Communication methods and devices

Abstract

Provided are a communication method and apparatus for solving the problem that a terminal device cannot perform normal communication on other accesses by means of operations performed on common parameters through several accesses of the terminal device. The method includes the following. When the terminal device on a first access is switched from a first PLMN to a second PLMN, if the state of the terminal device on a second access is that the terminal device is registered with or has been registered with the first PLMN, the terminal device determines not to delete the first mobility management parameters for the first access. If the state of the terminal device on the second access is that the terminal device has not been registered with the first PLMN, the terminal device determines to delete the first mobility management parameters for the first access. The first access and the second access belong to different access types. The registration status for the second access is considered when the first mobility management parameters are deleted, and thus the impact on communication on the second access can be reduced.

Description

Technical Field

[0001] Cross-reference to Related Applications This application claims the priority of Chinese Patent Application No. 202210479701.2, titled "COMMUNICATION METHOD AND APPARATUS", filed with the State Intellectual Property Office of China on May 5, 2022, the entire content of which is incorporated herein by reference.

[0002] This application relates to the field of communication technologies, and particularly, to communication methods and apparatuses.

Background Art

[0003] With the development of communication, currently, terminal devices are supported to communicate with the core network via multiple types of accesses. For example, a terminal device can communicate with the core network via accesses of 3rd generation partnership project (3GPP) wireless access technology and non-3GPP access technology.

[0004] When a terminal device registers with the same public land mobile network (PLMN) via multiple accesses, some parameters can be shared across multiple accesses of the terminal device during communication. For example, non-access stratum (NAS) integrity protection algorithms, NAS encryption algorithms, globally unique temporary UE identity (GUTI), etc. are shared across multiple accesses of the terminal device.

[0005] Since several parameters are shared across multiple accesses of a terminal device, if an action such as deletion or modification is performed on these parameters via one access of the terminal device, communication on other accesses will be affected. For example, if NAS security context information is deleted via one access of a terminal device, integrity protection and encryption may not be performed in uplink signaling for other accesses, and downlink signaling may not be received properly due to integrity check failures. In another example, if GUTI is deleted for one access of a terminal device, some messages for other accesses may not be able to carry the GUTI information. Consequently, the PLMN may not be able to identify the terminal device, and the terminal device may not be able to receive paging from the PLMN.

[0006] Therefore, a way to avoid the impact of actions performed on common parameters via several accesses of terminal devices on other accesses is an urgent issue that needs to be resolved. [Overview of the project]

[0007] This application provides a communication method and apparatus to solve the problem that a terminal device cannot perform normal communication over other accesses due to operations performed over common parameters over several accesses of the terminal device.

[0008] According to a first aspect, the present application provides a communication method. The method may be implemented by a terminal device, or by a chip, circuit, or other component configured to implement the functions of a terminal device. The terminal device is used as an example. The method includes: When a terminal device on a first access is switched from a first PLMN to a second PLMN, if the state of the terminal device on the second access is that the terminal device is registered with the first PLMN, or has been registered with the first PLMN, the terminal device decides not to delete the first mobility management parameters for the first access. If the state of the terminal device on the second access is that the terminal device has not been registered with the first PLMN, the terminal device decides to delete the first mobility management parameters for the first access. The first access and the second access belong to different access types.

[0009] Whether a first PLMN (i.e., a PLMN registered via the first access) is registered via the second access can be used to determine whether a terminal device needs to use the first mobility management parameters for communication over the second access. In this embodiment of the present application, if a terminal device on the second access does not register with the first PLMN, the terminal device removes the first mobility management parameters for the first access, and thus the information maintenance cost of the terminal device can be reduced without affecting the communication performed by the terminal device on the second access, and the use of invalid parameters (i.e., the first mobility management parameters) by the terminal device for communication over the first access can be further avoided, thereby improving the communication performance of the terminal device on the first access.

[0010] When a terminal device on the second access has registered with the first PLMN, or is registered with the first PLMN, the first mobility management parameters are not deleted, and therefore, it can be guaranteed that the terminal device can perform normal communication on the second access.

[0011] In a possible design, if a PLMN registered via the first access is the same as a PLMN registered via the second access, the mobility management parameters of the first access are shared across both the first and second accesses.

[0012] In a possible design, before the terminal device on the first access switches from the first PLMN to the second PLMN, the method further includes the following: The terminal device determines that the first PLMN was registered via the first access.

[0013] In a possible design, after it is determined that the first mobility management parameter will not be removed, the method further includes the following: If the switch is performed from the first PLMN to the third PLMN via the second access, the terminal device decides to remove the first mobility management parameter.

[0014] After a terminal device on the second access switches from the first PLMN to another PLMN, the terminal device does not use the first mobility management parameters for communication on the second access. Therefore, after a terminal device on the second access switches from the first PLMN to another PLMN, the first mobility management parameters are promptly removed, thus reducing the parameter maintenance cost of the terminal device, and further avoiding the terminal device using invalid parameters (i.e., the first mobility management parameters) for communication on the first and / or second access.

[0015] In a possible design, the first mobility management parameter includes at least one of either a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0016] In a possible design, the NAS security context information includes the security encryption algorithm, which is a null encryption algorithm.

[0017] The security of NAS security context information is lower when the security encryption algorithm is a null encryption algorithm. Therefore, in the above method, the first mobility management parameter is removed when the security encryption algorithm in the NAS security context information identified by the key set identifier is a null encryption algorithm, thereby facilitating communication security for terminal devices.

[0018] According to a second aspect, the present application provides a communication method, which may be implemented by a terminal device or by a chip, circuit, or other component configured to implement the functions of a terminal device. The terminal device is used as an example. The method includes: The terminal device obtains first information via a first access of the terminal device and, based on the first information and information about a second access of the terminal device, determines whether to remove a first mobility management parameter for the first access. The first information indicates the reason why a core network device rejects the terminal device's request and that the first access and the second access belong to different access types.

[0019] In this embodiment of the present application, when the first mobility management parameter for the first access is removed, considering the information for the second access, the first mobility management parameter may not be removed when the first mobility management parameter is required on the second access, and therefore the terminal device can communicate on the second access by using the first mobility management parameter. This avoids the problem that normal communication may not be performed on the second access because the first mobility management parameter for the first access is removed in inappropriate scenarios (for example, when the first mobility management parameter is required on the second access), and reduces the impact on communication on the second access.

[0020] Furthermore, the terminal device can decide whether to remove the first mobility management parameter for the first access, thus providing flexibility and greater accuracy in handling the first mobility management parameter.

[0021] In a possible design, if a PLMN registered via the first access is the same as a PLMN registered via the second access, the mobility management parameters of the first access are shared across both the first and second accesses.

[0022] In a possible design, the first information is not applicable to the second access. The terminal device's decision to delete the first mobility management parameter based on the first information and the terminal device's information about the second access includes: The terminal device decides whether to delete the first mobility management parameter based on the first information and the registration information about the second access.

[0023] Registration information for the second access may be used to determine whether the terminal device needs to use the first mobility management parameters for communication over the second access. In this way, the terminal device can avoid deleting the first mobility management parameters when it uses them for communication over the second access, thereby ensuring that normal communication is performed by the terminal device over the second access.

[0024] In a possible design, the terminal device's decision to delete a first mobility management parameter based on first information and registration information for second access includes the following: The terminal device decides to delete the first mobility management parameter when the registration information for second access satisfies one of the following conditions: namely, the PLMN is not registered via second access, or the PLMN registered via second access is different from the PLMN registered via first access.

[0025] If registration is not performed via a second access on a PLMN registered via a first access, it may be determined that the terminal device does not need to use the first mobility management parameter for communication over the second access. In the above scheme, the terminal device removes the first mobility management parameter when it does not need to use it for communication over the second access, and thus the information maintenance cost of the terminal device can be reduced without affecting the communication performed by the terminal device over the second access, and the use of invalid parameters (i.e., the first mobility management parameter) by the terminal device for communication over the first access can be further avoided, thereby improving the communication performance of the terminal device over the first access.

[0026] In a possible design, for the terminal device to determine whether to delete the first mobility management parameter based on the first information and the registration information about the second access, it includes the following. When the registration information about the second access satisfies the following condition, that is, the PLMN registered via the second access is the same as the PLMN registered via the first access, the terminal device determines not to delete the first mobility management parameter.

[0027] When the PLMN registered via the first access is also registered via the second access, it can be determined that the terminal device needs to use the first mobility management parameter for communication on the second access. In the above manner, when the terminal device needs to use the first mobility management parameter for communication on the second access, the terminal device does not delete the first mobility management parameter, and thus it can be guaranteed that normal communication is carried out by the terminal device on the second access.

[0028] In a possible design, the first information is applicable to the second access. For the terminal device to determine whether to delete the first mobility management parameter based on the first information and the information about the second access of the terminal device, it includes the following. The terminal device determines whether to delete the first mobility management parameter based on the first information, the registration information about the second access, and the service information about the second access, and the service information about the second access is information about whether an emergency service is being carried out on the second access.

[0029] In the above design, the degradation of communication quality caused by the deletion of the first mobility management parameter when there is an emergency service on the second access can be reduced. Thus, it can be guaranteed that the emergency service usually carried out via the second access is carried out normally, and the user experience is improved.

[0030] In a possible design, an emergency service is a service corresponding to a protocol data unit (PDU) session that carries a first identifier, and the first identifier identifies that the service implemented on the PDU session is an emergency service.

[0031] In a possible design, for a terminal device to process first mobility management parameters based on first information, registration information about a second access, and service information about the second access, the following is included. The terminal device determines to delete the first mobility management parameters when the registration information about the second access and the service information about the second access satisfy one of the following conditions: the public land mobile network (PLMN) is not registered via the second access; the PLMN registered via the second access is different from the PLMN registered via the first access; or the PLMN registered via the second access is the same as the PLMN registered via the first access and an emergency service is not being implemented on the second access.

[0032] In the above design, the information maintenance cost of the terminal device can be reduced without affecting the communication performed by the terminal device on the second access or the emergency service being implemented on the second access, and the terminal device is further prevented from using parameters that are invalid for communication on the first access (i.e., the first mobility management parameters), thereby improving the communication performance of the terminal device on the first access.

[0033] In a possible design, the terminal device processing the first mobility management parameter based on the first information, registration information for the second access, and service information for the second access includes the following: The terminal device decides not to delete the first mobility management parameter when the registration information for the second access and the service information for the second access satisfy the following conditions: namely, the PLMN registered via the second access is the same as the PLMN registered via the first access, and emergency services are being performed on the second access.

[0034] Based on the above explanation, it is guaranteed that emergency services on the second access point will be successfully implemented, thereby improving the user experience.

[0035] In a possible design, the terminal device decides to remove the first mobility management parameter after the emergency service has ended. In the above design, the information maintenance cost of the terminal device may be reduced, and the use of an invalid parameter (i.e., the first mobility management parameter) for communication on the first access may be avoided, thereby improving the communication performance of the terminal device on the first access.

[0036] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes: the terminal device removes the second mobility management parameter, the second mobility management parameter including at least one of the last visited tracking area identification for the second access or the tracking area identification list for the second access. In the above design, the information maintenance cost of the terminal device may be reduced.

[0037] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes: the terminal device suspends the service being performed over the second access. In the above design, communication resources may be saved.

[0038] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes: the terminal device starting a first timer for a second access, the first timer being used to trigger the terminal device to release the N1 NAS signaling connection, or releasing the N1 NAS signaling connection. In the above design, N1 NAS signaling connection resources may be conserved.

[0039] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes: If the mobility management procedure is being performed on the second access, the terminal device stops the mobility management procedure. In the above design, communication resources may be saved.

[0040] In a possible design, the first mobility management parameter includes at least one of either a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0041] According to a third aspect, the present application provides a communication method, which may be implemented by a core network device or by a chip, circuit, or other component configured to implement the functions of a core network device. The core network device is used as an example. The method includes: the core network device transmits first information to a terminal device via a first access of the terminal device, the first information indicating why the core network device is rejecting the terminal device's request; the core network device determines, based on the first information and information about a second access of the terminal device, whether to remove a first mobility management parameter for the first access, where the first access and the second access belong to different access types.

