Implementation method of an NRF dual-machine selection strategy for ensuring connection stability

Abstract

The present invention relates to a method for implementing an NRF dual-machine selection strategy to ensure connection stability. It is characterized in that: two NRFs, namely NRF1 and NRF2, are configured in the common configuration of the 5GC system. They share data and are equal in status. When an NF registers with one of the NRFs, the other NRF can also obtain the information of the NF at the same time. The NF maintains the connection relationship with these two NRFs through a heartbeat process, and only needs to discover services from one NRF during service discovery. In the present invention, the two NRFs are configured as a common configuration and are in an equal position. The preferred NRF is selected by the private configuration of the NF, with flexible configuration and obvious load sharing effect; the two NRFs share data. If one NRF fails, the other NRF can seamlessly continue the service without service interruption.

Description

Technical Field

[0001] The present invention relates to a method for implementing an NRF dual - machine selection strategy to ensure connection stability. Background Art

[0002] In the current 5GC system, generally, an NRF (Network Repository Function) is used to implement the NF service selection function. As Figure 1 shown, this method has an obvious defect. Once the NRF fails, other NFs will not be able to select the services of other NFs through the NRF, resulting in the unavailability of the entire 5GC network service, which has a huge impact. Therefore, the stable connection of the NRF is crucial.

[0003] To ensure the stability of the NRF, the traditional approach is to use the primary - standby method to back up the NRF. Although this solution ensures the stability of the NRF function to a certain extent, due to the distinction between the primary and the standby, most of the time, the primary NRF bears a great deal of pressure, while the standby NRF is in an idle state, causing serious imbalance in resource utilization and affecting the processing performance. Summary of the Invention

[0004] Aiming at the problems existing in the prior art, the purpose of the present invention is to provide a technical solution for a method for implementing an NRF dual - machine selection strategy to ensure connection stability.

[0005] The described method for implementing an NRF dual - machine selection strategy to ensure connection stability is characterized in that: two NRFs are configured in the 5GC system public configuration, namely NRF1 and NRF2. NRF1 and NRF2 share data and have equal status. When an NF registers with one of the NRFs, the other NRF can also obtain the information of this NF simultaneously. The NF maintains the connection relationship with these two NRFs through a heartbeat process, and only needs to discover services from one NRF during service discovery.

[0006] The described method for implementing an NRF dual - machine selection strategy to ensure connection stability is characterized in that each NRF information includes an IP and a port, which is used as the public configuration of all network elements; then, the preferred NRF configuration information is configured in the private configuration of each NF to select a certain NRF as the preferred NRF, so that each NF can flexibly select an NRF; after the NF starts up, the NF registers with the preferred NRF according to the NRF1 configuration information, NRF2 configuration information obtained from the public configuration and the preferred NRF configuration information obtained from the private configuration. If a registration - success response is received within the specified time of 5 seconds, then the heartbeat maintenance process is carried out; otherwise, the NF registers with the other NRF; if the registration fails with both NRFs, the NF registers with the two NRFs at a frequency of 80 seconds in a cycle, hoping to register with the NRF;

[0007] After NF and one of the NRFs are successfully registered, initiate the heartbeat process with both NRFs simultaneously. After receiving the heartbeat response within the specified time of 5 seconds, initiate the heartbeat maintenance process at the periodic heartbeat time returned by the NRF. If the heartbeat fails for both NRFs, initiate the heartbeat again. After 5 consecutive failures, initiate the registration process again;

[0008] When an NF needs to discover the services of other NFs through the NRF, the NF preferentially selects the preferred NRF in the connected state and sends a service discovery message to it. If the preferred NRF does not give a response, send a service discovery message to the other NRF.

[0009] The implementation method of an NRF dual - machine selection strategy for ensuring connection stability is characterized in that the implementation of the NRF dual - machine selection strategy is divided into three processes, and each process contains multiple sub - processes or steps. The first process is the service registration process, the second process is the maintenance of the registration state, and the third process is the service discovery process.

