Network switching method and device

Abstract

The invention discloses a network switching method and a network switching device, which are used for solving the problem that terminal equipment cannot carry out IMS (IP Multimedia Subsystem) voice service. The method comprises: a first access network device receiving first session management information from a session management network element, the first session management information being used for requesting to establish a user plane tunnel for a voice service of a terminal device; and the first access network equipment sends a switching request to the first mobility management network element according to the first session management information and a first condition, the switching request is used for switching the terminal equipment from the first network to the second network, and the first condition comprises that the first network cannot perform the voice service. The application is applicable to the technical field of communication.

Description

[0001] This application is a divisional application. The application number of the original application is 201710693995.8, and the original application date is August 14, 2017. The entire content of the original application is incorporated into this application by reference. Technical Field

[0002] The present application relates to the field of communication technology, and in particular to a network switching method and device. Background Art

[0003] At present, on the one hand, many operators have not or do not plan to deploy Internet protocol multimedia subsystem (IMS) voice services in the fifth-generation (5G) wireless communication system. On the other hand, the spectrum in the 5G network is mostly in the high frequency band, and the high-frequency signal coverage range is small, while the IMS voice service requires a relatively large signal coverage range, which makes the terminal equipment in the 5G network unable to perform IMS voice services. Summary of the invention

[0004] The embodiments of the present application provide a network switching method and apparatus for solving the problem that a terminal device cannot perform an IMS voice service.

[0005] To achieve the above objectives, the present application provides the following technical solutions:

[0006] In a first aspect, a network switching method is provided, including: a first access network device receives first session management information from a session management network element, the first session management information is used to request to establish a user plane tunnel for a voice service of a terminal device; the first access network device sends a switching request to a first mobility management network element according to the first session management information and a first condition, the switching request is used to switch the terminal device from a first network to a second network, and the first condition includes: the first network cannot provide voice services.

[0007] The method provided in the first aspect can switch the terminal device to the second network when the terminal device in the first network performs voice service, so that the terminal device can perform voice service in the second network, thereby solving the problem that the terminal device in the first network cannot perform voice service.

[0008] In one possible design, the first condition also includes: the second network supports voice services, the signal quality of the second network meets the voice service requirements, and the network equipment and terminal equipment of the first network support at least one of switching between the first network and the second network.

[0009] In one possible design, the method further includes: the first access network device sends second session management information to the session management network element, the second session management information including information that the establishment of the user plane tunnel for the voice service is accepted. In this possible design, the network element in the first network will establish a user plane tunnel for the voice service of the terminal device.

[0010] In one possible design, before the first access network device sends the second session management information to the session management network element, the method further includes: the first access network device determines not to allocate wireless resources for the user plane tunnel of the voice service according to the first session management information and the first condition. In this possible design, the network element in the first network establishes a user plane tunnel for the voice service of the terminal device.

[0011] In one possible design, the method further includes: the first access network device sends third session management information to the session management network element, and the third session management information includes information that the establishment of the user plane tunnel for the voice service is rejected. In this possible design, after the terminal device completes the switch from the first network to the second network, the network element in the second network will establish a user plane tunnel for the voice service of the terminal device.

[0012] In one possible design, the information that the establishment of the user plane tunnel for the voice service is rejected includes the reason information for the rejection. In this possible design, after the terminal device completes the switching from the first network to the second network, the network element in the second network will establish a user plane tunnel for the voice service of the terminal device.

[0013] In one possible design, the reason information is: the terminal device is executing a switching process. In this possible design, after the terminal device completes the switching from the first network to the second network, the network element in the second network will establish a user plane tunnel for the voice service of the terminal device.

[0014] In one possible design, the first condition also includes: the second network cannot perform voice services, and the method also includes: the first access network device sends fourth session management information to the session management network element, the fourth session management information includes information that the establishment of a user plane tunnel for the voice service is rejected, and the information that the establishment of a user plane tunnel for the voice service is rejected includes insufficient wireless resources. In this possible design, after the terminal device completes the switch from the first network to the second network, the network element in the second network will not establish a user plane tunnel for the voice service of the terminal device.

[0015] In a second aspect, a network switching method is provided, including: a session management network element receives third session management information sent by a first access network device, the third session management information including reason information that establishment of a user plane tunnel for a voice service of a terminal device is rejected; the session management network element determines that the terminal device switches from a first network to a second network; and the session management network element establishes a user plane tunnel for the voice service in the second network according to the reason information.

[0016] The method provided by the second aspect is that when a terminal device in a first network switches from the first network to a second network, the session management network element establishes a user plane tunnel for the voice service in the second network according to the reason information. If the second network can provide voice services, the user plane tunnel can be established successfully, so that the terminal device can provide voice services in the second network, solving the problem that the terminal device in the first network cannot provide voice services.

[0017] In one possible design, the cause information is: the terminal device is executing a switching process.

[0018] In a possible design, the session management network element establishes a user plane tunnel for the voice service in the second network according to the cause information, including: the session management network element establishes a user plane tunnel for the voice service in the second network after a first preset time period according to the cause information and a second condition, and the second condition includes that the second network cannot perform voice services. This possible design reserves a first preset time period for the terminal device to complete the joint registration. By reasonably setting the first preset time period, the terminal device can initiate a CSFB call after completing the joint registration, thereby ensuring that the terminal device successfully initiates the CSFB call.

