RU2811790C2 - Communication device and communication method - Google Patents

Abstract

FIELD: communications.

SUBSTANCE: when service of a terminal device is transferred from a source network access device in the first area to a target network access device in the second area, the target mobility network element selected for the terminal device is determined based on the set of segments for the home target terrestrial network public mobile communication HPLMN and the segment set for the HPLMN corresponds to the segment set for the first area, so that the selected target mobility network element can serve, in the second area, the segment set for the HPLMN.

EFFECT: ability to select the appropriate set of segments for the target public land mobile network PLMN for the user device.

19 cl, 16 dwg

Description

TECHNICAL FIELD

[0001] This application relates to the field of mobile communication technology, and in particular to a communication method and a communication device.

BACKGROUND OF THE ART

[0002] Due to a reason such as the movement of a terminal device, the network access device accessed by the terminal device performs a handover (specifically, service of the terminal device is transferred from the source network access device to the target network access device). In addition, a mobility network element that provides an access service to a terminal device may also perform handover (specifically, service of a terminal device is transferred from a source mobility network element to a target mobility network element).

[0003] The segment identifier included in the set of segments to which the terminal device is permitted to access in the first region and the segment identifier included in the set of segments to which the terminal device is permitted to access in the second region may have different values. Based on this premise, there is currently no corresponding solution on how to select an appropriate target mobility network element for a terminal device.

SUMMARY OF THE INVENTION

[0004] This application provides a communication method and a communication device to select an appropriate target mobility control network element for a terminal device.

[0005] According to a first aspect, this application provides a communication method including: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, obtaining, by the source mobility network element in the first area, information about a target mobility network element in a second region based on the set of segments for the first region; and sending the source mobility network element a set of segments for the Home Public Land Mobile Network (HPLMN) of the terminal device to the target mobility network element, wherein the set of segments for the HPLMN corresponds to the set of segments for the first area, and the set segments for HPLMN is used to define a set of segments for the second region. Based on such a solution, the target mobility network element selected for the terminal device is determined based on the segment set for the HPLMN, and the segment set for the HPLMN corresponds to the segment set for the first region, so that the selected target mobility network element can serve, in the second region, set of segments for the HPLMN, thereby selecting the appropriate target mobility management network element and providing assistance in realizing normal communication of the terminal device.

[0006] First case: The first region is a source PLMN, and the second region is a target PLMN.

[0007] In an exemplary implementation, the source mobility network element determines, based on the mapping between the segment set for the source PLMN and the segment set for the HPLMN, a set of segments that is intended for the HPLMN and that corresponds to the segment set for the source PLMN.

[0008] In an exemplary implementation, obtaining, by the source mobility network element, information about a target mobility network element in a second region based on a segment set for the first region includes: the source mobility network element sending a segment set for an HPLMN and information about a target PLMN on first device; and the source mobility network element receiving from the first device information about the target mobility network element, wherein the first device is a source segment selection network element or a source network element of a repository network in the source PLMN.

[0009] In an exemplary implementation, obtaining, by the source mobility network element, information about a target mobility network element in a second region based on a segment set for the first region, includes: the source mobility network element sending a set of segments for the HPLMN to the source network element selecting a segment in the original PLMN; the source mobility management network element receiving from the source network element a segment selection of a set of segments for the target PLMN; sending the source mobility management network element a set of segments for the target PLMN and information about the target PLMN to the source network element of the network repository in the source PLMN; and receiving, from the source network element of the network repository, information about the target mobility control network element by the source mobility network element.

[0010] In an exemplary implementation, the source mobility management network element sends a set of segments for the source PLMN to the source segment selection network element in the source PLMN; and the source mobility management network element receives from the source segment selection network element a set of segments for the HPLMN.

[0011] In an exemplary implementation, obtaining, by a source mobility network element, information about a target mobility network element in a second region based on a set of segments for the first region, includes:

sending the source mobility management network element information about the target PLMN to the source segment selection network element in the source PLMN; And

the source mobility network element receiving from the source segment selection network element information about the target mobility network element.

[0012] In an exemplary implementation, obtaining, by the source mobility network element, information about a target mobility network element in a second region based on a set of segments for the first region, includes: receiving by the source mobility network element from the source network element a selection of a segment in the source PLMN of the set segments for target PLMN; sending the source mobility management network element a set of segments for the target PLMN and information about the target PLMN to the source network element of the network repository in the source PLMN; and receiving, from the source network element of the network repository, information about the target mobility control network element by the source mobility network element.

[0013] Second case: The first region and the second region are in the same PLMN.

[0014] In an exemplary implementation, the source network mobility control element determines, based on the mapping between the segment set for the first region and the segment set for the HPLMN, a segment set that is intended for the HPLMN and that corresponds to the segment set for the first region.

[0015] In an exemplary implementation, obtaining, by the source mobility network element, information about a target mobility network element in a second region based on a segment set for the first region includes: the source mobility network element sending a set of segments for the HPLMN and information about a second region in segment selection network element; and receiving by the source mobility network element from the segment selection network element information about the target mobility network element, wherein information about the target mobility network element is determined based on the set of segments for the HPLMN and the second region information.

[0016] In an exemplary implementation, the source mobility control network element sends a set of segments for the first region to the segment selection network element; and the source mobility management network element receives from the segment selection network element a set of segments that is intended for the HPLMN and that corresponds to a set of segments for the first region.

[0017] In an exemplary implementation, obtaining, by the source mobility network element, information about a target mobility network element in a second region based on a segment set for the first region includes: the source mobility network element sending a set of segments for the first region and information about the second region to the segment selection network element; and receiving, by the source mobility network element, from the segment selection network element, information about the target mobility network element, wherein information about the target mobility network element is determined based on the set of segments for the first region and the information about the second region.

[0018] According to a second aspect, this application provides a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, obtaining, by the first device in the source PLMN, a set of segments that is intended for the HPLMN of the terminal device and which corresponds to the set of segments for the original PLMN; sending, by the first device, a set of segments for the HPLMN to a second device in the target PLMN, wherein the set of segments for the HPLMN is used to determine a target mobility management network element in the target PLMN; receiving, by the first device, information about the target mobility network element from the second device; and sending, by the first device, information about the target mobility network element to the source mobility network element in the source PLMN. Based on such a decision, the target mobility network element selected for the terminal device is determined based on the segment set for the HPLMN, and the segment set for the HPLMN corresponds to the segment set for the source PLMN, so that the selected target mobility network element can serve, in the target PLMN, set of segments for the HPLMN, thereby selecting the appropriate target mobility management network element and providing assistance in realizing normal communication of the terminal device.

[0019] In an exemplary implementation, receiving by the first device in the source PLMN a set of segments that is intended for the HPLMN and which corresponds to the set of segments for the source PLMN includes: receiving by the first device from the source mobility network element a set of segments for the source PLMN and determining the set of segments , which is for the HPLMN and which corresponds to the set of segments for the original PLMN; or the first device receiving from the source mobility network element a set of segments for the HPLMN.

[0020] In an exemplary implementation, the first device is a source segment selection network element in the source PLMN, and the second device is a target segment selection network element in the target PLMN; or the first device is a source network repository network element in the source PLMN, and the second device is a target network repository network element in the target PLMN.

[0021] In an exemplary implementation, the first device receives information about the target PLMN from the source mobility network element; and the first device selects the second device based on information about the target PLMN.

[0022] According to a third aspect, this application provides a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, obtaining, by the source network element, a selection of a segment in the source PLMN of a set of segments , which is intended for the HPLMN of the terminal device and which corresponds to the set of segments for the source PLMN; sending the source segment selection network element of a set of segments for the HPLMN to the target network element of the selection of a segment in the target PLMN, wherein the set of segments for the HPLMN is used to determine a set of segments for the target PLMN; receiving by the source network element a segment selection from the target network element a segment selection of a set of segments for the target PLMN; and sending the segment selection source network element of the set of segments for the target PLMN to the source mobility management network element. Based on such a decision, the target mobility management network element selected for the terminal device is determined based on the segment set for the target PLMN, wherein the segment set for the target PLMN corresponds to the segment set for the HPLMN, and the segment set for the HPLMN corresponds to the segment set for the source PLMN, so that the selected target mobility network element may serve, in the target PLMN, a set of segments for the HPLMN, thereby selecting the appropriate target mobility network element and providing assistance in realizing normal communication of the terminal device.

[0023] In an exemplary implementation, obtaining, by the source network element, a selection of a segment in the source PLMN, a set of segments that is intended for the HPLMN of the terminal device and that corresponds to a set of segments for the source PLMN, includes: receiving by the source network element a selection of the segment from the source mobility management network element a set of segments for the source PLMN and determining a set of segments that is intended for the HPLMN and which corresponds to a set of segments for the source PLMN; or the source network element receiving a segment selection from the source mobility control network element of a set of segments for the HPLMN.

[0024] In an exemplary implementation, the source segment selection network element receives information about the target PLMN from the source mobility management network element; and the source segment selection network element selects the target segment selection network element based on the information about the target PLMN.

[0025] According to a fourth aspect, this application provides a communication method including: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, obtaining, by the network element, a selection of a segment of a set of segments that is intended for HPLMN of the terminal device and which corresponds to a set of segments for the first area, and information about the second area; determining by the network element a segment selection of a set of segments for a second region based on the set of segments for the HPLMN and information about the second region; determining by the network element segment selection information about the target mobility network element based on the set of segments for the second region; and the segment selection network element sending information about the target mobility network element to the source mobility network element. Based on such a solution, the target mobility network element selected for the terminal device is determined based on the segment set for the HPLMN, and the segment set for the HPLMN corresponds to the segment set for the first region, so that the selected target mobility network element can serve, in the second region, set of segments for the HPLMN, thereby selecting the appropriate target mobility management network element and providing assistance in realizing normal communication of the terminal device.

[0026] In an exemplary implementation, receiving, by the network element, a segment selection of a segment set that is intended for an HPLMN terminal device and that corresponds to a segment set for a first region, includes: the network element receiving a segment selection from a source mobility management network element in a first region of the segment set. for the first region and determining a set of segments that is intended for the HPLMN and which corresponds to the set of segments for the first region; or the network element receiving a segment selection from the source mobility network element of a set of segments for the HPLMN.

[0027] In an exemplary implementation, the segment selection network element stores a mapping between a set of segments for a first region and a set of segments for an HPLMN, as well as a mapping between a set of segments for a second region and a set of segments for an HPLMN.

[0028] According to a fifth aspect, this application provides a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, the source network element receiving a network repository in the source PLMN from the source network a mobility control element in the source PLMN of the segment set for the target PLMN; sending the source network repository network element a set of segments for the target PLMN to the target network repository network element in the target PLMN; receiving, by the source network repository network element, information about the target mobility management network element from the target network repository network element; and sending the source network repository network element information about the target mobility control network element to the source mobility control network element.

[0029] In an exemplary implementation, the source network repository network element receives information about the target PLMN from the source mobility management network element, and the source network repository network element determines the target network repository network element based on the information about the target PLMN.

[0030] According to a sixth aspect, this application provides a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, receiving by the target network element a selection of a segment in the target PLMN from the source network a segment selection element in the source PLMN of the segment set for the HPLMN of the terminal device; determining, by the target segment selection network element, information about the target mobility management network element that supports a set of segments for the target PLMN, wherein the set of segments for the target PLMN corresponds to the set of segments for the HPLMN; and sending the target segment selection network element information about the target mobility control network element to the source segment selection network element. Based on such a decision, the target mobility management network element selected for the terminal device is determined based on the segment set for the target PLMN, the segment set for the target PLMN corresponds to the segment set for the HPLMN, and the segment set for the HPLMN corresponds to the segment set for the source PLMN, so that the selected the target mobility network element may serve, in the target PLMN, a set of segments for the HPLMN, thereby selecting the appropriate target mobility network element and providing assistance in realizing normal communication of the terminal device.

[0031] In an exemplary implementation, the target segment selection network element determines a set of segments for the target PLMN based on a mapping between the set of segments for the HPLMN and the set of segments for the target PLMN.

[0032] According to a seventh aspect, this application provides a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, receiving by the target network element a selection of a segment in the target PLMN from the source network a segment selection element in the source PLMN or from a target network repository network element in a target segment set PLMN for the terminal device's HPLMN; and sending the segment selection target network element to the segment selection source network element or the target network element of a network repository of a segment set for the target PLMN that corresponds to the segment set for the HPLMN, wherein the segment set for the target PLMN is used to determine information about the target mobility management network element at target PLMN. Based on such a decision, the target mobility management network element selected for the terminal device is determined based on the segment set for the target PLMN, the segment set for the target PLMN corresponds to the segment set for the HPLMN, and the segment set for the HPLMN corresponds to the segment set for the source PLMN, so that the selected the target mobility network element may serve, in the target PLMN, a set of segments for the HPLMN, thereby selecting the appropriate target mobility network element and providing assistance in realizing normal communication of the terminal device.

[0033] In an exemplary implementation, the target segment selection network element determines a set of segments for the target PLMN based on a mapping between the set of segments for the HPLMN and the set of segments for the target PLMN.

[0034] According to an eighth aspect, this application provides a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, receiving by the target network element a network repository in the target PLMN from the target network a segment selection element in the target PLMN or a source network repository network element in the source PLMN of a segment set that is intended for the target PLMN and that corresponds to a segment set for the terminal device's HPLMN; determining by the target network element a network repository of information about the target mobility management network element that maintains a set of segments for the target PLMN; and sending the target network repository network element information about the target mobility control network element to the source network repository network element. Based on such a decision, the target mobility management network element selected for the terminal device is determined based on the segment set for the target PLMN, the segment set for the target PLMN corresponds to the segment set for the HPLMN, and the segment set for the HPLMN corresponds to the segment set for the source PLMN, so that the selected the target mobility network element may serve, in the target PLMN, a set of segments for the HPLMN, thereby selecting the appropriate target mobility network element and providing assistance in realizing normal communication of the terminal device.

[0035] According to a ninth aspect, this application provides a communication device. The device has the function of implementing a communication method according to any of the above aspects or any implementation of the above aspects. The function may be implemented by hardware or may be implemented by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above function.

[0036] According to a tenth aspect, this application provides a communication device including a processor and a memory. The memory is configured to store a computer-executable instruction. When the device is operated, the processor executes a computer-executable instruction stored in memory such that the device performs a communication method according to any of the foregoing aspects or any implementation of the foregoing aspects.

[0037] According to an eleventh aspect, this application provides a communication device including blocks or means for performing steps according to any of the foregoing aspects.

[0038] According to a twelfth aspect, this application provides a communication device including a processor and an interface circuit. The processor is configured to: communicate with another device via an interface circuit; and perform a method according to any of the foregoing aspects. There are one or more processors.

[0039] According to a thirteenth aspect, this application provides a communication device including a processor configured to: connect to a memory and call a program stored in the memory to perform a method according to any of the foregoing aspects or any implementation of any of the foregoing aspects. The memory may be located within the device or may be located external to the device. In addition, there are one or more processors.

[0040] According to a fourteenth aspect, this application further provides a computer-readable medium, and the computer-readable medium stores an instruction. When an instruction is executed on a computer, the computer is enabled to perform a method according to any of the foregoing aspects.

[0041] According to a fifteenth aspect, this application provides a computer program product including instructions. When the computer program product is operated on a computer, it is possible for that computer to perform a method according to any of the foregoing aspects.

[0042] According to a sixteenth aspect, this application further provides a chip system including a processor configured to perform a method according to any of the above-mentioned aspects.

[0043] According to a seventeenth aspect, this application further provides a communication method including: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, receiving by the target mobility management network element in a second area from the source a mobility control network element in a first segment set region for the HPLMN of the terminal device, the segment set for the HPLMN corresponding to the segment set for the first region; and obtaining, by the target mobility network element, a set of segments for the second region based on the set of segments for the HPLMN.

[0044] In an exemplary implementation, the target mobility network element obtaining a set of segments for the second region based on the segment set for the HPLMN includes: the target mobility network element determining the set of segments for the second region based on the configuration information.

[0045] In an exemplary implementation, the configuration information includes a mapping between a segment set for the second region and a segment set for the HPLMN; or the configuration information includes a roaming agreement between the second region and the HPLMN, and the roaming agreement is used to determine the mapping between the segment set for the second region and the segment set for the HPLMN.

[0046] In an exemplary implementation, obtaining a segment set for a second region by the target mobility network element based on the segment set for the HPLMN includes: the target mobility network element sending first information to the target network element selecting a segment in the second region, wherein the first information includes includes a set of segments for HPLMN; and receiving, from the target network element, a segment selection of the set of segments for the second region by the target mobility management network element.

[0047] In an exemplary implementation, the first information further includes indication information, and this indication information is used to indicate the target NSSF to generate a set of segments for the target PLMN.

[0048] In an exemplary implementation, the target mobility management network element receives from the target segment selection network element a mapping between the set of segments for the HPLMN and the set of segments for the second region.

[0049] In an exemplary implementation, the first region is a source PLMN and the second region is a target PLMN.

[0050] According to an eighteenth aspect, this application further provides a communication method including: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, sending, by the source network element, a mobility control in the first area a message requesting a target network element of a network repository function in a second region; receiving, by the source mobility network element from the target network element of the network repository function, an identifier of the target mobility network element in the second region; and sending the source mobility network element a segment set for the terminal device's HPLMN to the target mobility network element, wherein the segment set for the HPLMN corresponds to a segment set for the first region, and the segment set for the HPLMN is used to determine the segment set for the second region.

[0051] In an exemplary implementation, the first region is a source PLMN and the second region is a target PLMN.

[0052] According to a nineteenth aspect, this application further provides a communication method including: configuring, by a target network element, a network repository function in a second area, an identifier of a target mobility management network element in a second area; when service of the terminal device is transferred from the source network access device in the first area to the target network access device in the second area, receiving, by the target network element of the network repository function, a request message from the source mobility control network element in the first area; and sending, by the target network element to the network repository function, an identifier of the target mobility control network element to the source mobility control network element.

[0053] In an exemplary implementation, the first region is a source PLMN and the second region is a target PLMN.

[0054] According to the twentieth aspect, this application further provides a communication device. The apparatus has the function of implementing a communication method according to any aspect of the seventeenth aspect to the nineteenth aspect or any implementations of the aspects of the seventeenth aspect to the nineteenth aspect. The function may be implemented by hardware or may be implemented by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above function.