[0010] The implementation method of an NRF dual - machine selection strategy for ensuring connection stability is characterized in that: The specific steps of the service registration process of NF1 are as follows:

[0011] 1) Configure the information of two NRFs to be connected in the common configuration items of the 5GC system, namely the IP and port of NRF1 and the IP and port of NRF2. In the system, NF1, NF2, and NF3 all have two common NRFs to connect to;

[0012] 2) Configure the NRF selection items in the private configuration items of the NF. There are two options: preferred NRF1 and preferred NRF2. NF1 prefers NRF1, NF2 prefers NRF2, and NF3 prefers NRF1;

[0013] 3) After NF1 starts, according to the NRF selection item, preferentially send an NFRegister message to NRF1 with the NFProfile content and wait for the registration response message of NRF1. If a registration success response is received, complete the service registration process, set the connection state with the NRF as the connected state, set the connection state with NRF1 as the connected state, save the heartbeat interval period in the registration response, and set the heartbeat failure times with both NRFs to 0. Otherwise, enter step 4);

[0014] 4) NF1 sends an NFRegister message to another NRF, i.e., to NRF2, with the same content as the previous time. If a registration success response from NRF2 is received, the registration is successful. Set the connection status with the NRF to the connected state, set the connection status with NRF2 to the connected state, save the heartbeat interval period in the registration response, and set the heartbeat failure counts with the two NRFs to 0. Otherwise, the registration fails for both NRFs, and proceed to step 5).

[0015] 5) According to the system configuration information, NF1 waits for 80 seconds and then initiates registrations with the two NRFs respectively in the same process as before until the registration is successful.

[0016] An implementation method of an NRF dual - machine selection strategy for ensuring connection stability, characterized in that the specific steps for maintaining the registration status of NF1 are as follows:

[0017] A) Connection status maintenance

[0018] a) After NF1 registers with one of the NRFs, it sends a heartbeat request message to the preferred NRF1, sets the status of NRF1 to the waiting - for - heartbeat - response state, and at the same time starts the NRF1 heartbeat waiting timer to wait for the heartbeat response; meanwhile, NF1 sends a heartbeat request message to NRF2, sets the status of NRF2 to the waiting - for - heartbeat - response state, and at the same time starts the NRF2 heartbeat waiting timer to wait for the heartbeat response.

[0019] b) After receiving the heartbeat request message from NF1, NRF1 and NRF2 check whether NF1 has been registered on the NRF. If so, they return a heartbeat - normal response message; otherwise, they return a heartbeat - failure response message.

[0020] c) When NF1 receives the heartbeat - normal response message from NRF1, it sets the connection status with the NRF to the connected state, sets the connection status with NRF1 to the connected state, and at the same time sets the heartbeat failure count with NRF1 to 0, and starts the NRF1 heartbeat period timer.

[0021] d) When NF1 receives the heartbeat - normal response message from NRF2, it sets the connection status with the NRF to the connected state, sets the connection status with NRF2 to the connected state, and at the same time sets the heartbeat failure count with NRF2 to 0, and starts the NRF2 heartbeat period timer.

[0022] B) Disconnection status

[0023] a) When NF1 receives a heartbeat failure response message from NRF1 or the NRF1 heartbeat waiting timer times out, it sets the connection status with NRF1 to the disconnected state. It then determines whether the connection status with NRF2 is also in the disconnected state. If so, it sets the connection status with NRF to the disconnected state; otherwise, it sets the connection status with NRF to the connected state. At the same time, it increments the NRF1 heartbeat failure count by 1, starts the NRF1 heartbeat cycle timer, and if the NRF1 heartbeat failure count is greater than or equal to the configured heartbeat failure count for re-registration, it sets the NRF1 heartbeat failure count to the configured heartbeat failure count for re-registration.

