Communication method and apparatus

Abstract

The application provides a communication method and device, relates to the technical field of wireless communication, can avoid TAU failure, helps shorten the network interruption time of a terminal device, and reduces the power consumption of the terminal device. The method comprises the following steps: a second network unit determines that a third public land mobile network (PLMN) serving a terminal device belongs to a first PLMN, wherein the second network unit is a network unit in a home PLMN of the terminal device, the number of the first PLMN is at least one, and the first PLMN is different from the home PLMN of the terminal device. The second network unit does not send a first target parameter to the terminal device, or the second network unit sends indication information to the terminal device, wherein the indication information indicates that the first target parameter is deleted. The first target parameter comprises that the parameter mapping of a protocol data unit (PDU) session of a first communication mode is mapped to a parameter of a second communication mode.

Description

TECHNICAL FIELD

[0001] Embodiments of the present application relate to the field of wireless communication, and in particular, to a communication method and apparatus. BACKGROUND

[0002] Currently, when a terminal device in an idle state moves from a fifth generation (5G) network to a fourth generation (4G) network, if there is at least one protocol data unit (PDU) session that supports interworking in a PDU session that has been established on the terminal device, the terminal device initiates a tracking area update (TAU) request in the 4G network. If the PDU session of the terminal device saves corresponding 4G parameters, it can be understood that the PDU session is a PDU session that supports interworking. Correspondingly, the mobility management entity (MME) of the core network of the 4G network obtains the context information of the terminal device from the access and mobility management function (AMF) of the core network of the 5G network, thereby completing the TAU.

[0003] However, in a roaming scenario, the session management function (SMF) of the home network always sends the terminal device the 4G parameters corresponding to the PDU session. Moreover, when the AMF of the visited network and the MME of the home network do not open an interface, if the terminal device moves from the 5G network of the visited network to the 4G network of the home network, the MME cannot obtain the context information, resulting in a TAU failure, an increase in the power consumption and the offline time of the terminal device, and a poor user experience. SUMMARY

[0004] Embodiments of the present application provide a communication method and apparatus, which can avoid the problem of TAU failure, help shorten the offline time of the terminal device, and reduce the power consumption of the terminal device.

[0005] To achieve the above object, embodiments of the present application adopt the following technical solutions:

[0006] In a first aspect, a communication method is provided. The execution subject of the method can be a second network element or a chip applied in the second network element. Hereinafter, the execution subject is taken as an example of the second network element. The method comprises: determining, by the second network element, that a third public land mobile network (PLMN) providing service for a terminal device belongs to a first PLMN, wherein the second network element is a network element in a home PLMN of the terminal device, the number of the first PLMN is at least one, and the first PLMN is different from the home PLMN of the terminal device. The second network element does not send a first target parameter to the terminal device, or the second network element sends indication information to the terminal device, wherein the indication information indicates that the first target parameter is deleted. The first target parameter comprises mapping of a parameter of a protocol data unit (PDU) session of a first communication standard to a parameter of a second communication standard, the communication standard of the third PLMN providing service for the terminal device comprises the first communication standard, the communication standard of the home PLMN of the terminal device comprises the second communication standard, and the first communication standard is different from the second communication standard.

[0007] In this way, when the third PLMN providing service for the terminal device belongs to the first PLMN, the terminal device will not receive the first target parameter or delete the received first target parameter. When the terminal device reselects from the third PLMN of the first communication standard currently providing service for the terminal device to the home PLMN of the second communication standard of the terminal device, since the terminal device does not store the first target parameter, the terminal device no longer initiates TAU, thereby avoiding the problem of TAU failure, which helps to shorten the offline time of the terminal device and reduce the power consumption of the terminal device.

[0008] In a possible design, the communication method further comprises: receiving, by the second network element, first information from a third mobility management entity, wherein the third mobility management entity is a network element in the third PLMN providing service for the terminal device, and the first information comprises information of an operator to which the third mobility management entity belongs. The determining, by the second network element, that the third PLMN providing service for the terminal device belongs to the first PLMN comprises: determining, by the second network element according to the first information, that the third PLMN providing service for the terminal device belongs to the first PLMN.

[0009] That is, the second network element can determine that the third PLMN providing service for the terminal device belongs to the first PLMN based on the information of the operator to which the third mobility management entity belongs.

[0010] In a possible design, the determining, by the second network element, that the third PLMN providing service for the terminal device belongs to the first PLMN comprises: when the second network element determines that the terminal device is in a roaming state, determining, by the second network element, that the third PLMN providing service for the terminal device belongs to the first PLMN, so as to simplify the processing procedure of the second network element.

[0011] In a possible design, the method further includes: receiving, by the second network element, second information from a third network element or a third border gateway (BG), where the third network element is a network element in a third PLMN that provides services for the terminal device, and the third BG is used to connect the second network element and the third network element; and determining, by the second network element, that the terminal device is in a roaming state according to the second information.

[0012] That is, the second network element can receive information from the third network element or the third BG, and it can be considered that the terminal device is in a roaming state.

[0013] In a possible design, the method further includes: sending, by the second network element, a PDU session establishment accept message to the terminal device. The second network element does not send the first target parameter to the terminal device, including that the PDU session establishment accept message does not carry the first target parameter, and accordingly, the terminal device cannot receive the first target parameter.

[0014] In a possible design, the second network element sends indication information to the terminal device through a PDU session modification command message, to provide the indication information to the terminal device in a session modification process.

[0015] In a possible design, the first PLMN is preconfigured.

[0016] In a possible design, the method further includes: determining, by the second network element, that a fourth PLMN that provides services for the terminal device does not belong to the first PLMN; and sending, by the second network element, a second target parameter to the terminal device, where the second target parameter includes mapping of a parameter of a PDU session in a first communication mode to a parameter in a second communication mode, and a communication mode of the fourth PLMN that provides services for the terminal device includes the first communication mode, to enable the terminal device to normally acquire the second target parameter. It should be understood that, for the first target parameter, in the first target parameter, the PDU session in the first communication mode is a PDU session in the third PLMN. For the second target parameter, in the second target parameter, the PDU session in the first communication mode is a PDU session in the fourth PLMN.

[0017] In a possible design, the fourth PLMN that provides services for the terminal device is a home PLMN of the terminal device. That is, the PLMN currently accessed by the terminal device is the home PLMN of the terminal device.

[0018] In a possible design, the fourth PLMN that provides services for the terminal device is different from a country to which an operator of the home PLMN of the terminal device belongs. That is, the terminal device is in a roaming state in a foreign country.

[0019] In a possible design, the second network element determines that the fourth PLMN providing services for the terminal device does not belong to the first PLMN, including: when the second network element determines that the terminal device is in a roaming state, the second network element determines that the fourth PLMN providing services for the terminal device does not belong to the first PLMN, so as to simplify the processing procedure of the second network element.

[0020] In a possible design, the communication method further includes: the second network element receives fourth information from a fourth network element or a fourth border gateway (BG), where the fourth network element is a network element in a fourth PLMN providing services for the terminal device, and the fourth BG is used to connect the second network element and the fourth network element. The second network element determines that the terminal device is in a roaming state according to the fourth information. That is, the second network element can receive information from the fourth network element or the fourth BG, and it is considered that the terminal device is in a roaming state.

[0021] In a possible design, the communication method further includes: the second network element receives first information from a fourth mobility management entity, where the fourth mobility management entity is a network element in a fourth PLMN providing services for the terminal device, and the first information includes information of an operator to which the fourth mobility management entity belongs. The second network element determines that the fourth PLMN providing services for the terminal device does not belong to the first PLMN, including: the second network element determines that the fourth PLMN providing services for the terminal device does not belong to the first PLMN according to the first information.

[0022] That is, the second network element can determine that the fourth PLMN providing services for the terminal device does not belong to the first PLMN based on the information of the operator to which the fourth mobility management entity belongs.

[0023] In a possible design, the first information includes a globally unique access and mobility management function identity (GUAMI).

[0024] In a second aspect, the present application provides a communication method. The execution subject of the method can be a second network element or a chip applied in the second network element. Hereinafter, the execution subject is taken as the second network element for example. The method comprises: determining, by the second network element, that a public land mobile network (PLMN) providing services for a terminal device does not belong to a first PLMN, wherein the second network element is a network element in a home PLMN of the terminal device, the number of the first PLMN is at least one, and the first PLMN is different from the home PLMN of the terminal device. The method further comprises: sending, by the second network element, a target parameter to the terminal device, wherein the target parameter comprises a mapping of a parameter of a protocol data unit (PDU) session of a first communication standard to a parameter of a second communication standard, the communication standard of the PLMN providing services for the terminal device comprises the first communication standard, the communication standard of the home PLMN of the terminal device comprises the second communication standard, and the first communication standard is different from the second communication standard.

[0025] That is, in the case that the PLMN providing services for the terminal device does not belong to the first PLMN, the second network element can provide the target parameter for the terminal device, so that the terminal device can normally obtain the target parameter.

[0026] In a possible design, the PLMN providing services for the terminal device is the home PLMN of the terminal device.

[0027] In a possible design, the PLMN providing services for the terminal device is different from a country to which an operator of the home PLMN of the terminal device belongs.

[0028] In a possible design, the determining, by the second network element, that the PLMN providing services for the terminal device does not belong to the first PLMN comprises: when the second network element determines that the terminal device is in a roaming state, determining, by the second network element, that the PLMN providing services for the terminal device does not belong to the first PLMN.

[0029] In a possible design, the communication method further comprises: receiving, by the second network element, first information from a first network element or a border gateway (BG), wherein the first network element is a network element in the PLMN providing services for the terminal device, and the BG is used to connect the first network element and the second network element. The second network element determines, according to the first information, that the terminal device is in the roaming state.

[0030] In a possible design, the method further includes: receiving, by the second network element, second information from the first mobile management entity, where the first mobile management entity is a network element in a PLMN that provides services for the terminal device, and the second information includes information of an operator to which the first mobile management entity belongs. The determining, by the second network element, that the PLMN that provides services for the terminal device does not belong to the first PLMN includes: determining, by the second network element according to the second information, that the PLMN that provides services for the terminal device does not belong to the first PLMN.

[0031] In a possible design, the second information includes a globally unique access and mobility management function identifier (GUAMI).

[0032] In a possible design, the first PLMN is preconfigured.

[0033] In a third aspect, this application provides a communication method, an execution subject of the method can be a terminal device or a chip applied in the terminal device. Hereinafter, the execution subject is taken as an example for description. The method includes: when the terminal device moves from a first communication mode of a first public land mobile network (PLMN) to a second communication mode of a home PLMN of the terminal device, sending, by the terminal device, a registration request message to a second mobile management entity of the home PLMN of the terminal device, where the first PLMN and the home PLMN of the terminal device are different, the first communication mode is different from the second communication mode, the terminal device stores a target parameter, and the target parameter includes mapping of a protocol data unit (PDU) session parameter of the first communication mode to a parameter of the second communication mode. The terminal device receives a registration accept message from the second mobile management entity.

[0034] For example, when the terminal device moves from the first communication mode of the first PLMN to the second communication mode of the home PLMN of the terminal device, if the terminal device moves in an idle state, the terminal device reselects from the first communication mode of the first PLMN to the second communication mode of the home PLMN of the terminal device. If the terminal device moves in a connected state, the terminal device switches from the first communication mode of the first PLMN to the second communication mode of the home PLMN of the terminal device.

[0035] In this way, even if the first PLMN is different from the home PLMN of the terminal device, and the terminal device stores the target parameter, when the terminal device moves from the first communication mode of the first PLMN to the second communication mode of the home PLMN of the terminal device, the terminal device initiates the registration request message, and no longer initiates TAU, thereby avoiding TAU failure, helping to shorten the offline time of the terminal device and reduce the power consumption of the terminal device.

[0036] In a possible design, the method further includes: determining, by the terminal device, that the first PLMN is different from a home PLMN of the terminal device according to the first information, where the first information includes information of at least one third PLMN, the third PLMN is different from the home PLMN of the terminal device, and the third PLMN includes the first PLMN.

[0037] That is, the first information includes information of at least one preconfigured third PLMN. In this way, the terminal device determines that the first PLMN is different from the home PLMN of the terminal device based on the first information.

[0038] In a possible design, the method further includes: receiving, by the terminal device, the first information from the second mobility management entity, so as to obtain the first information from the second mobility management entity of the home network.

[0039] In a possible design, the first information is carried in a same message as equivalent public land mobile network (EPLMN), where the EPLMN at least includes the first PLMN. That is, the terminal device can obtain the first information in a registration procedure of the home network, so that the terminal device can timely initiate a registration request message when the terminal device reselects from a first communication mode of the first PLMN to a second communication mode of the home PLMN of the terminal device, thereby effectively avoiding a TAU failure problem.

[0040] In a possible design, the method further includes: receiving, by the terminal device, the first information from a second network element, where the second network element belongs to network elements in the home PLMN of the terminal device, so as to obtain the first information from the second network element.

[0041] In a possible design, the terminal device receives the first information from the second network element through a PDU session establishment accept message. That is, the terminal device can obtain the first information in a PDU session establishment procedure, so that the terminal device can timely initiate a registration request message when the terminal device reselects from a first communication mode of the first PLMN to a second communication mode of the home PLMN of the terminal device, thereby effectively avoiding a TAU failure problem.

