CN114391279B

CN114391279B - Method and device for discovering target AMF

Info

Publication number: CN114391279B
Application number: CN202080062897.4A
Authority: CN
Inventors: 姜志健; 李章原
Original assignee: Huawei Technologies Co Ltd
Current assignee: Huawei Technologies Co Ltd
Priority date: 2020-08-17
Filing date: 2020-08-17
Publication date: 2024-04-12
Anticipated expiration: 2040-08-17
Also published as: WO2022036508A1; CN114391279A

Abstract

The application discloses a method and a device for discovering a target AMF, when terminal equipment needs to be switched from source access network equipment in a first network to target access network equipment in a second network, a first network element in the first network acquires a target identification of a first slice of the terminal equipment in the first network in the second network, and then the first network element determines the target AMF in the second network based on the target identification, wherein the target AMF supports the first slice. Because the first network element determines the target AMF in the second network based on the target identification, the first network element can accurately hit the AMF supporting the first slice in the target network, ensure that the subsequent switching process cannot fail due to the selection error of the target AMF, solve the problem that the target AMF is found inaccurately when the terminal equipment switches access network equipment across networks, and improve the KPI of network switching.

Description

Method and device for discovering target AMF

Technical Field

The present application relates to the field of communications technologies, and in particular, to a method and apparatus for discovering target access and mobility management functions (Access and Mobility Management Function, AMF).

Background

When a terminal device switches access Network devices across networks, a Target AMF (T-AMF) in a Target Network after switching and a Source AMF (Source AMF) in a Source Network before switching are required to simultaneously support at least one Network Slice (NS) of the terminal device.

The cross-network handover comprises two kinds of handover between networks of different operators and handover between different sub-networks in the same operator network. In a switching scene among different operator networks, the source network does not carry slice information of the terminal equipment when the target AMF is found, so that the target AMF selected by the source AMF can not provide the original slice service for the terminal equipment with high probability, and the switching failure rate is high. In the switching scene between different subnets in the same operator network, the source network can carry the slice information of the terminal equipment in the source network when the target AMF is found, but in practice, different network slice plans may exist between different subnets, so in the switching process of the cross-subnets, the problems of switching failure or misuse of network slices and the like are often caused by the fact that the target network cannot identify the slices of the source network.

In the prior art, when terminal equipment switches access network equipment across networks, the problem of inaccurate target AMF discovery exists.

Disclosure of Invention

The embodiment of the application provides a method and a device for discovering an AMF (advanced mobile switching center), which are used for solving the problem that a terminal device discovers a target AMF inaccurately when switching access network devices across networks.

In a first aspect, a method for discovering an AMF is provided, including: when the terminal equipment needs to be switched from source access network equipment in a first network to target access network equipment in a second network, a first network element in the first network acquires a target identification of a first slice of the terminal equipment in the first network in the second network, and then the first network element determines a target AMF in the second network based on the target identification, wherein the target AMF supports the first slice.

In the embodiment of the application, because the first network element determines the target AMF in the second network based on the target identification of the first slice in the second network, the first network element can accurately hit the AMF supporting the first slice in the target network and take the AMF as the target AMF, thereby ensuring that the subsequent switching flow cannot fail due to the selection error of the target AMF, solving the problem that the target AMF is inaccurate when the terminal equipment switches access network equipment across networks, and improving the KPI of network switching.

In a possible implementation manner, the first network element in the first network acquires the target identifier of the first slice in the second network, which specifically may include: the first network element sends a first request message to a source network slice selection function NSSF in a first network, wherein the first request message comprises a source identifier of a first slice in the first network; the first network element receives a first response message from the source NSSF, wherein the first response message comprises a target identifier of a first slice in a second network, and the second network supports the first slice.

In this embodiment, the first network element obtains the target identifier of the first slice in the second network through the source NSSF, and the method is simple and reliable.

In a possible implementation manner, the source NSSF stores a mapping relationship between slice identifiers of the first network and slice identifiers of the second network; or, the target NSSF in the second network stores a mapping relationship between the slice identifier of the first network and the slice identifier of the second network, and the first response message is generated by the source NSSF according to the target identifier of the first slice in the second network queried from the target NSSF.

In this embodiment, the source NSSF may determine, for the first network element, the target identifier of the first slice in the second network based on the mapping relationship stored in the source NSSF, or may initiate a request to the target NSSF to further obtain, through the target NSSF, the target identifier of the first slice in the second network, thereby improving flexibility of the scheme.

In a possible implementation manner, the first network element in the first network acquires the target identifier of the first slice in the second network, which specifically may include: the first network element determines a target identifier of the first slice in the second network according to a mapping relationship among a source identifier of the first slice in the first network, a slice identifier of the first network and a slice identifier of the second network.

In this embodiment, the first network element may directly determine the target identifier of the first slice in the second network based on the mapping relationship, and the method is simple and reliable.

In a possible implementation manner, the first network element stores a mapping relationship between slice identifiers of the first network and slice identifiers of the second network.

In this embodiment, the first network element may directly determine the target identifier of the first slice in the second network based on the mapping relationship stored in the first network element, so that the interaction flow may be reduced, and the method is more efficient.

In a possible implementation manner, the first network element is a source AMF or a source network repository function NRF in the first network.

It should be understood that the source AMF or source NRF herein is only an example and not limiting, and that the embodiments of the present application do not exclude the possibility of other implementations.

In a possible implementation manner, before the first network element in the first network obtains the target identifier of the first slice of the terminal device in the first network in the second network, the method further includes: the method comprises the steps that a first network element determines that a public land mobile network PLMN identifier of a first network is different from a PLMN identifier of a second network; alternatively, the first network element determines that the PLMN identity of the first network and the PLMN identity of the second network are the same and that the tracking area identity TAI of the first network and the TAI of the second network are different.

In this embodiment, when the first network element determines that the terminal device is Inter-PLMN handover (i.e., the PLMN identifier of the first network and the PLMN identifier of the second network are different) or Intra-PLMN handover (i.e., the PLMN identifier of the first network and the PLMN identifier of the second network are the same and the TAI of the first network and the TAI of the second network are different), the target identifier of the first slice in the second network is acquired, so that the reliability of the scheme is further ensured.

In a second aspect, a method for discovering a target AMF is provided, including: when terminal equipment needs to be switched from source access network equipment in a first network to target access network equipment in a second network, a second network element receives a request message, wherein the request message comprises a source identifier of a first slice of the terminal equipment in the first network, and the second network element stores a mapping relation between the slice identifier of the first network and the slice identifier of the second network; the second network element determines a target identifier of the first slice in the second network according to the source identifier and the mapping relation; and the second network element generates a response message according to the target identifier, and the second network element sends the response message.

In a possible implementation manner, the second network element selects a function NSSF for a source network slice in the first network; the second network element receives a request message, including: the source NSSF receives a first request message from a first network element; the second network element generates a response message according to the target identifier, and the second network element sends the response message, including: and the source NSSF generates a first response message according to the target identifier, and the source NSSF sends the first response message to the first network element.

In a possible implementation manner, the second network element is a target NSSF in the second network; the second network element receives a request message, including: the target NSSF receiving a second request message from a source NSSF in the first network; the second network element generates a response message according to the target identifier, and the second network element sends the response message, including: and the target NSSF generates a second response message according to the target identifier, and the target NSSF sends the second response message to the source NSSF.

In a third aspect, a communication device is provided, which is located in a first network, and may be, for example, a first network element or a chip arranged inside the first network element, the device comprising means for performing the method according to the first aspect or any one of the possible implementations of the first aspect.

Illustratively, the apparatus may include:

an obtaining unit, configured to obtain, when a terminal device needs to be handed over from a source access network device in the first network to a target access network device in a second network, a target identifier of a first slice of the terminal device in the first network in the second network;

a determining unit, configured to determine a target AMF in the second network based on the target identifier, where the target AMF supports the first slice.

In a possible implementation manner, the acquiring unit is specifically configured to: transmitting a first request message to a source network slice selection function NSSF in the first network, wherein the first request message comprises a source identifier of the first slice in the first network; a first response message from the source NSSF is received, the first response message including a target identification of the first slice in the second network, wherein the second network supports the first slice.

In a possible implementation manner, the acquiring unit is specifically configured to:

and determining the target identification of the first slice in the second network according to the mapping relation among the source identification of the first slice in the first network, the slice identification of the first network and the slice identification of the second network.

In a possible implementation manner, the apparatus further includes a storage unit, configured to store a mapping relationship between slice identifiers of the first network and slice identifiers of the second network.

In a possible implementation manner, the device is a source AMF or a source network repository function NRF in the first network.

In a possible embodiment, the determining unit is further configured to: before the acquiring unit acquires the target identifier of the first slice of the terminal equipment in the first network in the second network, determining that the public land mobile network PLMN identifier of the first network is different from the PLMN identifier of the second network; or determining that the PLMN identity of the first network and the PLMN identity of the second network are the same and the tracking area identity TAI of the first network and the TAI of the second network are different.

In a fourth aspect, a communication device is provided, which is located in a first network or a second network, and may be, for example, the second network element or a chip arranged inside the second network element, the device comprising means for performing the method according to any one of the possible implementations of the second aspect or the second aspect.

Illustratively, the apparatus may include:

a receiving unit, configured to receive a request message when a terminal device needs to be handed over from a source access network device in the first network to a target access network device in the second network, where the request message includes a source identifier of a first slice of the terminal device in the first network, and the apparatus stores a mapping relationship between a slice identifier of the first network and a slice identifier of the second network;

the processing unit is used for determining a target identifier of the first slice in the second network according to the source identifier and the mapping relation; generating a response message according to the target identifier;

and the sending unit is used for sending the response message.

In a possible implementation, the apparatus selects a function NSSF for a source network slice in the first network; the receiving unit is specifically configured to: receiving a first request message from a first network element; the sending unit is specifically configured to: and sending the first response message to the first network element.

In a possible implementation manner, the device is a target NSSF in the second network; the receiving unit is specifically configured to: receiving a second request message from a source NSSF in the first network; the sending unit is specifically configured to: and sending the second response message to the source NSSF.