[0042] In this embodiment of the present application, when the first mobility management parameter for the first access is removed, considering the information for the second access, the first mobility management parameter may not be removed when the first mobility management parameter is required on the second access, and therefore the terminal device may use the first mobility management parameter for communication on the second access. This avoids the problem that normal communication may not occur on the second access because the first mobility management parameter for the first access is removed, and reduces the impact on communication on the second access.

[0043] In a possible design, if a PLMN registered via the first access is the same as a PLMN registered via the second access, the mobility management parameters of the first access are shared across both the first and second accesses.

[0044] In a possible design, the first information is not applicable to the second access. The core network device's decision on whether to remove the first mobility management parameter based on the first information and the information about the second access includes: The core network device decides whether to remove the first mobility management parameter based on the first information and the registration information about the second access.

[0045] Registration information for the second access may be used to determine whether the core network device needs to use the first mobility management parameters for communication over the second access. In this way, the terminal device can avoid deleting the first mobility management parameters when it uses them for communication over the second access, thereby ensuring that normal communication is performed by the terminal device over the second access.

[0046] In a possible design, the core network device's decision to remove the first mobility management parameter based on the first information and the registration information for the second access includes the following: The core network device decides to remove the first mobility management parameter when the registration information for the second access satisfies one of the following conditions, namely, that the PLMN is not registered via the second access.

[0047] If registration is not performed via a second access on a PLMN registered via a first access, it may be determined that the terminal device does not need to use the first mobility management parameters for communication over the second access. In the above scheme, the first mobility management parameters are removed when the terminal device does not need to use them for communication over the second access, and therefore the information maintenance cost of the core network device can be reduced without affecting the communication performed by the terminal device over the second access.

[0048] In a possible design, the core network device's decision to remove the first mobility management parameter based on the first information and the registration information for the second access includes the following: The core network device decides not to remove the first mobility management parameter when the registration information for the second access satisfies the following condition: namely, the PLMN registered via the second access is the same as the PLMN registered via the first access.

[0049] If a PLMN registered via the first access is also registered via the second access, it may be determined that the terminal device needs to use the first mobility management parameters for communication over the second access. In the above scheme, the terminal device does not delete the first mobility management parameters when it needs to use them for communication over the second access, and thus it can be guaranteed that normal communication is performed by the terminal device over the second access.

[0050] In a possible design, the first information is applicable to the second access. The core network device's decision on whether to remove the first mobility management parameter based on the first information and the information about the second access includes: the core network device deciding whether to remove the first mobility management parameter based on the first information, registration information for the second access, and service information for the second access, where the service information for the second access is information about whether emergency services are being performed on the second access.

[0051] The above design may reduce the impact on the service for second access and improve the user experience.

[0052] In a possible design, the core network device processing the first mobility management parameter based on the first information, registration information for the second access, and service information for the second access includes the following: The core network device decides to remove the first mobility management parameter when the registration information for the second access and the service information for the second access satisfy one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN registered via the second access is the same as the PLMN registered via the first access, and emergency services are not performed on the second access.

[0053] In the above design, the information maintenance cost of the core network device can be reduced without affecting communications performed by terminal devices on the second access or emergency services performed on the second access.

[0054] In a possible design, the core network device processing the first mobility management parameter based on the first information, registration information for the second access, and service information for the second access includes the following: The core network device decides not to delete the first mobility management parameter when the registration information for the second access and the service information for the second access satisfy the following conditions: namely, the PLMN registered via the second access is the same as the PLMN registered via the first access, and emergency services are being performed on the second access.

[0055] Based on the above explanation, it is guaranteed that emergency services on the second access point will be successfully implemented, thereby improving the user experience.

[0056] In a feasible design, the core network device decides to remove the first mobility management parameter after the emergency service has ended. This design can reduce the information maintenance costs of the core network device.

[0057] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes: the core network device removes the second mobility management parameter, the second mobility management parameter including at least one of the last visited tracking area identification for the second access or the tracking area identification list for the second access. In the above design, the information maintenance cost of the core network device may be reduced.

[0058] In a possible design, if it is determined that the first mobility management parameter is to be removed, this method further includes: the core network device discontinues the service being performed over the second access. In the above design, communication resources may be saved.

[0059] In possible designs, if it is determined that the first mobility management parameter is removed, this method further includes: the core network device releases the N1 NAS signaling connection. In the above design, N1 NAS signaling connection resources may be saved.

[0060] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes the following: If the mobility management procedure is being performed on the second access, the core network device stops the mobility management procedure. In the above design, communication resources may be saved.

[0061] In a possible design, the first mobility management parameter includes at least one of either a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0062] According to a fourth aspect, the present application provides a communication method, which may be implemented by a terminal device or by a chip, circuit, or other component configured to perform functions of a terminal device. The terminal device is used as an example. The method includes: the terminal device receiving first indication information via a first access of the terminal device, the first indication information indicating whether to remove a first mobility management parameter for the first access, and determining, based on the first indication information, whether to remove a first mobility management parameter for the first access, wherein the first access and the second access belong to different access types.

[0063] In this embodiment of the present application, the network device indicates to the terminal device whether to remove a first mobility management parameter, thereby reducing the complexity of the terminal device.

[0064] In a possible design, if a PLMN registered via the first access is the same as a PLMN registered via the second access, the mobility management parameters of the first access are shared across both the first and second accesses.

[0065] In a possible design, the terminal device's decision to remove a first mobility management parameter based on first indication information includes: The terminal device decides to remove a first mobility management parameter based on the first indication information and information about a second access.

[0066] In the above method, when the first mobility management parameter for the first access is deleted, considering the information for the second access, the first mobility management parameter may not be deleted when it is required on the second access, and therefore the terminal device may use the first mobility management parameter for communication on the second access. This avoids the problem that normal communication may not occur on the second access because the first mobility management parameter for the first access is deleted, and reduces the impact on communication on the second access.

[0067] In a possible design, the terminal device's decision to delete a first mobility management parameter based on first indication information and second access information includes: The terminal device decides to delete a first mobility management parameter based on first indication information and second access registration information.

[0068] Registration information for the second access may be used to determine whether the terminal device needs to use the first mobility management parameters for communication over the second access. In this way, the terminal device can avoid deleting the first mobility management parameters when it uses them for communication over the second access, thereby ensuring that normal communication is performed by the terminal device over the second access.

[0069] In a possible design, the terminal device's decision to delete a first mobility management parameter based on first indication information and second access registration information includes the following: If the first indication information indicates that the first mobility management parameter should be deleted, the terminal device decides to delete the first mobility management parameter if the second access registration information satisfies one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN registered via the second access is different from the PLMN registered via the first access.

[0070] If registration is not performed via a second access on a PLMN registered via a first access, it may be determined that the terminal device does not need to use the first mobility management parameter for communication over the second access. In this scheme, the terminal device removes the first mobility management parameter when it does not need to use it for communication over the second access, and thus the information maintenance cost of the terminal device can be reduced without affecting the communication performed by the terminal device over the second access, and the use of invalid parameters (i.e., the first mobility management parameter) by the terminal device for communication over the first access can be further avoided, thereby improving the communication performance of the terminal device over the first access.

[0071] In a possible design, a terminal device's decision to remove a first mobility management parameter based on first indication information and registration information for a second access includes: If the first indication information indicates that the first mobility management parameter should be removed, and a PLMN registered via the second access is the same as a PLMN whose registration is not performed via the first access, the terminal device decides whether to remove the first mobility management parameter based on service information for the second access, where service information for the second access is information about whether emergency services are being performed on the second access.

[0072] The above design may reduce the impact on the service for second access and improve the user experience.

[0073] In a possible design, the terminal device's decision on whether to remove the first mobility management parameter based on service information for the second access includes: if emergency services are being performed on the second access, the terminal device decides not to remove the first mobility management parameter; or if emergency services are not being performed on the second access, the terminal device decides to remove the first mobility management parameter.

[0074] The above design ensures that emergency services performed successfully on the second access point will also be performed successfully, thereby potentially improving the user experience.

[0075] In a possible design, if it is determined that the first mobility management parameter will be removed, the method further includes: The terminal device decides to remove the first mobility management parameter after the emergency service has ended. In the above design, the information maintenance cost of the terminal device may be reduced, and the use of an invalid parameter (i.e., the first mobility management parameter) by the terminal device for communication on the first access may be avoided, thereby improving the communication performance of the terminal device on the first access.

[0076] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes: the terminal device removes the second mobility management parameter, the second mobility management parameter including at least one of the last visited tracking area identification for the second access or the tracking area identification list for the second access. In the above design, the information maintenance cost of the terminal device may be reduced.

[0077] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes: the terminal device suspends the service being performed over the second access. In the above design, communication resources may be saved.

[0078] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes: the terminal device starting a first timer for a second access, the first timer being used to trigger the terminal device to release the N1 NAS signaling connection, or releasing the N1 NAS signaling connection. In the above design, N1 NAS signaling connection resources may be conserved.

[0079] In a possible design, if it is determined that the first mobility management parameter is to be removed, the method further includes: If the mobility management procedure is being performed on the second access, the terminal device stops the mobility management procedure. In the above design, communication resources may be saved.

[0080] In a possible design, the first mobility management parameter includes at least one of either a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0081] According to a fifth aspect, the present application provides a communication method, which may be implemented by a core network device or by a chip, circuit, or other component configured to implement the functions of a core network device. The core network device is used as an example. The method includes: the core network device determines first indication information, transmits the first indication information to a terminal device via a first access of the terminal device, the first indication information indicates whether to remove a first mobility management parameter for the first access, and the first access and the second access belong to different access types.

[0082] In this embodiment of the present application, the network device indicates to the terminal device whether to remove a first mobility management parameter, thereby reducing the complexity of the terminal device.

[0083] In a possible design, if a PLMN registered via the first access is the same as a PLMN registered via the second access, the mobility management parameters of the first access are shared across both the first and second accesses.

[0084] In a possible design, the core network device determining the first indication information includes: the core network device determining the first indication information based on the second indication information and information about the second access, where the second indication information indicates why the core network device is rejecting the terminal device's request.

[0085] In this embodiment of the present application, when the first mobility management parameter for the first access is removed, considering the information for the second access, the first mobility management parameter may not be removed when the first mobility management parameter is required on the second access, and therefore the terminal device may use the first mobility management parameter for communication on the second access. This avoids the problem that normal communication may not occur on the second access because the first mobility management parameter for the first access is removed, and reduces the impact on communication on the second access.

[0086] In possible designs, the second indication information is not applicable to the second access. The core network device determining the first indication information based on the second indication information and information about the second access includes: The core network device determining the first indication information based on the second indication information and registration information about the second access.

[0087] Registration information for the second access may be used to determine whether the core network device needs to use the first mobility management parameters for communication over the second access. In this way, the terminal device can avoid deleting the first mobility management parameters when it uses them for communication over the second access, thereby ensuring that normal communication is performed by the terminal device over the second access.

[0088] In a possible design, the core network device determining the first indication information based on the second indication information and the registration information for the second access includes the following: The core network device indicates, based on the first indication information, that the registration information for the second access satisfies one of the following conditions, i.e., PLMN is not registered via the second access; or alternatively, the core network device indicates, based on the first indication information, that the registration information for the second access satisfies the following condition, i.e., PLMN is registered or registered via the second access; or alternatively, that the core network device does not delete the first mobility management parameter.

[0089] If registration is not performed via a second access on a PLMN registered via a first access, it may be determined that the terminal device does not need to use the first mobility management parameters for communication over the second access. In the above scheme, the first mobility management parameters are removed when the terminal device does not need to use them for communication over the second access, and therefore the information maintenance cost of the core network device can be reduced without affecting the communication performed by the terminal device over the second access.

[0090] If a PLMN registered via the first access is also registered via the second access, it may be determined that the terminal device needs to use the first mobility management parameters for communication over the second access. In the above scheme, the terminal device does not delete the first mobility management parameters when it needs to use them for communication over the second access, and thus it can be guaranteed that normal communication is performed by the terminal device over the second access.

[0091] In a possible design, the second indication information is applicable to the second access. The core network device determining the first indication information based on the second indication information and information about the second access includes: the core network device determining the first indication information based on the second indication information, registration information for the second access, and service information for the second access, where the service information for the second access is information about whether emergency services are being performed on the second access.

[0092] The above design may reduce the impact on the service for second access and improve the user experience.