[0042] In a fourth aspect, the present application provides a communication method. The execution subject of the method can be a terminal device or a chip applied in the terminal device. Hereinafter, the execution subject is taken as an example for description. The method comprises the following steps: a terminal device sends a registration request message to a first mobile management entity of a first public land mobile network (PLMN), wherein the first PLMN is different from a home PLMN of the terminal device; the terminal device receives a registration accept message from the first mobile management entity; the terminal device deletes a target parameter, or does not generate the target parameter, or does not save the target parameter when the terminal device receives the target parameter from a second network element, wherein the second network element is a network element in the home PLMN of the terminal device, and the target parameter comprises a parameter mapping from a protocol data unit (PDU) session of a first communication standard to a second communication standard, and the communication standard of the first PLMN comprises the first communication standard, and the communication standard of the home PLMN of the terminal device comprises the second communication standard.

[0043] That is to say, even if the first PLMN is different from the home PLMN of the terminal device, and the terminal device has registered in the first PLMN, the terminal device deletes the target parameter, or does not generate the target parameter, or does not save the target parameter when the terminal device receives the target parameter from the second network element. In this way, when the terminal device reselects from the first communication standard of the first PLMN to the second communication standard of the home PLMN of the terminal device, since the terminal device does not save the target parameter, the terminal device initiates the registration request message and does not initiate the TAU, thereby avoiding the problem of TAU failure, helping to shorten the offline time of the terminal device and reduce the power consumption of the terminal device.

[0044] In a possible design, the communication method further comprises: the terminal device determines, according to the first information, that the first PLMN is different from the home PLMN of the terminal device. The first information comprises information of at least one third PLMN, the third PLMN is different from the home PLMN of the terminal device, and the third PLMN comprises the first PLMN.

[0045] In a possible design, the communication method further comprises: the terminal device receives the first information from a second mobile management entity, wherein the second mobile management entity is a network element in the home PLMN of the terminal device.

[0046] In a possible design, the first information is carried in a same message as an equivalent public land mobile network (EPLMN). The EPLMN comprises at least the first PLMN.

[0047] In a possible design, the communication method further comprises: the terminal device receives the first information from a second network element, wherein the second network element is a network element in the home PLMN of the terminal device.

[0048] In a possible design, the terminal device receives the first information from the second network element through a PDU session establishment accept message.

[0049] In a fifth aspect, a communication apparatus is provided. The communication apparatus can be the second network element in the first aspect or any possible design of the first aspect, or a chip realizing the functions of the second network element. The communication apparatus includes modules, units, or means realizing the corresponding functions of the method, which can be implemented by hardware, software, or by a combination of hardware and software.

[0050] The communication apparatus includes a processing unit, a sending unit, and a receiving unit. The processing unit is configured to determine that a third public land mobile network (PLMN) serving a terminal device belongs to a first PLMN, and the communication apparatus is a network element in a home PLMN of the terminal device, and the number of the first PLMN is at least one and different from the home PLMN of the terminal device. The sending unit is configured not to send a first target parameter to the terminal device, or the sending unit is configured to send indication information to the terminal device, and the indication information indicates that the first target parameter is deleted. The first target parameter includes mapping of a protocol data unit (PDU) session parameter of a first communication mode to a parameter of a second communication mode, the third PLMN serving the terminal device includes the first communication mode, the home PLMN of the terminal device includes the second communication mode, and the first communication mode is different from the second communication mode.

[0051] In a possible design, the receiving unit is configured to receive first information from a third mobility management entity, and the third mobility management entity is a network element in the third PLMN serving the terminal device, and the first information includes information of an operator to which the third mobility management entity belongs. The processing unit is configured to determine that the third PLMN serving the terminal device belongs to the first PLMN, and includes: determining, according to the first information, that the third PLMN serving the terminal device belongs to the first PLMN.

[0052] In a possible design, the processing unit is configured to determine that the third PLMN serving the terminal device belongs to the first PLMN, and includes: determining that the third PLMN serving the terminal device belongs to the first PLMN when it is determined that the terminal device is in a roaming state.

[0053] In one possible design, the receiving unit is further configured to receive second information from a third network unit or a third border gateway (BG), wherein the third network unit is a network unit in a third PLMN that provides services to the terminal device, and the third BG is used to connect the communication device and the third network unit. The processing unit is further configured to determine, based on the second information, that the terminal device is in a roaming state.

[0054] In one possible design, the sending unit is further configured to send a PDU session establishment accept message to the terminal device. However, the sending unit is not configured to send the first target parameter to the terminal device, meaning the PDU session establishment accept message does not carry the first target parameter.

[0055] In one possible design, the sending unit is used to send indication information to the terminal device by modifying the command message through the PDU session.

[0056] In one possible design, the first PLMN is pre-configured.

[0057] In one possible design, the processing unit is further configured to determine that the fourth PLMN providing services to the terminal device does not belong to the first PLMN. The sending unit is further configured to send a second target parameter to the terminal device, wherein the second target parameter includes parameters of the PDU session of the first communication standard mapped to parameters of the second communication standard, and the communication standard of the fourth PLMN providing services to the terminal device includes the first communication standard.

[0058] In one possible design, the fourth PLMN that provides services to the terminal device is the terminal device's home PLMN.

[0059] In one possible design, the fourth PLMN that provides services to the terminal device is located in a different country than the operator of the PLMN to which the terminal device belongs.

[0060] In one possible design, the processing unit, used to determine that the fourth PLMN providing services to the terminal device does not belong to the first PLMN, includes: when it is determined that the terminal device is in a roaming state, determining that the fourth PLMN providing services to the terminal device does not belong to the first PLMN.

[0061] In one possible design, the receiving unit is further configured to receive fourth information from a fourth network unit or a fourth border gateway (BG), wherein the fourth network unit is a network unit in a fourth PLMN that provides services to the terminal device, and the fourth BG is used to connect the communication device and the fourth network unit. The processing unit is further configured to determine, based on the fourth information, that the terminal device is in a roaming state.

[0062] In a possible design, the receiving unit is further configured to receive first information from a fourth mobility management entity, where the fourth mobility management entity is a network element in a fourth PLMN that provides services for the terminal device, and the first information includes information of an operator to which the fourth mobility management entity belongs. The processing unit is configured to determine that the fourth PLMN that provides services for the terminal device does not belong to the first PLMN, including: determining, according to the first information, that the fourth PLMN that provides services for the terminal device does not belong to the first PLMN.

[0063] In a possible design, the first information includes a globally unique access and mobility management function identifier (GUAMI).

[0064] In a sixth aspect, this application provides a communication apparatus, which can be the second network unit in the second aspect or any possible design of the second aspect, or a chip realizing the functions of the second network unit. The communication apparatus includes modules, units, or means realizing the corresponding functions of the above method, which can be realized by hardware, software, or by executing corresponding software with hardware. The hardware or software includes one or more modules or units corresponding to the above functions.

[0065] The communication apparatus includes a processing unit, a sending unit, and a receiving unit. The processing unit is configured to determine that a public land mobile network (PLMN) that provides services for a terminal device does not belong to a first PLMN, where the communication apparatus is a network element in a home PLMN of the terminal device, and the number of the first PLMN is at least one and different from the home PLMN of the terminal device. The sending unit is configured to send, to the terminal device, target parameters, where the target parameters include mapping of parameters of a protocol data unit (PDU) session of a first communication system to parameters of a second communication system, the communication system of the PLMN that provides services for the terminal device includes the first communication system, the communication system of the home PLMN of the terminal device includes the second communication system, and the first communication system is different from the second communication system.

[0066] In a possible design, the PLMN that provides services for the terminal device is the home PLMN of the terminal device.

[0067] In a possible design, the PLMN that provides services for the terminal device is different from the home PLMN of the terminal device in terms of the country to which the operator belongs.

[0068] In a possible design, the processing unit is configured to determine that the PLMN that provides services for the terminal device does not belong to the first PLMN, including: when it is determined that the terminal device is in a roaming state, determining that the PLMN that provides services for the terminal device does not belong to the first PLMN.

[0069] In a possible design of the method, the receiving unit is further configured to receive first information from a first network element or a border gateway (BG), where the first network element is a network element in a PLMN that provides services for the terminal device, and the BG is configured to connect the first network element and the communication apparatus. The processing unit is further configured to determine, according to the first information, that the terminal device is in a roaming state.

[0070] In a possible design of the method, the receiving unit is further configured to receive second information from a first mobility management entity, where the first mobility management entity is a network element in a PLMN that provides services for the terminal device, and the second information includes information about an operator to which the first mobility management entity belongs. The processing unit is configured to determine that the PLMN that provides services for the terminal device does not belong to the first PLMN, by determining, according to the second information, that the PLMN that provides services for the terminal device does not belong to the first PLMN.

[0071] In a possible design of the method, the second information includes a globally unique access and mobility management function identity (GUAMI).

[0072] In a possible design of the method, the first PLMN is preconfigured.

[0073] In a seventh aspect, a communication apparatus is provided, which can be the terminal device in the third aspect or any possible design of the third aspect, or a chip realizing the functions of the terminal device. The communication apparatus includes modules, units, or means realizing the corresponding functions of the above method, which can be realized by hardware, software, or by executing corresponding software with hardware. The hardware or software includes one or more modules or units corresponding to the above functions.

[0074] The communication apparatus includes a processing unit, a sending unit, and a receiving unit. The processing unit is configured to determine that a terminal device moves from a first communication mode of a first public land mobile network (PLMN) to a second communication mode of a PLMN to which the terminal device belongs, and control the sending unit to send, to a second mobility management entity of the PLMN to which the terminal device belongs, a registration request message. The first PLMN and the PLMN to which the terminal device belongs are different, the first communication mode is different from the second communication mode, and the terminal device stores a target parameter, where the target parameter includes mapping of a protocol data unit (PDU) session parameter of the first communication mode to a parameter of the second communication mode. The processing unit is further configured to control the receiving unit to receive a registration accept message from the second mobility management entity.

[0075] In a possible design of the method, the processing unit is further configured to determine, according to the first information, that the first PLMN is different from a home PLMN of the communication apparatus. The first information comprises information of at least one third PLMN, the third PLMN being different from the home PLMN of the communication apparatus, and the third PLMN comprising the first PLMN.

[0076] In a possible design of the method, the receiving unit is further configured to receive the first information from a second network element.

[0077] In a possible design of the method, the first information is carried in a same message as an equivalent public land mobile network (EPLMN). The EPLMN comprises at least the first PLMN.

[0078] In a possible design of the method, the receiving unit is further configured to receive the first information from a second network element, wherein the second network element belongs to network elements in the home PLMN of the communication apparatus.

[0079] In a possible design of the method, the receiving unit is configured to receive the first information from the second network element through a PDU session establishment accept message.

[0080] In an eighth aspect, a communication apparatus is provided. The communication apparatus can be the terminal device in the fourth aspect or any possible design of the fourth aspect, or a chip realizing the functions of the terminal device. The communication apparatus comprises modules, units, or means realizing the corresponding functions of the above method, which can be realized by hardware, software, or by executing corresponding software with hardware. The hardware or software comprises one or more modules or units corresponding to the above functions.

[0081] The communication apparatus comprises a processing unit, a sending unit, and a receiving unit. The sending unit is configured to send, to a first mobile management entity of a first public land mobile network (PLMN), a registration request message, wherein the first PLMN is different from a home PLMN of the communication apparatus. The receiving unit is configured to receive a registration accept message from the first mobile management entity. The processing unit is configured to delete a target parameter, or the processing unit is configured not to generate the target parameter, or the receiving unit is further configured to receive the target parameter from a second network element, and the processing unit is configured not to save the target parameter, wherein the second network element is a network element in the home PLMN of the communication apparatus, and the target parameter comprises mapping of a protocol data unit (PDU) session parameter of a first communication mode to a parameter of a second communication mode, the communication mode of the first PLMN comprises the first communication mode, and the communication mode of the home PLMN of the communication apparatus comprises the second communication mode.

[0082] In a possible design of the processing unit, the processing unit is further configured to determine, according to the first information, that the first PLMN is different from a home PLMN of the communication apparatus. The first information includes information of at least one third PLMN, the third PLMN being different from the home PLMN of the communication apparatus, and the third PLMN including the first PLMN.

[0083] In a possible design of the receiving unit, the receiving unit is further configured to receive the first information from a second network element, the second network element being a network element in the home PLMN of the communication apparatus.

[0084] In a possible design of the first information, the first information is carried in a same message as an equivalent public land mobile network (EPLMN). The EPLMN includes at least the first PLMN.

[0085] In a possible design of the receiving unit, the receiving unit is further configured to receive the first information from a second network element, the second network element being a network element in the home PLMN of the communication apparatus.

[0086] In a possible design of the receiving unit, the receiving unit is configured to receive the first information from the second network element through a PDU session establishment accept message.

