Downlink data notification DDN fault state notification method

Abstract

The embodiment of the invention provides a DDN (Downlink Data Notification) fault state notification method, which comprises the following steps: a first access and mobility management function AMF communicating with user equipment UE sends a first message to an access side session management function A-SMF, and the first message is used for subscribing to a DDN fault state notification; the first AMF sends a second message to a session management function (I-SMF) in a multimedia subsystem based on an internet protocol under the condition that the UE moves across regions, and the second message is used for subscribing to a DDN fault state notification; and the first AMF sends a third message to the A-SMF through the I-SMF, and the third message is used for cancelling a subscription DDN fault state notification. Through application of the embodiment of the invention, the problem that the A-SMF cannot release related subscription resources in time due to the fact that a mechanism for notifying the A-SMF to cancel the subscription DDN fault state notification is not provided for the scene of cross-region movement of the UE in the related technology is solved.

Description

Technical Field

[0001] The embodiments of the present application relate to the field of communications, and in particular, to a method for notifying the failure status of a Downlink Data Notification (DDN). Background Art

[0002] In the related art, for some application layer services, such as the control system of Internet of Things terminals, when providing services, upgrading, or controlling the terminals, it cannot be implemented when the terminals are unreachable and can only be implemented when the terminals become reachable. To solve this problem, the event subscription function of the Availability-after-DDN-failure type is introduced in the 5G standard, which is a mechanism for subscribing to availability notifications after the failure of downlink data notifications. When the UE becomes reachable again after the failure of downlink data transfer, this event is detected. Thus, the application layer service can continue to send data to the terminal, and then perform actions such as service upgrading on the terminal again.

[0003] However, the related art lacks the scenario of Session Management Function (SMF) insertion after the UE moves across regions. Currently, the 5G standard does not provide a mechanism to notify the Access and Session Management Function (A-SMF) to subscribe to the failure status notification of the Downlink Data Notification (DDN). As a result, the A-SMF fails to release the relevant subscription resources in a timely manner and stop monitoring the downlink data. Summary of the Invention

[0004] The embodiments of the present application provide a method for notifying the failure status of a Downlink Data Notification (DDN), so as to at least solve the problem in the related art that in the scenario where the UE moves across regions, since there is no mechanism to notify the A-SMF to cancel the subscription to the DDN failure status notification, the A-SMF cannot release the relevant subscription resources in a timely manner.

[0005] According to an embodiment of the present application, a method for notifying the failure status of a Downlink Data Notification (DDN) is provided, including: a first Access and Mobility Management Function (AMF) that communicates with a User Equipment (UE) sends a first message to an Access and Session Management Function (A-SMF), where the first message is used to subscribe to the failure status notification of the Downlink Data Notification (DDN); in the case where the UE moves across regions, the first AMF sends a second message to a Session Management Function (I-SMF) in the Internet Protocol Multimedia Subsystem, where the second message is used to subscribe to the DDN failure status notification; the first AMF sends a third message to the A-SMF through the I-SMF, where the third message is used to cancel the subscription to the DDN failure status notification.

[0006] According to another embodiment of the present application, there is also provided a computer-readable storage medium storing a computer program, wherein the computer program is configured to execute the steps in any one of the above method embodiments when running.

[0007] According to another embodiment of the present application, there is also provided an electronic device including a memory and a processor, wherein a computer program is stored in the memory, and the processor is configured to run the computer program to execute the steps in any one of the above method embodiments.

[0008] Through the present application, the Access and Mobility Management Function (AMF) communicating with the User Equipment (UE) subscribes to the DDN fault status notification from the A-SMF. However, in the case of the UE moving across regions, the AMF subscribes to the DDN fault status notification from the Internet Protocol-based Multimedia Subsystem Session Management Function (I-SMF). To avoid the A-SMF being unable to release the relevant subscribed resources in a timely manner, the AMF notifies the A-SMF to cancel the subscription to the DDN fault status notification through the I-SMF. Therefore, it is possible to solve the problem in the related art that in the scenario of the UE moving across regions, due to the lack of a mechanism to notify the A-SMF to cancel the subscription to the DDN fault status notification, the A-SMF cannot release the relevant subscribed resources in a timely manner. The technical effect of achieving that the A-SMF does not retain unnecessary resources while ensuring that the AMF normally subscribes to the DDN fault status notification is achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a hardware structure block diagram of a computer terminal for the method of notifying the DDN fault status of downlink data according to an embodiment of the present application;