[0093] In a possible design, the core network device determining the first indication information based on the second indication information, the registration information for the second access, and the service information for the second access includes the following: The core network device indicates by the first indication information that the first mobility management parameter will be removed when the registration information for the second access and the service information for the second access satisfy one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN is registered or registered via the second access and emergency services are not performed on the second access.

[0094] In the above design, the information maintenance cost of the core network device can be reduced without affecting communications performed by terminal devices on the second access or emergency services performed on the second access.

[0095] In a possible design, the core network device determining the first indication information based on the second indication information, the registration information for the second access, and the service information for the second access includes the following: The core network device indicates, based on the first indication information, that it will not remove the first mobility management parameter if the registration information for the second access and the service information for the second access satisfy the following conditions: namely, the PLMN is registered or registered via the second access, and emergency services are not performed on the second access.

[0096] Based on the above explanation, it is guaranteed that emergency services on the second access point will be successfully implemented, thereby improving the user experience.

[0097] In a possible design, the first mobility management parameter includes at least one of either a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0098] According to a sixth aspect, the present application further provides a communication device having the function of implementing any method provided in the first, second, or fourth aspects. The communication device may be implemented by hardware or by hardware running corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0099] In possible designs, the communication device includes a processor. The processor is configured to support the communication device in performing the corresponding functions of the terminal device in the manner described above. The communication device may further include memory. The memory may be coupled to the processor and stores program instructions and data required for the communication device. Optionally, the communication device may further include interface circuitry, which is configured to support communication between the communication device and another device.

[0100] In possible designs, the communication device includes corresponding functional modules, each configured to perform the steps in the method described above. The functions may be implemented by hardware or by hardware running corresponding software. The hardware or software includes one or more modules corresponding to the functions described above.

[0101] In possible designs, the structure of the communication device includes a processing module and a communication module. The modules may perform the corresponding functions in the example methods described above. For further details, please refer to the descriptions of the methods provided in the first, second, or fourth embodiments. Details will not be described again here.

[0102] According to the seventh aspect, the present application further provides a communication device having the function of implementing any method provided in the third or fifth aspect. The communication device may be implemented by hardware or by hardware running corresponding software. The hardware or software includes one or more units or modules corresponding to the above-described function.

[0103] In possible designs, the communication device includes a processor. The processor is configured to support the communication device in performing the corresponding functions of the network device in the manner described above. The communication device may further include memory. The memory may be coupled to the processor and stores program instructions and data required for the communication device. Optionally, the communication device may further include interface circuitry, which is configured to support communication between the communication device and another device.

[0104] In possible designs, the communication device includes corresponding functional modules, each configured to perform the steps in the method described above. This functionality may be implemented by hardware or by hardware running corresponding software. The hardware or software includes one or more modules corresponding to the aforementioned functionality.

[0105] In possible designs, the structure of the communication device includes a processing module and a communication module. The modules may perform the corresponding functions in the example methods described above. For further details, please refer to the description of the methods provided in the third or fifth embodiment. Details are not described again here.

[0106] According to the eighth aspect, a communication device is provided, comprising a processor and an interface circuit. The interface circuit is configured to receive signals from a communication device other than the communication device and transmit signals to the processor, or transmit signals from the processor to a communication device other than the communication device. The processor is configured to implement the methods and possible designs of any one of the first, second, or fourth aspects by using logic circuits or by executable code instructions.

[0107] According to the ninth aspect, a communication device is provided, comprising a processor and an interface circuit. The interface circuit is configured to receive signals from a communication device other than the communication device and transmit signals to the processor, or transmit signals from the processor to a communication device other than the communication device. The processor is configured to implement the methods and possible designs of the third or fifth aspect by using logic circuits or by executable code instructions.

[0108] According to the tenth aspect, a computer-readable storage medium is provided. The computer-readable storage medium stores a computer program or instruction. When the computer program or instruction is executed by a processor, one of the methods and possible designs in any one of the first to fifth aspects is implemented.

[0109] According to the eleventh aspect, a computer program product for storing instructions is provided. When the instructions are executed by a processor, one of the methods and possible designs in any one of the first to fifth aspects is implemented.

[0110] According to the twelfth aspect, a chip system is provided. The chip system includes a processor and further includes memory, and can implement any one of the methods and possible designs in any one of the first to fifth aspects. The chip system may include a chip, or may include a chip and other separate devices.

[0111] According to the thirteenth aspect, a communication system is provided. The system includes an apparatus according to the first aspect (e.g., a terminal device) and may further include a core network device.

[0112] According to the fourteenth aspect, a communication system is provided. The system includes devices according to the second aspect (e.g., terminal devices) and devices according to the third aspect (e.g., core network devices).

[0113] According to the 15th aspect, a communication system is provided. The system includes devices according to the fourth aspect (e.g., terminal devices) and devices according to the fifth aspect (e.g., core network devices). [Brief explanation of the drawing]

[0114] [Figure 1] This is a diagram of a 5G network architecture based on a service-based architecture according to an embodiment of this application. [Figure 2] This is a diagram of the architecture of an unreliable non-3GPP access network according to an embodiment of the present application. [Figure 3] This is a diagram of the architecture of a reliable non-3GPP access network according to an embodiment of the present application. [Figure 4] This is a schematic flowchart of the communication method according to the embodiment of this application. [Figure 5] This is a schematic flowchart of the communication method according to the embodiment of this application. [Figure 6] This is a schematic flowchart of the communication method according to the embodiment of this application. [Figure 7] This is a schematic flowchart of the communication method according to the embodiment of this application. [Figure 8] This is a diagram showing the structure of a communication device according to an embodiment of the present application. [Figure 9] This is a diagram showing the structure of a communication device according to an embodiment of the present application. [Modes for carrying out the invention]

[0115] To further clarify the purpose, technical solutions, and advantages of the embodiments of this application, the embodiments of this application will be described in more detail below with reference to the accompanying drawings.

[0116] The following describes the architecture of a network system to which the method provided in this application is applied.

[0117] Figure 1 is a diagram of a 5G network architecture based on a service-based architecture. The 5G network architecture shown in Figure 1 may include three parts: terminal devices, data network (DN), and carrier network. The following is a brief explanation of the functions of some network elements.

[0118] A carrier network may include one or more network elements such as the authentication server function (AUSF), network exposure function (NEF), policy control function (PCF), unified data management (UDM), unified data repository (UDR), network repository function (NRF), access and mobility management function (AMF), session management function (SMF), access network, and user plane function (UPF). In a carrier network, the portion other than the wireless access network is sometimes referred to as the core network portion. In possible implementations, the carrier network may further include application function (AF) network elements. Alternatively, AF network elements may belong to a third party rather than the carrier network.

[0119] A terminal device is a device with wireless transceiver functionality that can be deployed on land, including indoor or outdoor devices, handheld devices, or in-vehicle devices, or on water (e.g., on a ship), or in the air (e.g., on an airplane, balloon, or satellite). Terminal devices may include mobile phones, tablet computers, computers with wireless transceiver functionality, virtual reality (VR) terminals, augmented reality (AR) terminals, wireless terminals in industrial control, wireless terminals in self-driving systems, wireless terminals in remote medical systems, wireless terminals in smart grids, wireless terminals in transportation safety systems, wireless terminals in smart cities, wireless terminals in smart homes, and UEs (Uninterruptible Equipment).

[0120] A terminal device may establish a connection to the carrier network through an interface provided by the carrier network (e.g., N1) and use services such as data services and / or voice services provided by the carrier network. The terminal device may further access the DN through the carrier network and use carrier services and / or services provided by third parties deployed on the DN. Third parties may be service parties other than the carrier network and the terminal device, and may provide services such as data services and / or voice services for the terminal device. The specific form of representation of a third party may be determined based on actual application scenarios and is not limited herein.

[0121] The core network portion includes user plane functions and control plane functions.

[0122] The user plane functionality includes UPF network elements. As an interface to the data network, UPF network elements perform functions such as forwarding user plane data (e.g., data packets), quality of service (QoS) control, collecting session / flow-level billing statistics, and bandwidth limiting.

[0123] The control plane functions are primarily for user registration and authentication, mobility management, and the delivery of data packet forwarding policies and QoS control policies to the user plane functions. The control plane functions can be further classified and include other network elements besides the UPF network elements, such as the AMF network elements and SMF network elements.

[0124] The AMF network element primarily performs functions such as registration procedures during user access and location management, and access authentication / authorization while users are on the move. Furthermore, the AMF network element is also responsible for transferring user policies between the UE and PCF.

[0125] SMF network elements are primarily configured to establish corresponding session connections when a user initiates a service, provide specific services to the user, and, for example, deliver data packet forwarding policies and QoS policies to UPF based on the NG4 interface between SMF and UPF.

[0126] The AUSF network element is primarily responsible for authenticating users, determining the validity of user devices, and deciding whether to allow a user or device to access the network.

[0127] The UDM network element is primarily responsible for functions such as storing user device and user access authentication subscription data.

[0128] The UDR is primarily responsible for storing and accessing subscription data, policy data, application data, and other types of data.

[0129] The PCF network element is primarily responsible for delivering service-related policies to the AMF or SMF.

[0130] NEF network elements are primarily configured to support the exposure of capabilities and events.

[0131] The AF network element primarily forwards application-side requirements for the network side to the PCF, which then generates the corresponding policy. The AF can be a third-party functional entity or a carrier-deployed application service, such as an Internet Protocol (IP) Multimedia Subsystem (IMS) voice call service.

[0132] An NRF network element may be configured to provide network element discovery functionality and, based on a request from another network element, provide network element information corresponding to the network element type. The NRF further provides network element management services, such as registration, renewal, and deregistration of network elements and subscriptions, as well as push notifications of network element status.

[0133] A DN (Data Network) is a network outside of a carrier network. A carrier network can access multiple DNs, and multiple services can be deployed on the DN to provide data services and / or voice services to terminal devices. For example, a DN could be the private network of a smart factory, where sensors installed in the smart factory's workshops could be terminal devices, and a control server for the sensors could be deployed within the DN, providing services to the sensors. The sensors could communicate with the control server to obtain commands from the control server and transmit collected sensor data to the control server based on those commands. In another example, a DN could be a company's internal office network, where an employee's mobile phone or computer could be a terminal device, and the employee's mobile phone or computer could access information, data resources, etc., on the company's internal office network.

[0134] In Figure 1, Nausf, Nnef, Npcf, Nudm, Naf, Namf, Nsmf, N1, N2, N3, N4, and N6 are interface sequence numbers. For the meaning of these interface sequence numbers, please refer to the definitions in the 3rd Generation Partnership Project (3GPP) standard protocol, which are not limited to those definitions.

[0135] An access network is a subnetwork of a carrier network and is an implementation system between service nodes in the carrier network and terminal devices. To access the carrier network, terminal devices can first pass through the access network and then connect to service nodes in the carrier network through the access network.

[0136] Access networks may include 3GPP access networks and / or non-3GPP access networks; that is, terminal devices may access the core network by using 3GPP access networks (or 3GPP access technologies) and / or non-3GPP access networks (or N3GPP access technologies). Non-3GPP access networks are non-3GPP access networks such as wireless local area networks (WLANs), wireless fidelity (Wi-Fi) networks, worldwide interoperability for microwave access (WiMAX), and fixed networks. Non-3GPP access networks may include trusted non-3GPP access networks, untrusted non-3GPP access networks, wired networks, etc. Untrusted non-3GPP access networks may include, for example, untrusted WLANs, untrusted Wi-Fi networks, and untrusted WiMAX. A reliable non-3GPP access network may include, for example, a reliable WLAN, a reliable Wi-Fi network, and a reliable WiMAX, while a wired network may include, for example, a fixed network.

[0137] Access by terminal devices on a 3GPP access network is sometimes called 3GPP access, while access by terminal devices on a non-3GPP access network is sometimes called non-3GPP access.

[0138] Access devices in a 3GPP access network can be devices that provide wireless communication capabilities to terminal devices, and are sometimes also called access network devices. Access devices in a 3GPP access network include, but are not limited to, 5G next-generation node B (gNodeB, gNB), evolved node B (eNB), radio network controller (RNC), node B (NodeB, NB), base station controller (BSC), base transceiver station (BTS), home base station (e.g., home evolved node B or home node B, HNB), baseband unit (BBU), transmission reception point (TRP), transmitting point (TP), mobile switching center, etc.