[0019] In one possible design, the session management network element establishes a user plane tunnel for the voice service in the second network after a first preset time period based on the cause information and the second condition, including: the session management network element sends a tunnel establishment request to the service gateway of the second network after the first preset time period based on the cause information and the second condition, and the tunnel establishment request is used to request to establish a user plane tunnel for the voice service.

[0020] In one possible design, the session management network element establishes a user plane tunnel for the voice service in the second network after a first preset time period according to the cause information and the second condition, including: the session management network element sends a tunnel establishment request to the service gateway of the second network according to the cause information, the tunnel establishment request is used to request to establish a user plane tunnel for the voice service; the session management network element receives a tunnel establishment response sent by the service gateway, the tunnel establishment response includes information that the establishment of the user plane tunnel for the voice service is rejected; the session management network element sends a first message to the policy function control network element after the first preset time period according to the second condition, the first message is used to indicate that the establishment of the user plane tunnel for the voice service has failed.

[0021] According to a third aspect, a network switching method is provided, including: a second mobility management network element receives a tunnel establishment request sent by a service gateway, the tunnel establishment request is used to request to establish a user plane tunnel for a voice service for a terminal device; the second mobility management network element sends a tunnel establishment response to the service gateway according to a second condition, the tunnel establishment response includes information that establishment of a user plane tunnel for the voice service of the terminal device is rejected, and the second condition includes that the second network cannot provide voice services.

[0022] The method provided by the third aspect is that the second mobility management network element sends a tunnel establishment response to the service gateway when the second network cannot perform voice services, so that the service gateway transmits the information that the user plane tunnel establishment is rejected to the IMS network, so that the IMS network can trigger the CSFB service of the terminal device, and then enable the terminal device to perform CS voice services.

[0023] In a possible design, the second condition also includes: the terminal device is a terminal device that switches from the first network to the second network.

[0024] In one possible design, before the second mobility management network element sends a tunnel establishment response to the service gateway according to the second condition, the method further includes: the second mobility management network element determines that the terminal device has completed the joint registration. This possible design can ensure that the terminal device successfully initiates a CSFB call.

[0025] In one possible design, the second mobility management network element determines that the terminal device has completed the joint registration, including: the second mobility management network element determines that a joint registration completion message is received from the terminal device.

[0026] In a fourth aspect, a network switching method is provided, comprising: a second mobility management network element sends a wireless tunnel establishment request to a second access network device, the wireless tunnel establishment request is used to request to establish a user plane tunnel for a voice service of a terminal device; the second mobility management network element receives a wireless tunnel establishment response sent by the second access network device, the wireless tunnel establishment response includes information that establishment of a user plane tunnel for the voice service of the terminal device is rejected; the second mobility management network element sends a tunnel establishment response to a service gateway according to a second condition, the tunnel establishment response includes information that establishment of a user plane tunnel for the voice service of the terminal device is rejected, and the second condition includes that the second network cannot perform voice services.

[0027] The method provided by the fourth aspect is that the second mobility management network element sends the information that the user plane tunnel establishment is rejected to the service gateway, so that the service gateway transmits the information that the user plane tunnel establishment is rejected to the IMS network, so that the IMS network can trigger the CSFB service of the terminal device, and then enable the terminal device to perform CS voice service.

[0028] In a possible design, the second condition also includes: the terminal device is a terminal device that switches from the first network to the second network.

[0029] In one possible design, the second mobility management network element sends a tunnel establishment response to the service gateway according to the second condition, including: the second mobility management network element determines that the second condition is met and the terminal device completes the joint registration; the second mobility management network element sends a tunnel establishment response to the service gateway. This possible design can ensure that the terminal device successfully initiates a CSFB call.

[0030] In one possible design, the second mobility management network element determines that the terminal device completes the joint registration, including: the second mobility management network element determines that a registration completion message is received from the terminal device.

[0031] In a fifth aspect, a network switching method is provided, including: a second mobility management network element receives a tunnel establishment request sent by a service gateway, the tunnel establishment request is used to request to establish a user plane tunnel for a voice service for a user equipment terminal device; if a second condition is met, the second mobility management network element determines that the terminal device completes joint registration, and the second condition includes that the second network cannot perform voice services; the second mobility management network element sends a wireless tunnel establishment request to a second access network device, the wireless tunnel establishment request is used to request to establish a user plane tunnel for the voice service of the terminal device; the second mobility management network element receives a wireless tunnel establishment response sent by the second access network device, the wireless tunnel establishment response includes information that the user plane tunnel establishment for the voice service of the terminal device is rejected; the second mobility management network element sends a tunnel establishment response to the service gateway based on the wireless tunnel establishment response, the tunnel establishment response includes information that the user plane tunnel establishment for the voice service of the terminal device is rejected.

[0032] The method provided in the fifth aspect is that the second mobility management network element sends the information that the user plane tunnel establishment is rejected to the service gateway after determining that the terminal device has completed the joint registration, so that the service gateway transmits the information that the user plane tunnel establishment is rejected to the IMS network, thereby enabling the IMS network to trigger the CSFB service of the terminal device, thereby enabling the terminal device to perform CS voice service, and also ensuring that the terminal device successfully initiates a CSFB call.

[0033] In a possible design, the second condition also includes: the terminal device is a terminal device that switches from the first network to the second network.

