A communication method and apparatus

Abstract

The application provides a communication method and device, so that the terminal device registered in the first network can establish a first PDU session associated with a DNN and an S-NSSAI in the first network. The terminal device can also send a first registration request message to the first network device, and the first registration request message is used to request registration to a second network. The terminal device can also receive first information from the first network device, and the first information is determined according to the interworking mode between the first network and the second network. The terminal device can also establish a PDU session of the terminal device according to the first information, and the PDU session is associated with the DNN and the S-NSSAI, which can improve the efficiency of UE switching in a non-public network.

Description

[0001] This application claims priority to the Chinese Patent Application No. 202010808903.8, filed on August 12, 2020, and entitled "A Communication Method and Device", the content of which is incorporated herein by reference in its entirety. TECHNICAL FIELD

[0002] The present application relates to the field of mobile communication technology, and in particular to a communication method and device. BACKGROUND

[0003] In the fifth generation (5th generation, 5G) wireless communication system, non-public network (non-public network, NPN) is supported as a non-public 5G network. Among them, the NPN includes public network integrated NPN (public network integrated NPN, PNI-NPN) implemented under the support of public land mobile network (public land mobile network, PLMN) and standalone NPN (standalone NPN, SNPN) which can be implemented without relying on PLMN.

[0004] In addition, there are currently two ways to support interworking between PLMN and SNPN. For example Figure 1 As shown, interworking between PLMN and SNPN can be implemented through non-3rd generation partnership project (non-3rd generation partnership project, non-3GPP) interworking function network element (interworking function, N3IWF). Or, interworking between PLMN and SNPN can be implemented through the roaming architecture as Figure 2 shown. Of course, the two ways also support interworking between SNPN and SNPN.

[0005] Therefore, when the current network supports interworking between one SNPN and other SNPNs or PLMN, there are several possibilities as follows: no interworking, interworking based on N3IWF architecture, and interworking based on roaming architecture. Due to the difference in interworking mode, the UE moves between two networks, such as between SNPN and PLMN or between two SNPNs, the UE performs switching in different ways, but the UE cannot know the interworking mode supported by the current network, and cannot reasonably select the switching mode, resulting in low switching efficiency or incorrect switching to maintain service continuity when the UE switches between two networks. SUMMARY

[0006] The application provides a communication method and device to solve the problem of low switching efficiency or incorrect switching of a UE between NPN networks.

[0007] In a first aspect, an embodiment of the application provides a communication method, which can be implemented by a terminal device or a component (such as a chip, a circuit, etc.) of the terminal device. The terminal device can be a UE.

[0008] Taking a terminal device as an execution subject, according to the method, the terminal device registered in a first network can establish a first protocol data unit (PDU) session associated to a data network name (DNN) and a single network slice selection assistance information (S-NSSAI) in the first network, and send a first registration request message to a first network device. The first message is used to request registration to a second network. Taking the first message as a first registration request message as an example, it should not be understood as being limited to a registration request. The terminal device can also receive first information from the first network device, and the first information is determined according to an interworking mode between the first network and the second network. The terminal device can also establish a PDU session of the terminal device according to the first information, and the PDU session is associated to the DNN and the S-NSSAI.

[0009] According to the method, after registration from the first network to the second network, the UE can receive first information from a first network device in the second network. Since the first information is related to the interworking mode between the first network and the second network, the PDU session of the UE associated to the DNN and the S-NSSAI can be more efficiently recovered according to the first information, so as to improve the switching efficiency and ensure service continuity.

[0010] In a possible design, the first registration request message can include a non-public network switching indication, which is used to indicate that the terminal device performs non-public network switching.

[0011] In a possible design, the interworking mode between the first network and the second network includes that the first network and the second network do not interwork, the first network and the second network interwork based on N3IWF, or the first network and the second network interwork based on roaming.

[0012] In a possible design, in the case that the interworking manner includes no interworking between the first network and the second network, the terminal device can send, to the first network device, a second message including a request type information element with a value of initial request, or in other words, the second message is used to request establishment of an initial PDU session. The following is described by taking the second message as an example of a first PDU session request message, but should not be understood as limiting the second message to the PDU session request message. The first PDU session request message can include information of the DNN and information of the S-NSSAI, to request establishment of a PDU session associated to the DNN and the S-NSSAI. Accordingly, in the case that the first network and the second network do not interwork, the UE can newly establish, in the second network, a PDU session associated to the DNN and the S-NSSAI, to achieve resumption of the PDU session associated to the DNN and the S-NSSAI, and improve handover efficiency.

[0013] In a possible design, in the case that the interworking manner includes no interworking between the first network and the second network, the first information is used to indicate that the first network and the second network do not interwork, or the first information is used to indicate that the terminal device sends the first PDU session request to the first network device. Accordingly, flexible indication of the interworking manner can be implemented.

[0014] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on N3IWF, the terminal device can send, to the first network device, a third message, where the third message is used to request establishment of a second PDU session. Hereinafter, the third message is taken as an example for description of a second PDU session request message, but it should not be understood as the third message being limited to the PDU session request message. The terminal device can further establish a connection with the N3IWF by using the second PDU session, where the N3IWF belongs to the first network. The terminal device can further send, to a second network device, a fourth message by using the connection, where the fourth message is used to request registration with the first network in an N3GPP manner, and the second network device belongs to the first network. Hereinafter, the fourth message is taken as an example for description of a second registration request message, but it should not be understood as the fourth message being limited to the registration request message. The terminal device can further send, to the second network device, a fifth message, where the fifth message includes a request type information element with a value of an existing PDU session, or in other words, the fifth message is used to request establishment of an existing PDU session. Hereinafter, the fifth message is taken as an example for description of a third PDU session request message, but it should not be understood as the fifth message being limited to the PDU session request message. The third PDU session request message can carry information of the DNN and information of the S-NSSAI. In this way, in a case where the first network and the second network interwork based on N3IWF, the UE can establish, by using the N3IWF and the second network device, a third PDU session associated with the information of the DNN and the information of the S-NSSAI, so as to achieve resumption of the PDU session of the UE associated with the DNN and the S-NSSAI, and improve switching efficiency.

[0015] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on N3IWF, the first information can be used to indicate that the first network and the second network interwork based on N3IWF, or used to indicate that the terminal device sends, to the first network device, the second PDU session request, sends, to the second network device, the second registration request by using the N3IWF, and sends, to the second network device, the third PDU session request message.

[0016] In a possible design, in the case where the interworking manner includes roaming-based interworking between the first network and the second network, the terminal device can send, to the first network device, a sixth message including a request type information element with a value of existing PDU session, information of the DNN, and information of the S-NSSAI. The following takes the sixth message as an example of the fourth PDU session request message, but this should not be understood as a limitation on the sixth message being the PDU session request message. Therefore, in the case where the interworking manner includes roaming-based interworking between the first network and the second network, the UE can establish, through the first network device, the fourth PDU session associated to the information of the DNN and the S-NSSAI, so as to realize resumption of the PDU session of the UE associated to the DNN and the S-NSSAI, and improve switching efficiency.

[0017] In a possible design, in the case where the interworking manner includes roaming-based interworking between the first network and the second network, the first information can be used to indicate roaming-based interworking between the first network and the second network, or used to indicate that the terminal device sends the fourth PDU session request message to the first network device.

[0018] In a possible design, the fourth PDU session request message includes a lossless switching indication. Therefore, in the case where the interworking manner includes roaming-based interworking between the first network and the second network, lossless network switching of the UE can be supported.

[0019] In a second aspect, an embodiment of the present application provides a communication method, which can be executed by a first network device or a component thereof. The first network device can include a core access and mobility management function (AMF).

[0020] Taking the first network device as an execution subject for example, according to the method, the first network device can receive a first registration request message from a terminal device, the first network device belongs to a second network, and the first registration request message is used to request registration to the second network. The first network device can further obtain a context of the terminal device, and determine, according to the context, that the terminal device has registered in a first network. The first network device can further send first information to the terminal device according to an interworking manner between the first network and the second network.

[0021] In a possible design, the first network device can determine that the terminal device performs cross-non-public network switching according to a cross-non-public network switching indication included in the first registration request message, where the cross-non-public network switching indication is used to indicate that the terminal device performs cross-non-public network switching. Alternatively, the first network device can determine that the terminal device performs cross-non-public network switching according to an identifier of the first network, where the identifier of the first network is included in the context. Alternatively, the first network device can determine that the terminal device performs cross-non-public network switching according to an identifier of the second network device, where the identifier of the second network device is included in the context of the terminal device. The second network device is a network device accessed by the terminal device when the terminal device is registered in the first network, such as an AMF.

[0022] In a possible design, the first network device can receive the context of the terminal device from a second network device, where the second network device is deployed in the first network. The first network device can obtain information of the second network device from a unified data management (UDM), and request the context of the terminal device.

[0023] Alternatively, the first network device receives the context of the terminal device from a data storage node, where the data storage node is shared by the first network and the second network.

[0024] In a possible design, the data storage node includes a UDM or an authentication, authorization, and accounting (AAA) server.

[0025] In a possible design, the interworking manner between the first network and the second network includes that the first network and the second network do not interwork, the first network and the second network interwork based on N3IWF, or the first network and the second network interwork based on roaming.

[0026] In a possible design, in a case where the interworking manner includes no interworking between the first network and the second network, the first information can be used to indicate that there is no interworking between the first network and the second network, or the first information can be used to indicate that the terminal device sends a first PDU session request message to the first network device. The first PDU session request message includes a request type information element with a value of initial request, or in other words, the first PDU session request message is used to request establishment of an initial PDU session. In addition, the first PDU session request message further includes a DNN (or information of a DNN) associated with a PDU session established by the terminal device in the first network and an S-NSSAI (or information of an S-NSSAI) associated with the PDU session, or in other words, the first information is further used to indicate that the UE carries, in the first PDU session request message, information of a DNN associated with a PDU session established by the terminal device in the first network and information of an S-NSSAI associated with the PDU session.

[0027] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on N3IWF, the first information can be used to indicate that there is interworking between the first network and the second network based on N3IWF. Alternatively, the first information can be used to indicate that the terminal device sends a second PDU session request message to the first network device, sends a second registration request message to the second network device through the N3IWF, and sends a third PDU session request message to the second network device. The second PDU session request message is used to request establishment of a second PDU session, and the second PDU session is used to establish a connection between the terminal device and the N3IWF. The second registration request message is used to request registration in the first network through an N3GPP manner. The third PDU session request message includes a request type information element with a value of existing PDU session, information of a DNN associated with a PDU session established by the terminal device in the first network, and information of an S-NSSAI associated with the PDU session.

[0028] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the first information can indicate interworking between the first network and the second network based on roaming. Alternatively, the first information can indicate that the terminal device sends, to the first network device, a fourth PDU session request message, where the fourth PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the fourth PDU session request message is used to request establishment of an existing PDU session. The fourth PDU session request message further includes information about a DNN associated with a PDU session established by the terminal device in the first network and information about an S-NSSAI associated with the PDU session, or in other words, the first information is further used to indicate that the terminal device carries, in the fourth PDU session request message, information about a DNN associated with a PDU session established by the terminal device in the first network and information about an S-NSSAI associated with the PDU session.

[0029] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the first network device can further receive the fourth PDU session request message from the terminal device. The first network device can further send the fourth PDU session request message to a first SMF, where the first SMF is an intermediate SMF, the first SMF is connected to a second SMF, and the second SMF maintains a first PDU session associated with the DNN and the S-NSSAI established by the terminal device in the first network, and the fourth PDU session request message can be forwarded by the first SMF to the second SMF, and path switching can be performed by the second SMF. Alternatively, the first SMF belongs to the first network, and the first SMF maintains a first PDU session associated with the DNN and the S-NSSAI established by the terminal device in the first network.

[0030] In a possible design, the first network device can further send, to the first SMF, a cross-non-public network switching indication, where the cross-non-public network switching indication is used to indicate that the terminal device performs cross-non-public network switching.

[0031] In a possible design, the fourth PDU session request includes a lossless switching indication.

[0032] The second aspect and the possible designs of the second aspect have the beneficial effects as described for the method of the first aspect and the possible designs of the first aspect.

[0033] In a third aspect, an embodiment of the present application provides a communication method, which can be implemented by a terminal device or a component (such as a chip, a circuit, or the like) of the terminal device. The terminal device can be a UE.

[0034] The following takes the terminal device as an example. According to the method, the terminal device registered in the first network can establish a first PDU session associated to a DNN and an S-NSSAI in the first network, and the terminal device can also send a first registration request message to the first network device, where the first registration request message is used to request registration to the second network. In addition, the terminal device establishes (or requests to establish) a PDU session of the terminal device according to a first order, where the PDU session is associated to the DNN and the S-NSSAI associated to the first PDU session. The first order is used to indicate the order of establishing the PDU session of the terminal device according to the third method, the second method and the first method. In other words, the terminal device attempts to establish the PDU session of the terminal device according to the third method, the second method and the first method in the first order until the PDU session is established.

[0035] For example, the first information can indicate the priority of the first method, the second method and the third method respectively, where the priority of the third method is the highest, and the priority of the second method is higher than that of the first method. The UE can perform the third method, the second method and the first method according to the priority from high to low. If the PDU session is successfully established according to a certain method, the terminal device no longer attempts to establish the PDU session according to the method with lower priority. Here, the successful establishment of the PDU session means that a PDU session establishment response message is received from the network side, where the PDU session establishment response message indicates the successful establishment of the PDU session.

[0036] According to the above process, after the terminal device registers from the first network to the second network, the terminal device can recover the PDU session according to the first order through the first method, the second method and / or the third method, so as to improve the switching efficiency.

[0037] In a possible design, the first registration request message includes a cross-non-public network switching indication, where the cross-non-public network switching indication is used to indicate that the terminal device performs cross-non-public network switching.

[0038] In a possible design, when the PDU session of the terminal device is established according to the first method, the terminal device can send a first PDU session request message to the first network device, where the first PDU session request message includes a request type information element with a value of initial request, or in other words, the first PDU session request message is used to request to establish an initial PDU session. The first PDU session request message includes the information of the DNN and the information of the S-NSSAI, so as to request to establish a PDU session associated to the DNN and the S-NSSAI.

[0039] In a possible design, the terminal device can send, to the first network device, a second PDU session request message, where the second PDU session request is used to request establishment of a second PDU session. The terminal device can establish a connection with the N3IWF through the second PDU session, where the N3IWF belongs to the first network. The terminal device can send, to the second network device, a second registration request message through the connection, where the second registration request message is used to request registration with the first network in the N3GPP manner, and the second network device belongs to the first network. When the PDU session is established in the second manner, the terminal device can send, to the second network device, a third PDU session request message, where the third PDU session request message includes a request type information element with a value of existing PDU session, or the third PDU session request message is used to request establishment of an existing PDU session. The third PDU session request message can include information of the DNN and information of the S-NSSAI.

[0040] In a possible design, when the PDU session of the terminal device is established in the third manner, the terminal device can send, to the first network device, a fourth PDU session request message, where the fourth PDU session request message includes a request type information element with a value of existing PDU session, or the fourth PDU session request message is used to request establishment of an existing PDU session. The fourth PDU session request message further includes information of the DNN and information of the S-NSSAI. Therefore, the terminal device can preferentially establish, through the fourth PDU session request message, a PDU session associated to the DNN and the S-NSSAI, thereby improving switching efficiency.

[0041] In a possible design, the fourth PDU session request message includes a lossless switching indication to support lossless switching.

[0042] In a possible design, the first order is determined according to a local configuration. Alternatively, the terminal device can receive indication information of the first order from the first network device. Optionally, the indication information of the first order can be determined according to a local configuration of the first network device, or determined by the first network device according to an interworking manner between the first network and the second network. Alternatively, the terminal device can receive indication information of the first order from the second network device. Optionally, the indication information of the first order can be determined according to a local configuration of the second network device, or determined by the second network device according to an interworking manner between the first network and the second network. Therefore, the first order can be flexibly determined.

[0043] In a possible design, the first registration request message includes a non-public network cross switching indication, where the non-public network cross switching indication is used to indicate that the terminal device performs non-public network cross switching.

[0044] In a fourth aspect, an embodiment of the present application provides a communication method, which can be performed by a session management function (SMF) or a component thereof.

[0045] In the following, taking the SMF as an example, according to the method, the SMF can establish a first PDU session of a terminal device to a DNN and an S-NSSAI, where the terminal device is registered in a first network. The first PDU session is a PDU session between a first access network element and a first UPF, and the first access network element belongs to the first network. The SMF can receive a fourth PDU session request message, where the fourth PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the fourth PDU session request message can be used to request to establish an existing PDU session. The fourth PDU session request message further includes information of the DNN and information of the S-NSSAI, to request to establish a PDU session associated with the DNN and the S-NSSAI. The SMF can further send second information to the first UPF, where the second information is used to instruct the first UPF to send an end marker to the first access network element after path switching of the first PDU session, and is used to instruct the first UPF to forward downlink data from the terminal device of the first access network element to the terminal device through the switched path, where the downlink data includes the end marker. The SMF can further send third information to the first access network element, where the third information is used to instruct the first access network element to forward downlink data of the terminal device buffered by the first access network element to the first UPF, until the end marker is received and forwarded.

[0046] By using the above process, the SMF can support lossless path switching of the terminal device to maintain service continuity.

[0047] In a possible design, the fourth PDU session request message includes a lossless switching indication, or the SMF can determine to perform lossless switching for the terminal device according to local configuration.

[0048] In a possible design, the SMF can further receive a non-public network switching indication.

[0049] In a possible design, the fourth PDU request message above comes from a first network device, and the first network device belongs to a second network. For example, the SMF belongs to the second network, and the first network device is connected to the SMF. Or, the fourth PDU session request message is sent by the first network device to an intermediate SMF, and is forwarded to the SMF by the intermediate SMF. For example, the SMF does not belong to the second network, and the first network device is not directly connected to the SMF, and needs to forward messages through the intermediate SMF.

[0050] In a fifth aspect, an embodiment of the present application provides a communication apparatus, which can implement the method in the first aspect or any possible implementation manner of the first aspect. The apparatus comprises corresponding units or components for performing the above method. The units included in the apparatus can be implemented by software and / or hardware. The apparatus can be, for example, a terminal device, or a chip, chip system, or processor, etc. that can support the terminal device to implement the above method.

[0051] In a possible design, the communication apparatus can include a communication module and a processing module, etc. in its structure, which can perform the corresponding functions of the terminal device in the first aspect or each possible design example of the first aspect. For example, the communication module can be used for the communication apparatus to perform the receiving and sending of signals, data, information or messages, and the processing module can be used for processing the signals, data, information or messages received by the communication module, or for generating the signals, data, information or messages sent by the communication module.

[0052] In implementing the method in the first aspect, the communication apparatus can be registered with the first network, the communication module can establish a first PDU session associated with a DNN and an S-NSSAI in the first network, and the communication module can send a first registration request message to the first network device, where the first registration request message is used to request registration to the second network. The communication module can further receive first information from the first network device, where the first information is determined according to an interworking mode between the first network and the second network. The communication module can further establish a PDU session according to the first information, where the PDU session is associated with the DNN and the S-NSSAI.

[0053] In a possible design, the first registration request message can include a cross-non-public network switching indication, which is used to indicate that the communication apparatus performs cross-non-public network switching.

[0054] In a possible design, the interworking mode between the first network and the second network includes that the first network and the second network do not interwork, the first network and the second network interwork based on N3IWF, or the first network and the second network interwork based on roaming.