[0055] According to a twenty-first aspect, this application further provides a communication device including a processor and a memory. The memory is configured to store a computer-executable instruction. When the device operates, the processor executes a computer-executable instruction stored in memory such that the device executes a communication method according to any aspect of the seventeenth aspect to the nineteenth aspect or any implementations of the seventeenth aspect to the nineteenth aspect.

[0056] According to a twenty-second aspect, this application provides a communication device including blocks or means for performing the steps of any of the seventeenth aspects through the nineteenth aspects.

[0057] According to a twenty-third aspect, this application further provides a communication device including a processor and an interface circuit. The processor is configured to: communicate with another device through an interface circuit and perform any method according to any aspect from the seventeenth aspect to the nineteenth aspect. There are one or more processors.

[0058] According to a twenty-fourth aspect, this application further provides a communication device including a processor configured to: connect to a memory and call a program stored in the memory to perform a method according to any aspect of the seventeenth aspect to the nineteenth aspect or any implementations of the aspects from the seventeenth aspect to the nineteenth aspect. The memory may be located within the device or may be located external to the device. In addition, there are one or more processors.

[0059] According to a twenty-fifth aspect, the present application further provides a computer-readable medium, and the computer-readable medium stores an instruction. When an instruction is executed on a computer, the computer is enabled to execute the method according to any aspect from the seventeenth aspect to the nineteenth aspect.

[0060] According to the twenty-sixth aspect, this application further provides a computer program product including instructions. When the computer program product is operated on a computer, the computer is enabled to perform the method according to any aspect from the seventeenth aspect to the nineteenth aspect.

[0061] According to a twenty-seventh aspect, this application further provides a chip system including a processor configured to perform a method according to any aspect from the seventeenth aspect to the nineteenth aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

[0062] FIG. 1 is a schematic representation of a possible network architecture to which this application is applicable;

[0063] FIG. 2 is a schematic representation of an application scenario to which this application is applicable;

[0064] FIG. 3 is a schematic representation of the first specific application scenario to which this application is applicable;

[0065] FIG. 4 is a schematic representation of a second specific application scenario to which this application is applicable;

[0066] FIG. 5 is a schematic representation of a first communication method according to this application;

[0067] FIG. 6 is a schematic representation of a second communication method according to this application;

[0068] FIG. 7 is a schematic representation of a third communication method according to this application;

[0069] FIG. 8 is a schematic representation of a fourth communication method according to this application;

[0070] FIG. 9 is a schematic representation of a fifth communication method according to this application;

[0071] FIG. 10 is a schematic representation of a sixth communication method according to this application;

[0072] FIG. 11 is a schematic diagram of a seventh communication method according to this application;

[0073] FIG. 12 is a schematic diagram of a communication device according to this application;

[0074] FIG. 13 is a schematic diagram of another communication device according to this application;

[0075] FIG. 14 is a schematic diagram of another communication device according to this application;

[0076] FIG. 15 is a schematic diagram of another communication device according to this application; And

[0077] FIG. 16 is a schematic diagram of an eighth communication method according to this application.

DESCRIPTION OF IMPLEMENTATION OPTIONS

[0078] To clarify the objectives, technical solutions and advantages of the present application, the following is a detailed description of this application with reference to the accompanying drawings. The specific operating method in a method embodiment may also be applied to a device embodiment or a system embodiment. In the specifications of this application, unless otherwise indicated, “multiple” means two or more than two.

[0079] FIG. 1 is a schematic representation of the 5th generation (5G) network architecture. The figure shows some of the network elements in the 5G architecture. The user plane function (UPF) network element includes user plane-related functions such as data packet routing and transmission, packet discovery, service usage reporting, Quality of Service (QoS) processing, legal intercepting, detecting uplink data packets and storing downlink data packets.

[0080] The access and mobility management function (AMF) network element is responsible for managing user mobility, including mobility status management, temporary user identity allocation, and user authentication and authorization.

[0081] The session management function (SMF) network element includes session-related functions such as session management (e.g., session establishment, modification, and release, including maintaining a tunnel between the UPF and the AN), selection, and UPF network element management, selection of Service and Session Continuity (SSC) mode, and roaming.

[0082] The Network Slice Selection Function (NSSF) network element is responsible for determining the network slice instance, selecting the AMF network element, and so on.

[0083] The Network Repository Function (NRF) network element is responsible for the network element registration function and discovery function, and also stores information about the network element, for example, instance ID, type, PLMN, segment associated ID, Internet address Internet Protocol (IP), functionality, and supported service of the network element.

[0084] The mobility management network element in this application may be the AMF network element shown in FIG. 1, or there may be a network element having an AMF network element function in a future communication system. The user plane network element in this application may be the UPF network element shown in FIG. 1, or there may be a network element having a UPF network element function in a future communication system. The session management network element in this application may be the SMF network element shown in FIG. 1, or there may be a network element having an SMF network element function in a future communication system. The segment selection network element in this application may be the NSSF network element shown in FIG. 1, or there may be a network element having the function of an NSSF network element in a future communication system. The network repository network element in this application may be the NRF network element shown in FIG. 1, or there may be a network element having the function of an NRF network element in a future communication system.

[0085] A network access device (which is also referred to as a radio access network (RAN) device) in this application is a device that provides a wireless communication function for a terminal. A network access device includes, but is not limited to: g nodeB (gNB), evolved node B (eNB), radio network controller (RNC), node B (NB) ), base station controller (BSC), base transceiver station (BTS), home Node B (for example, home advanced node B or home node B, HNB), baseband unit (BBU) ), transmitting and receiving point (TRP), transmitting point (TP), mobile switching center, etc. in 5G.

[0086] A terminal device (which may also be referred to as a user equipment (UE)) in this application is a device having wireless transmission and reception functions, and it can be deployed on land, such deployment including indoor use or outdoors, or be portable or mounted on a vehicle, can be deployed on water (for example, on a ship) or can be deployed in the air (for example, on an aircraft, balloon and satellite). The terminal device can be a mobile phone (mobile phone), tablet (pad), computer with wireless reception and transmission functions, virtual reality (VR) terminal, augmented reality (AR) terminal, wireless terminal in industrial control ( industrial control), wireless terminal in self-driving, wireless terminal in telemedicine, wireless terminal in smart grid, wireless terminal in transportation safety, wireless terminal in smart city city), a wireless terminal in a smart home, and the like.

[0087] For ease of description, this application is further described using an example in which the mobility management network element is an AMF network element, the segment selection network element is an NSSF network element, the session control network element is an SMF network element, the user plane network element is a network element UPF, and the network repository network element is the NRF network element. In addition, the AMF NE is referred to as AMF for short, the NSSF NE is referred to as NSSF for short, the SMF NE is referred to as SMF for short, the UPF NE is referred to as UPF for short, the NRF NE is referred to as NRF for short, Terminal Device is referred to as UE for short, and the network access device is referred to as RAN for short. More specifically, the AMF described later in this application may be replaced by a mobility control network element, the NSSF may be replaced by a segment selection network element, the SMF may be replaced by a session control network element, the NRF may be replaced by a network repository network element, the UPF may be replaced by user plane network element, the RAN may be replaced by a network access device, and the UE may be replaced by a terminal device.

[0088] It should be noted that in this application, "network segment" and "segment" refer to the same content, one of the terms is used for description in different places, and the two terms are interchangeable.

[0089] Currently, different scenarios impose different requirements, such as charging, policy, security and mobility requirements, in the 3rd Generation Partnership Project (3GPP) ecosystem. 3GPP emphasizes that network segments do not influence each other. For example, a large number of packet meter reading services should not interfere with regular mobile broadband services. To meet diverse requirements and provide isolation between segments, service-independent operations, administration, and maintenance are required, and customizable service functionality and analysis capabilities are provided. Instances of different service types are deployed on different network segments, and instances of the same service type can also be deployed on different network segments.

[0090] When a network slice is deployed to the core network and a user initially joins (or, to put it another way, registers with) the network, the network slice selection process is initiated. The segment selection process depends on the user's subscription data, local configuration information, roaming agreement, operator policy, and the like. During the network segment selection process, the above parameters must be comprehensively considered to select the optimal segment type for the UE.

[0091] When a UE needs to access a network segment, the UE may provide the requested network segment to the core network so that the core network can select an instance of the network segment for the UE. The network slice requested by the UE may be indicated by the requested network slice selection assistance information requested by NSSAI. The requested NSSAI includes one or more pieces of single network slice selection assistance information (S-NSSAI). Each part of the S-NSSAI is used to identify a type of network segment, and alternatively, the S-NSSAI may be understood to be used to identify a network segment, or the S-NSSAI may be understood to be a network segment identity.

[0092] After the UE registers with the network, the core network element (eg, AMF or NSSF) makes a comprehensive determination based on information such as the UE's subscription data, the UE's own requested NSSAI, roaming agreement, and local configuration, and selects a set network segments that the UE is allowed to access. The set of network segments to which access is permitted can be represented by an allowed NSSAI, and all S-NSSAIs included in the allowed NSSAI are valid S-NSSAIs for the current network. If the UE registers with a roaming network, and the S-NSSAI included in the allowed NSSAI for the current registered network is different from the S-NSSAI that is in the HPLMN and that is included in the UE's subscription data, the core network element (e.g., AMF or NSSF) optionally returns a mapping to the UE to indicate the mapping between the S-NSSAI included in the allowed NSSAI and the S-NSSAI for the HPLMN. When the UE needs to initiate a service request subsequently, the UE may select an S-NSSAI from the allowed NSSAI to initiate the service.

[0093] This application is specific to a scenario in which, due to a reason such as relocation of the UE, the RAN accessed by the UE needs to perform a handover, namely, the service of the UE needs to be transferred from the source RAN to the target RAN. and when the source RAN cannot handover to the target RAN through the Xn interface, the handover between the source RAN and the target RAN must be completed through the N2 interface (namely, the interface between the RAN and the AMF).

[0094] FIG. 2 shows the application scenario to which this application is applicable. Before moving the UE, the UE accesses the home RAN in the first area, and the AMF that provides access service for this UE is the home AMF in the first area. After the UE moves, the UE accesses the target RAN in the second area, and the AMF that provides the access service for this UE is the target AMF in the second area.

[0095] The following describes the application scenario shown in FIG. 2, with reference to two specific scenarios.

[0096] FIG. 3 shows the first specific application scenario to which this application is applicable. Before a UE moves, the source RAN and the source AMF that serve that UE are located in the source PLMN. After the UE moves, the target RAN and target AMF that serve that UE are located in the target PLMN. In addition, the source PLMN further includes a source NSSF and a source NRF, and the target PLMN further includes a target NSSF and a target NRF. That is, in FIG. 2, the first region refers to the source PLMN, and the second region refers to the target PLMN.

[0097] Based on this application scenario, in the first case, the source PLMN is a visited public land mobile network (VPLMN), and the target PLMN is also a VPLMN. In the second case, the source PLMN is VPLMN and the target PLMN is HPLMN. In the third case, the source PLMN is HPLMN and the target PLMN is VPLMN. In the fourth case, the source PLMN is an HPLMN and the target PLMN is also an HPLMN. This application is intended for the first three cases. In addition, the source PLMN and the target PLMN are different PLMNs.

[0098] In this application, a UE's allowed NSSAI for the source PLMN is referred to as a set of segments for the source PLMN or is referred to as a valid NSSAI for the source PLMN. When the source PLMN is a VPLMN, there is a mapping between each part of the segment set S-NSSAI for the source PLMN and the S-NSSAI for the HPLMN. Thus, the set of segments that is intended for the HPLMN and which corresponds to the set of segments for the original PLMN can be determined based on this mapping. The set of segments for the HPLMN may also be referred to as the valid NSSAI for the HPLMN, or referred to as the S-NSSAI that is in the HPLMN and that corresponds to the resolved NSSAI for the original PLMN. In different PLMNs, the S-NSSAI values corresponding to different PLMNs may be used to store the allowed NSSAI of the UE.

[0099] Table 1 shows an example of a mapping (referred to herein as mapping-1) between a set of segments for a source PLMN and a set of segments for an HPLMN.

Table 1

Set of segments for the original PLMN
(NSSAI UE allowed for original PLMN) Set of segments for HPLMN
(S-NSSAI that is in the HPLMN and that matches the authorized NSSAI for the original PLMN) S-NSSAI-A S-NSSAI-AA S-NSSAI-B S-NSSAI-BB

[0100] In an implementation, the mapping may be stored in the UE, the source AMF, or the source NSSF; or may be simultaneously stored in multiple devices in the UE, the source AMF and the source NSSF.

[0101] The mapping may be used to perform a mapping transformation between a set of UE segments in the source PLMN and a set of UE segments in the HPLMN. The mapping may be determined according to the roaming agreement between the source PLMN and the HPLMN. Of course, if the source PLMN is also an HPLMN, mapping may not be required.

[0102] In this application, a UE's allowed NSSAI for a target PLMN is referred to as a set of segments for a target PLMN or is referred to as a valid NSSAI for a target PLMN. When the target PLMN is a VPLMN, there is a mapping between the segment set for the target PLMN and the segment set for the HPLMN.

[0103] Table 2 shows an example of a mapping (referred to herein as mapping-2) between a set of segments for a target PLMN and a set of segments for an HPLMN.

table 2

Set of segments for target PLMN
(NSSAI allowed UE for target PLMN) Set of segments for HPLMN
(S-NSSAI that is in the HPLMN and that matches the resolved NSSAI for the target PLMN) S-NSSAI-C S-NSSAI-AA S-NSSAI-D S-NSSAI-BB

[0104] In an implementation, the mapping may be stored in the UE, the target AMF, or the target NSSF; or may be simultaneously stored in multiple devices in the UE, the target AMF and the target NSSF.

[0105] The mapping may be used to perform a mapping transformation between a set of UE segments in a target PLMN and a set of UE segments in an HPLMN. The mapping may be determined according to a roaming agreement between the target PLMN and the HPLMN. Of course, if the target PLMN is also an HPLMN, mapping may not be required.

[0106] FIG. 4 shows a second specific application scenario to which this application is applicable. Before the UE moves, the source RAN and the source AMF that serve that UE are in the first area (physical area). After the UE moves, the target RAN and the target AMF that serve the UE are in the second area (physical area). In addition, the first region and the second region are in the same PLMN, and this PLMN may be a VPLMN or an HPLMN.

[0107] For example, in a real application, the scenario may be an Enhancing Topology of SMF and UPF in 5G Networks (ETSUN) scenario. In the ETSUN scenario, the UE initiates a session establishment request that carries the S-NSSAI (eg, segment 1). The network selects SMF and UPF for the session. SMF and UPF are referred to as anchor SMF and anchor UPF. Subsequently, the UE moves to the first area and leaves the service area of the anchor SMF, the network performs insertion of I-SMF 1 and I-UPF 1 to ensure continuity of session service. If segment 1 in the first area is not deployed, the I-SMF 1 selected by the network is in some segment, for example, segment A, different from the segment in which the anchor SMF is located. Subsequently, the UE continues to move from the first area to the second area and the UE leaves the service area of I-SMF 1. In this case, the network needs to select a new I-SMF 2 and a new I-UPF 2 to serve the UE. If neither Segment 1 nor Segment A in the second region is deployed, I-SMF 2 selected by the network is in some segment, eg, Segment B, different from the segment in which the anchor SMF is located.

[0108] In addition, there is a mapping between the set of segments of the UE in the first area (which may also be referred to as the allowed NSSAI UE in the first area) and the set of segments of the UE in the HPLMN (which may also be referred to as the S-NSSAI that is in the HPLMN, and which corresponds to the NSSAI allowance for the first area).

[0109] Table 3 shows an example of a mapping (referred to herein as mapping-3) between a set of segments for the first region and a set of segments for the HPLMN.

Table 3

Set of segments for the first area
(NSSAI UE allowed in first area) Set of segments for HPLMN
(S-NSSAI which is in HPLMN and which corresponds to the authorized NSSAI for the first area) S-NSSAI-A1 S-NSSAI-AA1 S-NSSAI-B1 S-NSSAI-BB1

[0110] In an implementation, the mapping may be stored in the UE, the source AMF, or the NSSF; or may be simultaneously stored in multiple devices in the UE, the source AMF, and the NSSF.

[0111] In addition, there is a mapping between the set of segments of the UE in the second area (which may also be referred to as the allowed NSSAI UE in the second area) and the set of segments of the UE in the HPLMN (which may also be referred to as the S-NSSAI that is in the HPLMN, and which corresponds to the NSSAI allowance for the second area).

[0112] Table 4 shows an example of a mapping (referred to herein as mapping-4) between a set of segments for the second region and a set of segments for the HPLMN.

Table 4

Set of segments for the second area
(NSSAI UE allowed in second area) Set of segments for HPLMN
(S-NSSAI which is in HPLMN and which corresponds to the authorized NSSAI for the second area) S-NSSAI-C1 S-NSSAI-AA1 S-NSSAI-D1 S-NSSAI-BB1

[0113] In an implementation, the mapping may be stored in the UE, target AMF, or NSSF; or may be simultaneously stored in multiple devices in the UE, target AMF and NSSF.

[0114] Based on the application scenario shown in FIG. 3 or FIG. 4, selecting a proper target AMF for the UE after moving the UE is a problem to be solved in this application.

[0115] It should be noted that the following embodiments specific to FIGS. 3 are described using an example in which both the source PLMN and the target PLMN are in the VPLMN.

[0116] FIG. 5 is a schematic representation of a first communication method according to this application. This method can be used for the scenario shown in FIG. 3, to select the proper target AMF for the UE. The method includes the following steps.

[0117] Step 501: When the UE service is transferred from the source RAN to the target RAN, the source AMF determines, based on the segment set for the source PLMN, a segment set that is intended for the HPLMN and which corresponds to the segment set for the source PLMN.

[0118] For example, if the source AMF stores a mapping (as shown in Table 1) between a set of segments for the source PLMN and a set of segments for the HPLMN, the source AMF may determine, based on the mapping, a set of segments that is intended for the HPLMN and that corresponds to the set of segments for the original PLMN. For example, based on Table 1, it is determined that the segment set that is intended for the HPLMN and that corresponds to the segment set (including S-NSSAI-A and S-NSSAI-B) in the original PLMN includes S-NSSAI-AA and S-NSSAI-BB.