[0034] In one possible design, the second mobility management network element determines that the terminal device completes the joint registration, including: the second mobility management network element determines that a registration completion message sent by the terminal device is received.

[0035] In a sixth aspect, a network switching method is provided, comprising: a second access network device receives a wireless tunnel establishment request sent by a second mobility management network element, the wireless tunnel establishment request is used to request the second access network device to establish a user plane tunnel for a voice service for a terminal device; the second access network device sends a wireless tunnel establishment response to the second mobility management network element according to a second condition, the wireless tunnel establishment response includes information that establishment of the user plane tunnel for the voice service is rejected, and the second condition includes that the second network cannot provide voice services.

[0036] The method provided in the sixth aspect is that the second access network device refuses to allocate wireless resources for the user plane tunnel when the second network cannot perform voice services, and carries the information that the establishment of the user plane tunnel for the voice service is rejected in the wireless tunnel establishment response to the second mobility management network element. The second mobility management network element can pass the information that the establishment of the user plane tunnel is rejected to the IMS network, so that the IMS network triggers the CSFB service of the terminal device, and then enables the terminal device to perform CS voice services.

[0037] In a possible design, the second condition also includes: the terminal device is a terminal device that switches from the first network to the second network.

[0038] In the seventh aspect, a network switching method is provided, including: the IMS network element receives a request message for establishing a voice service for a terminal device in a PS domain; the IMS network element determines that a voice service cannot be established in the PS domain of a first network or a second network; the IMS network element determines that the terminal device completes joint registration; and the IMS network element triggers a CSFB service of the terminal device.

[0039] The method provided in the seventh aspect is that when the IMS network element determines that it is impossible to establish a voice service in the PS domain of the first network or the second network and the terminal device completes the joint registration, the CSFB service of the terminal device is triggered. Since the completion of the joint registration by the terminal device is a necessary condition for the terminal device to initiate a CSFB call, the method provided in the seventh aspect can also ensure that the terminal device successfully initiates a CSFB call, thereby enabling the terminal device to perform CS voice services.

[0040] In one possible design, after the IMS network element receives a request message for establishing a voice service for the terminal device in the PS domain, the method further includes: the IMS network element determines that the terminal device is registered in the first network.

[0041] In one possible design, the IMS network element determines that a voice service cannot be established in the PS domain of the first network or the second network, including: the IMS network element obtains voice service establishment failure information from the PS domain of the first network; or, the IMS network element obtains voice service establishment failure information from the PS domain of the second network.

[0042] In one possible design, the IMS network element determines that the terminal device has completed the joint registration, including: the IMS network element determines that the terminal device has completed the joint registration after a second preset time period from when the IMS network element determines that a voice service cannot be established in the PS domain of the first network or the second network; or, the IMS network element determines that the terminal device has completed the joint registration based on the registration location information of the terminal device obtained from the policy control network element or the home user server.

[0043] In one possible design, the terminal device is a calling terminal device for a voice service, and the IMS network element triggers the CSFB service of the terminal device, including: the IMS network element sends a second message to the calling terminal device, and the second message is used to trigger the calling terminal device to initiate a CSFB calling service.

[0044] In one possible design, the terminal device is a called terminal device for a voice service, and the IMS network element triggers the CSFB service of the terminal device, including: the IMS network element sends a third message to the called domain selection device, and the third message is used to indicate that the establishment of the called voice service in the PS domain of the first network or the second network has failed, so that the called domain selection device triggers the CSFB called voice service of the called terminal device.

[0045] In the eighth aspect, a network switching method is provided, including: a second mobility management network element receives a fourth message sent by the first mobility management network element, the fourth message is used to confirm that the terminal device has completed relocation; the second mobility management network element sends a tunnel modification request to the service gateway according to a second condition, the tunnel modification request is used to modify the signaling plane tunnel information of the voice service of the terminal device, and the second condition includes that the second network cannot provide voice services.

[0046] The method provided in the eighth aspect is that when the second network cannot provide voice services, the second mobility management network element sends a tunnel modification request to the service gateway, and the service gateway forwards the tunnel modification request to the session management network element. Since the session management network element will send a message for triggering the terminal device to initiate a CSFB call (i.e., the second message below) to the terminal device only after receiving the tunnel modification request, the method provided in the eighth aspect can trigger the terminal device to initiate a CSFB call when the second network cannot provide voice services, thereby enabling the terminal device to perform CS voice services.

[0047] In one possible design, the second mobility management network element sends a tunnel modification request to the service gateway according to the second condition, including: the second mobility management network element determines that the second condition is met and the UE completes the joint registration; the second mobility management network element sends a tunnel modification request to the service gateway. This possible design can ensure that the terminal device successfully initiates a CSFB call.

[0048] In the ninth aspect, a network registration method is provided, the method comprising: a first mobility management network element receives a registration request from a terminal device, the registration request is used to request that the terminal device be registered in a first network; if the third condition is met, the first mobility management network element sends a first indication message to the terminal device, the first indication message is used to indicate that the voice service of the PS domain is supported, and the third condition includes: the first network supports moving the terminal device to a second network. In the method provided in the ninth aspect, regardless of whether the first network supports the voice service of the terminal device, as long as the first network has the ability to switch the terminal device back to a network that can provide voice services when the terminal device initiates voice services, when the terminal device registers with the first network, the first mobility management network element indicates that the voice service of the PS domain of the terminal device is supported, thereby ensuring that the terminal device registers and resides in the first network without reselecting to other networks, saving network resources, and ensuring that the terminal device normally executes the PS domain voice service registration process and initiates the PS domain voice call process through the first network.

