switching across PLMNs.

[0057] In this embodiment, cross-PLMN switching includes one of the following: national roaming, shared network, inter-network roaming, and core network roaming. There are two ways for the source AMF to determine whether the user terminal is cross-PLMN switching. One way is for the source RAN to determine whether the user terminal is cross-PLMN switching, and send the result identifier corresponding to the judgment result to the source AMF. When the source AMF trusts the judgment result of the source NG-RAN, the source AMF directly determines whether the user terminal is cross-PLMN switching based on the received result identifier. See steps S1-S2 for details. This method can save the computing resources of the source AMF and improve the efficiency of target AMF selection. The other way is when the source AMF does not trust the judgment result of the source RAN, the source AMF determines on its own whether the user terminal is cross-PLMN switching. The reasons why the source AMF does not trust the source NG-RAN may be: the operator's configuration, or the source NG-RAN and the source AMF are from different manufacturers or different construction units. Therefore, this method can ensure the accuracy of the judgment result of cross-PLMN switching. The following details two specific ways to determine whether the user terminal is cross-PLMN switching:

[0058] S1. The source AMF receives a handover request sent by the source NG-RAN, where the handover request includes a result identifier of the source NG-RAN determining whether the user terminal is handing over across PLMNs.

[0059] In this embodiment, the UE moves from the source PLMN (HPLMN) network to the 5G area of ​​the target PLMN. The source NG-RAN assists the source AMF in determining whether the user terminal is performing an inter-PLMN handover. For example, the source NG-RAN compares the PLMN used in the target network with the PLMN of the source Global RAN Node ID and carries parameters corresponding to the judgment result to the next network element source AMF, including an indication of "intra-system handover". In the case of handover to the target PLMN, the source NG-RAN determines the PLMN to be used in the target network. The source NG-RAN should indicate the selected PLMN ID (or PLMN ID and NID) to the AMF as part of the tracking area ID sent in the HO required message. This embodiment proposes that the source NG-RAN needs to compare the PLMN used in the target network with the PLMN of the source Global RAN Node ID. If the target PLMN is the same as the source PLMN, the source NG-RAN will carry the result flag "intra-system handover" in the handover request sent to the source AMF; if they are not the same, the source NG-RAN will not carry the "intra-system handover" or the source NG-RAN will carry the result flag "intra-system handover" in the handover request, but the result flag "intra-system handover" = 0;

[0060] For example:

[0061] Global RAN Node ID also contains

[0062] PLMN Identity = 460abc (Source PLMN)

[0063] CHOICE gNB ID

[0064] >gNB ID

[0065] >>gNB ID

[0066] The gNB ID is a BIT STRING (SIZE(22..32)) equal to the leftmost bits of the NR Cell Identity IE contained in the NR CGI IE for each cell served by the gNB.

[0067] Target PLMN Identity = 460xyz (target PLMN)

[0068] CHOICE Target ID

[0069] >NG-RAN

[0070] >>Global RAN Node ID

[0071] >>Selected TAI

[0072] S2: The source AMF determines whether the user terminal is switching across PLMNs based on the result flag "intra-system switching" (none, 0, 1) carried by the source NG-RAN in the switching request.

[0073] In this embodiment, the first message seen by the source AMF is a handover request message from the source NG-RAN to the source AMF (carrying a target identifier (i.e., target ID), source-to-target transparency information, a SMN2 information list, a protocol data unit (PDU) session ID, and an intra-system handover). The value of the intra-system handover is determined as described in step S1. The source-to-target transparency data (container) includes NG-RAN information created by the source RAN for use by the target RAN and is transparent to the 5G core network (5GC). It also contains user plane security mandatory information for each PDU session, Quality of Service (QoS) flow / DRB information, and other information. When the source AMF receives a handover request from the radio side, it first checks whether it carries the result flag "intra-system handover." If the handover request does not carry the result flag "intra-system handover" or the result flag "intra-system handover = 0," the source AMF determines that the user terminal is performing an inter-PLMN handover. If the result flag "intra-system handover" in the handover request = 1, the source AMF determines that the user terminal is not performing an inter-PLMN handover. If "intra-system handover = 1," the source AMF executes the intra-system handover process according to existing techniques.

[0074] When the source AMF does not trust the source NG-RAN, the source AMF determines on its own whether the user terminal is switching across PLMNs.

[0075] Specifically, the source AMF determines whether the user terminal is switched across PLMNs, including: obtaining the target TAI, cell identifier, and global RAN node identifier in the switching request; determining whether the PLMN of the target TAI or cell identifier is the same as the PLMN of the global RAN node identifier; in response to the judgment result being different, determining that the user terminal is switched across PLMNs; in response to the judgment result being the same, determining that the user terminal is switched within the system.

[0076] In this embodiment, the handover request includes the result identifier of the source NG-RAN judging whether the user terminal is an inter-PLMN handover, and / or the first parameter, and / or the target PLMN, where the first parameter includes the target TAI, the cell ID, and the global RAN node ID. The source AMF can judge whether the user terminal meets the conditions for inter-PLMN handover by the target TAI or the cell ID. First, it is judged that the user terminal enters the handover process by the handover request handover require message, and then it is judged whether it is an inter-PLMN handover. Specifically, by judging the PLMN in the target ID, if there is no PLMN for the current session in the system, it is an inter-PLMN handover, and the source PLMN can be identified by the PLMN Identity in the Global RAN Node ID and other methods. The specific method of identification is: in order to reduce the system load, the right matching method can be used, because the MCC in China is the same. If it involves cross-border inter-PLMN handover, the left matching is required. If it is an int type, use "==" to judge whether it is equal; if it is an Integer type, the equals method can be used for equality comparison. For example:

[0077] >int target ID PLMN = 10;

[0078] >int local set PLMN = 10;

[0079] >System.out.print(target ID PLMN==local set PLMN)

[0080] If System.out.print = 1, the PLMN in the target ID is equal to the local PLMN, and the handover is not between PLMNs. The subsequent AMF selection, AMF reselection, and handover procedures can be implemented according to existing technologies.

[0081] If System.out.print = 0, the PLMN in the target ID is not equal to the local PLMN, and inter-PLMN handover requires AMF selection for inter-PLMN handover;

[0082] The local set PLMN determined above can be the system-configured AMF PLMN or source RAN information retrieved via the N2 interface. The former is less accurate. In a special scenario where the AMF serves two PLMNs simultaneously, meaning there are two local set PLMNs, the RAN information from the N2 interface is still used to determine the PLMN to be used for the current call. If the AMF is configured with only one default PLMN, the N2 interface information is not required.