[0087] In a ninth aspect, an embodiment of the present application provides a communication apparatus, including: a processor and a memory; the memory is configured to store computer instructions, when the processor executes the instructions, the communication apparatus performs the method performed by the second network element in any of the above aspects or any possible design of the above aspects. The communication apparatus can be the second network element in the first aspect or any possible design of the first aspect, or the communication apparatus can be the second network element in the second aspect or any possible design of the second aspect, or a chip realizing the function of the second network element.

[0088] In a tenth aspect, an embodiment of the present application provides a communication apparatus, including: a processor; the processor is coupled with a memory, and is configured to read instructions in the memory and execute the instructions, so that the communication apparatus performs the method performed by the second network element in any of the above aspects or any possible design of the above aspects. The communication apparatus can be the second network element in the first aspect or any possible design of the first aspect, or the communication apparatus can be the second network element in the second aspect or any possible design of the second aspect, or a chip realizing the function of the second network element.

[0089] In an eleventh aspect, an embodiment of the present application provides a chip, comprising a processing circuit and an input / output interface. The input / output interface is configured to communicate with a module outside the chip, for example, the chip can be a chip for implementing the function of the second network element in the first aspect or any possible design of the first aspect. The processing circuit is configured to run a computer program or an instruction to implement the method in the first aspect or any possible design of the first aspect. For another example, the chip can be a chip for implementing the function of the second network element in the second aspect or any possible design of the second aspect. The processing circuit is configured to run a computer program or an instruction to implement the method in the second aspect or any possible design of the second aspect.

[0090] In a twelfth aspect, an embodiment of the present application provides a communication apparatus, comprising: a processor and a memory; the memory is configured to store a computer instruction, when the processor executes the instruction, the communication apparatus performs the method performed by the terminal device in any one of the aspects or any possible design of the aspect. The communication apparatus can be the terminal device in the third aspect or any possible design of the third aspect, or the communication apparatus can be the terminal device in the fourth aspect or any possible design of the fourth aspect, or a chip for implementing the function of the terminal device.

[0091] In a thirteenth aspect, an embodiment of the present application provides a communication apparatus, comprising: a processor; the processor is coupled with a memory, and is configured to read the instruction in the memory and execute the instruction, so that the communication apparatus performs the method performed by the terminal device in any one of the aspects or any possible design of the aspect. The communication apparatus can be the terminal device in the third aspect or any possible design of the third aspect, or the communication apparatus can be the terminal device in the fourth aspect or any possible design of the fourth aspect, or a chip for implementing the function of the terminal device.

[0092] In a fourteenth aspect, an embodiment of the present application provides a chip, comprising a processing circuit and an input / output interface. The input / output interface is configured to communicate with a module outside the chip, for example, the chip can be a chip for implementing the function of the terminal device in the third aspect or any possible design of the third aspect. The processing circuit is configured to run a computer program or an instruction to implement the method in the third aspect or any possible design of the third aspect. For another example, the chip can be a chip for implementing the function of the terminal device in the fourth aspect or any possible design of the fourth aspect. The processing circuit is configured to run a computer program or an instruction to implement the method in the fourth aspect or any possible design of the fourth aspect.

[0093] In a fifteenth aspect, embodiments of this application provide a computer-readable storage medium storing instructions that, when executed on a computer, enable the computer to perform the methods of any of the preceding aspects.

[0094] In a sixteenth aspect, embodiments of this application provide a computer program product containing instructions that, when run on a computer, enable the computer to perform the method of any of the preceding aspects.

[0095] In a seventeenth aspect, embodiments of this application provide a circuit system including a processing circuit configured to perform the method as described in any of the preceding aspects.

[0096] The technical effects of any of the designs in aspects five through seventeen can be found in the beneficial effects of the corresponding methods provided above, and will not be repeated here. Attached Figure Description

[0097] Figure 1 A schematic diagram of the architecture of a communication system used in an embodiment of this application;

[0098] Figure 2 A schematic diagram of the architecture of another communication system used in an embodiment of this application;

[0099] Figure 3 A schematic diagram of the architecture of another communication system used in an embodiment of this application;

[0100] Figure 4 A schematic diagram of the architecture of another communication system used in an embodiment of this application;

[0101] Figure 5 A schematic diagram of the architecture of another communication system used in an embodiment of this application;

[0102] Figure 6 A flowchart illustrating a communication method provided in an embodiment of this application;

[0103] Figure 7 A flowchart illustrating another communication method provided in an embodiment of this application;

[0104] Figure 8a A flowchart illustrating yet another communication method provided in an embodiment of this application;

[0105] Figure 8b A flowchart illustrating yet another communication method provided in an embodiment of this application;

[0106] Figure 9 A flowchart illustrating yet another communication method provided in an embodiment of this application;

[0107] Figure 10a A flowchart of another communication method provided by an embodiment of the application is shown in FIG. 6.

[0108] Figure 10b A flowchart of another communication method provided by an embodiment of the application is shown in FIG. 6.

[0109] Figure 11 A flowchart of another communication method provided by an embodiment of the application is shown in FIG. 6.

[0110] Figure 12 A flowchart of another communication method provided by an embodiment of the application is shown in FIG. 6.

[0111] Figure 13 A flowchart of another communication method provided by an embodiment of the application is shown in FIG. 6.

[0112] Figure 14 A structural diagram of a communication device provided by an embodiment of the application is shown in FIG. 7.

[0113] Figure 15 A structural diagram of a communication device provided by an embodiment of the application is shown in FIG. 7. DETAILED DESCRIPTION

[0114] Figure 1 A structural diagram of a communication system provided by an embodiment of the application is shown in FIG. 8. As shown in FIG. 8, the communication system includes a terminal device, an access network device and a core network. Figure 1

[0115] ​The terminal device can include a user equipment (UE), a wireless terminal device, a mobile terminal device, a device-to-device (D2D) terminal device, a vehicle to everything (V2X) terminal device, a machine-to-machine / machine-type communications (M2M / MTC) terminal device, an internet of things (IoT) terminal device, a subscriber unit, a subscriber station, a mobile station, a remote station, an access point (AP), a remote terminal, an access terminal, a user terminal, a user agent, or a user device, etc. For example, it can include a mobile phone (or called a "cellular" phone), a computer with a mobile terminal device, a portable, pocket, handheld, built-in computer mobile device, etc. For example, it can include a personal communication service (PCS) phone, a cordless phone, a session initiation protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA), etc. It can also include a limited device, such as a device with low power consumption, a device with limited storage capacity, a device with limited computing capacity, etc. For example, it can include a bar code, a radio frequency identification (RFID), a sensor, a global positioning system (GPS), a laser scanner, etc.

[0116] And as the above introduction of various terminal devices, if located on the vehicle (for example, placed in the vehicle or installed in the vehicle), can be considered as a vehicle terminal device, vehicle terminal device, for example, also known as on-board unit (on-board unit, OBU).

[0117] In the embodiment of the application, the terminal device can also include a relay. Or it can be understood that all devices capable of data communication with the base station can be regarded as terminal devices.

[0118] In the embodiment of the application, the device for realizing the function of the terminal device can be a terminal device, or a device capable of supporting the terminal device to realize the function, such as a chip system, which can be installed in the terminal device. In the embodiment of the application, the chip system can be composed of a chip, or can include a chip and other discrete devices. In the technical solution provided in the embodiment of the application, the device for realizing the function of the terminal is taken as an example to introduce the terminal device.

[0119] The access network device can be an access point of wireless communication or wired communication, such as a base station or a base station controller, a wireless fidelity (wireless-fidelity, wifi) access point or a wifi controller, or a fixed network access point, etc. Among them, the base station can include various types of base stations, such as micro base station (also known as small station), macro base station, relay station, access point, etc., which are not limited in the embodiment of the application. In the embodiment of the application, the base station can be a base station (base transceiver station, BTS) in global system for mobile communication (global system for mobile communication, GSM), code division multiple access (code division multiple access, CDMA), base station (node B) in wideband code division multiple access (wideband code division multiple access, WCDMA), evolved base station (evolutional node B, eNB or e-NodeB) in long term evolution (longterm evolution, LTE), eNB in internet of things (internet of things, IoT) or narrow band internet of things (narrow band-internet of things, NB-IoT), base station in the fifth generation (the fifth generation, 5G) mobile communication network or future evolved public land mobile network (public land mobile network, PLMN), which is not limited in the embodiment of the application.

[0120] The core network includes various core network devices, such as an access management network element, a session management network element, and the like. Among them, the access management network element is mainly used for mobility management and access management, and can be used to implement functions other than session management in the mobility management entity (MME) function, for example, lawful interception, access authorization / authentication, and the like. In the 5G communication system, the access management network element can include a core access and mobility management function (AMF) network element. The session management network element is mainly used for session management, internet protocol (IP) address allocation and management of a terminal device, selection of a manageable user plane function, a terminal point of a policy control and charging function interface, and downlink data notification. In the fifth generation (5G) communication system, the session management network element can include a session management function (SMF) network element. The MME can be referred to for details Figure 2 , the AMF network element and the SMF network element can be referred to for details Figure 3 . It should be understood that the core network device can also include other network elements, such as a user plane function (UPF) network element, and the like, which will not be described one by one here.

[0121] An exemplary Figure 2 shows a schematic diagram of an architecture of a fourth generation (4G) communication system. The 4G communication system includes an evolved universal mobile telecommunications system (UMTS) territorial radio access network (E-UTRAN) device, an MME, a serving gateway (SGW), a packet data network (PDN) gateway (PGW), a policy and charging rules function (PCRF) network element, and a home subscriber server (HSS) and the like network element or device.

[0122] The terminal device accesses the E-UTRAN device via LTE-Uu, the E-UTRAN device communicates with the MME via S1-MME, the E-UTRAN device communicates with the SGW via S1-U, and different MMEs communicate with each other via S10. Figure 2 The example given is only an MME. The MME communicates with the HSS through S6a, the MME communicates with the SGW through S11, the PGW communicates with the PCRF network element through Gx, the PCRF network element communicates with the server through Rx, the SGW communicates with the PGW through S5, and the PGW accesses the server through SGi.

[0123] The E-UTRAN equipment is used to implement radio-related functions of the evolved network. The MME is responsible for mobility management on the control plane, including user context and mobility state management, and assigning temporary user identities. The SGW is the user plane anchor point between 3GPP access networks and serves as the interface for terminating E-UTRAN. The PGW is the user plane anchor point between 3GPP and non-3GPP access networks and serves as the interface for terminating external PDNs. PCRF network elements are used for policy control decisions and flow charging control functions. The HSS stores user subscription information. Servers provide Internet Protocol (IP) services, such as voice / video services and packet-switched streaming services (PSS) based on the Internet Protocol Multimedia Subsystem (IMS).

[0124] For example, Figure 3An architecture diagram of a 5G communication system is shown. The 5G communication system includes a radio access network (RAN) device, a user plane function (UPF) network element, an AMF network element, an SMF network element, an authentication server function (AUSF) network element, a network slice selection function (NSSF) network element, a network exposure function (NEF) network element, a network exposure function repository function (NRF) network element, a policy control function (PCF) network element, a unified data management (UDM) network element, a unified data repository (UDR) network element, an application function (AF) network element, or a charging function (CHF) network element, and the like.

[0125] It should be noted that, Figure 3 Some examples of network elements or entities in the 5G communication system are only exemplarily given, and the 5G communication system can further include some network data analytics function (NWDAF) network elements and the like. Figure 3 The network elements or entities not shown in the figure are not limited in the embodiments of the present application.

[0126] As shown in the figure, Figure 3 The terminal device accesses the 5G network through the RAN device, and the terminal device communicates with the AMF through an N1 interface (N1 for short); the RAN device communicates with the AMF network element through an N2 interface (N2 for short); the RAN device communicates with the UPF network element through an N3 interface (N3 for short); the SMF network element communicates with the UPF network element through an N4 interface (N4 for short), and the UPF network element accesses a data network (DN) through an N6 interface (N6 for short). In the architecture shown in the figure, Figure 3 N1, N2, N3, N4 and N6 respectively represent reference points between related network elements / network functions.

[0127] In addition, Figure 3The control plane functions such as the AUSF network element, the AMF network element, the SMF network element, the NSSF network element, the NEF network element, the NRF network element, the PCF network element, the UDM network element, the UDR network element, the CHF network element, or the AF network element, etc. adopt a service interface for interaction. For example, the service interface provided by the AUSF network element to the outside is Nausf; the service interface provided by the AMF network element to the outside is Namf; the service interface provided by the SMF network element to the outside is Nsmf; the service interface provided by the NSSF network element to the outside is Nnssf; the service interface provided by the NEF network element to the outside is Nnef; the service interface provided by the NRF network element to the outside is Nnrf; the service interface provided by the PCF network element to the outside is Npcf; the service interface provided by the UDM network element to the outside is Nudm; the service interface provided by the UDR network element to the outside is Nudr; the service interface provided by the CHF network element to the outside is Nchf; and the service interface provided by the AF network element to the outside is Naf. The related function description and interface description can refer to the 5G system architecture (5G system architecture) figure in the 23501 standard, and will not be described here.