[0139] Access devices in untrusted non-3GPP access networks are sometimes referred to as non-3GPP interworking function (N3IWF) devices or next-generation packet data gateways (ngPDG). N3IWF network elements are similar to evolved packet data gateways (ePDG) in long-term evolution (LTE) and are used in 5G to establish Internet Protocol Security (IPsec) tunnels with terminal devices when they access the core network through a non-3GPP access network. The name N3IWF may change in future 5G definitions. In this application, only one example of a non-3GPP network access gateway being an N3IWF device is used for illustrative purposes.

[0140] For example, an N3IWF device may include a router.

[0141] Access devices in a trusted non-3GPP access network may include trusted non-3GPP access points (TNAPs) and / or trusted non-3GPP gateway functions (TNGFs). TNAPs are configured to communicate with terminal devices, and TNGFs are configured to communicate with core network devices. TNAPs may include, but are not limited to, WLAN access points (APs), fixed access network devices (FANs), switches, routers, and the like.

[0142] In possible examples, Figure 2 may show a terminal device accessing the core network through a 3GPP access network and an untrusted non-3GPP access network. For example, the interface between a UPF and a 3GPP access network element may be called an N3 interface, the interface between a UPF and an N3IWF device may be called an N3 interface, the interface between a 3GPP access network element and an AMF may be called an N2 interface, and the interface between an N3IWF device and an AMF may be called an N2 interface. Other interfaces are shown in Figure 2 and will not be discussed again here.

[0143] In another possible example, as shown in Figure 3, a terminal device may access the core network through a 3GPP access network and a trusted non-3GPP access network. For example, the interface between a UPF and a 3GPP access network element may be called an N3 interface, and the interface between a UPF and a TNGF network element may be called an N3 interface. The interface between a 3GPP access network element and an AMF may be called an N2 interface, the interface between a TNGF network element and an AMF may be called an N2 interface, and the interface between a TNGF network element and a TNAP may be called a Ta. Other interfaces are shown in Figure 3 and will not be discussed again here.

[0144] Please understand that Figures 2 and 3 are merely diagrams of the architecture of unreliable non-3GPP access networks and reliable non-3GPP access networks, and do not limit the type and number of access networks through which terminal devices access the core network. In a particular implementation, a terminal device may access the core network through two or more access networks. The access networks through which a terminal device accesses the core network may be, but are not limited to, one or more of the types of access networks: 3GPP access networks, unreliable non-3GPP access networks, or reliable non-3GPP access networks, or other types of access networks that may emerge in future communication developments. For the types of networks included in unreliable non-3GPP access networks and reliable non-3GPP access networks, please refer to the above explanation of unreliable non-3GPP access networks and reliable non-3GPP access networks. Details will not be explained again here.

[0145] Access by terminal devices on a 3GPP access network is sometimes called 3GPP access, while access by terminal devices on a non-3GPP access network is sometimes called non-3GPP access.

[0146] It should be understood that 3GPP access and non-3GPP access are merely examples of names, and 3GPP access may also be described as a 3GPP access link, 3GPP transmit channel, 3GPP transmit route, 3GPP transmit link, 3GPP communication link, etc. The use of 3GPP access as described in this application may be understood to be conditional on the communication link being based on 3GPP access technology.

[0147] Non-3GPP access may also be described as a non-3GPP access link, non-3GPP transmit channel, non-3GPP transmit route, non-3GPP transmit link, etc. It may be understood that non-3GPP access as described in this application is used on the condition that the communication link is based on non-3GPP access technology.

[0148] It may be understood that in the following provisions of this application, the first access may also be referred to as the first access link, the first transmission channel, the first transmission path, the first transmission link, the first communication link, and so on.

[0149] In the following, the second access may also be referred to as the second access link, second transmission channel, second transmission path, second transmission link, second communication link, etc.

[0150] It can be understood that the network elements or functions described above may be network elements in a hardware device, software functions running on dedicated hardware, or virtual functions instantiated on a platform (e.g., a cloud platform). One or more services may be obtained through the division into the network elements or functions described above. Furthermore, services may exist independently of network functions. In this application, instances of functions, instances of services contained within functions, or instances of services that exist independently of network functions may be referred to as service instances.

[0151] Furthermore, network element a is sometimes abbreviated as a. For example, an AF network element is sometimes abbreviated as AF, an NEF network element is sometimes abbreviated as NEF, and an AMF network element is sometimes abbreviated as AMF.

[0152] Figures 1 to 3 are merely examples of applicable network architectures, and it should be understood that the network architecture actually applied may include more or fewer network elements than those shown in Figures 1 to 3. In the embodiments of this application, the names of the network elements used above may be changed, but the functions of the network elements may remain the same in future communication systems.

[0153] The above describes the network architecture in the embodiments of this application. The following explains some terms used in the embodiments of this application to facilitate understanding for those skilled in the art.

[0154] Mobility management parameters: Mobility management parameters may include, but are not limited to, parameters such as key set identifiers (ngKSI or eKSI), globally unique temporary UE identity (GUTI), or tracking area identity (TAI) of the last visited tracking area.

[0155] Key set identifier: The key set identifier identifies NAS security context information. NAS security context information may include, but is not limited to, information such as the NAS integrity protection algorithm, the NAS encryption algorithm, the AMF key in the serving network (KAMF), and the security capability information of user equipment (UE).

[0156] The NAS integrity protection algorithm, sometimes called the 5G integrity protection algorithm or integrity protection algorithm, is used to perform integrity verification on NAS messages.

[0157] NAS encryption algorithms, sometimes called 5G encryption algorithms or security encryption algorithms, are used to encrypt NAS messages.

[0158] A temporary identifier assigned to GUTI:UE by the core network.

[0159] In embodiments of this application, “at least one” means one or more, and “multiple” means two or more. “And / or” indicates an association between related objects, and indicates that three relationships may exist. For example, A and / or B may mean: A exists alone, both A and B exist, or B exists alone, where A and B may be singular or plural. The letter “ / ” usually indicates an “or” relationship between related objects. “At least one of the following items (parts)” or a similar expression thereto means any combination of these items, including a single item (part) or any combination of multiple items (parts). For example, at least one item (part) of a, b, or c may mean a, b, c, a and b, a and c, b and c, or a, b, and c, where a, b, and c may be singular or plural.

[0160] Unless otherwise specified, the ordinal terms such as “first” and “second” as described in the embodiments of this application are used to distinguish between multiple objects and do not limit the size, content, sequence, time sequence, priority, importance, etc., of the multiple objects. For example, “first access” and “second access” are used merely to distinguish between different accesses and do not indicate different priorities, importance, etc., of the two accesses.

[0161] The following describes the technical features of the embodiments of this application.

[0162] As shown in Figure 2 or Figure 3, a terminal device can communicate with the core network via multiple accesses. For example, a terminal device can communicate with the core network via 3GPP access and non-3GPP access. When terminal devices on multiple accesses register with the same PLMN, some parameters may be shared across the terminal device's multiple accesses during communication; that is, the terminal device and the core network device maintain a set of parameters. For example, NAS security context information and GUTI are shared across the terminal device's multiple accesses to achieve password isolation and replay protection.

[0163] Since several parameters are shared across multiple accesses of a terminal device, if an action is performed on these parameters via one access of the terminal device, communication on other accesses will be affected. For example, a terminal device receives a rejection message via access A, and the rejection message carries a reason value. Based on the reason value, the terminal device may remove the keyset identifier and / or GUTI for access A.

[0164] For example, the reason value carried in the rejection message is #3 or #6, and the reason value indicates an Illegal UE. Currently, after receiving the reason value, the terminal device may perform at least one of the following actions: update the 5GS status to 5U3 ROAMING NOT ALLOWED; delete one or more of the GUTI, the TAI of the last visited tracking area, the TAI list, and the key set identifier; and, in the case of a PLMN, deactivate or delete the universal integrated circuit card (UICC) containing the universal subscriber identity module (USIM) or consider the USIM invalid for 5GS service until timer T3245 expires.

[0165] In another example, the reason value carried in the rejection message is #7, and the reason value indicates that 5GS services are not allowed. Currently, after receiving the reason value, the terminal device may perform at least one of the following actions: update the 5GS status to 5U3 roaming not allowed; delete one or more of the GUTI, the TAI of the last visited tracking area, the TAI list, and the key set identifier; and, in the case of PLMN, disable or delete the UICC including the USIM or consider the USIM invalid for 5GS services until timer T3245 expires.

[0166] In another example, the reason value carried in the rejection message is #11, and the reason value indicates PLMN not allowed. Currently, after receiving the reason value, the terminal device may perform at least one of the following actions: update the 5GS status to 5U3 roaming not allowed, and delete one or more of the GUTI, the TAI of the last visited tracking area, the TAI list, and the key set identifier.

[0167] In another example, the reason value carried in the rejection message is #72, which indicates that non-3GPP access to the 5G Core Network (5GCN) is not allowed. Currently, after receiving the reason value, the terminal device may perform at least one of the following actions if the core network is accessed via non-3GPP access: update the 5GS state to 5U3 roaming not allowed, and delete one or more of the GUTI, the TAI of the last visited tracking area, the TAI list, and the keyset identifier.

[0168] In another example, the reason value carried in the rejection message is #12, and the reason value indicates that the tracking area is not allowed. Currently, after receiving the reason value, the terminal device may perform at least one of the following actions: update the 5GS status to 5U3 roaming not allowed, delete one or more of the GUTI, the TAI of the last visited tracking area, the TAI list, and the key set identifier, and reset the registration attempt counter.

[0169] In another example, the reason value carried in the rejection message is #78, which indicates that PLMN is not allowed to operate at the present UE location. Currently, after receiving the reason value, the terminal device may perform at least one of the following actions: update the 5GS status to 5U3 roaming not allowed, and delete one or more of the GUTI, the TAI of the last visited tracking area, the TAI list, and the keyset identifier.

[0170] Since the terminal device maintains a set of NAS security context information and GUTI for access A and access B, if the key set identifier for access A is deleted, the NAS security context information for both access A and access B is deleted. Consequently, integrity protection and encryption may not be performed on uplink signaling on access B, and downlink signaling may not be received properly due to integrity check failures. If the GUTI on access A is deleted, some messages on access B will not be able to carry the GUTI information. Consequently, the PLMN may not be able to identify the terminal device, and the terminal device may not be able to receive paging from the PLMN.

[0171] Based on this, embodiments of this application provide a communication method and apparatus to solve the problem that a terminal device cannot perform normal communication over other accesses due to operations performed over common parameters over several accesses of the terminal device. The method and apparatus are based on the same concept. The method and apparatus have similar problem-solving principles. Therefore, for implementations of the apparatus and method, refer to each other. Repeated content will not be explained again.

[0172] The communication methods provided in this application may be applied to various communication systems, such as the Internet of Things (IoT), Narrowband Internet of Things (NB-IoT), Long Term Evolution (LTE), 5th Generation (5G) communication systems, LTE and 5G hybrid architectures, 5G New Radio (NR) systems, and 6G systems or new communication systems that may emerge with future advancements in communication. The communication systems in this application may, alternatively, be machine-to-machine (M2M) networks, non-terrestrial networks (NTN) networks, or other networks.

[0173] The network architectures and service scenarios described in the embodiments of this application are intended to provide a clearer explanation of the technical solutions in the embodiments of this application and do not constitute a limitation on the technical solutions provided in the embodiments of this application. Those skilled in the art will know that, with the development of network architectures and the emergence of new service scenarios, the technical solutions provided in the embodiments of this application are applicable to similar technical problems.

[0174] In the embodiments of this application, "in the case of" can be replaced with "in the case of," "assuming," "when," etc. For example, "in the case where the state of the terminal device on the second access is that the terminal device is registered with the first PLMN or has already been registered with the first PLMN" can be replaced with "assuming the state of the terminal device on the second access is that the terminal device is registered with the first PLMN or has already been registered with the first PLMN," "in the case where the state of the terminal device on the second access is that the terminal device is registered with the first PLMN or has already been registered with the first PLMN," or "when the state of the terminal device on the second access is that it is registered with the first PLMN or has already been registered with the first PLMN."