[0083] Optionally, when determining whether the user terminal initiates handover when the source PLMN is the HPLMN, the process specifically includes steps 1011 to 1012:

[0084] Step 1011: Determine whether the protocol data unit PDU context saved by the user terminal in the source AMF or the user information when the user terminal is registered in the source AMF contains the S-NSSAI of the VPLMN.

[0085] Step 1012: In response to the PDU context or user information not including the S-NSSAI of the VPLMN, it is determined that the user terminal initiates a handover when the source PLMN is the local public land mobile network HPLMN.

[0086] In this embodiment, during the PDU session establishment process, after the UE determines the corresponding HPLMN S-NSSAl according to the rules in the terminal routing policy URSP, the UE also needs to further determine the VPLMN S-NSSAl corresponding to the HPLMN S-NSSAI based on the locally configured network slice mapping relationship between the home domain and the visited domain. At this time, the AMF should save the VPLMN S-NSSAI information based on this information, and the subsequent AMF can determine whether the UE is accessed through the VPLMN based on this parameter. Therefore, the source AMF can determine whether the protocol data unit PDU context saved by the user terminal in the source AMF contains the S-NSSAI of the VPLMN to determine whether the user terminal initiates handover in the source PLMN for the local public land mobile network HPLMN. Alternatively, when the UE initially registers to the network slice, the UE determines the mapping relationship between the S-NSSAI in the Requested NSSAI and the S-NSSAl of the HPLMN based on the configuration information, and provides the mapping relationship to the network. If the UE accesses from a VPLMN, VPLMN S-NSSAI information will exist. The function of providing the mapping relationship to the network is not supported by all UEs. The UE may not have the ability to report the VPLMN S-NSSAI information, or due to triggering conditions, the VPLMN S-NSSAI is not reported. If the UE has the function of providing the mapping relationship to the network, it can be determined through the registration process that the UE is in the VPLMN. Therefore, if the user information includes the VPLMN S-NSSAI, the user terminal initiates handover for the roaming user in the VPLMN. If the user information does not include the VPLMN S-NSSAI, the user terminal initiates handover for the roaming user in the HPLMN.

[0087] Step 102: In response to the user terminal switching across PLMNs, obtain the network slice selection auxiliary information NSSAI of the target PLMN.

[0088] In this embodiment, when the user terminal accesses the HPLMN and is not registered in the VPLMN, the source AMF does not obtain the VPLMN's S-NSSAI of the UE's allowed NSSAI and the corresponding S-NSSAI of the HPLMN to which the allowed NSSAI is mapped. This is because the user terminal is only registered in the HPLMN through the HPLMN access network and has no relationship with the VPLMN. At this time, there is no VPLMN registration, and no VPLMN-related information is generated. Therefore, the source AMF only stores the local network information. When the source AMF receives a handover request message, it can obtain the target PLMN and target PLMN TAI information of the target network from the handover request. However, at this time, the source AMF does not have the target network's NSSAI information. The following two methods are used to query the target network's NSSAI.

[0089] Specifically, obtaining the NSSAI of the target PLMN includes: obtaining the NSSAI of the target PLMN based on NRF query or based on network slice selection function NSSF query.

[0090] In this embodiment, it can be determined through network settings whether the NSSAI of the target PLMN is obtained based on NRF query or based on network slice selection function NSSF query.

[0091] Optionally, obtaining the NSSAI of the target PLMN based on a network element service storage function NRF query or a network slice selection function NSSF query specifically includes:

[0092] Step 1021, determine whether the slice type of the source PLMN+NSSAI is greater than a preset threshold.

[0093] Step 1022: In response to a negative judgment result, obtain the NSSAI of the target PLMN based on the network storage function NRF query.

[0094] Step 1023: In response to the judgment result being yes, obtain the NSSAI of the target PLMN based on the network slice selection function NSSF query.

[0095] In this embodiment, the first method (i.e., step 1022) is generally used when NSSF is not deployed or NSSF query cannot be used due to the operator and roaming agreement, and the target network information is completely queried through NRF. The second method (i.e., step 1023) is generally used when the slice type exceeds a preset threshold, which can be set to 3. When it is necessary to obtain the subdivided slices of the target network, the target network information, i.e., the NSSAI of the target PLMN, is queried through NSSF.

[0096] Optionally, the NRF-based query to obtain the NSSAI of the target PLMN specifically includes: obtaining the target PLMN in the switching request; sending a first query request to the source NRF, the first query request including the source PLMN+NSSAI and the target PLMN, so that the source NRF is routed to the target NRF according to the target PLMN, and the target NRF queries the S-NSSAI of the source PLMN and the corresponding S-NSSAI mapping relationship of the target PLMN according to the source PLMN, and finds the S-NSSAI matching the target PLMN according to the mapping relationship, and returns the S-NSSAI matching the target PLMN to the source NRF; receiving the S-NSSAI matching the target PLMN returned by the source NRF to obtain the NSSAI of the target PLMN.

[0097] Optionally, before sending the first query request to the source NRF, the method for selecting the AMF for cross-PLMN switching further includes: configuring the corresponding S-NSSAI mapping relationship between the S-NSSAI of the source PLMN and the target PLMN in the source NRF or the target NRF.

[0098] In this embodiment, the NRF includes a source NRF and a target NRF. The target NRF configures a mapping relationship between the S-NSSAI of the source PLMN corresponding to the source PLMN and the corresponding S-NSSAI of the target PLMN. When the source AMF sends a first query request to the source NRF, the source NRF communicates with the target NRF. The target NRF can return the corresponding target NSSAI based on the mapping relationship between the S-NSSAI of the source PLMN corresponding to the PLMN and the corresponding S-NSSAI of the target PLMN. At the same time, the target NRF of this embodiment accurately selects the target AMF through the target NSSAI and the target TAI.

[0099] The NRF of the target network configures the mapping relationship between the S-NSSAI of the source PLMN and the corresponding S-NSSAI of the target PLMN. When signing a roaming agreement, the network needs to configure the target NRF accordingly. The slice-level mapping relationship is saved in the target NRF according to the roaming agreement. For example, the target network NRF can be configured as follows:

[0100] ->Mapping PLMN ID = abc ppq, S-NSSAI = {sequence 1, sequence 2, sequence 3, sequence 4, sequence 5, ...},

[0101] ->Home PLMN ID=xyz ijk, S-NSSAI={sequence 21, sequence 22, sequence 23, sequence 24, sequence 25, ...},

[0102] ->Mapping PLMN ID=abc ppq, S-NSSAI={sequence 1} corresponds to Home PLMN ID=xyz ijk, S-NSSAI={sequence 23}.