[0128] It should be understood that the name of each core network device described above, such as the MME, the SMF, and the AMF, is only a name and does not constitute a limitation on the device itself. It can be understood that in the 5G network and other future networks, other names can also be used, and the embodiments of the present application do not make specific limitations thereon. For example, the AMF network element can also be referred to as AMF or AMF entity, and in the embodiments of the present application, only the AMF network element is taken as an example for introduction. Similarly, the SMF network element can also be referred to as SMF or SMF entity, and in the embodiments of the present application, only the SMF network element is taken as an example for introduction.

[0129] Optionally, the core network device can be implemented by one device, or can be implemented by multiple devices together, or can be a functional module in one device, and the embodiments of the present application do not make specific limitations thereon. It can be understood that the functional module can be a network element in a hardware device, or a software functional module running on a special hardware, or a virtualized functional module instantiated on a platform (for example, a cloud platform).

[0130] In order to facilitate understanding of the embodiments of the present application, the terms involved in the embodiments of the present application will be briefly described below. It should be understood that these descriptions are only for the purpose of facilitating understanding of the embodiments of the present application, and should not constitute any limitation on the present application.

[0131] 1, communication system

[0132] Communication systems, including but not limited to: 2nd-generation wireless telephone technology (2G) networks, 3rd-generation wireless telephone technology (3G) networks, 4th-generation wireless telephone technology (4G) networks, 5th-generation wireless telephone technology (5G) networks, 6th-generation wireless telephone technology (6G) networks, and the like. The 4G network can also be referred to as an evolved packet system (EPS) network, and the 5G network can also be referred to as a new radio (NR) network.

[0133] 2. PLMN

[0134] A PLMN is a network established and operated by a government or its approved operator to provide land mobile communication services for the public. The PLMN is interconnected with the public switched telephone network to form a communication network of the entire region or country.

[0135] A PLMN is composed of a mobile country code (MCC) and a mobile network code (MNC). The MCC uniquely represents the country to which a mobile user belongs. For example, the MCC of China is 460. The MNC can uniquely represent the network in the country. For example, the MNC corresponding to China Mobile can include 00, and the MNC corresponding to China Unicom includes 01. Different operators can correspond to different PLMNs. For example, the PLMN of China Mobile can include 46000, 46002, 46004, 46007, and 46008; the PLMN of China Unicom can include 46001, 46006, 46009, and 46010. The PLMN of China Telecom can include 46003, 46011, and 46012; the PLMN of China Radio and Television can include 46015. The PLMNs corresponding to future operators can also include others, which are not limited by the embodiments of the present application.

[0136] 3. Visited network operator, visited network

[0137] The visited network side refers to an operator that provides inter-network roaming services to terminal devices of other operators in a roaming area. The network that provides inter-network roaming services to terminal devices of other operators is described as a visited network. Exemplarily, the inter-network roaming service can be a 5G core network inter-network roaming service.

[0138] 4、Home network operator, home network

[0139] The home network side refers to an operator that provides inter-network roaming services to terminal devices of the home network through other operator networks in a roaming area. The network that provides inter-network roaming services to terminal devices of the home network through other operator networks is described as a home network. Exemplarily, the inter-network roaming service can be a 5G core network inter-network roaming service.

[0140] Exemplarily, the visited network can be a 5G network of a visited operator, and the home network can be a 5G network of a home operator. As shown in FIG. 1, in a 5G standalone networking mode, the visited network and the home network are connected through a border gateway (BG). In some embodiments, the connection between network elements in the visited network and network elements in the home network is as shown in FIG. 2. As shown in FIG. 2, the visited network and the home network are connected through a BG. Figure 4 Figure 5 As shown in FIG. 3, in the visited network, the SMF network element is referred to as a visited SMF (V-SMF) network element. In the home network, the SMF network element is referred to as a home SMF (H-SMF) network element. In the home network, the PCF network element is referred to as a home PCF (H-PCF) network element. Figure 5

[0141] 5、Radio resource control (RRC)

[0142] In a 4G network, two RRC states are supported, i.e., an RRC idle state (RRC_IDLE) and an RRC connected state (RRC_CONNECTED). In a 5G network, three RRC states are supported, i.e., an RRC idle state (RRC_IDLE), an RRC inactive state (RRC_INACTIVE), and an RRC connected state (RRC_CONNECTED). Different RRC states can be switched between each other.

[0143] ​​Currently, when a terminal device in idle state moves from a 5G network to a 4G network, if there is at least one PDU session supporting interoperation in a PDU session established on the terminal device, the terminal device initiates a TAU request in the 4G network; if not, an initial attach request is initiated. For example, if the PDU session of the terminal device saves corresponding 4G parameters, it can be understood that the PDU session is a PDU session supporting interoperation. Conversely, if the PDU session of the terminal device does not save corresponding 4G parameters, it can be understood that the PDU session is a PDU session not supporting interoperation. The 4G parameters corresponding to the PDU session include parameters such as EPS bearer identity (EBI) and quality of service (QoS) flow parameters of the 4G network, which are mapped from the PDU session in the 5G network to the 4G network. In the case where the terminal device initiates TAU, the core network element MME of the 4G network obtains the context information of the terminal device from the core network element AMF of the 5G network, thereby completing TAU.

[0144] However, in a roaming scenario, the terminal device still uses the SMF network element of the home network (i.e., the H-SMF network element) to provide services. The SMF network element of the home network always sends the 4G parameters corresponding to the PDU session to the terminal device. Moreover, when the interface between the AMF network element of the visited network and the MME network element of the home network is not opened, if the terminal device moves from the 5G network of the visited network to the 4G network of the home network, the MME cannot obtain the context information, resulting in TAU failure, increased power consumption and downtime of the terminal device, and poor user experience.

[0145] Therefore, the embodiments of the present application provide three communication methods, and the communication method (such as the first communication method, the second communication method, or the third communication method) of the embodiments of the present application can be applied to the communication system as shown in the figure. Figure 1 In the embodiments of the present application, for the network elements in the PLMN providing services for the terminal device, such as the mobile management entity, it can be described as the first mobile management entity, and the network unit can be described as the first network unit. For the network elements in the terminal device home PLMN, such as the mobile management entity, it can be described as the second mobile management entity, and the network unit can be described as the second network unit. The names of messages between various network elements and the names of various parameters in the messages in the following embodiments of the present application are only examples, and other names can also be used in specific implementations. Here, the following will not be described in detail.

[0146] In the first communication method provided by the embodiment of the present application, the second network element determines that the PLMN providing services for the terminal device belongs to the first PLMN. The number of the first PLMN is at least one and is different from the home PLMN of the terminal device. Then, the second network element does not send the target parameter to the terminal device, or the second network element sends the indication information to the terminal device. The indication information indicates to delete the target parameter. The target parameter includes the mapping of the parameters of the PDU session of the first communication mode to the parameters of the second communication mode, and the communication mode of the PLMN providing services for the terminal device includes the first communication mode. The communication mode of the home PLMN of the terminal device includes the second communication mode, and the first communication mode is different from the second communication mode. In this way, when the PLMN providing services for the terminal device belongs to the first PLMN, the terminal device will not receive the target parameter or delete the received target parameter. When the terminal device reselects from the first communication mode PLMN currently providing services for itself to the second communication mode PLMN belonging to itself, since the terminal device does not store the target parameter, the terminal device does not initiate TAU any more, thereby avoiding the problem of TAU failure, which helps to shorten the offline time of the terminal device and reduce the power consumption of the terminal device.

[0147] As shown in Figure 6 , the first communication method 600 provided by the embodiment of the present application includes the following steps:

[0148] S601, the second network element determines that the PLMN providing services for the terminal device belongs to the first PLMN.

[0149] The second network element is a network element in the home PLMN of the terminal device and has at least a session management function. For example, Figure 5 , the second network element can be an H-SMF network element. It should be understood that with the evolution of communication technology, the second network element can also have other names, and the embodiment of the present application does not limit the name of the network element.

[0150] The PLMN providing services for the terminal device is different from the home PLMN of the terminal device. For example, Figure 5The PLMN providing services for the terminal device can be a visited PLMN accessed by the terminal device. The communication mode of the PLMN providing services for the terminal device can be the same as or different from the communication mode of the home PLMN of the terminal device. In the embodiments of the present application, only the case where the communication mode of the PLMN providing services for the terminal device is different from the communication mode of the home PLMN of the terminal device is taken as an example for description. For example, the PLMN providing services for the terminal device can be a 5G network, and the home PLMN of the terminal device can be a 4G network, a 3G network, or a 2G network. Alternatively, the PLMN providing services for the terminal device can be a 4G network, and the home PLMN of the terminal device can be a 3G network or a 2G network. Alternatively, the PLMN providing services for the terminal device can be a 3G network, and the home PLMN of the terminal device can be a 2G network. In the embodiments of the present application, only the case where the PLMN providing services for the terminal device is a 5G network and the home PLMN of the terminal device is a 4G network is taken as an example for description.

[0151] The number of the first PLMNs is at least one and different from the home PLMN of the terminal device. For example, the operator of the home PLMN of the terminal device is China Mobile, and the first PLMN can be a network of another operator (such as China Unicom, China Telecom, etc.) other than China Mobile. For example, the first PLMN can include the PLMNs identified by 46001 and 46006. Alternatively, the first PLMN can be a PLMN provided by a certain operator to another operator for sharing services. The coverage area of the first PLMN can be a remote area, such as Xinjiang. For example, the operator China Mobile provides sharing services to China Unicom, and the access network device of China Mobile broadcasts two PLMN IDs, 460,00 and 460,30. The PLMN identified by 460,00 provides services for the terminal device of China Mobile. The PLMN identified by 460,30 is a PLMN shared by China Mobile to China Unicom to provide services for the terminal device of China Unicom. The PLMN identified by 460,30 belongs to the first PLMN. For example, the first PLMN can be preconfigured for the second network element.

[0152] In some embodiments, the information of the first PLMN can be stored in the form of a table or in other forms. In the case of storage in the form of a table, the table can be described as a specified PLMN list or other names, which are not limited in the embodiments of the present application.

[0153] It should be noted that in the first communication method 600 of the embodiments of the present application, the country to which the operator of the first PLMN and the home PLMN of the terminal device belongs can be the same or different, which is not limited herein.

[0154] Optionally, as Figure 7As shown, the second network unit also performs S603, and the implementation process of S601 includes S601a accordingly. Wherein, S603 and S601a are described as follows:

[0155] S603, the first mobile management entity sends the first information to the second network unit. Correspondingly, the second network unit receives the first information from the first mobile management entity.

[0156] Wherein, the first mobile management entity is a network element in the PLMN serving the terminal device, mainly used for mobility management and access management, etc. For example, the first mobile management entity can be an AMF network element in the visited PLMN. It should be understood that with the evolution of communication technology, the first mobile management entity can also have other names, and the name of the entity is not limited in the embodiments of the present application. Figure 5 For example, the first mobile management entity can be an AMF network element in the visited PLMN. It should be understood that with the evolution of communication technology, the first mobile management entity can also have other names, and the name of the entity is not limited in the embodiments of the present application.

[0157] Wherein, the second network unit can refer to the description of S601, which will not be repeated here.

[0158] Wherein, the first information at least includes the information of the operator to which the first mobile management entity belongs. For example, the first information includes a globally unique access and mobility management function identifier (globally unique AMF identifier, GUAMI). Wherein, the GUAMI is composed of MCC and MNC corresponding to the AMF network element, 8-bit AMF region ID, 10-bit AMF set ID, and 6-bit AMF pointer. MCC identifies the country to which the operator belongs, and MNC is the network identifier of the operator. AMF region ID and AMF set ID combined together represent a group of AMF network elements serving the same tracking area (TA) range, which is also called AMF pool (AMF pool). AMF region ID, AMF set ID and AMF pointer combined together are called AMF identifier (AMF identifier, AMI), which is unique under a group of MCC and MNC. AMF region ID is unique under a group of MCC and MNC, and AMF set ID is unique under AMF region ID.

[0159] For example, the first mobile management entity can be an AMF network element in the visited PLMN. It should be understood that with the evolution of communication technology, the first mobile management entity can also have other names, and the name of the entity is not limited in the embodiments of the present application. Figure 5For example, the first mobile management entity (i.e., the AMF network element) sends the GUAMI to the second network element (i.e., the H-SMF network element) through the V-SMF network element and the BG. Correspondingly, the second network element (i.e., the H-SMF network element) receives the GUAMI from the first mobile management entity (i.e., the AMF network element) through the V-SMF network element and the BG. The GUAMI can be transmitted through a PDU session creation context request message, can be transmitted through a PDU session update request message, or can be transmitted through other messages, which is not limited in the embodiments of the present application. Next, the transmission process of the first information is introduced in combination with Figure 8a and Figure 8b the first information.

[0160] For example, in the session establishment process of the 5G network, the first mobile management entity (i.e., the AMF network element) sends the GUAMI to the second network element (i.e., the H-SMF network element) through a PDU session creation context request message. As shown in Figure 8a , the session establishment process includes the following steps:

[0161] S11, the terminal device sends a PDU session establishment request message to the AMF network element. Correspondingly, the AMF network element receives the PDU session establishment request message from the terminal device.

[0162] The PDU session establishment request message requests to establish a PDU session.

[0163] That is, the terminal device initiates the PDU session establishment request message to the AMF network element of the visited PLMN.