[0010] Figure 2 is a network architecture diagram of the method of notifying the DDN fault status of downlink data according to an embodiment of the present application;

[0011] Figure 3 is a flowchart of the method of notifying the DDN fault status of downlink data according to an embodiment of the present application;

[0012] Figure 4 is a flowchart of the method of notifying the DDN fault status of downlink data in Scenario Embodiment (1);

[0013] Figure 5 It is a flowchart of the method for notifying the failure status of the downlink data notification DDN in Scenario Embodiment (2);

[0014] Figure 6 It is a flowchart of the method for notifying the failure status of the downlink data notification DDN in Scenario Embodiment (3);

[0015] Figure 7 It is a flowchart of the method for notifying the failure status of the downlink data notification DDN in Scenario Embodiment (4). Detailed implementation manners

[0016] In the following, embodiments of the present application will be described in detail with reference to the accompanying drawings and in conjunction with the embodiments.

[0017] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and do not necessarily have to be used to describe a specific order or sequence.

[0018] The method embodiments provided in the embodiments of the present application can be executed on a mobile terminal, a computer terminal or a similar computing device. Taking running on a computer terminal as an example, Figure 1 It is a hardware structure block diagram of a computer terminal for the method of notifying the failure status of the downlink data notification DDN in an embodiment of the present application. As Figure 1 shown, the computer terminal may include one or more ( Figure 1 only one is shown in the figure) processors 102 (the processors 102 may include, but are not limited to, processing devices such as a microprocessor MCU or a programmable logic device FPGA) and a memory 104 for storing data. Among them, the above-mentioned computer terminal may further include a transmission device 106 for communication functions and an input / output device 108. Those of ordinary skill in the art can understand that Figure 1 the structure shown in the figure is only schematic and does not limit the structure of the above-mentioned computer terminal. For example, the computer terminal may further include more or fewer components than those shown in Figure 1 the figure, or have a different configuration from that shown in Figure 1 the figure.

[0019] The memory 104 can be used to store computer programs, such as software programs and modules of application software, such as the computer program corresponding to the downlink data notification DDN fault status notification method in the embodiments of the present application. The processor 102 executes various functional applications and data processing by running the computer program stored in the memory 104, that is, the above-mentioned method is implemented. The memory 104 may include a high-speed random access memory, and may also include a non-volatile memory, such as one or more magnetic storage devices, flash memory, or other non-volatile solid-state memories. In some instances, the memory 104 may further include a memory remotely disposed relative to the processor 102, and these remote memories may be connected to the computer terminal through a network. Examples of the above network include but are not limited to the Internet, enterprise intranet, local area network, mobile communication network, and combinations thereof.

[0020] The transmission device 106 is used to receive or send data via a network. Specific examples of the above network may include a wireless network provided by a communication provider of a computer terminal. In one instance, the transmission device 106 includes a network adapter (Network Interface Controller, abbreviated as NIC), which can be connected to other network devices through a base station and thus communicate with the Internet. In one instance, the transmission device 106 may be a radio frequency (Radio Frequency, abbreviated as RF) module, which is used to communicate with the Internet wirelessly.

[0021] The embodiments of the present application can run on Figure 2 the network architecture shown, such as Figure 2 shown, the network architecture includes: AMF, Unified Data Management (UDM), Network Enabled Functionality (NEF), Application Function (AF), I-SMF, and A-SMF.

[0022] In this embodiment, a downlink data notification DDN fault status notification method running on the above computer terminal is provided. Figure 3 is a flowchart of the downlink data notification DDN fault status notification method according to the embodiments of the present application, as Figure 3 shown, the process includes the following steps:

[0023] Step S302, the first access and mobility management function AMF communicating with the user equipment UE sends a first message to the access side session management function A-SMF, where the first message is used to subscribe to the downlink data notification DDN fault status notification;

[0024] In step S302 of the embodiment of the present application, it includes: the first AMF receives a fourth message sent by the Unified Data Management UDM, where the fourth message is used to subscribe to the availability after the DDN fails; the first AMF sends a first message to the A-SMF in response to the fourth message, where the first message is used to subscribe to the DDN failure status notification.

[0025] In an exemplary embodiment of the present application, after receiving the fourth message, the first AMF first confirms that it is necessary to execute the subscription to the DDN failure status notification, and then subscribes to the DDN failure status notification by sending a message to the A-SMF.