[0049] In one possible design, the core networks of the first network and the second network are the same, but the access standards are different; or, the core networks and the access standards of the first network and the second network are different.

[0050] In one possible design, the first network supports moving the terminal device to the second network, including: a first access network device in the first network supports connecting the terminal device to the second network upon receiving first session management information from a session management network element, the first session management information being used to request establishment of a user plane tunnel for a voice service of the terminal device.

[0051] In one possible design, the third condition also includes: supporting switching interoperability between the first network and the second network, and the second network can support at least one of the voice services in the PS domain.

[0052] In one possible design, the first network and the second network support handover interoperability, including: a handover interoperability interface exists between the first network and the second network.

[0053] In one possible design, before the first mobility management network element sends the first indication information to the terminal device, the method further includes: the first mobility management network element determines that the terminal device is a terminal device that mainly provides voice services. Since the terminal device that mainly provides data services has nothing to do with voice services, this optional method can distinguish the terminal type, and it is not necessary to execute this solution for the terminal device that mainly provides data services, that is, it is not necessary to determine whether the third condition is met, and it is not necessary to send the first indication information.

[0054] In one possible design, the registration request carries indication information that the terminal device is a terminal device mainly providing voice services, and the first mobility management network element determines that the terminal device is a terminal device mainly providing voice services, including: the first mobility management network element determines that the terminal device is a terminal device mainly providing voice services based on the registration request.

[0055] In a possible design, before the first mobility management network element sends the first indication information to the terminal device, the method further includes: the first mobility management network element determines that the terminal device supports the process of moving from the first network to the second network and continuing the process of initiating the voice service through the second network during the process of initiating the voice service. Since the method provided in the first aspect can only be implemented if the terminal device supports the process of moving from the first network to the second network and continuing the process of initiating the voice service through the second network during the process of initiating the voice service, the information can be determined in advance to avoid affecting the terminal device that cannot support the process of moving from the first network to the second network and continuing the process of initiating the voice service through the second network during the process of initiating the voice service.

[0056] In one possible design, the registration request also carries indication information that the terminal device supports moving from the first network to the second network and continuing the voice service initiation process through the second network during the voice service initiation process. The first mobility management network element determines that the terminal device supports moving from the first network to the second network and continuing the voice service initiation process through the second network during the voice service initiation process, including: the first mobility management network element determines, based on the registration request, that the terminal device supports moving from the first network to the second network and continuing the voice service initiation process through the second network.

[0057] In the tenth aspect, a network registration method is provided, the method comprising: a terminal device generates a registration request, the registration request is used to request that the terminal device be registered in a first network, the registration request carries indication information that the terminal device is a terminal device mainly providing voice services; the terminal device sends the registration request to a first mobility management network element.

[0058] In one possible design, the registration request also includes indication information that the terminal device supports moving from the first network to the second network during the voice service initiation process and continuing the voice service initiation process through the second network.

[0059] In one possible design, the core networks of the first network and the second network are the same, but the access standards are different; or, the core networks and the access standards of the first network and the second network are different.

[0060] In the eleventh aspect, a network device is provided, which can be a first access network device, a session management network element, a second mobility management network element, a second access network device, an IMS network element or a first mobility management network element. When the network device is a first access network device, the network device has the function of implementing any one of the methods provided in the first aspect; when the network device is a session management network element, the network device has the function of implementing any one of the methods provided in the second aspect; when the network device is a second mobility management network element, the network device has the function of implementing any one of the methods provided in the third aspect, the fourth aspect, the fifth aspect or the eighth aspect; when the network device is a second access network device, the network device has the function of implementing any one of the methods provided in the sixth aspect; when the network device is an IMS network element, the network device has the function of implementing any one of the methods provided in the seventh aspect; when the network device is a first mobility management network element, the network device has the function of implementing any one of the methods provided in the ninth aspect. The functions implemented by the network device can be implemented by hardware, or by hardware executing corresponding software. The hardware or software includes one or more functional units corresponding to the above methods.

[0061] In a twelfth aspect, a terminal device is provided, which has the function of implementing any one of the methods provided in the tenth aspect, and the function implemented by the terminal device can be implemented by hardware, or by hardware executing corresponding software. The hardware or software includes one or more functional units corresponding to the method provided in the tenth aspect.

[0062] In the thirteenth aspect, a network device is provided, including: a memory, a processor and a communication interface; the memory is used to store computer execution instructions, the processor executes the computer execution instructions stored in the memory, and enables the network device to implement the method provided in the above aspects through the communication interface. Specifically, the network device can be a first access network device, a session management network element, a second mobility management network element, a second access network device, an IMS network element or a first mobility management network element. When the network device is the first access network device, the network device can implement any one of the methods provided in the first aspect; when the network device is a session management network element, the network device can implement any one of the methods provided in the second aspect; when the network device is a second mobility management network element, the network device can implement any one of the methods provided in the third aspect, the fourth aspect, the fifth aspect or the eighth aspect; when the network device is the second access network device, the network device can implement any one of the methods provided in the sixth aspect; when the network device is an IMS network element, the network device can implement any one of the methods provided in the seventh aspect; when the network device is the first mobility management network element, the network device has the function of implementing any one of the methods provided in the ninth aspect.