In a fifth aspect, there is provided a communication apparatus comprising:

at least one processor; and a communication interface communicatively coupled to the at least one processor; the at least one processor, by executing the instructions stored in the memory, causes the apparatus to perform the method as described in the first aspect or any one of the possible implementations of the first aspect through the communication interface.

Optionally, the memory is located outside the device.

Optionally, the apparatus includes the memory, the memory being coupled to the at least one processor, the memory storing instructions executable by the at least one processor.

In a sixth aspect, there is provided a communication apparatus comprising:

at least one processor; and a communication interface communicatively coupled to the at least one processor; the at least one processor, by executing the instructions stored in the memory, causes the apparatus to perform the method as in the second aspect or any one of the possible implementations of the second aspect through the communication interface.

Optionally, the memory is located outside the device.

In a seventh aspect, a computer readable storage medium is provided, comprising a program or instructions which, when run on a computer, cause the method as in the first aspect or any one of the possible implementations of the first aspect to be performed.

In an eighth aspect, there is provided a computer readable storage medium comprising a program or instructions which, when run on a computer, cause the method as in the second aspect or any one of the possible implementations of the second aspect to be performed.

In a ninth aspect, there is provided a chip coupled to a memory for reading and executing program instructions stored in the memory such that the method of the first aspect or any one of the possible implementations of the first aspect is performed.

In a tenth aspect, there is provided a chip coupled to a memory for reading and executing program instructions stored in the memory such that the method of the second aspect or any one of the possible implementations of the second aspect is performed.

In an eleventh aspect, there is provided a computer program product comprising instructions which, when run on a computer, cause the method of the first aspect or any one of the possible implementations of the first aspect to be performed.

In a twelfth aspect, there is provided a computer program product comprising instructions which, when run on a computer, cause the method of the second aspect or any one of the possible implementations of the second aspect to be performed.

Drawings

FIG. 1 is a schematic diagram of the content of target information;

FIG. 2A is a schematic diagram of an Intra-AMF handover;

FIG. 2B is a schematic diagram of an Inter-AMF handover;

FIG. 3 is a schematic diagram of one possible network slice deployment approach;

fig. 4 is a flow chart of Inter-PLMN handover;

fig. 5 is a flow chart of Intra-PLMN handover;

FIG. 6 is a network architecture diagram of one possible communication system applicable to embodiments of the present application;

fig. 7 is a flowchart of a method for discovering a target AMF according to an embodiment of the present application;

FIG. 8 is a flow chart of a handoff preparation phase;

FIG. 9 is a flow chart of a handoff execution phase;

FIG. 10 is a flowchart of a specific method for discovering a target AMF according to an embodiment of the present application;

FIG. 11 is a flowchart of another specific method for discovering a target AMF according to an embodiment of the present application;

FIG. 12 is a flowchart of another specific method for discovering a target AMF according to an embodiment of the present application;

fig. 13 is a schematic structural diagram of a communication device according to an embodiment of the present application;

fig. 14 is a schematic structural diagram of another communication device according to an embodiment of the present application;

fig. 15 is a schematic structural diagram of another communication device according to an embodiment of the present application;

fig. 16 is a schematic structural diagram of another communication device according to an embodiment of the present application.

Detailed Description

Handover (Handover) is a basic concept in a telecommunication network, and is a scheme for guaranteeing service continuity of terminal equipment, namely: the Source access network device (Source NG-RAN, S-NG-RAN) senses mobility of the terminal device through measurement data such as signal strength of the terminal device, and when the terminal device leaves the access network device to enter a coverage area of an adjacent access network device, the Source access network device selects a Target access network device (Target NG-RAN, T-NG-RAN) for the terminal device, and notifies the core network and the Target access network device of preparing resources completely and then notifies the terminal device of accessing the Target access network device.

In the handover procedure, the source access network device sends a handover request message to the AMF to send the Target information (Target ID) of the handover to the AMF. Fig. 1 is a schematic diagram of the content of target information, where the target information includes information such as a target access network device identifier (e.g., RAN Node ID, eNB ID, RNC-ID), a target tracking area identifier (Tracking Area Identity, TAI), and the target access network device identifier further includes a public land mobile network (Public Land Mobile Network, PLMN) identifier of the target network.

After the AMF receives the handover request message (Handover Required) from the source access network device, checking whether the target access network device has an N2 connection with itself, if so, defining handover to Intra-AMF (Intra-AMF) handover, as shown in fig. 2A, only the access network device needs to be handed over, but not the AMF; otherwise, an Inter-AMF (Inter-AMF) handover is required, as shown in fig. 2B, for switching access network devices and for switching AMFs.

In the switching flow of Inter-AMF, the source AMF needs to find a target AMF according to the switching target information provided by the source access network equipment, then the target AMF informs the target access network equipment to prepare resources in advance, and the source access network equipment informs the terminal equipment to switch to the target access network equipment.

The basic concept of handover is introduced above. In Fifth Generation mobile communication technology (5G) networks, the third Generation partnership project (3rd Generation Partnership Project,3GPP) protocol introduced the concept of Network Slicing (NS) (Network slicing may also be referred to herein simply as "slicing"). The network slice is simply understood to be a virtual network, and by allocating different resources to the virtual networks, the differentiated application requirements of various industries on the telecommunication network can be met. The network slices are identified by single network slice selection assistance information (Single Network Slice Selection Assistance Information, S-nsai), which may be colloquially referred to as network slice identification.

There are differences in Network slices supported by various Network Functions (NFs) in a telecommunications Network. For example, referring to fig. 3, an AMF in the network 1 supports slice 1 (hereinafter abbreviated NS 1), NS2 (hereinafter abbreviated NS 2), and an AMF in the network 2 supports NS3 (hereinafter abbreviated NS 3).

In the Inter-AMF handover process, the source AMF needs to find a target AMF that can satisfy the current slice used by the terminal device, and the handover can be successful, for example, when the terminal device needs to move from the access network device of the network 1 to the access network device of the network 2, the terminal device is using the NS1, but the source AMF selects a target AMF that only supports the NS2 for the source AMF, and the handover will fail. Based on this, the source AMF needs to carry network slice information that the terminal device is using when selecting the target AMF, so as to ensure that the target AMF can support at least one slice that the terminal device is using.

In practice, however, most of the network slices are planned by the operators, except for a few standard slices, and the identities of the same slice in the networks of different operators may be different based on the planning of the different operators, and the identities of the different slices in the networks of different operators may also be the same. For example, chinese mobile plans NS1 as a medical network slice, but hong kong telecommunications department (PCCW) plans NS9 as a medical network slice. In addition, the cross-network scenario includes handover between different subnets of the same operator (i.e. different PLMNs) as well as handover between different operators, such as planning differences of network slicing between provinces of china mobile. This presents a problem in that during a handover across networks, the source AMF finds the target network element to be unreliable based on the network slice identity of the home network to other networks.

For the scene of switching access network equipment of terminal equipment across networks, the following two switching schemes currently exist:

in case of handover across operator networks (i.e. Inter-PLMN handover), the handover scheme given by 3GPP is: the source AMF discovers the target AMF through a source network repository function (NF Repository Function, NRF) and the target NRF, and network slice information is not carried in the discovery request, so that the target AMF selected by the source AMF can not provide the original slice service for the terminal equipment with high probability. If the target AMF initially selected by the source AMF cannot provide the original slice service for the terminal device, the source AMF may reselect the target AMF capable of supporting the relevant network slice by means of AMF redirection (REroute). However, in practice, not all AMFs support the AMF redirection function, so if the initially selected AMF cannot provide the corresponding network slice service and does not support the AMF redirection function, the handover procedure may fail. In addition, for the AMF supporting the AMF redirection function, since the initially selected AMF is not an accurate AMF, the source has a defect (such as inaccurate discovery parameters), so even the subsequent reselection is not necessarily able to select an accurate AMF. This increases the probability of handover failure in the network, as well as increases the handover delay.

Exemplary, referring to fig. 4, a flowchart for Inter-PLMN handover includes:

s401, source access network equipment sends a switching request to a source AMF, wherein the switching request contains switching Target information (Target ID);

s402, the source AMF determines that the target access network equipment is connected with the source AMF without N2 according to the target information, and determines that the target AMF needs to be found through NRF;

s403, the source AMF sends a discovery request to the source NRF, wherein the discovery request comprises a query condition which can comprise an identifier of a target PLMN (such as PLMN 2), a target network function type (such as AMF) and the like;

s404, the source NRF sends a discovery request to the target NRF, wherein the discovery request comprises a query condition which can comprise an identifier of a target PLMN (such as PLMN 2), a target network function type (such as AMF) and the like;

s405, the target NRF determines that AMFs in the PLMN2 network all meet the query condition, and determines to send the information of the AMFs in the PLMN2 network to the source NRF (for example, an AMF list supported by the PLMN2 network can be sent to the source NRF);

s406, the target NRF sends a discovery response to the source NRF, wherein the discovery response comprises information of AMFs in the PLMN2 network (for example, comprises an AMF list supported by the PLMN2 network);

s407, the source NRF sends a discovery response to the source AMF, wherein the discovery response comprises information of the AMF in the PLMN2 network;

S408, the source AMF selects one AMF from the AMFs in the discovery response according to factors such as priority, weight, load and the like to serve as a target AMF, for example, a target AMF1;

s409, the source AMF sends a request (Namf_communication_ CreateUEContext Request) for creating the UE context to the target AMF1; the target AMF1 receives a request from a source AMF;

s410, if the target AMF1 does not support the slice used by the current protocol data unit (Protocol Data Unit, PDU) session, the current PDU session handover fails; an extreme case is: the target AMF1 does not support slicing of all PDU sessions being used by the terminal, and then the entire handover procedure fails.