[0103] This Home PLMN ID is for the target NRF. This parameter corresponds to the VPLMN and HPLMN and is configured with each other. There can be multiple Mapping PLMNIDs and Home PLMN IDs. At this time, the source AMF (the source AMF is the AMF of the HPLMN) determines that the NRF selection mechanism should be used to query the target AMF process. At this time, the NRF process itself is an existing process, but the source AMF needs to determine whether the user switches from the HPLMN to the VPLMN, and needs to query through the NRF to obtain accurate slice information. Specifically, the network element function entity NF service user can request to create a subscription to a specific NF instance or a group of NF instances based on the "subscrCond" attribute of the "SubscriptionData" object type, according to the requested instance type reqNfType, the instance's FQDN reqNfFqdn, the requested NSSAI reqSnssais, the requested NSSAI of each PLMN reqPerPlmnSnssais, the requested PLMN list reqPlmnList, etc.

[0104] It should be noted that the source NRF can also directly configure the mapping relationship between the S-NSSAI of the source PLMN and the corresponding S-NSSAI of the target PLMN. In this case, the query between the source NRF and the target NRF can carry the mapping relationship. If the mapping relationship of the target NRF has been updated, the source NRF and the target NRF can negotiate and update to the latest mapping relationship. In order to complete the query between the source NRF and the target NRF, the source NRF needs to support routing for the target NRF. The source NRF routes the target PLMN NRF according to the target PLMN and carries the source PLMN+NSSAI, the target PLMN and the target TAI. The target NRF queries the target network's NRF for the S-NSSAI of the source PLMN corresponding to the target PLMN configured by the NRF of the target network based on the source PLMN+NSSAI and the target PLMN, finds the corresponding S-NSSAI of the target PLMN, that is, the NSSAI of the target PLMN and returns it to the source AMF.

[0105] Optionally, the obtaining of the NSSAI of the target PLMN based on the NSSF query specifically includes: sending a second query request to the NSSF, the second query request including the source PLMN+NSSAI, the target PLMN and an indication bit, the indication bit representing the query of the target network switching information during the PDU switching process in the home roaming scenario, so that the NSSF queries the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI according to the source PLMN+NSSAI and the target PLMN, wherein the target NSSF stores the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI; receiving the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI returned by the NSSF according to the indication bit to obtain the NSSAI of the target PLMN.

[0106] In this embodiment, the source AMF obtains the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI through an NSSF query, wherein the mapping between the target PLMN+NSSAI and the source PLMN+NSSAI is stored in the target NSSF. After completing the NSSF query, the source AMF can carry the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI obtained by the source AMF through the NSSF query corresponding to the PDU session in subsequent NRF query instances. That is, when the source AMF queries the NRF, it carries the PLMN+NSSAI of the service requesting user and the target PLMN+NSSAI, wherein the PLMN+NSSAI is the S-NSSAI of the serving PLMN and the serving PLMN of the allowed NSSAI, and the target PLMN+NSSAI is the corresponding S-NSSAI of the target PLMN. If there are many types of VPLMN and HPLMN slices, not only the three major types of slices are supported, but also subdivided slices are supported. The S-NSSAI of the VPLMN of the UE's allowed NSSAI and the corresponding S-NSSAI of the HPLMN of the allowed NSSAI mapping are obtained through the roaming agreement with a coarse granularity. For example, the S-NSSAI of the VPLMN can only be mapped to one of the three major slice types of the HPLMN, and cannot be mapped to the subdivided slice. At this time, the accuracy can be further improved through NSSF query. Compared with the query mechanism only through NRF, the accuracy of NSSF query is further improved. Specifically, (1) the source AMF determines whether to initiate an NSSF query based on the operator configuration and policy, as well as the roaming agreement data configuration. For example, if the roaming agreement data configuration is of high granularity, then based on the validity of the user information in the source AMF, the source AMF calls the Nnssf_NSSelection_Get service operation from the NSSF, using the NSSF of the ServingPLMN, carrying information including: the S-NSSAI (source PLMN + NSSAI) of the serving PLMN that allows NSSAI requested by the UE, the target PLMN and the target PLMN TAI information, and an indicator bit, which indicates that the request is for a PDU handover process in a home roaming scenario, and the target instance to be obtained is the target AMF. "PDU handover process in a home roaming scenario" means "the roaming user is not initiating handover in a VPLMN" (the indicator bit indicates whether further slice information needs to be obtained). Here, the Serving PLMN is the source PLMN (HPLMN); that is, if the UE initiates handover from the HPLMN, the NSSF+NRF method can be used to improve the accuracy of selecting the target AMF.In contrast, the judgment can be made directly by the NRF-only method. The source AMF can judge that the source PLMN+NSSAI is a slice of a segmented scenario, and trigger the NSSF query mechanism in order to more accurately judge whether there is a slice that can be accurately matched in the destination PLMN. (2) Alternatively, if the slice configuration information of the S-NSSAI in the serving PLMN is not available (for example, the S-NSSF / S-NRF has no cached information, or the granularity is large), the NSSF of the serving PLMN will call Nnssf_NSSelection_Get from the NSSF of the serving PLMN based on the S-NSSAI (source PLMN+NSSAI) of the serving PLMN that allows NSSAI requested by the UE, the target PLMN and the target PLMN TAI information, and an indication bit (PDU switching process "indication bit" in the home roaming scenario), for the source AMF to call Nnssf_NSSelection_Get from the NSSF of the serving PLMN through the serving PLMN S-NSSAI and other information. service operation. How to determine whether to call the NSSF query of the serving PLMN can be based on the "PDU switching process in the home roaming scenario" indicator bit. If "PDU switching process in the home roaming scenario" = 1, it means that the serving PLMN (HPLMN) switches to further query the target network switching information. Otherwise, the NSSF query of the HPLMN will not be performed. (3) If there is a source NSSF and a target NSSF in the network, then the NSSF+NRF mechanism to obtain the target AMF needs to support the mechanism of querying from the source NSSF to the target NSSF. For example, the source NSSF / source NRF has no cached information, or the granularity is large, or the source NSSF needs the assistance of the target NSSF to determine the reliable mapping slice of the subdivided scenario. For example, after the target NSSF mapping rule is changed, the source NSSAI (destination PLMN+destination NSSAI) result will change. If necessary, the NSSF in the HPLMN can carry the network slice instance NSI ID in the returned Nnssf_NSSelection_Get response. The NSI ID is the network slice instance selected by the H-NSSF based on the HPLMN. The slice instance selected by the S-NSSAI. The NSSF in the HPLMN also includes the appropriate hNRF, included in the Nnssf_NSSelection_Get response, for the NFs / services subsequently selected by the NRF in the HPLMN. This embodiment requires that if the serving PLMN NSSF wishes to obtain the NSSAI, it needs to set the PDU switching in the home roaming scenario to 1, and the HPLMN NSSF returns the target PLMN and the corresponding target PLMN NSSAI based on this parameter. (4) The serving NSSF includes all the information received from the NSSF in the serving PLMN in the Nnssf_NSSelection_Get response, which will appear when the serving NSSF sends the AMF.Includes NSI ID, hNRF, source PLMN+NSSAI, target PLMN+NSSAI and the correspondence between source PLMN+NSSAI, and target PLMN TAI information.