[0063] In the fourteenth aspect, a terminal device is provided, including: a memory, a processor and a communication interface; the memory is used to store computer execution instructions, the processor executes the computer execution instructions stored in the memory, and through the communication interface, the terminal device implements any one of the methods provided in the tenth aspect.

[0064] In a fifteenth aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enable the computer to execute any one of the methods provided in the first aspect.

[0065] In the sixteenth aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enables the computer to execute any one of the methods provided in the second aspect.

[0066] In the seventeenth aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enable the computer to execute any one of the methods provided in the third aspect.

[0067] In the eighteenth aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enable the computer to execute any one of the methods provided in the fourth aspect.

[0068] In the nineteenth aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enables the computer to execute any one of the methods provided in the fifth aspect.

[0069] In the twentieth aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enables the computer to execute any one of the methods provided in the sixth aspect.

[0070] In the twenty-first aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enable the computer to execute any one of the methods provided in the seventh aspect.

[0071] In the twenty-second aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enables the computer to execute any one of the methods provided in the eighth aspect.

[0072] In the twenty-third aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enables the computer to execute any one of the methods provided in the ninth aspect.

[0073] In the twenty-fourth aspect, a computer-readable storage medium is provided, comprising instructions, which, when executed on a computer, enables the computer to execute any one of the methods provided in the tenth aspect.

[0074] In the twenty-fifth aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the first aspect.

[0075] In the twenty-sixth aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the second aspect.

[0076] In the twenty-seventh aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the third aspect.

[0077] In the twenty-eighth aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the fourth aspect.

[0078] In the twenty-ninth aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the fifth aspect.

[0079] In the thirtieth aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the sixth aspect.

[0080] In the thirty-first aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the seventh aspect.

[0081] In the thirty-second aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the eighth aspect.

[0082] In the thirty-third aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the ninth aspect.

[0083] In the thirty-fourth aspect, a computer program product comprising instructions is provided, which, when executed on a computer, enables the computer to execute any one of the methods provided in the tenth aspect.

[0084] The technical effects brought about by any design method in aspects 11 to 34 can refer to the technical effects brought about by different design methods in aspects 1 to 10, and will not be repeated here. BRIEF DESCRIPTION OF THE DRAWINGS

[0085] Figure 1 A schematic diagram of the architecture of a 5G network provided in an embodiment of the present application;

[0086] Figure 1A A schematic diagram of a terminal device accessing a 5G CN provided in an embodiment of the present application;

[0087] Figure 2 A schematic diagram of the architecture of an EPS network provided in an embodiment of the present application;

[0088] Figure 3 A schematic diagram of the network architecture after the 5G network and EPS network are integrated according to an embodiment of the present application;

[0089] Figure 4 A communication diagram of an EPS network and an IMS network provided in an embodiment of the present application;

[0090] Figure 5 A schematic diagram of IMS voice communication between terminal devices provided in an embodiment of the present application;

[0091] Figure 6 A schematic diagram of the composition of a network device provided in an embodiment of the present application;

[0092] Fig. 6A A schematic diagram of the composition of a terminal device provided in an embodiment of the present application;

[0093] Figure 7 An interactive flow chart of a network switching method provided in an embodiment of the present application;

[0094] Figure 8 and Fig. 9 They are respectively a process flow chart of a network switching provided in an embodiment of the present application;

[0095] Figure 10-12 They are schematic diagrams of a process of establishing a user plane tunnel provided in an embodiment of the present application;

[0096] Figure 13-Figure 17 They are schematic diagrams of a method for ensuring that a terminal device successfully initiates a CSFB call, respectively, provided in an embodiment of the present application;

[0097] Figure 18-Figure 28 They are respectively interactive flow charts of a network switching method provided in an embodiment of the present application;

[0098] Fig.28A A flowchart of a network registration method provided in an embodiment of the present application;

[0099] Fig.28B A flowchart of another network registration method provided in an embodiment of the present application;

[0100] Fig.29 A schematic diagram of a network device provided in an embodiment of the present application;

[0101] Fig.29A A schematic diagram of a terminal device provided in an embodiment of the present application. DETAILED DESCRIPTION

[0102] The technical solutions in the embodiments of the present application will be described below in conjunction with the drawings in the embodiments of the present application. In the description of the present application, unless otherwise specified, " / " means or, for example, A / B can mean A or B; "and / or" in this article is only a description of the association relationship of associated objects, indicating that there can be three relationships, for example, A and / or B can mean: A exists alone, A and B exist at the same time, and B exists alone. In addition, in the description of the present application, "multiple" means two or more than two.

[0103] The method provided in the embodiments of the present application can be applied to wireless communication systems, such as: global system of mobile communication (GSM) system, code division multiple access (CDMA) system, wideband code division multiple access (WCDMA) system, general packet radio service (GPRS) system, universal mobile communications system (UMTS), EPS network and 5G network, and can also be used in future wireless communication systems.

[0104] Specifically, the method provided in the embodiment of the present application can be applied to Figure 1 The 5G network shown, Figure 1As shown, the 5G network may include: an authentication server function (AUSF) network element, an access and mobility management function (AMF) network element, a data network (DN), a unified data management (UDM) network element, a policy control function (PCF) network element, (radio) access network (RAN) equipment, a user plane function (UPF) network element, a terminal device, an application function (AF) network element, and a session management function (SMF) network element.