[0026] In an exemplary embodiment, after the first AMF sends a first message to the A-SMF in response to the fourth message, it further includes: when the A-SMF is informed that the UE is unreachable, the first AMF receives the DDN failure status notification sent by the A-SMF.

[0027] It should be noted that the A-SMF being informed that the UE is unreachable means that the SMF receives a signal indicating that it is unable to establish communication with the UE or access the UE. This may be caused by the UE being in an unavailable state, unstable signal, or other network problems.

[0028] In an exemplary embodiment, after the first AMF receives the DDN failure status notification sent by the A-SMF, it further includes: the first AMF detects whether the UE is reachable; when the first AMF detects that the UE is reachable, the first AMF reports the availability after the DDN failure to the Application Function AF through the Network Exposure Function NEF.

[0029] In an exemplary embodiment, when the first AMF reports the message of the availability after the DDN failure to the Application Function AF, it includes: the first AMF sends a message carrying the availability event after the DDN failure to the AF through the NEF.

[0030] Step S304, when the UE undergoes cross-region movement, the first AMF sends a second message to the Session Management Function I-SMF in the Internet Protocol Multimedia Subsystem, where the second message is used to subscribe to the DDN failure status notification;

[0031] In the case where the UE undergoes cross-region movement, that is, I-SMF insertion occurs, the first AMF sends a request message for subscribing to DDN failure status notification to the I-SMF. The request message carries the TransferDdnFailureSubs parameter, and the functions of this parameter include specifying the data transfer failure subscription that should be transferred when a failure occurs in data transfer. It is usually used to specify an alternative subscription so that when the primary subscription fails, it can automatically switch to the alternative subscription to ensure the continuity and reliability of data transfer.

[0032] Before step S304 of the embodiment of the present application, it further includes: the first AMF sends a session creation request to the I-SMF in the area where the UE is located after moving.

[0033] In an exemplary embodiment, in the case where the UE undergoes cross-region inter-office movement, the second AMF sends a fifth message to the I-SMF, where the fifth message is used to subscribe to DDN failure status notification.

[0034] Step S306, the first AMF sends a third message to the A-SMF through the I-SMF, where the third message is used to cancel the subscription to DDN failure status notification.

[0035] In an exemplary embodiment, the third message is further used to notify the A-SMF to stop monitoring downlink data and release the subscribed resources.

[0036] Through the description of the above embodiments, those skilled in the art can clearly understand that the method according to the above embodiments can be implemented by means of software plus a necessary general hardware platform. Of course, it can also be implemented by hardware, but in many cases, the former is a better implementation method. Based on such an understanding, the technical solution of the present application, in essence, or the part that contributes to the prior art, can be embodied in the form of a software product. This computer software product is stored in a storage medium (such as ROM / RAM, magnetic disk, optical disc), and includes several instructions to enable a terminal device (which can be a mobile phone, computer, server, or network device, etc.) to execute the methods described in various embodiments of the present application.

[0037] To facilitate the understanding of the technical solution provided by the present application, the following will elaborate on it in detail in combination with the embodiments of specific scenarios.

[0038] Figure 4 It is a flowchart of the downlink data notification DDN failure status notification method in Scenario Embodiment (1). Scenario Embodiment (1) belongs to the traditional DDN failure status notification method. As Figure 4 shown, this process includes the following steps:

[0039] Step S401, AF subscribes to events of the Availability-after-DDN-failure type initiated by the user;

[0040] Step S402, the AMF subscribes to the DDN Failure status notification from the A-SMF;

[0041] Specifically, after the AMF subscribes to the DDN Failure status notification from the A-SMF, the A-SMF applies for subscribed resources and starts monitoring downlink data.

[0042] Step S403, when an I-SMF is inserted, the AMF subscribes to the DDN Failure status notification from the I-SMF;

[0043] Specifically, in the case of cross-area movement of the UE, when an I-SMF is inserted, the AMF subscribes to the DDN Failure status notification from the I-SMF. The I-SMF applies for subscribed resources and starts monitoring downlink data. When the I-SMF finds that the UE is unreachable, it discards the downlink data.

[0044] Step S404, the I-SMF notifies the AMF that the UE is unreachable;

[0045] Step S405, the AMF reports an event of the Availability-after-DDN-failure type.

[0046] Specifically, when the AMF detects that the UE is reachable, the AMF reports an event of the Availability-after-DDN-failure type.