[0055] In a possible design, in the case where the interworking manner includes no interworking between the first network and the second network, the communication module can send, to the first network device, a first PDU session request message, where the first PDU session request message includes a request type information element with a value of initial request, or in other words, the first PDU session request message is used to request establishment of an initial PDU session. The first PDU session request message includes information of the DNN and information of the S-NSSAI, to request establishment of a PDU session associated to the DNN and the S-NSSAI. Accordingly, in the case where the first network and the second network do not interwork, the UE can newly establish, in the second network, a PDU session associated to the DNN and the S-NSSAI, to implement recovery of the PDU session associated to the DNN and the S-NSSAI, thereby improving handover efficiency.

[0056] In a possible design, in the case where the interworking manner includes no interworking between the first network and the second network, the first information is used to indicate that the first network and the second network do not interwork, or the first information is used to indicate that the communication apparatus sends, to the first network device, the first PDU session request. Accordingly, flexible indication of the interworking manner can be implemented.

[0057] In a possible design, in the case where the interworking manner includes interworking between the first network and the second network based on N3IWF, the communication module can send, to the first network device, a second PDU session request message, where the second PDU session request is used to request establishment of a second PDU session. The communication module can further establish, through the second PDU session, a connection with the N3IWF, where the N3IWF belongs to the first network. The communication module can further send, to a second network device, a second registration request message through the connection, where the second registration request message is used to request registration with the first network in an N3GPP manner, and the second network device belongs to the first network. The communication module can further send, to the second network device, a third PDU session request message, where the third PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the third PDU session request message is used to request establishment of an existing PDU session. The third PDU session request message can carry information of the DNN and information of the S-NSSAI. Accordingly, in the case where the first network and the second network interwork based on N3IWF, the UE can establish, through the N3IWF and the second network device, a third PDU session associated to the information of the DNN and the information of the S-NSSAI, to implement recovery of the PDU session associated to the DNN and the S-NSSAI of the UE, thereby improving handover efficiency.

[0058] In a possible design, in a case where the interworking manner includes N3IWF-based interworking between the first network and the second network, the first information can be used for indicating the N3IWF-based interworking between the first network and the second network, or for indicating that the second PDU session request is sent to the first network device, the second registration request is sent to the second network device through the N3IWF, and the third PDU session request message is sent to the second network device.

[0059] In a possible design, in a case where the interworking manner includes roaming-based interworking between the first network and the second network, the communication module can send, to the first network device, a fourth PDU session request message, where the fourth PDU session request message includes a request type information element with a value of existing PDU session, information of the DNN, and information of the S-NSSAI. Therefore, in the roaming-based interworking manner between the first network and the second network, the UE can establish, through the first network device, the fourth PDU session associated to the information of the DNN and the S-NSSAI, so as to realize the resumption of the PDU session of the UE associated to the DNN and the S-NSSAI, and improve the switching efficiency.

[0060] In a possible design, in a case where the interworking manner includes roaming-based interworking between the first network and the second network, the first information can be used for indicating the roaming-based interworking between the first network and the second network, or for indicating that the fourth PDU session request message is sent to the first network device.

[0061] In a possible design, the fourth PDU session request message includes a lossless switching indication. Therefore, in a case where the interworking manner includes roaming-based interworking between the first network and the second network, lossless network switching of the UE can be supported.

[0062] In addition, the communication apparatus can include a processor, and optionally further include a communication interface (such as a transceiver) and a memory. The communication interface can be used to transceive information or data, and to enable the communication apparatus to communicate with other communication apparatuses (such as the first network device) in a network system. The processor is configured to support the communication apparatus to perform the corresponding functions of the terminal device in the first aspect or in each possible design example of the first aspect. The memory is coupled to the processor, and is used to store program instructions and data necessary for the communication apparatus. For example, the transceiver can be used to perform the steps performed by the communication module in the fifth aspect, and the processor can be used to perform the steps performed by the processing module in the fifth aspect.

[0063] The benefits of the fifth aspect and the possible designs thereof can refer to the benefits of the method in the first aspect and the possible designs thereof.

[0064] In a sixth aspect, an embodiment of the present application provides a communication apparatus, which can implement the method in the second aspect or any possible implementation manner of the second aspect. The apparatus includes corresponding units or components for performing the method. The units included in the apparatus can be implemented by software and / or hardware. The apparatus can be, for example, a first network device, or a chip, chip system, or processor, etc. that can support the first network device to implement the second aspect or any possible implementation manner of the method.

[0065] In a possible design, the communication apparatus can include a communication module, a processing module, and the like, which can perform corresponding functions of the first network device in the second aspect or any possible implementation manner of the second aspect. For example, the communication module can be used for the communication apparatus to receive and send signals, data, information, or messages, and the processing module can be used for processing signals, data, information, or messages received by the communication module, or for generating signals, data, information, or messages sent by the communication module.

[0066] In implementation of the method in the second aspect, the communication module can receive a first registration request message from a terminal device, the communication apparatus belongs to a second network, and the first registration request message is used to request registration to the second network. The processing module can obtain a context of the terminal device, and determine that the terminal device has registered in a first network according to the context. The communication module can further send first information to the terminal device according to an interworking mode between the first network and the second network.

[0067] In a possible design, the processing module can further determine that the terminal device performs cross-non-public network switching according to a cross-non-public network switching indication included in the first registration request message, where the cross-non-public network switching indication is used to indicate that the terminal device performs cross-non-public network switching. Alternatively, the processing module can determine that the terminal device performs cross-non-public network switching according to an identifier of the first network, where the identifier of the first network is included in the context. Alternatively, the processing module can determine that the terminal device performs cross-non-public network switching according to an identifier of a second network device, where the identifier of the second network device is included in the context of the terminal device. The second network device is a network device accessed by the terminal device when registering in the first network, such as an AMF.

[0068] In a possible design, the communication module can receive the context of the terminal device from a second network device, where the second network device is deployed in the first network. The communication module can obtain information of the second network device from a UDM, and request the context of the terminal device.

[0069] Alternatively, the communication module can receive the context of the terminal device from a data storage node, where the data storage node is shared by the first network and the second network.

[0070] In a possible design, the data storage node includes a UDM or an AAA server.

[0071] In a possible design, the interworking manner between the first network and the second network includes no interworking between the first network and the second network, interworking between the first network and the second network based on N3IWF, or interworking between the first network and the second network based on roaming.

[0072] In a possible design, when the interworking manner includes no interworking between the first network and the second network, the first information can be used to indicate that there is no interworking between the first network and the second network, or the first information can be used to instruct the terminal device to send a first PDU session request message to the communication device. The first PDU session request message includes a request type information element with a value of initialrequest, or in other words, the first PDU session request message is used to request establishment of an initial PDU session. In addition, the first PDU session request message further includes a DNN (or information of a DNN) associated with a PDU session established by the terminal device in the first network and an S-NSSAI (or information of an S-NSSAI) associated with the PDU session, or in other words, the first information is further used to instruct the UE to carry, in the first PDU session request message, information of the DNN associated with the PDU session established by the terminal device in the first network and information of the S-NSSAI associated with the PDU session.

[0073] In a possible design, when the interworking manner includes interworking between the first network and the second network based on N3IWF, the first information can be used to indicate that there is interworking between the first network and the second network based on N3IWF. Alternatively, the first information can be used to instruct the terminal device to send a second PDU session request message to the communication device, send a second registration request message to a second network device through the N3IWF, and send a third PDU session request message to the second network device. The second PDU session request message is used to request establishment of a second PDU session, and the second PDU session is used to establish a connection between the terminal device and the N3IWF. The second registration request message is used to request registration in the first network in an N3GPP manner. The third PDU session request message includes a request type information element with a value of existing PDU session, information of a DNN associated with a PDU session established by the terminal device in the first network, and information of an S-NSSAI associated with the PDU session.

[0074] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the first information can indicate interworking between the first network and the second network based on roaming. Alternatively, the first information can indicate that the terminal device sends, to the communication apparatus, a fourth PDU session request message, where the fourth PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the fourth PDU session request message is used to request establishment of an existing PDU session. The fourth PDU session request message further includes information about a DNN associated with a PDU session established by the terminal device in the first network and information about an S-NSSAI associated with the PDU session, or in other words, the first information is further used to indicate that the terminal device carries, in the fourth PDU session request message, the information about the DNN associated with the PDU session established by the terminal device in the first network and the information about the S-NSSAI associated with the PDU session.

[0075] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the communication module can further receive the fourth PDU session request message from the terminal device. The communication module can further send, to a first SMF, the fourth PDU session request message, where the first SMF is an intermediate SMF, the first SMF is connected to a second SMF, and the second SMF maintains a first PDU session associated with the DNN and the S-NSSAI and established by the terminal device in the first network, and the fourth PDU session request message can be subsequently forwarded by the first SMF to the second SMF for path switching by the second SMF. Alternatively, the first SMF belongs to the first network, and the first SMF maintains the first PDU session associated with the DNN and the S-NSSAI and established by the terminal device in the first network.

[0076] In a possible design, the communication module can further send, to the first SMF, a cross-non-public network switching indication, where the cross-non-public network switching indication is used to indicate that the terminal device performs cross-non-public network switching.

[0077] In a possible design, the fourth PDU session request includes a lossless switching indication.

[0078] In addition, the communication apparatus can include a processor, and optionally further include a communication interface (such as a wired communication interface, etc.) and a memory. The communication interface can be configured to receive and send information or data, and configured to enable the communication apparatus to communicate with other communication apparatuses (such as terminal devices, etc.) in the network system. The processor is configured to support the communication apparatus to perform the corresponding functions of the first network device in the second aspect or in any possible implementation of the second aspect. The memory is coupled to the processor, and configured to store program instructions and data necessary for the communication apparatus. For example, the transceiver can be configured to perform the steps performed by the communication module in the sixth aspect, and the processor can be configured to perform the steps performed by the processing module in the sixth aspect.

[0079] The beneficial effects of the sixth aspect and possible designs thereof can be referred to the description of the beneficial effects of the method in the first aspect and possible designs thereof.

[0080] In the seventh aspect, an embodiment of the present application provides a communication apparatus, which can implement the method in the third aspect or in any possible implementation of the third aspect. The apparatus includes corresponding units or components for performing the above method. The units included in the apparatus can be implemented by software and / or hardware. The apparatus can be, for example, a terminal device, or a chip, chip system, or processor, etc. that can support the terminal device to implement the above method.

[0081] In one possible design, the communication apparatus can include a communication module and a processing module, etc. These modules can perform the corresponding functions of the terminal device in the third aspect or in any possible design of the third aspect. For example, the communication module can be configured to enable the communication apparatus to receive and send signals, data, information or messages, and the processing module can be configured to process the signals, data, information or messages received by the communication module, or to generate the signals, data, information or messages sent by the communication module.

[0082] In the implementation of the method in the third aspect, the communication apparatus is registered in the first network, and the communication module can establish a first PDU session associated with a DNN and an S-NSSAI in the first network. The communication module can also send a first registration request message to the first network device, where the first registration request message is used to request registration to the second network. In addition, the communication module establishes a PDU session according to a first order, where the PDU session is associated with the DNN and the S-NSSAI. The first order is used to indicate that the PDU session is established according to the third mode, the second mode and the first mode in sequence. Alternatively, the processing module establishes (or requests to establish) the PDU session according to the third mode, the second mode and the first mode in sequence through the communication module according to the first order, until the PDU session is established.

[0083] In a possible design, the first registration request message includes a cross-non-public network switching indication, where the cross-non-public network switching indication is used to indicate cross-non-public network switching.

[0084] In a possible design, when the PDU session is established according to the first manner, the communication module can send a first PDU session request message to the first network device, where the first PDU session request message includes a request type information element with a value of initial request, or in other words, the first PDU session request message is used to request establishment of an initial PDU session. The first PDU session request message includes information of the DNN and information of the S-NSSAI, to request establishment of a PDU session associated with the DNN and the S-NSSAI.

[0085] In a possible design, the communication module can send a second PDU session request message to the first network device, where the second PDU session request is used to request establishment of a second PDU session. The communication module can establish a connection with an N3IWF through the second PDU session, where the N3IWF belongs to the first network. The communication module sends a second registration request message to a second network device through the connection, where the second registration request message is used to request registration with the first network in an N3GPP manner, and the second network device belongs to the first network. When the PDU session is established according to the second manner, the communication module can send a third PDU session request message to the second network device, where the third PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the third PDU session request message can be used to request establishment of an existing PDU session. The third PDU session request message can include information of the DNN and information of the S-NSSAI.

[0086] In a possible design, when the PDU session is established according to the third manner, the communication module can send a fourth PDU session request message to the first network device, where the fourth PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the fourth PDU session request message can be used to request establishment of an existing PDU session. The fourth PDU session request message further includes information of the DNN and information of the S-NSSAI.

[0087] In a possible design, the fourth PDU session request message includes a lossless switching indication to support lossless switching.

[0088] In a possible design, the first sequence is determined according to a local configuration. Alternatively, the communication module can receive indication information of the first sequence from the first network device. Optionally, the indication information of the first sequence can be determined according to a local configuration of the first network device, or determined by the first network device according to an interworking mode between the first network and the second network. Alternatively, the communication module can receive indication information of the first sequence from the second network device. Optionally, the indication information of the first sequence can be determined according to a local configuration of the second network device, or determined by the second network device according to an interworking mode between the first network and the second network. Therefore, the first sequence can be flexibly determined.

[0089] In addition, the communication apparatus can include a processor, and optionally further include a communication interface and a memory. The communication interface can be used to transceive information or data, and used for the communication apparatus to communicate with other communication apparatuses (such as the first network device) in the network system. The processor is configured to support the communication apparatus to perform the corresponding functions of the terminal device in the third aspect or in each possible design example of the third aspect. The memory is coupled to the processor, and used to store program instructions and data necessary for the communication apparatus. For example, the transceiver can be used to perform the steps performed by the communication module in the seventh aspect, and the processor can be used to perform the steps performed by the processing module in the seventh aspect.

[0090] The beneficial effects of the seventh aspect and possible designs thereof can refer to the description of the beneficial effects of the method in the third aspect and possible designs thereof.

[0091] In the eighth aspect, an embodiment of the present application provides a communication apparatus, which can implement the method in the fourth aspect or in any possible implementation manner of the fourth aspect. The apparatus includes units or components for performing the corresponding steps of the method. The units included in the apparatus can be implemented by software and / or hardware. The apparatus can be, for example, an SMF, or a chip, chip system, or processor, etc. that can support the SMF to implement the fourth aspect or any possible method of the fourth aspect.

[0092] In a possible design, the communication apparatus can include a communication module and a processing module, etc. These modules can perform the corresponding functions of the SMF in the fourth aspect or in each possible design example of the fourth aspect. For example, the communication module can be used for the communication apparatus to perform the receiving and sending of signals, data, information or messages, and the processing module can be used for processing the signals, data, information or messages received by the communication module, or for generating the signals, data, information or messages sent by the communication module.

[0093] In the method of the fourth aspect, the processing module can establish a first PDU session associated with a DNN and an S-NSSAI for a terminal device registered with a first network. The first PDU session is a PDU session between a first access network element belonging to the first network and a first UPF. The communication module can receive a fourth PDU session request message including a request type information element with a value of existing PDU session, or the fourth PDU session request message can be used to request establishment of an existing PDU session. The fourth PDU session request message further includes information of the DNN and information of the S-NSSAI to request establishment of a PDU session associated with the DNN and the S-NSSAI. The communication module can further send second information to the first UPF, the second information being used to instruct the first UPF to send an end marker to the first access network element after path switching of the first PDU session, and to instruct the first UPF to forward downlink data from the terminal device of the first access network element to the terminal device through the switched path, the downlink data including the end marker. The communication module can further send third information to the first access network element, the third information being used to instruct the first access network element to forward downlink data of the terminal device buffered by the first access network element to the first UPF until the end marker is received and forwarded.

[0094] In a possible design, the fourth PDU session request message includes a lossless switching indication, or the processing module can determine, according to local configuration, to perform lossless switching for the terminal device.

[0095] In a possible design, the communication module can further receive a non-public network switching indication.

[0096] In a possible design, the fourth PDU session request message is from a first network device belonging to a second network, for example, the communication apparatus belongs to the second network and the first network device is connected to the communication apparatus. Alternatively, the fourth PDU session request message is sent by the first network device to an intermediate SMF and forwarded by the intermediate SMF to the communication module, for example, the communication apparatus does not belong to the second network and the first network device is not directly connected to the communication apparatus, and the message needs to be forwarded through the intermediate SMF.

[0097] In addition, the communication device can include a processor, and optionally further include a communication interface and a memory. The communication interface can be used to receive and send information or data, and to communicate with other communication devices (e.g., the first network device) in the network system. The processor is configured to support the communication device to perform the corresponding functions of the SMF in the fourth aspect or the various possible design examples of the fourth aspect. The memory is coupled to the processor, and is used to store the necessary program instructions and data of the communication device. For example, the transceiver can be used to perform the steps performed by the communication module in the eighth aspect, and the processor can be used to perform the steps performed by the processing module in the eighth aspect.

[0098] The beneficial effects of the eighth aspect and the possible designs thereof can refer to the description of the beneficial effects of the method in the fourth aspect and the possible designs thereof.

[0099] In a ninth aspect, an embodiment of the present application provides a communication method, which can be implemented by a terminal device or a component (e.g., a chip, a circuit, or the like) of the terminal device. The terminal device can be a UE.

[0100] In the following, taking the terminal device as an example, according to the method, the terminal device registered in the first network establishes a first PDU session associated with a DNN and an S-NSSAI in the first network; the terminal device sends a first message to the first network device, and the first message is used to request registration to the second network; the terminal device receives first information from the first network device, and the first information is determined according to an interworking mode between the first network and the second network, and the first network and the second network are not interworked without roaming; and the terminal device determines to resume the PDU session of the terminal device in a manner supporting N3WIF or determines not to establish the PDU session of the terminal device according to the first information, and the PDU session is associated with the DNN and the S-NSSAI.

[0101] By using the method, the PDU session of the terminal device can be resumed after the terminal device moves to the second network device in the case that the first network and the second network are not interworked without roaming, and the switching efficiency is improved; or the terminal device does not establish the PDU session, so as to save the signaling overhead.

[0102] In a possible design, the terminal device can send, to the first network device, a third message, where the third message is used to request establishment of a second PDU session; the terminal device establishes a connection with an N3IWF through the second PDU session, where the N3IWF belongs to the first network; the terminal device sends, to a second network device through the connection, a fourth message, where the fourth message is used to request registration with the first network in an N3GPP manner, and the second network device belongs to the first network; and the terminal device can send, to the second network device, a fifth message, where the fifth message is used to request establishment of an existing PDU session, and the fifth message includes information of the DNN and information of the S-NSSAI.

[0103] In a possible design, the first information is used to indicate that roaming interworking is not supported between the first network and the second network.

[0104] In a tenth aspect, an embodiment of the present application provides a communication method, which can be performed by a first network device or a component thereof. The first network device can include an AMF.

[0105] According to the method, the first network device can receive a first message from a terminal device, where the first network device belongs to a second network, and the first message is used to request registration with the second network; the first network device obtains an identifier of the terminal device and determines an identifier of the first network; and the first network device sends first information to the terminal device according to a roaming interworking mode between the first network and the second network.