[0105] Among them, the (R)AN equipment of the 5G network can be the next generation (NG)RAN equipment or the evolved universal terrestrial radio access network (E-UTRAN) equipment. The 5G network can be connected to the above two access network equipment at the same time, that is, the 5G network may have two different radio access types (RAT) at the same time. Figure 1A The terminal device can access the 5G core network (CN) through the E-UTRAN device or the NG RAN device. The embodiment of the present application takes the example of the terminal device registering in the 5G network through the NG RAN and initiating a voice service under the NG RAN access standard to exemplify the method provided in the embodiment of the present application.

[0106] The control plane (CP) functional network elements include: UDM network element, AUSF network element, PCF network element, AMF network element and SMF network element.

[0107] Specifically, the main functions of (R)AN equipment include: providing wireless connection; the main functions of UPF network element include: enabling data packet routing and forwarding, mobility anchor point, uplink classifier to support routing service flow to DN, BP to support multi-home packet data unit (PDU) session, etc.; DN can provide operator services, Internet access or third-party services; the main functions of AMF network element include managing user registration, reachability detection, SMF node selection, mobile state transition management, etc.; the main functions of SMF network element include: controlling session establishment, modification and deletion, user plane node selection, etc.; the main functions of PCF network element include: policy decision point, providing rules based on service data flow and application detection, gating, quality of service (QoS) and flow-based charging control; the main functions of AF network element include: interacting with the 3rd generation partnership project (3GPP) core network to provide services, to affect service flow routing, access network capability opening, policy control, etc.; the main functions of AUSF network element include: providing authentication services; the main functions of UDM network element include: storing user contract data.

[0108] Among them, the terminal device may also be referred to as user equipment (UE), access terminal, user unit, user station, mobile station, mobile station, remote station, remote terminal, mobile device, user terminal, terminal, wireless communication device, user agent or user device. The terminal device may also be a station (ST) in a wireless local area network (WLAN), a cellular phone, a cordless phone, a session initiation protocol (SIP) phone, a wireless local loop (WLL) station, a personal digital assistant (PDA) device, a handheld device with wireless communication function, a computing device or other processing device connected to a wireless modem, a vehicle-mounted device, a wearable device (also referred to as a wearable smart device). The terminal device may also be a terminal device in a next generation communication system, for example, a terminal device in 5G or a terminal device in a future evolved public land mobile network (PLMN), a terminal device in a new radio (NR) communication system, etc.

[0109] Specifically, the method provided in the embodiment of the present application can also be applied to Figure 2The evolved packet system (EPS) network (commonly known as the 4G network) shown in FIG. Figure 2 As shown, the EPS network may include the following multiple functional network elements: terminal equipment, E-UTRAN (specifically, eNodeB), service gateway (serving gateway, referred to as SGW), packet data gateway (packet data network gateway, referred to as PGW), mobility management network element (mobility management entity, referred to as MME), home subscriber server (home subscriber server, referred to as HSS), mobile switching center (mobile switching center, referred to as MSC) and policy and charging rules function (policy and charging rules function, referred to as PCRF) network element.

[0110] When both 5G and EPS networks are deployed, the functional network elements in the 5G network can be integrated with the functional network elements in the EPS network so that the 5G network and the EPS network can interact with each other. Figure 3 , the functional network elements in the integrated network include: HSS+UDM functional network element (referring to a functional network element that has both the function of HSS and the function of UDM), PCF+PCRF functional network element (referring to a functional network element that has both the function of PCF and the function of PCRF), SMF+PGW-C functional network element (referring to a functional network element that has both the function of SMF and the function of packet data network gateway-control plane (PGW-C for short)), UPF+PGW-U functional network element (referring to a functional network element that has both the function of UPF and the function of packet data network gateway-userplane (PGW-U for short)), SGW, MME, E-UTRAN, AMF, NGRAN and terminal equipment. In each embodiment of the present application, HSS+UDM functional network element, PCF+PCRF functional network element, SMF+PGW-C functional network element, UPF+PGW-U are only examples, and each network element may also be two separate network elements, which are not limited here.

[0111] At present, the more mature voice service solutions include the IMS voice service solution in the EPS network and the circuit switching (CS) voice service solution in the 2G / 3G network. Since the 5G network in the prior art does not support IMS and CS voice services, the embodiment of the present application provides a network switching method, so that the terminal device can switch from the 5G network to the EPS network or the 2G / 3G network for voice services when voice services are needed.

[0112] See also Figure 2 If the operator's IP service is an IMS voice service, the communication diagram between the EPS network and the IMS network can be found in Figure 4 , wherein the IMS network includes: Proxy-Call Session Control Function (P-CSCF) / Session Border Control (SBC), interrogating-call session control function (I-CSCF) / serving-call session control function (S-CSCF), telephony application server (TAS) and IMS media gateway (IMSMGW), wherein the terminating access domain selection function module (T-ADS) can be included in TAS, therefore, the called domain selection device in the following text can be considered as TAS. TAS can also be a service centralization and continuity application server (SCC AS).

[0113] When the terminal equipment is performing IMS voice services, the communication process between the calling terminal equipment and the called terminal equipment can be seen in Figure 5 Specifically, the calling terminal device sends the call-related information to the calling access network. The call-related information passes through the calling access network, the calling core network, the calling IMS network, the called IMS network, the called core network and the called access network before reaching the called terminal device. The information fed back by the called terminal device to the calling terminal device can be sent in the opposite direction.