[0119] Optionally, the mapping may be stored in the UE context.

[0120] In the implementation before step 501, the source AMF receives a handover required message sent by the source RAN, wherein the message may carry a target ID, wherein the target ID includes the target RAN ID and the target identity tracking area identity (TAI) of the target RAN, and these target TAIs further include information about the target PLMN (eg, ID of the target PLMN).

[0121] Optionally, before determining a set of segments that is intended for the HPLMN and that matches the set of segments for the source PLMN, the source AMF determines that this handover is an inter-PLMN system handover and therefore triggers execution of step 501.

[0122] For example, if the source AMF determines that the target PLMN included in the target TAIs is different from the PLMN in which the source AMF is located, the source AMF may determine that this handover is a system handover between PLMNs.

[0123] Step 502: The source AMF sends the set of segments for the HPLMN to the source NSSF. Accordingly, the source NSSF may receive a set of segments for the HPLMN.

[0124] For example, the source AMF may initiate a request message to the source NSSF by calling the Nnssf_NSSelection_Get service operation of the source NSSF, and this request message carries a set of segments for the HPLMN.

[0125] By calling the above overhead operation, the source AMF may further send the home PLMN ID of the UE itself and the target TAIs to the source NSSF. The home PLMN ID of the UE itself is the HPLMN ID.

[0126] Step 503: The source NSSF sends the segment set for the HPLMN, the HPLMN ID, and the target TAIs to the target NSSF. Accordingly, the target NSSF may receive a set of segments for the HPLMN, the HPLMN ID, and the target TAIs.

[0127] For example, the source NSSF initiates a request message to the target NSSF by calling the Nnssf_NSSelection_Get service operation of the target NSSF, and this request message carries a set of segments for the HPLMN, the HPLMN ID, and the target TAIs. The HPLMN ID is used to indicate that the segment set is the segment set for the HPLMN.

[0128] For example, the source NSSF determines information about the target PLMN based on the received target TAIs, and then determines (or selects) the target NSSF based on the information about the target PLMN to send a set of segments for the HPLMN to the target NSSF.

[0129] Step 504: The target NSSF determines a segment set for the target PLMN based on the mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0130] After receiving a segment set for the HPLMN, the HPLMN ID and the target TAIs, the target NSSF determines based on the HPLMN ID that the received segment set is the segment set for the HPLMN, and determines based on information about the target PLMN in the target TAIs that the segment set should be selected for target PLMN. In addition, the target NSSF may determine a segment set for the target PLMN based on a mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0131] The target NSSF may store a mapping (as shown in Table 2) between a set of segments for the target PLMN and a set of segments for the HPLMN, such that the target NSSF can determine, based on this mapping, a set of segments that is intended for the target PLMN and that matches set of segments for HPLMN. For example, if a segment set that is intended for an HPLMN and that is received by the target NSSF includes S-NSSAI-AA and S-NSSAI-BB, based on Table 2, it may be determined that the segment set for the target PLMN includes S- NSSAI-C and S-NSSAI-D.

[0132] Step 505: The target NSSF determines information about the target AMF that supports a set of segments for the target PLMN.

[0133] The target AMF information may be a set of target AMFs (AMF set) that support a set of segments for the target PLMN, and this target AMF set includes a target AMF that serves the UE and that is located in the target PLMN.

[0134] The target NSSF determines a set of segments for the target PLMN based on the set of segments for the HPLMN, and then determines information about the target AMF based on the set of segments for the target PLMN. Therefore, it is understood that the set of segments for HPLMN can be used to determine the target AMF. In addition, the target NSSF may further determine target AMF information on the target side based on the received target TAIs.

[0135] Step 506: The target NSSF sends target AMF information to the source NSSF. Accordingly, the source NSSF may receive information about the target AMF.

[0136] For example, the target NSSF sends a Nnssf_NSSelection_Get response to the source NSSF, and this Nnssf_NSSelection_Get response carries information about the target AMF.

[0137] Step 507: The source NSSF sends target AMF information to the source AMF. Accordingly, the source AMF may receive information about the target AMF.

[0138] For example, the source NSSF sends a Nnssf_NSSelection_Get response to the source AMF, and this Nnssf_NSSelection_Get response carries information about the target AMF.

[0139] After receiving the target AMF information, the source AMF selects an AMF, namely the target AMF, from the set of AMFs indicated by the target AMF information.

[0140] Step 508: The source AMF sends the set of segments for the HPLMN to the target AMF. Accordingly, the target AMF may receive a set of segments for the HPLMN.

[0141] For example, the source AMF sends a Namf_Communication_CreateUEContext request to the target AMF, and this Namf_Communication_CreateUEContext request carries the segment set for the HPLMN.

[0142] Optionally, the source AMF may optionally send to the target AMF a list of protocol data unit (PDU) sessions associated with the segment set for the HPLMN. Optionally, other UE context information may be additionally sent, such as SMF information on the source side.

[0143] Optionally, after receiving the segment set for the HPLMN, the target AMF may obtain the segment set for the target PLMN based on the segment set for the HPLMN. For example, the target AMF may obtain the segment set for the target PLMN based on the segment set for the HPLMN in either of the following two ways.

[0144] Method 1: The target AMF determines a segment set for the target PLMN based on the segment set for the HPLMN and configuration information. For example, the target AMF may store configuration information. The configuration information includes a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN. Alternatively, the configuration information includes a roaming agreement between the target PLMN and the HPLMN. The target AMF may define a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN in accordance with the roaming agreement. In this case, the target AMF may determine, based on the set of segments for the HPLMN and the mapping, a set of segments that is intended for the target PLMN and which corresponds to the set of segments for the HPLMN.

[0145] For example, if the segment set that is intended for the HPLMN and that is received by the target AMF includes S-NSSAI-AA and S-NSSAI-BB, based on Table 2 it may be determined that the segment set for the target PLMN includes themselves S-NSSAI-C and S-NSSAI-D.

[0146] Method 2: The target AMF does not store a mapping between the segment set for the target PLMN and the segment set for the HPLMN. Alternatively, the target AMF does not store the roaming agreement between the target PLMN and the HPLMN. In this case, the target AMF sends first information to the target NSSF in the target PLMN, the first information including a set of segments for the HPLMN; and the target AMF receives from the target NSSF a set of segments for the target PLMN.

[0147] Optionally, the first information further includes first indication information. The first indication information is used to indicate the target NSSF to generate a set of segments for the target PLMN.

[0148] For example, the target AMF may send the first information to the target NSSF by calling the Nnssf_NSSelection_Get service operation on the target NSSF.

[0149] By calling the above overhead operation, the target AMF may send a set of segments for the HPLMN, the target RAN TAI, and the HPLMN ID to the target NSSF.

[0150] For example, the target NSSF may return a set of segments for the target PLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Optionally, the target NSSF may alternatively return a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Accordingly, the target AMF receives a mapping between the segment set for the HPLMN and the segment set for the target PLMN from the target NSSF.

[0151] For example, if the segment set that is intended for the HPLMN and that is sent by the target AMF to the target NSSF includes S-NSSAI-AA and S-NSSAI-BB, the target NSSF maps S-NSSAI-AA and S-NSSAI- BB in S-NSSAI-C and S-NSSAI-D based on Table 2. In this case, the segment set for the target PLMN is S-NSSAI-C and S-NSSAI-D.

[0152] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF can determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE. Also, in this solution, the source side does not send the target side the resolved NSSAI on the source side or the mapping between the segment set for the HPLMN and the segment set for the source PLMN, but sends the target side a set of segments that is intended for the HPLMN and which corresponds to the segment set for the source PLMN . This helps avoid the following possible problems: (1) Because different roaming agreements exist between different VPLMNs and a particular HPLMN, there are different mappings between the valid S-NSSAI for those different VPLMNs and the valid S-NSSAI for that HPLMN (e.g., mapping-1 in Table 1 is different from Mapping-2 in Table 2) and hence the target side (eg target AMF) may not recognize the segment set for the source PLMN. (2) The mapping between the segment set for the HPLMN and the segment set for the source PLMN is determined according to the roaming agreement between the source PLMN and the HPLMN. If the source AMF directly sends the mapping to the target party, there may be a security risk in revealing the roaming agreement between the source PLMN and the HPLMN.

[0153] FIG. 6 is a schematic representation of a second communication method according to this application. This method can be used for the scenario shown in FIG. 3, to select the proper target AMF for the UE. The method includes the following steps.

[0154] Step 601: When the UE service is transferred from the source RAN to the target RAN, the source AMF sends a set of segments for the source PLMN to the source NSSF. Accordingly, the source NSSF may receive a set of segments for the source PLMN.

[0155] For example, the source AMF may initiate a request message to the source NSSF by calling the Nnssf_NSSelection_Get service operation of that NSSF in the source PLMN, and this request message carries a set of segments for the source PLMN.

[0156] By calling the above overhead operation, the source AMF may further send the home PLMN ID of the UE itself and the target TAIs to the source NSSF. The home PLMN ID of the UE itself is the HPLMN ID.

[0157] In the implementation before step 601, the source AMF receives a handover required message sent by the source RAN, wherein the message may carry a target ID, wherein the target ID includes the target RAN ID and target TAIs of the target RAN, and these target TAIs further include information about the target PLMN (eg, ID of the target PLMN).

[0158] Optionally, before determining a set of segments that is intended for the HPLMN and that matches the set of segments for the source PLMN, the source AMF determines that this handover is an inter-PLMN system handover and therefore triggers execution of step 601.

[0159] For example, if the source AMF determines that the target PLMN included in the target TAIs is different from the PLMN in which the source AMF is located, the source AMF may determine that this handover is a system handover between PLMNs.

[0160] Step 602: The source NSSF determines, based on the segment set for the source PLMN and the HPLMN ID, a segment set that is intended for the HPLMN and that corresponds to the segment set for the source PLMN.

[0161] For example, if the source NSSF stores a mapping (as shown in Table 1) between a set of segments for the source PLMN and a set of segments for the HPLMN, the source NSSF may determine, based on this mapping, the set of segments that is intended for the HPLMN and that corresponds to the set segments for the original PLMN. For example, if the segment set that is intended for the source PLMN and which is received by the source NSSF from the source AMF includes S-NSSAI-A and S-NSSAI-B, based on Table 1 it is determined that the segment set that is intended for the HPLMN and which corresponds to the segment set for the original PLMN includes S-NSSAI-AA and S-NSSAI-BB.

[0162] Optionally, the mapping may be stored locally in the source NSSF.

[0163] Steps 603 to 606 are the same as steps 503 to 506 in the embodiment of FIG. 5. Refer to the above parts of the description.

[0164] Step 607: The source NSSF sends information about the target AMF and a set of segments for the HPLMN to the source AMF. Accordingly, the source AMF may receive information about the target AMF and a set of segments for the HPLMN.

[0165] For example, the source NSSF sends a Nnssf_NSSelection_Get response to the source AMF, and this Nnssf_NSSelection_Get response carries information about the target AMF and a set of segments for the HPLMN.

[0166] In yet another implementation, the source NSSF may alternatively send information about the target AMF and a set of segments for the HPLMN to the source AMF separately using two stages. For example, the source NSSF may send the set of segments for the HPLMN to the source AMF at any step after step 602 and before step 608. The source NSSF may send information about the target AMF to the source AMF after step 606 and before step 608.

[0167] After receiving the target AMF information, the source AMF selects an AMF, namely the target AMF, from the set of AMFs indicated by the target AMF information.

[0168] Step 608: The source AMF sends the set of segments for the HPLMN to the target AMF. Accordingly, the target AMF may receive a set of segments for the HPLMN.

[0169] For example, the source AMF sends a Namf_Communication_CreateUEContext request to the target AMF, and this Namf_Communication_CreateUEContext request carries the segment set for the HPLMN.

[0170] Optionally, the source AMF may further send to the target AMF a list of session PDUs associated with the segment set for the HPLMN. Optionally, other UE context information may be additionally sent, such as SMF information on the source side.

[0171] Optionally, after receiving the segment set for the HPLMN, the target AMF may obtain the segment set for the target PLMN based on the segment set for the HPLMN. For example, the target AMF may obtain the segment set for the target PLMN based on the segment set for the HPLMN in either of the following two ways.

[0172] Method 1: The target AMF determines a segment set for the target PLMN based on the segment set for the HPLMN and configuration information. For example, the target AMF may store configuration information. The configuration information includes a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN. Alternatively, the configuration information includes a roaming agreement between the target PLMN and the HPLMN. The target AMF may define a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN in accordance with the roaming agreement. In this case, the target AMF may determine, based on the set of segments for the HPLMN and the mapping, a set of segments that is intended for the target PLMN and which corresponds to the set of segments for the HPLMN.

[0173] For example, if the segment set that is intended for the HPLMN and that is received by the target AMF includes S-NSSAI-AA and S-NSSAI-BB, based on Table 2 it can be determined that the segment set for the target PLMN includes themselves S-NSSAI-C and S-NSSAI-D.

[0174] Method 2: The target AMF does not store a mapping between the segment set for the target PLMN and the segment set for the HPLMN. Alternatively, the target AMF does not store the roaming agreement between the target PLMN and the HPLMN. In this case, the target AMF sends first information to the target NSSF in the target PLMN, the first information including a set of segments for the HPLMN; and the target AMF receives from the target NSSF a set of segments for the target PLMN.

[0175] Optionally, the first information further includes first indication information. The first indication information is used to indicate the target NSSF to generate a set of segments for the target PLMN.

[0176] For example, the target AMF may send the first information to the target NSSF by calling the Nnssf_NSSelection_Get service operation on the target NSSF.

[0177] By calling the above overhead operation, the target AMF may send a set of segments for the HPLMN, the target RAN TAI, and the HPLMN ID to the target NSSF.

[0178] For example, the target NSSF may return a set of segments for the target PLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Optionally, the target NSSF may alternatively return a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Accordingly, the target AMF receives a mapping between the segment set for the HPLMN and the segment set for the target PLMN from the target NSSF.

[0179] For example, if the segment set that is intended for the HPLMN and that is sent by the target AMF to the target NSSF includes S-NSSAI-AA and S-NSSAI-BB, the target NSSF maps S-NSSAI-AA and S-NSSAI- BB in S-NSSAI-C and S-NSSAI-D based on Table 2. In this case, the segment set for the target PLMN is S-NSSAI-C and S-NSSAI-D.

[0180] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF can determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE. Also, in this solution, the source side does not send the target side the resolved NSSAI on the source side or the mapping between the segment set for the HPLMN and the segment set for the source PLMN, but sends the target side a set of segments that is intended for the HPLMN and which corresponds to the segment set for the source PLMN . This helps avoid the following possible problems: (1) Because different roaming agreements exist between different VPLMNs and a particular HPLMN, there are different mappings between the valid S-NSSAI for those different VPLMNs and the valid S-NSSAI for that HPLMN (e.g., mapping-1 in Table 1 is different from Mapping-2 in Table 2) and hence the target side (eg target AMF) may not recognize the segment set for the source PLMN. (2) The mapping between the segment set for the HPLMN and the segment set for the source PLMN is determined according to the roaming agreement between the source PLMN and the HPLMN. If the source AMF directly sends the mapping to the target party, there may be a security risk in revealing the roaming agreement between the source PLMN and the HPLMN.

[0181] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, obtaining, by the source AMF in the first area, information about the target AMF in the second area areas based on the set of segments for the first area (refer to the description of step 501, step 601 and step 607); and sending the source AMF of the segment set for the HPLMN of the terminal device to the target AMF, wherein the segment set for the HPLMN corresponds to the segment set for the first region, and the segment set for the HPLMN is used to determine the segment set for the second region (refer to the description of step 508 and step 608) .

[0182] In an exemplary implementation, the first region is a source PLMN and the second region is a target PLMN.

[0183] In an exemplary implementation, the source AMF determines, based on the mapping between the segment set for the source PLMN and the segment set for the HPLMN, a set of segments that is intended for the HPLMN and that corresponds to the segment set for the source PLMN.

[0184] In an exemplary implementation, obtaining, by the source AMF, information about a target AMF in a second region based on a segment set for the first region includes: sending the source AMF a segment set for the HPLMN and information about the target PLMN to the first device; and receiving the source AMF from the first device information about the target AMF, wherein the first device is the source NSSF in the source PLMN (refer to the description of step 502 and step 507).

[0185] In a possible implementation, the source AMF sends a set of segments for the source PLMN to the source NSSF in the source PLMN; and the source AMF receives from the source NSSF a set of segments for the HPLMN (refer to the description of step 601 and step 607).

[0186] In an exemplary implementation, obtaining, by the source AMF, information about a target AMF in a second region based on a set of segments for the first region includes: sending, through the source AMF, information about a target PLMN to a source NSSF in the source PLMN; and receiving, by the source AMF, information about the target AMF from the source NSSF.

[0187] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, obtaining, by the first device in the source PLMN, a set of segments that is intended to HPLMN of the terminal device and which corresponds to the set of segments for the source PLMN (refer to the description of step 502 and step 602); sending, by the first device, a set of segments for the HPLMN to a second device in the target PLMN, wherein the set of segments for the HPLMN is used to determine the target AMF in the target PLMN; receiving, by the first device, information about the target AMF from the second device; and sending the first device information about the target AMF to the source AMF in the source PLMN (refer to the description of step 503 and step 603).

[0188] In a possible implementation, the first device is a source NSSF in the source PLMN, and the second device is a target NSSF in the target PLMN.

[0189] In an exemplary implementation, receiving by the first device in the source PLMN a set of segments that is intended for the HPLMN and which corresponds to the set of segments for the source PLMN includes: receiving by the first device from the source AMF a set of segments for the source PLMN and determining the set of segments that is intended for HPLMN and which corresponds to the set of segments for the original PLMN; or the first device receiving from the source AMF a set of segments for the HPLMN.

[0190] In an exemplary implementation, the first device receives information about the target PLMN from the source AMF; and the first device selects the second device based on information about the target PLMN.

[0191] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, receiving by the target NSSF in the target PLMN from the source NSSF in the source PLMN a set of segments for the HPLMN terminal device (refer to the description of step 503 and step 603); determining, by the target NSSF, information about the target AMF that supports a set of segments for the target PLMN, wherein the set of segments for the target PLMN corresponds to the set of segments for the HPLMN; and sending, by the target NSSF, information about the target AMF to the source NSSF (refer to the description of step 506 and step 606).