[0175] In the embodiments of this application, "switching from... to..." may be described as, alternatively, "handover from... to (or from)...", "re-selection from... to (or from)...", "selection from... to (or from)...", "change from... to (or from)...", "conversion from... to (or from)...", or "moving from... to (or from)...".

[0176] For example, the following phrase, "The terminal device on the first access is switched from the first PLMN to the second PLMN," can be explained as, "The terminal device on the first access is handed over from the first PLMN to the second PLMN," "The terminal device on the first access is re-selected from the first PLMN to the second PLMN," "The terminal device on the first access is selected from the first PLMN to the second PLMN," "The terminal device on the first access is changed from the first PLMN to the second PLMN," "The terminal device on the first access is converted from the first PLMN to the second PLMN," or "The terminal device on the first access is moved from the first PLMN to the second PLMN."

[0177] To facilitate the explanation, the following uses an example in which a terminal device accesses the core network via a first access and a second access. The first access and the second access may be described as belonging to different access types or using different access technologies. For example, the first access is a 3GPP access, and the second access is a trusted non-3GPP access or an untrusted non-3GPP access. Alternatively, the first access may be a trusted non-3GPP access or an untrusted non-3GPP access, and the second access may be a 3GPP access.

[0178] In another example, the first access is a trusted non-3GPP access, and the second access is an untrusted non-3GPP access. Alternatively, the first access is an untrusted non-3GPP access, and the second access is a trusted non-3GPP access.

[0179] It should be understood that the embodiments of this application are not limited to cases where the terminal device has only two types of access. In a specific implementation, the terminal device may have further access to the core network via a first access, a second access, and other accesses (such as a third and fourth access). The other accesses, the first access, and the second access all belong to different access types, i.e., they correspond to (or apply) different access technologies.

[0180] In embodiments of this application, a terminal device may communicate with a core network device via an access device of the access network. For example, in a 3GPP access network, a terminal device may communicate with a core network device via an access network device. In another example, in a non-3GPP access network, a terminal device may communicate with a core network device via an N3IWF device.

[0181] The technical solutions of the embodiments of this application will be described below with reference to the accompanying drawings.

[0182] Embodiments of this application may be applicable to scenarios where a first mobility management parameter for a first access of a terminal device needs to be removed. If a PLMN registered via the first access is the same as a PLMN registered via the second access, the first mobility management parameter is shared across the first and second accesses.

[0183] For example, the first mobility management parameter may include at least one of a key set identifier or GUTI. The first mobility management parameter may further include other parameters shared over the first and second access, which are not listed individually here.

[0184] The following describes three cases in which the first mobility management parameter for the first access needs to be removed. It should be understood that this application is not limited to the following three cases in which the first mobility management parameter for the first access needs to be removed. The first mobility management parameter for the first access may be considered to need to be removed in the embodiments of this application, provided that the first mobility management parameter for the first access needs to be removed in a particular case. The way in which a terminal device handles the first mobility management parameter for the first access in a different scenario is similar to the way a terminal device handles the first mobility management parameter for the first access in the following three cases in this application.

[0185] Example 1: The terminal device on the first access is switched from the first PLMN to the second PLMN.

[0186] The second PLMN is any PLMN other than the registered PLMN (RPLMN) and the equivalent PLMN (EPLMN) accessed via the first access.

[0187] Example 2: A terminal device obtains information through a first access, and this information indicates why the core network device is rejecting the terminal device's request. In this example, based on the information, the terminal device may decide that a first mobility management parameter for the first access needs to be removed.

[0188] In possible implementations, a terminal device may receive a registration denial message via the first access, and the registration denial message may carry a reason value. Alternatively, a terminal device may receive a service denial message via the first access, and the service denial message may carry a reason value. Alternatively, a terminal device may receive a deregistration request message via the first access, and the deregistration request message may carry a reason value. In this example, the reason value may be understood as the first piece of information described above.

[0189] For example, if the reason value received by the terminal device on the first access is #3 or #6, #7, #11, #72, #12, or #78, the terminal device may determine that the first mobility management parameter for the first access needs to be removed.

[0190] Here, only seven reason values ​​are shown as examples, and it should be understood that the cases in which the first mobility management parameter for the first access is removed are not limited to those determined solely by these seven reason values.

[0191] Example 3: An alternative scenario in which the first mobility management parameter for the first access needs to be removed is as follows: The terminal device receives the first message via the first access. In this example, after receiving the first message, the terminal device may decide that the first mobility management parameter for the first access needs to be removed. The first message does not carry the first information.

[0192] In this example, the first message could be an authentication denial message or another message received by the terminal device on the first access.

[0193] An example is used where the first message is an authentication denial message. After the terminal device receives the authentication denial message via the first access, if the NAS integrity check of the authentication denial message is successful, it may be determined that the first mobility management parameter for the first access needs to be removed.

[0194] The following describes the communication method provided in the embodiments of this application with respect to the three cases mentioned above.

[0195] Regarding Example 1 described above, Figure 4 is a schematic flowchart of the communication method according to the embodiment of this application.

[0196] S401: The terminal device decides that the terminal device on the first access will be switched from the first PLMN to the second PLMN.

[0197] After S401, S402 or S403 may be performed.

[0198] Optionally, the first PLMN is registered via the first access before S401.

[0199] The following describes the implementation of S401 for 3GPP access and non-3GPP access.

[0200] If the first access is a 3GPP access, the terminal device may determine that the terminal device on the first access is switched from the first PLMN to the second PLMN in the following manner: The terminal device on the first access is switched from the first cell to the second cell, and the PLMN corresponding to the first cell is the first PLMN. The terminal device receives system information broadcast by the second cell via the first access, and the system information may carry the PLMN information of the second cell. Based on the PLMN information carried in the system information and the PLMN information stored locally on the first access, the terminal device on the first access may determine that it is switched from the first PLMN to the second PLMN.

[0201] If the first access is a non-3GPP access, the terminal device may determine that the terminal device on the first access is switched from the first PLMN to the second PLMN in the following manner: The terminal device determines that the connection to the first access device is interrupted, and the PLMN corresponding to the first access device is the first PLMN. The terminal device sends a request message to the second access device, which requests the establishment of a communication connection to the second access device, and the PLMN corresponding to the second access device is the second PLMN. The terminal device receives a response message from the second access device, which indicates to the terminal device that it will access the second access device. Based on the PLMN corresponding to the second access device, the terminal device determines that the terminal device on the first access is switched from the first PLMN to the second PLMN.

[0202] For details regarding the first and second access devices, please refer to the relevant explanation of access devices for non-3GPP access networks in the above description of the network architecture.

[0203] S402: If the status for the second access is that the terminal device is registering with the first PLMN or is already registered with the first PLMN, the terminal device decides not to delete the first mobility management parameter for the first access.

[0204] Optionally, if deregistration is performed on the first PLMN via a second access after S402 (or if deregistration or disconnection is performed on the first PLMN), the terminal device may decide to remove the first mobility management parameter for the first access.

[0205] For example, in an implementation scenario where the deregistration of the first PLMN is performed via a second access, the switchover is performed from the first PLMN to the third PLMN on the second access. The third PLMN is different from the first PLMN, and the third PLMN may be the same as or different from the second PLMN.

[0206] S403: If the status for the second access is that the terminal device is not registered with the first PLMN, the terminal device decides to delete the first mobility management parameter for the first access.

[0207] In a possible implementation, assuming that the first mobility management parameter includes a key set identifier, the NAS security context information identified by the key set identifier includes a security encryption algorithm, which could be a null encryption algorithm, such as the 5G-EA0 algorithm, or another algorithm that emerges with future communication developments.

[0208] Therefore, before deciding to remove the first mobility management parameter for the first access, the terminal device may determine that the security encryption algorithm is a null encryption algorithm.

[0209] When the security encryption algorithm is a null encryption algorithm, the NAS Air Interface message is not encrypted, resulting in lower security for the NAS Air Interface message. In the above method, the first mobility management parameter is removed when the security encryption algorithm in the NAS security context information identified by the key set identifier is a null encryption algorithm, thereby facilitating communication security for terminal devices.

[0210] After optionally deciding not to delete the first mobility management parameter, the terminal device (or core network device) may perform a corresponding action. For example, the first mobility management parameter may not be deleted, the first mobility management parameter may be reserved, or the first mobility management parameter may not be processed.

[0211] After deciding to optionally remove the first mobility management parameter, the terminal device (or core network device) may perform a corresponding action. For example, the first mobility management parameter may be removed.

[0212] The key set identifier in the first mobility management parameter is used as an example. Removing the key set identifier can be done in the following way, namely: Set the value of the key set identifier to "No keys available" (set ngKSI to that value), and Determining that one or more of the following are invalid: KAMF key, K'AMF key, NAS encryption key, and NAS integrity key. This can be achieved by at least one of the following.

[0213] "One or more of the KAMF, K'AMF, NAS encryption key, and NAS integrity key are invalid" can also be described as the NAS security context information related to the key set identifier being invalid or no longer valid.

[0214] GUTI in the first mobility management parameter is used as an example. Removing GUTI can be achieved by configuring it to be disabled.

[0215] Whether a first PLMN (i.e., a PLMN registered via the first access) is registered via the second access can be used to determine whether a terminal device needs to use the first mobility management parameters for communication over the second access. In this embodiment of the present application, when a terminal device on the second access is not registered with the first PLMN, the terminal device removes the first mobility management parameters for the first access, and thus the information maintenance cost of the terminal device can be reduced without affecting the communication performed by the terminal device on the second access, and the use of invalid parameters (i.e., the first mobility management parameters) for communication over the first access can be further avoided, thereby improving the communication performance of the terminal device on the first access.

[0216] When a terminal device on the second access is already registered with the first PLMN or is registered with the first PLMN, the first mobility management parameters are not deleted, and therefore, it can be guaranteed that the terminal device can perform normal communication on the second access.

[0217] Regarding the above example 2, Figure 5 is a schematic flowchart of the communication method according to the embodiment of this application.

[0218] S501: The core network device transmits first information to the terminal device via first access. Correspondingly, the terminal device obtains first information via first access.

[0219] The first piece of information may be carried in messages such as registration denial messages, service denial messages, or deregistration messages. Only a few examples are provided here for illustrative purposes; please understand that the specific messages carrying the first piece of information are not limited to those mentioned above.

[0220] For the first piece of information, please refer to the relevant explanation in Case Study 2 above. We will not explain the details again here.

[0221] For example, a core network device may be the core network device accessed by the first access.

[0222] S502: The terminal device decides whether to delete the first mobility management parameter for the first access based on the first information and the second access information.

[0223] For example, information about a second access may include at least one of the following: registration information for the second access or service information for the second access, or information about a second access may further include other information. This is not limited to the information provided herein.

[0224] Registration information may represent the PLMN registration status for the second access, and service information for the second access indicates whether emergency services are being provided on the second access.

[0225] In possible implementations, the terminal device may determine, based on the first information, that the first mobility management parameter for the first access needs to be removed. The terminal device may then determine, based on the information for the second access, whether to remove the first mobility management parameter for the first access. For implementations in which the terminal device determines, based on the first information, that the first mobility management parameter for the first access needs to be removed, please refer to the relevant explanation in Example 2 above.

[0226] In the illustrative example, the first piece of information is applicable to the first access but not to the second access. Alternatively, the first piece of information is applicable to both the first and second accesses. The following explains, with specific reason values, whether the first piece of information is applicable to both the first and second accesses.

[0227] For example, if the first piece of information is reason value #3 or reason value #6 above, the reason value indicates an illegal terminal, i.e., the terminal device is not permitted. Therefore, neither the first nor the second access to the terminal device is permitted, i.e., the first piece of information is applicable to both the first and second access.

[0228] In another example, if the first piece of information is reason value #7 above, the reason value indicates that 5GS service is not permitted, i.e., 5GS service for the terminal device is not permitted. Therefore, neither the first nor the second access to the terminal device is permitted, i.e., the first piece of information is applicable to both the first and second access.

[0229] In another example, if the first piece of information is reason value #11 above, the reason value indicates that the PLMN is not permitted, i.e., the first access is not permitted on the PLMN. A PLMN registered (or already registered) via the second access is the same as a PLMN registered via the first access, and the first piece of information is also applicable to the second access. A PLMN registered (or already registered) via the second access is different from a PLMN registered via the first access, and the first piece of information is not applicable to the second access.