[0106] The beneficial effects of the tenth aspect and possible designs thereof can refer to the beneficial effects of the method in the ninth aspect and possible designs thereof.

[0107] In an eleventh aspect, an embodiment of the present application provides a communication apparatus, which can implement the method in the ninth aspect or any possible implementation manner of the ninth aspect. The apparatus includes corresponding units or components for performing the above method. The units included in the apparatus can be implemented by software and / or hardware. The apparatus can be, for example, a terminal device, or a chip, chip system, or processor that can support the terminal device to implement the above method.

[0108] In a possible design, the structure of the communication apparatus can include a communication module and a processing module, and the like, which can perform the corresponding functions of the terminal device in the first aspect or each possible design example of the first aspect. For example, the communication module can be used for the communication apparatus to perform the receiving and sending of signals, data, information, or messages, and the processing module can be used for processing the signals, data, information, or messages received by the communication module, or for generating the signals, data, information, or messages sent by the communication module.

[0109] In the method of the ninth aspect, the communication module of the terminal device registered in the first network establishes a first PDU session associated with a DNN and an S-NSSAI in the first network; the communication module sends a first message to the first network device, the first message being used to request registration to the second network; the communication module receives first information from the first network device, the first information being determined according to an interworking manner between the first network and the second network, the first network and the second network being not roaming interworking; and the processing module determines to resume the PDU session in a manner of supporting N3IWF or determines not to establish the PDU session of the terminal device associated with the DNN and the S-NSSAI according to the first information.

[0110] In a possible design, the communication module can be configured to send a third message to the first network device, the third message being used to request establishment of a second PDU session; the communication module establishes a connection with an N3IWF through the second PDU session, the N3IWF belonging to the first network; the communication module sends a fourth message to a second network device through the connection, the fourth message being used to request registration in an N3GPP manner in the first network, the second network device belonging to the first network; and the communication module can send a fifth message to the second network device, the fifth message being used to request establishment of an existing PDU session, the fifth message comprising information of the DNN and information of the S-NSSAI.

[0111] In a possible design, the first information is used to indicate that the first network does not support non-roaming interworking.

[0112] In a twelfth aspect, an embodiment of the present application provides a communication apparatus, which can implement the method in the tenth aspect or any possible implementation manner of the tenth aspect. The apparatus comprises corresponding units or components for performing the above method. The units included in the apparatus can be implemented by software and / or hardware. The apparatus can be, for example, a first network device, or a chip, a chip system, or a processor, etc. that can support the first network device to implement the tenth aspect or any possible implementation manner of the tenth aspect.

[0113] In the method of the tenth aspect, the communication module can receive a first message from a terminal device, the first network device belonging to a second network, the first message being used to request registration to the second network; the first network device obtains an identifier of the terminal device and determines an identifier of the first network; and the communication module sends first information to the terminal device according to a roaming interworking manner between the first network and the second network.

[0114] In a thirteenth aspect, the embodiments of the present application provide a communication system. The communication system can include the communication apparatus provided in the fifth aspect and the communication apparatus provided in the sixth aspect.

[0115] The beneficial effects of the thirteenth aspect and possible designs thereof can refer to the description of the beneficial effects of the method in the first aspect and possible designs thereof.

[0116] The communication system further includes the communication apparatus provided in the eighth aspect.

[0117] When the communication apparatus provided in the eighth aspect is included, the beneficial effects of the thirteenth aspect and possible designs thereof can refer to the description of the beneficial effects of the method in the fourth aspect and possible designs thereof.

[0118] The communication system can include the communication apparatus provided in the eleventh aspect and the communication apparatus provided in the twelfth aspect.

[0119] In a fourteenth aspect, the embodiments of the present application provide a communication system. The communication system can include the communication apparatus provided in the seventh aspect and the first network device.

[0120] The beneficial effects of the tenth aspect and possible designs thereof can refer to the description of the beneficial effects of the method in the third aspect and possible designs thereof.

[0121] The communication system further includes the communication apparatus provided in the eighth aspect.

[0122] When the communication apparatus provided in the eighth aspect is included, the beneficial effects of the tenth aspect and possible designs thereof can refer to the description of the beneficial effects of the method in the fourth aspect and possible designs thereof.

[0123] In a fifteenth aspect, the embodiments of the present application provide a computer storage medium, which stores a program or, when the program is invoked on a computer, causes the computer to execute the method in any one of the first aspect and possible designs thereof, the second aspect and possible designs thereof, the third aspect and possible designs thereof, or the fourth aspect and possible designs thereof, or the ninth aspect and possible designs thereof, or the tenth aspect and possible designs thereof.

[0124] The beneficial effects of the eleventh aspect and possible designs thereof can refer to the description of the beneficial effects of the method in the first aspect and possible designs thereof when the method in any one of the first aspect and possible designs thereof or the second aspect and possible designs thereof is executed. The beneficial effects of the eleventh aspect and possible designs thereof can refer to the description of the beneficial effects of the method in the third aspect and possible designs thereof when the method in any one of the third aspect and possible designs thereof or the fourth aspect and possible designs thereof is executed.

[0125] In the thirteenth aspect, the present application provides a computer program product, which can include a program or instructions, when the computer program product is run on a computer, causing the computer to execute any of the methods of the first aspect and its possible designs, the second aspect and its possible designs, the third aspect and its possible designs, or the fourth aspect and its possible designs, or the ninth aspect and its possible designs, or the tenth aspect and its possible designs.

[0126] In the execution of any of the methods of the first aspect and its possible designs or the second aspect and its possible designs, the beneficial effects of the twelfth aspect and its possible designs can refer to the description of the beneficial effects of the methods of the first aspect and its possible designs. In the execution of any of the methods of the third aspect and its possible designs, the beneficial effects of the twelfth aspect and its possible designs can refer to the description of the beneficial effects of the methods of the third aspect and its possible designs. In the execution of any of the methods of the fourth aspect and its possible designs, the beneficial effects of the twelfth aspect and its possible designs can refer to the description of the beneficial effects of the methods of the third aspect and its possible designs.

[0127] In the thirteenth aspect, the present application provides a chip or a chip system (or circuit) including a chip, which can include a processor. The chip can also include a memory (or storage module) and / or a transceiver (or communication module). The chip can be used to execute any of the methods of the first aspect and its possible designs, the second aspect and its possible designs, the third aspect and its possible designs, or the fourth aspect and its possible designs, or the ninth aspect and its possible designs, or the tenth aspect and its possible designs. The chip system can be composed of the above-mentioned chip, or can include the above-mentioned chip and other discrete devices, such as a memory (or storage module) and / or a transceiver (or communication module).

[0128] In the execution of any of the methods of the first aspect and its possible designs or the second aspect and its possible designs, the beneficial effects of the twelfth aspect and its possible designs can refer to the description of the beneficial effects of the methods of the first aspect and its possible designs. In the execution of any of the methods of the third aspect and its possible designs, the beneficial effects of the twelfth aspect and its possible designs can refer to the description of the beneficial effects of the methods of the third aspect and its possible designs. In the execution of any of the methods of the fourth aspect and its possible designs, the beneficial effects of the twelfth aspect and its possible designs can refer to the description of the beneficial effects of the methods of the third aspect and its possible designs.

[0129] In a tenth aspect, a communication system is provided, the communication system comprising a first terminal device, a second terminal device, the communication apparatus described in the third aspect, any possible implementation of the third aspect, and any possible implementation of the fourth aspect. Attached Figure Description

[0130] Figure 1 This application provides a schematic diagram of the architecture of a communication system.

[0131] Figure 2 This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0132] Figure 3 This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0133] Figure 4 This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0134] Figure 5 This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0135] Figure 6 This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0136] Figure 7a This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0137] Figure 7b This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0138] Figure 7c This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0139] Figure 8 This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0140] Figure 9 This is a schematic diagram of the architecture of another communication system provided in an embodiment of this application;

[0141] Figure 10 A flowchart illustrating a communication method provided in an embodiment of this application;

[0142] Figure 11 A flowchart illustrating another communication method provided in an embodiment of this application;

[0143] Figure 12 A flowchart illustrating another communication method provided in an embodiment of this application;

[0144] Figure 13 A flowchart of another communication method provided for an embodiment of the present application is shown in FIG. 6;

[0145] Figure 14a A flowchart of another communication method provided for an embodiment of the present application is shown in FIG. 6;

[0146] Figure 14b A flowchart of another communication method provided for an embodiment of the present application is shown in FIG. 6;

[0147] Figure 14c A flowchart of another communication method provided for an embodiment of the present application is shown in FIG. 6;

[0148] Figure 15 A structural diagram of a communication device provided for an embodiment of the present application is shown in FIG. 7;

[0149] Figure 16 A structural diagram of another communication device provided for an embodiment of the present application is shown in FIG. 7. DETAILED DESCRIPTION

[0150] In order to solve the problem of low efficiency or incorrect switching of the UE between cross-SNPN networks, the present application provides a communication method. The present application will be described in further detail below with reference to the accompanying drawings. It should be understood that the specific operation method in the method embodiment introduced below can also be applied to the device embodiment or the system embodiment.

[0151] The next generation (i.e., 5G) mobile communication system architecture (NextGen / NG) is composed of a UE (or NextGen UE), a (wireless) access network ((radio) access network, (R)AN / NextGen (R)AN), a core network (core / NextGen core), and a data network (DN), wherein the UE, the access network, and the core network are the main components of the architecture, and logically they can be divided into user plane and control plane. The control plane is responsible for the management of the mobile network, and the user plane is responsible for the transmission of service data. Among them, the NG2 reference point is located between the access network control plane and the core network control plane, the NG3 reference point is located between the access network user plane and the core network user plane, and the NG6 reference point is located between the core network user plane and the data network.

[0152] It should be understood that in the present application, the UE is the entrance for mobile users to interact with the network, and can provide basic computing power, storage capacity, display service windows to users, and accept user operation input. The NextGen UE will adopt new air interface technology to establish signal connection and data connection with the AN, so as to transmit control signals and service data to the mobile network.

[0153] The access network is similar to the base station in the traditional network, deployed near the UE, provides access function for authorized users in a specific area, and can determine different quality transmission tunnels according to the level of the user, the demand of the service, etc. to transmit user data. The AN can manage its own resources, rationally utilize, provide access services for the UE on demand, and be responsible for forwarding control signals and user data between the UE and the core network.

[0154] The core network is responsible for maintaining the subscription data of the mobile network, managing the network elements of the mobile network, providing session management, mobility management, policy management, security authentication, etc. for the UE. When the UE is attached, it provides network access authentication for the UE; when the UE has a service request, it allocates network resources for the UE; when the UE moves, it updates the network resources for the UE; when the UE is idle, it provides a fast recovery mechanism for the UE; when the UE detaches, it releases the network resources for the UE; when the UE has service data, it provides data routing functions for the UE, such as forwarding uplink data to the data network; or receiving downlink data of the UE from the data network, forwarding to the AN, and thus sending to the UE.

[0155] The data network is a network that provides service for users, and the client is generally located in the UE and the server is located in the data network. The data network can be a private network such as a local area network, can be an external network not controlled by the operator such as the Internet, or can be a dedicated network jointly deployed by the operator such as a network providing IP multimedia network subsystem (IMS) service.

[0156] The UE is a device with wireless transceiver function, which can be deployed on land, including indoor or outdoor, handheld, wearable or vehicle-mounted; can also be deployed on water (such as ships, etc.); can also be deployed in the air (such as airplanes, balloons and satellites, etc. The terminal device can communicate with the core network through the radio access network (RAN), and exchange voice and / or data with the RAN. The terminal device can be a mobile phone, a tablet computer (Pad), a computer with wireless transceiver function, a mobile internet device (MID), a wearable device, a virtual reality (VR) terminal device, an augmented reality (AR) terminal device, a wireless terminal in industrial control, a wireless terminal in self driving, a wireless terminal in remote medical treatment, a wireless terminal in smart grid, a wireless terminal in transportation safety, a wireless terminal in smart city, a wireless terminal in smart home, etc. The embodiments of the present application do not limit the application scenarios. The embodiments of the present application do not limit the specific technology, device form and name of the terminal device.

[0157] The access network can include an access network device. The access network device is a device in a network for accessing a terminal device to a wireless network. The access network device can be a node in a wireless access network, also referred to as a base station, and can also be referred to as a radio access network (RAN) node (or device). The network device can include an evolved Node B (eNB or e-NodeB, evolutional Node B) in a long term evolution (LTE) system or an evolved LTE system (LTE-Advanced, LTE-A), such as a conventional macro base station eNB and a micro base station eNB in a heterogeneous network scenario, or can also include a next generation Node B (gNB) in a 5th generation mobile communication technology (5th generation, 5G) new radio (new radio, NR) system, or can also include a radio network controller (RNC), a Node B (Node B, NB), a base station controller (base station controller, BSC), a base transceiver station (base transceiver station, BTS), a transmission reception point (transmission reception point, TRP), a home base station (for example, home evolved NodeB, or home Node B, HNB), a baseband unit (base band unit, BBU), a baseband pool BBU pool, or a WiFi access point (access point, AP), or can also include a centralized unit (centralized unit, CU) and a distributed unit (distributed unit, DU) in a cloud radio access network (cloud radio access network, CloudRAN) system, and the embodiments of the present application are not limited. In a separate deployment scenario where the access network device includes a CU and a DU, the CU supports radio resource control (radio resource control, RRC), packet data convergence protocol (packet data convergence protocol, PDCP), service data adaptation protocol (service data adaptation protocol, SDAP) and other protocols; the DU mainly supports radio link control layer (radio link control, RLC), media access control layer (media access control, MAC) and physical layer protocols.

[0158] The core network can include the following network elements or nodes:

[0159] An access management network element (the embodiment of the present application can also be referred to as an access mobile management network element), which is mainly used for attachment, mobility management, tracking area update process of a terminal in a mobile network, and the access management network element terminates non-access stratum (NAS) messages, completes registration management, connection management, and reachability management, and distributes a tracking area list (TA list) and mobility management, and transparently routes session management (SM) messages to a session management network element. In a 5th generation (5G) communication system, the access management network element can be an access and mobility management function (AMF), and in a future communication system (such as a 6G communication system), the mobility management network element can still be an AMF network element, or can also have other names, which are not limited by the present application.

[0160] A session management network element, which is mainly used for session management in a mobile network, such as session establishment, modification, and release. The specific functions are, for example, allocating an internet protocol (IP) address for a terminal and selecting a user plane network element that provides message forwarding functions. In a 5G communication system, the session management network element can be a session management function (SMF), and in a future communication system (such as a 6G communication system), the session management network element can still be an SMF network element, or can also have other names, which are not limited by the present application.

[0161] A user plane network element, which is mainly used for processing user messages, such as forwarding, charging, lawful interception, etc. The user plane network element can also be referred to as a protocol data unit (PDU) session anchor (PSA). In a 5G communication system, the user plane network element can be a user plane function (UPF), and in a future communication system (such as a 6G communication system), the user plane network element can still be a UPF network element, or can also have other names, which are not limited by the present application.

[0162] The policy control network element includes a user subscription data management function, a policy control function, a charging policy control function, a quality of service (QoS) control, and the like. In the 5G communication system, the policy control network element can be a policy control function (PCF). In future communication systems (e.g., a 6G communication system), the policy control network element can still be a PCF network element, or can have another name, which is not limited in the present application.

[0163] The network slice selection function network element is mainly used for selecting a suitable network slice for a service of a terminal device. In the 5G communication system, the network slice selection network element can be a network slice selection function (NSSF) network element. In future communication systems (e.g., a 6G communication system), the network slice selection network element can still be an NSSF network element, or can have another name, which is not limited in the present application.

[0164] The network storage function network element is mainly used for providing a registration and discovery function of a network element or a service provided by the network element. In the 5G communication system, the network storage function network element can be a network repository function (NRF). In future communication systems (e.g., a 6G communication system), the network storage function network element can still be an NRF network element, or can have another name, which is not limited in the present application.

[0165] The network data analysis network element can collect data from various network functions (NFs), such as a policy control network element, a session management network element, a user plane network element, an access management network element, and an application function network element (through a network capability exposure function network element), and perform analysis and prediction. In the 5G communication system, the network data analysis network element can be a network data analytics function (NWDAF). In future communication systems (e.g., a 6G communication system), the network data analysis network element can still be an NWDAF network element, or can have another name, which is not limited in the present application.

[0166] The unified data management network element is mainly used for managing subscription information of a terminal device. In the 5G communication system, the unified data management network element can be a unified data management (UDM). In future communication systems (e.g., a 6G communication system), the unified data management network element can still be a UDM network element, or can have another name, which is not limited in the present application.

[0167] Unified data storage network element, mainly used for storing structured data information, including subscription information, policy information, and network data or service data with standard format definition. In the 5G communication system, the unified data storage network element can be a unified data repository (UDR). In future communication systems (such as 6G communication systems), the unified data storage network element can still be a UDR network element, or it can also have other names, which are not limited by the present application.

[0168] Authentication service function network element, mainly used for security authentication of terminal devices. In the 5G communication system, the authentication service function network element can be an authentication server function (AUSF). In future communication systems (such as 6G communication systems), the authentication service function network element can still be an AUSF network element, or it can also have other names, which are not limited by the present application.

[0169] Network capability exposure network element, which can expose part of the network functions to applications in a controlled manner. In the 5G communication system, the network capability exposure network element can be a network exposure function (NEF). In future communication systems (such as 6G communication systems), the network capability exposure network element can still be an NEF network element, or it can also have other names, which are not limited by the present application.

[0170] Application function network element, which can provide service data of various applications to the control plane network element of the operator's communication network, or obtain network data information and control information from the control plane network element of the communication network. In the 5G communication system, the application function network element can be an application function (AF). In future communication systems (such as 6G communication systems), the application function network element can still be an AF network element, or it can also have other names, which are not limited by the present application.

[0171] Data network, mainly used for providing data transmission services for terminal devices. The data network can be a private network, such as a local area network, or a public data network (PDN) network, such as the Internet, or a dedicated network jointly deployed by operators, such as an IP multimedia core network subsystem (IMS) service.

[0172] It should be understood that the above network elements or functions can be network elements in a hardware device, software functions running on a dedicated hardware, or virtualized functions instantiated on a platform (e.g., a cloud platform). Optionally, the above network elements or functions can be implemented by one device, or by multiple devices together, or can be a functional module within a device, and the embodiments of the present application do not make specific limitations thereto.

[0173] For the convenience of description, in the subsequent description of the present application, the access management network element is taken as the AMF network element, and the network slice selection function network element is taken as the NSSF network element. Further, the AMF network element is referred to as AMF, and the NSSF network element is referred to as NSSF. That is, the AMF described in the subsequent description of the present application can be replaced by an access management network element, and the NSSF can be replaced by a network slice selection function network element.

[0174] As shown in Figure 3 , taking the 5G architecture as an example, the user plane of the communication system provided in the embodiments of the present application can include a user plane function (UPF), and the core network control plane can include an authentication server function (AUSF), a core network access and mobility management function (AMF), a session management function (SMF), a network slice selection function (NSSF), a network exposure function (NEF), a network function repository function (NRF), a unified data management (UDM), a policy control function (PCF), and an application function (AF).

[0175] As shown in Figure 3 , the core network control plane adopts a service-oriented architecture, and the interaction between the control plane network elements adopts a service calling manner to replace the point-to-point communication manner in the traditional architecture. In the service-oriented architecture, the control plane network element will open services to other control plane network elements for calling by other control plane network elements; in the point-to-point communication, there will be a specific set of messages for the communication interface between the control plane network elements, which can only be used by the control plane network elements at both ends of the interface when communicating.