For the 2 nd, intra-PLMN (Intra-PLMN) handover) scenario, the handover scheme currently presented is: the source AMF discovers the target AMF through the source NRF and the target NRF, and the discovery request carries network slice information. However, if an operator is internally subdivided into a plurality of subnets according to factors such as coverage areas, and different network slicing schemes exist among different subnets, the problem of handover failure or misuse of network slicing caused by that the target network cannot identify the slicing of the source network in the handover process of the cross-subnets can be solved.

Exemplary, referring to fig. 5, a flow chart for Intra-PLMN handover, includes:

s501, source access network equipment sends a switching request to a source AMF, wherein the switching request contains switching Target information (Target ID);

s502, the source AMF determines that the target access network equipment is connected with the source AMF without N2 according to the target information, and determines that the target AMF needs to be found through NRF;

s503, the source AMF sends a discovery request to the source NRF, wherein the discovery request comprises query conditions which can include identifiers (such as NS1 and NS 2) of slices used by the terminal equipment in the intranet 1, target network function types (such as AMF) and the like;

s504, the source NRF sends a discovery request to the target NRF, wherein the discovery request comprises query conditions which can include identifiers (such as NS1 and NS 2) of slices used by the terminal equipment in the intranet 1, target network function types (such as AMF) and the like;

s505, the target NRF determines that all AMFs in the subnet 2 can not provide services of the NS1 and the NS2, and determines that the discovery of the target AMF fails;

due to the different network slice planning between sub-network 1 and sub-network 2, the identity of the same slice (or the same functional slice) in sub-network 1 and sub-network 2 is different. For example, the slice identity NS1 in subnet 1 and the slice identity NS3 in subnet 2 are different, but the slice identified by NS1 and the slice identified by NS3 are essentially the same slice, in other words, the AMF within subnet 2 is a service that can provide the slice identified by NS 1.

However, the sub-network 2 does not know the correspondence between the slice identifier in the sub-network 1 and the slice identifier in the sub-network 2, and the sub-network 2 determines whether the same slice is deployed in the sub-network 1 and the sub-network 2 only according to whether the same slice identifier exists in the sub-network 1 and the sub-network 2. For example, the target NRF searches whether there is NS1 or NS2 in the identities of the slices supported by the AMF in the subnet 2, discovers that the identities of the slices supported by the AMF in the home network are only NS3, and NS3 is different from NS1 and NS2, so it is determined that the AMF in the subnet 2 cannot provide the service of the slice identified by NS1 or the service of the slice identified by NS2, and it is determined that the discovery of the target AMF fails this time.

S506, the target NRF sends a discovery response to the source NRF, wherein the discovery response contains error information and is used for indicating that the discovery of the target AMF fails;

s507, the source NRF sends a discovery response to the source AMF, wherein the discovery response contains error information and is used for indicating that the discovery of the target AMF fails;

s508, the source AMF and the source access network equipment determine that the discovery of the target AMF fails, and the handover is terminated.

Since the target NRF misjudges that the AMF in the subnet 2 cannot provide the service of NS1 at S505, the terminal device cannot switch to the subnet 2. In practice, however, the AMF in subnet 2 is capable of providing the service of the slice identified by NS1 and the terminal device is capable of switching to subnet 2.

As can be seen from the above figures 4 and 5: when the terminal equipment switches access network equipment across networks, the problem that the target AMF is found inaccurately exists.

In view of this, the embodiment of the application provides a method and a device for discovering a target AMF. When the terminal equipment needs to switch the access network equipment across the network, the source network firstly maps the source identifier of the slice used by the terminal equipment in the source network to the target identifier in the target network, then discovers the target AMF in the target network based on the target identifier, so that the AMF supporting the slice used by the terminal equipment in the target network can be precisely hit, the follow-up switching process is ensured not to fail due to the selection error of the target AMF, the problem that the target AMF is inaccurate when the terminal equipment switches the access network equipment across the network is solved, and the key performance index (Key Performance Indicator, KPI) of network switching can be improved. The specific embodiments will be described in further detail below.

The technical solution of the embodiment of the application can be applied to various communication systems, for example: the technical solutions of the embodiments of the present application may be adopted in the fourth generation (4th generation,4G) communication system, the fifth generation (5th generation,5G) communication system, the sixth generation (6th generation,6G) communication system, or other future evolution systems, or other various wireless communication systems using a radio access technology, as long as the terminal device in the communication system has a requirement of discovering the target AMF.

For example, fig. 6 is a network architecture diagram of one possible communication system to which embodiments of the present application are applicable. The communication system comprises a terminal device, a source access network device, a source NRF, a source AMF, a source network slice selection function (Network Slice Selection Function, NSSF), a target NSSF, a target NRF, a target access network device and a target AMF. Wherein the source access network device, the source NRF, the source AMF, and the source NSSF are located in a first network, and the target NSSF, the target NRF, the target access network device, and the target AMF are located in a second network. The terminal device may be moved from the service area of the first network to the service area of the second network. Of course, in practice the terminal device may also be moved from the service area of the second network to the service area of the first network. For ease of description, in the following embodiments, the movement of the terminal device from the service area of the first network to the service area of the second network, i.e. the movement of the terminal device from the source access network device to the target access network device, is mainly taken as an example.

The network elements in the first network and the network elements in the second network can be deployed independently or uniformly.

For example, the first network and the second network are networks of two different operators, respectively (i.e. the terminal device switches access network devices across the operator networks), the network elements in the first network and the network elements in the second network are each deployed independently of the respective operators, in other words, the first network and the second network elements have no shared network element.

For example, if the first network and the second network are different subnets within the same operator (i.e. the terminal device switches access network devices within the operator's subnet), the first network and the second network may or may not share a network element. For example: the source AMF in the first network and the target AMF in the second network element are two different AMFs, the source NRF in the first network and the target NRF in the second network element may be the same NRF, and the source NSSF in the first network and the target NSSF in the second network element may be the same NSSF or two different NSSFs. The AMF is an access and mobility management function element of a core network in a 5G network, and includes a mobility management function of a mobility management entity (mobility management entity, MME) in a network frame in long term evolution (long term evolution, LTE), and adds an access management function. The AMF may be used to manage access control and mobility of the terminal device, for example, may perform registration, connection, reachability, mobility management of the terminal device, may provide a session management message transmission channel for the terminal device and the SMF, and may also provide authentication, authentication functions, etc. for the terminal device when accessing. It should be understood that the AMF is just a name in the 5G network, and in future communication systems, such as 6G, the access and mobility management function element of the core network may still be the AMF, or have other names, which are not limited in this application.

NSSF is a centralized management point of network slice information in the 5G core network, and supports determining network slice examples which the UE is allowed to access according to slice selection auxiliary information, subscription information and the like of the UE.

NRF, a function providing NF registration and NF discovery functions, NFs in different networks can discover each other and communicate through API interfaces.

An access network device, including for example a base station (e.g., an access point), may refer to a device in an access network that communicates over the air-interface, through one or more sectors, with wireless terminals. The base station may be configured to inter-convert the received air frames with Internet Protocol (IP) packets as a router between the terminal and the rest of the access network, which may include an IP network. The base station may also coordinate attribute management for the air interface. For example, the base station may include an evolved base station (eNB or e-NodeB, evolutional Node B) in an LTE system or an evolved LTE system (LTE-Advanced, LTE-a), or a small base station (micro/pico eNB) in an LTE system or an LTE-a system, or may also include a next generation node B (next generation node B, gNB) in an NR system, or a transmission point (transmission point, TP), or a transceiver node (transmission and receiver point, TRP), or the like, which is not limited in the embodiments of the present application.

Terminal devices, which may also be referred to as terminals, include devices that provide voice and/or data connectivity to a user, and may include, for example, a handheld device having wireless connectivity, or a processing device connected to a wireless modem. The terminal device may communicate with the core network via a radio access network (radio access network, RAN), exchanging voice and/or data with the RAN. The terminal device may include a User Equipment (UE), a wireless terminal device, a mobile terminal device, a device-to-device (D2D) terminal device, a V2X terminal device, a machine-to-machine/machine-type communications, an M2M/MTC terminal device, an internet of things (internet of things, ioT) terminal device, a subscriber unit (subscriber unit), a subscriber station (subscriber station), a mobile station (mobile station), a remote station (remote station), an Access Point (AP), a remote terminal (remote terminal), an access terminal (access terminal), a user agent (user agent), or a user equipment (user device), etc. For example, mobile telephones (or "cellular" telephones) computers with mobile terminal devices, portable, pocket, hand-held, computer-built mobile devices, and the like may be included. Such as personal communication services (personal communication service, PCS) phones, cordless phones, session initiation protocol (session initiation protocol, SIP) phones, wireless local loop (wireless local loop, WLL) stations, personal digital assistants (personal digital assistant, PDAs), and the like. But also limited devices such as devices with lower power consumption, or devices with limited memory capabilities, or devices with limited computing capabilities, etc. Examples include bar codes, radio frequency identification (radio frequency identification, RFID), sensors, global positioning systems (global positioning system, GPS), laser scanners, and other information sensing devices.

By way of example, and not limitation, in embodiments of the present application, the terminal device may also be a wearable device. The wearable device can also be called as a wearable intelligent device or an intelligent wearable device, and is a generic name for intelligently designing daily wear and developing wearable devices, such as glasses, gloves, watches, clothes, shoes, and the like, by applying wearable technology. The wearable device is a portable device that is worn directly on the body or integrated into the clothing or accessories of the user. The wearable device is not only a hardware device, but also can realize a powerful function through software support, data interaction and cloud interaction. The generalized wearable intelligent device includes full functionality, large size, and may not rely on the smart phone to implement complete or partial functionality, such as: smart watches or smart glasses, etc., and focus on only certain types of application functions, and need to be used in combination with other devices, such as smart phones, for example, various smart bracelets, smart helmets, smart jewelry, etc. for physical sign monitoring.

While the various terminal devices described above, if located on a vehicle (e.g., placed in a vehicle or mounted in a vehicle), may be considered as in-vehicle terminal devices, for example, also referred to as in-vehicle units (OBUs).

It should be understood that the network functions in fig. 6 are only examples and not limiting, and in actual cases, the first network or the second network may also comprise other network functions, such as unified data management (Unified Data Management, UDM) or the like.