[0024] b) When NF1 receives a heartbeat failure response message from NRF2 or the NRF2 heartbeat waiting timer times out, it sets the connection status with NRF2 to the disconnected state. It then determines whether the connection status with NRF1 is also in the disconnected state. If so, it sets the connection status with NRF to the disconnected state; otherwise, it sets the connection status with NRF to the connected state. At the same time, it increments the NRF2 heartbeat failure count by 1, starts the NRF2 heartbeat cycle timer, and if the NRF2 heartbeat failure count is greater than or equal to the configured heartbeat failure count for re-registration, it sets the NRF2 heartbeat failure count to the configured heartbeat failure count for re-registration.

[0025] C) Exit the registration state

[0026] a) If the connection status between NF1 and NRF is in the disconnected state and the heartbeat failure counts with NRF1 and NRF2 are greater than or equal to the configured heartbeat failure count for re-registration, then it enters the re-registration process.

[0027] The implementation method of an NRF dual-machine selection strategy for ensuring connection stability is characterized in that the specific steps of the service discovery process of NF1 are as follows:

[0028] ) NF1 first determines whether the connection status with NRF is in the connected state. If not, it ends the service discovery process. If so, it then determines whether the connection status with the preferred NRF1 is in the connected state. If so, it sends a service discovery message to NRF1 and starts the waiting service discovery response timer. If not, it proceeds to step )

[0029] ) NF1 determines whether the connection status with NRF2 is in the connected state. If so, it sends a service discovery message to NRF2 and starts the waiting service discovery response timer. If not, it ends the service discovery process;

[0030] )After NRF1 or NRF2 receives the service discovery message from NF1, it queries whether the service to be discovered exists and returns a service discovery response to NF1 according to the query result;

[0031] )If NF1 receives the service discovery response from NRF1 or NRF2, it processes the corresponding service. Otherwise, it processes the waiting service discovery response timer to end the service discovery process.

[0032] In the present invention, two NRFs are configured with a common configuration and are in an equal position. The preferred NRF is selected by the private configuration of the NF, with flexible configuration and obvious load sharing effect; the two NRFs share data. If one NRF fails, the other NRF can seamlessly continue the service without service interruption. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the 5GC system framework in the prior art;

[0034] Figure 2 It is a connection block diagram of NF and NRF in the present invention;

[0035] Figure 3 It is a registration flow chart of NF in the present invention. Detailed Embodiments

[0036] The present invention will be further described below in conjunction with the drawings of the specification:

[0037] The present invention proposes a method for implementing an NRF dual - machine selection strategy. There are two NRFs in the 5GC system, namely NRF1 and NRF2. They share data and are in an equal position. When an NF registers with one of the NRFs, the other NRF can also obtain the information of this NF at the same time. The NF maintains the connection relationship with these two NRFs through a heartbeat process. When performing service discovery, it only needs to discover from one NRF.

[0038] Two NRF information are configured in the 5GC public configuration. Each NRF information contains an IP and a port, which serves as the public configuration for all network elements. Then, the preferred NRF configuration information is configured in the private configuration of each NF to select a certain NRF as the preferred NRF, so that each NF can flexibly select an NRF. After the NF starts up, the NF registers with the preferred NRF according to the NRF1 configuration information, NRF2 configuration information obtained from the public configuration and the preferred NRF configuration information obtained from the private configuration (carrying information such as the services supported by the NF, the NF service priority, its own slice and the supported slices, etc.). If a registration success response is received within the specified time of 5 seconds, the heartbeat maintenance process is carried out; otherwise, registration is carried out with another NRF. If registration fails with both NRFs, the NF registers with the two NRFs at a frequency of 80 seconds (system configuration) in order to register with the NRF.

[0039] After the NF registers successfully with one of the NRFs, the heartbeat processes with both NRFs are initiated simultaneously. After receiving a heartbeat response within the specified time of 5 seconds, the heartbeat maintenance process is initiated at the periodic heartbeat time returned by the NRF. If the heartbeats of both NRFs fail, the heartbeat is restarted. After failing continuously 5 times (system configuration), the registration process is restarted.

[0040] When the NF needs to discover the services of other NFs through the NRF, the NF preferentially selects the connected preferred NRF and sends a service discovery message to it. If the preferred NRF does not give a response, a service discovery message is sent to the other NRF.