[0176] For example, the UPF can be used to perform user data packet forwarding according to the routing rules of the SMF, such as sending uplink data to the DN or other UPF, and / or forwarding downlink data to other UPF or RAN. The AUSF can be used to perform security authentication of the UE. The AMF can be used for access management and mobility management (MM) of the UE, responsible for state maintenance of the UE, reachability management of the UE, forwarding of non-MM non-access-stratum (NAS) messages, and forwarding of SM N2 messages. The SMF can be used for UE session management, allocating resources for the session of the UE, and releasing resources; wherein the resources include session QoS, session path, forwarding rules, etc. The NSSF can be used to select network slices for the UE. The NEF can be used to open network functions to third parties in the form of northbound application programming interface (API) interfaces. The NRF can be used to provide network function entity information storage and selection functions for other network elements. The UDM can be used for user subscription context (or subscription data, UE context, etc.) storage and management. The PCF can be used for user policy management. The AF can be used for application management.

[0177] As shown in Figure 1 and Figure 2 , the current NPN network includes PNI-NPN and SNPN.

[0178] Among them, the PNI-NPN can be implemented using network slices in the PLMN, and additional closed access group (CAG) functions are used to prevent unauthorized UEs from attempting to access and select PNI-NPN. The CAG can be used to identify a group of users who are allowed to access cells associated with the CAG (i.e., CAG cells). In order to prevent UEs that are not allowed to access CAG cells from automatically selecting and accessing CAG cells, the CAG cell broadcasts one or more CAG identifiers (IDs), the UE is configured with a list of available CAGs and an indication (indicating whether the UE is only allowed to access the 5GS through the CAG cell), and the UDM UE subscription data includes the available CAG list and the indication.

[0179] SNPN network is independently deployed without relying on PLMN network, and the SNPN network uses a PLMN ID and a network identifier (NID) to identify, wherein the PLMN ID can be a reserved inherent value for a third-party operator, or a specific value of a PLMN operator deploying the SNPN. In the SNPN network, a cell broadcasts a PLMN ID and a NID, and a UE selects an accessed NPN network according to the broadcast information and configured network selection information. If the UE finds that the combination of the PLMN ID and the NID1 included in the configured network selection information is different from the combination of the broadcast PLMN ID or the combination of the PLMN ID and the NID2, the UE will not select to access it.

[0180] As shown in Figure 4 , the PNI-NPN limits the access of the UE by broadcasting a CAG ID and configuring a CAG ID available to the UE, and the SNPN allows the UE to correctly select a cell and a network by broadcasting a PLMN ID and a NID.

[0181] As shown in Figure 1 , the R16 currently supports interworking between the SNPN and the PLMN through the N3IWF architecture, and the UE can be subscribed to the SNPN and the PLMN respectively. Among them, the UE can use the private network subscription of the SNPN to select an SNPN ID, access an SNPN base station, and perform 3GPP registration in an SNPN network. In addition, the UE can use the public network subscription of the PLMN to select a PLMN ID and select a PLMN N3IWF, establish a PDU session to access the PLMN N3IWF in the SNPN network, and perform N3GPP registration in the PLMN network.

[0182] As shown in Figure 2 , the SNPN under R17 needs to support the terminal to access the SNPN network using "external subscription", that is, the user subscription of the terminal is owned by an external entity (such as a mobile network operator (MNO)) independent of the SNPN network, and the SNPN network allows such terminals to access the SNPN using external subscription. For example, when the UE accesses the SNPN network, the SNPN network entity (such as AMF / SMF) needs to interact with the PLMN network entity (such as UDM / AUSF), such as requesting the PLMN network to authenticate and authenticate the UE, requesting the PLMN network to provide the subscription information of the UE, and requesting the PLMN network to configure resources for the PDU session of the UE, etc. In this case, the roaming architecture is used to support the interworking between the SNPN and the PLMN, and the UE is only subscribed to the PLMN, and the subscription data can be stored in the UDM of the PLMN, such as Figure 2As shown, the UE selects a SNPN ID using the public network subscription of the PLMN, selects a SNPN base station, registers in the SNPN network, and establishes a PDU session in the SNPN, and the SNPN network determines the local breakout (LBO) / home routed (HR) mode according to the UE public network subscription.

[0183] In addition to the user subscription of the terminal being provided by the PLMN, the user subscription can also be provided by a third-party SNPN network, and the interworking of the two SNPNs in this case is similar to the above description.

[0184] In addition, the user subscription can also be provided by a third-party AAA (authentication, authorization, accounting) server (AAA-server, AAA-S). As shown, the network elements of the SNPN, such as the AMF and the SMF, need to authenticate the UE or obtain the saved subscription data from the AAA server, and interact with the AAA server through an AAA proxy (AAA-proxy, AAA-P) (such as the NSSAAF or the AUSF). Figure 5

[0185] When the external subscription of the UE is provided by other PLMNs, SNPNs, or AAA servers, the UE moves between two SNPNs, both of which can be connected to the PLMN, SNPN, or AAA server that saves the subscription of the UE as shown above. In another scenario, when the UE moves from SNPN #1 to SNPN #2, SNPN #2 can also be an SNPN that saves the subscription of the UE. In addition, the UE can also move between an SNPN and a PLMN. In one scenario, when the UE moves from SNPN #1 to a PLMN, the PLMN can be a VPLMN or a home PLMN (HPLMN) that saves the subscription of the UE.

[0186] As shown, several typical UE cross-private network movement scenarios are shown. Figure 6 to Figure 9

[0187] Figure 6 In this scenario, the UE can move from SNPN #1 to SNPN #2. Among them, the subscription of the UE is saved by a third-party AAA server, and SNPN #1 and SNPN #2 can be connected to this AAA server. SNPN #1 and SNPN #2 support the roaming interworking mode shown. Figure 2

[0188] Figure 7a ​​​In the scenario, the UE can move from SNPN #1 to SNPN #2 or a visited PLMN (VPLMN). Where the UE subscription is held by the UDM of the HPLMN, SNPN #1 and SNPN #2 or VPLMN can be connected to this HPLMN. The roaming interworking between SNPN #1 and HPLMN, and between SNPN #2 or VPLMN and HPLMN is supported. Figure 1 The N3IWF interworking mode shown.

[0189] Figure 7b In the scenario, the UE can move from SNPN #1 to SNPN #2 or a visited PLMN (VPLMN). Where the UE subscription is held by the UDM of the HPLMN, SNPN #1 and SNPN #2 or VPLMN can be connected to this HPLMN. The roaming interworking between SNPN #1 and HPLMN, and between SNPN #2 or VPLMN and HPLMN is supported.

[0190] Figure 7c In the scenario, the UE can move between SNPN #1 and SNPN #2. Where the UE subscription is held by the UDM of the HPLMN, SNPN #1 and SNPN #2 can be connected to this HPLMN. The roaming interworking between SNPN #1 and HPLMN, and between SNPN #2 and HPLMN through N3IWF interworking is supported. The UE can establish a HR PDU session through SNPN #1, that is, the anchor UPF is in the PDU session of the HPLMN. The UE can establish a PDU session to the HPLMN in the manner shown. Figure 1 The roaming interworking mode shown.

[0191] Figure 8 In the scenario, the UE can move from SNPN #1 to HPLMN. Where the UE subscription is held by the UDM of the HPLMN. The roaming interworking between SNPN #1 and HPLMN is supported. Figure 2 The roaming interworking mode shown.

[0192] Figure 9 In the scenario, the UE can move from SNPN #1 to HPLMN. Where the UE subscription is held by the UDM of the HPLMN. The roaming interworking between SNPN #1 and HPLMN is supported. Figure 2 The roaming interworking mode shown.

[0193] The application provides a communication method for solving the problem of low switching efficiency or incorrect switching of the UE between cross-NPN networks.

[0194] The communication method can be performed by a terminal device and a first network device. The terminal device is registered in a first network (or source network or home network), and the first network device belongs to a second network (or destination network). The first network and / or the second network are NPN networks. Therefore, when the terminal device performs cross-non-public network switching between the first network and the second network, the communication method provided in the embodiments of the present application can improve the switching efficiency and success rate. It should be understood that the scenario of switching the terminal device between the first network and the second network can refer to the scenario shown in FIG. 8. Figure 6 to Figure 9

[0195] For example, the terminal device is UE. The communication method provided in the embodiments of the present application can include the following steps shown in FIG. 9: Figure 10

[0196] S101: The UE establishes a first PDU session in the first network.

[0197] The first PDU session is associated with a data network name (DNN) and single network slice selection assistance information (S-NSSAI).

[0198] The process of establishing the first PDU session is not limited in the present application.

[0199] S102: The UE sends a first registration request message to a first network device in the second network.

[0200] Correspondingly, the first network device receives the first registration request message. The first registration request message can be used to request registration to the second network.

[0201] For example, the first network device is an AMF deployed in the second network.

[0202] Optionally, the first registration request message can carry a cross-non-public network switching indication (or cross-private network switching indication), which is used to indicate that the terminal device performs cross-non-public network switching.

[0203] S103: The first network device obtains the context of the UE.

[0204] The context of the UE can be stored in a second network device of the first network or a data storage node.

[0205] ​​The second network device is deployed in the AMF of the first network for example, and the AMF can manage the registration request of the UE in the first network. The first network device can obtain the information of the UE registered in the first network from the UDM, such as a temporary identifier, and then obtain the information of the second network device, so as to obtain the context of the UE through the second network device.

[0206] The data storage node can be shared by the first network and the second network, so the context of the UE registered in the first network can be obtained by the first network device. For example, the data storage node is deployed in the second network and shared by the first network and the second network (i.e., the context of the UE registered in the first network and the second network is stored), or the data storage node can be deployed in a third network other than the first network and the second network, and shared by the first network and the second network. The data storage node is UDM or AAA for example.

[0207] S104: The first network device determines that the UE has registered in the first network according to the context of the UE.

[0208] For example, the context of the UE can include the identifier of the first network or the identifier of the second network device, and the first network device can know that the UE has registered in the first network according to the identifier of the first network or the identifier of the second network device.

[0209] S105: The first network device determines the first information according to the interworking mode between the first network and the second network.

[0210] The first information can indicate how to switch the PDU session in the UE registration process.

[0211] Specifically, the interworking mode between the first network and the second network includes: no interworking between the first network and the second network, interworking between the first network and the second network based on N3IWF as shown in the figure, and interworking between the first network and the second network based on roaming. Figure 1

[0212] It should be understood that in S105, the interworking mode between the first network and the second network is different, and the first information is different.

[0213] ​Exemplarily, in the case that the first network and the second network are not interworked, the first information can indicate that the first network and the second network are not interworked, for example, the first information is indication information of non-interworking. Alternatively, the first information can indicate that the UE sends a first PDU session request to the first network device. The first PDU session request includes a request type (request type information element) with a value of initial request, or in other words, the first PDU session request is used to request to establish an initial PDU session. The first PDU session request message includes information of the DNN and information of the S-NSSAI, or in other words, the first PDU session request message includes information of the DNN associated with the PDU session established by the UE in the first network and information of the S-NSSAI associated with the PDU session.

[0214] In the case that the first network and the second network are interworked based on N3IWF, the first information can indicate that the first network and the second network are interworked based on N3IWF, for example, the first information is indication information of interworking based on N3IWF. Alternatively, the first information can indicate that the UE sends a second PDU session request to the first network device, sends a second registration request to the second network device through N3IWF, and sends a third PDU session request message to the second network device. The second PDU session request is used to request to establish a second PDU session, and the UE can establish a connection between the UE and the N3IWF through the second PDU session. The second registration request can be used to request to register in the first network through the N3GPP mode. The third PDU session request message includes a request type type with a value of existing PDU session, or in other words, the third PDU session request message is used to establish an existing PDU session. The third PDU session request message includes information of the DNN and information of the S-NSSAI, or in other words, the third PDU session request message includes information of the DNN associated with the PDU session established by the UE in the first network and information of the S-NSSAI associated with the PDU session.

[0215] In a case that the first network and the second network interwork based on roaming, the first information can indicate that the first network and the second network interwork based on roaming, for example, the first information is indication information of interworking based on roaming. Alternatively, the first information can be used to instruct the UE to send a fourth PDU session request message to the first network device. The fourth PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the fourth PDU session request message is used to request to establish an existing PDU session. The fourth PDU session request message includes information of the DNN and information of the S-NSSAI, or in other words, the fourth PDU session request message includes information of the DNN associated with the PDU session established by the UE in the first network and information of the S-NSSAI associated with the PDU session.

[0216] S106: The first network device sends the first information to the UE.

[0217] Correspondingly, the UE receives the first information from the AMF#2, and the first information is determined according to the interworking mode between the SNPN#1 and the SNPN#2.

[0218] S107: The UE establishes a PDU session of the UE according to the first information, and the PDU session is associated with the DNN and the S-NSSAI.

[0219] Specifically, in a case that the first network and the second network do not interwork, or in a case that the first information indicates that the first network and the second network do not interwork, or in a case that the UE is instructed to send a first PDU session request to the first network device, the UE can send a first PDU session request message to the first network device, and the first PDU session includes a request type information element with a value of initial request and information of the DNN and information of the S-NSSAI. Accordingly, in a case that the first network and the second network do not interwork, the UE can newly establish a PDU session associated with the DNN and the S-NSSAI in the second network, thereby realizing the recovery of the PDU session associated with the DNN and the S-NSSAI. Since the PDU session recovery mode based on N3IWF interworking and the PDU session recovery mode based on roaming interworking are both not feasible in the case that the first network and the second network do not interwork, the UE performs a corresponding switching process according to the first information, which can improve the switching efficiency and avoid trial and error.

[0220] In a case that the first network and the second network interwork based on the N3IWF, or in a case that the first information is used to indicate that the first network and the second network interwork based on the N3IWF, or is used to indicate that the UE sends the second PDU session request to the first network device, sends the second registration request to the second network device through the N3IWF, and sends the third PDU session request message to the second network device, the UE can send the second PDU session request message to the first network device, the second PDU session request being used to request to establish a second PDU session. The UE can also establish a connection with the N3IWF through the second PDU session, the N3IWF belonging to the first network. Thereafter, the UE can send the second registration request to the second network device through the connection, the second registration request being used to request to register to the first network in a N3GPP manner. The UE can also send the third PDU session request message to the second network device, the third PDU session request message being used to request to establish an existing PDU session (the PDU session can be referred to as a third PDU session), the third PDU session request message comprising the information of the DNN and the information of the S-NSSAI. Accordingly, in a case that the first network and the second network interwork based on the N3IWF, the UE can establish the third PDU session associated to the information of the DNN and the information of the S-NSSAI through the N3IWF and the second network device, and realize the restoration of the PDU session of the UE associated to the DNN and the S-NSSAI. Since in the case of interworking based on the N3IWF, neither the PDU session restoration manner based on non-interworking nor the PDU session restoration manner based on roaming interworking is feasible, the UE performs the corresponding switching process according to the first information, which can improve the switching efficiency and avoid trial and error.

[0221] In a case that the first network and the second network interwork based on roaming, or in a case that the first information is used to indicate that the first network and the second network interwork based on roaming, or is used to indicate that the UE sends the fourth PDU session request message to the first network device, the UE can send the fourth PDU session request message to the first network device. The fourth PDU session request message comprises a request type information element with a value of existing PDU session, or is used to request to establish an existing PDU session (the PDU session can be referred to as a fourth PDU session). The fourth PDU session request message comprises the information of the DNN and the information of the S-NSSAI. Accordingly, in a case that the first network and the second network interwork based on roaming, the UE can establish the fourth PDU session associated to the information of the DNN and the information of the S-NSSAI through the first network device, and realize the restoration of the PDU session of the UE associated to the DNN and the S-NSSAI. Since in the case of roaming interworking, neither the PDU session restoration manner based on non-interworking nor the PDU session restoration manner based on N3IWF interworking is feasible, the UE performs the corresponding switching process according to the first information, which can improve the switching efficiency and avoid trial and error.

[0222] Based on the above procedure, after registering from the first network to the second network, the UE can receive first information from the first network device in the second network, since the first information is related to the interworking mode between the first network and the second network, the PDU session associated to the DNN and the S-NSSAI of the UE can be more efficiently resumed according to the first information, so as to improve the switching efficiency and ensure the service continuity.

[0223] It should be understood that one of the above first network and the second network is an NPN network. For example, at least one of the first network and the second network is an SNPN.

[0224] In the case of roaming interworking between the first network and the second network, data lossless switching of the UE path can also be supported. For example, the UE can carry a lossless switching indication in the fourth PDU session request message. Alternatively, the lossless switching indication can also be sent independently of the fourth PDU session request message. The first network device can send the lossless switching indication to the SMF, wherein the SMF is an SMF managing the first PDU session; or the SMF is an intermediate SMF connected to the SMF managing the first PDU session, and thereafter the lossless switching indication can be forwarded by the intermediate SMF to the SMF managing the first PDU session.

[0225] After receiving the lossless switching indication, the SMF managing the first PDU session can send second information to the first UPF to instruct the first UPF to send an end marker to the first access network element after the path switching of the first PDU session, and to instruct the first UPF to forward the downlink data from the first access network element to the UE through the switched path, the downlink data including the end marker. In addition, the SMF managing the first PDU session can send third information to the first access network element to instruct the first access network element to forward the downlink data of the UE buffered by the first access network element to the first UPF until the end marker is received and forwarded. The above first PDU session is the PDU session between the first access network element and the first UPF. Accordingly, the downlink data of the UE before path switching can be forwarded by the first UPF and the first access network element to the UE through the switched path, realizing lossless path switching.

[0226] Hereinafter, the first network is taken as SNPN#1, and the second network is taken as SNPN#2 as an example, wherein the SNPN#2 here can also be replaced by VPLMN#2 (i.e. one VPLMN).

[0227] As shown in Figure 11 A communication method provided by an embodiment of the present application can include the following procedure:

[0228] S201: The UE registers with SNPN#1 and establishes a first PDU session. The SMF and UPF of the first PDU session are SMF#1 and UPF#1, respectively. This first PDU session can be associated with the first DNN and the first S-NSSAI.

[0229] S202: SMF#1 sends an SMF registration message to the UDM or AAA server. This registration message may include the UE ID, SNPN#1ID, SMF#1ID, and the ID of the first PDU session. The UDM or AAA server may be deployed in a PLMN or a third-party network.

[0230] S203: The UE moves to the target network SNPN#2, and the UE sends a first registration request message to AMF#2 in SNPN#2. Figure 11 (AMF#2 is the first network device) and carries the UE ID.

[0231] Optionally, the first registration request message may carry a cross-private network (PPPoE) indication. This PPPoE HO indication indicates that the purpose of the AMF#2 registration is a cross-private network handover, not an initial registration. The HO indication can be a location update registration or a new cell.

[0232] S204: If there is an interface between AMF#2 and AMF#1, AMF#2 can obtain the UE's context from AMF#1, including at least one of the following: UEID, SNPN#1ID, SMF#1ID, or the ID of the first PDU session. The information from AMF#1 can be obtained by AMF#2 from the UDM or AAA server. Otherwise, if there is no interface between AMF#2 and AMF#1, AMF#2 can obtain the UE's context from the UDM or AAA.