[0107] Step 103: Send an AMF instance query request to the network element service storage function NRF, where the AMF instance query request includes the NSSAI of the target PLMN and the target tracking area identifier TAI, so that the NRF selects the target AMF according to the NSSAI and target TAI of the target PLMN.

[0108] In this embodiment, the NRF first determines the target AMF set based on the NSSAI of the target PLMN, and then selects a target AMF from the target AMF set based on the target TAI. Alternatively, the NRF first determines the target AMF set based on the target TAI, and then selects a target AMF from the target AMF set based on the NSSAI of the target PLMN.

[0109] Specifically, after the source AMF obtains the NSSAI of the target PLMN based on the NRF query, it sends an AMF instance query to the NRF as an example to illustrate that the NRF selects the target AMF according to the NSSAI of the target PLMN and the target tracking area identifier TAI.

[0110] If the target NRF is configured as:

[0111] ->Mapping PLMN ID = abc ppq, S-NSSAI = {sequence 1, sequence 2, sequence 3, sequence 4, sequence 5, ...},

[0112] ->Home PLMN ID=xyz ijk, S-NSSAI={sequence 21, sequence 22, sequence 23, sequence 24, sequence 25, ...},

[0113] ->Mapping PLMN ID=abc ppq, S-NSSAI={sequence 1} corresponds to Home PLMN ID=xyz ijk, S-NSSAI={sequence 23}.

[0114] ->>Source PLMN carried by the source NRF + NSSAI = {abc ppq, sequence 1},

[0115] ->>Then the NSSAI found should be the target PLMN + NSSAI = {xyz ijk, sequence 23},

[0116] ->>The target NRF should return {xyz ijk, sequence 23} and should search according to sequence 23 when searching for the target AMF. In this embodiment, the source AMF cannot obtain the S-NSSAI of the VPLMN of the UE's allowed NSSAI and the corresponding S-NSSAI of the HPLMN to which the allowed NSSAI mapping is applied. Therefore, when the source AMF queries the AMF instance through the source NRF, it cannot carry the target PLMN+NSSAI of the user requesting service. The source NRF cannot route to the target NRF based on the target PLMN+NSSAI and cannot use the target PLMN+NSSAI as one of the criteria for selecting the target AMF when selecting the target AMF. Therefore, in this embodiment, when the source AMF queries the source NRF, it carries the source PLMN+NSSAI, target PLMN, and target TAI. The source NRF carries this information to the target NRF. The target NRF then queries the mapping relationship between the S-NSSAI of the source PLMN (HPLMN) and the corresponding S-NSSAI of the target PLMN to find the S-NSSAI that matches the target PLMN. It then finds the appropriate AMF instance based on the target TAI and returns it to the source NRF, including the AMF area, AMF set, GUAMI, NSSAI, and FQDN to which the target AMF belongs. The source NRF then returns the target AMF to the source AMF. In addition, when the source AMF receives the handover request message, it performs target AMF selection: when the source AMF can no longer serve the UE, the source AMF selects the target AMF. When moving across PLMNs, the source AMF selects the AMF instance in the target PLMN by querying the target PLMN-level NRF using the source PLMN-level NRF using the target PLMN ID. The target PLMN-level NRF returns the AMF instance address based on the target network configuration. When the source AMF sends a query request to the source NRF, if the target NF is AMF, the request may include: AMF area, AMF set, GUAMI and target TAI. In this embodiment, if the source NRF can obtain the mapping relationship of the slice, it needs to be carried, such as target PLMN+NSSAI, or it may not be carried. The source NRF carries this information to the target NRF. The target NRF selects the regional affiliation (large region) of the AMF according to the AMF area, and then selects an AMF set (a province) in the large region. However, GUAMI is generally inaccurate and is not even carried in cross-region selection. Of course, the AMF area and AMF set may not be carried in cross-region selection.The only valid parameters are the target PLMN or target PLMN+NSSAI and TAI. The target NRF needs to use the configured VPLMN's S-NSSAI and the mapped HPLMN's corresponding S-NSSAI as the basis for selecting the target AMF. The target AMF is selected based on the target PLMN or target PLMN+NSSAI, TAI, and mapping configuration. The target NRF can then select a relatively accurate AMF instance based on the network configuration and return it to the source NRF, including the AMF's AMF area, AMF set, GUAMI, NSSAI, FQDN, and IP address. For example, the target NRF first determines whether the source NRF has signed an inter-PLMN handover network selection agreement with it. If the target NRF determines that the agreement is reasonable, it extracts the target PLMN+NSSAI and TAI information, first matching the NSSAI supported by the AMF. After selecting a subset of AMFs (i.e., the target AMF set), the matching is performed against the target TAI information. This can further improve the accuracy of target AMF selection. This embodiment does not limit the matching order of the selected parameters (PLMN+NSSAI, target TAI). Find the appropriate AMF instance based on the target TAI and return it to the target NRF, including the AMF area, AMF collection, GUAMI, NSSAI and FQDN to which the AMF belongs.

[0117] Optionally, taking the example of obtaining the NSSAI of the target PLMN based on the NSSF query and then obtaining the target AMF based on the NRF query, the target AMF is selected based on the NSSAI of the target PLMN and the target tracking area identifier TAI, specifically including: sending an AMF instance query request to the NRF, the AMF instance query request including the NSSAI and target TAI of the target PLMN, so that the NRF finds a matching target AMF set based on the NSSAI of the target PLMN, and then selects the target AMF from the target AMF set based on the target TAI; and receiving the target AMF returned by the NRF.

[0118] In this embodiment, since the source AMF has obtained the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI through NSSF query, the NRF selection mechanism should be used to query the target AMF when performing target AMF selection. Specifically, the NF service user can request to create a subscription to a specific NF instance or a group of NF instances based on the "subscrCond" attribute of the "SubscriptionData" object type, according to the requested instance type reqNfType, the instance's FQDN reqNfFqdn, the requested NSSAI reqSnssais, the requested NSSAI of each PLMN reqPerPlmnSnssais, the requested PLMN list reqPlmnList, etc. After completing the NSSF query, the source AMF in this embodiment can carry the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI corresponding to the PDU session when querying the AMF instance through NRF. That is, when the source AMF queries the NRF, it carries the PLMN+NSSAI of the user requesting the service and the target PLMN+NSSAI. The PLMN+NSSAI is the S-NSSAI of the serving PLMN and the serving PLMN of the allowed NSSAI. The target PLMN+NSSAI is the corresponding S-NSSAI of the target PLMN.