[0192] In an exemplary implementation, the target NSSF determines a set of segments for the target PLMN based on a mapping between the set of segments for the HPLMN and the set of segments for the target PLMN. Based on the above solution, after receiving the segment set for the HPLMN, the target AMF can determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE.

[0193] FIG. 7 is a schematic representation of a third communication method according to this application. This method can be used for the scenario shown in FIG. 3, to select the proper target AMF for the UE. The method includes the following steps.

[0194] Step 701: When the UE service is transferred from the source RAN to the target RAN, the source AMF determines, based on the segment set for the source PLMN, a segment set that is intended for the HPLMN and that corresponds to the segment set for the source PLMN.

[0195] For example, if the source AMF stores a mapping (as shown in Table 1) between a set of segments for the source PLMN and a set of segments for the HPLMN, the source AMF may determine, based on the mapping, a set of segments that is intended for the HPLMN and that corresponds to the set of segments for the original PLMN. For example, based on Table 1, it is determined that the segment set that is intended for the HPLMN and that corresponds to the segment set (including S-NSSAI-A and S-NSSAI-B) in the original PLMN includes S-NSSAI-AA and S-NSSAI-BB.

[0196] Optionally, the mapping may be stored in the UE context.

[0197] In the implementation before step 701, the source AMF receives a handover required message sent by the source RAN, wherein the message may carry a target ID, wherein the target ID includes the target RAN ID and target TAIs of the target RAN, and these target TAIs further include information about the target PLMN (eg, ID of the target PLMN).

[0198] Optionally, before determining a set of segments that is intended for the HPLMN and that matches the set of segments for the source PLMN, the source AMF determines that this handover is an inter-PLMN system handover and therefore triggers execution of step 701.

[0199] For example, if the source AMF determines that the target PLMN included in the target TAIs is different from the PLMN in which the source AMF is located, the source AMF may determine that this handover is a system handover between PLMNs.

[0200] Step 702: The source AMF sends the set of segments for the HPLMN to the source NSSF. Accordingly, the source NSSF may receive a set of segments for the HPLMN.

[0201] For example, the source AMF initiates a request message to the source NSSF by calling the Nnssf_NSSelection_Get service operation of the source NSSF, and this message carries a set of segments for the HPLMN.

[0202] By calling the above overhead operation, the source AMF further sends the home PLMN ID of the UE itself and information about the target PLMN to the source NSSF. The home PLMN ID of the UE itself is the HPLMN ID.

[0203] Step 703: The source NSSF sends the segment set for the HPLMN, the HPLMN ID, and the target PLMN information to the target NSSF. Accordingly, the target NSSF may receive a set of segments for the HPLMN, an HPLMN ID, and information about the target PLMN.

[0204] For example, the source NSSF initiates a request message to the target NSSF by calling the Nnssf_NSSelection_Get service operation of the target NSSF, and this request message carries the segment set for the HPLMN, the HPLMN ID, and information about the target PLMN.

[0205] Before sending the segment set for the HPLMN to the target NSSF, the source NSSF determines (or selects) the target NSSF based on information about the target PLMN to send the segment set for the HPLMN to the target NSSF.

[0206] Step 704: The target NSSF determines a segment set for the target PLMN based on the mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0207] After receiving the segment set for the HPLMN, the HPLMN ID and the target PLMN information, the target NSSF determines based on the HPLMN ID that the received segment set is the segment set for the HPLMN, and determines based on the target PLMN information in the target TAIs that it should select a set of segments for the target PLMN. In addition, the target NSSF may determine a segment set for the target PLMN based on a mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0208] The target NSSF may store a mapping (as shown in Table 2) between a set of segments for the target PLMN and a set of segments for the HPLMN, such that the target NSSF can determine, based on this mapping, a set of segments that is intended for the target PLMN and that matches set of segments for HPLMN. For example, if a segment set that is intended for an HPLMN and that is received by the target NSSF includes S-NSSAI-AA and S-NSSAI-BB, based on Table 2, it may be determined that the segment set for the target PLMN includes S- NSSAI-C and S-NSSAI-D.

[0209] Step 705: The target NSSF sends a set of segments for the target PLMN to the source NSSF. Accordingly, the source NSSF may receive a set of segments for the target PLMN.

[0210] For example, the target NSSF sends a Nnssf_NSSelection_Get response to the source NSSF, and this nssf_NSSelection_Get response carries a segment set for the target PLMN.

[0211] Step 706: The source NSSF sends a set of segments for the target PLMN to the source AMF. Accordingly, the source AMF may receive a set of segments for the target PLMN.

[0212] For example, the source NSSF sends a Nnssf_NSSelection_Get response to the source AMF, and this Nnssf_NSSelection_Get response carries a set of segments for the target PLMN.

[0213] Step 707: The source AMF sends a set of segments for the target PLMN and target TAIs to the source NRF. Accordingly, the source NRF may receive a set of segments for the target PLMN and target TAIs.

[0214] For example, the source AMF sends a request message by calling the Nnrf_NFDiscovery_Request service operation of the source NRF to request discovery of the AMF network element. The request message carries a set of segments for the target PLMN and target TAIs. Optionally, the request message further carries information that the requested network element type is an AMF network element.

[0215] Step 708: The source NRF sends a set of segments for the target PLMN and target TAIs to the target NRF. Accordingly, the target NRF may receive a set of segments for the target PLMN and target TAIs.

[0216] For example, the source NRF sends a request message by calling the Nnrf_NFDiscovery_Request service operation of the target NRF. The request message carries a set of segments for the target PLMN and target TAIs. Optionally, the request message further carries information that the requested network element type is an AMF network element.

[0217] Before sending the segment set for the target PLMN to the target NRF, the source NRF may further determine (or select) the target NRF based on information about the target PLMN that is carried in the target TAIs to send the segment set for the target PLMN to the target NRF.

[0218] Step 709: The target NRF determines target AMF information that supports a set of segments for the target PLMN.

[0219] The target NRF determines target AMF information based on the set of segments for the target PLMN. Therefore, it can be understood that a set of segments for a target PLMN can be used to determine the target AMF.

[0220] The target AMF information may be a list of possible target AMFs (list of possible AMFs) that support a set of segments for the target PLMN, and this list of possible target AMFs includes a target AMF that serves the UE and which is in the target PLMN.

[0221] Step 710: The target NRF sends target AMF information to the source NRF. Accordingly, the source NRF may receive information about the target AMF.

[0222] For example, the target NRF sends a Nnrf_NFDiscovery_Response to the source NRF, and this Nnrf_NFDiscovery_Response carries information about the target AMF.

[0223] Step 711: The source NRF sends information about the target AMF to the source AMF. Accordingly, the source AMF may receive information about the target AMF.

[0224] For example, the source NRF sends a Nnrf_NFDiscovery_Response to the source AMF, and this Nnrf_NFDiscovery_Response carries information about the target AMF.

[0225] Optionally, at step 709, the target NRF determines a list of candidate target AMFs (list of candidate AMFs) that support a set of segments for the target PLMN, and this list of candidate AMFs includes the target AMF. Thus, at step 710, the target NRF sends a list of possible AMFs to the source NRF. At step 711, the source NRF sends a list of candidate AMFs to the source AMF, and the source AMF selects an AMF, namely the target AMF, from the list of candidate AMFs.

[0226] Step 712: The source AMF sends the set of segments for the HPLMN to the target AMF. Accordingly, the target AMF may receive a set of segments for the HPLMN.

[0227] For example, the source AMF sends a Namf_Communication_CreateUEContext request to the target AMF, and this Namf_Communication_CreateUEContext request carries the segment set for the HPLMN.

[0228] Optionally, the source AMF may further send to the target AMF a list of session PDUs associated with the segment set for the HPLMN. Optionally, other UE context information may be additionally sent, such as SMF information on the source side.

[0229] Optionally, after receiving the segment set for the HPLMN, the target AMF may obtain the segment set for the target PLMN based on the segment set for the HPLMN. For example, the target AMF may obtain the segment set for the target PLMN based on the segment set for the HPLMN in either of the following two ways.

[0230] Method 1: The target AMF determines a segment set for the target PLMN based on the segment set for the HPLMN and configuration information. For example, the target AMF may store configuration information. The configuration information includes a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN. Alternatively, the configuration information includes a roaming agreement between the target PLMN and the HPLMN. The target AMF may define a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN in accordance with the roaming agreement. In this case, the target AMF may determine, based on the set of segments for the HPLMN and the mapping, a set of segments that is intended for the target PLMN and which corresponds to the set of segments for the HPLMN.

[0231] For example, if the segment set that is intended for the HPLMN and that is received by the target AMF includes S-NSSAI-AA and S-NSSAI-BB, based on Table 2 it can be determined that the segment set for the target PLMN includes themselves S-NSSAI-C and S-NSSAI-D.

[0232] Method 2: The target AMF does not store a mapping between the segment set for the target PLMN and the segment set for the HPLMN. Alternatively, the target AMF does not store the roaming agreement between the target PLMN and the HPLMN. In this case, the target AMF sends first information to the target NSSF in the target PLMN, the first information including a set of segments for the HPLMN; and the target AMF receives from the target NSSF a set of segments for the target PLMN.

[0233] Optionally, the first information further includes first indication information. The first indication information is used to indicate the target NSSF to generate a set of segments for the target PLMN.

[0234] For example, the target AMF may send the first information to the target NSSF by calling the Nnssf_NSSelection_Get service operation on the target NSSF.

[0235] By calling the above overhead operation, the target AMF may send a set of segments for the HPLMN, the target RAN TAI, and the HPLMN ID to the target NSSF.

[0236] For example, the target NSSF may return a set of segments for the target PLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Optionally, the target NSSF may alternatively return a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Accordingly, the target AMF receives a mapping between the segment set for the HPLMN and the segment set for the target PLMN from the target NSSF.

[0237] For example, if the segment set that is intended for the HPLMN and that is sent by the target AMF to the target NSSF includes S-NSSAI-AA and S-NSSAI-BB, the target NSSF maps S-NSSAI-AA and S-NSSAI- BB in S-NSSAI-C and S-NSSAI-D based on Table 2. In this case, the segment set for the target PLMN is S-NSSAI-C and S-NSSAI-D.

[0238] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF can determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE. Also, in this solution, the source side does not send the target side the resolved NSSAI on the source side or the mapping between the segment set for the HPLMN and the segment set for the source PLMN, but sends the target side a set of segments that is intended for the HPLMN and which corresponds to the segment set for the source PLMN . This helps avoid the following potential problems: Since different roaming agreements exist between different VPLMNs and a particular HPLMN, there are different mappings between the valid S-NSSAI for those different VPLMNs and the valid S-NSSAI for that HPLMN (for example, mapping-1 in Table 1 is different from mapping-2 in Table 2) and hence the target side (e.g. target AMF) may not recognize the segment set for the source PLMN.

[0239] FIG. 8 is a schematic representation of a fourth communication method according to this application. This method can be used for the scenario shown in FIG. 3, to select the proper target AMF for the UE. The method includes the following steps.

[0240] Step 801: When the UE service is transferred from the source RAN to the target RAN, the source AMF sends a set of segments for the source PLMN to the source NSSF. Accordingly, the source NSSF may receive a set of segments for the source PLMN.

[0241] For example, the source AMF initiates a request message to the source NSSF by calling the Nnssf_NSSelection_Get service operation of the source NSSF, and this message carries a set of segments for the source PLMN.

[0242] By calling the above overhead operation, the source AMF may further send the home PLMN ID of the UE itself and information about the target PLMN to the source NSSF. The home PLMN ID of the UE itself is the HPLMN ID.

[0243] In the implementation before step 801, the source AMF receives a handover required message sent by the source RAN, wherein the message may carry a target ID, wherein the target ID includes the target RAN ID and target TAIs of the target RAN, and these target TAIs further include information about the target PLMN (eg, ID of the target PLMN).

[0244] Optionally, before determining a set of segments that is intended for the HPLMN and that matches the set of segments for the source PLMN, the source AMF determines that this handover is an inter-PLMN system handover and therefore triggers execution of step 801.

[0245] For example, if the source AMF determines that the target PLMN included in the target TAIs is different from the PLMN in which the source AMF is located, the source AMF may determine that this handover is a system handover between PLMNs.

[0246] Step 802: The source NSSF determines, based on the segment set for the source PLMN and the HPLMN ID, a segment set that is intended for the HPLMN and that corresponds to the segment set for the source PLMN.

[0247] For example, if the source NSSF stores a mapping (as shown in Table 1) between a set of segments for the source PLMN and a set of segments for the HPLMN, the source NSSF may determine, based on this mapping, the set of segments that is intended for the HPLMN and that corresponds to the set segments for the original PLMN. For example, if the segment set that is intended for the source PLMN and which is received by the source NSSF from the source AMF includes S-NSSAI-A and S-NSSAI-B, based on Table 1 it is determined that the segment set that is intended for the HPLMN and which corresponds to the segment set for the original PLMN includes S-NSSAI-AA and S-NSSAI-BB.

[0248] Optionally, the mapping may be stored locally in the source NSSF.

[0249] Steps 803 to 805 are the same as steps 703 to 705 in the embodiment of FIG. 7. Refer to the above parts of the description.

[0250] Step 806: The source NSSF sends the segment set for the target PLMN and the segment set for the HPLMN to the source AMF. Accordingly, the source AMF may receive a set of segments for the target PLMN and a set of segments for the HPLMN.

[0251] For example, the source NSSF sends a Nnssf_NSSelection_Get response to the source AMF, and this Nnssf_NSSelection_Get response carries a segment set for the target PLMN and a segment set for the HPLMN.

[0252] In yet another implementation, the source NSSF may alternatively separately send the segment set for the target PLMN and the segment set for the HPLMN to the source AMF using two stages. For example, the source NSSF may send the segment set for the HPLMN to the source AMF at any step after step 802 and before step 812. The source NSSF may send the segment set for the target PLMN to the source AMF after step 805 and before step 807.

[0253] Steps 807 to 812 are the same as steps 707 to 712 in the embodiment of FIG. 7. Refer to the above parts of the description.

[0254] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF can determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE. Also, in this solution, the source side does not send the target side the resolved NSSAI on the source side or the mapping between the segment set for the HPLMN and the segment set for the source PLMN, but sends the target side a set of segments that is intended for the HPLMN and which corresponds to the segment set for the source PLMN . This helps avoid the following potential problems: Since different roaming agreements exist between different VPLMNs and a particular HPLMN, there are different mappings between the valid S-NSSAI for those different VPLMNs and the valid S-NSSAI for that HPLMN (for example, mapping-1 in Table 1 is different from mapping-2 in Table 2) and hence the target side (e.g. target AMF) may not recognize the segment set for the source PLMN.

[0255] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, obtaining, by the source AMF in the first area, information about the target AMF in the second area regions based on the set of segments for the first region (refer to the description of step 711 and step 811); and sending the source AMF of the segment set for the HPLMN of the terminal device to the target AMF, wherein the segment set for the HPLMN corresponds to the segment set for the first region, and the segment set for the HPLMN is used to determine the segment set for the second region (refer to the description of step 712 and step 812) .

[0256] In an exemplary implementation, the first region is a source PLMN and the second region is a target PLMN.

[0257] In an exemplary implementation, the source AMF determines, based on the mapping between the segment set for the source PLMN and the segment set for the HPLMN, a set of segments that is intended for the HPLMN and that corresponds to the segment set for the source PLMN.

[0258] In an exemplary implementation, obtaining, by the source AMF, information about the target AMF in the second region based on the segment set for the first region includes: sending the source AMF the segment set for the HPLMN and information about the target PLMN to the first device (refer to the description of step 702) ; and receiving the source AMF from the first device information about the target AMF (refer to the description of step 711), wherein the first device is the source NSSF in the source PLMN.

[0259] In an exemplary implementation, obtaining, by the source AMF, information about a target AMF in a second region based on a segment set for the first region includes: sending the source AMF a segment set for the HPLMN to the source NSSF in the source PLMN; receiving a source AMF from the source NSSF segment set for the target PLMN; sending the source AMF a set of segments for the target PLMN and information about the target PLMN to the source NRF in the source PLMN; and receiving, by the source AMF, information about the target AMF from the source NRF (refer to the description of step 706 and step 806).

[0260] In a possible implementation, the source AMF sends a set of segments for the source PLMN to the source NSSF in the source PLMN (refer to the description of step 801); and the source AMF receives from the source NSSF a set of segments for the HPLMN (refer to the description of step 806).

[0261] In an exemplary implementation, obtaining, by the source AMF, information about a target AMF in a second region based on a set of segments for the first region includes: receiving a source AMF from a source NSSF in a source PLMN of a set of segments for the target PLMN; sending the source AMF a set of segments for the target PLMN and information about the target PLMN to the source NRF in the source PLMN (refer to the description of step 707 and step 807); and receiving, by the source AMF, information about the target AMF from the source NRF (refer to the description of step 711 and step 811).

[0262] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, obtaining, by the source NSSF in the source PLMN, a set of segments that is intended to HPLMN of the terminal device and which corresponds to the set of segments for the source PLMN (refer to the description of step 702 and step 802); sending the source NSSF a segment set for the HPLMN to the target NSSF in the target PLMN, wherein the segment set for the HPLMN is used to determine a segment set for the target PLMN (refer to the description of step 703 and step 803); receiving, by the source NSSF, from the target NSSF, a set of segments for the target PLMN; and sending, by the source NSSF, a set of segments for the target PLMN to the source AMF (refer to the description of step 706 and step 806).

[0263] In an exemplary implementation, receiving, by the source NSSF in the source PLMN, a set of segments that is intended for the HPLMN of the terminal device and that corresponds to a set of segments for the source PLMN, includes: receiving, by the source NSSF from the source AMF, a set of segments for the source PLMN, and determining the set segments that are intended for the HPLMN and that correspond to the set of segments for the original PLMN; or receiving, by the source NSSF, from the source AMF, a set of segments for the HPLMN.

[0264] In a possible implementation, the source NSSF receives information about the target PLMN from the source AMF; and the source NSSF selects the target NSSF based on information about the target PLMN.