[0041] The implementation of the NRF dual-machine selection strategy of the present invention is divided into three processes, and each process contains multiple sub-processes or steps. Taking NF1 as an example for illustration.

[0042] The first process is the service registration process, and the specific steps are as follows:

[0043] 1) Configure two NRF information to be connected in the 5GC system public configuration item, namely the IP and port of NRF1 and the IP and port of NRF2. As shown in Figure 2, NF1, NF2, and NF3 all have two common NRFs to connect to;

[0044] 2) Configure the NRF selection item in the private configuration item of the NF, with two options: preferred NRF1 and preferred NRF2; as Figure 2 shown, NF1 prefers NRF1, NF2 prefers NRF2, and NF3 prefers NRF1;

[0045] 3) After NF1 starts, according to the NRF selection option, it first sends an NFRegister message to NRF1 (implemented by calling the interface message of SBIAP), and carries the NFProfile content (including instance ID, NF type, NF status "registered state", etc.), and waits for the registration response message from NRF1. If a registration success response is received, the service registration process is completed, the connection status with the NRF is set to the connected state, the connection status with NRF1 is set to the connected state, the heartbeat interval period in the registration response is saved, and the heartbeat failure count for both NRFs is set to 0. Otherwise, go to step 4).

[0046] 4) NF1 sends an NFRegister message to the other NRF, namely NRF2, with the same content as the previous time. If a registration success response from NRF2 is received, the registration is successful, the connection status with the NRF is set to the connected state, the connection status with NRF2 is set to the connected state, the heartbeat interval period in the registration response is saved, and the heartbeat failure count for both NRFs is set to 0. Otherwise, both NRF registrations fail and go to step 5).

[0047] 5) NF1 waits for 80 seconds according to the system configuration information and then initiates registrations with the two NRFs respectively in the same process as before until the registration is successful. The service registration flow chart is shown in Figure 3.

[0048] The second process is the maintenance of the registration state (heartbeat maintenance process), including the following subroutines:

[0049] A) Connection status maintenance

[0050] a) After NF1 is registered with one of the NRFs, it sends a heartbeat request message to the preferred NRF1, sets the status of NRF1 to the waiting heartbeat response state, and at the same time starts the NRF1 heartbeat waiting timer to wait for the heartbeat response; meanwhile, NF1 sends a heartbeat request message to NRF2, sets the status of NRF2 to the waiting heartbeat response state, and at the same time starts the NRF2 heartbeat waiting timer to wait for the heartbeat response;

[0051] b) After NRF1 and NRF2 receive the heartbeat request message from NF1, they check whether NF1 has been registered on the NRF. If so, they return a heartbeat normal response message; otherwise, they return a heartbeat failure response message;

[0052] c) When NF1 receives the heartbeat normal response message from NRF1, it sets the connection status with the NRF to the connected state, the connection status with NRF1 to the connected state, and at the same time sets the heartbeat failure count with NRF1 to 0 and starts the NRF1 heartbeat period timer;

[0053] d) NF1 receives the heartbeat normal response message from NRF2, sets the connection status with NRF to the connected state, sets the connection status with NRF2 to the connected state, simultaneously sets the heartbeat failure count with NRF2 to 0, and starts the NRF2 heartbeat cycle timer.

[0054] B) Disconnection state

[0055] a) When NF1 receives the heartbeat failure response message from NRF1 or the NRF1 heartbeat waiting timer times out, it sets the connection status with NRF1 to the disconnected state. It then determines whether the connection status with NRF2 is also the disconnected state. If so, it sets the connection status with NRF to the disconnected state; otherwise, it sets the connection status with NRF to the connected state. At the same time, it increments the heartbeat failure count with NRF1 by 1, starts the NRF1 heartbeat cycle timer, and if the heartbeat failure count with NRF1 is greater than or equal to the configured heartbeat failure count for re-registration, it sets the heartbeat failure count with NRF1 to the configured heartbeat failure count for re-registration.