[0164] For the AMF network element, in response to the PDU session establishment request message, the AMF network element selects one SMF network element from at least one SMF network element in the visited PLMN as the V-SMF network element, and selects one SMF network element from at least one SMF network element in the terminal device home PLMN as the H-SMF network element.

[0165] S12, the AMF network element sends a PDU session creation context request message to the V-SMF network element. Correspondingly, the V-SMF network element receives the PDU session creation context request message from the AMF network element.

[0166] Exemplarily, the PDU session create context request message in S12 can be denoted as a PDU session create context request (Nsmf_PDU Session_CreateSMContext request) message transmitted by the Nsmf interface. The message includes the PDU session establishment request message and the GUAMI. The GUAMI is the GUAMI of the AMF network element in S12.

[0167] S13, the V-SMF network element sends a PDU session create context request message to the H-SMF network element. Correspondingly, the H-SMF network element receives the PDU session create context request message from the V-SMF network element.

[0168] Wherein, the PDU session create context request message in S13 can refer to the introduction of S12, which will not be repeated here.

[0169] In this way, in the case that the H-SMF network element is the second network element and the GUAMI is the first information, the second network element can receive the first information through the session establishment process.

[0170] For example, in the session modification process of the 5G network, the first mobility management entity (i.e. the AMF network element) sends the GUAMI to the second network element (i.e. the H-SMF network element) through a PDU session update context request message. In some embodiments, the terminal device can move from the 5G network of the home network side to the 5G network of the visited network side. In this case, the terminal device can initiate the session modification process. Moreover, the mobility management entities involved in the session establishment process are two, i.e. the AMF network element of the home PLMN accessed by the terminal device before moving, described as the old AMF (old AMF) network element, and the AMF network element of the visited PLMN accessed by the terminal device after moving, described as the new AMF (new AMF) network element. In this case, the first mobility management entity is the new AMF network element. As shown in the following table, the session modification process includes the following steps: Figure 8b

[0171] S21, the terminal device sends a registration request message to the new AMF network element. Correspondingly, the new AMF network element receives the registration request message from the terminal device.

[0172] Exemplarily, the registration request message includes registration type information, and the registration type information indicates mobility registration updating.

[0173] ​S22, the new AMF network element sends a context request message to the old AMF network element. Correspondingly, the old AMF network element receives the context request message from the new AMF.

[0174] The context request message is used to request the context information of the terminal device. For example, the context request message can include a user equipment context transfer (Namf_Communication_UEContextTransfer) request message transmitted by the Namf interface.

[0175] S23, the old AMF network element sends the context information to the new AMF network element. Correspondingly, the new AMF network element receives the context information from the old AMF.

[0176] The context information in S23 includes the context information of the terminal device. For example, the context information can be carried in a user equipment context transfer response (Namf_Communication_UEContextTransfer response) message transmitted by the Namf interface.

[0177] For example, the context information of the terminal device includes, but is not limited to, the following information: the identifier of the PDU session, the internet protocol (IP) address used by the PDU session, the service and session continuity (SSC) mode of the PDU session, the context information of the QoS flow, etc. The PDU session is the session currently established by the terminal device, and the number of the PDU session can be one or multiple, which is not limited by the embodiments of the present application.

[0178] S24, the new AMF network element sends a PDU session update request message to the H-SMF network element. Correspondingly, the H-SMF network element receives the PDU session update request message from the new AMF network element.

[0179] The PDU session update request message includes the GUAMI. The GUAMI in S24 is the GUAMI of the new AMF network element.

[0180] For example, the PDU session update request message in S24 can be denoted as a PDU session update SM context request (Nsmf_PDU Session_UptadeSMContext request) message transmitted by the Nsmf interface.

[0181] It should be noted that the AMF network element of the visited PLMN (i.e. the new AMF network element) sending the PDU session update request message to the SMF network element of the home PLMN (H-SMF network element) in the embodiments of the present application means that the AMF network element of the visited PLMN (i.e. the new AMF network element) sends the PDU session update request message to the SMF network element of the visited PLMN (i.e. V-SMF network element), and the SMF network element of the visited PLMN (i.e. V-SMF network element) sends the PDU session update request message to the SMF network element of the home PLMN (H-SMF network element). Since the SMF network element of the visited PLMN (i.e. V-SMF network element) plays a role of transparent transmission in this step, for the sake of simplicity of description, it is directly described in the embodiments of the present application and the accompanying drawings that the new AMF network element sends the PDU session update request message to the H-SMF network element.

[0182] In this way, in the case that the H-SMF network element is the second network element and the GUAMI is the first information, the second network element can receive the first information through the session modification procedure.

[0183] For the second network element, after obtaining the first information, S601a can be executed:

[0184] S601a, the second network element determines, according to the first information, that the PLMN providing services for the terminal device belongs to the first PLMN.

[0185] For example, taking the first information as the GUAMI, if the MNC and MCC in the GUAMI are consistent with the MNC and MCC in the first PLMN, the second network element determines that the first mobility management entity belongs to the first PLMN, i.e. the PLMN providing services for the terminal device belongs to the first PLMN.

[0186] For example, in combination with the examples in Figure 8a and Figure 8b , in Figure 8a , the GUAMI in the PDU session creation context request message is the information of the AMF network element of the visited PLMN. In Figure 8b , taking the terminal device moving from the 5G network of the home network side to the 5G network of the visited network side as an example, the GUAMI in the PDU session update request message is also the information of the AMF network element of the visited network side. In this case, the second network element determines, based on the information of the AMF network element of the visited PLMN of the terminal device, such as the information of the operator to which the AMF network element belongs, that the PLMN providing services for the terminal device belongs to the first PLMN.

[0187] Optionally, as shown in Figure 7 , before executing S601, the second network element further executes S604:

[0188] S604, The second network unit determines that the terminal device is in roaming mode.

[0189] In this context, roaming status refers to a situation where the operator of the PLMN providing services to the terminal device is different from the operator of the PLMN to which the terminal device belongs. For example, if the operator of the terminal device's PLMN to which it belongs is China Mobile, and the operator of the PLMN currently providing services to the terminal device is another operator besides China Mobile, such as one of China Unicom, China Telecom, or China Broadcasting Network, then the terminal device is in a roaming status.

[0190] Roaming status is categorized by the country of origin of the operator, including domestic roaming and international roaming. Domestic roaming refers to a situation where the PLMN providing services to the terminal device is different from the PLMN to which the terminal device belongs, but the PLMN providing services to the terminal device is in the same country as the operator of the terminal device's PLMN. International roaming refers to a situation where the PLMN providing services to the terminal device is different from the PLMN to which the terminal device belongs, and both the PLMN providing services to the terminal device and the operator of the terminal device's PLMN are in different countries.

[0191] In S604, the terminal device can be in a domestic roaming state or in a foreign roaming state. In the first communication method 600 of this application embodiment, only the case where the terminal device is in a domestic roaming state is described.

[0192] Optionally, the implementation process of S604 is described below:

[0193] Still with Figure 5 For example, the first network unit is the SMF network element visiting the PLMN, i.e., the V-SMF network element, and the second network unit is the SMF network element belonging to the PLMN, i.e., the H-SMF network element. If the terminal device is in roaming mode, the message transmission process between the first network unit (V-SMF network element) and the second network unit (H-SMF network element) is as follows: steps a and b:

[0194] Step a: The V-SMF network element sends a message to the BG. Correspondingly, the BG receives the message from the V-SMF network element.

[0195] The message in step a may include the aforementioned PDU session creation context request message, the aforementioned PDU session update request message, or other messages; this embodiment of the application does not limit this. The message in step a carries at least information about the V-SMF network element, such as the identifier of the V-SMF network element.

[0196] Step b: BG sends a message to the H-SMF network element. Correspondingly, the H-SMF network element receives the message from BG.

[0197] The message in step b is determined based on the message in step a. For example, the message in step b includes the message in step a. The message in step b also includes information about BG, such as the identifier of BG.

[0198] For the H-SMF network element, when the H-SMF network element acts as the second network unit, S604 can be implemented as follows: if the second network unit executes step b, then it is determined that the terminal device is in a roaming state. Alternatively, the second network unit (i.e., the aforementioned H-SMF network element) determines that the terminal device is in a roaming state based on the identifier carried in the message of step b (such as the identifier of the aforementioned V-SMF network element, or the identifier of BG).

[0199] It should be understood that when steps a and b are executed, it can also be interpreted as the second network unit receiving a message from the first network unit. In this case, the second network unit also determines that the terminal device is in a roaming state. The first network unit at least possesses session management functionality. In this embodiment, only... Figure 5 For example, the first network element can be a V-SMF network element. It should be understood that with the evolution of communication technology, the first network element may also have other names, and the embodiments of this application do not limit the name of the network element.

[0200] For example, combined with Figure 8a and Figure 8b The example in Figure 8a In the scenario shown, the V-SMF network element sends a message to the H-SMF network element, and steps a and b are executed. Figure 8b In the scenario shown, when the terminal device moves from the home network's 5G network to the visited network's 5G network, the V-SMF network element also sends a message to the H-SMF network element, and steps a and b are executed. In both of these cases, the second network element (i.e., the aforementioned H-SMF network element) determines that the terminal device is in a roaming state. Conversely, if steps a and b are not executed, the second network element determines that the terminal device is not in a roaming state.

[0201] For the second network unit, S601 is executed only if the terminal device is in roaming mode; otherwise, it is not required to execute S601, thus simplifying the processing procedure. It should be understood that... Figure 7 In this example, taking the case where S601 is implemented as S601a as an example, the execution order of S604 and S601 is shown.

[0202] It should be noted that S603 and S604 are optional steps. In the case where both S603 and S604 are performed, if the message in step a (or step b) includes the PDU session creation context request message or the PDU session update request message described above, the second network element can first perform S603 and then perform S604. If the message in step a (or step b) includes other messages, the second network element can first perform S603 and then perform S604, or first perform S604 and then perform S603, or perform S603 and S604 at the same time, and the embodiments of the present application do not limit this.

[0203] For the second network element, after performing S601, S602a as shown in the block of method 1 in Figure 6 may be performed, or S602b as shown in the block of method 2 in Figure 6 may be performed. The descriptions of S602a and S602b are as follows:

[0204] S602a, the second network element does not send the target parameter to the terminal device.

[0205] The target parameter includes the mapping of the parameters of the PDU session of the first communication mode to the parameters of the second communication mode. The first communication mode and the second communication mode are different, for example, the first communication mode can be 5G, and the second communication mode can be 4G, 3G, or 2G, or the first communication mode can be 4G, and the second communication mode can be 3G or 2G. In the embodiments of the present application, only the case where the first communication mode is 5G and the second communication mode is 4G is taken as an example for description.

[0206] For example, the target parameter is described as follows: in the 5G network, the terminal device accesses the DN by creating a PDU session, and one session can include one or more data flows, such as quality of service flows (QoS flows). In the 4G network, the terminal device accesses the DN by creating a packet data network connection (PDN connection), and one connection can include multiple EPS bearers. As the terminal device moves, the terminal device can move from the 5G network to the 4G network. The QoS flow in the 5G network and the EPS bearer in the 4G network have a corresponding matching relationship. For the quality of service flow (QoS flow) that can be switched to the 4G network, the second network element will allocate a corresponding EPS bearer identity (EBI). In this case, the target parameter can include the 4G parameters of the PDU session, such as the parameters of the QoS flow, the EBI, and the like.

[0207] Optionally, the second network element does not assign the target parameter to the terminal device. In this case, the second network element does not send the target parameter to the terminal device. Exemplarily, the session establishment process of the 5G network is introduced in detail:

[0208] As shown in Figure 8a , the session establishment process includes the following steps:

[0209] S14, when the H-SMF network element does not assign the target parameter to the terminal device, the H-SMF network element sends the PDU session creation context response message to the V-SMF network element. Correspondingly, the V-SMF network element receives the PDU session creation context response message from the H-SMF network element.

[0210] Exemplarily, the PDU session creation context response message in S14 can be denoted as the PDU session creation context response (Nsmf_PDU Session_CreateSMContext response) message transmitted by the Nsmf interface. The message includes the PDU session establishment accept message. The PDU session establishment accept message does not carry the target parameter.

[0211] S15, the V-SMF network element sends the PDU session creation context response message to the AMF network element. Correspondingly, the AMF network element receives the PDU session creation context response message from the V-SMF network element.

[0212] Among them, the PDU session creation context response message in S15 can refer to the introduction of S14, which will not be repeated here.

[0213] S16, the AMF network element sends the PDU session establishment accept message to the terminal device. Correspondingly, the terminal device receives the PDU session establishment accept message from the AMF network element.

[0214] Among them, the PDU session establishment accept message in S16 can refer to the introduction of S14, which will not be repeated here.

[0215] In this way, when the H-SMF network element is the second network element and does not assign the target parameter to the terminal device, the second network element sends the PDU session establishment accept message without carrying the target parameter. In this way, the second network element does not send the target parameter to the terminal device, which can be specifically implemented as the PDU session establishment accept message does not carry the target parameter, and correspondingly, the terminal device cannot receive the target parameter from the second network element.