[0233] S205: AMF#2 determines that the UE is performing a cross-private network handover based on the UE's cross-private network HO indication or UE context, such as SNPN#1ID or SMF#1ID, and determines the handover method based on the interoperability between SNPN#2 and SNPN#1 (no interoperability, interoperability based on N3IWF, or interoperability based on roaming), such as determining whether the UE performs the handover according to roaming interoperability or not.

[0234] S206: AMF#2 sends a registration response message to the UE, carrying the handover mode indication (i.e., the first information). If SNPN#1 and SNPN#2 do not interwork, the handover mode information can indicate that the UE performs handover in a non-interworking manner, or indicate that SNPN#1 and SNPN#2 do not interwork; if SNPN#1 and SNPN#2 interwork in an N3IWF-based manner, the handover mode information can indicate that the UE performs handover in an N3IWF-based interworking manner, or indicate that SNPN#1 and SNPN#2 interwork in an N3IWF-based manner; if SNPN#1 and SNPN#2 interwork in a roaming manner, the handover mode information can indicate that the UE performs handover in a roaming interworking manner, or indicate that SNPN#1 and SNPN#2 interwork in a roaming manner.

[0235] Then one of S207-S209 is performed.

[0236] S207: If SNPN#1 and SNPN#2 do not interwork, the UE re-establishes a PDU session, i.e., sends a first PDU session request message with a request type of initial request to AMF#2. The first PDU session request message carries the first DNN and the first S-NSSAI, so the newly established PDU session can be associated with the first DNN and the first S-NSSAI.

[0237] In this case, the handover mode indication can be used to indicate that SNPN#1 and SNPN#2 do not interwork, or to indicate that the UE sends the first PDU session request to AMF#2.

[0238] S208: If SNPN#1 and SNPN#2 interwork in an N3IWF-based manner, the UE first establishes an N3IWF-based PDU session (i.e., a second PDU session) connected to SNPN#1 in SNPN#2 to establish a user plane connection; then the UE initiates N3GPP registration in SNPN#1 through N3IWF, or sends a second registration request to AMF#1 through N3IWF to request registration to the first network through N3GPP, and then the UE can initiate a PDU session handover flow from 3GPP to N3GPP, i.e., initiate a third PDU session request message with a request type of existing PDU session, and the third PDU session request message carries the first DNN and the first S-NSSAI, so the newly established N3GPP PDU session can be associated with the first DNN and the first S-NSSAI.

[0239] In this case, the switching mode indication can be used to indicate that the interworking between SNPN#1 and SNPN#2 is based on N3IWF, or to indicate that the UE initiates a PDU session from SNPN#1 to SNPN#2 in SNPN#2.

[0240] S209: If the interworking between SNPN#1 and SNPN#2 is based on roaming, the UE initiates a PDU session switching procedure from SNPN#1 to SNPN#2 in SNPN#2, i.e., sends a fourth PDU session request message to AMF#2 with request type as existing PDU session, and then performs S210-S220. Among them, the fourth PDU session request message carries the information of the DNN and the information of the S-NSSAI to request to resume the PDU session associated with the DNN and S-NSSAI.

[0241] Optionally, if the UE needs lossless switching, a lossless switching indication can be additionally carried in the fourth PDU session request.

[0242] In this case, the switching mode indication can be used to indicate that the interworking between SNPN#1 and SNPN#2 is based on roaming, or to indicate that the UE initiates a PDU session switching procedure from SNPN#1 to SNPN#2 in SNPN#2.

[0243] S210: AMF#2 determines that the UE is performing cross-private network switching according to the cross-private network HO indication, the request type of existing PDU session or the SMF#1 ID, and determines to insert an I-SMF.

[0244] S211: AMF#2 sends an SMF discovery request message to NRF.

[0245] S212: NRF sends a candidate SMF to AMF#2 according to the SMF discovery request message.

[0246] S213: AMF#2 selects SMF#2 as I-SMF according to the candidate SMF.

[0247] S214: AMF#2 sends the fourth PDU session request message and the cross-private network HO indication to SMF#2.

[0248] S215: SMF#2 sends the fourth PDU session request message and the cross-private network HO indication to SMF#1.

[0249] Optionally, if SMF#2 receives the lossless switching indication sent by the UE, SMF#2 can forward the lossless switching indication to SMF#1.

[0250] Optionally, when SMF#2 inserts UPF#2 as I-UPF (e.g. UPF#2) according to existing mechanism, additionally, SMF#2 can configure charging rules on I-UPF according to HO indication.

[0251] S216: SMF#1 sends path switch indication to UPF#1 to instruct UPF#1 to switch path to UE.

[0252] For example, UPF#1 switches the path from UPF#1 to UE from UPF#1→RAN#1→UE to UPF#1→UPF#2→RAN#2→UE.

[0253] In addition, SMF indicates UPF#1 to keep traffic continuity according to cross-private network HO indication and local configuration or lossless switch indication through second information.

[0254] S217: UPF#1 sends end marker to RAN#1 on old path according to second information of SMF after switching to new path.

[0255] Here, the old path refers to the path between UPF#1 and RAN#1.

[0256] S218: SMF#1 (or AMF#1) sends release request to RAN#1 to request RAN#1 to release first PDU session.

[0257] In addition, SMF#1 (or AMF#1) can determine that lossless switch is needed according to local configuration after receiving cross-private network HO indication, and thus sends third indication to RAN#1 to instruct RAN#1 to forward buffered downlink data (including end marker sent by UPF#1) to UPF#1 before releasing context. Subsequently, data from RAN#1 can be forwarded to UE by UPF#1 through new path.

[0258] Alternatively, SMF#1 / AMF#1 can instruct RAN#1 to forward buffered downlink data (including end marker sent by UPF#1) to UPF#1 before releasing context through third information after receiving lossless switch indication from SMF#2. Subsequently, data from RAN#1 can be forwarded to UE by UPF#1 through new path.

[0259] S219: RAN#1 forwards buffered UE data to UPF#1, and releases resources of first PDU session, and the data includes end marker.

[0260] S220: UPF#1 forwards the data from RAN#1 to UE in the new path, i.e., forwards the data in the path of UPF#1→UPF#2→RAN#2→UE. The subsequent data of UE is forwarded in the path of .

[0261] If UPF#1 receives the indication of switching path from SMF, it needs to forward the data from RAN#1 first before forwarding the new data in the downlink direction, i.e., UPF#1 forwards the packets received from the original path first until the end marker is received, and then forwards the new downlink data packets.

[0262] S221: The PDU session is resumed in SNPN#2.

[0263] By using the above method, the UE can be instructed by the AMF#2 to adopt the cross-private network switching mode, and the UE can be instructed to perform cross-private network switching by the indicated switching mode, so that the UE can be correctly switched to the target network, thereby improving the efficiency of cross-private network switching. In addition, when the cross-private network switching is performed based on the roaming mode, the UE can be provided with lossless data switching.

[0264] As shown in Figure 12 , another communication method provided by the embodiments of the present application is described by taking the first network as SNPN#1 and the second network as HPLMN#2 as an example. Here, the HPLMN#2 can also be replaced by a home SNPN (H-SNPN) H-SNPN#2, and the scenario is as shown in Figure 8 .

[0265] As shown in Figure 12 , the another communication method provided by the embodiments of the present application can include the following flow:

[0266] S301: The UE registers in SNPN#1 through RAN#1 and establishes a first PDU session. The SMF and UPF of the first PDU session are SMF#1 and UPF#1 respectively. The first PDU session can be associated with a first DNN and a first S-NSSAI.

[0267] S302: The SMF#2 sends an SMF registration message to the UDM. The registration message can include the UE ID, the SNPN#1 ID, the SMF#1 ID and the ID of the first PDU session. The UDM is deployed in HPLMN#2.

[0268] S303: The UE moves to the target network HPLMN#2, and sends a first registration request message to the AMF#2 in HPLMN#2 Figure 12The first registration request message can further carry a cross- private network HO indication. The cross-private network HO indication is used to indicate that the purpose of the AMF#2 registration is cross-private network handover, rather than initial registration. The HO indication can be a location update registration or a new information element.

[0269] S304: If there is an interface between AMF#2 and AMF#1, AMF#2 can obtain the context of the UE from AMF#1, including at least one of the UE ID, the SNPN#1 ID, the SMF#1 ID, or the ID of the first PDU session; otherwise, if there is no interface between AMF#2 and AMF#1, AMF#2 obtains the context of the UE from the UDM.

[0270] S305: AMF#2 determines that the UE is performing cross-private network handover according to the cross-private network HO indication of the UE or the UE context, such as the SNPN#1 ID or the SMF#2 ID, and determines the handover mode according to the interworking mode of HPLMN#2 and SNPN#1, wherein the interworking mode of HPLMN#2 and SNPN#1 is roaming interworking.

[0271] S306: AMF#2 sends a registration response message to the UE, carrying the handover mode indication (i.e., the first information). The handover mode information can indicate that the UE performs handover according to the roaming interworking mode, or indicate that the SNPN#1 and the HPLMN#2 perform roaming interworking.

[0272] S307: The UE initiates a PDU session handover procedure from SNPN#1 to HPLMN#2 in HPLMN#2, i.e., sends a fourth PDU session request message with a request type of existing PDU session to AMF#2. The fourth PDU session request message carries information of the DNN and information of the S-NSSAI to request to resume the PDU session associated with the DNN and the S-NSSAI.

[0273] Optionally, if lossless handover is required by the UE, a lossless handover indication can be additionally carried in the session request.

[0274] S308: AMF#2 determines that the UE is performing cross-private network handover according to the cross-private network HO indication, the request type of existing PDU session, or the SMF#1 ID, and determines to insert an I-SMF.

[0275] S309: AMF#2 sends an SMF discovery request to NRF.

[0276] S310: NRF sends candidate SMFs to AMF#2 according to the SMF discovery request.

[0277] S311: AMF#2 selects SMF#2 as I-SMF according to the candidate SMF.

[0278] S312: AMF#2 sends a fourth PDU session request message and a cross-private network HO indication to SMF#2.

[0279] S313: SMF#2 sends the fourth PDU session request message and the cross-private network HO indication to SMF#2, and sends the cross-private network HO indication to SMF#1.

[0280] Optionally, if SMF#2 receives a lossless handover indication sent by the UE, SMF#2 can forward the lossless handover indication to SMF#1.

[0281] Optionally, when SMF#2 inserts UPF#2 as I-UPF (such as UPF#2) according to the existing mechanism, additionally, SMF#2 can configure charging rules on the I-UPF according to the HO indication.

[0282] S314: SMF#1 sends a path switching indication to UPF#1 to instruct UPF#1 to switch the path to the UE.

[0283] For example, UPF#1 switches the path from UPF#1 to RAN#1 to UE to UPF#1 to UPF#2 to RAN#2 to UE.

[0284] In addition, the SMF indicates the UPF#1 to maintain traffic continuity according to the cross-private network HO indication and the local configuration or the lossless handover indication through the second information.

[0285] S315: After switching to the new path, UPF#1 can send an end marker to RAN#1 on the old path according to the second information.

[0286] Here, the old path refers to the path between UPF#1 and RAN#1.

[0287] S316: SMF#1 (or AMF#1) sends a release request to RAN#1 to request RAN#1 to release the first PDU session.

[0288] Furthermore, upon receiving a cross-private network HO indication, SMF#1 (or AMF#1) can determine the need for lossless handover based on its local configuration. It can then instruct RAN#1 via third information to forward the cached downlink data (including the end marker sent by UPF#1) to UPF#1 before releasing the context. Alternatively, upon receiving a lossless handover indication from SMF#2, SMF#1 / AMF#1 can instruct RAN#1 via third information to forward the cached downlink data (including the end marker sent by UPF#1) to UPF#1 before releasing the context. Subsequently, UPF#1 can forward the data from RAN#1 to the UE via the new path.

[0289] S317: RAN#1 forwards the cached UE data to UPF#1, which includes an end marker, and releases the resources of the first PDU session.

[0290] S318: UPF#1 forwards data from RAN#1 to the UE via a new path, i.e., data is forwarded along the path UPF#1→UPF#2→RAN#2→UE. Subsequent data from the UE is then transmitted via... Forwarding via the path.

[0291] If UPF#1 receives a path switching instruction from SMF, it needs to forward data from RAN#1 before forwarding new data in the downlink direction. That is, UPF#1 forwards the messages received from the original path until it receives the end marker, and then forwards the new downlink data packets.

[0292] S318: Resume PDU session in HPLMN#2.

[0293] Using the above methods, when the first network and the second network share a UDM, the core network can instruct the UE to adopt a roaming-based cross-private network handover approach to improve the efficiency of cross-private network handover. Furthermore, it can provide lossless data handover for the UE.

[0294] For example Figure 9 In the scenario shown, the UE switches from SNPN#1 to HPLMN#2 (or H-SNPN#2). At this time, SNPN#1 and HPLMN#2 (or H-SNPN#2) share the core network. Therefore, the communication method provided in this application embodiment may include, as follows: Figure 13 The following steps are shown:

[0295] S401: The UE registers with SNPN#1 via RAN#1 and establishes a first PDU session. The SMF and UPF of the first PDU session are SMF#2 and UPF#2, respectively. This first PDU session can be associated with the first DNN and the first S-NSSAI.

[0296] S402: SMF#2 sends a SMF registration message to UDM. The registration message can include UE ID, SNPN#1 ID, SMF#2 ID and the ID of the first PDU session.

[0297] S403: The UE moves to the target network HPLMN#2, and sends a first registration request message to AMF#2 (as the first network device) in HPLMN#2, carrying the UE ID. The first registration request message can also carry a cross-private network HO indication. The cross-private network HO indication is used to indicate that the purpose of the registration of AMF#2 is cross-private network handover, rather than initial registration. The HO indication can be a location update registration or a new information element. Figure 13

[0298] S404: AMF#2 obtains the context of the UE from UDM.

[0299] S405: AMF#2 determines that the UE is performing cross-private network handover according to the cross-private network HO indication of the UE or the UE context, such as the SNPN#1 ID, and determines the handover mode according to the interworking mode between HPLMN#2 and SNPN#1, wherein the interworking mode between HPLMN#2 and SNPN#1 is roaming interworking.

[0300] S406: AMF#2 sends a registration response message to the UE, carrying the handover mode indication (i.e. the first information). The handover mode information can indicate that the UE performs handover according to roaming interworking, or indicate that the SNPN#1 and HPLMN#2 perform handover according to roaming interworking.

[0301] S407: The UE initiates a PDU session handover procedure from SNPN#1 to HPLMN#2 in HPLMN#2, i.e. sends a fourth PDU session request message with request type existing PDU session to AMF#2. The fourth PDU session request message carries the information of the DNN and the information of the S-NSSAI to request the PDU session associated with the DNN and S-NSSAI to be resumed.

[0302] Optionally, if lossless handover is required, a lossless handover indication can be additionally carried in the session request.

[0303] S408: AMF#2 determines that the UE is performing cross-private network handover according to the cross-private network HO indication, the request type of existing PDU session or the SNPN#1 ID.

[0304] S409: AMF#2 forwards the fourth PDU session request message and the cross-private network HO indication to SMF#2. ​

[0305] S410: The first PDU session is resumed at the HPLMN #2.

[0306] S411: The SMF #2 (or the AMF #2) sends a release request to the RAN #1 to request the RAN #1 to release the first PDU session.

[0307] In addition, after receiving the cross-private network HO indication, the SMF #2 / AMF #2 can determine according to local configuration that lossless handover is needed, and thus instructs the RAN #1 to forward the buffered downlink data to the UPF #2 before releasing the context through the third information. Alternatively, after receiving the lossless handover indication from the UE, the SMF #2 / AMF #2 can instruct the RAN #1 to forward the buffered downlink data to the UPF #2 before releasing the PDU session through the third information. Subsequently, the data from the RAN #1 can be forwarded to the UE by the UPF #2 through a new path.

[0308] S412: The RAN #1 forwards the buffered UE data to the UPF #2, and releases the resources of the first PDU session, the data including an end marker.

[0309] S413: The UPF #2 forwards the data packets from the RAN #1 on a new path, i.e., the data packets are forwarded on the UPF #2<->RAN #2<->UE; if the UPF #2 receives the indication of the switching path from the SMF, the packets received from the RAN #1 (i.e., the original path) need to be forwarded first before forwarding the new downlink data packets, until the end marker is received.

[0310] By using the above method, in the case that the first network and the second network share the core network, the UE can be instructed by the core network to perform cross-private network handover based on roaming, so as to improve the efficiency of cross-private network handover. In addition, lossless handover of data can be provided for the UE.

[0311] When the UE is registered in the home network, i.e., the first network is the home network, the UE accesses the home network through the source network, and establishes a PDU session in the home network, the communication method provided by the embodiments of the present application can include the steps shown in Figure 14a and / or Figure 14b . Wherein the home network here can be an HPLMN or a home SNPN (HSNPN).

[0312] Figure 14a As shown in the above, when the first network is an HPLMN and the second network is an SNPN #2, another communication method provided by the embodiments of the present application is shown. The method can be applied to Figure 7b / 7c shown scenario. The SNPN #2 here can also be replaced by a VPLMN #2 (i.e., one VPLMN).

[0313] The method can include the following steps:

[0314] S601: The UE registers in the SNPN#1 and establishes a first PDU session, an anchor point UPF of the first PDU session being UPF#3 in the HPLMN, and an anchor point SMF of the PDU session being SMF#3 in the HPLMN. The first PDU session can be associated with a first DNN and a first S-NSSAI.

[0315] The SNPN#1 and the HPLMN interwork based on a roaming mode.

[0316] S602: The SMF#1 and the SMF#3 respectively send an SMF registration message to a UDM. The registration message can include a UE ID, an SNPN#1 ID, an SMF#1 ID (or an SMF#3 ID), and an ID of the first PDU session. The UDM can be deployed in the HPLMN.

[0317] S603: The UE moves to a target network SNPN#2 and sends a first registration request message to an AMF#2 in the SNPN#2, carrying a UE ID.

[0318] Optionally, the first registration request message can carry a cross-private network HO indication. The cross-private network HO indication is used to indicate that the purpose of the registration of the AMF#2 is cross-private network switching, rather than initial registration. The HO indication can be a location update registration or a new information element.

[0319] S604: The AMF#2 determines, according to the cross-private network HO indication of the UE, that the UE is performing cross-private network switching, and determines a switching mode according to the interworking mode (based on non-roaming interworking or based on roaming interworking) of the SNPN#2 and the HPLMN, such as determining whether the UE performs switching according to roaming interworking or not.

[0320] The AMF#2 can determine the ID of the home network of the UE according to the UE ID (such as a subscription permanent identifier (SUPI) or a subscription concealed identifier (SUCI)) in the first registration request message of the UE, which can be the network ID of the HPLMN or the network ID of the SNPN#2. At the same time, the AMF#2 can obtain the network ID of the SNPN#2 from the RAN, and then determine the interworking mode of the SNPN#2 and the HPLMN according to the ID of the home network.

[0321] S605: The AMF#2 sends a registration response message to the UE, carrying a switching mode indication (i.e., first information).

[0322] If the SNPN#2 interworks with the HPLMN based on non-roaming way, the handover mode indication can indicate that the SNPN#2 interworks with the HPLMN based on non-roaming way. Or, the handover mode indication can indicate the UE that if the UE does not support N3IWF to the HPLMN, e.g. no N3IWF configuration of the HPLMN or not support connection to N3IWF, the UE does not establish the first PDU session to the HPLMN after registering to the SNPN#2.