[0119] The NRF needs to support the PLMN+NSSAI and target PLMN+NSSAI carried by the service requester, as well as the NRF's authorization for this query method. It then routes the target PLMN NRF based on the target PLMN+NSSAI and carries the target PLMN+NSSAI. The target PLMN NRF uses the target PLMN+NSSAI query and the data from the roaming agreement between the VPLMN NRF and the HPLMN NRF to determine the target AMF selection criteria. For example, when the source AMF receives a handover request message, it performs target AMF selection: when the source AMF can no longer serve the UE, the source AMF selects the target AMF. When moving across PLMNs, the source AMF selects the AMF instance in the target PLMN by querying the target PLMN-level NRF using the target PLMN ID. The target PLMN-level NRF returns the AMF instance address based on the target network configuration. When the source AMF of the source PLMN sends a query request to the source PLMN NRF, if the target NF being queried is AMF, the request may include: AMF area, AMF set, GUAMI and target TAI. In this embodiment, the target PLMN+NSSAI also needs to be carried. The source PLMN NRF carries this information to the target PLMN NRF. The target PLMN NRF selects the regional affiliation (large region) of the AMF according to the AMF area, and then selects an AMF set (a province) in the large region. However, GUAMI is generally inaccurate and is not even carried in cross-region selection. Of course, the AMF area and AMF set may not be carried in cross-region selection (because they are AMF parameters across PLMNs, and AMF parameters are only valid within the PLMN). Then the only valid parameters will be the target PLMN+NSSAI and the target TAI. At this time, the NRF of the target PLMN can select a relatively accurate AMF instance through network configuration and return it to the source PLMN NRF, including the AMF area, AMF set, GUAMI, NSSAI, FQDN and IP address to which the AMF belongs. Of course, for network security, the AMF area and other information may be desensitized. For example, the target PLMN NRF first determines whether the source PLMN NRF has signed an inter-PLMN handover network selection agreement with it. If the target PLMN NRF determines that the contract is reasonable, it extracts the target PLMN+NSSAI and target TAI information, first matches the NSSAI supported by the AMF, selects a part of the AMF, and then corresponds it with the target TAI information, which can further improve the accuracy of the AMF selection. This embodiment does not limit the order of parameter matching.Based on the target TAI, a suitable AMF instance is found and returned to the destination NRF. This information includes the AMF's AMF area, AMF set, GUAMI, NSSAI, and FQDN. It should be noted that target TAI information can be segmented and maintained consistent across PLMNs through planning. For example, the granularity of planning for the target TAI varies depending on the range specified by different parameters. The more refined the planning, the more accurate the AMF found based on the target TAI, but this may also increase operational burden. Determining the target AMF based on the target PLMN + NSSAI and TAI information significantly improves AMF accuracy during handover, reduces quality of service (QoS) issues such as call drops, and better meets service level agreements (SLAs). In summary, the NSSF and NRF-based target AMF selection approach is suitable for scenarios with a wide range of slice types. It supports not only the three major slice types but also slice segmentation. The target PLMN + NSSAI is determined by searching the source PLMN NSSF, and then the target AMF is selected. The NRF-based target AMF selection approach is suitable for coarse-grained slice query and target AMF selection in scenarios where NSSF is not deployed and there are fewer slice types.

[0120] The AMF selection method for inter-PLMN handover in this embodiment obtains the target PLMN's network slice selection assistance information (NSSAI) when the user terminal is handing over inter-PLMN, and sends an AMF instance query request to the NRF. The NRF selects the target AMF based on the target PLMN's NSSAI and the target tracking area identifier (TAI). The AMF handover is then performed based on the target AMF provided by the NRF, thereby ensuring the continuity of the user terminal's connected services and avoiding service interruptions caused by an inaccurate target AMF selection that fails to meet the user terminal's service capabilities. The NRF-based target AMF selection method is suitable for scenarios where NSSF is not deployed and where coarse-grained slice queries are performed with a small number of slice types. However, if the VPLMN and HPLMN have a large number of slice types, supporting not only the three major slice categories but also finer slices, the NSSAI of the target PLMN can be obtained through an NSSF query to further improve the accuracy of target AMF selection. Therefore, the NSSF- and NRF-based target AMF selection method is suitable for scenarios with a large number of slice types. By searching the source PLMN NSSF to confirm a more accurate target PLMN+NSSAI, the accuracy of target AMF selection is further improved.

[0121] Example 2:

[0122] This embodiment provides a method for selecting an AMF for inter-PLMN handover, which is applied to an NRF and includes:

[0123] Step 201: Receive an AMF instance query request sent by a source AMF, wherein the AMF instance query request includes the NSSAI and target TAI of the target PLMN. Before the source AMF sends the AMF instance query request, the source AMF determines whether the user terminal is switched across PLMNs. In response to the user terminal being switched across PLMNs, the source AMF obtains the network slice selection auxiliary information NSSAI of the target PLMN.

[0124] Step 202: Select a target AMF based on the NSSAI and target TAI of the target PLMN.

[0125] Step 203: Feedback the target AMF to the source AMF so that the source AMF performs AMF handover to support service continuity of user terminals that switch across PLMNs.

[0126] The inter-PLMN handover includes one of the following: national roaming, shared network roaming, inter-network roaming, and core network roaming. Before the source AMF determines whether the user terminal is inter-PLMN handover, the method further includes: the source AMF receiving a handover request sent by the source 5G radio access network NG-RAN, wherein the handover request includes a result identifier of the source NG-RAN's determination of whether the user terminal is inter-PLMN handover.

[0127] The source AMF determines whether the user terminal is performing an inter-PLMN handover, specifically including: the source AMF obtains the target TAI, cell identifier, and global RAN node identifier in the handover request; the source AMF determines whether the PLMN of the target TAI or cell identifier is the same as the PLMN of the global RAN node identifier; in response to the determination result being different, the source AMF determines that the user terminal is performing an inter-PLMN handover; in response to the determination result being the same, the source AMF determines that the user terminal is performing an intra-system handover. The handover request includes an identifier of the result of the source NG-RAN determining whether the user terminal is performing an inter-PLMN handover, and / or a first parameter, and / or a target PLMN, where the first parameter includes the target TAI, cell identifier, and global RAN node identifier.