[0216] S602b, the second network element sends indication information to the terminal device. Correspondingly, the terminal device receives the indication information from the second network element.

[0217] The indication information indicates the target parameter to be deleted. The target parameter in S602b is consistent with the target parameter in S602a, which will not be repeated here.

[0218] For example, in combination with the session modification process of the 5G network, the transmission process of the indication information is described in detail:

[0219] As shown in Figure 8b , still taking the terminal device moving from the 5G network of the home network side to the 5G network of the visited network side as an example, the session modification process includes the following steps:

[0220] S25, the H-SMF network element sends a PDU session update response message to the new AMF network element. Correspondingly, the new AMF network element receives the PDU session update response message from the H-SMF network element.

[0221] The PDU session update response message includes a PDU session modification command message, and the PDU session modification command message carries the indication information to indicate the terminal device to delete the target parameter.

[0222] For example, the PDU session update response message can be transmitted through the Nsmf interface, denoted as Nsmf_PDUSession_UptateSMContext response message. The PDU session modification command message can be denoted as PDU SessionModification Command message. The PDU Session Modification Command message includes mapped EPS bearer contexts. The mapped EPS bearer contexts carry a delete new EPS bearer indication in the operation code. The above indication information can be implemented as the above delete new EPS bearer indication.

[0223] S26, the new AMF network element sends a registration accept message to the terminal device. Correspondingly, the terminal device receives the registration accept message from the new AMF network element.

[0224] S27, the new AMF network element sends a PDU session modification command message to the terminal device. Correspondingly, the terminal device receives the PDU session modification command message from the new AMF network element.

[0225] The PDU session modification command message in S27 carries a mapped EPS bearer context to transmit indication information to the terminal device.

[0226] In S28, the terminal device sends a PDU session modification command acknowledgement message to the new AMF network element. Correspondingly, the new AMF network element receives the PDU session modification command acknowledgement message from the terminal device.

[0227] For example, the PDU session modification command acknowledgement message can be denoted as PDU Session Modification Command ACK. Correspondingly, the terminal device deletes the 4G parameters corresponding to the PDU session, such as EBI and 4G QoS parameters.

[0228] In this way, when the H-SMF network element is the second network element and sends indication information to the terminal device, the second network element sends the indication information to the terminal device by sending a PDU session modification command message to instruct the terminal device to delete the target parameters.

[0229] The above only takes the first PLMN as an example, which provides services for the terminal device. Of course, the PLMN that provides services for the terminal device can also not belong to the first PLMN. In this case, the second network element sends the target parameters to the terminal device, which will be described in detail in the processing steps shown in Figure 9

[0230] In S901, the second network element determines that the PLMN that provides services for the terminal device does not belong to the first PLMN.

[0231] The second network element and the first PLMN can be referred to the description of S601, which will not be repeated here.

[0232] The PLMN that provides services for the terminal device is introduced as follows:

[0233] As a possible implementation, the PLMN that provides services for the terminal device is the same as the terminal device's home PLMN. That is, the PLMN currently accessed by the terminal device is the terminal device's home PLMN. In this case, the terminal device is not in a roaming state, and the first PLMN can be the same as or different from the country where the terminal device's home PLMN operator belongs. Here, no limitation is made. For example, taking the terminal device's home PLMN as China Mobile operator network, the first PLMN can include the PLMN of domestic operators or the PLMN of operators in other countries.

[0234] ​As another possible implementation, the PLMN serving the terminal device is different from the country where the terminal device's home PLMN operator belongs to. That is, the PLMN currently accessed by the terminal device is a network of a foreign operator. In this case, the terminal device is in a foreign roaming state. In this implementation, the first PLMN is the same as the country where the terminal device's home PLMN operator belongs to. For example, still taking the terminal device's home PLMN as the network of China Mobile as an example, the first PLMN only includes the PLMN of domestic operators, and does not include the PLMN of operators in other countries.

[0235] Optionally, as shown in Figure 10a , the second network element also performs S903, and correspondingly, the implementation process of S901 includes S901a. Wherein, S903 and S901a are described as follows:

[0236] S903, the first mobility management entity sends the first information to the second network element. Correspondingly, the second network element receives the first information from the first mobility management entity.

[0237] Wherein, the second network element and the first information can be referred to the description of S603, which will not be repeated here.

[0238] Wherein, the first mobility management entity is a network element in the PLMN currently serving the terminal device, mainly used for mobility management and access management, etc. For example, in a 5G network, the first mobility management entity can be an AMF network element. It should be understood that with the evolution of communication technology, the first mobility management entity can also have other names, and the name of the entity is not limited in the present application. For example, when the PLMN serving the terminal device is the same as the terminal device's home PLMN, the first mobility management entity is a network element in the terminal device's home PLMN. When the PLMN serving the terminal device is different from the country where the terminal device's home PLMN operator belongs to, the first mobility management entity is a network element in the PLMN of an operator in another country.

[0239] For example, taking the first mobility management entity as a network element in the terminal device's home PLMN as an example, the transmission process of the first information is introduced: the terminal device moves from the 5G network of the visited network side to the 5G network of the home network side. In this case, the terminal device can initiate a session modification process. Moreover, the mobility management entities involved in the session establishment process are two, a new AMF network element and an old AMF network element. In this scenario, the first mobility management entity is a network element of the terminal device's home PLMN, still belonging to the new AMF network element, and the specific process can still be referred to the description of Figure 8b , which will not be repeated here.

[0240] For the second network element, after obtaining the first information, it can perform S901a:

[0241] S901a, the second network element determines, according to the first information, that the PLMN providing services for the terminal device does not belong to the first PLMN.

[0242] For example, taking the first information as GUAMI, if the MNC and MCC in the GUAMI are inconsistent with the MNC and MCC in the first PLMN, the second network element determines that the first mobile management entity does not belong to the first PLMN, i.e., the PLMN providing services for the terminal device does not belong to the first PLMN.

[0243] For example, as a possible scenario, taking the terminal device moving from the 5G network of the visited network side to the 5G network of the home network side as an example, in combination with Figure 8b , the GUAMI is also the information of the AMF network element of the home network side. In this case, the second network element determines, based on the information of the AMF network element of the home network side, that the PLMN providing services for the terminal device does not belong to the first PLMN.

[0244] As another possible scenario, the PLMN providing services for the terminal device is different from the country where the operator of the terminal device's home PLMN belongs to. That is, the terminal device is in a roaming state, and belongs to a foreign roaming state. Since the first PLMN is the same as the country where the operator of the terminal device's home PLMN belongs to. In this case, the PLMN providing services for the terminal device also does not belong to the first PLMN.

[0245] In this way, the second network element can determine that the PLMN providing services for the terminal device does not belong to the first PLMN based on the information of the operator to which the first mobile management entity belongs.

[0246] Optionally, as Figure 10b indicated, for the case where the PLMN providing services for the terminal device is different from the country where the operator of the terminal device's home PLMN belongs to, i.e., the terminal device is in a foreign roaming state, the second network element can also perform S904 before performing S901:

[0247] S904, the second network element determines that the terminal device is in a roaming state.

[0248] Wherein, the roaming state can refer to the introduction of S604, which will not be repeated here.

[0249] For example, the implementation process of S904 can refer to the introduction of S604, such as steps a and b in S604, which will not be repeated here. Still taking the PLMN providing services for the terminal device as the PLMN of the operator of other countries as an example, steps a and b are performed, and the second network element can determine that the terminal device is in a roaming state.

[0250] For the second network element, if the terminal device is in a roaming state, the second network element performs S901, and then judges whether the PLMN providing service for the terminal device belongs to the first PLMN, so as to simplify the processing procedure of the second network element. It should be understood that in this case, the first PLMN is the same as the country where the terminal device belongs to the PLMN operator.

[0251] It should be noted that S903 and S904 are optional steps. In the case where both S903 and S904 are performed, if the message in step a (or step b) includes the PDU session creation context request message or the PDU session update request message, the second network element can first perform S903, and then perform S904. If the message in step a (or step b) includes other messages, the second network element can first perform S903, and then perform S904, or first perform S904, and then perform S903, or simultaneously perform S903 and S904, and the embodiments of the present application are not limited thereto.

[0252] S902, the second network element sends the target parameter to the terminal device. Correspondingly, the terminal device receives the target parameter from the second network element.

[0253] Among them, the target parameter can refer to the introduction of S602a, which will not be repeated here.

[0254] For example, in combination with the session modification process, the transmission process of the target parameter is described in detail:

[0255] For example, in combination with the session modification process, the transmission process of the target parameter is described in detail: Figure 8bAs shown, still taking the terminal device moving from the 5G network of the visited network side to the 5G network of the home network side as an example, the PDU session modification command message includes the following parameters: PDU session ID, QoS flow level QoS parameters corresponding to the QoS flow, and mapped EPS bearer contexts. The PDU session ID is used to identify a PDU session, the QoS flow level QoS parameters carry the EBI corresponding to the QoS flow, and the mapped EPS bearer contexts carry one or more 4G QoS parameters and EBIs corresponding to the QoS flow, and the mapped EPS bearer contexts carry a create new EPS bearer indication in the operation code. The above-mentioned EBI and 4G QoS parameters are both target parameters. That is, compared with the PDU session modification command message in S602b, the PDU session modification command message no longer carries the indication information, but carries the target parameters.

[0256] In this way, in the case of the H-SMF network element as the second network element, the second network element sends the target parameters to the terminal device by sending the PDU session modification command message, so as to provide the target parameters for the terminal device.

[0257] In the second communication method provided by the embodiment of the present application, when the terminal device reselects from the first communication mode of the first PLMN to the second communication mode of the home PLMN of the terminal device, a registration request message is sent to the second mobility management entity of the home PLMN of the terminal device. The first PLMN and the home PLMN of the terminal device are different, the first communication mode and the second communication mode are different, the terminal device saves the target parameters, and the target parameters include the mapping of the parameters of the protocol data unit (PDU) session of the first communication mode to the parameters of the second communication mode. Then, the terminal device receives a registration accept message from the second mobility management entity. In this way, even if the first PLMN and the home PLMN of the terminal device are different, and the terminal device saves the target parameters, when the terminal device moves from the first communication mode of the first PLMN to the second communication mode of the home PLMN of the terminal device, the terminal device initiates the registration request message, and no longer initiates the TAU, thereby avoiding the problem of TAU failure, helping to shorten the offline time of the terminal device, and reducing the power consumption of the terminal device.

[0258] As Figure 11 As shown, the second communication method 1100 provided by the embodiment of the present application includes the following steps:

[0259] S1101, The terminal device determines to reselect or handover from a first communication mode of a first PLMN to a second communication mode of a home PLMN of the terminal device.

[0260] The first communication mode and the second communication mode can refer to the description of S602a, which will not be repeated here. For example, the scenario shown in S1101 includes that the terminal device moves from a 5G network of a visited PLMN to a 4G network of a home PLMN of the terminal device. In this case, the terminal device performs the process including S1101 described above. For example, if the terminal device moves in an idle state, the terminal device reselects from the first communication mode of the first PLMN to the second communication mode of the home PLMN of the terminal device. If the terminal device moves in a connected state, the terminal device handovers from the first communication mode of the first PLMN to the second communication mode of the home PLMN of the terminal device.

[0261] The first PLMN is a PLMN currently providing services for the terminal device. For example, the first PLMN can be a visited PLMN of the terminal device, which can refer to the description of S601, which will not be repeated here. Figure 5 For example, the first PLMN can be a visited PLMN of the terminal device, which can refer to the description of S601, which will not be repeated here.

[0262] The terminal device stores a target parameter, which can refer to the description of S602a, which will not be repeated here. For example, the target parameter stored by the terminal device can be generated by the terminal device itself or received from the second network element, which will be described in detail in S902, which will not be repeated here.

[0263] S1102, The terminal device sends a registration request message to the second mobility management entity. Correspondingly, the second mobility management entity receives the registration request message from the terminal device.

[0264] The second mobility management entity is a network element in the home PLMN of the terminal device, which is mainly used for mobility management and access management, etc. For example, in a 4G network, the second mobility management entity can be an MME. It should be understood that with the evolution of communication technology, the first mobility management entity can also have other names, and the name of the entity is not limited by the embodiments of the application. The registration request message can be recorded as an initial attach message. That is, the terminal device sends an initial attach message to the MME. Correspondingly, the MME receives the initial attach message from the terminal device.

[0265] S1103, The second mobility management entity sends a registration acceptance message to the terminal device. Correspondingly, the terminal device receives the registration acceptance message from the second mobility management entity.

[0266] Exemplarily, still taking the 4G network as an example, the second mobility management entity can be an MME. The registration acceptance message can be denoted as an attach accept message. That is, the MME sends the attach accept message to the terminal device. Correspondingly, the terminal device receives the attach accept message from the MME.

[0267] In some embodiments, as shown in FIG. 11B, before S1102, the terminal device further performs S1104: Figure 12

[0268] S1104, the terminal device determines, according to the first information, that the first PLMN is different from a home PLMN of the terminal device.