[0056] b) When NF1 receives the heartbeat failure response message from NRF2 or the NRF2 heartbeat waiting timer times out, it sets the connection status with NRF2 to the disconnected state. It then determines whether the connection status with NRF1 is also the disconnected state. If so, it sets the connection status with NRF to the disconnected state; otherwise, it sets the connection status with NRF to the connected state. At the same time, it increments the heartbeat failure count with NRF2 by 1, starts the NRF2 heartbeat cycle timer, and if the heartbeat failure count with NRF2 is greater than or equal to the configured heartbeat failure count for re-registration, it sets the heartbeat failure count with NRF2 to the configured heartbeat failure count for re-registration.

[0057] C) Exit the registration state

[0058] a) If the connection status between NF1 and NRF is the disconnected state, and the heartbeat failure counts with NRF1 and NRF2 are greater than or equal to the configured heartbeat failure count for re-registration, then it enters the re-registration process.

[0059] The third process is the service discovery process, and the specific steps are as follows:

[0060] ) NF1 first determines whether the connection status with NRF is the connected state. If not, it ends the service discovery process. If so, it then determines whether the connection status with the preferred NRF1 is the connected state. If it is, it sends a service discovery message to NRF1 and starts the waiting service discovery response timer. If not, it proceeds to step )

[0061] )Determine whether the connection status between NF1 and NRF2 is the connected state. If it is, send a service discovery message to NRF2 and start the waiting service discovery response timer. If not, end the service discovery process;

[0062] )After receiving the service discovery message from NF1, NRF1 or NRF2 queries whether the service to be discovered exists and returns a service discovery response to NF1 according to the query result;

[0063] )If NF1 receives a service discovery response from NRF1 or NRF2, it processes the corresponding service. Otherwise, it processes the waiting service discovery response timer and ends the service discovery process.

[0064] Term Explanation

[0065] 5GC: 5G Core, the core network of the 5th generation mobile communication technology

[0066] NF: Network Function

[0067] NRF: Network Repository Function

[0068] Nnrf: Service-based interface exhibited by NRF

[0069] NSSF: Network Slice Selection Function

[0070] Nnssf: Service-based interface exhibited by NSSF

[0071] NEF: Network Exposure Function

[0072] Nnef: Service-based interface exhibited by NEF

[0073] PCF: Policy Control Function

[0074] Npcf: Service-based interface exhibited by PCF

[0075] UDM: Unified Data Management, Unified Data Management

[0076] Nudm: Service-based interface exhibited by UDM, Service-based interface exhibited by UDM

[0077] AF: Application Function, Application Function

[0078] Naf: Service-based interface exhibited by AF, Service-based interface exhibited by AF

[0079] NSSAAF: Network Slice-Specific Authentication and AuthorizationFunction, Network Slice-Specific Authentication and AuthorizationFunction

[0080] Nnssaaf: Service-based interface exhibited by NSSAAF, Service-based interface exhibited by NSSAAF

[0081] AUSF: Authentication Server Function, Authentication Server Function

[0082] Nausf: Service-based interface exhibited by AUSF, Service-based interface exhibited by AUSF

[0083] AMF: Access and Mobility Management Function, Access and Mobility Management Function

[0084] Namf: Service-based interface exhibited by AMF, Service-based interface exhibited by AMF

[0085] SMF: Session Management Function, Session Management Function

[0086] Nsmf: Service-based interface exhibited by SMF, Service-based interface exhibited by SMF

[0087] SCP: Service Communication Proxy, the service communication proxy

[0088] UE: User Equipment, the user equipment

[0089] (R)AN: (Radio) Access Network, the (radio) access network

[0090] UPF: User Plane Function, the user plane function

[0091] DN: Data Network, the data network

[0092] N1: Reference point between the UE and the AMF, the reference point between the UE and the AMF

[0093] N2: Reference point between the (R)AN and the AMF, the reference point between the (R)AN and the AMF

[0094] N3: Reference point between the (R)AN and the UPF, the reference point between the (R)AN and the UPF

[0095] N4: Reference point between the SMF and the UPF, the reference point between the SMF and the UPF

[0096] N6: Reference point between the UPF and a Data Network, the reference point between the UPF and a data network

[0097] N9: Reference point between two UPFs, the reference point between two UPFs

[0098] NFRegister: Network Function Register, the network function register

[0099] SBIAP: Service Based Interface Access Point, the service - based interface access point

[0100] NFProfile: Network Function Profile, the network function profile

[0101] ID: Identity Document, identity identification number

[0102] IP: Internet Protocol, Internet interconnection protocol.