[0114] like Figure 6As shown, it is a schematic diagram of the hardware structure of a network device 60 provided in an embodiment of the present application, which includes at least one processor 601, a communication bus 602, a memory 603 and at least one communication interface 604. The network device 60 may be the first access network device, or the second access network device, or the first mobility management network element, or the second mobility management network element, or the session management network element, or the IMS network element, or the user plane gateway, or the serving gateway in the present application.

[0115] The processor 601 may be a general-purpose central processing unit (CPU), a microprocessor, an application-specific integrated circuit (ASIC), or one or more integrated circuits for controlling the execution of the program of the present application.

[0116] Communication bus 602 may include a pathway for transmitting information between the above-mentioned components.

[0117] The communication interface 604 uses any transceiver-like device for communicating with other devices or communication networks, such as Ethernet, radio access network (RAN), wireless local area networks (WLAN), etc.

[0118] The memory 603 may be a read-only memory (ROM) or other types of static storage devices that can store static information and instructions, a random access memory (RAM) or other types of dynamic storage devices that can store information and instructions, or an electrically erasable programmable read-only memory (EEPROM), a compact disc read-only memory (CD-ROM) or other optical disc storage, optical disc storage (including compressed optical disc, laser disc, optical disc, digital versatile disc, Blu-ray disc, etc.), a magnetic disk storage medium or other magnetic storage device, or any other medium that can be used to carry or store the desired program code in the form of instructions or data structures and can be accessed by a computer, but is not limited thereto. The memory may exist independently and be connected to the processor via a bus. The memory may also be integrated with the processor.

[0119] The memory 603 is used to store the application code for executing the solution of the present application, and the execution is controlled by the processor 601. The processor 601 is used to execute the application code stored in the memory 603, so as to implement the method described below.

[0120] In a specific implementation, as an embodiment, the processor 601 may include one or more CPUs, such as Figure 6 CPU0 and CPU1 in.

[0121] In a specific implementation, as an embodiment, the network device 60 may include multiple processors, such as Figure 6 601 and processor 608 in the embodiment of the present invention. Each of these processors may be a single-CPU processor or a multi-CPU processor. The processor herein may refer to one or more devices, circuits, and / or processing cores for processing data (e.g., computer program instructions).

[0122] In a specific implementation, as an embodiment, the network device 60 may further include an output device 605 and an input device 606. The output device 605 communicates with the processor 601 and may display information in a variety of ways.

[0123] like Fig. 6A As shown, it is a schematic diagram of the hardware structure of a terminal device 60A provided in an embodiment of the present application. The terminal device 60A includes at least one processor 601A, a communication bus 602A, a memory 603A and at least one communication interface 604A.

[0124] In a specific implementation, as an embodiment, the processor 601A may include one or more CPUs, such as Fig. 6A CPU0 and CPU1 in.

[0125] In a specific implementation, as an embodiment, the terminal device 60A may include multiple processors, such as Fig. 6A Processor 601A and processor 608A in.

[0126] In a specific implementation, as an embodiment, the terminal device 60A may also include an output device 605A and an input device 606A. Fig. 6A The functions of the various components shown in and other descriptions can be exemplified by referring to the above.

[0127] In the embodiment of the present application, the first network and the second network may refer to two networks with different access standards and different core networks, for example, a 5G network with an NG RAN access standard and an EPS network with an E-UTRAN access standard; or may refer to two networks with different access standards but the same core network, for example, a 5G network with an NG RAN access standard and a 5G network with an E-UTRAN access standard. In the embodiment of the present application, the first network and the second network are used as two networks with different access standards and core networks to illustrate the method provided in the embodiment of the present application, but this should not be regarded as a limitation on the scope of protection of the present application. The method provided in the embodiment of the present application is also applicable to two networks with the same core network but different access standards.

[0128] The solution provided in the embodiment of the present application can be based on a service-oriented architecture, and the communication between various network elements can be based on a service-oriented interface or a non-service-oriented traditional interface. The embodiment of the present application does not specifically limit this.

[0129] The present application embodiment provides a network switching method, such as Figure 7 As shown, the method may include:

[0130] 701. A first access network device receives first session management information from a session management (SM) network element, where the first session management information is used to request establishment of a user plane tunnel for a voice service of a terminal device.

[0131] Specifically, the first session management information is used to request to establish a user plane tunnel for a voice service of the terminal device in the first network. The voice service of the terminal device may be an IMS voice service.

[0132] The terminal device can be a calling terminal device of a voice service or a called terminal device of a voice service. The user plane tunnel can be called a QoS flow in a 5G network.

[0133] 702. The first access network device sends a handover request (handover required) to the first mobility management network element according to the first session management information and the first condition, where the handover request is used to switch the terminal device from the first network to the second network, and the first condition includes: the first network cannot provide voice services.

[0134] Among them, the first access network device can be NG RAN, the session management network element can be SMF+PGW-C functional network element, the first mobility management network element can be AMF, the first network can be a 5G network, and the second network can be an EPS network. In addition, the first network and the second network can both be 5G networks. The difference is that the access standards of the first network and the second network are different.