[0269] The first information includes information of at least one third PLMN, the third PLMN is different from the home PLMN of the terminal device, and the third PLMN includes the first PLMN. Exemplarily, taking the operator of the home PLMN of the terminal device as China Mobile as an example, the third PLMN can be a network of another operator (such as China Unicom, China Telecom, etc.) other than China Mobile. Taking China Unicom as an example, the third PLMN can include the PLMNs identified by 46001 and 46006. Alternatively, the third PLMN can be a PLMN provided by a certain operator to another operator for sharing services. The third PLMN coverage area can be a remote area, such as Xinjiang. Exemplarily, taking the sharing service provided by China Mobile to China Unicom as an example, the access network device of China Mobile broadcasts two PLMN IDs, i.e., 460,00 and 460,30. The PLMN identified by 460,00 provides services for the terminal device of China Mobile. The PLMN identified by 460,30 is a PLMN shared by China Mobile to China Unicom to provide services for the terminal device of China Unicom. The PLMN identified by 460,30 belongs to the third PLMN. Exemplarily, the third PLMN can be preconfigured. The first information includes information of at least one preconfigured third PLMN.

[0270] In some embodiments, the information of the first PLMN can be stored in the form of a list or in other forms. In the case of being stored in the form of a list, the list can be described as a specified PLMN list or other names, which are not limited in the embodiments of the present application.

[0271] It should be noted that, in the second communication method 1100 of the embodiments of the present application, the third PLMN can be the same as or different from the country to which the operator of the home PLMN of the terminal device belongs, which is not limited herein.

[0272] ​It should be understood that S1104 is an optional step, in the case where S1104 is performed, the terminal device can perform S1104 first and then perform S1101, or perform S1101 first and then perform S1104, or perform S1101 and S1104 at the same time, and the embodiments of the present application do not make any limitation in this regard.

[0273] For example, the manner in which the terminal device acquires the first information includes the following two manners:

[0274] Optionally, as shown in the block of "manner 1" in the Figure 12 As shown in the block of "manner 1" in the

[0275] S1105a, the second mobility management entity sends the first information to the terminal device. Correspondingly, the terminal device receives the first information from the second mobility management entity.

[0276] The first information in S1105a is consistent with the first information in S1104, which will not be described here again.

[0277] For example, the terminal device can acquire the first information in the registration process of the home network. Specifically, the terminal device sends a registration request message to the second mobility management entity. Correspondingly, the second mobility management entity receives the registration request message from the terminal device. Then, the second mobility management entity sends a registration accept message to the terminal device. Correspondingly, the terminal device receives the registration accept message from the second mobility management entity. The registration accept message includes the first information and equivalent public land mobile network (EPLMN) information. In this case, the EPLMN information includes the information of the first PLMN, so that the terminal device camps on the first PLMN.

[0278] In this way, the terminal device can acquire the first information in the registration process of the home network, so that when the terminal device reselects from the first communication mode of the first PLMN to the second communication mode of the home PLMN of the terminal device, the terminal device can timely initiate a registration request message, thereby effectively avoiding the problem of TAU failure.

[0279] Optionally, as shown in the block of "manner 2" in the Figure 12 As shown in the block of "manner 2" in the

[0280] S1105b, the second network unit sends the first information to the terminal device. Correspondingly, the terminal device receives the first information from the second network unit.

[0281] The second network unit can refer to the description of S601, which will not be described here again.

[0282] The first information in S1105b is consistent with the first information in S1104, which will not be repeated here.

[0283] For example, in the PDU session establishment process, the second network element sends the first information to the terminal device through a PDU session establishment accept message. Correspondingly, the terminal device receives the first information from the second network element through the PDU session establishment accept message. The steps of the PDU session establishment process can be referred to as shown in Figure 8a In the implementation process of S1105b, the PDU session establishment accept message of S14, S15 and S16 all carries the first information.

[0284] In this way, the terminal device can obtain the first information in the PDU session establishment process, so that when the terminal device reselects from the first communication mode of the first PLMN to the second communication mode of the terminal device home PLMN, the terminal device can timely initiate a registration request message, thereby effectively avoiding the problem of TAU failure.

[0285] In the third communication method provided by the embodiment of the application, the terminal device sends a registration request message to a first mobility management entity of a first PLMN. The first PLMN is different from a terminal device home PLMN. The terminal device receives a registration accept message from the first mobility management entity. Then, the terminal device deletes a target parameter, or the terminal device does not generate the target parameter, or when the terminal device receives the target parameter from a second network element, the terminal device does not save the target parameter. The target parameter includes a parameter mapping of a protocol data unit (PDU) session of the first communication mode to a parameter of the second communication mode. The communication mode of the first PLMN includes the first communication mode, and the communication mode of the terminal device home PLMN includes the second communication mode. That is, even if the first PLMN is different from the terminal device home PLMN, and the terminal device has registered in the first PLMN, the terminal device deletes the target parameter, or does not generate the target parameter, or when the terminal device receives the target parameter from the second network element, the terminal device does not save the target parameter. In this way, when the terminal device reselects from the first communication mode of the first PLMN to the second communication mode of the terminal device home PLMN, since the terminal device does not save the target parameter, the terminal device initiates a registration request message, and does not initiate TAU, thereby avoiding the problem of TAU failure, which helps to shorten the offline time of the terminal device and reduce the power consumption of the terminal device.

[0286] As shown in Figure 13 The third communication method 1300 provided by the embodiment of the application includes the following steps:

[0287] S1301, the terminal device sends a registration request message to a first mobility management entity of a first PLMN. Correspondingly, the first management network element receives the registration request message from the terminal device.

[0288] The first PLMN is different from the PLMN to which the terminal device belongs. Please refer to the introduction in S1101 for details, which will not be repeated here.

[0289] The first mobility management entity is a network element in the PLMN that provides services to terminal devices, primarily used for mobility management and access management. For example, using... Figure 5 For example, the first PLMN is the terminal device visited network, and the first mobility management entity is the AMF network element in the terminal device visited network. It should be understood that with the evolution of communication technology, the first mobility management entity may have other names; this embodiment does not limit the name of the entity. The terminal device sends a registration request message to the AMF network element. Correspondingly, the AMF network element receives the registration request message from the terminal device.

[0290] S1302, The first mobility management entity sends a registration acceptance message to the terminal device. Correspondingly, the terminal device receives the registration acceptance message from the first mobility management entity.

[0291] For example, still using Figure 5 For example, the first PLMN is the network visited by the terminal device, and the first mobility management entity is the AMF (Advanced Mobility Management) element in the visited network. The AMF element sends a registration acceptance message to the terminal device. Correspondingly, the terminal device receives the registration acceptance message from the AMF element. In this way, the terminal device can complete the registration process in the first PLMN and be in a registered state in the first PLMN.

[0292] For the terminal device, after executing S1302, it can execute S1303a, such as... Figure 13 As shown in the box containing "Method 1", S1303b can also be executed, as shown below. Figure 13 As shown in the box containing "Method 2", S1303c can also be executed, as follows: Figure 13 The box containing "Method 3" is shown in the image. The descriptions of S1303a, S1303b, and S1303c are as follows:

[0293] S1303a, Delete target parameters on terminal device.

[0294] The target parameters can be found in the description of S602a, and will not be repeated here.

[0295] For example, the target parameter deleted by the terminal device may be a parameter received from the second network unit, as described in S902, which will not be repeated here.

[0296] S1303b: The terminal device does not generate target parameters.

[0297] The target parameter can refer to the description of S602a, and details are not described herein.

[0298] That is, the terminal device does not generate the target parameter after the terminal device is registered in the first PLMN. Alternatively, the terminal device does not generate the target parameter when the terminal device reselects from the first communication mode of the first PLMN to the second communication mode of the terminal device home PLMN.

[0299] S1303c, when the terminal device receives the target parameter from the second network element, the target parameter is not saved.

[0300] The second network element can refer to the description of S601, and the target parameter can refer to the description of S602a, and details are not described herein.

[0301] For example, the second network element sends a PDU session modification command message to the terminal device in the PDU session modification process, which is described in detail in the description of S25 and S27 in Figure 8b The target parameter is carried in the PDU session modification command message. In this case, even if the terminal device receives the target parameter from the second network element, the target parameter is not saved.

[0302] In some embodiments, before S1303a (or S1303b, or S1303c), the terminal device also performs S1104, that is, the terminal device determines that the first PLMN and the terminal device home PLMN are different according to the first information. The terminal device can obtain the first information in the manner described in S1105a and S1105b, and details are not described herein.

[0303] The above mainly introduces the scheme provided by the embodiments of the application from the perspective of interaction between network elements. Correspondingly, the embodiments of the application also provide a communication device, which can be a network element in the above method embodiments, or a device containing the above network element, or a component that can be used for the network element. It can be understood that the communication device contains the corresponding hardware structure and / or software module for executing each function in order to realize the above functions. Those skilled in the art should easily realize that the units and algorithm steps of the examples described in combination with the embodiments disclosed in the present application can be realized in the form of hardware or a combination of hardware and computer software. Whether a certain function is realized in hardware or computer software driven hardware depends on the specific application and design constraints of the technical solution. Professional technicians can use different methods to realize the described functions for each specific application, but such implementation should not be considered beyond the scope of the present application.

[0304] For example, Figure 14A structural diagram of a communication apparatus 1400 is shown. The communication apparatus 1400 includes a processing unit 1401, a sending unit 1402, and a receiving unit 1403.

[0305] In a possible example, taking the communication apparatus 1400 as a terminal device for example, the processing unit 1401 is configured to support the terminal device to perform the following processing operation in the method 600. Figure 6 In a possible example, taking the communication apparatus 1400 as a terminal device for example, the sending unit 1402 is configured to support the terminal device to perform the following sending operation in the method 600. Figure 6 In a possible example, taking the communication apparatus 1400 as a terminal device for example, the receiving unit 1403 is configured to support the terminal device to perform the following receiving operation in the method 600. Figure 6 In a possible example, taking the communication apparatus 1400 as a terminal device for example, the receiving unit 1403 is configured to support the terminal device to perform the following receiving operation in the method 600.

[0306] In another possible example, taking the communication apparatus 1400 as a terminal device for example, the processing unit 1401 is configured to support the terminal device to perform the following processing operation in the method 1100. Figure 11 In another possible example, taking the communication apparatus 1400 as a terminal device for example, the sending unit 1402 is configured to support the terminal device to perform the following sending operation in the method 1100. Figure 11 In another possible example, taking the communication apparatus 1400 as a terminal device for example, the receiving unit 1403 is configured to support the terminal device to perform the following receiving operation in the method 1100. Figure 11 In another possible example, taking the communication apparatus 1400 as a terminal device for example, the receiving unit 1403 is configured to support the terminal device to perform the following receiving operation in the method 1100.

[0307] In yet another possible example, taking the communication apparatus 1400 as a terminal device for example, the processing unit 1401 is configured to support the terminal device to perform the following processing operation in the method 1300. Figure 13 In yet another possible example, taking the communication apparatus 1400 as a terminal device for example, the sending unit 1402 is configured to support the terminal device to perform the following sending operation in the method 1300. Figure 13 In yet another possible example, taking the communication apparatus 1400 as a terminal device for example, the receiving unit 1403 is configured to support the terminal device to perform the following receiving operation in the method 1300. Figure 13 In yet another possible example, taking the communication apparatus 1400 as a terminal device for example, the receiving unit 1403 is configured to support the terminal device to perform the following receiving operation in the method 1300.

[0308] In a possible example, taking the communication apparatus 1400 as a second network unit for example, the processing unit 1401 is configured to support the second network unit to perform the following processing operation in the method 600. Figure 6 In a possible example, taking the communication apparatus 1400 as a second network unit for example, the sending unit 1402 is configured to support the second network unit to perform the following sending operation in the method 600. Figure 6 In a possible example, taking the communication apparatus 1400 as a second network unit for example, the receiving unit 1403 is configured to support the second network unit to perform the following receiving operation in the method 600.Figure 6 other receiving operations that the second network element needs to perform.

[0309] In yet another possible implementation, taking the communication apparatus 1400 as an example of the second mobile management entity, the processing unit 1401 is configured to support the second mobile management entity to perform other processing operations that the second mobile management entity needs to perform in the method. Figure 11 The sending unit 1402 is configured to support the second mobile management entity to perform S1103 in the method, and / or other sending operations that the second mobile management entity needs to perform in the embodiments. Figure 11 The receiving unit 1403 is configured to support the second mobile management entity to perform S1102 in the method, and / or other receiving operations that the second mobile management entity needs to perform in the embodiments. Figure 11 The receiving unit 1403 is configured to support the second mobile management entity to perform S1102 in the method, and / or other receiving operations that the second mobile management entity needs to perform in the embodiments.

[0310] In yet another possible implementation, taking the communication apparatus 1400 as an example of the first mobile management entity, the processing unit 1401 is configured to support the first mobile management entity to perform other processing operations that the first mobile management entity needs to perform in the method. Figure 13 The sending unit 1402 is configured to support the first mobile management entity to perform S1302 in the method, and / or other sending operations that the first mobile management entity needs to perform in the embodiments. Figure 13 The receiving unit 1403 is configured to support the first mobile management entity to perform S1301 in the method, and / or other receiving operations that the first mobile management entity needs to perform in the embodiments. Figure 13 The receiving unit 1403 is configured to support the first mobile management entity to perform S1301 in the method, and / or other receiving operations that the first mobile management entity needs to perform in the embodiments.