[0265] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, the source NRF in the source PLMN receives from the source AMF in the source PLMN a set segments for the target PLMN (refer to the description of step 707 and step 807); sending, by the source NRF, a set of segments for the target PLMN to the target NRF in the target PLMN (refer to the description of step 708 and step 808); receiving, by the source NRF, information about the target AMF from the target NRF; and sending, through the source NRF, information about the target AMF to the source AMF (refer to the description of step 711 and step 811).

[0266] In an exemplary implementation, the source NRF receives information about the target PLMN from the source AMF, and the source NRF determines the target NRF based on the target PLMN information.

[0267] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, receiving by the target NSSF in the target PLMN from the source NSSF in the source PLMN a set of segments for the HPLMN terminal device (refer to the description of step 703 and step 803); and sending, by the target NSSF to the source NSSF, a set of segments that is intended for the target PLMN and that corresponds to a set of segments for the HPLMN, wherein the set of segments for the target PLMN is used to determine information about the target AMF in the target PLMN (refer to the description of step 705 and step 805 ).

[0268] In an exemplary implementation, the target NSSF determines a segment set for the target PLMN based on a mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0269] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF can determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE.

[0270] FIG. 9 is a schematic representation of a fifth communication method according to this application. This method can be used for the scenario shown in FIG. 3, to select the proper target AMF for the UE. The method includes the following steps.

[0271] Step 901: When the UE service is transferred from the source RAN to the target RAN, the source AMF determines, based on the segment set for the source PLMN, a segment set that is intended for the HPLMN and which corresponds to the segment set for the source PLMN.

[0272] For example, if the source AMF stores a mapping (as shown in Table 1) between a set of segments for the source PLMN and a set of segments for the HPLMN, the source AMF may determine, based on the mapping, a set of segments that is intended for the HPLMN and that corresponds to the set of segments for the original PLMN. For example, based on Table 1, it is determined that the segment set that is intended for the HPLMN and that corresponds to the segment set (including S-NSSAI-A and S-NSSAI-B) in the original PLMN includes S-NSSAI-AA and S-NSSAI-BB.

[0273] Optionally, the mapping may be stored in the UE context.

[0274] In the implementation before step 901, the source AMF receives a handover required message from the source RAN, wherein the message may carry a target ID, wherein the target ID includes the target RAN ID and target TAIs of the target RAN , and these target TAIs further include information about the target PLMN (eg, ID of the target PLMN).

[0275] Optionally, before determining a set of segments that is intended for the HPLMN and that matches the set of segments for the source PLMN, the source AMF determines that this handover is an inter-PLMN system handover and therefore triggers execution of step 901.

[0276] For example, if the source AMF determines that the target PLMN included in the target TAIs is different from the PLMN in which the source AMF is located, the source AMF may determine that this handover is a system handover between PLMNs.

[0277] Step 902: The source AMF sends a set of segments for the HPLMN to the source NRF. Accordingly, the source NRF may receive a set of segments for the HPLMN.

[0278] For example, the source AMF sends a request message by calling the Nnrf_NFDiscovery_Request service operation of the source NRF to request discovery of the AMF network element. The request message carries a set of segments for HPLMN. Optionally, the request message may further carry information that the requested network element type is an AMF network element.

[0279] By calling the above overhead operation, the source AMF may further send the home PLMN ID of the UE itself and the target TAIs to the source NSSF. The home PLMN ID of the UE itself is the HPLMN ID.

[0280] Optionally, in an implementation, the source AMF may send the segment set for the HPLMN, the HPLMN ID, and the target TAIs to the source NSSF, and then the source NSSF sends the segment set for the HPLMN, the HPLMN ID, and the target TAIs to the source NRF, that is, the source AMF sends set of segments for HPLMN, HPLMN ID and target TAIs to source NRF via source NSSF.

[0281] Step 903: The source NRF sends the set of segments for the HPLMN, the HPLMN ID, and the target TAIs to the target NRF. Accordingly, the target NRF may receive a set of segments for the HPLMN, the HPLMN ID, and the target TAIs.

[0282] For example, the source NRF sends a request message by calling the Nnrf_NFDiscovery_Request service operation of the target NRF. The request message carries the segment set for the HPLMN, the home PLMN ID of the UE itself, and the target TAIs. Optionally, the request message may further carry information that the requested network element type is an AMF network element.

[0283] Before sending the segment set for the HPLMN to the target NRF, the source NRF may further determine (or select) the target NRF based on information about the target PLMN that is carried in the target TAIs to send the segment set for the HPLMN to the target NRF.

[0284] Step 904: The target NRF sends the segment set for the HPLMN, the HPLMN ID, and information about the target PLMN to the target NSSF. Accordingly, the target NSSF may receive a set of segments for the HPLMN, an HPLMN ID, and information about the target PLMN.

[0285] For example, the target NRF sends a request message by calling the Nnssf_NSSelection_Get service operation of the target NSSF. The request message carries the segment set for the HPLMN, the HPLMN ID, and information about the target PLMN.

[0286] Step 905: The target NSSF determines a segment set for the target PLMN based on the mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0287] After receiving the segment set for the HPLMN, the HPLMN ID, and the target PLMN information, the target NSSF determines based on the HPLMN ID that the received segment set is the segment set for the HPLMN, and determines based on the target PLMN information that the segment set should be selected for target PLMN. In addition, the target NSSF may determine a segment set for the target PLMN based on a mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0288] The target NSSF may store a mapping (as shown in Table 2) between a set of segments for the target PLMN and a set of segments for the HPLMN, such that the target NSSF can determine, based on this mapping, a set of segments that is intended for the target PLMN and that matches set of segments for HPLMN. For example, if a segment set that is intended for an HPLMN and that is received by the target NSSF includes S-NSSAI-AA and S-NSSAI-BB, based on Table 2, it may be determined that the segment set for the target PLMN includes S- NSSAI-C and S-NSSAI-D.

[0289] Step 906: The target NSSF sends a set of segments for the target PLMN to the target NRF. Accordingly, the target NRF may receive a set of segments for the target PLMN.

[0290] For example, the target NSSF sends a Nnssf_NSSelection_Get response to the target NRF, and this Nnssf_NSSelection_Get response carries a set of segments for the target PLMN.

[0291] Step 907: The target NRF determines target AMF information that supports a set of segments for the target PLMN.

[0292] The target NRF determines target AMF information based on the set of segments for the target PLMN. Therefore, it can be understood that a set of segments for a target PLMN can be used to determine the target AMF.

[0293] The target AMF information may be a list of possible target AMFs (list of possible AMFs) that support a set of segments for the target PLMN, and this list of possible target AMFs includes a target AMF that serves the UE and which is in the target PLMN.

[0294] Step 908: The target NRF sends target AMF information to the source NRF. Accordingly, the source NRF may receive information about the target AMF.

[0295] For example, the target NRF sends a Nnrf_NFDiscovery_Response to the source NRF, and this Nnrf_NFDiscovery_Response carries information about the target AMF.

[0296] Step 909: The source NRF sends information about the target AMF to the source AMF. Accordingly, the source AMF may receive information about the target AMF.

[0297] For example, the source NRF sends a Nnrf_NFDiscovery_Response to the source AMF, and this Nnrf_NFDiscovery_Response carries information about the target AMF.

[0298] Optionally, at step 907, the target NRF determines a list of candidate target AMFs (list of candidate AMFs) that support a set of segments for the target PLMN, and this list of candidate AMFs includes the target AMF. Thus, at step 908, the target NRF sends a list of possible AMFs to the source NRF. At step 909, the source NRF sends a list of candidate AMFs to the source AMF, and the source AMF selects an AMF, namely the target AMF, from the list of candidate AMFs.

[0299] Step 910: The source AMF sends the set of segments for the HPLMN to the target AMF. Accordingly, the target AMF may receive a set of segments for the HPLMN.

[0300] For example, the source AMF sends a Namf_Communication_CreateUEContext request to the target AMF, and this Namf_Communication_CreateUEContext request carries the segment set for the HPLMN.

[0301] Optionally, the source AMF may further send to the target AMF a list of session PDUs associated with the segment set for the HPLMN. Optionally, other UE context information may be additionally sent, such as SMF information on the source side.

[0302] Optionally, after receiving the segment set for the HPLMN, the target AMF may obtain the segment set for the target PLMN based on the segment set for the HPLMN. For example, the target AMF may obtain the segment set for the target PLMN based on the segment set for the HPLMN in either of the following two ways.

[0303] Method 1: The target AMF determines a segment set for the target PLMN based on the segment set for the HPLMN and configuration information. For example, the target AMF may store configuration information. The configuration information includes a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN. Alternatively, the configuration information includes a roaming agreement between the target PLMN and the HPLMN. The target AMF may define a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN in accordance with the roaming agreement. In this case, the target AMF may determine, based on the set of segments for the HPLMN and the mapping, a set of segments that is intended for the target PLMN and which corresponds to the set of segments for the HPLMN.

[0304] For example, if the segment set that is intended for the HPLMN and that is received by the target AMF includes S-NSSAI-AA and S-NSSAI-BB, based on Table 2 it may be determined that the segment set for the target PLMN includes themselves S-NSSAI-C and S-NSSAI-D.

[0305] Method 2: The target AMF does not store a mapping between the segment set for the target PLMN and the segment set for the HPLMN. Alternatively, the target AMF does not store the roaming agreement between the target PLMN and the HPLMN. In this case, the target AMF sends first information to the target NSSF in the target PLMN, the first information including a set of segments for the HPLMN; and the target AMF receives from the target NSSF a set of segments for the target PLMN.

[0306] Optionally, the first information further includes first indication information. The first indication information is used to indicate the target NSSF to generate a set of segments for the target PLMN.

[0307] For example, the target AMF may send the first information to the target NSSF by calling the Nnssf_NSSelection_Get service operation on the target NSSF.

[0308] By calling the above overhead operation, the target AMF may send a set of segments for the HPLMN, the target RAN TAI, and the HPLMN ID to the target NSSF.

[0309] For example, the target NSSF may return the segment set for the target PLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Optionally, the target NSSF may alternatively return a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Accordingly, the target AMF receives a mapping between the segment set for the HPLMN and the segment set for the target PLMN from the target NSSF.

[0310] For example, if the segment set that is intended for the HPLMN and that is sent by the target AMF to the target NSSF includes S-NSSAI-AA and S-NSSAI-BB, the target NSSF maps S-NSSAI-AA and S-NSSAI- BB in S-NSSAI-C and S-NSSAI-D based on Table 2. In this case, the segment set for the target PLMN is S-NSSAI-C and S-NSSAI-D.

[0311] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF may determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE. Also, in this solution, the source side does not send the target side the resolved NSSAI on the source side or the mapping between the segment set for the HPLMN and the segment set for the source PLMN, but sends the target side a set of segments that is intended for the HPLMN and which corresponds to the segment set for the source PLMN . This helps avoid the following possible problems: (1) Because different roaming agreements exist between different VPLMNs and a particular HPLMN, there are different mappings between the valid S-NSSAI for those different VPLMNs and the valid S-NSSAI for that HPLMN (e.g., mapping-1 in Table 1 is different from Mapping-2 in Table 2) and hence the target side (eg target AMF) may not recognize the segment set for the source PLMN. (2) The mapping between the segment set for the HPLMN and the segment set for the source PLMN is determined according to the roaming agreement between the source PLMN and the HPLMN. If the source AMF directly sends the mapping to the target party, there may be a security risk in revealing the roaming agreement between the source PLMN and the HPLMN.

[0312] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, obtaining, by the source AMF in the first area, information about the target AMF in the second area regions based on the set of segments for the first region (refer to step 909); and sending the source AMF of the segment set for the HPLMN of the terminal device to the target AMF, wherein the segment set for the HPLMN corresponds to the segment set for the first region, and the segment set for the HPLMN is used to determine the segment set for the second region (refer to the description of step 910).

[0313] In an exemplary implementation, the first region is a source PLMN and the second region is a target PLMN.

[0314] In an exemplary implementation, the source AMF determines, based on the mapping between the segment set for the source PLMN and the segment set for the HPLMN, a set of segments that is intended for the HPLMN and that corresponds to the segment set for the source PLMN.

[0315] In an exemplary implementation, obtaining, by the source AMF, information about the target AMF in the second region based on the segment set for the first region includes: sending the source AMF the segment set for the HPLMN and information about the target PLMN to the first device (refer to the description of step 902) ; and receiving the source AMF from the first device information about the target AMF, wherein the first device is the source NRF in the source PLMN (refer to the description of step 909).

[0316] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, the first device in the source PLMN obtaining a set of segments that is intended for an HPLMN terminal device and which corresponds to the set of segments for the source PLMN (refer to the description of step 902); sending, by the first device, a set of segments for the HPLMN to a second device in the target PLMN, wherein the set of segments for the HPLMN is used to determine the target AMF in the target PLMN (refer to the description of step 903); receiving, by the first device, information about the target AMF from the second device; and sending, by the first device, information about the target AMF to the source AMF in the source PLMN (refer to the description of step 908).

[0317] In a possible implementation, the first device is a source NRF in the source PLMN, and the second device is a target NRF in the target PLMN.

[0318] In an exemplary implementation, the first device in the source PLMN receiving a set of segments that is intended for the HPLMN and which corresponds to the segment set for the source PLMN includes: the first device in the source AMF receiving the set of segments for the HPLMN (refer to the description of step 902).

[0319] In an exemplary implementation, the first device receives information about the target PLMN from the source AMF; and the first device selects the second device based on information about the target PLMN.

[0320] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, receiving by the target NSSF in the target PLMN from the target NRF in the target PLMN a set of segments for the HPLMN terminal device (refer to the description of step 904); and sending, by the target NSSF to the target NRF, a set of segments that is intended for the target PLMN and that corresponds to a set of segments for the HPLMN, wherein the set of segments for the target PLMN is used to determine information about the target AMF in the target PLMN (refer to the description of step 906).

[0321] In an exemplary implementation, the target NSSF determines a segment set for the target PLMN based on a mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0322] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, receiving by the target NRF in the target PLMN from the target NSSF in the target PLMN a set of segments that is intended for the target PLMN and that corresponds to a set of segments for the HPLMN of the terminal device (refer to the description of step 906); determining, by the target NRF, information about the target AMF that supports the set of segments for the target PLMN (refer to the description of step 907); and sending, by the target NRF, information about the target AMF to the source NRF (refer to the description of step 909).

[0323] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF can determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE.

[0324] FIG. 10 is a schematic representation of a sixth communication method according to this application. This method can be used for the scenario shown in FIG. 4, to select a proper target AMF for the UE. The method includes the following steps.

[0325] Step 1001: When the UE service is transferred from the source RAN to the target RAN, the source AMF determines, based on the segment set for the first region, a segment set that is intended for the HPLMN and that corresponds to the segment set for the first region.

[0326] For example, if the source AMF stores a mapping (as shown in Table 3) between the set of segments for the first region and the set of segments for the HPLMN, the source AMF may determine, based on this mapping, the set of segments that is intended for the HPLMN and that corresponds to the set segments for the first area. For example, based on Table 3, it is determined that the segment set that is intended for HPLMN and which corresponds to the segment set (including S-NSSAI-A1 and S-NSSAI-B1) in the first area includes S-NSSAI-AA1 and S -NSSAI-BB1.

[0327] Optionally, the mapping may be stored in the UE context.

[0328] In the implementation before step 1001, the source AMF receives a handover required message sent from the source RAN, wherein the message may carry a target ID, where the target ID includes the target RAN ID and the target TAIs the target RAN, and these target TAIs further include information about the target PLMN (eg, ID of the target PLMN).

[0329] The target PLMN in which the target RAN is located and the source PLMN in which the source RAN is located are the same PLMN.

[0330] Step 1002: The source AMF sends the segment set for the HPLMN and the second area information to the NSSF. Accordingly, the NSSF may receive a set of segments for the HPLMN and information about the second region.

[0331] For example, the source AMF initiates a request message to the NSSF by calling the Nnssf_NSSelection_Get service operation of that NSSF, and this request message carries the segment set for the HPLMN and the second region information. The second area information includes target TAIs of the target RAN.

[0332] Step 1003: The NSSF determines a segment set for the second region based on the mapping between the segment set for the HPLMN and the segment set for the second region.

[0333] After receiving the segment set for the HPLMN and the second region information, the NSSF determines that a segment set for the second region should be selected. In addition, the NSSF may determine a segment set for the second region based on a mapping between the segment set for the HPLMN and the segment set for the second region.

[0334] The NSSF may store a mapping (as shown in Table 4) between the segment set for the second region and the segment set for the HPLMN, such that the NSSF may determine, based on this mapping, a segment set that is intended for the second region and that corresponds to the segment set for HPLMN. For example, if the segment set that is intended for HPLMN and that is received by the NSSF includes S-NSSAI-AA1 and S-NSSAI-BB1, based on Table 4, it may be determined that the segment set for the second region includes S- NSSAI-C1 and S-NSSAI-D1.

[0335] Step 1004: The NSSF determines, based on the information about the second region and the set of segments for the second region, information about the target AMF that supports the set of segments for the second region.

[0336] Step 1005: The NSSF sends information about the target AMF to the source AMF. Accordingly, the source AMF may receive information about the target AMF.

[0337] The target AMF information may be a target AMF set (AMF set) that supports a set of segments for the second region, and this target AMF set includes a target AMF that serves the UE and that is located in the second region.

[0338] The NSSF determines a set of segments for the second region based on the set of segments for the HPLMN, and then determines target AMF information based on the set of segments for the second region. Therefore, it is understood that the set of segments for HPLMN can be used to determine the target AMF.

[0339] For example, the NSSF sends a Nnssf_NSSelection_Get response to the source AMF, and this Nnssf_NSSelection_Get response carries information about the target AMF.

[0340] After receiving the target AMF information, the source AMF selects an AMF, namely the target AMF, from the set of AMFs indicated by the target AMF information.

[0341] Step 1006: The source AMF sends a set of segments for the HPLMN to the target AMF. Accordingly, the target AMF may receive a set of segments for the HPLMN.

[0342] For example, the source AMF sends a Namf_Communication_CreateUEContext request to the target AMF, and this Namf_Communication_CreateUEContext request carries the segment set for the HPLMN.

[0343] Optionally, the source AMF may further send to the target AMF a list of session PDUs associated with the segment set for the HPLMN. Optionally, other UE context information may be additionally sent, such as SMF information on the source side.