[0047] Figure 5 It is a flowchart of the method for notifying the DDN failure status of downlink data in Scenario Embodiment (2). As Figure 5 shown, the difference from the traditional DDN failure status notification method shown in Figure 4 is that Figure 5 after the I-SMF applies for subscribed resources and starts monitoring downlink data, the AMF subscribes to the DDN Failure status notification from the A-SMF through the I-SMF. In the case of discarding downlink data when the UE is unreachable, the A-SMF stops monitoring downlink data and releases the subscribed resources. Therefore, Figure 5 in the embodiment shown in Figure 4 there is no residual resource on the A-SMF, while in the embodiment shown in

[0048] in Scenario Embodiment (2), the user may experience in-site movement or inter-site movement. The in-site movement scenario is as Figure 6 shown, and the inter-site movement scenario is as Figure 7As shown

[0049] Figure 6 is a flowchart of the downlink data notification DDN fault status notification method for scenario implementation example (3), as Figure 6 shown, the process includes the following steps:

[0050] Step S601, the SMF configures the relevant User Plane Function (UPF) to forward the data packet to the SMF;

[0051] Step S602, the AF sends an Nnef_EventExposure_Subscribe Request to the NEF to request notification of the "availability after DDN failure" of a UE or a group of UEs;

[0052] Step S603, the NEF sends an Nudm_EventExposure_Subscribe Request to the UDM;

[0053] Step S604, the UDM sends a Namf_EventExposure_Subscribe message to the AMF to subscribe to the "availability after DDN failure";

[0054] Step S605, the AMF confirms the execution of Namf_EventExposure_Subscribe;

[0055] Step S606, the AMF subscribes to the DDN fault status notification by sending an Nsmf_PDUSession_UpdateSMContext request message to each SMF, requesting the SMF to notify of the DDN fault;

[0056] Step S607, the SMF sends an Nsmf_PDUSession_UpdateSMContext response message to the AMF;

[0057] Step S608, the UDM sends an Nudm_EventExposure_Subscribe response to the NEF;

[0058] Step S609, the NEF sends an Nudm_EventExposure_Subscribe response to the AF;

[0059] Steps S610 - S611, the SMF is informed that the UE is unreachable, decides to discard the downlink data received from the UPF, and sends the DDN fault status to the AMF through the Nsmf_PDUSession_SMContextStatusNotify message;

[0060] Steps S612 - S613, the AMF detects that the UE is reachable and reports an event of the type "Availability after DDN failure" through the Namf_EventExposure_Notify message;

[0061] Step S614, the NEF sends an Nnef_EventExposure_Notify message with the "Availability after DDN failure" event to the AF;

[0062] Step S615, the UE makes an inter - area handover;

[0063] Steps S616 - S617, the AMF sends an Nsmf_PDUSession_CreateSMContextRequest message to the I - SMF, and the I - SMF replies with an Nsmf_PDUSession_CreateSMContext Response message;

[0064] Specifically, during the mobility process, when an I - SMF insertion occurs in the user session, the AMF sends an Nsmf_PDUSession_CreateSMContext Request message to the I - SMF, carrying the DdnFailureSubs parameter (ddnFailureSubsInd is set to true) to trigger the SMF to start downlink data detection, and the I - SMF replies with an Nsmf_PDUSession_CreateSMContext Response message.

[0065] Step S618a, the AMF sends an Nsmf_PDUSession_UpdateSMContext Request message to the I - SMF;

[0066] Specifically, after the successful insertion of the I - SMF, the AMF sends an Nsmf_PDUSession_UpdateSMContextRequest message to the I - SMF, and the message carries the TransferDdnFailureSubs parameter.

[0067] Step S618b, the I - SMF sends an Nsmf_PDUSession_UpdateSMContext Response message to the AMF;

[0068] Step S619a, the I - SMF sends an Nsmf_PDUSession_Update Request message to the A - SMF;

[0069] Specifically, the message carries the TransferDdnFailureSubs parameter, indicating that the A-SMF stops monitoring the failure of the user's downlink data transfer and deletes the subscription resources related to the DDN Failure status notification.

[0070] Step S619b, the A-SMF sends an Nsmf_PDUSession_Update Response message to the I-SMF;

[0071] Steps S620 - 621, the I-SMF is informed that the UE is unreachable, decides to discard the downlink data received from the UPF, and sends the DDN failure status to the AMF through the Nsmf_PDUSession_SMContextStatusNotify message.

[0072] Steps S622 - 623, the AMF detects that the UE is reachable and, based on the Notify on available after DDN failure flag, sends an event report to the NEF through the Namf_EventExposure_Notify message.