In order to make the objects, technical solutions and advantages of the embodiments of the present application more apparent, the technical solutions of the embodiments of the present application will be described in further detail below with reference to the accompanying drawings.

It should be understood that the terms "system" and "network" in embodiments of the present application may be used interchangeably. "at least one" means one or more, and "a plurality" means two or more. "and/or", describes an association relationship of an association object, and indicates that there may be three relationships, for example, a and/or B, and may indicate: a alone, a and B together, and B alone, wherein a, B may be singular or plural. The character "/" generally indicates that the context-dependent object is an "or" relationship. "at least one of" or the like means any combination of these items, including any combination of single item(s) or plural items(s), such as at least one of a, b, or c, may mean: a, b, or c, or a and b, or b and c, or a and b and c.

And, unless specified to the contrary, the embodiments of the present application refer to the ordinal terms "first," "second," etc., as used to distinguish between multiple objects, and are not to be construed as limiting the order, timing, priority, or importance of the multiple objects. For example, the first priority criterion and the second priority criterion are merely for distinguishing between different criteria, and are not indicative of the difference in content, priority, or importance of the two criteria, etc.

Furthermore, the terms "comprising" and "having" in the embodiments and claims of the present application and in the drawings are not exclusive. For example, a process, method, system, article, or apparatus that comprises a list of steps or modules is not limited to only those steps or modules but may include other steps or modules not listed.

Fig. 7 is a flowchart of a method for discovering a target AMF according to an embodiment of the present application. In the following description, this method is exemplified as applied to the communication system shown in fig. 6.

S701, when the terminal device needs to be handed over from a source access network device in the first network to a target access network device in the second network, a first network element in the first network obtains a target identifier of a first slice of the terminal device in the first network in the second network.

When the terminal equipment moves from the coverage (or service coverage) of the source access network equipment to the coverage (or service coverage) of the target access network equipment in the moving process, the terminal equipment needs to be switched from the source access network equipment in the first network to the target access network equipment in the second network. As shown in fig. 6, the oval-shaped dashed box around the source access network device characterizes the coverage of the source access network device, and the oval-shaped dashed box around the target access network device characterizes the coverage of the target access network device.

When the terminal equipment needs to be switched from source access network equipment in a first network to target access network equipment in a second network, the first network element determines that the switching is cross-network switching, and then the target identification of a first slice in the first network in the second network is obtained.

The manner in which the first network element determines that the handover is a scenario of a cross-network handover includes, but is not limited to, the following two:

the first network element determines that the handover is a cross-network handover if the public land mobile network PLMN identity of the 1 st, first network is different from the PLMN identity of the second network. For example, the handover is between different operator networks.

The 2 nd, first network element determines that the PLMN identity of the first network and the PLMN identity of the second network are the same and the tracking area identity TAI of the first network and the TAI of the second network are different, the first network element determines that the handover is a cross-network handover. For example, the handover is between different sub-networks within the same operator.

In this embodiment of the present application, the second network element stores a mapping relationship between the slice identifier of the first network and the slice identifier of the second network. The second network element may be a source AMF in the first network, or a source NRF in the first network, or a source NSSF in the first network, or a target NRF in the second network, or a target NSSF in the second network, or the like, which is not limited in the embodiments of the present application.

It should be appreciated that the mapping between the slice identity of the first network and the slice identity of the second network includes, but is not limited to, the following: one slice identifier in the first network corresponds to a plurality of slice identifiers in the second network; or, one slice identifier in the second network corresponds to a plurality of slice identifiers in the first network; or, the slice identifiers of the first network are in one-to-one correspondence with the slice identifiers of the second network. The mapping relationships are not specifically limited in the embodiments of the present application, and in the following embodiments, the mapping relationships are mainly exemplified as one-to-one correspondence for convenience of description.

The first network element may be any network element in the first network, for example, a source AMF or a source NRF, which is not limited in the embodiment of the present application. Correspondingly, the first network element can determine the target identifier of the first slice in the second network according to the mapping relation between the slice identifier of the first network and the slice identifier of the second network and the source identifier of the first slice in the first network; or, the second network element may determine the target identifier of the first slice in the second network according to the mapping relationship between the slice identifier of the first network and the slice identifier of the second network, and the source identifier of the first slice in the first network, and then send the determined target identifier to the first network element.

The following list a few possible specific implementations of the first network element to obtain the target identity of the first slice in the second network.

In mode 1, the first network element is a source AMF, and the second network element is the same as the first network element, that is, the source AMF stores a mapping relationship between a slice identifier of the first network and a slice identifier of the second network.

After receiving a switching request message from source access network equipment, a source AMF determines a source identifier of a first slice used in a first network by terminal equipment in the first network; then, the source AMF searches for a target identifier of the first slice in the second network based on a mapping relationship between the slice identifier of the first network and the slice identifier of the second network, and a source identifier of the first slice in the first network.

In mode 2, the first network element is a source AMF, and the second network element is a source NSSF, i.e. the source NSSF stores a mapping relationship between a slice identifier of the first network and a slice identifier of the second network.

After receiving a switching request message from source access network equipment, a source AMF determines a source identifier of a first slice used in a first network by terminal equipment in the first network; the source AMF sends a first request message to the source NSSF, wherein the first request message comprises a source identifier of the first slice in the first network; after receiving the first request message, the source NSSF searches for a target identifier of the first slice in the second network according to a mapping relation between the slice identifier of the first network and the slice identifier of the second network and a source identifier of the first slice in the first network, generates a first response message based on the target identifier of the first slice in the second network, wherein the first response message comprises the target identifier of the first slice in the second network, and sends the first response message to the source AMF; the source AMF receives a first response message from the source NSSF and obtains from the first response message an identification of a target of the first slice in the second network.

Or after receiving the switching request message from the source access network device, the source AMF determines the source identification of a first slice used by the terminal device in the first network; the source AMF sends a first request message to the source NSSF, wherein the first request message comprises a source identifier of the first slice in the first network; after receiving the first request message, the source NSSF generates a first response message according to the mapping relation between the slice identifier of the first network and the slice identifier of the second network, wherein the first response message comprises the mapping relation between the slice identifier of the first network and the slice identifier of the second network, and sends the first response message to the source AMF; the source AMF receives a first response message from the source NSSF, and searches for a target identifier of the first slice in the second network according to a mapping relation between the slice identifier of the first network and the slice identifier of the second network and the source identifier of the first slice in the first network.

In mode 3, the first network element is a source AMF, and the second network element is a target NSSF, i.e. the target NSSF stores a mapping relationship between a slice identifier of the first network and a slice identifier of the second network.

After receiving a switching request message from source access network equipment, a source AMF determines a source identifier of a first slice used in a first network by terminal equipment in the first network; the source AMF sends a first request message to the source NSSF, wherein the first request message comprises a source identifier of the first slice in the first network; after receiving the first request message, the source NSSF sends a second request message to the target NSSF, wherein the second request message comprises a source identifier of the first slice in the first network; after receiving the second request message, the target NSSF searches the target identifier of the first slice in the second network according to the mapping relation between the slice identifier of the first network and the slice identifier of the second network and the source identifier of the first slice in the first network, generates a second response message based on the target identifier of the first slice in the second network, wherein the second response message comprises the target identifier of the first slice in the second network, and sends the second response message to the source NSSF; after receiving the second response message, the source NSSF sends a first response message to the source AMF, wherein the first response message comprises a target identifier of the first slice in the second network; the source AMF receives a first response message from the source NSSF and obtains from the first response message an identification of a target of the first slice in the second network.

Or after receiving the switching request message from the source access network device, the source AMF determines the source identification of a first slice used by the terminal device in the first network; the source AMF sends a first request message to the source NSSF, wherein the first request message comprises a source identifier of the first slice in the first network; after receiving the first request message, the source NSSF sends a second request message to the target NSSF, wherein the second request message comprises a source identifier of the first slice in the first network; after receiving the second request message, the target NSSF generates a second response message according to the mapping relation between the slice identifier of the first network and the slice identifier of the second network, wherein the second response message comprises the mapping relation between the slice identifier of the first network and the slice identifier of the second network, and sends the second response message to the source NSSF; after receiving the second response message, the source NSSF sends a first response message to the source AMF, wherein the first response message comprises a mapping relation between the slice identifier of the first network and the slice identifier of the second network; the source AMF receives a first response message from the source NSSF, and searches for a target identifier of the first slice in the second network according to a mapping relation between the slice identifier of the first network and the slice identifier of the second network and the source identifier of the first slice in the first network.

Or after receiving the switching request message from the source access network device, the source AMF determines the source identification of a first slice used by the terminal device in the first network; the source AMF sends a first request message to the source NSSF, wherein the first request message comprises a source identifier of the first slice in the first network; after receiving the first request message, the source NSSF sends a second request message to the target NSSF, wherein the second request message comprises a source identifier of the first slice in the first network; after receiving the second request message, the target NSSF generates a second response message according to the mapping relation between the slice identifier of the first network and the slice identifier of the second network, wherein the second response message comprises the mapping relation between the slice identifier of the first network and the slice identifier of the second network, and sends the second response message to the source NSSF; after receiving the second request message, the source NSSF searches for a target identifier of the first slice in the second network according to a mapping relation between the slice identifier of the first network and the slice identifier of the second network and a source identifier of the first slice in the first network, generates a first response message based on the target identifier of the first slice in the second network, wherein the first response message comprises the target identifier of the first slice in the second network, and sends the first response message to the source AMF; the source AMF receives a first response message from the source NSSF and obtains from the first response message an identification of a target of the first slice in the second network.

In mode 4, the first network element is a source NRF, and the second network element is a source NSSF, that is, the source NSSF stores a mapping relationship between a slice identifier of the first network and a slice identifier of the second network.