Claims

1. An implementation method of an NRF dual-machine selection strategy for ensuring connection stability, characterized in that: In the 5GC system public configuration, two NRFs are configured, namely NRF1 and NRF2. NRF1 and NRF2 share data and are equal in status. When an NF registers with one of the NRFs, the other NRF can also obtain the information of this NF simultaneously. The NF maintains the connection relationship with these two NRFs through the heartbeat process, and only needs to discover services from one NRF during service discovery; Each NRF information includes the IP and port, which are used as the public configuration of all network elements. Then, the preferred NRF configuration information is configured in the private configuration of each NF to select a certain NRF as the preferred NRF, so that each NF can flexibly select the NRF. After the NF starts up, the NF registers with the preferred NRF according to the NRF1 configuration information, NRF2 configuration information obtained from the public configuration and the preferred NRF configuration information obtained from the private configuration. If a registration success response is received within the specified time of 5 seconds, the heartbeat maintenance process is carried out, otherwise, it registers with the other NRF. If the registration fails with both NRFs, the NF registers with the two NRFs at a frequency of 80 seconds in order to register with the NRF; After the NF successfully registers with one of the NRFs, it simultaneously initiates the heartbeat processes with the two NRFs. After receiving the heartbeat response within the specified time of 5 seconds, it initiates the heartbeat maintenance process at the periodic heartbeat time returned by the NRF. If the heartbeats of both NRFs fail, it reinitiates the heartbeat. After failing continuously 5 times, it reinitiates the registration process; When the NF needs to discover the services of other NFs through the NRF, the NF preferentially selects the connected preferred NRF and sends a service discovery message to it. If the preferred NRF does not give a response, it sends a service discovery message to the other NRF.

2. The implementation method of an NRF dual-machine selection strategy for ensuring connection stability according to claim 1, characterized in that The implementation of the NRF dual-machine selection strategy is divided into three processes, and each process contains multiple sub-processes or steps. The first process is the service registration process, the second process is the maintenance of the registration status, and the third process is the service discovery process.

3. The implementation method of an NRF dual-machine selection strategy for ensuring connection stability according to claim 2, characterized in that: The specific steps of the service registration process of NF1 are as follows: 1) Configure the information of two NRFs to be connected in the 5GC system public configuration item, namely the IP and port of NRF1 and the IP and port of NRF2. In the system, NF1, NF2, and NF3 all have two common NRFs to connect; 2) Configure the NRF selection item in the private configuration item of the NF. There are two options, namely preferred NRF1 and preferred NRF2. NF1 prefers NRF1, NF2 prefers NRF2, and NF3 prefers NRF1; 3) After NF1 starts up, it sends an NFRegister message to NRF1 according to the preferred NRF1 in the NRF selection item, and carries the NFProfile content, waiting for the registration response message of NRF1. If a registration success response is received, the service registration process is completed, the connection status with the NRF is set to the connected state, the connection status with NRF1 is set to the connected state, the heartbeat interval period in the registration response is saved, and the heartbeat failure times with the two NRFs are set to 0. Otherwise, go to step 4); 4) NF1 sends an NFRegister message to another NRF, i.e., to NRF2, with the same content as the previous time. If a registration success response from NRF2 is received, the registration is successful. Set the connection status with the NRF to the connected state, set the connection status with NRF2 to the connected state, save the heartbeat interval period in the registration response, and set the heartbeat failure counts with both NRFs to 0. Otherwise, the registrations with both NRFs fail, and proceed to step 5). 5) According to the system configuration information, NF1 waits for 80 seconds and then initiates registrations with the two NRFs respectively in the same process as before until the registrations are successful.