[0073] Step S624, the NEF sends an Nnef_EventExposure_Notify message with the "Availability after DDN failure" event to the AF.

[0074] Figure 7 It is a flowchart of the method for notifying the DDN failure status of downlink data in Scenario Example (4). As Figure 7 shown, the process includes the following steps:

[0075] Step S701, the relevant UPF configured by the SMF forwards the data packet to the SMF;

[0076] Step S702, the AF sends an Nnef_EventExposure_Subscribe Request to the NEF, requesting the "Availability after DDN failure" notification for the UE or a group of UEs;

[0077] Step S703, the NEF sends an Nudm_EventExposure_Subscribe Request to the UDM;

[0078] Step S704, the UDM sends a Namf_EventExposure_Subscribe message to the AMF to subscribe to the "Availability after DDN failure";

[0079] Step S705, the AMF confirms the execution of the Namf_EventExposure_Subscribe.

[0080] Step S706: The AMF subscribes to the DDN failure status notification by sending an Nsmf_PDUSession_UpdateSMContext request message to each SMF, requesting the SMF to notify of the DDN failure;

[0081] Step S707: The SMF sends an Nsmf_PDUSession_UpdateSMContext response message to the AMF;

[0082] Step S708: The UDM sends an Nudm_EventExposure_Subscribe response to the NEF;

[0083] Step S709: The NEF sends an Nudm_EventExposure_Subscribe response to the AF;

[0084] Steps S710 - S711: The SMF is informed that the UE is unreachable, decides to discard the downlink data received from the UPF, and sends the DDN failure status to the AMF via the Nsmf_PDUSession_SMContextStatusNotify message;

[0085] Steps S712 - S713: The AMF detects that the UE is reachable and reports an event of the "Availability after DDN failure" type via the Namf_EventExposure_Notify message;

[0086] Step S714: The NEF sends an Nnef_EventExposure_Notify message with the "Availability after DDN failure" event to the AF;

[0087] Step S715: The UE undergoes cross - area movement and the AMF changes.

[0088] Steps S716 - S717: The Target - AMF sends an Nsmf_PDUSession_CreateSMContextRequest message to the I - SMF, and the I - SMF replies with an Nsmf_PDUSession_CreateSMContext Response message;

[0089] Specifically, during the mobility process, when an I-SMF is inserted into the user session on the Target-AMF, the Target-AMF sends an Nsmf_PDUSession_CreateSMContext Request message to the I-SMF, carrying the DdnFailureSubs parameter (with ddnFailureSubsInd set to true) to trigger the SMF to start detecting downlink data. The I-SMF replies with an Nsmf_PDUSession_CreateSMContext Response message.

[0090] Step S718a: The Target-AMF sends an Nsmf_PDUSession_UpdateSMContextRequest message to the I-SMF.

[0091] Specifically, after the successful insertion of the I-SMF, the Target-AMF sends an Nsmf_PDUSession_UpdateSMContext Request message to the I-SMF, carrying the TransferDdnFailureSubs parameter.

[0092] Step S718b: The I-SMF sends an Nsmf_PDUSession_UpdateSMContextResponse message to the Target-AMF.

[0093] Step S719a: The I-SMF sends an Nsmf_PDUSession_Update Request message to the A-SMF.

[0094] Specifically, the I-SMF sends an Nsmf_PDUSession_Update Request message to the A-SMF, carrying the TransferDdnFailureSubs parameter, indicating to the A-SMF to stop monitoring for user downlink data transfer failures and delete the subscription resources related to the DDNFailure status notification.

[0095] Step S719b: The A-SMF sends an Nsmf_PDUSession_Update Response message to the I-SMF.

[0096] Steps S720 - S721: The I-SMF is informed that the UE is unreachable, decides to discard the downlink data received from the UPF, and sends the DDN failure status to the Target-AMF through the Nsmf_PDUSession_SMContextStatusNotify message.

[0097] In steps S722 - S723, Target-AMF detects that the UE is reachable and sends an event report to the NEF via the Namf_EventExposure_Notify message based on the Notify on available after DDN failure flag.

[0098] Specifically, in this way, the AF that is notified of the DL service transmission failure is informed.

[0099] In step S724, the NEF sends an Nnef_EventExposure_Notify message with the "Availability after DDN failure" event to the AF.