[0128] The source AMF obtains the network slice selection auxiliary information NSSAI of the target PLMN, specifically including: the source AMF obtains the NSSAI of the target PLMN based on the network element service storage function NRF query or based on the network slice selection function NSSF query.

[0129] Specifically, the source AMF obtains the NSSAI of the target PLMN based on the network element service storage function NRF query or the network slice selection function NSSF query, including: the source AMF determines whether the slice type of the source PLMN+NSSAI is greater than a preset threshold; in response to the judgment result being no, the source AMF obtains the NSSAI of the target PLMN based on the network storage function NRF query; in response to the judgment result being yes, the source AMF obtains the NSSAI of the target PLMN based on the network slice selection function NSSF query.

[0130] The source AMF obtains the NSSAI of the target PLMN based on the NRF query, specifically including: the source AMF obtains the target PLMN in the handover request; the source AMF sends a first query request to the source NRF, the first query request including the source PLMN+NSSAI and the target PLMN, so that the source NRF is routed to the target NRF according to the target PLMN, and the target NRF queries the S-NSSAI of the source PLMN and the corresponding S-NSSAI of the target PLMN according to the source PLMN, and finds the S-NSSAI matching the target PLMN according to the mapping relationship, and returns the S-NSSAI matching the target PLMN to the source NRF; the source AMF receives the S-NSSAI matching the target PLMN returned by the source NRF to obtain the NSSAI of the target PLMN.

[0131] Optionally, before the source AMF sends the first query request to the source NRF, the method further includes: configuring the corresponding S-NSSAI mapping relationship between the S-NSSAI of the source PLMN and the target PLMN in the source NRF or the target NRF.

[0132] The source AMF obtains the NSSAI of the target PLMN based on the NSSF query, specifically including: the source AMF sends a second query request to the NSSF, the second query request includes the source PLMN+NSSAI, the target PLMN and the indication bit, the indication bit represents the query of the target network switching information during the PDU switching process in the home roaming scenario, so that the NSSF queries the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI according to the source PLMN+NSSAI and the target PLMN, wherein the target NSSF stores the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI; the source AMF receives the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI returned by the NSSF according to the indication bit to obtain the NSSAI of the target PLMN.

[0133] Optionally, the NRF selects a target AMF based on the NSSAI and target TAI of the target PLMN, specifically including: the NRF finds a matching target AMF set based on the NSSAI of the target PLMN; the NRF selects the target AMF from the target AMF set based on the target TAI. Alternatively, the NRF finds a matching target AMF set based on the target TAI; the NRF selects the target AMF from the target AMF set based on the NSSAI of the target PLMN.

[0134] Example 3:

[0135] As shown in Figure 2, this embodiment provides an AMF selection device for inter-PLMN handover, which is applied to the source AMF, including:

[0136] The judging module 21 is configured to judge whether the user terminal is switching across PLMNs.

[0137] The acquisition module 22 is connected to the judgment module 21 and is configured to acquire the NSSAI of the target PLMN in response to the user terminal performing an inter-PLMN handover.

[0138] The sending module 23 is connected to the acquisition module 22, and is used to send an AMF instance query request to the network element service storage function NRF, wherein the AMF instance query request includes the NSSAI and target TAI of the target PLMN, so that the NRF selects the target AMF according to the NSSAI and target TAI of the target PLMN.

[0139] The first receiving module 24 is configured to receive the target AMF fed back by the NRF and perform AMF switching to support service continuity of the user terminal switched across PLMNs.

[0140] Inter-PLMN handover includes one of the following: national roaming, shared network roaming, different network roaming, and core network roaming.

[0141] Optionally, the AMF selection device for cross-PLMN switching also includes a second receiving module.

[0142] The second receiving module is connected to the judgment module and is used to receive a handover request sent by the source 5G wireless access network NG-RAN, wherein the handover request includes a result identifier of the source NG-RAN judging whether the user terminal is an inter-PLMN handover.

[0143] Optionally, the judgment module includes a first acquisition unit and a first judgment unit.

[0144] A first acquiring unit is configured to acquire a target TAI, a cell identifier, and a global RAN node identifier in a handover request. The handover request includes an identifier of a result of the source NG-RAN determining whether the user terminal is performing an inter-PLMN handover, and / or a first parameter and / or a target PLMN, where the first parameter includes the target TAI, the cell identifier, and the global RAN node identifier.

[0145] The first judgment unit is connected to the first acquisition unit, and is used to determine whether the PLMN identified by the target TAI or cell is the same as the PLMN identified by the global RAN node, and is used to determine that the user terminal is switched across PLMNs in response to the judgment result being different, and is used to determine that the user terminal is switched within the system in response to the judgment result being the same.

[0146] Optionally, the acquisition module is configured to acquire the NSSAI of the target PLMN based on an NRF query or an NSSF query.

[0147] Optionally, the acquisition module includes a second judgment unit, a second acquisition unit and a third acquisition unit.

[0148] The second judgment unit is used to determine whether the slice type of the source PLMN+NSSAI is greater than a preset threshold.

[0149] The second acquiring unit is connected to the second judging unit and is configured to acquire the NSSAI of the target PLMN based on the NRF query in response to a negative judgment result.

[0150] The third acquiring unit is connected to the second judging unit and is configured to acquire the NSSAI of the target PLMN based on the NSSF query in response to a yes judgment result.

[0151] Optionally, the second acquisition unit is used to obtain the target PLMN in the switching request and send a first query request to the source NRF, where the first query request includes the source PLMN+NSSAI and the target PLMN, so that the source NRF is routed to the target NRF according to the target PLMN, and the target NRF queries the mapping relationship between the S-NSSAI of the source PLMN and the corresponding S-NSSAI of the target PLMN according to the source PLMN, and finds the S-NSSAI matching the target PLMN according to the mapping relationship, returns the S-NSSAI matching the target PLMN to the source NRF, and receives the S-NSSAI matching the target PLMN returned by the source NRF to obtain the NSSAI of the target PLMN.

[0152] Optionally, the AMF selection device for cross-PLMN switching also includes a configuration module.

[0153] The configuration module is used to configure the mapping relationship between the S-NSSAI of the source PLMN and the corresponding S-NSSAI of the target PLMN in the source NRF or the target NRF.

[0154] Optionally, the third acquisition unit is used to send a second query request to the NSSF, the second query request includes the source PLMN+NSSAI, the target PLMN and an indication bit, the indication bit represents the query of the target network switching information in the PDU switching process in the home roaming scenario, so that the NSSF queries the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI based on the source PLMN+NSSAI and the target PLMN, wherein the target NSSF stores the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI, and is used to receive the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI returned by the NSSF based on the indication bit to obtain the NSSAI of the target PLMN.