After receiving a switching request message from source access network equipment, a source AMF determines a source identifier of a first slice used by terminal equipment in a first network in the first network, and sends a discovery request to a source NRF, wherein the discovery request comprises the source identifier of the first slice in the first network; after receiving a discovery request from a source AMF, a source NRF sends a first request message to a source NSSF, wherein the first request message comprises a source identifier of a first slice in a first network; after receiving the first request message, the source NSSF searches for a target identifier of the first slice in the second network according to a mapping relation between the slice identifier of the first network and the slice identifier of the second network and a source identifier of the first slice in the first network, generates a first response message based on the target identifier of the first slice in the second network, wherein the first response message comprises the target identifier of the first slice in the second network, and sends the first response message to the source NRF; the source NRF receives a first response message from the source NSSF and obtains from the first response message the destination identification of the first slice in the second network.

Or after receiving a switching request message from source access network equipment, the source AMF determines a source identifier of a first slice used by the terminal equipment in a first network in the first network, and sends a discovery request to the source NRF, wherein the discovery request comprises the source identifier of the first slice in the first network; after receiving a discovery request from a source AMF, a source NRF sends a first request message to a source NSSF, wherein the first request message comprises a source identifier of a first slice in a first network; after receiving the first request message, the source NSSF generates a first response message according to the mapping relation between the slice identifier of the first network and the slice identifier of the second network, wherein the first response message comprises the mapping relation between the slice identifier of the first network and the slice identifier of the second network, and sends the first response message to the source NRF; the source NRF receives the first response message from the source NSSF, and searches the target identification of the first slice in the second network according to the mapping relation between the slice identification of the first network and the slice identification of the second network and the source identification of the first slice in the first network.

In mode 5, the first network element is a source NRF, and the second network element is a target NSSF, that is, the target NSSF stores a mapping relationship between a slice identifier of the first network and a slice identifier of the second network.

After receiving a switching request message from source access network equipment, a source AMF determines a source identifier of a first slice used by terminal equipment in a first network in the first network, and sends a discovery request to a source NRF, wherein the discovery request comprises the source identifier of the first slice in the first network; after receiving a discovery request from a source AMF, a source NRF sends a first request message to a source NSSF; after receiving the first request message, the source NSSF sends a second request message to the target NSSF, wherein the second request message comprises a source identifier of the first slice in the first network; after receiving the second request message, the target NSSF searches the target identifier of the first slice in the second network according to the mapping relation between the slice identifier of the first network and the slice identifier of the second network and the source identifier of the first slice in the first network, generates a second response message based on the target identifier of the first slice in the second network, wherein the second response message comprises the target identifier of the first slice in the second network, and sends the second response message to the source NSSF; after receiving the second request message, the source NSSF sends a first response message to the source NRF, wherein the first response message comprises a target identifier of the first slice in the second network; the source NRF receives a first response message from the source NSSF and obtains from the first response message the destination identification of the first slice in the second network.

Or after receiving a switching request message from source access network equipment, the source AMF determines a source identifier of a first slice used by the terminal equipment in a first network in the first network, and sends a discovery request to the source NRF, wherein the discovery request comprises the source identifier of the first slice in the first network; after receiving a discovery request from a source AMF, a source NRF sends a first request message to a source NSSF; after receiving the first request message, the source NSSF sends a second request message to the target NSSF, wherein the second request message comprises a source identifier of the first slice in the first network; after receiving the second request message, the target NSSF generates a second response message according to the mapping relation between the slice identifier of the first network and the slice identifier of the second network, wherein the second response message comprises the mapping relation between the slice identifier of the first network and the slice identifier of the second network, and sends the second response message to the source NSSF; after receiving the second response message, the source NSSF sends a first response message to the source NRF, wherein the first response message comprises a mapping relation between a slice identifier of the first network and a slice identifier of the second network; the source NRF receives the first response message from the source NSSF, and searches the target identification of the first slice in the second network according to the mapping relation between the slice identification of the first network and the slice identification of the second network and the source identification of the first slice in the first network.

Or after receiving a switching request message from source access network equipment, the source AMF determines a source identifier of a first slice used by the terminal equipment in a first network in the first network, and sends a discovery request to the source NRF, wherein the discovery request comprises the source identifier of the first slice in the first network; after receiving a discovery request from a source AMF, a source NRF sends a first request message to a source NSSF; after receiving the first request message, the source NSSF sends a second request message to the target NSSF, wherein the second request message comprises a source identifier of the first slice in the first network; after receiving the second request message, the target NSSF generates a second response message according to the mapping relation between the slice identifier of the first network and the slice identifier of the second network, wherein the second response message comprises the mapping relation between the slice identifier of the first network and the slice identifier of the second network, and sends the second response message to the source NSSF; after receiving the second request message, the source NSSF searches for a target identifier of the first slice in the second network according to a mapping relation between the slice identifier of the first network and the slice identifier of the second network and a source identifier of the first slice in the first network, generates a first response message based on the target identifier of the first slice in the second network, wherein the first response message comprises the target identifier of the first slice in the second network, and sends the first response message to the source NRF; the source NRF receives a first response message from the source NSSF and obtains from the first response message the destination identification of the first slice in the second network.

It should be understood that the above five manners are merely examples and are not limiting, and in practical applications the possibility that the first network element obtains the target identifier of the first slice in the second network in other manners is not excluded.

It should be noted that in the embodiment of the present application, there may be a plurality of slices used by the terminal device in the first network. For example, the slices used by the terminal device in the first network include a first slice and a second slice. Accordingly, the source AMF may search for the corresponding target identifier for each of the plurality of slices used by the terminal device in the first network, and the specific search mode for each slice may refer to the above-mentioned mode for searching for the target identifier of the first slice in the second network. For example: the source AMF searches a target identifier of the first slice in the second network based on a mapping relation between the slice identifier of the first network and the slice identifier of the second network and a source identifier of the first slice in the first network; the source AMF searches for a target identifier of the second slice in the second network based on a mapping relation between the slice identifier of the first network and the slice identifier of the second network and a source identifier of the second slice in the first network.

It should be further noted that each slice used by the terminal device in the first network does not necessarily have to have a target identifier in the second network. For example, the slice used by the terminal device in the first network includes a first slice and a second slice, but the second network only deploys the first slice and does not deploy the second slice, so the source AMF or the source NRF can only acquire the target identifier of the first slice in the second network. For example, the slices used by the terminal device in the first network include a first slice, a second slice and a third slice, but the second network only deploys the first slice and the third slice does not deploy the second slice, so the source AMF or the source NRF can only acquire the target identifiers of the first slice and the third slice in the second network. Of course, the possibility that each slice used in the first network does not have the target identity in the second network is not precluded, i.e. the second network is not deployed with any slice used by the terminal device in the first network, in which case the handover fails.

Hereinafter, taking the example that the second network deploys the first slice and the source AMF or the source NRF can acquire the target identification of the first slice in the second network.

S702, the first network element determines a target AMF in the second network based on the target identification, wherein the target AMF supports the first slice.

Specifically, after the first network element obtains the target identifier of the first slice in the second network, a process of discovering the target AMF is initiated based on the target identifier of the first slice in the second network, so that the target NRF in the second network queries the AMF capable of providing the first slice service in the second network according to the target identifier of the first slice in the second network, and returns the queried information of the AMF capable of providing the first slice service in the second network to the first network element; the first network element selects one AMF from the AMFs capable of providing the first slice service in the second network as a target AMF, performs a procedure of a handover preparation phase, for example, informs the target AMF to perform a preparation activity related to handover, updates access network equipment information of the terminal equipment, and the like. After the process of the handover preparation phase is completed, the process of accessing the terminal equipment to the target access network equipment is performed.

Referring to fig. 8, for a flow chart of a handover preparation phase, the preparation flow includes:

s801, S-AMF receives a switching request from S-NG-RAN, determines that terminal equipment needs to be switched from S-NG-RAN to T-NG-RAN, and determines that the switching is cross-network switching;

S802, S-AMF executes a process of finding a target AMF;

the specific implementation procedures of S801 to S802 may refer to the specific implementation procedures of S701 to S702, and are not described herein.

S803, the S-AMF sends a UE context creation request (Nsmf_Communication_ CreateUEContext Request) to the T-AMF;

s804, the T-AMF sends an update session management (Session Management, SM) context request (Nsmf_PDUSation_ UpdateSMContext Request) to the SMF;

s805, SMF selects a user plane function (User Plane Function, UPF) (UPF Selection);

S806A, (optional) SMF sends an N4session modification request (N4 Session Modification Request) to a protocol data unit session anchor (PDU Session Anchor, PSA) UPF;

S806B, (optional) UPF sends an N4session modification response (N4 Session Modification Response) to SMF;

S806C, (optional) the SMF sends an N4session setup request (N4 Session Establishment Request) to the Target UPF (T-UPF);

S806D, (optional) T-UPF sends an N4session setup response (N4 Session Establishment Response) to SMF;

s807, the SMF sends an update SM context response (Nsmf_PDUSation_ UpdateSMContext Response) to the T-AMF;

s808, the T-AMF performs PDU handover response monitoring (PDU Handover Response Supervision), i.e. if the handover involves multiple PDU sessions, the T-AMF waits for update response messages for these PDU sessions, respectively, and then proceeds further down.

S809, the T-AMF sends a Handover Request (Handover Request) to the T-NG-RAN;

s810, the T-NG-RAN sends a switching request acknowledgement (Handover Request Acknowledge) to the T-AMF;

S811A, T-AMF sends an update SM session context request (nsmf_pduse_ UpdateSMContext Request) to SMF;

S811B, (optional) the SMF sends an N4session modification request (N4 Session Modification Request) to the T-UPF;

S811C, (optional) T-UPF sends an N4session modification response (N4 Session Modification Response) to SMF;

S811D, (optional) SMF sends an N4session setup request (N4 Session Establishment Request) to Source-UPF (Source UPF, S-UPF);

S811E, (optional) S-UPF sends an N4session setup response (N4 Session Establishment Response) to the SMF;

S811F, SMF sends an update SM session context response (nsmf_pduse_ UpdateSMContext Response) to the T-AMF;

s812, the T-AMF sends a create UE context response (nsmf_communication_ CreateUEContext Response) to the S-AMF.