[0323] In addition, if the SNPN#2 interworks with the HPLMN based on non-roaming way, the handover mode indication can also indicate the UE that if the UE supports N3IWF to the HPLMN, e.g. the UE has N3IWF configuration of the HPLMN or support connection to N3IWF, the UE establishes the PDU session to the N3IWF of the HPLMN, through which the procedure of the first PDU session from 3GPP to N3GPP is triggered, and the SMF#1 / UPF#1 of the first PDU session is deleted.

[0324] If the SNPN#2 interworks with the HPLMN based on non-roaming way, the handover mode indication can indicate that the SNPN#2 interworks with the HPLMN based on non-roaming way. Or, the handover mode indication can indicate the UE that if the UE does not support N3IWF to the HPLMN, e.g. no N3IWF configuration of the HPLMN or not support connection to N3IWF, the UE does not establish the first PDU session to the HPLMN after registering to the SNPN#2.

[0325] The UE then performs one of S606-S608 according to the handover mode indication.

[0326] S606: If the SNPN#2 interworks with the HPLMN based on non-roaming way, but the UE does not support N3IWF to the HPLMN, the UE does not attempt to establish the first PDU session to the SNPN#2 any more.

[0327] S607: If the SNPN#2 interworks with the HPLMN based on non-roaming way, and the UE supports N3IWF to the HPLMN, the UE first establishes a PDU session (i.e. second PDU session) to the N3IWF of the HPLMN in the SNPN#2, and establishes the user plane connection; then the UE initiates the handover of the first PDU session from 3GPP to N3GPP in the SNPN#1 through the N3IWF, i.e. sends a third PDU session request message with requesttype as existing PDU session to the SNPN#1, and carries the first DNN and the first S-NSSAI in the third PDU session request message, so that the PDU session of the N3GPP after the handover can be associated to the first DNN and the first S-NSSAI, and the SMF#1 and UPF#1 of the first PDU session are deleted.

[0328] S608: If SNPN#2 interworks with HPLMN based on roaming, the UE can send a fourth PDU session request message with request type as existing PDU session to AMF#2, carrying the first DNN and the first S-NSSAI, to request to resume the PDU session associated to the DNN and S-NSSAI. When the fourth session request is received by AMF#2, the I-SMF / I-UPF switching procedure of the PDU session in the presence of the mechanism is triggered, and SMF#2 / UPF#2 is selected to replace the original SMF#1 / UPF#1 to resume the first PDU session.

[0329] In this case, the switching mode indication can be used to indicate that the SNPN#1 interworks with the SNPN#2 based on roaming, or to indicate that the UE initiates the PDU session switching procedure from the SNPN#1 to the SNPN#2 in the SNPN#2. The specific switching mode can refer to the steps shown in S210-S221.

[0330] Based on the above procedure, when the source SNPN#1 interworks with the HPLMN based on roaming, and the UE registered in the SNPN#1 establishes the HR PDU session of the HPLMN, the UE can be instructed by the AMF in the SNPN#2 to perform the PDU session switching, thereby improving the PDU session switching efficiency.

[0331] It should be understood that in the above procedure, the HPLMN can be replaced by a home SNPN (HSNPN).

[0332] Figure 14b As shown, when the first network is the HPLMN and the second network is the SNPN#2, another communication method provided by the embodiments of the present application is provided. The method can be applied to the scenario shown in FIG. 7c. Figure 7b The SNPN#2 in this case can also be replaced by a VPLMN#2 (i.e., a VPLMN).

[0333] The method can include the following steps:

[0334] S701: The UE connects to the N3IWF of the HPLMN through the SNPN#1, registers in the HPLMN and establishes a first PDU session through the N3WIF, the anchor UPF of the first PDU session is UPF#3 in the HPLMN, and the anchor SMF of the PDU session is SMF#3 in the HPLMN. The first PDU session can be associated to a first DNN and a first S-NSSAI.

[0335] Wherein, the SNPN#1 interworks with the HPLMN based on N3IWF.

[0336] S702: SMF#3 sends a SMF registration message to UDM. The registration message can include UE ID, network ID of HPLMN, SMF#3 ID and ID of the first PDU session. The UDM can be deployed in HPLMN.

[0337] S703: The UE moves to the target network SNPN#2 and sends a first registration request message to AMF#2 in SNPN#2, which carries the UE ID.

[0338] Optionally, the first registration request message can carry a cross-private network HO indication. The cross-private network HO indication is used to indicate that the purpose of the registration of AMF#2 is cross-private network handover, rather than initial registration. The HO indication can be a location update registration or a new information element.

[0339] S704: AMF#2 determines that the UE is performing cross-private network handover according to the cross-private network HO indication of the UE, and determines the handover mode according to the interworking mode between SNPN#2 and HPLMN (non-roaming based interworking or roaming based interworking), such as determining whether the UE performs handover according to roaming interworking or not.

[0340] Wherein, AMF#2 can determine the ID of the home network of the UE according to the UE ID (such as SUPI or SUCI) in the first registration request message of the UE. The ID of the home network can be the network ID of HPLMN, or the network ID of SNPN#2. At the same time, AMF#2 can obtain the network ID of SNPN#2 from RAN, and then determine the interworking mode between SNPN#2 and HPLMN according to the ID of the home network.

[0341] S705: AMF#2 sends a registration response message to the UE, which carries the handover mode indication (i.e. the first information).

[0342] If SNPN#2 and HPLMN interwork based on non-roaming mode, the handover mode indication can indicate that SNPN#2 and HPLMN interwork based on non-roaming mode. Alternatively, the handover mode indication can indicate to the UE that if the UE does not support N3IWF to HPLMN, for example, does not have N3IWF configuration of HPLMN or does not support connection to N3IWF, then after registering to SNPN#2, the first PDU session to HPLMN does not need to be established.

[0343] In addition, if SNPN#2 interworks with HPLMN based on non-roaming manner, the handover manner indication can further indicate the UE that if the UE supports N3IWF to HPLMN, e.g. the UE has N3IWF configuration to HPLMN or supports connection to N3IWF, the UE establishes a PDU session to N3IWF of HPLMN through which the PDU session is established to HPLMN over N3GPP, and the PDU session is associated to the first DNN and the first S-NSSAI.

[0344] If SNPN#2 interworks with HPLMN based on roaming manner, the handover manner indication can indicate that SNPN#2 interworks with HPLMN based on roaming manner, or the handover manner indication can indicate the UE to resume the first PDU session in the following manner: the AMF#2 triggers the I-SMF / I-UPF insertion procedure for the PDU session in the discovery mechanism, and newly inserts SMF#2 and / or UPF#2 in SNPN#2.

[0345] The UE then performs one of S706-S708 according to the handover manner indication.

[0346] S706: If SNPN#2 interworks with HPLMN based on non-roaming manner, but the UE does not support N3IWF to HPLMN, the UE no longer attempts to establish the first PDU session of SNPN#2.

[0347] S707: If SNPN#2 interworks with HPLMN based on non-roaming manner, and the UE supports N3IWF to HPLMN, the UE first establishes a PDU session (i.e. a second PDU session) to N3IWF of HPLMN in SNPN#2, and establishes a user plane connection; and then the UE establishes an N3GPP PDU session to HPLMN over N3IWF with request type as existing PDU session, and the PDU session is associated to the first DNN and the first S-NSSAI.

[0348] S708: If SNPN#2 interworks with HPLMN based on roaming manner, the UE can send a fourth PDU session request message with request type as existing PDU session to AMF#2, carrying the first DNN and the first S-NSSAI, to request to resume the PDU session associated to the DNN and S-NSSAI. When the AMF#2 receives the fourth session request, it triggers the I-SMF / I-UPF insertion procedure for the PDU session in the discovery mechanism, and newly inserts SMF#2 and / or UPF#2 in SNPN#2 for the handover of the first PDU session from N3GPP to 3GPP.

[0349] In this case, the switching mode indication can be used to indicate that the roaming interworking between the SNPN #1 and the SNPN #2 is based on, or to indicate that the UE initiates a PDU session switching process from the SNPN #1 to the SNPN #2 in the SNPN #2. The specific switching mode can refer to the steps shown in S210-S221.

[0350] Based on the above process, when the source SNPN #1 and the HPLMN interwork based on the N3IWF, and the UE registered in the SNPN #1 establishes a PDU session of the HPLMN through the N3IWF of the HPLMN, the UE can be instructed by the AMF in the SNPN #2 to perform PDU session switching, thereby improving the efficiency of PDU session switching.

[0351] It should be understood that in the above process, the HPLMN can be replaced by a home SNPN.

[0352] As shown in Figure 14c Another communication method provided by the embodiments of the present application can include the following steps:

[0353] S501: The UE establishes a first PDU session in a first network.

[0354] The first PDU session is associated with a DNN and an S-NSSAI.

[0355] S502: The UE sends a first registration request message to a first network device in a second network.

[0356] Correspondingly, the first network device receives the first registration request message. The first registration request message can be used to request registration to the second network.

[0357] Illustratively, the first network device is an AMF deployed in the second network.

[0358] Optionally, the first registration request message can carry a cross-non-public network switching indication, the cross-non-public network switching indication being used to indicate that the terminal device performs cross-non-public network switching.

[0359] S503: Establish a PDU session of the UE in the first order, the PDU session being associated with the DNN and the S-NSSAI. The first order can indicate the execution order of the third mode, the second mode and the first mode respectively, wherein the third mode is prior to the second mode and the first mode, and the second mode is prior to the first mode.

[0360] It should be understood that the first order can only include the execution order of two of the third mode, the second mode and the first mode, and the terminal device no longer executes the mode not included in the first order, so as to further improve the switching efficiency.

[0361] The first order can indicate that the third manner is prior to the second manner, and the second manner is prior to the first manner, and the UE can prefer to establish the PDU session in the third manner, and if the PDU session associated with the DNN and the S-NSSAI is successfully established, the UE does not attempt to establish the PDU session in the second manner and the first manner; otherwise, if the PDU session associated with the DNN and the S-NSSAI cannot be established according to the third manner, the UE can attempt to establish the PDU session associated with the DNN and the S-NSSAI according to the second manner; if the PDU session associated with the DNN and the S-NSSAI cannot be established according to the second manner, the UE can attempt to establish the PDU session associated with the DNN and the S-NSSAI according to the first manner.

[0362] With the above process, after the UE registers from the first network to the second network, the UE can restore the PDU session in the first order through the third manner, the second manner and / or the first manner, so as to improve the switching efficiency.

[0363] Optionally, the first manner, the second manner and the third manner can be respectively one interworking manner between the first network and the second network. In other words, the first manner, the second manner and the third manner are respectively one manner for the UE to establish the PDU session associated with the DNN and the S-NSSAI in the interworking manner between the first network and the second network.

[0364] For example, the first manner can include a non-interworking switching manner. The non-interworking switching manner can be used to implement the switching of the PDU session of the UE in the case that the first network and the second network are not interconnected, and the non-interworking switching manner specifically includes that the terminal device sends a first PDU session request message to the first network device, and the first PDU session request message includes a request type information element with a value of initialrequest, information of the DNN and information of the S-NSSAI. In other words, the first manner can include a manner for the UE to establish the PDU session associated with the DNN and the S-NSSAI when the first network and the second network are not interconnected, and specific steps can be referred to the foregoing description.

[0365] The second approach may include an N3IWF interoperability handover method, which can be used to enable UE PDU session handover when the first network and the second network interoperate based on N3IWF. The N3IWF interoperability handover method may include the following steps: the UE sends a second PDU session request message to the first network device, the second PDU session request being used to request the establishment of a second PDU session, through which the UE establishes a connection with the N3IWF, which belongs to the first network; the UE sends a second registration request message to the second network device through this connection, the second registration request message being used to request registration in the first network via N3GPP, the second network device belonging to the first network; the UE sends a third PDU session request message to the second network device, the third PDU session request message including a request type information element with the value "existing PDU session", the information of the DNN, and the information of the S-NSSAI. Alternatively, the second approach may include the method when the UE establishes a PDU session associated with the DNN and S-NSSAI when the first network and the second network are interconnected based on N3IWF. For specific steps, please refer to the foregoing description.

[0366] The third approach may include a roaming interoperability handover method, which can be used to achieve UE PDU session handover when roaming between the first network and the second network. The roaming interoperability handover method may include the following steps: the terminal device sends a fourth PDU session request message to the first network device. This fourth PDU session request message includes a request type information element with the value "existing PDU session", information about the DNN, and information about the S-NSSAI. Optionally, the fourth PDU session request message may include a lossless handover indication to achieve lossless handover; specific steps can be found in [reference needed]. Figure 11 to Figure 13 The lossless handover steps are based on SMF#1 (or UPF#2), UPF#1 (or UPF#2), and RAN#1. Alternatively, the third method may include the method used when the UE establishes a PDU session associated with the DNN and S-NSSAI during roaming interoperability between the first and second networks; specific steps are described above. This third method can be replaced by a roaming interoperability handover method, or rather, the third method can be called a roaming interoperability handover method, used to achieve UE PDU session handover during roaming interoperability between the first and second networks.

[0367] Therefore, when the terminal device switches from the first network to the second network, the PDU session associated with the DNN and the S-NSSAI can be preferentially restored through the roaming interworking switching mode, the second scheme can be used to restore the PDU session associated with the DNN and the S-NSSAI through the N3IWF interworking switching mode, and the third scheme can be used to restore the PDU session associated with the DNN and the S-NSSAI through the non-interworking switching mode, so as to improve the switching efficiency.

[0368] For example, the first order can indicate that the third mode is preferred to the second mode, and the second mode is preferred to the first mode. Therefore, the UE can preferentially establish the PDU session according to the third mode. If the PDU session associated with the DNN and the S-NSSAI is successfully established, the UE will no longer attempt to establish the PDU session through the second mode and the first mode. Otherwise, if the PDU session associated with the DNN and the S-NSSAI cannot be established according to the third mode, the UE can attempt to establish the PDU session associated with the DNN and the S-NSSAI according to the second mode. If the PDU session associated with the DNN and the S-NSSAI cannot be established according to the second mode, the UE can attempt to establish the PDU session associated with the DNN and the S-NSSAI according to the first mode.

[0369] For example, the first order can be determined by local configuration. Alternatively, the first order can be indicated by the first network device. For example, when the UE registers to the second network, the first network device sends the indication information of the first order to the UE. Alternatively, the first order can be indicated by the second network device deployed in the first network. For example, when the UE registers to the first network, the second network device sends the indication information of the first order to the UE.

[0370] It should be understood that the indication information of the first order can include the priority of the first mode, the second mode and the third mode respectively. For example, the indication information can carry the priority of the first mode, the priority of the second mode and the priority of the third mode.

[0371] Alternatively, the indication information can directly indicate the UE to perform in the order of the third mode, the second mode and the first mode.

[0372] In addition, the indication information can also include information of the first mode, the second mode and the third mode respectively to indicate the first mode, the second mode and the third mode. For example, the indication information indicates the interworking mode between the first network and the second network corresponding to the first mode, the second mode and the third mode respectively, for example, indicates that the first mode is not interworking between the first network and the second network, indicates that the second mode is interworking between the first network and the second network based on N3IWF, and indicates that the third mode is interworking between the first network and the second network based on roaming. For another example, the indication information can also indicate the switching mode of the first mode, the second mode and the third mode respectively, for example, indicates that the first mode is a non-interworking switching mode, indicates that the second mode is an N3IWF interworking switching mode, and indicates that the third mode is a roaming interworking switching mode.

[0373] In addition, the UE can also determine the first mode, the second mode and the third mode according to the local configuration, for example, determines the first mode as a non-interworking switching mode according to the local configuration, determines the second mode as an N3IWF interworking switching mode according to the local configuration, and determines the third mode as a roaming interworking switching mode according to the local configuration.

[0374] It should be understood that the above indication information of the first order is only an example, and in specific implementation, the above combination of several modes can be implemented, and the specific implementation mode should not be understood as being limited by the above example.

[0375] In addition, the first network device and the second network device can indicate the execution order of the first mode, the second mode and the third mode in other ways, for example, the indication information includes information of the first mode, the second mode and the third mode respectively (such as the interworking mode corresponding to the first mode, the second mode and the third mode respectively, or the information of the PDU session establishment mode corresponding to the first mode, the second mode and the third mode respectively), and the arrangement order of the interworking mode can represent the execution order of the first mode, the second mode and the third mode respectively.

[0376] In a possible implementation, in the case of Figure 10 and Figure 14c Based on the flow shown in the above, the embodiment of the present application supports the UE to determine the recovery mode of the PDU session according to the following method:

[0377] After the UE establishes a PDU session associated with the DNN and S-NSSAI on the first network and registers with the second network, if the UE receives first information from the first network device deployed on the second network (the first information can be referred to in the description of the first information in the embodiments of this application), the UE can establish a PDU session associated with the DNN and the S-NSSAI based on the first information. Otherwise, if the UE does not receive the first information from the second network, it can execute the above handover method in the order of the third method, the second method, and the first method to attempt to establish a PDU session associated with the DNN and the S-NSSAI, where the order is the first order in the embodiments of this application. The first order can be determined by the UE according to its local configuration or according to the indication information of the first order from the second network device.

[0378] Based on the same concept, in order to achieve the functions of the methods provided in the embodiments of this application, this application also provides a communication device. This communication device can be used to implement the functions of the session management network element, user plane network element, policy management network element, terminal device, or access network element. The communication device may include hardware structures and / or software modules, implementing the above functions in the form of hardware structures, software modules, or a combination of hardware structures and software modules. Whether a particular function is executed in the form of hardware structures, software modules, or a combination of hardware structures and software modules depends on the specific application and design constraints of the technical solution.

[0379] like Figure 15 As shown, an embodiment of this application provides a communication device that may include a communication module 1501 and a processing module 1502, which are coupled to each other. This communication device 1500 can be used to perform the above... Figure 3 to Figure 8 The diagram shows a terminal device (UE) and a first network device (such as...). Figure 11 to Figure 13 As shown, AMF#2) or SMF (or session management network element, for example) Figure 11 and Figure 12 SMF#1 or Figure 13 The steps performed by the SMF#2 in the above method embodiment are described. The communication module 1501 can be used to support communication by the communication device 1500. The communication module 1501 can also be referred to as a communication unit, communication interface, transceiver module, or transceiver unit. The communication module 1501 may have wireless communication and / or wired communication functions. The processing module 1502 can also be referred to as a processing unit, and can be used to support the communication device 1500 in performing processing actions of the terminal device, the first network device, or the SMF in the above method embodiment, including but not limited to: generating information or messages sent by the communication module 1501, and / or demodulating and decoding signals received by the communication module 1501, etc.

[0380] In executionFigure 10 to Figure 13 In the action performed by the terminal device, the communication module 1501 can establish a first PDU session associated to a DNN and an S-NSSAI in a first network, and send a first registration request message to a first network device, the first registration request message being used to request registration to a second network. The communication module 1501 can further receive first information from the first network device, the first information being determined according to an interworking manner between the first network and the second network. The communication module 1501 can further establish a PDU session according to the first information, the PDU session being associated to the DNN and the S-NSSAI.

[0381] In a possible design, the first registration request message can include a cross-non-public network switching indication, which is used to indicate that the communication apparatus performs cross-non-public network switching.

[0382] In a possible design, the interworking manner between the first network and the second network includes that the first network and the second network do not interwork, the first network and the second network interwork based on N3IWF, or the first network and the second network interwork based on roaming.