[0230] In another example, if the first piece of information is reason value #72 above, the reason value indicates that non-3GPP access is not permitted for 5GCN.

[0231] It can be understood that the terminal device receives reason value #72 via the first access. It can be understood that the first access is a non-3GPP access and the first information is applicable to the first access. If the second access is a 3GPP access, the first information is not applicable to the second access.

[0232] In another example, if the first piece of information is reason value #12 above, the reason value indicates that the tracking area is not permitted, and the reason value is applicable to 3GPP access.

[0233] It can be understood that the terminal device receives reason value #12 via the first access. The first information is applicable to the first access, i.e., it can be understood that the first access is a 3GPP access. If the second access is a non-3GPP access, the first information is not applicable to the second access.

[0234] In another example, if the first piece of information is reason value #78, the reason value indicates that PLMN is not permitted to operate at the current terminal device location. The reason value is applicable to 3GPP access.

[0235] It can be understood that the terminal device receives reason value #78 via the first access. The first information is applicable to the first access, meaning that the first access is a 3GPP access. Therefore, if the second access is a non-3GPP access, the first information is not applicable to the second access.

[0236] Referring to a scenario where the first information is applicable to the first access, but the first information is not applicable to the second access, the following describes an implementation in which a terminal device determines whether to remove the first mobility management parameter for the first access based on the information about the second access.

[0237] Assume that the first information is not applicable to the second access. In one implementation, the terminal device may decide whether to remove the first mobility management parameters for the first access based on the registration information for the second access.

[0238] Optionally, the terminal device may decide to delete the first mobility management parameter for the first access if the registration information for the second access satisfies one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN registered via the second access is different from the PLMN registered via the first access.

[0239] The terminal device may decide not to delete the first mobility management parameters for the first access if the registration information for the second access satisfies the condition that the PLMN registered via the second access is the same as the PLMN registered via the first access.

[0240] The fact that a PLMN registered via a second access is different from a PLMN registered via a first access can be understood as the PLMN registered via a second access being different from the PLMN currently registered via a first access, the PLMN registered via a second access being not the PLMN registered via a first access, and the second PLMN being not the EPLMN registered via a first access. Accordingly, the fact that a PLMN registered via a second access is the same as a PLMN registered via a first access can be understood as the PLMN registered via a second access being the same as the PLMN currently registered via a first access, or the PLMN registered via a second access being the PLMN registered via a first access, or the second PLMN being the EPLMN registered via a first access.

[0241] Please note that the understanding of PLMNs registered via the second access and those registered via the first access differs below, while the understanding of PLMNs registered via the second access and those registered via the first access is the same as described here. Further details will not be explained one by one below.

[0242] Assume that the first information is applicable to the second access. In one implementation, the terminal device may decide whether to remove the first mobility management parameters for the first access based on the registration information and service information for the second access.

[0243] The terminal device may optionally decide to delete the first mobility management parameter for the first access if the registration information for the second access satisfies one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN registered via the second access is different from the PLMN registered via the first access.

[0244] The terminal device may decide to delete the first mobility management parameter for the first access if the registration information for the second access and the service information for the second access satisfy one of the following conditions: namely, the PLMN registered via the second access is the same as the PLMN registered via the first access, and emergency services are not performed on the second access.

[0245] The terminal device may decide not to delete the first mobility management parameters for the first access if the registration information for the second access and the service information for the second access satisfy the following conditions: namely, the PLMN registered via the second access is the same as the PLMN registered via the first access, and emergency services are being performed on the second access.

[0246] In a discretionary solution, the terminal device may decide whether to remove the first mobility management parameter for the first access after the emergency service on the second access has ended.

[0247] The following describes an implementation that determines whether a terminal device removes the first mobility management parameter for the first access based on information about the second access.

[0248] Optionally, for actions taken after the core network device has sent the first information, the core network device may, as an alternative, decide whether to remove the first mobility management parameter for the first access based on the first information and the information for the second access.

[0249] An implementation in which a core network device determines whether to delete the first mobility management parameter for a first access based on the first information and the information about the second access is similar to an implementation in which a terminal device determines whether to delete the first mobility management parameter for a first access based on the first information and the information about the second access. The difference is as follows: A terminal device may decide to delete the first mobility management parameter for a first access if the registration information for the second access satisfies one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN registered via the second access is different from the PLMN registered via the first access. A core network device may decide to delete the first mobility management parameter for a first access if the registration information for the second access satisfies one of the following conditions: namely, the PLMN is not registered via the second access. For further details, please refer to the implementation that determines whether the terminal device removes the first mobility management parameter for the first access based on the first information and the second access information.

[0250] Optionally, terminal devices and / or core network devices may further implement one or more of the following four solutions:

[0251] Solution 1: If it is determined that the first mobility management parameter is to be removed on the first access, the second and / or third mobility management parameters may be removed. The second mobility management parameter includes at least one of the last visited tracking area TAI for the second access, or the TAI list for the second access. The third mobility management parameter includes at least one of the last visited tracking area TAI for the first access, or the TAI list for the first access.

[0252] For example, "the last visited tracking area TAI for the second access" may also be described as the last visited tracking area TAI corresponding to the second access, the last visited tracking area TAI of the terminal device in the access network corresponding to the second access, etc. "The last visited tracking area TAI for the first access" may also be described as the last visited tracking area TAI corresponding to the first access, the last visited tracking area TAI of the terminal device in the access network corresponding to the first access, etc.

[0253] It should be understood that the second and third mobility management parameters may, as alternatives, include other parameters. This is not limited to the examples provided here.

[0254] Solution 2: If it is decided that the first mobility management parameter will be removed, the services running on the second access may be stopped.

[0255] Please note that in this embodiment of the present application, "stop" may also be described as "end," "cancel," "interrupt," or "cut in."

[0256] Solution 3: If it is decided to remove the first mobility management parameter, the terminal device may start the first timer for the second access or release the N1 NAS signaling connection for the second access. The core network device may release the N1 NAS signaling connection for the second access.

[0257] The first timer is used to trigger a terminal device to release the N1 NAS signaling connection for the second access. In the illustrative description, the first timer is used to allow a core network device to release the N1 NAS signaling connection for the second access.

[0258] In a discretionary solution, the terminal device may release the N1 NAS signaling connection for the second access when the first timer expires.

[0259] Optionally, if the core network device releases the N1 NAS signaling connection for the second access before the first timer expires, the terminal device may stop the first timer.

[0260] Solution 4: If it is determined that the first mobility management parameter will be removed and the mobility management procedure is being performed on the second access, the mobility management procedure may be stopped.

[0261] For example, mobility management procedures may include one or more of the following: common procedures (5GMM common procedures), specific procedures (5GMM specific procedures), and connection management procedures (5GMM connection management procedures).

[0262] Common procedures may include, but are not limited to, identification and authentication procedures, authentication procedures, security mode control procedures, UE configuration update procedures, uplink transmission procedures, downlink transmission procedures, slice authentication procedures, etc.

[0263] Specific procedures may include, but are not limited to, registration procedures and deregistration procedures.

[0264] Connection management procedures are not limited to, but may include service request procedures, paging procedures, etc.

[0265] Please understand that mobility management procedures may include other steps, which will not be listed individually here.

[0266] In the four discretionary solutions described above, it should be noted that the terminal device may decide to remove the first mobility management parameter based on information about the second access, or after the emergency service on the second access has ended.

[0267] After optionally deciding not to delete the first mobility management parameter, the terminal device (or core network device) may perform a corresponding action. For example, the first mobility management parameter may not be deleted, the first mobility management parameter may be reserved, or the first mobility management parameter may not be processed.

[0268] After deciding to optionally remove the first mobility management parameter, the terminal device (or core network device) may perform a corresponding action. For example, the first mobility management parameter may be removed.

[0269] For an implementation of removing the first mobility management parameter, please refer to the related explanation of the method in Figure 4.

[0270] In this embodiment of the present application, when the first mobility management parameter for the first access is removed, considering the information for the second access, the first mobility management parameter may not be removed when the first mobility management parameter is required on the second access, and therefore the terminal device may use the first mobility management parameter for communication on the second access. This avoids the problem that normal communication may not occur on the second access because the first mobility management parameter for the first access is removed, and reduces the impact on communication on the second access.

[0271] Furthermore, the terminal device can decide whether to remove the first mobility management parameter, thus providing greater flexibility and improved accuracy.

[0272] Regarding the above example 3, Figure 6 is a schematic flowchart of the communication method according to the embodiment of this application.

[0273] S601: The core network device sends a first message to the terminal device via a first access. Correspondingly, the terminal device receives the first message via the first access.

[0274] For the first message, please refer to the relevant explanation in Example 3 above. We will not explain the details again here.

[0275] S602: The terminal device decides whether to remove the first mobility management parameter for the first access based on the first message and the information about the second access.

[0276] In a possible implementation, the terminal device may determine, based on the first message, that the first mobility management parameter for the first access should be removed. The terminal device may then determine, based on information about the second access, whether to remove the first mobility management parameter for the first access.

[0277] For an implementation in which a terminal device determines, based on the first message, that the first mobility management parameter for the first access needs to be removed, please refer to the relevant explanation in Example 3 above.

[0278] For an implementation in which a terminal device determines whether to remove the first mobility management parameter for the first access based on information about the second access, please refer to the implementation in Figure 5 in which a terminal device determines whether to remove the first mobility management parameter for the first access based on information about the second access. Details will not be explained again here.

[0279] Optionally, for actions taken after the core network device has sent the first information, the core network device may, as an alternative, decide whether to remove the first mobility management parameter for the first access based on the first information and the information for the second access.

[0280] For an implementation in which a core network device determines whether to remove the first mobility management parameter for the first access based on the first information and the information about the second access, please refer to the implementation in Figure 5 in which a core network device determines whether to remove the first mobility management parameter for the first access based on the first information and the information about the second access. Details will not be explained again here.

[0281] Optionally, terminal devices and / or core network devices may further implement one or more of the following four solutions: delete the second mobility management parameter and / or the third mobility management parameter; stop the services being performed on the second access; start the first timer for the second access or release the N1 NAS signaling connection; or stop the mobility management procedures being performed on the second access.

[0282] For implementations of deleting the second and / or third mobility management parameters, stopping services performed via the second access, starting the first timer for the second access or releasing the N1 NAS signaling connection, and stopping mobility management procedures performed on the second access, please refer to the relevant explanation of the method in Figure 5.

[0283] After optionally deciding not to delete the first mobility management parameter, the terminal device (or core network device) may perform a corresponding action. For example, the first mobility management parameter may not be deleted, the first mobility management parameter may be reserved, or the first mobility management parameter may not be processed.

[0284] After deciding to optionally remove the first mobility management parameter, the terminal device (or core network device) may perform a corresponding action. For example, the first mobility management parameter may be removed.

[0285] For an implementation of removing the first mobility management parameter, please refer to the related explanation of the method in Figure 4.

[0286] In this embodiment of the present application, when the first mobility management parameter for the first access is deleted, considering the information about the second access, the first mobility management parameter may not be deleted when it is required on the second access. Therefore, the terminal device can use the first mobility management parameter for communication on the second access. This avoids the problem that normal communication may not be carried out on the second access because the first mobility management parameter for the first access is deleted, and reduces the impact on communication on the second access.

[0287] Furthermore, the terminal device determines whether to delete the first mobility management parameter. Therefore, the flexibility is higher and the accuracy is better.

[0288] The above describes a method for the terminal device to determine whether to delete the first mobility management parameter. Regarding the above Case 2 and Case 3, the following describes a method for the core network device to indicate to the terminal device whether to delete the first mobility management parameter.

[0289] FIG. 7 is a schematic flowchart of a communication method according to an embodiment of the present application.

[0290] S701: The core network device determines the first indication information.

[0291] The terminal device can access the core network device via the first access.

[0292] In a possible implementation, the core network device can determine whether to delete the first mobility management parameter for the first access based on the second indication information and the information about the second access. The second indication information indicates the reason why the core network device rejects the request of the terminal device.

[0293] The second indication information could be the first piece of information in Example 2 above.

[0294] For an implementation in which a core network device determines whether to remove the first mobility management parameter for the first access based on the second indication information and the information about the second access, please refer to the implementation in Figure 5 in which a core network device determines whether to remove the first mobility management parameter for the first access based on the first information and the information about the second access.