[0155] Optionally, the NRF is used to find a matching target AMF set based on the NSSAI of the target PLMN, and the NRF is used to select a target AMF from the target AMF set based on the target TAI.

[0156] Example 4:

[0157] As shown in FIG3 , this embodiment provides an AMF selection device for inter-PLMN handover, which is applied to an NRF, including:

[0158] The third receiving module 31 is used to receive the AMF instance query request sent by the source AMF, wherein the AMF instance query request includes the NSSAI and target TAI of the target PLMN. Before the source AMF sends the AMF instance query request, the source AMF determines whether the user terminal is switched across PLMNs. In response to the user terminal being switched across PLMNs, the source AMF obtains the network slice selection auxiliary information NSSAI of the target PLMN.

[0159] The feedback module 32 is connected to the third receiving module 31, and is used to select a target AMF according to the NSSAI and target TAI of the target PLMN, and to feed back the target AMF to the source AMF so that the source AMF performs AMF switching to support service continuity of user terminals switched across PLMNs.

[0160] Optionally, the feedback module includes a selection unit, which is used to find a matching target AMF set according to the NSSAI of the target PLMN, and to select a target AMF from the target AMF set according to the target TAI.

[0161] In addition, the detailed functions of the source AMF and NRF are as described in Example 1 and will not be repeated here.

[0162] Example 5:

[0163] As shown in Figure 4, this embodiment provides an electronic device, including a memory 41 and a processor 42, wherein the memory 41 stores a computer program, and the processor 42 is configured to run the computer program to implement the AMF selection method for inter-PLMN switching as described in Example 1 or Example 2.

[0164] Example 6:

[0165] This embodiment provides a computer-readable storage medium having a computer program stored thereon. When the computer program is executed by a processor, the AMF selection method for inter-PLMN switching as described in Example 1 or Example 2 is implemented.

[0166] The AMF selection device for cross-PLMN switching of Example 3 and Example 4, the electronic device of Example 5, and the computer-readable storage medium of Example 6 are used to obtain the network slice selection auxiliary information NSSAI of the target PLMN when the user terminal switches across PLMNs, and send an AMF instance query request to the NRF, so that the NRF selects the target AMF according to the NSSAI of the target PLMN and the target tracking area identifier TAI, receives the target AMF fed back by the NRF, and performs AMF switching, so that the connection state service of the user terminal continues, avoiding the situation where the service interruption occurs due to the inaccurate selection of the target AMF and the inability to meet the service capabilities of the user terminal. Among them, the method of selecting the target AMF based on NRF is suitable for scenarios where NSSF is not deployed and the types of slices are relatively few and the slices are not coarse-grained. If there are many types of VPLMN and HPLMN slices, not only the three major types of slices are supported, but also subdivided slices are supported. The NSSAI of the target PLMN can be obtained through NSSF query to further improve the accuracy of target AMF selection. Therefore, the method of selecting the target AMF based on NSSF and NRF is suitable for scenarios with many types of slices. By looking up the source PLMN NSSF to confirm a more accurate target PLMN+NSSAI, the accuracy of target AMF selection can be further improved.

[0167] It will be understood that the above embodiments are merely exemplary embodiments for illustrating the principles of the present invention, and the present invention is not limited thereto. Those skilled in the art will appreciate that various modifications and improvements can be made without departing from the spirit and substance of the present invention, and such modifications and improvements are also considered to be within the scope of protection of the present invention.

Claims

1. A method for selecting an access and mobility management function AMF for handover across a public land mobile network PLMN, applied to a source AMF, characterized in that: include: Determine whether the user terminal is switched across PLMNs; In response to the user terminal being handed over across PLMNs, obtaining network slice selection auxiliary information NSSAI of the target PLMN; Send an AMF instance query request to the network element service storage function NRF, wherein the AMF instance query request includes the NSSAI of the target PLMN and the target tracking area identifier TAI, so that the NRF selects the target AMF according to the NSSAI of the target PLMN and the target TAI; The target AMF receives NRF feedback and performs AMF switching to support service continuity of user terminals switched across PLMNs.

2. The method according to claim 1, characterized in that Inter-PLMN switching includes one of the following: national roaming, shared network, different network roaming, and core network roaming.

3. The method according to claim 1, characterized in that: Before determining whether the user terminal is switched across PLMNs, the method further includes: Receive a handover request sent by a source 5G wireless access network NG-RAN, wherein the handover request includes a result identifier of the source NG-RAN determining whether the user terminal is an inter-PLMN handover.

4. The method according to claim 1, characterized in that: The determining whether the user terminal is switched across PLMNs specifically includes: Obtain the target TAI, cell ID, and global RAN node ID in the handover request; Determine whether the PLMN identified by the target TAI or cell is the same as the PLMN identified by the global RAN node; In response to the determination result being different, determining that the user terminal is switched across PLMNs; In response to the determination result being the same, it is determined that the user terminal is switched within the system.

5. The method according to claim 1, characterized in that The obtaining of the network slice selection auxiliary information NSSAI of the target PLMN specifically includes: Obtain the NSSAI of the target PLMN based on NRF query or network slice selection function NSSF query.

6. The method according to claim 5, characterized in that The obtaining of the NSSAI of the target PLMN based on the NRF query or the network slice selection function NSSF query specifically includes: Determine whether the slice type of the NSSAI of the source PLMN is greater than a preset threshold; In response to a negative determination, obtaining the NSSAI of the target PLMN based on the NRF query; In response to the judgment result being yes, the NSSAI of the target PLMN is acquired based on the NSSF query.

7. The method according to claim 6, characterized in that The obtaining of the NSSAI of the target PLMN based on the NRF query specifically includes: Obtain the target PLMN in the handover request; Send a first query request to the source NRF, where the first query request includes the source PLMN+NSSAI and the target PLMN, so that the source NRF is routed to the target NRF according to the target PLMN, and the target NRF queries the mapping relationship between the S-NSSAI of the source PLMN and the corresponding S-NSSAI of the target PLMN according to the source PLMN, finds the S-NSSAI matching the target PLMN according to the mapping relationship, and returns the S-NSSAI matching the target PLMN to the source NRF; Receive the S-NSSAI matching the target PLMN returned by the source NRF to obtain the NSSAI of the target PLMN.

8. The method according to claim 7, characterized in that Before sending the first query request to the source NRF, the method further includes: The mapping relationship between the S-NSSAI of the source PLMN and the corresponding S-NSSAI of the target PLMN is configured on the source NRF or the target NRF.