[0100] The embodiment of the present application improves and optimizes the availability event subscription function after the downlink data notification failure event in the high-latency communication field. After the terminal moves across regions, relevant NFs are timely notified to release resources, reducing performance consumption, having a global resource strategy, and achieving precise control of network resources.

[0101] The embodiment of the present application also provides a computer-readable storage medium, in which a computer program is stored. The computer program is configured to execute the steps in any one of the above method embodiments when running.

[0102] In an exemplary embodiment, the above computer-readable storage medium may include, but is not limited to: USB flash drive, read-only memory (ROM for short), random access memory (RAM for short), mobile hard disk, magnetic disk, or optical disc, etc., various media that can store computer programs.

[0103] The embodiment of the present application also provides an electronic device, including a memory and a processor. A computer program is stored in the memory, and the processor is configured to run the computer program to execute the steps in any one of the above method embodiments.

[0104] In an exemplary embodiment, the above electronic device may further include a transmission device and an input / output device. The transmission device is connected to the above processor, and the input / output device is connected to the above processor.

[0105] Specific examples in this embodiment may refer to the examples described in the above embodiments and exemplary embodiments, and will not be elaborated here.

[0106] Obviously, those skilled in the art should understand that the above-mentioned modules or steps of the present application can be implemented by a general-purpose computing device. They can be concentrated on a single computing device or distributed on a network composed of multiple computing devices. They can be implemented by program codes executable by the computing device. Thus, they can be stored in a storage device and executed by the computing device. And in some cases, the steps shown or described can be executed in a sequence different from that here, or they can be separately fabricated into individual integrated circuit modules, or multiple modules or steps among them can be fabricated into a single integrated circuit module for implementation. In this way, the present application is not limited to any specific combination of hardware and software.

[0107] The above are only the preferred embodiments of the present application and are not used to limit the present application. For those skilled in the art, the present application can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the principle of the present application shall be included within the protection scope of the present application.

Claims

1. A method for notifying the failure status of a Downlink Data Notification (DDN), characterized in that, Including: A first Access and Mobility Management Function (AMF) that communicates with a User Equipment (UE) sends a first message to an Access Side Session Management Function (A-SMF), where the first message is used to subscribe to a Downlink Data Notification (DDN) fault status notification. When the UE undergoes cross-region mobility, the first AMF sends a second message to a Session Management Function (I-SMF) in an Internet Protocol Multimedia Subsystem, where the second message is used to subscribe to a DDN fault status notification. The first AMF sends a third message to the A-SMF through the I-SMF, where the third message is used to cancel the subscription to the DDN fault status notification.

2. The method according to claim 1, wherein The first AMF sending the first message to the A-SMF includes: The first AMF receives a fourth message sent by a Unified Data Management (UDM), where the fourth message is used to subscribe to the availability after a DDN fault. In response to the fourth message, the first AMF sends the first message to the A-SMF, where the first message is used to subscribe to the DDN fault status notification.

3. According to the method of claim 2, after the first AMF sends the first message to the A-SMF in response to the fourth message, it further includes: When the A-SMF is informed that the UE is unreachable, the first AMF receives a DDN fault status notification sent by the A-SMF.

4. The method according to claim 3, characterized in that, After the first AMF receives the DDN fault status notification sent by the A-SMF, it further includes: The first AMF detects whether the UE is reachable. When the first AMF detects that the UE is reachable, the first AMF reports the availability after the DDN fault to an Application Function (AF) through a Network Exposure Function (NEF).

5. The method according to claim 4, wherein The first AMF reporting the message of the availability after the DDN fault to the AF includes: The first AMF sends a message carrying an availability event after the DDN fault to the AF through the NEF.

6. The method according to claim 1, wherein Before the first AMF sends the second message to the I-SMF, it further includes: The first AMF sends a session creation request to the I-SMF in the area where the UE moves to.

7. The method according to claim 1, characterized in that The third message is also used to notify the A-SMF to stop monitoring downlink data and release the subscribed resources.

8. The method according to claim 1, wherein The method further includes: When the UE undergoes cross-region inter-office mobility, a second AMF sends a fifth message to the I-SMF, where the fifth message is used to subscribe to a DDN fault status notification.

9. A computer-readable storage medium, characterized in that, A computer program is stored in the computer-readable storage medium, where when the computer program is executed by a processor, it implements the steps of the method described in any one of claims 1 to 8.

10. An electronic device, comprising a memory, a processor, and a computer program stored on the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the steps of the method described in any one of claims 1 to 8.

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