After S812, the normal switching process is started.

Referring to fig. 9, for a flow chart of a handover execution phase, a handover procedure includes:

s901, S-AMF sends a Handover Command (Handover Command) to S-NG-RAN;

s902, S-NG-RAN sends a Handover Command (Handover Command) to terminal equipment;

S902A, (optional) source base station sends an uplink RAN status transmission (Uplink RAN Status Transfer) to the source AMF;

S902B, forwarding RAN state transfer information (namf_communication_n1n2message transfer) to the target AMF through the N1N2message transfer interface;

S902C, (optional) the target AMF sends a downlink RAN status transmission to the target base station (Downlink RAN Status Transfer);

S903A, (optional) S-NG-RAN sends direct data forwarding to T-NG-RAN (Derect data forwarding);

S903B, (optional) S-NG-RAN sends indirect data forwarding (Inderect data forwarding) to S-UPF;

s904, the terminal equipment sends a Handover Confirm (Handover Confirm) to the T-NG-RAN;

s905, the T-NG-RAN sends a Handover notification (Handover Notify) to the T-AMF;

S906A, the (optional) target AMF informs the source AMF that a handover notification_ (namf_communication_n2 infofold) of the target base station is received;

S906B, the (optional) source AMF returns a reply message (namf_communication_n2 infofotify ACK) to the target AMF;

S906C, the (optional) source AMF informs the SMF of releasing the SM context_ (nsmf_pduse_ ReleaseSMContext Request) of the handover failure;

s907, the target AMF sends an SM context update request (Nsmf_PDUSESTION_ UpdateSMContext Request) to the SMF;

S908A, (optional) SMF sends an N4 session modification request (N4 Session Modification Request) _ to the target UPF;

S908B, the (optional) target UPF returns an N4 session modification response (N4 Session Modification Response) to the SMF;

S909A, (optional) SMF sends an N4 session modification request (N4 Session Modification Request) to the source UPF;

S909B, the (optional) source UPF returns an N4 session modification response (N4 Session Modification Response) to the SMF;

S910A, (optional) SMF sends an N4 session modification request (N4 Session Modification Request) to the anchor UPF;

S910B, the (optional) anchor UPF returns an N4 session modification response (N4 Session Modification Response) to the SMF;

s911, SMF returns an update SM context response (Nsmf_PDUSation_ UpdateSMContext Response) to the target AMF;

s912, registration procedure (Registration Procedure);

because the terminal equipment moves across the AMF, the replacement equipment in the terminal equipment needs to trigger the registration update procedure after the handover procedure.

S913A, (optional) SMF sends an N4 session release request (N4 Session Release Request) to S-UPF;

S913B, (optional) S-UPF sends an N4 session release response (N4 Session Release Response) to the SMF;

S914A, S-AMF sends a user context release command to S-NG-RAN (UE Context Release Command);

S914B, S-NG-RAN sends a user context release order complete to S-AMF (UE Context Release Command Complete);

S915A, (optional) SMF sends an N4 session modification request (N4 Session Modification Request) to T-UPF;

S915B, (optional) T-UPF sends an N4 session modification response (N4 Session Modification Response) to the SMF.

As can be seen from the foregoing, in the embodiment of the present application, when a terminal device needs to be switched from a source access network device in a first network to a target access network device in a second network, a first network element in the first network first obtains a target identifier of a first slice of the terminal device in the first network in the second network, and then determines a target AMF in the second network based on the target identifier, so that the AMF supporting the first slice in the target network can be accurately hit, and the AMF supporting the first slice is used as the target AMF, thereby ensuring that a subsequent switching process cannot fail due to a selection error of the target AMF, solving the problem that the target AMF is inaccurate when the terminal device switches access network devices across networks, and improving a KPI of network switching.

It should be understood that the various implementations in the embodiments of the present application may be combined with each other to achieve different technical effects.

In order to facilitate a clearer understanding of the technical solutions provided by the embodiments of the present application, several more detailed embodiments are listed below.

Example 1

Referring to fig. 10, a flowchart of a specific method for discovering a target AMF is provided in an embodiment of the application. The mapping relation between the slice identifier of the source network (first network) and the slice identifier of the target network (second network) is stored on the source NSSF, and the specific method for selecting the target AMF by the source AMF comprises the following steps:

s1001, the source access network equipment initiates a switching flow and carries switching Target information (Target ID information element is shown in fig. 1) to the source AMF.

S1002, if the source AMF judges that the Inter-AMF switching is performed according to the target information, a request message is sent to the source NSSF, and the request message contains identifiers NS1 and NS2 of the slices used by the terminal equipment in the source network.

The source NSSF has a GetTargetNSSAI service that can provide a requester with a mapping function of network slices. Here the request message sent by the source AMF to the source NSSF is used to invoke the GetTargetNSSAI service. The request message provides information such as the Target ID information of the handover, the network slices (i.e., NS1 and NS 2) used by the terminal device in the source network, and the original Serving (Serving) PLMN (i.e., PLMN of the source network) of the terminal device.

S1003, the source NSSF uses GetTargetNSSAI service to query the destination identities of NS1 and NS2 in the destination network, and returns a response message (including the network slice information NS3 mapped by NS 1) to the source AMF.

Specifically, if the PLMNs of the source network and the target network are different, the source NSSF performs conversion according to the network slice correspondence relationship agreed by the operators of the two networks; if the PLMN of the source network is the same as that of the Target network, the source NSSF then identifies whether to switch across networks and how to do network slice mapping for different regions based on the Selected TAI in the Target ID information of the switch.

The source NSSF may maintain network slice availability information for each AMF in the source network, the network slice availability information having a structural composition of a list of TAIs supported under the AMF and a list of network slices supported under each TAI. Therefore, the source NSSF can check whether the Selected TAI in the handover Target ID information is included in the network slice availability list managed by itself, and can determine whether to switch across networks.

When the source NSSF identifies terminal equipment to switch across networks, a target network slice is acquired according to the mapping relation of slice identifiers among different networks stored locally by the source NSSF.

The source NSSF returns the mapped network slice information to the source AMF, which may specifically be in the form of a list. In fig. 10, NS1 of the source network corresponds to NS3 of the target network, and services related to NS2 are not deployed in the target network, so the source NSSF cannot find slice information corresponding to NS2, and only returns a mapping network slice list NS3 corresponding to NS1 to the AMF, but does not have a mapping network slice list corresponding to NS 2.

Optionally, the target network may carry indication information in the response message, so as to indicate that the source NSSF does not return the reason for the NS2 mapped network slice information (i.e. NS2 is not deployed in the target network); or the response message does not carry the indication information, and if the source AMF judges that the network slice information mapped by the NS2 is not included in the response message, the source AMF determines that the NS2 is not deployed in the target network.

In addition, if there is a slice that does not need mapping, i.e. the identification of the slice in the target network and the source network are the same, and no conversion is needed, the source NSSF may return a list of empty mapping network slices to the source AMF for the slice, so as to save resource overhead.

Alternatively, the request message sent by the source AMF to the source NSSF may multiplex the GET interface (nnssf_nsselection) selected by the network slice existing in the source NSSF.

Illustratively, the following cells may be added to the GET interface:

slice information conversion request (slice-info-request-for-handle).

Further, the slice-info-request-for-handover may specifically include the following sub-cells:

1) Target-id: target information representing handover, consisting of Target PLMN and Target TAI;

2) allowedNssaiCurrentAccess: representing a list of slices available to the UE to be handed over in the source network, the network slice identity needs to be mapped into the target network.

Accordingly, the response message returned by the source NSSF to the source AMF may multiplex the network slice GET response that the source NSSF already has. For example, the query results may be returned through a network slice map (MappingOfSnssai) defined in 3GPP technical specification (Technical Specification, TS) 29531.

S1004, the source AMF initiates a target AMF discovery procedure to the source NRF in the source network, where the source AMF carries the target PLMN, mapped network slice information (NS 3), and the like.

S1005, the source NRF sends a discovery request to the target NRF according to the target NRF in the target network addressed by the target PLMN, where the discovery request carries network slice information NS3.

S1006, the target NRF queries the AMF which can provide the NS3 slice service in the target network according to the network slice information NS3 in the discovery request, returns an AMF list which can provide the NS3 slice service to the source NRF, and returns the AMF list to the source AMF.

And then, the source AMF selects a target AMF from the AMF list according to factors such as priority, weight, load and the like, and a subsequent switching flow is carried out. The subsequent switching process may refer to the embodiments shown in fig. 8 and 9, and will not be described herein.

In this embodiment, when the terminal device needs to switch the access network device across the network, the source NSSF in the source network maps the source identifier (NS 1) of the slice used by the terminal device in the source network to the target identifier (NS 3) in the target network, and then the source AMF performs the AMF discovery process based on the mapped slice identifier (NS 3), so that the problem that the target network cannot identify the slice of the source network to cause a switching failure or misuse of the network slice can be avoided, and the KPI of the network switching is promoted.

Example 2

Referring to fig. 11, a flowchart of another specific method for discovering a target AMF according to an embodiment of the present application is provided. The mapping relation between the slice identifier of the source network (i.e. the first network) and the slice identifier of the target network (i.e. the second network) is stored on the target NSSF, and the specific method for selecting the target AMF by the source AMF includes:

s1101, the source access network device initiates a switching flow, and carries switching Target information (Target ID information element is shown in FIG. 1) to the source AMF.

S1102, if the source AMF judges that the Inter-AMF switching is performed according to the target base station information, a request message is sent to the source NSSF, and the request message contains identifiers NS1 and NS2 of the slices used by the terminal equipment in the source network.

S1103, the source NSSF sends a request message to the target NSSF, requesting to query the target identity of the slices (such as NS1 and NS 2) used by the terminal device in the source network in the target network. The request message contains the identities NS1 and NS2 of the slices used by the terminal device in the source network.

S1104, the target NSSF uses GetTargetNSSAI service to query the target identities of NS1 and NS2 in the target network, and returns a response message (including the network slice information NS3 mapped by NS 1) to the source NSSF.