4. The implementation method of an NRF dual-machine selection strategy for ensuring connection stability according to claim 2, characterized in that: The specific steps for maintaining the registration status of NF1 are as follows: A) Connection status maintenance a) After NF1 registers with one of the NRFs, it sends a heartbeat request message to the preferred NRF1, sets the status of NRF1 to the waiting heartbeat response state, and simultaneously starts the NRF1 heartbeat waiting timer to wait for the heartbeat response. At the same time, NF1 sends a heartbeat request message to NRF2, sets the status of NRF2 to the waiting heartbeat response state, and simultaneously starts the NRF2 heartbeat waiting timer to wait for the heartbeat response. b) After receiving the heartbeat request message from NF1, NRF1 and NRF2 check whether NF1 has been registered on the NRF. If so, they return a heartbeat normal response message; otherwise, they return a heartbeat failure response message. c) When NF1 receives the heartbeat normal response message from NRF1, it sets the connection status with the NRF to the connected state, sets the connection status with NRF1 to the connected state, and simultaneously sets the heartbeat failure count with NRF1 to 0, and starts the NRF1 heartbeat period timer. d) When NF1 receives the heartbeat normal response message from NRF2, it sets the connection status with the NRF to the connected state, sets the connection status with NRF2 to the connected state, and simultaneously sets the heartbeat failure count with NRF2 to 0, and starts the NRF2 heartbeat period timer. B) Disconnection status a) When NF1 receives the heartbeat failure response message from NRF1 or the NRF1 heartbeat waiting timer times out, it sets the connection status with NRF1 to the disconnected state. It judges whether the connection status with NRF2 is also the disconnected state. If so, it sets the connection status with the NRF to the disconnected state; otherwise, it sets the connection status with the NRF to the connected state. At the same time, it increments the heartbeat failure count with NRF1 by 1 and starts the NRF1 heartbeat period timer. If the heartbeat failure count with NRF1 is greater than or equal to the configured heartbeat failure count for re-registration, the heartbeat failure count with NRF1 is set to the configured heartbeat failure count for re-registration. b) When NF1 receives the heartbeat failure response message from NRF2 or the heartbeat waiting timer of NRF2 times out, it sets the connection status with NRF2 to the disconnected state. It then determines whether the connection status with NRF1 is also in the disconnected state. If so, it sets the connection status with NRF to the disconnected state; otherwise, it sets the connection status with NRF to the connected state. At the same time, it increments the heartbeat failure count with NRF2 by 1, starts the heartbeat cycle timer for NRF2. If the heartbeat failure count with NRF2 is greater than or equal to the configured heartbeat failure count for re-registration, the heartbeat failure count with NRF2 is set to the re-registration heartbeat failure count; C) Exit the registration state a) If the connection status between NF1 and NRF is in the disconnected state, and the heartbeat failure counts with NRF1 and NRF2 are greater than or equal to the configured heartbeat failure count for re-registration, then enter the re-registration process.

5. The implementation method of an NRF dual-machine selection strategy for ensuring connection stability according to claim 2, characterized in that: The specific steps of the service discovery process of NF1 are as follows: I) NF1 first determines whether the connection status with NRF is in the connected state. If not, it ends the service discovery process. If it is, it then determines whether the connection status with the preferred NRF1 is in the connected state. If so, it sends a service discovery message to NRF1 and starts the waiting service discovery response timer. If not, it proceeds to step II); II) NF1 determines whether the connection status with NRF2 is in the connected state. If so, it sends a service discovery message to NRF2 and starts the waiting service discovery response timer. If not, it ends the service discovery process; III) After receiving the service discovery message from NF1, NRF1 or NRF2 queries whether the service to be discovered exists and returns a service discovery response to NF1 based on the query result; IV) If NF1 receives the service discovery response from NRF1 or NRF2, it processes the corresponding service. Otherwise, it processes the waiting service discovery response timer and ends the service discovery process.

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