[0344] Optionally, after receiving the segment set for the HPLMN, the target AMF may obtain a segment set for the second region based on the segment set for the HPLMN. For example, the target AMF may obtain a set of segments for a second region based on a set of segments for an HPLMN in either of the following two ways.

[0345] Method 1: The target AMF determines a segment set for the target PLMN based on the segment set for the HPLMN and configuration information. For example, the target AMF may store configuration information. The configuration information includes a mapping (as shown in Table 4) between the segment set for the second region and the segment set for the HPLMN. Alternatively, the configuration information includes a roaming agreement between the second region and the HPLMN. The target AMF may define a mapping (as shown in Table 4) between the segment set for the second area and the segment set for the HPLMN in accordance with the roaming agreement. In this case, the target AMF may determine, based on the set of segments for the HPLMN and the mapping, a set of segments that is intended for the second region and that corresponds to the set of segments for the HPLMN.

[0346] For example, if the segment set that is intended for the HPLMN and that is received by the target AMF includes S-NSSAI-AA1 and S-NSSAI-BB1, based on Table 4, it may be determined that the segment set for the second region includes includes S-NSSAI-C1 and S-NSSAI-D1.

[0347] Method 2: The target AMF does not store a mapping between the segment set for the second region and the segment set for the HPLMN. In other words, the target AMF does not store the roaming agreement between the second area and the HPLMN. In this case, the target AMF sends first information to the target NSSF in the target PLMN, the first information including a set of segments for the HPLMN; and the target AMF receives from the target NSSF a set of segments for the second area.

[0348] Optionally, the first information further includes first indication information. The first indication information is used to indicate the target NSSF to generate a set of segments for the second region.

[0349] For example, the target AMF may send the first information to the target NSSF by calling the Nnssf_NSSelection_Get service operation on the target NSSF.

[0350] By calling the above overhead operation, the target AMF may send a set of segments for the HPLMN, the target RAN TAI, and the HPLMN ID to the target NSSF.

[0351] For example, the target NSSF may return the set of segments for the second region to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Optionally, the target NSSF may alternatively return the mapping (as shown in Table 4) between the segment set for the second region and the segment set for the HPLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Accordingly, the target AMF receives from the target NSSF a mapping between the segment set for the HPLMN and the segment set for the second region.

[0352] For example, if the segment set that is intended for the HPLMN and that is sent by the target AMF to the target NSSF includes S-NSSAI-AA1 and S-NSSAI-BB1, the target NSSF maps S-NSSAI-AA1 and S-NSSAI- BB1 in S-NSSAI-C1 and S-NSSAI-D1 based on Table 4. In this case, the segment set for the second region is S-NSSAI-C1 and S-NSSAI-D1.

[0353] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF may determine the segment set for the second region based on the segment set for the HPLMN to select an appropriate segment set for the second region for the UE, thereby realizing normal communication of the UE. Moreover, in this solution, the source side does not send the target side the allowed NSSAI (namely the segment set for the first region) on the source side or the mapping between the segment set for HPLMN and the segment set for the first region, but sends the target side a set of segments that is intended for HPLMN and which corresponds to the set of segments for the first region. This helps avoid the following potential problems: (1) Since the slices placed in different regions of the same PLMN are different, the mappings between the sets of segments in different regions of the PLMN and the slice set for the HPLMN (where, for example, mapping-3 in Table 3 is different from mapping-4 in Table 4) may be different, and hence the second region (eg, target AMF) may not recognize the set of segments for the first region. (2) If the source AMF directly sends a mapping between the segment set for HPLMN and the segment set for the first region to the AMF on the target side, there may be a security risk in revealing the placement of segments in the first region.

[0354] FIG. 11 is a schematic representation of a seventh communication method according to this application. This method can be used for the scenario shown in FIG. 4, to select a proper target AMF for the UE. The method includes the following steps.

[0355] Step 1101: When the UE service is transferred from the source RAN to the target RAN, the source AMF sends a set of segments for the first area and information about the second area to the NSSF. Accordingly, the NSSF may receive a set of segments for the first area and information about the second area.

[0356] In the implementation before step 1101, the source AMF receives a handover required message sent by the source RAN, wherein the message may carry a target ID, wherein the target ID includes the target RAN ID and the target TAIs the target RAN, and these target TAIs further include information about the target PLMN (eg, ID of the target PLMN).

[0357] The second area information includes the target TAIs of the target RAN, and the target PLMN in which the target RAN is located and the source PLMN in which the source RAN is located are the same PLMN.

[0358] Step 1102: The NSSF determines a set of segments that is intended for the HPLMN and that corresponds to a set of segments for the first region.

[0359] For example, if the NSSF stores a mapping (as shown in Table 3) between the segment set for the first region and the segment set for the HPLMN, the NSSF may determine, based on this mapping, the segment set that is intended for the HPLMN and that corresponds to the segment set for first area. For example, if the segment set that is intended for the first area and which is received by the NSSF includes S-NSSAI-A1 and S-NSSAI-B1, based on Table 3 it can be determined that the segment set that is intended for HPLMN and which corresponds to the set of slices for the first region, includes S-NSSAI-AA1 and S-NSSAI-BB1.

[0360] Optionally, the mapping may be stored in the UE context.

[0361] Step 1103 and step 1104 are the same as step 1003 and step 1004 in the embodiment of FIG. 10. Refer to the above parts of the description.

[0362] Step 1105: The NSSF sends information about the target AMF and a set of segments for the HPLMN to the source AMF. Accordingly, the source AMF may receive information about the target AMF and a set of segments for the HPLMN.

[0363] For example, the NSSF sends a Nnssf_NSSelection_Get response to the source AMF, and this Nnssf_NSSelection_Get response carries the target AMF information and segment set for the HPLMN.

[0364] In yet another implementation, the NSSF may alternatively separately send information about the target AMF and a set of segments for the HPLMN to the source AMF using two stages. For example, the NSSF may send the set of segments for the HPLMN to the source AMF at any step after step 1102 and before step 1106. The NSSF may send information about the target AMF to the source AMF after step 1103 and before step 1106.

[0365] The target AMF information may be a target AMF set (AMF set) that supports a set of segments for the second region, and this target AMF set includes a target AMF that serves the UE and that is in the second region.

[0366] The NSSF determines a set of segments for the second region based on the set of segments for the HPLMN, and then determines target AMF information based on the set of segments for the second region. Therefore, it is understood that the set of segments for HPLMN can be used to determine the target AMF.

[0367] After receiving the target AMF information, the source AMF selects an AMF, namely the target AMF, from the set of AMFs indicated by the target AMF information.

[0368] Step 1106: The source AMF sends a set of segments for the HPLMN to the target AMF. Accordingly, the target AMF may receive a set of segments for the HPLMN.

[0369] For example, the source AMF sends a Namf_Communication_CreateUEContext request to the target AMF, and this Namf_Communication_CreateUEContext request carries the segment set for the HPLMN.

[0370] Optionally, the source AMF may further send to the target AMF a list of session PDUs associated with the segment set for the HPLMN. Optionally, other UE context information may be additionally sent, such as SMF information on the source side.

[0371] Optionally, after receiving the segment set for the HPLMN, the target AMF may obtain the segment set for the second region based on the segment set for the HPLMN. For example, the target AMF may obtain a set of segments for a second region based on a set of segments for an HPLMN in either of the following two ways.

[0372] Method 1: The target AMF determines a segment set for the target PLMN based on the segment set for the HPLMN and configuration information. For example, the target AMF may store configuration information. The configuration information includes a mapping (as shown in Table 4) between the segment set for the second region and the segment set for the HPLMN. Alternatively, the configuration information includes a roaming agreement between the second region and the HPLMN. The target AMF may define a mapping (as shown in Table 4) between the segment set for the second area and the segment set for the HPLMN in accordance with the roaming agreement. In this case, the target AMF may determine, based on the set of segments for the HPLMN and the mapping, a set of segments that is intended for the second region and that corresponds to the set of segments for the HPLMN.

[0373] For example, if the segment set that is intended for the HPLMN and that is received by the target AMF includes S-NSSAI-AA1 and S-NSSAI-BB1, based on Table 4, it may be determined that the segment set for the second region includes includes S-NSSAI-C1 and S-NSSAI-D1.

[0374] Method 2: The target AMF does not store a mapping between the segment set for the second region and the segment set for the HPLMN. In other words, the target AMF does not store the roaming agreement between the second area and the HPLMN. In this case, the target AMF sends first information to the target NSSF in the target PLMN, the first information including a set of segments for the HPLMN; and the target AMF receives from the target NSSF a set of segments for the second area.

[0375] Optionally, the first information further includes first indication information. The first indication information is used to indicate the target NSSF to generate a set of segments for the second region.

[0376] For example, the target AMF may send the first information to the target NSSF by calling the Nnssf_NSSelection_Get service operation on the target NSSF.

[0377] By calling the above overhead operation, the target AMF may send a set of segments for the HPLMN, the target RAN TAI, and the HPLMN ID to the target NSSF.

[0378] For example, the target NSSF may return the set of segments for the second region to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Optionally, the target NSSF may alternatively return the mapping (as shown in Table 4) between the segment set for the second region and the segment set for the HPLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Accordingly, the target AMF receives from the target NSSF a mapping between the segment set for the HPLMN and the segment set for the second region.

[0379] For example, if the set of segments that is intended for HPLMN and that is sent by the target AMF to the target NSSF includes S-NSSAI-AA1 and S-NSSAI-BB1, the target NSSF maps S-NSSAI-AA1 and S-NSSAI- BB1 in S-NSSAI-C1 and S-NSSAI-D1 based on Table 4. In this case, the segment set for the second region is S-NSSAI-C1 and S-NSSAI-D1.

[0380] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF may determine the segment set for the second region based on the segment set for the HPLMN to select an appropriate segment set for the second region for the UE, thereby realizing normal communication of the UE. Moreover, in this solution, the source side does not send the target side the allowed NSSAI (namely the segment set for the first region) on the source side or the mapping between the segment set for HPLMN and the segment set for the first region, but sends the target side a set of segments that is intended for HPLMN and which corresponds to the set of segments for the first region. This helps avoid the following possible problems: (1) Since the slices placed in different regions of the same PLMN are different, the mappings between the sets of segments in different regions of the PLMN and the slice set for the HPLMN (e.g., mapping-3 in Table 3 is different from the mapping -4 in Table 4) may be different, and therefore the second region (eg, the target AMF) may not recognize the set of segments for the first region. (2) If the source AMF directly sends a mapping between the segment set for HPLMN and the segment set for the first region to the AMF on the target side, there may be a security risk in revealing the placement of segments in the first region.

[0381] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, obtaining, by the source AMF in the first area, information about the target AMF in the second area regions based on the set of segments for the first region (refer to the description of step 1005 and step 1105); and sending the source AMF of the segment set for the HPLMN of the terminal device to the target AMF, wherein the segment set for the HPLMN corresponds to the segment set for the first region, and the segment set for the HPLMN is used to determine the segment set for the second region (refer to the description of step 1006 and step 1106) .

[0382] In a possible implementation, the first region and the second region are in the same PLMN.

[0383] In an exemplary implementation, the source AMF determines, based on the mapping between the segment set for the first region and the segment set for the HPLMN, a set of segments that is intended for the HPLMN and that corresponds to the segment set for the first region.

[0384] In an exemplary implementation, obtaining, by the source AMF, information about a target AMF in a second area based on a set of segments for the first area includes: sending, through the source AMF, a set of segments for the HPLMN and information about the second area to the NSSF (refer to the description of step 1002) ; and receiving, by the source AMF, information about the target AMF from the NSSF, wherein the target AMF information is determined based on the set of segments for the HPLMN and the second region information.

[0385] In an exemplary implementation, the source AMF sends a set of segments for the first region to the NSSF (refer to the description of step 1101), and the source AMF receives from the NSSF a set of segments that is intended for the HPLMN and that corresponds to the set of segments for the first region.

[0386] In an exemplary implementation, obtaining, by the source AMF, information about a target AMF in a second area based on a set of segments for the first area includes: sending, through the source AMF, information about the second area to the NSSF (refer to the description of step 1002 and step 1101); and receiving, by the source AMF, information about the target AMF from the NSSF, wherein the target AMF information is determined based on the set of segments for the first area and the information about the second area (refer to the description of step 1005 and step 1105).

[0387] Therefore, the present invention discloses a communication method including: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, obtaining, by the NSSF, a set of segments that is intended for an HPLMN of the terminal device, and which corresponds to a set of segments for the first region, and information about the second region (refer to the description of step 1002, step 1101 and step 1102); determining, by the NSSF, a segment set for the second region based on the segment set for the HPLMN and the second region information (refer to the description of step 1003 and step 1103); determining by the NSSF information about the target AMF based on the set of segments for the second area (refer to the description of step 1004 and step 1104); and sending, by the NSSF, information about the target AMF to the source AMF (refer to the description of step 1005 and step 1105).

[0388] In an exemplary implementation, receiving by the NSSF a set of segments that is intended for an HPLMN of a terminal device and which corresponds to a set of segments for a first region includes: receiving by the NSSF from a source AMF in the first region a set of segments for the first region, and determining the set of segments , which is for HPLMN and which corresponds to the set of segments for the first region; or receiving by the NSSF from the source AMF a set of segments for the HPLMN.

[0389] In an exemplary implementation, the NSSF stores a mapping between a set of segments for a first region and a set of segments for an HPLMN, as well as a mapping between a set of segments for a second region and a set of segments for an HPLMN.

[0390] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF may determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE.

[0391] The solutions provided in this application are described above primarily from the perspective of interactions between network elements. It can be understood that in order to implement the above functions, each of the network elements includes a corresponding hardware structure and/or software module for performing the above functions. One skilled in the art will appreciate that, in combination with the example blocks and algorithm steps that are described in the embodiments disclosed in this specification, the present invention may be implemented using hardware or a combination of hardware and computer software. Whether a function is performed by hardware or by hardware driven by computer software depends on the specific applications and design limitations of the technical solutions. One skilled in the art may use different techniques to implement the described functions for each particular application, but such implementation should not be considered beyond the scope of the present invention.

[0392] FIG. 12 is a possible exemplary block diagram of a communication device 1200 according to this application. The communication device 1200 may exist in the form of software or hardware. The communication device 1200 may include a processing unit 1202 and a communication unit 1203. In an implementation, communication unit 1203 may include a receiving unit and a sending unit. The processing unit 1202 is configured to monitor and control the operation of the communication device 1200. The communication unit 1203 is configured to support communication of the communication device 1200 with another network entity. The communication device 1200 may further include a storage unit 1201 configured to store program code and data of the communication device 1200.

[0393] Processing unit 1202 may be a processor or controller, such as a central processing unit (CPU), a general purpose processor, a digital signal processor (DSP), an application specific integrated circuit, ASIC), field programmable gate array (FPGA) or other programmable logic device, transistor logic device, hardware component, or any combination thereof. The processing unit may implement or execute various examples of logical blocks, modules, and circuits described with reference to the contents disclosed herein. Alternatively, the processor may be a combination of processors that implement a computing function, such as a combination of one or more microprocessors, or a combination of a DSP and a microprocessor. The storage unit 1201 may be a memory. The communication unit 1203 is a device interface circuit and is configured to receive a signal from another device. For example, when the device is implemented using a chip, the communication unit 1203 is an interface circuit that is contained in the chip and that is configured to receive a signal from another chip or device, or is an interface circuit that is contained in the chip and that is configured sending a signal to another chip or device.

[0394] The communication device 1200 may be a mobility network element (eg, a source mobility network element or a target mobility network element) in any of the above embodiments, or may be a chip used for the mobility network element. For example, when the communication device 1200 is a mobility management network element, the processing unit 1202 may be, for example, a processor, and the communication unit 1203 may be, for example, a transceiver. Optionally, the transceiver may include RF circuitry, and the storage unit may be, for example, a memory. For example, when the communication device 1200 is a chip used for a mobility control network element, the processing unit 1202 may be, for example, a processor, and the communication unit 1203 may be, for example, an input/output interface, an output, or a circuit. The processing unit 1202 may execute a computer-executable instruction stored in the storage unit. Optionally, the storage unit is an on-chip storage unit, such as a register or cache. Alternatively, the storage unit may be a storage unit that resides in the network mobility element and that is located off-chip, such as a read-only memory (ROM) or other type of static storage device that can store static information and instructions, or random access memory (RAM).

[0395] In an embodiment, communications device 1200 is a source mobility management network element. When service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, the processing unit 1202 is configured to obtain information about the target mobility network element in the second area based on the set of segments for the first area; and the communication unit 1203 is configured to send the segment set for the HPLMN of the terminal device to the target mobility network element, wherein the segment set for the HPLMN corresponds to the segment set for the first region, and the segment set for the HPLMN is used to determine the segment set for the second region.

[0396] In an exemplary implementation, the first region is a source PLMN and the second region is a target PLMN.

[0397] In an exemplary implementation, processing unit 1202 is configured to determine, based on the mapping between the segment set for the source PLMN and the segment set for the HPLMN, a set of segments that is intended for the HPLMN and that corresponds to the segment set for the source PLMN.

[0398] In an exemplary implementation, communication unit 1203 is configured to: send a set of segments for the HPLMN and information about the target PLMN to the first device; and receiving from the first device information about the target mobility management network element, wherein the first device is a segment selection source network element or a repository network source network element in the source PLMN.

[0399] In an exemplary implementation, communication unit 1203 is configured to: send a set of segments for the HPLMN to a source segment selection network element in the source PLMN; receiving from the source network element a segment selection of a set of segments for the target PLMN; sending a set of segments for the target PLMN and information about the target PLMN to the source network repository network element in the source PLMN; and receiving from the source network element of the network repository information about the target mobility control network element.

[0400] In an exemplary implementation, communication unit 1203 is further configured to: send a set of segments for the source PLMN to a source segment selection network element in the source PLMN; and receiving from the source network element a segment selection of the set of segments for the HPLMN.

[0401] In an exemplary implementation, the communication unit 1203 is further configured to: send information about the target PLMN to the source segment selection network element in the source PLMN; and receiving from the source segment selection network element information about the target mobility control network element.

[0402] In an exemplary implementation, communication unit 1203 is configured to: receive from the source network element a selection of a segment in the source PLMN of a set of segments for the target PLMN; sending a set of segments for the target PLMN and information about the target PLMN to the source network repository network element in the source PLMN; and receiving from the source network element of the network repository information about the target mobility control network element.