9. The method according to claim 6, characterized in that The obtaining of the NSSAI of the target PLMN based on the NSSF query specifically includes: Send a second query request to NSSF, the second query request includes the source PLMN+NSSAI, the target PLMN and an indication bit, the indication bit indicates the PDU switching process in the home roaming scenario The query of the target network switching information enables the NSSF to query the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI according to the source PLMN+NSSAI and the target PLMN, wherein the target NSSF stores the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI; The receiving NSSF returns the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI according to the indication bit to obtain the NSSAI of the target PLMN.

10. A method for selecting an AMF for inter-PLMN handover, characterized in that: Applications to NRF include: receiving an AMF instance query request sent by a source AMF, wherein the AMF instance query request includes the NSSAI and the target TAI of the target PLMN. Before the source AMF sends the AMF instance query request, the source AMF determines whether the user terminal is switched across PLMNs. In response to the user terminal being switched across PLMNs, the source AMF obtains the NSSAI of the target PLMN. The target AMF is selected based on the NSSAI and target TAI of the target PLMN; the target AMF is fed back to the source AMF so that the source AMF performs AMF switching to support service continuity of user terminals switched across PLMNs.

11. The method according to claim 10, characterized in that Inter-PLMN switching includes one of the following: national roaming, shared network, different network roaming, and core network roaming.

12. The method according to claim 10, characterized in that The NRF selects the target AMF based on the NSSAI and target TAI of the target PLMN, including: NRF finds the matching target AMF set based on the NSSAI of the target PLMN; NRF selects the target AMF from the target AMF set based on the target TAI.

13. An AMF selection device for inter-PLMN handover, applied to a source AMF, characterized in that: include: A judgment module is used to judge whether the user terminal is switched across PLMNs. The acquisition module is connected to the judgment module and is used to obtain the NSSAI of the target PLMN in response to the user terminal switching across PLMNs. The sending module is connected to the acquisition module and is used to send data to the network element service storage function NRF. The AMF instance query request includes the NSSAI and target TAI of the target PLMN, so that the NRF selects the target AMF according to the NSSAI and target TAI of the target PLMN. The first receiving module is used to receive the target AMF fed back by the NRF and perform AMF switching to support service continuity of user terminals switched across PLMNs.

14. The device according to claim 13, characterized in that Inter-PLMN switching includes one of the following: national roaming, shared network, different network roaming, and core network roaming.

15. The device according to claim 13, characterized in that Also includes a second receiving module, The second receiving module is connected to the judgment module, and is used to receive a switching request sent by a source 5G wireless access network NG-RAN, wherein the switching request includes a result identifier of the source NG-RAN judging whether the user terminal is an inter-PLMN switching.

16. The device according to claim 13, characterized in that The judging module includes a first obtaining unit and a first judging unit. The first acquisition unit is configured to acquire a target TAI, a cell identifier, and a global RAN node identifier in a handover request. The first judgment unit is connected to the first acquisition unit and is used to judge whether the PLMN identified by the target TAI or cell is the same as the PLMN identified by the global RAN node. for determining that the user terminal is switched across PLMNs in response to the judgment result being different, And, in response to the judgment result being the same, determining that the user terminal is switched within the system.

17. The device according to claim 13, characterized in that The acquisition module is used to acquire the NSSAI of the target PLMN based on NRF query or NSSF query.

18. The device according to claim 17, characterized in that The acquisition module includes a second judgment unit, a second acquisition unit and a third acquisition unit. The second judgment unit is used to judge whether the slice type of the NSSAI of the source PLMN is greater than Preset threshold, The second acquisition unit is connected to the second judgment unit, and is configured to obtain the NSSAI of the target PLMN based on the NRF query in response to a judgment result of no. The third acquisition unit is connected to the second judgment unit, and is used to obtain the NSSAI of the target PLMN based on the NSSF query in response to the judgment result being yes.

19. The device according to claim 18, characterized in that The second acquisition unit is used to obtain the target PLMN in the switching request and send a first query request to the source NRF, the first query request includes the source PLMN+NSSAI and the target PLMN, so that the source NRF is routed to the target NRF according to the target PLMN, and the target NRF queries the S-NSSAI of the source PLMN and the corresponding S-NSSAI of the target PLMN according to the source PLMN. The S-NSSAI matching the target PLMN is found according to the mapping relationship, and the S-NSSAI matching the target PLMN is returned to the source NRF, and it is used to receive the S-NSSAI matching the target PLMN returned by the source NRF to obtain the NSSAI of the target PLMN.

20. The device according to claim 19, characterized in that Also includes configuration modules, The configuration module is used to configure the S-NSSAI mapping relationship between the source PLMN and the corresponding S-NSSAI of the target PLMN in the source NRF or the target NRF.

21. The device according to claim 18, characterized in that The third acquisition unit is used to send a second query request to the NSSF, the second query request includes the source PLMN+NSSAI, the target PLMN and an indication bit, the indication bit represents the query of the target network switching information in the PDU switching process in the home roaming scenario, so that the NSSF queries the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI according to the source PLMN+NSSAI and the target PLMN, wherein the target NSSF stores the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI, and is used to receive the mapping relationship between the target PLMN+NSSAI and the source PLMN+NSSAI returned by the NSSF according to the indication bit to obtain the NSSAI of the target PLMN.

22. An AMF selection device for inter-PLMN handover, applied to NRF, characterized in that: include: The third receiving module is configured to receive an AMF instance query request sent by a source AMF, wherein the AMF instance query request includes the NSSAI and the target TAI of the target PLMN. Before the source AMF sends the AMF instance query request, the source AMF determines whether the user terminal is switched across PLMNs. In response to the user terminal being switched across PLMNs, the source AMF obtains the network slice selection auxiliary information NSSAI of the target PLMN. The feedback module is connected to the third receiving module, and is used to select the target AMF according to the NSSAI and target TAI of the target PLMN, and to feed back the target AMF to the source AMF so that the source AMF performs AMF switching to support service continuity of user terminals switched across PLMNs.

23. The device according to claim 22, characterized in that The feedback module includes a selection unit, which is used to find a matching target AMF set according to the NSSAI of the target PLMN, and to select a target AMF from the target AMF set according to the target TAI.

24. An electronic device, characterized in that: It includes a memory and a processor, wherein a computer program is stored in the memory, and the processor is configured to run the computer program to implement the AMF selection method for inter-PLMN switching as described in any one of claims 1-9 or claims 10-12.

25. A computer-readable storage medium having a computer program stored thereon, characterized in that: When the computer program is executed by the processor, the method for selecting an AMF for inter-PLMN switching as described in any one of claims 1-9 or claims 10-12 is implemented.

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