[0383] In a possible design, in a case where the interworking manner includes that the first network and the second network do not interwork, the communication module 1501 can send a first PDU session request message to the first network device, the first PDU session request message including a request type information element with a value of initial request, or in other words, the first PDU session request message being used to request establishment of an initial PDU session. The first PDU session request message includes information of the DNN and information of the S-NSSAI, to request establishment of a PDU session associated to the DNN and the S-NSSAI. In this way, in the case where the first network and the second network do not interwork, the UE can newly establish a PDU session associated to the DNN and the S-NSSAI in the second network, implement recovery of the PDU session associated to the DNN and the S-NSSAI, and improve switching efficiency.

[0384] In a possible design, in a case where the interworking manner includes that the first network and the second network do not interwork, the first information is used to indicate that the first network and the second network do not interwork, or the first information is used to indicate that the communication apparatus sends the first PDU session request to the first network device. In this way, flexible indication of the interworking manner can be implemented.

[0385] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on N3IWF, the communication module 1501 can send, to the first network device, a second PDU session request message, where the second PDU session request is used to request establishment of a second PDU session. The communication module 1501 can further establish a connection with the N3IWF belonging to the first network through the second PDU session. The communication module 1501 can further send, to the second network device belonging to the first network, a second registration request message, where the second registration request message is used to request registration with the first network in an N3GPP manner. The communication module 1501 can further send, to the second network device, a third PDU session request message, where the third PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the third PDU session request message is used to request establishment of an existing PDU session. The third PDU session request message can carry information of the DNN and information of the S-NSSAI. In this way, in a case where the first network and the second network interwork based on N3IWF, the UE can establish, through the N3IWF and the second network device, a third PDU session associated with the information of the DNN and the information of the S-NSSAI, thereby achieving resumption of the PDU session of the UE associated with the DNN and the S-NSSAI, and improving handover efficiency.

[0386] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on N3IWF, the first information can be used to indicate that the first network and the second network interwork based on N3IWF, or used to indicate that the second PDU session request is sent to the first network device, the second registration request is sent to the second network device through the N3IWF, and the third PDU session request message is sent to the second network device.

[0387] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the communication module 1501 can send, to the first network device, a fourth PDU session request message, where the fourth PDU session request message includes a request type information element with a value of existing PDU session, information of the DNN, and information of the S-NSSAI. In this way, in a case where the first network and the second network interwork based on roaming, the UE can establish, through the first network device, a fourth PDU session associated with the information of the DNN and the information of the S-NSSAI, thereby achieving resumption of the PDU session of the UE associated with the DNN and the S-NSSAI, and improving handover efficiency.

[0388] In a possible design, the first information can be used to indicate that the interworking between the first network and the second network is based on roaming, or used to indicate that the fourth PDU session request message is sent to the first network device, in a case where the interworking manner includes interworking between the first network and the second network based on roaming.

[0389] In a possible design, the fourth PDU session request message includes a lossless handover indication. Therefore, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, lossless network handover of the UE can be supported.

[0390] In performing the actions shown by the first network device Figure 10 to Figure 13 In performing the actions shown by the first network device, the communication module 1501 can receive a first registration request message from a terminal device, the terminal device belonging to a second network, the first registration request message being used to request registration to the second network. The processing module 1502 can obtain a context of the terminal device, and determine, according to the context, that the terminal device has registered to a first network. The communication module 1501 can further send first information to the terminal device according to an interworking manner between the first network and the second network.

[0391] In a possible design, the processing module 1502 can further determine, according to a cross-non-public network handover indication included in the first registration request message, that the terminal device performs cross-non-public network handover, the cross-non-public network handover indication being used to indicate that the terminal device performs cross-non-public network handover. Alternatively, the processing module 1502 can determine, according to an identity of the first network, that the terminal device performs cross-non-public network handover, the identity of the first network being included in the context. Alternatively, the processing module 1502 can determine, according to an identity of a second network device, that the terminal device performs cross-non-public network handover, the identity of the second network device being included in the context of the terminal device. The second network device is a network device accessed by the terminal device when registering to the first network, such as an AMF.

[0392] In a possible design, the communication module 1501 can receive a context of a terminal device from a second network device, the second network device being deployed in a first network. The communication module 1501 can obtain information of the second network device from a UDM, and request the context of the terminal device.

[0393] Alternatively, the communication module 1501 can receive a context of a terminal device from a data storage node, the data storage node being shared by the first network and the second network.

[0394] In a possible design, the data storage node includes a UDM or an AAA server.

[0395] In a possible design, the interworking manner between the first network and the second network includes no interworking between the first network and the second network, interworking between the first network and the second network based on N3IWF, or interworking between the first network and the second network based on roaming.

[0396] In a possible design, when the interworking manner includes no interworking between the first network and the second network, the first information can be used to indicate that there is no interworking between the first network and the second network, or the first information can be used to indicate that the terminal device sends a first PDU session request message to the communication apparatus. The first PDU session request message includes a request type information element with a value of initialrequest, or in other words, the first PDU session request message is used to request establishment of an initial PDU session. In addition, the first PDU session request message further includes a DNN (or information of a DNN) associated with a PDU session established by the terminal device in the first network and an S-NSSAI (or information of an S-NSSAI) associated with the PDU session, or in other words, the first information is further used to indicate that the UE carries information of a DNN associated with a PDU session established by the terminal device in the first network and information of an S-NSSAI associated with the PDU session in the first PDU session request message.

[0397] In a possible design, when the interworking manner includes interworking between the first network and the second network based on N3IWF, the first information can be used to indicate that there is interworking between the first network and the second network based on N3IWF. Alternatively, the first information can be used to indicate that the terminal device sends a second PDU session request message to the communication apparatus, sends a second registration request message to a second network device through the N3IWF, and sends a third PDU session request message to the second network device. The second PDU session request message is used to request establishment of a second PDU session, and the second PDU session is used to establish a connection between the terminal device and the N3IWF. The second registration request message is used to request registration in the first network in an N3GPP manner. The third PDU session request message includes a request type information element with a value of existing PDU session, information of a DNN associated with a PDU session established by the terminal device in the first network, and information of an S-NSSAI associated with the PDU session.

[0398] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the first information can indicate interworking between the first network and the second network based on roaming. Alternatively, the first information can indicate that the terminal device sends, to the communication apparatus, a fourth PDU session request message, where the fourth PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the fourth PDU session request message is used to request establishment of an existing PDU session. The fourth PDU session request message further includes information about a DNN associated with a PDU session established by the terminal device in the first network and information about an S-NSSAI associated with the PDU session, or in other words, the first information is further used to indicate that the terminal device carries, in the fourth PDU session request message, the information about the DNN associated with the PDU session established by the terminal device in the first network and the information about the S-NSSAI associated with the PDU session.

[0399] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the communication module 1501 can further receive, from the terminal device, the fourth PDU session request message described above. The communication module 1501 can further send, to a first SMF, the fourth PDU session request message, where the first SMF is an intermediate SMF, the first SMF is connected to a second SMF, and the second SMF maintains a first PDU session associated with the DNN and the S-NSSAI and established by the terminal device in the first network, and the fourth PDU session request message can be subsequently forwarded by the first SMF to the second SMF for path switching by the second SMF. Alternatively, the first SMF belongs to the first network, and the first SMF maintains the first PDU session associated with the DNN and the S-NSSAI and established by the terminal device in the first network.

[0400] In a possible design, the communication module 1501 can further send, to the first SMF, a cross-non-public-network switching indication, where the cross-non-public-network switching indication is used to indicate that the terminal device performs cross-non-public-network switching.

[0401] In a possible design, the fourth PDU session request includes a lossless switching indication.

[0402] In the execution Figure 10 to Figure 13In the illustrated action performed by the SMF, the processing module 1502 can establish a first PDU session of a terminal device associated to a DNN and an S-NSSAI, the terminal device being registered with a first network. The first PDU session is a PDU session between a first access network element belonging to the first network and a first UPF. The communication module 1501 can receive a fourth PDU session request message, the fourth PDU session request message including a request type information element with a value of existing PDU session, or in other words, the fourth PDU session request message can be used to request establishment of an existing PDU session. The fourth PDU session request message further includes information of the DNN and information of the S-NSSAI, to request establishment of a PDU session associated to the DNN and the S-NSSAI. The communication module 1501 can further send second information to the first UPF, the second information being used to instruct the first UPF to send an end marker to the first access network element after path switching of the first PDU session, and to instruct the first UPF to forward downlink data from the terminal device of the first access network element to the terminal device via the switched path, the downlink data including the end marker. The communication module 1501 can further send third information to the first access network element, the third information being used to instruct the first access network element to forward downlink data of the terminal device buffered by the first access network element to the first UPF, until the end marker is received and forwarded.

[0403] In a possible design, the fourth PDU session request message includes a lossless switching indication, or the processing module 1502 can determine, according to local configuration, to perform lossless switching for the terminal device.

[0404] In a possible design, the communication module 1501 can further receive a non-public network switching indication.

[0405] In a possible design, the fourth PDU session request message is from a first network device, the first network device belonging to a second network. For example, the communication apparatus is connected with the second network, and the first network device is connected with the communication apparatus. Or, the fourth PDU session request message is sent by the first network device to an intermediate SMF, and forwarded by the intermediate SMF to the communication module 1501. For example, the communication apparatus does not belong to the second network, and the first network device is not directly connected with the communication apparatus, and needs to perform message forwarding through the intermediate SMF.

[0406] In the execution Figure 14cIn the illustrated action performed by the terminal device, the communication module 1501 can establish a first PDU session associated to a DNN and an S-NSSAI in a first network, and can send a first registration request message to a first network device, the first registration request message being used to request registration to a second network. In addition, the communication module 1501 can establish (or request establishment of) a PDU session according to a first order, the PDU session being associated to the DNN and the S-NSSAI. The first order is used to indicate that the PDU session is established according to a third manner, a second manner and a first manner in sequence. Alternatively, the processing module 1502 establishes (or requests establishment of) the PDU session according to the first order by the communication module 1501 according to the third manner, the second manner and the first manner in sequence until the PDU session is established.

[0407] In a possible design, the first registration request message includes a cross-non-public network switching indication, the cross-non-public network switching indication being used to indicate cross-non-public network switching.

[0408] In a possible design, when the PDU session is established according to the first manner, the communication module 1501 can send a first PDU session request message to the first network device, where the first PDU session request message includes a request type information element with a value of initialrequest, or the first PDU session request message is used to request establishment of an initial PDU session. The first PDU session request message includes information of the DNN and information of the S-NSSAI, to request establishment of a PDU session associated to the DNN and the S-NSSAI.

[0409] In a possible design, the communication module 1501 can send a second PDU session request message to the first network device, the second PDU session request being used to request establishment of a second PDU session. The communication module 1501 can establish a connection with an N3IWF belonging to the first network through the second PDU session. The communication module 1501 sends a second registration request message to a second network device belonging to the first network through the connection, the second registration request message being used to request registration to the first network in an N3GPP manner. When the PDU session is established according to the second manner, the communication module 1501 can send a third PDU session request message to the second network device, the third PDU session request message including a request type information element with a value of existing PDUsession, or the third PDU session request message can be used to request establishment of an existing PDU session. The third PDU session request message can include information of the DNN and information of the S-NSSAI.

[0410] In a possible design, when the PDU session is established according to the third manner, the communication module 1501 can send, to the first network device, a fourth PDU session request message, where the fourth PDU session request message includes a request type information element with a value of existing PDUsession, or in other words, the fourth PDU session request message can be used to request establishment of an existing PDU session. The fourth PDU session request message further includes information of the DNN and information of the S-NSSAI.

[0411] In a possible design, the fourth PDU session request message includes a lossless switching indication to support lossless switching.

[0412] In a possible design, the first order is determined according to a local configuration. Alternatively, the communication module 1501 can receive indication information of the first order from the first network device. Optionally, the indication information of the first order can be determined according to a local configuration of the first network device, or determined by the first network device according to an interworking manner between the first network and the second network. Alternatively, the communication module 1501 can receive indication information of the first order from the second network device. Optionally, the indication information of the first order can be determined according to a local configuration of the second network device, or determined by the second network device according to an interworking manner between the first network and the second network. Therefore, the first order can be flexibly determined.

[0413] In addition, in another possible implementation, if the session management network element is implemented by using hardware components, the structure can also be as shown in Figure 16 For ease of understanding, Figure 16 In the foregoing embodiments, only structures necessary for performing the methods shown in the present application are shown, and the present application does not limit the communication apparatus to have more components. The communication apparatus 1600 can include a communication interface 1601, a memory 1602, and a processor 1603. The communication interface 1601 can be used for the communication apparatus to communicate, for example, to send or receive signals through wires and / or wireless, so as to send and / or receive information, data, and messages, etc. The memory 1602 is coupled to the processor 1603, and is used to store programs and data necessary for the communication apparatus 1600 to implement various functions. The processor 1603 is configured to support the communication apparatus 1600 to perform processing functions performed by the session management network element in the foregoing methods, for example, to determine to generate information and messages sent by the communication interface 1601, and / or to demodulate and decode signals received by the communication interface 1601, etc. The memory 1602 and the processor 1603 can be integrated or independent.

[0414] For example, the communication interface 1601 may include a wired communication interface, which can be used to support the communication device 1600 in receiving and sending signaling and / or data via a wired manner. The communication interface 1601 may also be referred to as a transceiver unit or a communication unit. Alternatively, the communication interface 1601 may include a wireless transceiver (such as including a modem and / or antenna), which can be used to support the communication device 1600 in receiving and sending signaling and / or data wirelessly. The communication interface 1601 may also be referred to as a wireless transceiver or a wireless communication unit.

[0415] The processor 1603 can be implemented via a processing chip or processing circuit.

[0416] In execution Figure 10 to Figure 13 When the actions performed by the terminal device are shown, the communication interface 1601 can establish a first PDU session associated with the DNN and S-NSSAI on the first network. The communication interface 1601 can also send a first registration request message to the first network device, which requests registration with the second network. The communication interface 1601 can also receive first information from the first network device, which is determined based on the interoperability between the first and second networks. The communication interface 1601 can also establish a PDU session based on the first information, which is associated with the DNN and the S-NSSAI.

[0417] In one possible design, the first registration request message may include a cross-non-public network handover instruction to instruct the communication device to perform a cross-non-public network handover.

[0418] In one possible design, the interconnection methods between the first network and the second network include no interconnection between the first network and the second network, interconnection between the first network and the second network based on N3IWF, or interconnection between the first network and the second network based on roaming.

[0419] In one possible design, when the interoperability mode includes a lack of interoperability between the first network and the second network, the communication interface 1601 can send a first PDU session request message to the first network device. This first PDU session request message includes a request type information element with the value "initial request," or in other words, it requests the establishment of an initial PDU session. The first PDU session request message includes information about the DNN and the S-NSSAI to request the establishment of a PDU session associated with the DNN and the S-NSSAI. Accordingly, even when the first and second networks are not interoperable, the UE can establish a new PDU session associated with the DNN and S-NSSAI in the second network, thereby restoring the PDU session associated with the DNN and S-NSSAI and improving handover efficiency.

[0420] In a possible design, in a case where the interworking manner includes no interworking between the first network and the second network, the first information is used to indicate that there is no interworking between the first network and the second network, or the first information is used to indicate that the communication apparatus sends the first PDU session request to the first network device. Accordingly, flexible indication of the interworking manner can be implemented.

[0421] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on N3IWF, the communication interface 1601 can send, to the first network device, a second PDU session request message, where the second PDU session request is used to request establishment of a second PDU session. The communication interface 1601 can further establish a connection with the N3IWF belonging to the first network through the second PDU session. The communication interface 1601 can further send, to the second network device belonging to the first network, a second registration request message through the connection, where the second registration request message is used to request registration with the first network in an N3GPP manner. The communication interface 1601 can further send, to the second network device, a third PDU session request message, where the third PDU session request message includes a request type information element with a value of existing PDU session, or the third PDU session request message is used to request establishment of an existing PDU session. The third PDU session request message can carry information of the DNN and information of the S-NSSAI. Accordingly, in the case where the first network and the second network interwork based on N3IWF, the UE can establish, through the N3IWF and the second network device, the third PDU session associated with the information of the DNN and the information of the S-NSSAI, to implement recovery of the PDU session of the UE associated with the DNN and the S-NSSAI, and improve switching efficiency.

[0422] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on N3IWF, the first information can be used to indicate that the first network and the second network interwork based on N3IWF, or used to indicate that the second PDU session request is sent to the first network device, the second registration request is sent to the second network device through the N3IWF, and the third PDU session request message is sent to the second network device.

[0423] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the communication interface 1601 can send, to the first network device, a fourth PDU session request message including a request type information element with a value of existing PDU session, information of the DNN, and information of the S-NSSAI. Therefore, in the case where the interworking manner includes interworking between the first network and the second network based on roaming, the UE can establish, through the first network device, the fourth PDU session associated to the information of the DNN and the S-NSSAI, implement the resumption of the PDU session of the UE associated to the DNN and the S-NSSAI, and improve the switching efficiency.

[0424] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the first information can be used to indicate interworking between the first network and the second network based on roaming, or used to indicate sending of the fourth PDU session request message to the first network device.

[0425] In a possible design, the fourth PDU session request message includes a lossless switching indication. Therefore, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, lossless network switching of the UE can be supported.

[0426] In performing the actions performed by the first network device shown in Figure 10 to Figure 13 In performing the actions performed by the first network device shown in

[0427] In a possible design, the processor 1603 can further determine, according to a cross-non-public network switching indication included in the first registration request message, that the terminal device performs cross-non-public network switching, where the cross-non-public network switching indication is used to indicate that the terminal device performs cross-non-public network switching. Alternatively, the processor 1603 can determine, according to an identifier of the first network included in the context, that the terminal device performs cross-non-public network switching. Alternatively, the processor 1603 can determine, according to an identifier of the second network device included in the context of the terminal device, that the terminal device performs cross-non-public network switching. The second network device is a network device, such as an AMF, accessed by the terminal device when registering in the first network.

[0428] In a possible design, the communication interface 1601 can receive the context of the terminal device from a second network device, which is deployed in the first network. The communication interface 1601 can obtain the information of the second network device from a UDM, and request the context of the terminal device.

[0429] Alternatively, the communication interface 1601 can receive the context of the terminal device from a data storage node, which is shared by the first network and the second network.

[0430] In a possible design, the data storage node includes a UDM or an AAA server.

[0431] In a possible design, the above interworking manners between the first network and the second network include no interworking between the first network and the second network, interworking between the first network and the second network based on N3IWF, or interworking between the first network and the second network based on roaming.

[0432] In a possible design, in a case where the interworking manner includes no interworking between the first network and the second network, the first information can be used to indicate that there is no interworking between the first network and the second network, or the first information can be used to indicate that the terminal device sends a first PDU session request message to the communication apparatus. The first PDU session request message includes a request type information element with a value of initialrequest, or in other words, the first PDU session request message is used to request establishment of an initial PDU session. In addition, the first PDU session request message further includes a DNN (or information of the DNN) associated with a PDU session established by the terminal device in the first network and an S-NSSAI (or information of the S-NSSAI) associated with the PDU session, or in other words, the first information is further used to indicate that the UE carries information of the DNN associated with the PDU session established by the terminal device in the first network and information of the S-NSSAI associated with the PDU session in the first PDU session request message.