[0403] In an exemplary implementation, the first region and the second region are in the same PLMN.

[0404] In an exemplary implementation, processing unit 1202 is configured to determine, based on the mapping between the segment set for the first region and the segment set for the HPLMN, a set of segments that is intended for the HPLMN and that corresponds to the segment set for the first region.

[0405] In an exemplary implementation, communication unit 1203 is configured to: send a set of segments for the HPLMN and second region information to the segment selection network element; and receiving from the segment selection network element information about the target mobility network element, wherein the information about the target mobility network element is determined based on the set of segments for the HPLMN and the second region information.

[0406] In an exemplary implementation, communication unit 1203 is configured to: send a set of segments for the first region to a segment selection network element; and receiving from the network element a segment selection of a set of segments that is intended for the HPLMN and that corresponds to the set of segments for the first region.

[0407] In an exemplary implementation, communication unit 1203 is configured to: send information about the second region to the segment selection network element; and receiving from the segment selection network element information about the target mobility network element, wherein the information about the target mobility network element is determined based on the set of segments for the first region and the information about the second region.

[0408] It is understood that the specific implementation process and corresponding beneficial effects when using this communication device in the above-described communication method are described in the related description in the above method embodiment. The details are not repeated here.

[0409] FIG. 13 is a possible exemplary block diagram of a communication device 1300 according to this application. The communication device 1300 may exist in the form of software or hardware. The communication device 1300 may include a processing unit 1302 and a communication unit 1303. In an implementation, communication unit 1303 may include a receiving unit and a sending unit. The processing unit 1302 is configured to monitor and control the operation of the communication device 1300. The communication unit 1303 is configured to support communication of the communication device 1300 with another network entity. The communication device 1300 may further include a storage unit 1301 configured to store program code and data of the communication device 1300.

[0410] Processing unit 1302 may be a processor or controller, such as a general purpose central processing unit, general purpose processor, DSP, ASIC, FPGA or other programmable logic device, transistor logic device, hardware component, or any combination thereof. The processing unit may implement or execute various examples of logical blocks, modules, and circuits described with reference to the contents disclosed herein. Alternatively, the processor may be a combination of processors that implement a computing function, such as a combination of one or more microprocessors, or a combination of a DSP and a microprocessor. The storage unit 1301 may be a memory. The communication unit 1303 is a device interface circuit and is configured to receive a signal from another device. For example, when the device is implemented using a chip, the communication unit 1303 is an interface circuit that is contained in the chip and that is configured to receive a signal from another chip or device, or is an interface circuit that is contained in the chip and that is configured sending a signal to another chip or device.

[0411] The communication device 1300 may be a segment selection network element (eg, a source segment selection network element or a target segment selection network element) in any of the above embodiments, or may be a chip used for a segment selection network element. For example, when the communication device 1300 is a segment selection network element, the processing unit 1302 may be, for example, a processor, and the communication unit 1303 may be, for example, a transceiver. Optionally, the transceiver may include RF circuitry, and the storage unit may be, for example, a memory. For example, when the communication device 1300 is a chip used for a segment selection network element, the processing unit 1302 may be, for example, a processor, and the communication unit 1303 may be, for example, an input/output interface, an output, or a circuit. The processing unit 1302 may execute a computer-executable instruction stored in a storage unit. Optionally, the storage unit is an on-chip storage unit, such as a register or cache. Alternatively, the storage unit may be a storage unit that is located in a segment selection network element and that is located off-chip, such as a ROM or other type of static memory device that can store static information and instructions, or RAM.

[0412] In the first embodiment, the communication device 1300 is the source segment selection network element. When service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, the processing unit 1302 is configured to obtain a set of segments that is intended for the HPLMN of the terminal device and that corresponds to a set of segments for the source PLMN; and the communication unit is configured to: send a set of segments for the HPLMN to a target segment selection network element in the target PLMN, wherein the set of segments for the HPLMN is used to determine a target mobility management network element in the target PLMN; receiving from the target segment selection network element information about the target mobility control network element; and sending information about the target mobility network element to the source mobility network element in the source PLMN.

[0413] In an exemplary implementation, the communication unit 1303 is configured to: receive from the source mobility network element a set of segments for the source PLMN and determine a set of segments that is intended for the HPLMN and that corresponds to the set of segments for the source PLMN; or receiving from the source mobility network element a set of segments for the HPLMN.

[0414] In an exemplary implementation, communication unit 1303 is configured to receive information about a target PLMN from a source mobility network element; and the processing unit 1302 is configured to select a target segment selection network element based on information about the target PLMN.

[0415] In the second embodiment, the communication device 1300 is the source segment selection network element. When service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, the processing unit 1302 is configured to obtain a set of segments that is intended for the HPLMN of the terminal device and that corresponds to a set of segments for the source PLMN; and the communication unit 1303 is configured to: send a set of segments for the HPLMN to a target segment selection network element in the target PLMN, wherein the set of segments for the HPLMN is used to determine a set of segments for the target PLMN; receiving from the target network element a segment selection of a set of segments for the target PLMN; and sending the set of segments for the target PLMN to the source mobility network element.

[0416] In an exemplary implementation, communication unit 1303 is configured to receive from the source mobility network element a set of segments for the source PLMN, and processing unit 1302 is configured to determine a set of segments that is intended for the HPLMN and that corresponds to the set of segments for the source PLMN; or the communication unit 1303 is configured to receive from the source mobility network element a set of segments for the HPLMN.

[0417] In an exemplary implementation, communication unit 1303 is configured to receive information about a target PLMN from a source mobility management network element; and the processing unit 1302 is configured to select a target segment selection network element based on information about the target PLMN.

[0418] In a third embodiment, the communication device 1300 is a segment selection network element. When service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, processing unit 1302 is configured to: obtain a set of segments that is intended for the HPLMN of the terminal device and that corresponds to the set of segments for the first area, and information about the second area; determining a set of segments for a second region based on the set of segments for the HPLMN and information about the second region; and determining information about the target mobility network element based on the set of segments for the second region; and the communication unit 1303 is configured to send information about the target mobility network element to the source mobility network element.

[0419] In an exemplary implementation, communication unit 1303 is configured to receive from a source mobility network element in the first area a set of segments for the first area, and processing unit 1302 is configured to determine a set of segments that is intended for the HPLMN and that corresponds to the set of segments for the first regions; or the communication unit 1303 is configured to receive from the source mobility network element a set of segments for the HPLMN.

[0420] In an exemplary implementation, the storage unit is configured to store a mapping between a set of segments for a first region and a set of segments for an HPLMN, and a mapping between a set of segments for a second region and a set of segments for an HPLMN.

[0421] In a fourth embodiment, the communication device 1300 is a segment selection network element. When service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, the communication unit 1303 is configured to receive from the source network element a selection of a segment in the source PLMN a set of segments for the HPLMN of the terminal device; a processing unit 1302 is configured to determine information about a target mobility network element that supports a set of segments for the target PLMN, wherein the set of segments for the target PLMN corresponds to the set of segments for the HPLMN; and the communication unit 1303 is configured to send information about the target mobility control network element to the source segment selection network element.

[0422] In an exemplary implementation, processing unit 1302 is configured to determine a segment set for the target PLMN based on a mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0423] In a fifth embodiment, communication device 1300 is a segment selection target network element. When service of a terminal device is transferred from a source network access device in a source PLMN to a target network access device in a target PLMN, communication unit 1303 is configured to: receive from a source network element a selection of a segment in the source PLMN or from a target network repository network element in a target PLMN of a set segments for the HPLMN terminal device; and sending to the source segment selection network element or the target network element of the network repository a set of segments that is intended for the target PLMN and that corresponds to a set of segments for the HPLMN, wherein the set of segments for the target PLMN is used to determine information about the target mobility management network element in the target PLMN.

[0424] In an exemplary implementation, processing unit 1302 is configured to determine a segment set for the target PLMN based on a mapping between the segment set for the HPLMN and the segment set for the target PLMN.

[0425] It is understood that the specific implementation process and corresponding beneficial effects when using this communication device in the above-described communication method are described in the related description in the above method embodiment. The details are not repeated here.

[0426] FIG. 14 is a possible exemplary block diagram of a communication device 1400 according to this application. The communication device 1400 may exist in the form of software or hardware. The communication device 1400 may include a processing unit 1402 and a communication unit 1403. In an implementation, communication unit 1403 may include a receiving unit and a sending unit. The processing unit 1402 is configured to monitor and control the operation of the communication device 1400. The communication unit 1403 is configured to support communication of the communication device 1400 with another network entity. The communication device 1400 may further include a storage unit 1401 configured to store program code and data of the communication device 1400.

[0427] Processing unit 1402 may be a processor or controller, such as a general purpose central processing unit, general purpose processor, DSP, ASIC, FPGA or other programmable logic device, transistor logic device, hardware component, or any combination thereof. The processing unit may implement or execute various examples of logical blocks, modules, and circuits described with reference to the contents disclosed herein. Alternatively, the processor may be a combination of processors that implement a computing function, such as a combination of one or more microprocessors, or a combination of a DSP and a microprocessor. The storage unit 1401 may be a memory. The communication unit 1403 is a device interface circuit and is configured to receive a signal from another device. For example, when the device is implemented using a chip, the communication unit 1403 is an interface circuit that is contained in the chip and that is configured to receive a signal from another chip or device, or is an interface circuit that is contained in the chip and that is configured sending a signal to another chip or device.

[0428] The communication device 1400 may be a network repository network element (eg, a source network element of a network repository or a target network element of a network repository) in any of the above embodiments, or may be a chip used for a network repository network element. For example, when communication device 1400 is a network repository element, processing unit 1402 may be, for example, a processor, and communication unit 1403 may be, for example, a transceiver. Optionally, the transceiver may include RF circuitry, and the storage unit may be, for example, a memory. For example, when the communication device 1400 is a chip used for a network repository network element, the processing unit 1402 may be, for example, a processor, and the communication unit 1403 may be, for example, an input/output interface, an output, or a circuit. The processing unit 1402 may execute a computer-executable instruction stored in a storage unit. Optionally, the storage unit is an on-chip storage unit, such as a register or cache. Alternatively, the storage unit may be a storage unit that resides in a network repository network element and that is located off-chip, such as a ROM or other type of static storage device that can store static information and instructions, or RAM.

[0429] In the first embodiment, the communication device 1400 is the source network element of the network repository. When service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, the communication unit 1403 is configured to: receive from the source mobility network element in the source PLMN a set of segments for the target PLMN; sending a set of segments for the target PLMN to the target network repository network element in the target PLMN; receiving information about the target mobility control network element from the target network element of the network repository; and sending information about the target mobility network element.

[0430] In an exemplary implementation, communication unit 1403 is configured to receive information about a target PLMN from a source mobility network element; and processing unit 1402 is configured to determine a target network element of the network repository based on information about the target PLMN.

[0431] In the second embodiment, the communication device 1400 is the source network element of the network repository. When service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, the processing unit 1402 is configured to obtain a set of segments that is intended for the HPLMN of the terminal device and that corresponds to a set of segments for the source PLMN; and the communication unit 1403 is configured to: send a set of segments for the HPLMN to a target network repository network element in the target PLMN, wherein the set of segments for the HPLMN is used to determine the target mobility management network element in the target PLMN; receiving information about the target mobility control network element from the target network element of the network repository; and sending information about the target mobility network element to the source mobility network element in the source PLMN.

[0432] In an exemplary implementation, communication unit 1403 is configured to receive from the source mobility network element a set of segments for the source PLMN; and processing unit 1402 is configured to determine a set of segments that is intended for the HPLMN and that corresponds to a set of segments for the original PLMN. Alternatively, communication unit 1403 is configured to receive from the source mobility network element a set of segments for the HPLMN.

[0433] In an exemplary implementation, communication unit 1403 is configured to receive information about a target PLMN from a source mobility network element; and the processing unit 1402 is configured to select a target network element of the network repository based on information about the target PLMN.

[0434] In a third embodiment, communication device 1400 is a target network element of a network repository. When service of a terminal device is transferred from a source network access device in the source PLMN to a target network access device in the target PLMN, communication unit 1403 is configured to receive from the target network element a selection of a segment in the target PLMN or the source network element of a repository network in the source PLMN a set of segments, which is intended for the target PLMN and which corresponds to the set of segments for the HPLMN of the terminal device; a processing unit 1402 is configured to determine information about a target mobility network element that supports a set of segments for the target PLMN; and the communication unit 1403 is configured to send information about the target mobility control network element to the source network element of the network repository.

[0435] It is understood that the specific implementation process and corresponding beneficial effects when using this communication device in the above-described communication method are described in the related description in the above method embodiment. The details are not repeated here.

[0436] FIG. 15 is a schematic diagram of a communication device according to this application. The communication device may be the aforementioned mobility management network element (eg, a source mobility management network element or a target mobility management network element), a segment selection network element (eg, a source segment selection network element or a target segment selection network element), or a network repository network element (for example, a source network element of a network repository or a target network element of a network repository). The communication device 1500 includes a processor 1502, a communication interface 1503, and a memory 1501. Optionally, the communication device 1500 may further include a communication line 1504. Communication interface 1503, processor 1502, and memory 1501 may be coupled to each other via communication line 1504. Communication line 1504 may be a peripheral component interconnect (PCI), an extended industry standard architecture (EISA), or the like. Communication line 1504 may be divided into an address bus, a data bus, control bus, etc. For ease of presentation, FIG. 15 only one thick line is shown to indicate a communication line, but this does not mean that there is only one bus or only one type of bus.

[0437] Processor 1502 may be a central processing unit, a microprocessor, an ASIC, or one or more integrated circuits configured to control program execution in solutions of this application.

[0438] Communication interface 1503 may be any device, such as a transceiver, configured to communicate with another device or communication network, such as Ethernet, radio access network (RAN), wireless local area networks (WLAN) ) or wired access network.

[0439] Memory 1501 may be a ROM, another type of static storage device that can store static information and instructions, RAM, or another type of dynamic storage device that can store information and instructions; or may be an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM), or other compact disc storage, storage on an optical disc (including a CD, laser disc, optical disc, digital versatile disc, Blu-ray disc or the like), a magnetic disk storage medium or other magnetic storage medium, or any other medium that can be configured with the ability to carry or store expected program code in the form of an instruction or data structure, and which can be accessed by a computer. However, the 1501's memory is not limited to this. The memory may exist independently and be connected to the processor via communication line 1504. Alternatively, the memory can be integrated with the processor.

[0440] Memory 1501 is configured to store computer-executable instructions for executing solutions according to this application, and processor 1502 controls such execution. The processor 1502 is configured to execute a computer-executable instruction stored in the memory 1501 to implement the communication method provided in the above-mentioned embodiments of this application.

[0441] Optionally, the computer-executable instruction in this embodiment of this application may also be referred to as application program code. This is not particularly limited in this embodiment of this application.

[0442] FIG. 16 is a schematic diagram of an eighth communication method according to this application. This method can be used for the scenario shown in FIG. 3, to select the target AMF for the UE. The method includes the following steps.

[0443] Step 1600: The target NRF stores the identifier of the target AMF in the target PLMN.

[0444] It should be noted that step 1600 is an optional step. The target NRF may alternatively obtain the target AMF identifier in a different manner. For example, the target NRF receives the target AMF identifier from another network element.

[0445] Step 1601: When the UE service is transferred from the source RAN to the target RAN, the source AMF sends the target network element type and the target PLMN ID to the source NRF. Accordingly, the source NRF may receive the type of the target network element and the ID of the target PLMN.

[0446] For example, the target TAIs include the ID of the target PLMN. The source AMF sends the ID of the target PLMN to the source NRF using the target TAIs.

[0447] For example, the source AMF may initiate a request message to the source NRF by calling the Nnrf_NFDiscovery_Request service operation of the source NRF, and this request message carries the type of the target network element and the ID of the target PLMN. The target network element type is AMF and is used to indicate that the requested network element type is an AMF network element.

[0448] Optionally, the source AMF may further send second indication information to the source NRF, causing the above overhead operation. The second indication information is used to indicate that the service operation of the source NRF occurs in an intersystem handoff procedure.

[0449] In the implementation before step 1601, the source AMF receives a handover required message sent by the source RAN, wherein the message may carry a target ID, wherein the target ID includes the target RAN ID and the target TAIs the target RAN, and these target TAIs further include information about the target PLMN (eg, ID of the target PLMN).

[0450] Optionally, the source AMF determines based on the target identifier that this handover is an inter-PLMN system handover and therefore triggers execution of step 1601.

[0451] For example, if the source AMF determines that the target PLMN included in the target TAIs is different from the PLMN in which the source AMF is located, the source AMF may determine that this handover is a system handover between PLMNs.

[0452] Step 1602: The source NRF sends a discovery request to the target NRF. Accordingly, the target NRF may receive the discovery request.

[0453] In the implementation before step 1602, the source NRF determines an NRF network element (namely, the target NRF) in the target PLMN based on the ID of the target PLMN.

[0454] For example, a source NRF may send a discovery request to a target NRF by calling the Nnrf_NFDiscovery_Request service operation on the target NRF. The discovery request includes a target NE type and a target PLMN ID, which are received by the source NRF at step 1601.

[0455] Optionally, the source NRF may further send third indication information to the target NRF, causing the above overhead operation. The third indication information is used to indicate that the target NRF service operation occurs in an intersystem handover procedure.

[0456] Step 1603: The target NRF sends the target AMF identifier to the source NRF. Accordingly, the source NRF may receive information about the target AMF.

[0457] In the implementation, before step 1603, the target NRF determines the target AMF based on the ID of the target PLMN, which is received at step 1602.

[0458] For example, the target AMF identifier is the target AMF ID or the target AMF address information. For example, the identifier of the target AMF is stored in the target NRF at step 1600. The target AMF may be the default AMF in the target PLMN.

[0459] For example, the target NRF may send the target AMF identifier to the source NRF by calling the Nnrf_NFDiscovery_Response service operation on the target NRF.

[0460] Optionally, if the source NRF sends third indication information to the target NRF at step 1602, and the target NRF learns, based on this third indication information, that the service operation call to the target NRF at step 1602 occurs in an intersystem handoff procedure, the target NRF sends ID of the target AMF to the source NRF.