[0295] In another possible implementation, the core network device may decide whether to remove the first mobility management parameter for the first access based on the first message and information about the second access. For details on the first message, please refer to the relevant explanation in Example 3 above.

[0296] For an implementation in which a core network device determines whether to remove the first mobility management parameter for the first access based on the first message and information about the second access, see the implementation in Figure 6 in which a core network device determines whether to remove the first mobility management parameter for the first access based on the first message and information about the second access.

[0297] S702: The core network device transmits first indication information to the terminal device via first access. Accordingly, the terminal device receives first indication information via first access.

[0298] The first indication information shows whether to remove the first mobility management parameter for the first access.

[0299] The first indication information may indicate, in an explicit indication manner, whether to remove the first mobility management parameter for the first access. For example, the first indication information may indicate whether to remove the first mobility management parameter for the first access by using different values ​​for one or more bits. For example, the first indication information may indicate to remove the first mobility management parameter for the first access by using a first value for one or more bits, and to not remove the first mobility management parameter for the first access by using a second value.

[0300] Alternatively, the first indication information may implicitly indicate the removal of the first mobility management parameter for the first access. For example, if the first indication information carries a specific field, it may indicate that the first mobility management parameter for the first access is not removed, or if the first indication information does not carry a specific field, it may indicate that the first mobility management parameter for the first access is removed.

[0301] Alternatively, the first indication information may implicitly indicate that the first mobility management parameter for the first access should not be removed. For example, if the first indication information carries a specific field, it may indicate that the first mobility management parameter for the first access should be removed, or if the first indication information does not carry a specific field, it may indicate that the first mobility management parameter for the first access should not be removed.

[0302] S703: The terminal device determines whether to remove the first mobility management parameter for the first access based on the first indication information.

[0303] In a possible implementation, the terminal device may decide whether to remove the first mobility management parameter for the first access based on the first indication information and the second access information.

[0304] In a particular implementation, the terminal device may decide whether to remove the first mobility management parameter for the first access based on the first indication information and the registration information for the second access.

[0305] For example, if the first indication information indicates the deletion of the first mobility management parameter for the first access, the first mobility management parameter for the first access is determined to be deleted if the registration information for the second access satisfies one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN registered via the second access is different from the PLMN registered via the first access.

[0306] In another example, if the first indication information indicates that the first mobility management parameter for the first access should be removed, and the PLMN registered via the second access is the same as the PLMN registered via the first access, then whether to remove the first mobility management parameter for the first access is determined based on the service information for the second access. The service information for the second access is information about whether emergency services are being performed on the second access.

[0307] For example, if emergency services are being performed on the second access, it is determined that the first mobility management parameter for the first access will not be removed. Alternatively, if emergency services are being performed on the second access, it is determined that the first mobility management parameter will be removed on the first access.

[0308] Optionally, the terminal device may further perform one or more of the following four actions: deleting the second mobility management parameter and / or the third mobility management parameter, stopping the service being performed on the second access, starting the first timer for the second access or releasing the N1 NAS signaling connection, or stopping the mobility management procedure being performed on the second access.

[0309] For the implementation of deleting the second mobility management parameter and / or the third mobility management parameter, stopping the service being performed via the second access, starting the first timer for the second access or releasing the N1 NAS signaling connection, and stopping the mobility management procedure being performed on the second access, refer to the relevant description of the method in FIG. 5.

[0310] Optionally, after determining not to delete the first mobility management parameter, the terminal device (or core network device) may perform the corresponding action. For example, the first mobility management parameter is not deleted, or the first mobility management parameter is reserved, or the first mobility management parameter is not processed.

[0311] Optionally, after determining to delete the first mobility management parameter, the terminal device (or core network device) may perform the corresponding action. For example, the first mobility management parameter is deleted.

[0312] For the implementation of deleting the first mobility management parameter, refer to the relevant description of the method in FIG. 4.

[0313] In this embodiment of the present application, the network device indicates to the terminal device whether to delete the first mobility management parameter for the first access, thus reducing the complexity of the terminal device.

[0314] Furthermore, when the first mobility management parameter for the first access is removed, considering the information for the second access, the first mobility management parameter may not be removed when it is required on the second access, and therefore the terminal device may use the first mobility management parameter for communication on the second access. This avoids the problem that normal communication may not occur on the second access because the first mobility management parameter for the first access is removed, and reduces the impact on communication on the second access.

[0315] Based on the same concept as the method embodiment, embodiments of this application provide a communication device. The structure of the communication device is shown in Figure 8 and includes a processing module 801. Optionally, the device may further include a communication module 802.

[0316] In one implementation, the communication device may be configured to perform a method, in particular, as performed by a terminal device in the embodiment of Figure 4. The device may be a terminal device, or a chip, chip group, or part of a chip in a terminal device configured to perform a related method function. The processing module 801 is configured to determine when a terminal device on a first access is switched from a first PLMN to a second PLMN, and to determine not to delete the first mobility management parameter for the first access if the state of the terminal device on the second access is that the terminal device is registered with the first PLMN or has been registered with the first PLMN, and to determine to delete the first mobility management parameter if the state on the second access is that the terminal device has not been registered with the first PLMN, and the first access and the second access belong to different access types.

[0317] Optionally, the processing module 801 may be further configured to determine that the first access has registered with the first PLMN before the terminal device determines that the terminal device on the first access has switched from the first PLMN to the second PLMN.

[0318] The processing module 801 may be further configured to decide to delete the first mobility management parameter if, after the processing module has decided not to delete the first mobility management parameter, the switchover is performed from the first PLMN to the third PLMN on the second access.

[0319] For example, the first mobility management parameter includes at least one of a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0320] Optionally, the NAS security context information includes a security encryption algorithm, which is a null encryption algorithm.

[0321] In one implementation, the communication device may be configured to perform a method, in particular, as performed by a terminal device in the embodiment of Figure 5. The device may be a terminal device, or a chip, chip group, or part of a chip in a terminal device configured to perform the associated method function. The communication module 802 is configured to obtain first information via a first access of the terminal device. The processing module 801 is configured to determine whether to remove a first mobility management parameter for the first access based on the first information and information about a second access of the terminal device. The first information indicates the reason why the core network device rejected the terminal device's request and that the first access and the second access belong to different access types.

[0322] Optionally, the first information is not applicable to the second access. When deciding whether to delete the first mobility management parameter based on the first information and the information about the second access of the terminal device, the processing module 801 is configured to decide whether to delete the first mobility management parameter based, in particular, on the first information and the registration information about the second access.

[0323] When determining whether to delete the first mobility management parameter based on the first information and the registration information for the second access, the processing module 801 is configured to decide to delete the first mobility management parameter, in particular, when the registration information for the second access satisfies one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN registered via the second access is different from the PLMN registered via the first access.

[0324] When determining whether to delete the first mobility management parameter based on the first information and the registration information for the second access, the processing module 801 is configured to decide not to delete the first mobility management parameter, in particular, when the registration information for the second access satisfies the following condition: namely, the PLMN registered via the second access is the same as the PLMN registered via the first access.

[0325] Optionally, the first information is applicable to the second access. When determining whether to delete the first mobility management parameter based on the first information and information about the second access of the terminal device, the processing module 801 is configured to, in particular, determine whether to delete the first mobility management parameter based on the first information, registration information for the second access, and service information for the second access, wherein the service information for the second access is information about whether emergency services are being performed on the second access.

[0326] When processing the first mobility management parameter based on the first information, the registration information for the second access, and the service information for the second access, the processing module 801 is configured to decide to delete the first mobility management parameter, in particular, when the registration information for the second access and the service information for the second access satisfy one of the following conditions: namely, the PLMN is not registered via the second access, the PLMN registered via the second access is different from the PLMN registered via the first access, or the PLMN registered via the second access is the same as the PLMN registered via the first access and emergency services are not performed on the second access.

[0327] When processing the first mobility management parameter based on the first information, the registration information for the second access, and the service information for the second access, the processing module 801 is configured to decide not to delete the first mobility management parameter, in particular, when the registration information for the second access and the service information for the second access satisfy the following conditions: namely, the PLMN registered via the second access is the same as the PLMN registered via the first access, and emergency services are being performed on the second access.

[0328] Optionally, the processing module 801 may be further configured to decide to delete the first mobility management parameter after the emergency service has ended.

[0329] Optionally, if the processing module 801 decides to delete a first mobility management parameter, it may further be configured to delete a second mobility management parameter, wherein the second mobility management parameter includes at least one of the last visited tracking area identification for the second access or a list of tracking area identifications for the second access.

[0330] Optionally, if the processing module 801 decides to delete the first mobility management parameter, it is further configured to stop the service being performed on the second access.

[0331] Optionally, if the processing module 801 decides to delete a first mobility management parameter, it may start a first timer for a second access, the first timer being used to trigger a terminal device to release the N1 NAS signaling connection, or to release the N1 NAS signaling connection.

[0332] Optionally, the processing module 801 is further configured to stop the mobility management procedure if it is determined that the first mobility management parameter is deleted and the mobility management procedure is being performed on the second access.

[0333] For example, the first mobility management parameter includes at least one of a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0334] In one implementation, the communication device may be further configured to perform the method performed by the core network device in the embodiment of Figure 5. For details, see the related descriptions above. Details will not be described again here. The device may be the core network device, or a chip, chip group, or part of a chip in a core network device configured to perform the related method function. The communication module 802 is configured to transmit first information to a terminal device via a first access of the terminal device, the first information indicating the reason why the core network device is rejecting the terminal device's request. The processing module 801 is configured to determine, based on the first information and information about a second access of the terminal device, whether to remove a first mobility management parameter for the first access, the first access and the second access being of different access types.

[0335] Optionally, the first information is not applicable to the second access. When deciding whether to delete the first mobility management parameter based on the first information and the information about the second access, the processing module 801 is configured to decide whether to delete the first mobility management parameter based, in particular, on the first information and the registration information about the second access.

[0336] When determining whether to delete the first mobility management parameter based on the first information and the registration information for the second access, the processing module 801 may be configured to decide to delete the first mobility management parameter, in particular, when the registration information for the second access satisfies one of the following conditions, namely, that the PLMN is not registered via the second access.

[0337] When determining whether to delete the first mobility management parameter based on the first information and the registration information for the second access, the processing module 801 may be configured to decide not to delete the first mobility management parameter, in particular, when the registration information for the second access satisfies the following condition: namely, the PLMN registered via the second access is the same as the PLMN registered via the first access.

[0338] Optionally, the first information is applicable to the second access. When deciding whether to delete the first mobility management parameter based on the first information and the information about the second access, the processing module 801 may be configured to decide whether to delete the first mobility management parameter based on the first information, registration information for the second access, and service information for the second access, wherein the service information for the second access is information about whether emergency services are being performed on the second access.

[0339] When processing the first mobility management parameter based on the first information, the registration information for the second access, and the service information for the second access, the processing module 801 may be configured to decide to delete the first mobility management parameter, in particular, when the registration information for the second access and the service information for the second access satisfy one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN registered via the second access is the same as the PLMN registered via the first access, and emergency services are not performed on the second access.

[0340] When processing the first mobility management parameter based on the first information, the registration information for the second access, and the service information for the second access, the processing module 801 may be configured to decide not to delete the first mobility management parameter, in particular, when the registration information for the second access and the service information for the second access satisfy the following conditions: namely, the PLMN registered via the second access is the same as the PLMN registered via the first access, and emergency services are being performed on the second access.

[0341] Optionally, the processing module 801 may be further configured to decide to delete the first mobility management parameter after the emergency service has ended.

[0342] Optionally, if the processing module 801 decides to delete a first mobility management parameter, it may further be configured to delete a second mobility management parameter, wherein the second mobility management parameter includes at least one of the last visited tracking area identification for the second access or a list of tracking area identifications for the second access.

[0343] Optionally, if the processing module 801 decides to remove the first mobility management parameter, it is further configured to stop the service being performed on the second access.

[0344] Optionally, if the processing module 801 decides to remove the first mobility management parameter, it is further configured to release the N1 NAS signaling connection.

[0345] Optionally, the processing module 801 is further configured to stop the mobility management procedure if it is determined that the first mobility management parameter is deleted and the mobility management procedure is being performed on the second access.