[0311] Optionally, the communication apparatus 1400 further includes a storage unit 1404, configured to store program codes and data of the communication apparatus, and the data can include, but is not limited to, raw data or intermediate data, etc.

[0312] The processing unit 1401 can be a processor or a controller, for example, a CPU, a general-purpose processor, an application specific integrated circuit (ASIC), a field programmable gate array (FPGA) or other programmable logic device, transistor logic device, hardware component or any combination thereof. It can implement or execute the various exemplary logical blocks, modules and circuits described in connection with the disclosure. The processor can also be a combination of implementing computing functions, such as one or more microprocessor combinations, combinations of DSP and microprocessor, etc.

[0313] The transmitting unit 1402 may be a communication interface, a transmitter, or a transmitting circuit, etc. Here, the communication interface is a general term. In a specific implementation, the communication interface may include multiple interfaces, such as the interface between the terminal device and the second network unit and / or other interfaces.

[0314] The receiving unit 1403 may be a communication interface, a receiver, or a receiving circuit, etc. The communication interface is a general term. In a specific implementation, the communication interface may include multiple interfaces, such as the interface between the terminal device and the second network unit and / or other interfaces.

[0315] The transmitting unit 1402 and the receiving unit 1403 can be implemented as the same unit, either physically or logically.

[0316] Storage unit 1404 can be a memory.

[0317] When the processing unit 1401 is a processor, the sending unit 1402 and the receiving unit 1403 are communication interfaces, and the storage unit 1404 is a memory, the communication device involved in the embodiments of this application can be... Figure 15 As shown.

[0318] See Figure 15 As shown, the communication device includes a processor 1501, a communication interface 1502, and a memory 1503. Optionally, the communication device may also include a bus 1504. The communication interface 1502, processor 1501, and memory 1503 can be interconnected via the bus 1504; the bus 1504 can be a peripheral component interconnect (PCI) bus or an extended industry standard architecture (EISA) bus, etc. The bus 1504 can be divided into an address bus, a data bus, a control bus, etc. For ease of illustration, Figure 15 The bus is represented by a single thick line, but this does not mean that there is only one bus or one type of bus.

[0319] Optionally, embodiments of this application also provide a computer program product carrying computer instructions, which, when executed on a computer, causes the computer to perform the methods described in the above embodiments.

[0320] Optionally, embodiments of this application also provide a computer-readable storage medium that stores computer instructions that, when executed on a computer, cause the computer to perform the methods described in the above embodiments.

[0321] Optionally, the embodiment of the present application further provides a chip, comprising: a processing circuit and a transceiver circuit, wherein the processing circuit and the transceiver circuit are used to implement the method introduced in the above embodiment. The processing circuit is used to execute the processing action in the corresponding method, and the transceiver circuit is used to execute the receiving / sending action in the corresponding method.

[0322] In the above embodiments, the implementation can be achieved by software, hardware, firmware or any combination thereof, entirely or partially. When implemented by software, the implementation can be achieved in the form of a computer program product, entirely or partially. The computer program product comprises one or more computer instructions. When the computer instructions are loaded and executed on a computer, the flow or function described in the embodiment of the present application is generated, entirely or partially. The computer can be a general-purpose computer, a special-purpose computer, a computer network or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transferred from one computer-readable storage medium to another computer-readable storage medium, for example, the computer instructions can be transferred from one website, computer, server or data center to another website, computer, server or data center through wired (such as coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (such as infrared, wireless, microwave, etc.) mode. The computer-readable storage medium can be any available medium that can be accessed by a computer or a data storage device such as a server, data center, etc. integrated with one or more available media. The available medium can be a magnetic medium (such as a floppy disk, a hard disk, a magnetic tape), an optical medium (such as a digital video disc (DVD)), or a semiconductor medium (such as a solid state drive (SSD)) and the like.

[0323] In several embodiments provided in the present application, it should be understood that the disclosed system, device and method can be implemented by other ways. For example, the above-described device embodiment is only schematic, for example, the division of the modules is only a logical function division, and actual implementation can have another division manner, for example, a plurality of modules or components can be combined or integrated into another system, or some features can be ignored or not executed. In addition, the coupling or direct coupling or communication connection between the displayed or discussed each other can be indirect coupling or communication connection through some interfaces, devices or modules, which can be electrical or other forms.

[0324] The units described as separate components may or may not be physically separate, and the components displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed to multiple devices. Part or all of the units can be selected according to actual needs to achieve the purpose of the embodiment scheme.

[0325] Through the above description of the embodiments, those skilled in the art can clearly understand that the present application can be implemented by means of software plus necessary general hardware, and of course can also be implemented by hardware, but in many cases the former is a better implementation. Based on such understanding, the technical solutions of the present application can be embodied in the form of a software product, which is stored in a readable storage medium, such as a floppy disk, a hard disk or an optical disk of a computer, etc., and includes a number of instructions for making a computer device (which can be a personal computer, a server, or a network device, etc.) execute the methods described in various embodiments of the present application.

[0326] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto, and changes or replacements within the technical scope disclosed by the present application should be covered within the protection scope of the present application. Therefore, the protection scope of the present application should be subject to the protection scope of the claims.

Claims

1. A communication method characterized by comprising: The method comprises the following steps: The second network element determines that a third public land mobile network (PLMN) providing services for the terminal device belongs to a first PLMN, wherein the second network element is a network element in a home PLMN of the terminal device, the number of the first PLMN is at least one, and the first PLMN is different from the home PLMN of the terminal device; The second network element does not send a first target parameter to the terminal device, or the second network element sends indication information to the terminal device, wherein the indication information indicates that the first target parameter is deleted; the first target parameter comprises mapping of a parameter of a protocol data unit (PDU) session of a first communication mode to a parameter of a second communication mode, the communication mode of the third PLMN providing services for the terminal device comprises the first communication mode, the communication mode of the home PLMN of the terminal device comprises the second communication mode, and the first communication mode is different from the second communication mode.

2. The method of claim 1, wherein The method further comprises: The second network element receives first information from a third mobility management entity, wherein the third mobility management entity is a network element in a third PLMN providing services for the terminal device, and the first information comprises information of an operator to which the third mobility management entity belongs; The second network element determines that the third PLMN providing services for the terminal device belongs to the first PLMN, comprising: The second network element determines, according to the first information, that the third PLMN providing services for the terminal device belongs to the first PLMN.

3. The method according to claim 1 or 2, characterized in that, The second network element determines that the third PLMN providing services for the terminal device belongs to the first PLMN, comprising: When the second network element determines that the terminal device is in a roaming state, the second network element determines that the third PLMN providing services for the terminal device belongs to the first PLMN.

4. The method of claim 3, wherein, The method further comprises: The second network element receives second information from a third network element or a third border gateway (BG), wherein the third network element is a network element in a third PLMN providing services for the terminal device, and the third BG is used for connecting the second network element and the third network element; The second network element determines, according to the second information, that the terminal device is in a roaming state.

5. The method of any one of claims 1-2 and 4, wherein The method further comprises: The second network element sends a PDU session establishment acceptance message to the terminal device; The second network element does not send the first target parameter to the terminal device, comprising: The PDU session establishment acceptance message does not carry the first target parameter.

6. The method according to any of claims 1-2 and 4, characterized by, The second network element sends the indication information to the terminal device through a PDU session modification command message.

7. The method according to any of claims 1-2 and 4, characterized by, The first PLMN is preconfigured.

8. The method according to any of claims 1-2 and 4, characterized by, The method further comprises: The second network element determines that a fourth PLMN providing services for the terminal device does not belong to the first PLMN; The second network element sends a second target parameter to the terminal device, wherein the second target parameter comprises mapping of parameters of a PDU session of a first communication mode to parameters of a second communication mode, and a communication mode of a fourth PLMN serving the terminal device comprises the first communication mode.

9. The method of claim 8, wherein, The fourth PLMN serving the terminal device is a home PLMN of the terminal device.

10. The method of claim 8, wherein, The fourth PLMN serving the terminal device is different from a country to which an operator of the home PLMN of the terminal device belongs.

11. The method of claim 10, wherein, The second network element determines that the fourth PLMN serving the terminal device does not belong to the first PLMN, comprising: When the second network element determines that the terminal device is in a roaming state, the second network element determines that the fourth PLMN serving the terminal device does not belong to the first PLMN.

12. The method of claim 11, wherein, The method further comprises: The second network element receives fourth information from a fourth network element or a fourth border gateway (BG), wherein the fourth network element is a network element in a fourth PLMN serving the terminal device, and the fourth BG is used to connect the second network element and the fourth network element. The second network element determines that the terminal device is in a roaming state according to the fourth information.

13. The method of claim 8, wherein, The method further comprises: The second network element receives first information from a fourth mobility management entity, wherein the fourth mobility management entity is a network element in a fourth PLMN serving the terminal device, and the first information comprises information of an operator to which the fourth mobility management entity belongs. The second network element determines that the fourth PLMN serving the terminal device does not belong to the first PLMN, comprising: The second network element determines that the fourth PLMN serving the terminal device does not belong to the first PLMN according to the first information.

14. The method of claim 2 or 13, wherein, The first information comprises a globally unique access and mobility management function identifier (GUAMI).

15. A method of communication, comprising: Comprising: When a terminal device moves from a first communication mode of a first public land mobile network (PLMN) to a second communication mode of a home PLMN of the terminal device, a registration request message is sent to a second mobility management entity of the home PLMN of the terminal device, wherein the first PLMN and the home PLMN of the terminal device are different, the first communication mode and the second communication mode are different, the terminal device has a target parameter, and the target parameter comprises mapping of parameters of a protocol data unit (PDU) session of the first communication mode to parameters of the second communication mode. The terminal device receives a registration accept message from the second mobility management entity.

16. The method of claim 15, wherein, The method further comprises: The terminal device determines that the first PLMN and the home PLMN of the terminal device are different according to first information. The first information comprises information of at least one third PLMN, the third PLMN is different from the home PLMN of the terminal device, and the third PLMN comprises the first PLMN.

17. The method of claim 16, wherein, The method further comprises: The terminal device receives the first information from the second mobility management entity.

18. The method of claim 17, wherein, The first information is carried in a same message as an equivalent public land mobile network (EPLMN). The EPLMN includes at least the first PLMN.

19. The method of claim 16, wherein, The method further includes: The terminal device receives the first information from a second network element, wherein the second network element is a network element in a home PLMN of the terminal device.

20. The method of claim 19, wherein, The terminal device receives the first information from the second network element via a PDU session establishment accept message.

21. A method of communication, comprising: Comprising: A terminal device sends a registration request message to a first mobility management entity of a first public land mobile network (PLMN), wherein the first PLMN is different from a home PLMN of the terminal device. The terminal device receives a registration accept message from the first mobility management entity. The terminal device deletes a target parameter, or the terminal device does not generate a target parameter, or the terminal device does not save the target parameter when the terminal device receives the target parameter from a second network element, wherein the second network element is a network element in the home PLMN of the terminal device, the target parameter includes a mapping of a parameter of a protocol data unit (PDU) session of a first communication standard to a parameter of a second communication standard, and a communication standard of the first PLMN includes the first communication standard and a communication standard of the home PLMN of the terminal device includes the second communication standard.

22. The method of claim 21, wherein, The method further includes: The terminal device determines, according to first information, that the first PLMN is different from the home PLMN of the terminal device. The first information includes information of at least one third PLMN, the third PLMN is different from the home PLMN of the terminal device, and the third PLMN includes the first PLMN.

23. The method of claim 22, wherein, The method further includes: The terminal device receives the first information from a second mobility management entity, wherein the second mobility management entity is a network element in a home PLMN of the terminal device.

24. The method of claim 23, wherein, The first information is carried in a same message as an equivalent public land mobile network (EPLMN). The EPLMN includes at least the first PLMN.

25. The method of claim 22, wherein, The method further includes: The terminal device receives the first information from a second network element, wherein the second network element is a network element in a home PLMN of the terminal device.

26. The method of claim 25, wherein, The terminal device receives the first information from the second network element via a PDU session establishment accept message.

27. A communications device, characterized by Comprising units for performing the method according to any one of claims 1 to 14, or comprising units for performing the method according to any one of claims 15 to 20, or comprising units for performing the method according to any one of claims 21 to 26.

28. A communications device, characterized by Comprising: A processor and a memory coupled thereto, the memory storing program instructions that, when executed by the processor, implement the method of any of claims 1-14, or implement the method of any of claims 15-20, or implement the method of any of claims 21-26.

29. A chip, characterized by A chip including a processor and an input-output interface for communicating with modules outside the chip, the processor being configured to implement the method of any of claims 1-14, or implement the method of any of claims 15-20, or implement the method of any of claims 21-26, by logic circuitry or executing code instructions.

30. A computer-readable storage medium, characterized in that, The storage medium has stored therein a computer program or instructions that, when executed by a communication device, implement the method of any of claims 1-14, or implement the method of any of claims 15-20, or implement the method of any of claims 21-26.

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