[0461] Optionally, if the source NRF does not send the third indication information to the target NRF in step 1602, the target NRF sends the target AMF ID to the source NRF based on the target NE type and the target PLMN ID, which are carried in step 1602.

[0462] Step 1604: The source NRF sends the identifier of the target AMF to the source AMF. Accordingly, the source AMF may receive the identifier of the target AMF.

[0463] For example, the source NRF may send the identifier of the target AMF to the source AMF by calling the Nnrf_NFDiscovery_Response service operation on the source NRF.

[0464] Step 1605: The source AMF sends a set of segments for the HPLMN to the target AMF. Accordingly, the target AMF may receive a set of segments for the HPLMN.

[0465] In the implementation, before step 1605, the source AMF determines the target AMF based on the identifier of the target AMF. The source AMF further determines, based on the mapping (as shown in Table 1) between the segment set for the source PLMN and the segment set for the HPLMN, a set of segments that is intended for the HPLMN and that corresponds to the segment set for the source PLMN.

[0466] For example, the source AMF stores the UE context, and this UE context includes a set of segments for the source PLMN. The UE context that is stored in the source AMF further stores a mapping (as shown in Table 1) between the segment set for the source PLMN and the segment set for the HPLMN, so that the source AMF can determine, based on this mapping, the segment set that is intended for the HPLMN and which corresponds to the set of segments for the original PLMN. For example, if the segment set for the source PLMN includes S-NSSAI-A and S-NSSAI-B, based on Table 1, it is determined that the segment set that is intended for the HPLMN and which corresponds to the segment set for the source PLMN includes S -NSSAI-AA and S-NSSAI-BB.

[0467] Optionally, the source AMF may further send a list of PDU sessions to the target AMF, causing the above overhead operation.

[0468] Optionally, after step 1605, step 1606 is additionally included.

[0469] Step 1606: The target AMF determines a segment set for the target PLMN based on the segment set for the HPLMN and configuration information.

[0470] For example, the target AMF may store configuration information. The configuration information includes a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN. Alternatively, the configuration information includes a roaming agreement between the target PLMN and the HPLMN. The target AMF may define a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN in accordance with the roaming agreement. In this case, the target AMF may determine, based on the set of segments for the HPLMN and the mapping, a set of segments that is intended for the target PLMN and which corresponds to the set of segments for the HPLMN.

[0471] For example, if the segment set that is intended for the HPLMN and that is received by the target AMF includes S-NSSAI-AA and S-NSSAI-BB, based on Table 2 it may be determined that the segment set for the target PLMN includes themselves S-NSSAI-C and S-NSSAI-D.

[0472] Optionally, if the target AMF does not store a mapping between the segment set for the target PLMN and the segment set for the HPLMN, in other words, the target AMF does not store the roaming agreement between the target PLMN and the HPLMN, step 1606 is not performed after step 1605, and step 1607 and step 1608 are further included after step 1605.

[0473] Step 1607: The target AMF sends first information to the target NSSF in the target PLMN, wherein the first information includes a set of segments for the HPLMN.

[0474] Optionally, the first information further includes first indication information. The first indication information is used to indicate the target NSSF to generate a set of segments for the target PLMN.

[0475] For example, the HPLMN ID is also referred to as the Home PLMN ID of a specific UE.

[0476] For example, the target AMF may send the first information to the target NSSF by calling the Nnssf_NSSelection_Get service operation on the target NSSF.

[0477] By calling the above overhead operation, the target AMF may send a set of segments for the HPLMN, the target RAN TAI, and the HPLMN ID to the target NSSF.

[0478] Step 1608: The target NSSF sends a set of segments for the target PLMN to the target AMF. Accordingly, the target AMF receives from the target NSSF to the target PLMN a set of segments for the target PLMN.

[0479] For example, the target NSSF may return the segment set for the target PLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Optionally, the target NSSF may alternatively return a mapping (as shown in Table 2) between the segment set for the target PLMN and the segment set for the HPLMN to the target AMF by calling the Nnssf_NSSelection_Get response service operation. Accordingly, the target AMF receives a mapping between the segment set for the HPLMN and the segment set for the target PLMN from the target NSSF.

[0480] For example, if the set of segments that is intended for HPLMN and that is sent by the target AMF to the target NSSF includes S-NSSAI-AA and S-NSSAI-BB, the target NSSF maps S-NSSAI-AA and S-NSSAI- BB in S-NSSAI-C and S-NSSAI-D based on Table 2. In this case, the segment set for the target PLMN is S-NSSAI-C and S-NSSAI-D.

[0481] Optionally, after the handover procedure is completed, the UE initiates a mobility registration update. The registration request message sent by the UE to the target AMF carries the requested NSSAI. The target AMF performs a relocation of the AMF based on the requested NSSAI.

[0482] Based on the above solution, after receiving the segment set for the HPLMN, the target AMF can determine the segment set for the target PLMN based on the segment set for the HPLMN to select an appropriate segment set for the target PLMN for the UE, thereby realizing normal communication of the UE. Also, in this solution, the source side does not send the target side the resolved NSSAI on the source side or the mapping between the segment set for the HPLMN and the segment set for the source PLMN, but sends the target side a set of segments that is intended for the HPLMN and which corresponds to the segment set for the source PLMN . This helps avoid the following possible problems: (1) Because different roaming agreements exist between different VPLMNs and a particular HPLMN, there are different mappings between the valid S-NSSAI for those different VPLMNs and the valid S-NSSAI for that HPLMN (e.g., mapping-1 in Table 1 is different from Mapping-2 in Table 2) and hence the target side (eg target AMF) may not recognize the segment set for the source PLMN. (2) The mapping between the segment set for the HPLMN and the segment set for the source PLMN is determined according to the roaming agreement between the source PLMN and the HPLMN. If the source AMF directly sends the mapping to the target party, there may be a security risk in revealing the roaming agreement between the source PLMN and the HPLMN.

[0483] The communication device 1200 shown in FIG. 12 may further be configured to perform the target AMF operation of FIG. 16. For example, communications device 1200 is a target mobility management network element.

[0484] When service of a terminal device is transferred from a source network access device in a first region (eg, a source PLMN) to a target network access device in a second region (eg, a target PLMN), communication unit 1203 is configured to receive from the source network mobility control element (eg, the source AMF network element) in a first segment set region for the HPLMN of the terminal device, the segment set for the HPLMN corresponding to the segment set for the first region; and processing unit 1202 is configured to obtain a set of segments for the second region based on the set of segments for HPLMN.

[0485] In an exemplary implementation, processing unit 1202 determines a set of segments for the second region based on configuration information.

[0486] In an exemplary implementation, the configuration information includes a mapping between a segment set for the second region and a segment set for the HPLMN; or the configuration information includes a roaming agreement between the second region and the HPLMN, and the roaming agreement is used to determine the mapping between the segment set for the second region and the segment set for the HPLMN.

[0487] In an exemplary implementation, communication unit 1203 is configured to send first information to a target segment selection network element in a second area, and this first information includes a set of segments for the HPLMN. In addition, the communication unit 1203 is configured to receive from a target segment selection network element (eg, a target NSSF) a set of segments for the second region.

[0488] In an exemplary implementation, the first information further includes indication information, and this indication information is used to indicate the target NSSF to generate a set of segments for the target PLMN.

[0489] In an exemplary implementation, communication unit 1203 is configured to receive a mapping between the segment set for the HPLMN and the segment set for the second region from the target NSSF.

[0490] In an exemplary implementation, the first region is the source PLMN and the second region is the target PLMN.

[0491] It is understood that the specific implementation process and corresponding beneficial effects when using this communication device in the above-described communication method are described in the related description in the above method embodiment. The details are not repeated here.

[0492] The communication device 1200 shown in FIG. 12 may further be configured to perform the operation of the original AMF of FIG. 16. For example, communications device 1200 is a source mobility management network element.

[0493] When service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, communication unit 1203 is configured to send a request message to the target network element of the network repository function (eg, target network element NRF) at second area; the communication unit 1203 is configured to receive from the target network element of the network repository function an identifier of the target mobility control network element in the second area; and the communication unit 1203 is configured to send the segment set for the HPLMN of the terminal device to the target mobility management network element (eg, the target network element AMF), wherein the segment set for the HPLMN corresponds to the segment set for the first region, and the segment set for the HPLMN is used to determine set of segments for the second area.

[0494] In an exemplary implementation, the first region is a source PLMN and the second region is a target PLMN.

[0495] It is understood that the specific implementation process and corresponding beneficial effects when using this communication device in the above-described communication method are described in the related description in the above method embodiment. The details are not repeated here.

[0496] The communication device 1200 shown in FIG. 12 may further be configured to perform the target NRF operation of FIG. 16. For example, communications device 1200 is the target network element of a network repository function.

[0497] Processing unit 1202 configures the identifier of the target mobility management network element (eg, the target AMF network element) in the second area. When service of a terminal device is transferred from a source network access device in a first region to a target network access device in a second region, the communication unit 1203 is configured to receive a request message from a source mobility management network element (eg, a source AMF network element) in the first region; and the communication unit 1203 is configured to send an identifier of the target mobility network element to the source mobility network element.

[0498] In an exemplary implementation, the first region is a source PLMN and the second region is a target PLMN.

[0499] It is understood that the specific implementation process and corresponding beneficial effects when using this communication device in the above-described communication method are described in the related description in the above method embodiment. The details are not repeated here.

[0500] Referring to the schematic diagram of a communication device shown in FIG. 15, the communication device may be a mobility management network element (eg, source AMF or target AMF) or a network repository network element (eg, source NRF) shown in FIG. 16. For a specific description of the communication device, refer to the description of FIG. 15. The details are not repeated here.

[0501] One skilled in the art will understand that various reference numerals such as “first” and “second” in this application are used only to differentiate for ease of description and are not used to limit the scope of embodiments of this application or sequence representation . The term "and/or" describes an associative relationship to describe associated objects and represents that three relationships can exist. For example, A and/or B can represent the following three cases: Only A exists, both A and B exist, and only B exists. The "/" symbol typically indicates an "or" relationship between associated objects. The phrase "at least one" refers to one or more, and the phrase at least two refers to two or more. “At least one,” “any,” or similar expression means any combination of these elements, including any combination of a single element (amount) or a plurality of elements (amount). For example, at least one (one component) of a, b, or c may indicate: a, b, c, a-b, a-c, b-c, or a-b-c, where a, b, and c may be singular or plural. "Many" refers to two or more, and the other quantity is similar. Also, for element in the singular form, unless otherwise explicitly stated in the context, element does not mean “one or only one” but rather “one or more.” For example, "device" means one or more such devices.

[0502] All or some of the above embodiments may be implemented using software, hardware, firmware, or any combination thereof. When software is used to implement embodiments, all or some of the embodiments may be implemented in the form of a computer program product. A computer program product includes one or more computer instructions. When the instructions of a computer program 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 specialized computer, a network of computers, or other programmable devices. Computer instructions may be stored on a computer-readable medium or may be transmitted from one computer-readable medium to another computer-readable 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, fiber optic, or digital subscriber line (DSL) ) or wirelessly (such as infrared, radio and microwave or the like). Computer-readable media can be any usable media accessible to a computer, or a storage device, such as a server or data center, combining one or more usable media. The media used may be a magnetic media (eg, a soft disk, a hard disk, or a magnetic tape), an optical media (eg, a DVD), a semiconductor media (eg, a Solid State Disk (SSD)), or the like.

[0503] Various illustrative logical blocks and circuits described in embodiments of the present invention may implement or perform the described functions using a general purpose processor, digital signal processor, special purpose integrated circuit (ASIC), field programmable logic integrated circuit (FPGA), or other a programmable logic device, a discrete logic gate or transistor logic, a discrete hardware component, or a solution with any combination of the above. The general purpose processor may be a microprocessor. Optionally, the general purpose processor may alternatively be any conventional processor, controller, microcontroller, or state machine. The processor may alternatively be implemented by a combination of computing devices, such as a digital signal processor and a microprocessor, a plurality of microprocessors, one or more microprocessors together with a digital signal processor core, or any other similar configuration.

[0504] The steps of the methods or algorithms described in the embodiments of this application may be directly embedded in hardware, a software module executed by a processor, or a combination thereof. The software module may be stored in a RAM memory, flash memory, ROM memory, EPROM memory, EEPROM memory, register, hard disk, removable magnetic disk, CD-ROM, or any other type of storage medium in the prior art. For example, a storage medium may be coupled to a processor such that the processor may read information from the storage medium or may write information to the storage medium. Optionally, the storage medium can alternatively be integrated into the processor. The processor and storage media can be housed in an ASIC.

[0505] These computer program instructions may alternatively be loaded onto a computer or other programmable data processing device such that a series of operations and steps are performed on the computer or other programmable data processing device, thereby generating computer-implemented processing. Therefore, instructions executed on a computer or other programmable device provide steps for implementing a particular function in one or more procedures in flowcharts and/or in one or more blocks in flowcharts.

[0506] Although this application has been described with reference to specific functions and embodiments thereof, it is understood that various modifications and combinations may be made to this application without departing from the spirit and scope of this application. Accordingly, the description and accompanying drawings are merely exemplary of the description of this application as defined by the appended claims and are intended to constitute any and all modifications, variations, combinations or equivalents that fall within the scope of this application. It will be appreciated that one skilled in the art may make various modifications and changes to this application without departing from the scope of this application. These modifications and variations of this application are intended to be covered by this application provided that these modifications and variations of this application come within the scope of the claims of this application and equivalent technologies.

Claims (35)

1. Communication method containing: when service of a terminal device is transferred from a source network access device in a first region to a target network access device in a second region, receiving, by a target mobility network element in a second region, from a source mobility network element in a first region a set of segments for a shared home landline mobile network use (HPLMN) of the terminal device, wherein the set of segments for the HPLMN corresponds to the allowed network segment selection assistance information (NSSAI) of the terminal device in the first area; And obtaining, by the target mobility network element, an NSSAI-granted terminal device in the second area based on the segment set for the HPLMN. 2. The method of claim 1, wherein obtaining, by the target mobility network element, an NSSAI-granted terminal device in the second segment set-based region for the HPLMN, comprises: determining by the target mobility network element an NSSAI-authorized terminal device in the second area based on the set of segments for the HPLMN and the configuration information. 3. The method of claim 2, wherein the configuration information comprises a mapping between the allowed NSSAI of the terminal device in the second area and said set of segments for the HPLMN; or the configuration information contains a roaming agreement between the second region and the HPLMN, and the roaming agreement is used to determine the mapping between the NSSAI allowed of the terminal device in the second region and the segment set for the HPLMN. 4. The method of claim 1, wherein obtaining, by the target mobility network element, an NSSAI-authorized terminal device in the second segment set-based region for the HPLMN, comprises: the target mobility management network element sending first information to the target network element selecting a segment in a second region, the first information containing a set of segments for the HPLMN; And the target network element receiving from the target network element a selection of a NSSAI-allowed segment of the terminal device in the second region. 5. The method according to claim 4, wherein the method additionally contains receiving, by the target mobility management network element from the target segment selection network element, a mapping between said set of segments for the HPLMN and an NSSAI-enabled terminal device in the second region. 6. Method according to any one of paragraphs. 1-5, in which the first region is a source PLMN and the second region is a target PLMN. 7. Communication method containing, when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, sending the source mobility network element a set of segments for the home public land mobile network (HPLMN) of the terminal device to the target mobility network element in a second region, wherein the set of segments for the HPLMN corresponds to the allowed Network Segment Selection Assistance Information (NSSAI) of the terminal device in the first region, and the set of segments for the HPLMN is used to determine the allowed NSSAI of the terminal device in the second region. 8. The method of claim 7, wherein the first region is a source PLMN and the second region is a target PLMN. 9. Communication method containing: when service of a terminal device is transferred from a source network access device in a first area to a target network access device in a second area, sending, by the source mobility control network element in the first area, a set of segments for the home public land mobile network (HPLMN) of the terminal device in the target network a mobility control element in a second area, wherein the set of segments for the HPLMN corresponds to an allowed Network Segment Selection Assistance Information (NSSAI) of the terminal device in the first area; receiving, by the target mobility network element in the second region, from the source mobility network element in the first region, a set of segments for the HPLMN of the terminal device; And obtaining, by the target mobility network element, an NSSAI-granted terminal device in the second area based on the segment set for the HPLMN. 10. The method of claim 9, wherein obtaining, by the target mobility network element, an NSSAI-granted terminal device in the second segment set-based region for the HPLMN, comprises: determining by the target mobility network element an NSSAI-authorized terminal device in the second area based on the set of segments for the HPLMN and the configuration information. 11. The method of claim 10, wherein the configuration information comprises a mapping between an allowed NSSAI of the terminal device in the second area and said segment set for the HPLMN; or the configuration information contains a roaming agreement between the second region and the HPLMN, and the roaming agreement is used to determine the mapping between the NSSAI allowed of the terminal device in the second region and the segment set for the HPLMN. 12. The method of claim 9, wherein obtaining, by the target mobility network element, an NSSAI-granted terminal device in the second segment set-based region for the HPLMN, comprises: the target mobility management network element sending first information to the target network element selecting a segment in a second region, the first information containing a set of segments for the HPLMN; And the target network element receiving from the target network element a selection of a NSSAI-allowed segment of the terminal device in the second region. 13. The method according to claim 12, wherein the method additionally contains receiving, by the target mobility management network element from the target segment selection network element, a mapping between said set of segments for the HPLMN and an NSSAI-enabled terminal device in the second region. 14. Method according to any one of paragraphs. 9-13, in which the first region is a source PLMN and the second region is a target PLMN. 15. A communications device comprising at least one processor and a memory storing computer instructions that, when executed by the at least one processor, cause the device to perform the method described in any one of paragraphs. 1-6. 16. A communications device comprising at least one processor and a memory storing computer instructions that, when executed by the at least one processor, cause the device to perform the method described in claim 7 or 8. 17. A computer-readable medium containing an instruction, wherein, when the instruction is executed on a computer, it is possible for that computer to execute the method according to any one of claims. 1-6. 18. A computer-readable medium containing an instruction, wherein, when the instruction is executed on a computer, allowing that computer to perform the method of claim 7 or 8. 19. A communication system, characterized in that it contains a target network mobility control element and a source network mobility control element, wherein the target network mobility control element is configured to implement the method according to any one of claims. 1-6; and the source network mobility management element is configured to implement the method according to claim 7 or 8.

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