[0346] For example, the first mobility management parameter includes at least one of a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0347] In one implementation, the communication device may be configured to perform a method, in particular, as performed by a terminal device in the embodiment of Figure 7. The device may be a terminal device, or a chip, chip group, or part of a chip in a terminal device configured to perform a related method function. The communication module 802 is configured to receive first indication information via a first access of the terminal device, the first indication information indicating whether to remove a first mobility management parameter for the first access. The processing module 801 is configured to determine, based on the first indication information, whether to remove a first mobility management parameter for the first access, the first access and the second access belonging to different access types.

[0348] When determining whether to delete a first mobility management parameter based on first indication information, the processing module 801 may be configured to determine whether to delete the first mobility management parameter based, in particular, on the first indication information and information about second access.

[0349] When determining whether to delete a first mobility management parameter based on first indication information and second access information, the processing module 801 may be configured to determine whether to delete a first mobility management parameter based, in particular, on first indication information and second access registration information.

[0350] When determining whether to delete a first mobility management parameter based on the first indication information and the registration information for the second access, the processing module 801 may be configured to decide to delete the first mobility management parameter if, in particular, the first indication information indicates that the first mobility management parameter should be deleted, and the registration information for the second access satisfies one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN registered via the second access is different from the PLMN registered via the first access.

[0351] When determining whether to delete a first mobility management parameter based on first indication information and registration information for a second access, the processing module 801 may be configured to, in particular, determine whether to delete the first mobility management parameter based on service information for the second access, if the first indication information indicates that the first mobility management parameter should be deleted, and the PLMN registered via the second access is the same as a PLMN whose registration is not performed via the first access, the service information for the second access is information about whether emergency services are being performed on the second access.

[0352] When determining whether to remove the first mobility management parameter based on service information for the second access, the processing module 801 may be configured to, in particular, decide not to remove the first mobility management parameter if emergency services are being performed on the second access, or to decide to remove the first mobility management parameter if emergency services are not being performed on the second access.

[0353] Optionally, if the processing module 801 decides to delete the first mobility management parameter, it may be further configured to decide to delete the first mobility management parameter after the emergency service has ended.

[0354] Optionally, if the processing module 801 decides to delete a first mobility management parameter, it may further be configured to delete a second mobility management parameter, wherein the second mobility management parameter includes at least one of the last visited tracking area identification for the second access or a list of tracking area identifications for the second access.

[0355] Optionally, if the processing module 801 decides to remove the first mobility management parameter, it is further configured to stop the service being performed on the second access.

[0356] Optionally, if the processing module 801 decides to delete a first mobility management parameter, it may start a first timer for a second access, the first timer being used to trigger a terminal device to release the N1 NAS signaling connection, or to release the N1 NAS signaling connection.

[0357] Optionally, the processing module 801 is further configured to stop the mobility management procedure if it is determined that the first mobility management parameter is deleted and the mobility management procedure is being performed on the second access.

[0358] For example, the first mobility management parameter includes at least one of a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0359] In one implementation, the communication device may be further configured to perform the method performed by the core network device in the embodiment of Figure 7. See the related description above for details. Details will not be described again here. The device may be the core network device, or a chip, chip group, or part of a chip in the core network device configured to perform the related method function. Processing module 801 is configured to determine first indication information. Communication module 802 is configured to transmit the first indication information to the terminal device via a first access of the terminal device, wherein the first indication information indicates whether to remove a first mobility management parameter for the first access, and the first access and the second access belong to different access types.

[0360] The processing module 801 may be configured to determine first indication information based on second indication information and second access information, wherein the second indication information indicates the reason why the core network device is rejecting the terminal device's request.

[0361] The second indication information is not applicable to the second access. The processing module 801 may be configured to determine the first indication information based on the second indication information and the registration information for the second access.

[0362] Processing module 801, in particular, when the registration information for the second access satisfies one of the following conditions, namely, that PLMN has not been registered via the second access. 、 To remove the first mobility management parameter Decision madeAlternatively, the first indication information may be configured to indicate that the core network device will not delete the first mobility management parameter when the registration information for the second access satisfies the following conditions: namely, the PLMN is registered or registered via the second access.

[0363] The second indication information is applicable to the second access. The processing module 801 may be configured, in particular, to determine the first indication information based on the second indication information, registration information for the second access, and service information for the second access, wherein the service information for the second access is information about whether emergency services are being performed on the second access.

[0364] The processing module 801 may be configured in particular to indicate, by first indication information, that the first mobility management parameter should be deleted when the registration information for the second access and the service information for the second access satisfy one of the following conditions: namely, the PLMN is not registered via the second access, or the PLMN is registered or registered via the second access and emergency services are not performed on the second access.

[0365] The processing module 801 may be configured to indicate, in particular, by first indication information, that the first mobility management parameter will not be deleted when the registration information for the second access and the service information for the second access satisfy the following conditions: namely, the PLMN is registered or registered via the second access, and emergency services are not being performed on the second access.

[0366] For example, the first mobility management parameter includes at least one of a key set identifier or a globally unique temporary user device identifier, the key set identifier identifies NAS security context information.

[0367] Furthermore, the communication device may be further configured to perform a method carried out by a communication device (e.g., a terminal device or a core network device) in the embodiment of Figure 6. The device may be a communication device, or a chip, a group of chips, or a part of a chip in a communication device configured to perform a related method function.

[0368] In the embodiments of this application, the division into modules is merely an example and represents only a division of logical functions; other divisions may occur in actual implementations. Furthermore, the functional modules in the embodiments of this application may be integrated into a single processor, exist physically independently, or two or more modules may be integrated into a single module. The integrated module may be implemented in hardware form or in the form of a software functional module. For further information regarding the function or implementation of the modules in this embodiment of this application, please refer to the relevant descriptions in the method embodiments.

[0369] In possible configurations, the communication device may be shown in Figure 9. This device may be a communication device or a chip within a communication device. The communication device may be a terminal device or a network device in the above embodiment. This device includes a processor 901 and a communication interface 902, and may further include a memory 903. The processor module 801 may be the processor 901. The communication module 802 may be the communication interface 902.

[0370] The processor 901 may be a CPU, a digital processing unit, etc. The communication interface 902 may be a transceiver, an interface circuit such as a transceiver circuit, a transceiver chip, etc. The device further includes a memory 903 configured to store a program executed by the processor 901. The memory 903 may be non-volatile memory, such as a hard disk drive (HDD) or a solid-state drive (SSD), or volatile memory, such as random-access memory (RAM). The memory 903 may be, but is not limited to, any other medium that can carry and store program code expected in the form of instructions or data structures and can be accessed by the computer.

[0371] The processor 901 is configured to execute program code stored in memory 903, and in particular to perform the actions of processing module 801. Further details are not provided here. The communication interface 902 is configured to perform the actions of communication module 802. Further details are not provided here.

[0372] In this embodiment of the present application, the specific connection medium between the communication interface 902, the processor 901, and the memory 903 is not limited. In this embodiment of the present application, the memory 903, the processor 901, and the communication interface 902 are connected through a bus 904 in Figure 9. The bus is represented by using a thick line in Figure 9. The above is merely an example for illustrative purposes. The connection methods of other components are not limited thereto. Buses can be classified as address buses, data buses, control buses, etc. For ease of representation, only one thick line is used to represent a bus in Figure 9, but this does not mean that there is only one bus or only one type of bus.

[0373] Embodiments of this application further provide a computer-readable storage medium configured to store computer software instructions that need to be executed by the above-mentioned processor. The computer software instructions include programs that need to be executed by the above-mentioned processor.

[0374] Embodiments of this application further provide a communication system including a communication device configured to implement the functions of a terminal device in the embodiment of Figure 4 and a communication device configured to implement the functions of a network device in the embodiment of Figure 4.

[0375] Embodiments of this application further provide a communication system including a communication device configured to implement the functions of a terminal device in the embodiment of Figure 5 and a communication device configured to implement the functions of a network device in the embodiment of Figure 5.

[0376] Embodiments of this application further provide a communication system including a communication device configured to implement the functions of a terminal device in the embodiment of Figure 6 and a communication device configured to implement the functions of a network device in the embodiment of Figure 6.

[0377] Embodiments of this application further provide a communication system including a communication device configured to implement the functions of a terminal device in the embodiment of Figure 7 and a communication device configured to implement the functions of a network device in the embodiment of Figure 7.

[0378] Those skilled in the art will understand that embodiments of this application may be provided as methods, systems, or computer program products. Accordingly, this application may take the form of hardware-only embodiments, software-only embodiments, or embodiments using a combination of software and hardware. Furthermore, this application may take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk memory, CD-ROM, optical memory, etc.) containing computer-usable program code.

[0379] This application will be described with reference to flowcharts and / or block diagrams of the methods, devices (systems), and computer program products described herein. It should be understood that computer program instructions may be used to implement each step and / or block in the flowcharts and / or block diagrams, as well as combinations of steps and / or blocks in the flowcharts and / or block diagrams. These computer program instructions may be given for the processor of a general-purpose computer, a dedicated computer, an embedded processor, or any other programmable data processing device to generate a machine, and therefore, instructions executed by the processor of a computer or any other programmable data processing device will generate a machine to implement a particular function in one or more steps in the flowchart and / or one or more blocks in the block diagram.

[0380] These computer program instructions may, alternatively, be stored in computer-readable memory that can be directed to a computer or any other programmable data processing device to operate in a specific manner, and therefore, instructions stored in computer-readable memory generate an artifact that includes an instruction unit. The instruction unit implements a specific function in one or more steps in a flowchart and / or in one or more blocks in a block diagram.

[0381] Computer program instructions can, alternatively, be loaded onto a computer or another programmable data processing device, and thus a series of operations and steps are executed on the computer or another programmable device to generate computer implementation processing. Thus, instructions executed on the computer or another programmable device provide steps to realize a particular function in one or more steps in a flowchart and / or in one or more blocks in a block diagram.

[0382] Clearly, a person skilled in the art can make various modifications and changes to this application without departing from the spirit and scope of this application. In this way, if these modifications and changes to this application fall within the scope of the claims of this application and their equivalent art, this application is intended to cover these modifications and changes as well.

Claims

1. A communication method, wherein the method is applied to a terminal device, and the method is Steps to register with the first public land mobile network (PLMN) via the first access, The steps of determining that the terminal device on the first access will be switched from the first PLMN to a second PLMN other than the first PLMN and a PLMN equivalent to the first PLMN, and The step of deciding to delete a first parameter, which includes at least one of a key set identifier or a globally unique temporary user device identifier, if the state of the terminal device on the second access is that the terminal device is not registered with the first PLMN or is not registered with the first PLMN, or A step of obtaining first information via a first access of the terminal device, wherein the first information indicates the reason why the core network device rejects the registration request or service request of the terminal device, and The step of deciding to delete the first parameter when the information regarding the second access of the terminal device satisfies one of the following conditions: namely, the public land mobile network PLMN is not registered via the second access, or the PLMN registered via the second access is different from the PLMN registered via the first access. A method comprising the steps of determining to remove the first parameter if the state of the terminal device on the second access is that the terminal device is not registered with the first PLMN or is not registered with the first PLMN and the security encryption algorithm is a null encryption algorithm.

2. The first information is not applicable to the second access. The information relating to the second access of the terminal device is the registration information relating to the second access. The method according to claim 1.

3. The aforementioned key set identifier identifies the non-access layer NAS security context information. The method according to claim 1.

4. The NAS security context information includes a security encryption algorithm, and the security encryption algorithm is a null encryption algorithm. The method according to claim 3.

5. The aforementioned method, A step of deleting a second parameter, the second parameter comprising at least one of the last visited tracking area identifier for the first access, or a list of tracking area identifiers for the first access, further comprising: The method according to claim 1.

6. A communication device comprising a unit or module configured to carry out the method described in any one of claims 1 to 5.

7. A communication device, wherein the device includes a processor and a memory, and the processor is coupled to the memory. The memory is configured to store a program or instruction, A communication device wherein the processor is configured to call the program or the instruction, enabling the communication device to carry out the method according to any one of claims 1 to 5.

8. A computer-readable storage medium, wherein the computer-readable storage medium is configured to store computer instructions, and when the computer instructions are executed on a computer, the computer is able to perform the method according to any one of claims 1 to 5.

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