[0433] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on N3IWF, the first information can be used to indicate interworking between the first network and the second network based on N3IWF. Alternatively, the first information can be used to instruct the terminal device to send a second PDU session request message to the communication apparatus, send a second registration request message to the second network device through the N3IWF, and send a third PDU session request message to the second network device. The second PDU session request message is used to request establishment of a second PDU session, and the second PDU session is used to establish a connection between the terminal device and the N3IWF. The second registration request message is used to request registration in the first network in an N3GPP manner. The third PDU session request message includes a request type information element with a value of existing PDU session, information about a DNN associated with a PDU session established by the terminal device in the first network, and information about an S-NSSAI associated with the PDU session.

[0434] In a possible design, in a case where the interworking manner includes interworking between the first network and the second network based on roaming, the first information can be used to indicate interworking between the first network and the second network based on roaming. Alternatively, the first information can be used to instruct the terminal device to send a fourth PDU session request message to the communication apparatus. The fourth PDU session request message includes a request type information element with a value of existing PDU session, or in other words, the fourth PDU session request message is used to request establishment of an existing PDU session. The fourth PDU session request message further includes information about a DNN associated with a PDU session established by the terminal device in the first network, and information about an S-NSSAI associated with the PDU session, or in other words, the first information is further used to instruct the terminal device to carry, in the fourth PDU session request message, the information about the DNN associated with the PDU session established by the terminal device in the first network, and the information about the S-NSSAI associated with the PDU session.

[0435] In one possible design, where the interoperability includes roaming-based interoperability between the first and second networks, the communication interface 1601 can also receive the aforementioned fourth PDU session request message from the terminal device. The communication interface 1601 can also send the fourth PDU session request message to the first SMF, where the first SMF is an intermediate SMF connected to the second SMF. The second SMF maintains the first PDU session established by the terminal device in the first network, associating it with the DNN and the S-NSSAI. Subsequently, the first SMF can forward the fourth PDU session request message to the second SMF, which will then perform path switching. Alternatively, the first SMF belongs to the first network and maintains the first PDU session established by the terminal device in the first network, associating it with the DNN and the S-NSSAI.

[0436] In one possible design, the communication interface 1601 may also send a cross-non-public network handover instruction to the first SMF, the cross-non-public network handover instruction being used to instruct the terminal device to perform a cross-non-public network handover.

[0437] In one possible design, the fourth PDU session request includes a lossless handover indication.

[0438] In execution Figure 10 to Figure 13 When the action is performed by the SMF, the processor 1603 can establish a first PDU session associated with the terminal device and the DNN and S-NSSAI, the terminal device being registered in the first network. This first PDU session is a PDU session between a first access network element and a first UPF, the first access network element belonging to the first network. The communication interface 1601 can receive a fourth PDU session request message, which includes a request type information element with the value "existing PDU session," or in other words, this fourth PDU session request message can be used to request the establishment of an existing PDU session. The fourth PDU session request message also includes information about the DNN and the S-NSSAI to request the establishment of a PDU session associated with the DNN and the S-NSSAI. The communication interface 1601 can also send second information to the first UPF, which instructs the first UPF to send an end marker to the first access network element after the path switch of the first PDU session, and to instruct the first UPF to forward downlink data from the terminal device originating from the first access network element to the terminal device through the switched path, the downlink data including the end marker. The communication interface 1601 can also send third information to the first access network element, which instructs the first access network element to forward the downlink data of the terminal device cached by the first access network element to the first UPF until the end marker is received and forwarded.

[0439] In a possible design, the fourth PDU session request message includes a lossless handover indication, or the lossless handover is determined by the processor 1603 to be performed for the terminal device according to a local configuration.

[0440] In a possible design, the communication interface 1601 can further receive a non-public network handover indication.

[0441] In a possible design, the fourth PDU session request message is from a first network device, and the first network device belongs to the second network. For example, the communication apparatus belongs to the second network, and the first network device is connected to the communication apparatus. Alternatively, the fourth PDU session request message is sent by the first network device to an intermediate SMF, and forwarded to the communication interface 1601 by the intermediate SMF. For example, the communication apparatus does not belong to the second network, and the first network device is not directly connected to the communication apparatus, and needs to forward messages through the intermediate SMF.

[0442] In a possible design, the communication interface 1601 can establish a first PDU session associated to a DNN and an S-NSSAI with the first network, and send a first registration request message to the first network device, where the first registration request message is used to request registration to the second network. Figure 14c In a possible design, the communication interface 1601 can establish (or request to establish) a PDU session according to a first order, where the PDU session is associated to the DNN and the S-NSSAI. The first order is used to indicate that the PDU session is established according to a third manner, a second manner and a first manner in sequence. Alternatively, the processor 1603 establishes (or requests to establish) the PDU session according to the third manner, the second manner and the first manner in sequence through the communication interface 1601 according to the first order, until the PDU session is established.

[0443] In a possible design, the first registration request message includes a cross-non-public network handover indication, where the cross-non-public network handover indication is used to indicate cross-non-public network handover.

[0444] In a possible design, when the PDU session is established according to the first manner, the communication interface 1601 can send a first PDU session request message to the first network device, where the first PDU session request message includes a request type information element with a value of initialrequest, or the first PDU session request message is used to request to establish an initial PDU session. The first PDU session request message includes information of the DNN and information of the S-NSSAI, to request to establish a PDU session associated to the DNN and the S-NSSAI.

[0445] In a possible design, the communication interface 1601 can send, to the first network device, a second PDU session request message, where the second PDU session request is used to request establishment of a second PDU session. The communication interface 1601 can establish a connection with an N3IWF of the first network through the second PDU session, and send, to a second network device of the first network through the connection, a second registration request message used to request registration with the first network in an N3GPP manner, where the second network device belongs to the first network. When the PDU session is established in the second manner, the communication interface 1601 can send, to the second network device, a third PDU session request message, where the third PDU session request message includes a request type information element with a value of existing PDUsession, or the third PDU session request message is used to request establishment of an existing PDU session. The third PDU session request message can include information of the DNN and information of the S-NSSAI.

[0446] In a possible design, when the PDU session is established in the third manner, the communication interface 1601 can send, to the first network device, a fourth PDU session request message, where the fourth PDU session request message includes a request type information element with a value of existing PDUsession, or the fourth PDU session request message is used to request establishment of an existing PDU session. The fourth PDU session request message further includes information of the DNN and information of the S-NSSAI.

[0447] In a possible design, the fourth PDU session request message includes an indication of lossless switching, to support lossless switching.

[0448] In a possible design, the first order is determined according to a local configuration. Alternatively, the communication interface 1601 can receive indication information of the first order from the first network device. Optionally, the indication information of the first order can be determined according to a local configuration of the first network device, or determined by the first network device according to an interworking manner between the first network and the second network. Alternatively, the communication interface 1601 can receive indication information of the first order from the second network device. Optionally, the indication information of the first order can be determined according to a local configuration of the second network device, or determined by the second network device according to an interworking manner between the first network and the second network. Thus, the first order can be flexibly determined.

[0449] Based on the same idea as the above method embodiments, the embodiments of the present application also provide a computer readable storage medium, which stores a computer program (or instructions) and the program is executed by a processor to make the computer perform the operations performed by the terminal device, the first network device and / or the SMF in the above method embodiments, any one of the possible implementation manners of the method embodiments.

[0450] Based on the same idea as the above method embodiments, the present application also provides a computer program product, which, when invoked and executed by a computer, can make the computer implement the operations performed by the terminal device, the first network device and / or the SMF in the above method embodiments, any one of the possible implementation manners of the method embodiments.

[0451] Based on the same idea as the above method embodiments, the present application also provides a chip or chip system, which is coupled with a transceiver and used to implement the operations performed by the terminal device, the first network device and / or the SMF in the above method embodiments, any one of the possible implementation manners of the method embodiments. The chip system can include the chip, and components such as a memory and a communication interface.

[0452] Based on the same idea as the above method embodiments, the present application also provides a communication system, which can be used to implement the operations performed by the terminal device, the first network device and / or the SMF in the above method embodiments, any one of the possible implementation manners of the method embodiments. For example, the communication system has a structure as shown in any one of Figure 6 to Figure 9 The communication system can be used to perform the flow as shown in any one of Figure 10 to Figure 14c

[0453] Those skilled in the art should understand that the embodiments of the present application can be provided as a method, a system, or a computer program product. Therefore, the present application can take the form of an entirely hardware embodiment, an entirely software embodiment, or an embodiment combining software and hardware aspects. Moreover, the present application can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0454] The present application is described with reference to flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the present application. It should be understood that each flow and / or block in the flowcharts and / or block diagrams, and the combination of flows and / or blocks in the flowcharts and / or block diagrams can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing apparatus to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing apparatus produce a device that implements the functions described in the flowcharts and / or block diagrams.​Figure One apparatuses that implement the functions specified in the flow or flows and / or blocks. Figure One

[0455] These computer program instructions can also be stored in a computer readable memory that can direct a computer or other programmable data processing apparatus to function in a particular manner, such that the instructions stored in the computer readable memory produce an article of manufacture including instructions which implement the flow or flows and / or blocks. Figure One apparatuses that implement the functions specified in the flow or flows and / or blocks. Figure One

[0456] These computer program instructions can also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer implemented process such that the instructions that execute on the computer or other programmable apparatus provide steps for implementing the flow or flows and / or blocks. Figure One apparatuses that implement the functions specified in the flow or flows and / or blocks. Figure One

[0457] Obviously, numerous modifications and variations of the present application are possible in light of the above teachings. It is therefore to be understood that within the scope of the claims and their equivalents, the application can be practiced otherwise than as specifically described.​​​

Claims

1. A communication method, characterized in that, Applied to terminal devices, including: Terminal devices registered in the first network establish a first PDU session in the first network that is associated with the data network name DNN and the single network slice selection auxiliary information S-NSSAI; The terminal device sends a first message to the first network device, the first message being used to request registration with the second network; The terminal device receives first information from the first network device, and the first information is determined according to the interconnection method between the first network and the second network; The terminal device establishes a Protocol Data Unit (PDU) session based on the first information, and the PDU session is associated with the DNN and the S-NSSAI.

2. The method as described in claim 1, characterized in that, The first message includes a cross-non-public network handover instruction, which is used to instruct the terminal device to perform a cross-non-public network handover.

3. The method as described in claim 1, characterized in that, The interconnection methods include: The first network and the second network do not communicate with each other; or, The first network and the second network interoperate based on the non-3rd Generation Partnership Project (NGPP) interoperability function network element N3IWF; or, The first network and the second network are interconnected based on roaming.

4. The method according to any one of claims 1-3, characterized in that, The interoperability method includes no interoperability between the first network and the second network, and the terminal device establishing a PDU session based on the first information, including: The terminal device sends a second message to the first network device. The second message is used to request the establishment of an initial PDU session. The second message includes information about the DNN and information about the S-NSSAI.

5. The method as described in claim 4, characterized in that, The first information is used to indicate that the first network and the second network are not interconnected; or, The first information is used to instruct the terminal device to send the first PDU session request to the first network device.

6. The method according to any one of claims 1-3, characterized in that, The interconnection method includes N3IWF-based interconnection between the first network and the second network, and the method further includes: The terminal device sends a third message to the first network device, the third message being used to request the establishment of a second PDU session; The terminal device establishes a connection with the N3IWF through the second PDU session, and the N3IWF belongs to the first network; The terminal device sends a fourth message to the second network device through the connection. The fourth message is used to request registration in the first network via N3GPP. The second network device belongs to the first network. The terminal device establishes a PDU session based on the first information, including: The terminal device sends a fifth message to the second network device. The fifth message is used to request the establishment of an existing PDU session. The fifth message includes information about the DNN and information about the S-NSSAI.

7. The method as described in claim 6, characterized in that, The first information is used to indicate N3IWF-based interoperability between the first network and the second network; or, The first information is used to instruct the terminal device to send the third message to the first network device, to send the second registration request to the second network device through the N3IWF, and to send the fifth message to the second network device.

8. The method according to any one of claims 1-3, characterized in that, The interoperability method includes roaming-based interoperability between the first network and the second network, wherein the terminal device restores the protocol data unit (PDU) session associated with the DNN and the S-NSSAI based on the first information, including: The terminal device sends a sixth message to the first network device. The sixth message is used to request the establishment of an existing PDU session. The sixth message includes information about the DNN and information about the S-NSSAI.

9. The method as described in claim 8, characterized in that, The first information is used to indicate roaming-based interoperability between the first network and the second network; or, The first information is used to instruct the terminal device to send the sixth message to the first network device.

10. The method as described in claim 8, characterized in that, The sixth message includes a lossless switching instruction.

11. A communication method, characterized in that, include: A first network device receives a first message from a terminal device. The first network device belongs to a second network. The first message is used to request registration with the second network. The first network device obtains the context of the terminal device; The first network device determines, based on the context, that the terminal device has registered in the first network; The first network device sends first information to the terminal device according to the interconnection method between the first network and the second network; The first information is used by the terminal device to establish a Protocol Data Unit (PDU) session. The PDU session is associated with the DNN and S-NSSAI. The DNN and S-NSSAI are used by the terminal device to establish a first PDU session associated with the DNN and S-NSSAI in the first network.

12. The method as described in claim 11, characterized in that, Also includes: The first network device determines that the terminal device should perform a cross-non-public network handover based on the cross-non-public network handover indication included in the first message, wherein the cross-non-public network handover indication is used to instruct the terminal device to perform a cross-non-public network handover. or, The first network device determines that the terminal device is to perform a cross-public network handover based on the identifier of the first network, wherein the identifier of the first network is included in the context; or, The first network device determines that the terminal device is performing a cross-public network handover based on the identifier of the second network device, the identifier of the second network device being included in the context, and the second network device belonging to the first network.

13. The method as described in claim 12, characterized in that, The first network device obtains the context of the terminal, including: The first network device receives context from the terminal device from the second network device, which is deployed in the first network; or... The first network device receives context from the terminal device from the data storage node, which is shared by the first network and the second network.

14. The method as described in claim 13, characterized in that, The data storage nodes include UDM or Authentication, Authorization, and Accounting Agent (AAA) servers.

15. The method as described in claim 11, characterized in that, The interconnection methods include: The first network and the second network do not communicate with each other; or, The first network and the second network interconnect based on N3IWF; or, The first network and the second network are interconnected based on roaming.

16. The method according to any one of claims 11-15, characterized in that, The interconnection method includes no interconnection between the first network and the second network; The first information is used to indicate that the first network and the second network are not interconnected; or, The first information is used to instruct the terminal device to send a second message to the first network device. The second message is used to request the establishment of an initial PDU session. The second message includes information about the DNN associated with the PDU session established by the terminal device in the first network and information about the S-NSSAI associated with the PDU session.

17. The method according to any one of claims 11-15, characterized in that, The interconnection method includes N3IWF-based interconnection between the first network and the second network; The first information is used to indicate N3IWF-based interoperability between the first network and the second network; or, The first information is used to instruct the terminal device to send a third message to the first network device, a fourth message to the second network device through the N3IWF, and a fifth message to the second network device; The third message is used to request the establishment of a second PDU session, which is used to establish a connection between the terminal device and the N3IWF; the fourth message is used to request registration in the first network via N3GPP; the fifth message is used to request the establishment of an existing PDU session, which includes information about the DNN associated with the PDU session established by the terminal device in the first network and information about the S-NSSAI associated with the PDU session.

18. The method according to any one of claims 11-15, characterized in that, The interconnection method includes roaming-based interconnection between the first network and the second network; The first information is used to indicate roaming-based interoperability between the first network and the second network; or, The first information is used to instruct the terminal device to send a sixth message to the first network device. The sixth message is used to request the establishment of an existing PDU session. The sixth message includes information about the DNN associated with the PDU session established by the terminal device in the first network and information about the S-NSSAI associated with the PDU session.

19. The method as described in claim 18, characterized in that, The method further includes: The first network device receives the sixth message; The first network device sends the sixth message to the first session management function; The first session management function is an intermediate session management function, which is connected to the second session management function. The second session management function maintains the first PDU session established by the terminal device in the first network, and the first PDU session is associated with the DNN and the S-NSSAI; or... The first session management function belongs to the first network. The first session management function maintains the first PDU session established by the terminal device in the first network. The first PDU session is associated with the DNN and the S-NSSAI.

20. The method as described in claim 19, characterized in that, The method further includes: The first network device sends a cross-non-public network handover instruction to the first session management function, the cross-non-public network handover instruction being used to instruct the terminal device to perform a cross-non-public network handover.

21. The method as described in claim 18, characterized in that, The sixth message includes a lossless switching instruction.

22. A communication method, characterized in that, Applied to terminal devices, including: Terminal devices registered in the first network establish a first PDU session associated with DNN and S-NSSAI in the first network; The terminal device sends a first message to the first network device, the first message being used to request registration with the second network; The terminal device receives first information from the first network device. The first information is determined according to the interoperability between the first network and the second network. The first network and the second network do not roam or interoperate. The terminal device determines, based on the first information, to restore the PDU session of the terminal device in a manner that supports N3WIF, or determines not to establish the PDU session of the terminal device. The PDU session is associated with the DNN and the S-NSSAI.

23. The method as described in claim 22, characterized in that, The terminal device determines, based on the first information, to resume the PDU session of the terminal device in a manner that supports N3WIF, including: The terminal device sends a third message to the first network device, the third message being used to request the establishment of a second PDU session; The terminal device establishes a connection with the N3IWF through the second PDU session, and the N3IWF belongs to the first network; The terminal device sends a fourth message to the second network device through the connection. The fourth message is used to request registration in the first network via N3GPP. The second network device belongs to the first network. The terminal device establishes a PDU session based on the first information, including: The terminal device sends a fifth message to the second network device. The fifth message is used to request the establishment of an existing PDU session. The fifth message includes information about the DNN and information about the S-NSSAI.

24. The method as described in claim 23, characterized in that, The first information is used to indicate that roaming interoperability is not supported between the first network and the second network.

25. A communication method, characterized in that, include: A first network device receives a first message from a terminal device. The first network device belongs to a second network. The first message is used to request registration with the second network. The first network device obtains the identifier of the terminal device and determines the identifier of the first network; The first network device sends first information to the terminal device based on whether roaming interoperability is supported between the first network and the second network; The first information is used by the terminal device to determine whether to resume the PDU session of the terminal device in a manner that supports N3WIF, or to determine whether to no longer establish the PDU session of the terminal device. The PDU session is associated with DNN and S-NSSAI. DNN and S-NSSAI are used by the terminal device to establish a first PDU session associated with DNN and S-NSSAI in the first network.

26. A communication device, characterized in that, Including the processor and communication interface; The communication interface can be used to support the communication device in communication; The processor can be used to execute instructions to implement the method as described in any one of claims 1-10.

27. A communication device, characterized in that, Including the processor and communication interface; The communication interface can be used to support the communication device in communication; The processor can be used to execute instructions to implement the method as described in any one of claims 11-21.

28. A communication device, characterized in that, Including the processor and communication interface; The communication interface can be used to support the communication device in communication; The processor can be used to execute instructions to implement the method as described in any one of claims 22-24.

29. A communication device, characterized in that, Including the processor and communication interface; The communication interface can be used to support the communication device in communication; The processor can be used to execute instructions to implement the method as described in claim 25.

30. A communication system, characterized in that, It includes the communication device as described in claim 26 or 27, or the communication device as described in claim 28 or 29.

31. A computer-readable storage medium storing instructions, characterized in that, When the instructions are invoked and executed on a computer, the computer performs the method as described in any one of claims 1-25.

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