For the specific implementation of the GetTargetNSSAI service of the target NSSF, reference may be made to the specific implementation of the GetTargetNSSAI service of the source NSSF in embodiment 1, which is not described herein.

S1105, the source NSSF returns a response message (including the NS1 mapped network slice information NS 3) to the source AMF.

S1106, the source AMF initiates a target AMF discovery procedure to the source NRF in the source network, where the source AMF carries the target PLMN, the network slice information (NS 3) mapped by the NS1, and the like.

S1107, the source NRF addresses to a target NRF in the target network according to the target PLMN, and sends a discovery request to the target NRF, where the discovery request carries network slice information NS3.

S1108, the target NRF queries the AMF capable of providing the NS3 slice service in the target network according to the network slice information NS3 in the discovery request, returns an AMF list capable of providing the NS3 slice service to the source NRF, and returns the AMF list to the source AMF.

In this embodiment, when the terminal device needs to switch the access network device across networks, the target NSSF in the target network maps the source identifier (NS 1) of the slice used by the terminal device in the source network to the target identifier (NS 3) in the target network, and then the source AMF performs the AMF discovery process based on the mapped slice identifier (NS 3), so that the problem that the target network cannot identify the slice of the source network to cause a handover failure or misuse of the network slice can be avoided, and the KPI of the network handover is promoted.

Example 3

Referring to fig. 12, a flowchart of another specific method for discovering a target AMF is provided in an embodiment of the application. The mapping relation between the slice identifier of the source network (i.e. the first network) and the slice identifier of the target network (i.e. the second network) is stored on the target NSSF, and the specific method for selecting the target AMF by the source NRF includes:

s1201, the source access network device initiates a handover procedure, and carries the destination information (Target ID information element see fig. 1) of the handover to the source AMF.

S1202, the source AMF sends a discovery request to the source NRF, where the discovery request includes identifiers NS1 and NS2 of slices used by the terminal device in the source network.

S1203, the source NRF sends a request message to the source NSSF, where the request message contains the identities NS1 and NS2 of the slices used by the terminal device in the source network.

S1204, the source NSSF sends a request message to the target NSSF, where the request message includes identifiers NS1 and NS2 of slices used by the terminal device in the source network.

S1205, the target NSSF uses GetTargetNSSAI service to query the target identities of NS1 and NS2 in the target network, and returns a response message (including the network slice information NS3 mapped by NS 1) to the source NSSF.

S1206, the source NSSF returns a response message (including the NS1 mapped network slice information NS 3) to the source NRF.

S1207, after obtaining the network slice information NS3 mapped by the NS1, the source NRF sends a discovery request to the target NRF according to the target NRF addressed to the target network by the target PLMN, where the discovery request carries the network slice information NS3.

S1208, the target NRF queries the AMF which can provide the NS3 slice service in the target network according to the network slice information NS3 in the discovery request, returns an AMF list which can provide the NS3 slice service to the source NRF, and returns the AMF list to the source AMF.

In this embodiment, when the terminal device needs to switch the access network device across networks, the target NSSF in the target network maps the source identifier (NS 1) of the slice used by the terminal device in the source network to the target identifier (NS 3) in the target network, and then the source NRF executes the AMF discovery process based on the mapped slice identifier (NS 3), so that the problem that the target network cannot identify the slice of the source network to cause a switching failure or misuse of the network slice can be avoided, and the KPI of network switching is promoted.

The method provided by the embodiment of the present application is described above with reference to fig. 7 to 12, and the apparatus provided by the embodiment of the present application is described below with reference to fig. 13 to 16.

Based on the same technical concept, the embodiments of the present application provide a communication device 1300, where the device 1300 may be a first network element or a chip (the first network element is, for example, a source AMF or a source NRF) disposed inside the first network element. The apparatus 1300 has functions of implementing the first network element in the embodiments shown in fig. 7 to 12, for example, the apparatus 1300 includes modules or units or means (means) corresponding to the steps executed by the first network element in the embodiments shown in fig. 7 to 12, where the functions or units or means may be implemented by software, or implemented by hardware, or implemented by executing corresponding software by hardware.

For example, referring to fig. 13, an apparatus 1300 may include:

an obtaining unit 1301, configured to obtain, when a terminal device needs to be handed over from a source access network device in the first network to a target access network device in a second network, a target identifier of a first slice of the terminal device in the first network in the second network;

a determining unit 1302, configured to determine a target AMF in the second network based on the target identifier, where the target AMF supports the first slice.

In a possible implementation manner, the obtaining unit 1301 is specifically configured to:

transmitting a first request message to a source network slice selection function NSSF in the first network, wherein the first request message comprises a source identifier of the first slice in the first network;

a first response message from the source NSSF is received, the first response message including a target identification of the first slice in the second network, wherein the second network supports the first slice.

In a possible implementation manner, the source NSSF stores a mapping relationship between slice identifiers of the first network and slice identifiers of the second network; or,

and storing a mapping relation between the slice identifier of the first network and the slice identifier of the second network by a target NSSF in the second network, wherein the first response message is generated by the source NSSF according to the target identifier of the first slice in the second network inquired from the target NSSF.

In a possible implementation manner, the determining unit 1302 is further configured to:

before the acquiring unit 1301 acquires the target identifier of the first slice in the first network in the second network of the terminal device, determining that the public land mobile network PLMN identifier of the first network is different from the PLMN identifier of the second network; or determining that the PLMN identity of the first network and the PLMN identity of the second network are the same and the tracking area identity TAI of the first network and the TAI of the second network are different.

All relevant contents of each step related to the above method embodiment may be cited to the functional descriptions of the corresponding functional modules, which are not described herein.

Based on the same technical concept, the embodiments of the present application provide a communication device 1400, where the device 1400 may be a second network element or a chip disposed inside the second network element, and the second network element is, for example, a source NSSF or a target NSSF. The apparatus 1400 has a function of implementing the second network element in the embodiment shown in fig. 7 to 12, for example, the apparatus 1400 includes a module or a unit or means (means) corresponding to the step executed by the second network element in the embodiment shown in fig. 7 to 12, where the function or unit or means may be implemented by software, or implemented by hardware, or may be implemented by executing corresponding software by hardware.

For example, referring to fig. 14, the apparatus 1400 may include:

a receiving unit 1401, configured to receive a request message when a terminal device needs to be handed over from a source access network device in the first network to a target access network device in the second network, where the request message includes a source identifier of a first slice of the terminal device in the first network, and the apparatus stores a mapping relationship between a slice identifier of the first network and a slice identifier of the second network;

a processing unit 1402, configured to determine, according to the source identifier and the mapping relationship, a target identifier of the first slice in the second network; generating a response message according to the target identifier;

a sending unit 1403 is configured to send the response message.

In a possible implementation, the apparatus selects a function NSSF for a source network slice in the first network;

the receiving unit 1401 is specifically configured to: receiving a first request message from a first network element;

the transmitting unit 1403 specifically functions to: and sending the first response message to the first network element.

In a possible implementation manner, the device is a target NSSF in the second network;

the receiving unit 1401 is specifically configured to: receiving a second request message from a source NSSF in the first network;

the transmitting unit 1403 specifically functions to: and sending the second response message to the source NSSF.

Based on the same technical concept, referring to fig. 15, the embodiment of the present application further provides a communication apparatus 1500, including:

at least one processor 1501; and a communication interface 1503 communicatively coupled to the at least one processor 1501; the at least one processor 1501, by executing the instructions stored in the memory 1502, causes the apparatus to perform the method steps performed by the first network element in the embodiments shown in fig. 7-12 through the communication interface 1503.

Optionally, the memory 1502 is located outside the device 1500.

Optionally, the apparatus 1500 includes the memory 1502, where the memory 1502 is connected to the at least one processor 1501, and the memory 1502 stores instructions executable by the at least one processor 1501.

Optionally, the memory 1502 is located outside the device 1500.

Optionally, the apparatus 1500 includes the memory 1502, where the memory 1502 is connected to the at least one processor 1501, and the memory 1502 stores instructions executable by the at least one processor 1501. Fig. 15 shows, in dashed lines, that memory 1502 is optional for device 1500.

The processor 1501 and the memory 1502 may be coupled through an interface circuit, or may be integrated together, which is not limited herein.

The specific connection medium between the processor 1501, the memory 1502 and the communication interface 1503 is not limited in the embodiment of the present application. In the embodiment of the present application, the processor 1501, the memory 1502 and the communication interface 1503 are connected through the bus 1504 in fig. 15, the bus is shown by a thick line in fig. 15, and the connection manner between other components is only schematically illustrated, but not limited to. The buses may be classified as address buses, data buses, control buses, etc. For ease of illustration, only one thick line is shown in fig. 15, but not only one bus or one type of bus.

Based on the same technical concept, referring to fig. 16, the embodiment of the present application further provides a communication device 1600, including:

At least one processor 1601; and a communication interface 1603 communicatively coupled to the at least one processor 1601; the at least one processor 1601, by executing instructions stored in the memory 1602, causes the apparatus to perform method steps performed by a second network element in the embodiments shown in fig. 7-12 through the communication interface 1603.

Optionally, the memory 1602 is located outside the device 1600.

Optionally, the apparatus 1600 includes the memory 1602, the memory 1602 is connected to the at least one processor 1601, and the memory 1602 stores instructions executable by the at least one processor 1601.

Optionally, the memory 1602 is located outside the device 1600.

Optionally, the apparatus 1600 includes the memory 1602, the memory 1602 is connected to the at least one processor 1601, and the memory 1602 stores instructions executable by the at least one processor 1601. Fig. 16 shows, in dashed lines, that the memory 1602 is optional to the device 1600.

The processor 1601 and the memory 1602 may be coupled by an interface circuit or may be integrated together, which is not limited herein.

The specific connection medium between the processor 1601, the memory 1602, and the communication interface 1603 is not limited in the embodiments of the present application. In the embodiment of the present application, the processor 1601, the memory 1602 and the communication interface 1603 are connected by a bus 1604 in fig. 16, the bus is shown by a thick line in fig. 16, and the connection manner between other components is only schematically illustrated and not limited thereto. The buses may be classified as address buses, data buses, control buses, etc. For ease of illustration, only one thick line is shown in fig. 16, but not only one bus or one type of bus.

It should be understood that the processors mentioned in the embodiments of the present application may be implemented by hardware or may be implemented by software. When implemented in hardware, the processor may be a logic circuit, an integrated circuit, or the like. When implemented in software, the processor may be a general purpose processor, implemented by reading software code stored in a memory.

By way of example, the processor may be a central processing unit (Central Processing Unit, CPU), but may also be other general purpose processors, digital signal processors (Digital Signal Processor, DSP), application specific integrated circuits (Application Specific Integrated Circuit, ASIC), off-the-shelf programmable gate arrays (Field Programmable Gate Array, FPGA) or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, or the like. A general purpose processor may be a microprocessor or the processor may be any conventional processor or the like.

It should be understood that the memories mentioned in the embodiments of the present application may be volatile memories or nonvolatile memories, or may include both volatile and nonvolatile memories. The nonvolatile Memory may be a Read-Only Memory (ROM), a Programmable ROM (PROM), an Erasable PROM (EPROM), an Electrically Erasable EPROM (EEPROM), or a flash Memory. The volatile memory may be random access memory (Random Access Memory, RAM) which acts as an external cache. By way of example, and not limitation, many forms of RAM are available, such as Static RAM (SRAM), dynamic RAM (DRAM), synchronous DRAM (SDRAM), double Data rate Synchronous DRAM (DDR SDRAM), enhanced SDRAM (ESDRAM), synchronous Link DRAM (SLDRAM), and Direct RAM (DR RAM).

It should be noted that when the processor is a general purpose processor, DSP, ASIC, FPGA or other programmable logic device, discrete gate or transistor logic device, discrete hardware components, the memory (storage module) may be integrated into the processor.

It should be noted that the memory described herein is intended to comprise, without being limited to, these and any other suitable types of memory.

Based on the same technical concept, the embodiments of the present application also provide a computer readable storage medium, including a program or an instruction, which when executed on a computer, causes a method performed by a first network element in the embodiments shown in fig. 7 to 12 to be performed.

Based on the same technical concept, the embodiments of the present application also provide a computer readable storage medium, including a program or an instruction, which when run on a computer, causes a method performed by a second network element in the embodiments shown in fig. 7-12 to be performed.

Based on the same technical concept, the embodiments of the present application further provide a chip, where the chip is coupled to the memory, and is configured to read and execute the program instructions stored in the memory, so that the method performed by the first network element in the embodiments shown in fig. 7-12 is performed.

Based on the same technical concept, the embodiments of the present application also provide a chip, where the chip is coupled to a memory, and is configured to read and execute program instructions stored in the memory, so that the method performed by the second network element in the embodiments shown in fig. 7-12 is performed.

Based on the same technical idea, embodiments of the present application also provide a computer program product comprising instructions which, when run on a computer, cause a method performed by a first network element in the embodiments shown in fig. 7-12 to be performed.

Based on the same technical idea, embodiments of the present application also provide a computer program product comprising instructions which, when run on a computer, cause a method performed by a second network element in the embodiments shown in fig. 7-12 to be performed.

Since the communication device 1300, the communication device 1400, the communication device 1500, and the communication device 1600 provided in the embodiments of the present application can be used to perform the methods provided in the corresponding embodiments of the embodiments shown in fig. 7-12, the technical effects obtained by the method can be referred to the above-mentioned method embodiments, and will not be described herein.

It will be appreciated by those skilled in the art that embodiments of the present application may be provided as a method, system, or computer program product. Accordingly, the present application may take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present application may take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, and the like) having computer-usable program code embodied therein.

The present application is described with reference to flowchart illustrations and/or block diagrams of methods, apparatus (systems) and computer program products according to the application. It will be understood that each flow and/or block of the flowchart illustrations and/or block diagrams, and combinations of flows and/or blocks in the flowchart illustrations and/or block diagrams, can be implemented by computer program instructions. These computer program instructions may be provided to a processor of a general purpose computer, special purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, create means for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be stored in a computer-readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer-readable memory produce an article of manufacture including instruction means which implement the function specified in the flowchart flow or flows and/or block diagram block or blocks.

These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions which execute on the computer or other programmable apparatus provide steps for implementing the functions specified in the flowchart flow or flows and/or block diagram block or blocks.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present application without departing from the scope of the application. Thus, if such modifications and variations of the present application fall within the scope of the claims and the equivalents thereof, the present application is intended to cover such modifications and variations.

Claims

1. A method of discovering a target access and mobility management function, AMF, comprising:

when terminal equipment needs to be switched from source access network equipment in a first network to target access network equipment in a second network, a first network element in the first network acquires target identification of a first slice of the terminal equipment in the first network in the second network;

the first network element determining a target AMF in the second network based on the target identity, wherein the target AMF supports the first slice;

wherein before a first network element in the first network obtains a target identifier of a first slice of the terminal device in the first network in the second network, the method further comprises:

the first network element determines that the public land mobile network PLMN identifier of the first network and the PLMN identifier of the second network are different; or,

the first network element determines that a PLMN identity of the first network and a PLMN identity of the second network are the same and a tracking area identity TAI of the first network and a TAI of the second network are different.

2. The method of claim 1, wherein a first network element in the first network obtains a target identity of a first slice of the terminal device in the first network in the second network, comprising:

The first network element sends a first request message to a source network slice selection function NSSF in the first network, wherein the first request message comprises a source identifier of the first slice in the first network;

the first network element receives a first response message from the source NSSF, wherein the first response message includes a target identifier of the first slice in the second network, and the second network supports the first slice.

3. The method of claim 2, wherein,

the source NSSF stores the mapping relation between the slice identifier of the first network and the slice identifier of the second network; or,

4. The method of claim 1, wherein a first network element in the first network obtains a target identity of a first slice of the terminal device in the first network in the second network, comprising:

And the first network element determines a target identifier of the first slice in the second network according to the mapping relation among the source identifier of the first slice in the first network, the slice identifier of the first network and the slice identifier of the second network.

5. The method of claim 4, wherein the first network element stores a mapping between slice identifiers of the first network and slice identifiers of the second network.

6. The method according to any of claims 1-5, wherein the first network element is a source AMF or a source network repository function NRF in the first network.

7. A method of discovering a target access and mobility management function, AMF, comprising:

when terminal equipment needs to be switched from source access network equipment in a first network to target access network equipment in a second network, a second network element receives a request message, wherein the request message comprises a source identifier of a first slice of the terminal equipment in the first network, and the second network element stores a mapping relation between the slice identifier of the first network and the slice identifier of the second network;

The second network element determines a target identifier of the first slice in the second network according to the source identifier and the mapping relation;

the second network element generates a response message according to the target identifier, and the second network element sends the response message;

wherein the public land mobile network PLMN identity of the first network and the PLMN identity of the second network are different; alternatively, the PLMN identity of the first network and the PLMN identity of the second network are the same and the tracking area identity TAI of the first network and the TAI of the second network are different.

8. The method of claim 7, wherein the second network element selects a function NSSF for a source network slice in the first network;

the second network element receives a request message, including:

the source NSSF receives a first request message from a first network element;

the second network element generates a response message according to the target identifier, and the second network element sends the response message, including:

and the source NSSF generates a first response message according to the target identifier, and the source NSSF sends the first response message to the first network element.

9. The method of claim 8, wherein the first network element is a source AMF or a source network repository function NRF in the first network.

10. The method of claim 7, wherein the second network element is a target NSSF in the second network;

the second network element receives a request message, including:

the target NSSF receiving a second request message from a source NSSF in the first network;

and the target NSSF generates a second response message according to the target identifier, and the target NSSF sends the second response message to the source NSSF.

11. A communication device, the device being located in a first network, the device comprising:

a determining unit configured to determine a target AMF in the second network based on the target identification, wherein the target AMF supports the first slice;

wherein the determining unit is further configured to:

before the acquiring unit acquires the target identifier of the first slice of the terminal equipment in the first network in the second network, determining that the public land mobile network PLMN identifier of the first network is different from the PLMN identifier of the second network; or determining that the PLMN identity of the first network and the PLMN identity of the second network are the same and the tracking area identity TAI of the first network and the TAI of the second network are different.

12. The apparatus of claim 11, wherein the acquisition unit is specifically configured to:

13. The apparatus of claim 12, wherein the device comprises a plurality of sensors,

14. The apparatus of claim 11, wherein the acquisition unit is specifically configured to:

15. The apparatus of claim 14, further comprising a storage unit to store a mapping between slice identifiers of the first network and slice identifiers of the second network.

16. The apparatus according to any of claims 11-15, wherein the apparatus is a source AMF or a source network repository function NRF in the first network.

17. A communication device, the device being located in a first network or a second network, the device comprising:

A sending unit, configured to send the response message;

18. The apparatus of claim 17, wherein the apparatus selects a function NSSF for a source network slice in the first network;

the receiving unit is specifically configured to: receiving a first request message from a first network element;

the sending unit is specifically configured to: and sending a first response message to the first network element.

19. The apparatus of claim 18, wherein the first network element is a source AMF or a source network repository function NRF in the first network.

20. The apparatus of claim 17, wherein the apparatus is a target NSSF in the second network;

the receiving unit is specifically configured to: receiving a second request message from a source NSSF in the first network;

the sending unit is specifically configured to: and sending a second response message to the source NSSF.

21. A communication device, comprising:

at least one processor; and a memory communicatively coupled to the at least one processor, a communication interface;

wherein the memory stores instructions executable by the at least one processor, which, by executing the instructions stored by the memory, cause the apparatus to perform the method of any of claims 1-6 or 7-10 via the communication interface.

22. A computer readable storage medium comprising a program or instructions which, when run on a computer, cause the method of any of claims 1-6 or 7-10 to be performed.