[0135] The first session management information is session management information related to the user plane tunnel of the IMS voice service of the terminal device. The first session management information may include QoS parameters of the user plane tunnel of the IMS voice service of the terminal device, for example, 5G QoS indicator (5G QoS indicator, hereinafter referred to as 5QI) = 1, allocation / retention priority (allocation / retention priority, ARP for short), guaranteed bit rate (guaranteed bit rate, GBR for short) and maximum bit rate (maximum bit rate, MBR for short) and other parameters. The first session management information may also include other information.

[0136] The SMF+PGW-C functional network element can carry the first session management information in a session management request carrying a PDU modification command (session management with PDU modification command) and send it to the AMF. The AMF then carries the first session management information in an N2 session request (N2 session request) and sends it to the NG RAN.

[0137] The method provided in the embodiment of the present application can switch the terminal device to the EPS network when the terminal device in the 5G network performs voice services, so that the terminal device can perform IMS voice services in the EPS network, thereby solving the problem that the terminal device in the 5G network cannot perform IMS voice services.

[0138] According to the provisions of the current 5G network protocol, for voice-centric terminal devices, if the network side of the 5G network does not support IMS voice services, the voice-centric terminal devices should not initially choose NR to access the 5G core network (5G core network, referred to as 5GC), or even if they access the 5GC, they must reselect to access E-UTRAN and evolved packet core (EPC). If the 5G network does not support IMS voice services, the terminal devices will not be able to stay in the 5G network and enjoy high-speed data services. The method provided in the embodiment of the present application is that when the 5G network cannot perform IMS voice services, the NG RAN can send a switching request to the AMF, so that the terminal device in the 5G network switches from the 5G network to the EPS network, and the terminal device can perform IMS voice services in the EPS network, so that the terminal device can first stay in the 5G network to enjoy high-speed data services, and when the IMS voice service is needed, it will switch to the EPS network for IMS voice services.

[0139] Furthermore, in order to ensure that terminal devices in the 5G network can smoothly perform voice services, the embodiments of the present application provide a method for terminal devices to perform network switching in two scenarios.

[0140] Scenario 1: The first network cannot provide voice services, but the second network can provide voice services.

[0141] In this scenario, the first condition may also include: the second network supports voice services, the signal quality of the second network meets the voice service requirements, and the network equipment and terminal equipment of the first network support at least one of switching between the first network and the second network.

[0142] In this scenario, the terminal device can switch networks in any of the following ways: method 1 or method 2.

[0143] Method 1: By notifying the session management network element that the establishment of the user plane tunnel for the voice service has been accepted, the network device in the first network establishes a user plane tunnel for the voice service of the terminal device. During the process of the terminal device switching from the first network to the second network, the user plane tunnel established by the network device in the first network for the voice service of the terminal device will be switched to the user plane tunnel for the voice service in the second network.

[0144] See also Figure 8 , Method 1 may specifically include:

[0145] S11. The first access network device sends second session management information to the session management network element, where the second session management information includes information that establishment of a user plane tunnel for a voice service is accepted.

[0146] Specifically, the first access network device can carry the second session management information in the N2 session response (N2session response) and send it to the first mobility management network element, and the first mobility management network element can then carry the second session management information in the session management response carrying the PDU session modification command (session management with PDUmodification command ack) and send it to the session management network element.

[0147] It should be noted that, since the first network cannot perform voice services, although the second session management information includes information that the establishment of the user plane tunnel for the voice service is accepted, in fact, the first access network device does not allocate radio resources to the voice service.

[0148] Optional, see Figure 8Before step S11, the method may further include: the first access network device determines not to allocate wireless resources for the user plane tunnel of the voice service according to the first session management information and the first condition.

[0149] S12: The session management network element receives the second session management information sent by the first access network device, and determines the user plane tunnel related information of the voice service according to the second session management information.

[0150] Specifically, the user plane tunnel related information of the voice service of the terminal device may be data detection (packet detection), enforcement rule (enforcement rule), reporting rule (reporting rule), core network tunnel information (core network tunnel information), etc. related to the user plane tunnel of the voice service.

[0151] S13. The session management network element sends user plane tunnel related information of the voice service to the user plane gateway.

[0152] Among them, the user plane gateway can be a UPF+PGW-U functional network element.

[0153] The SMF+PGW-C functional network element may carry the user plane tunnel related information of the voice service in the N4 session modification request (N4 session modification request) and send it to the UPF+PGW-U functional network element.

[0154] S14. The user plane gateway receives the user plane tunnel related information of the voice service sent by the session management network element, and establishes a user plane tunnel for the voice service according to the user plane tunnel related information of the voice service.

[0155] Steps S11-S14 can be executed before step 702, or after step 702 and before the user plane tunnel of the voice service starts to switch. By switching the user plane tunnel of the voice service, the user plane tunnel established by the user plane gateway for the voice service can also be switched to the user plane tunnel of the voice service in the second network, so that the terminal device can perform voice services in the second network.

[0156] Method 2: by notifying the session management network element of the reason why establishment of the user plane tunnel for the voice service is rejected, the session management network element re-establishes the user plane tunnel for the voice service of the terminal device after the terminal device completes switching from the first network to the second network.

[0157] See also Fig. 9 , the second method may specifically include:

[0158] S21. The first access network device sends third session management information to the session management network element, where the third session management information includes reason information about why establishment of a user plane tunnel for a voice service of the terminal device is rejected.

[0159] Specifically, NG RAN can carry the third session management information in the N2 session response and send it to AMF, and AMF then carries the third session management information in the session management response carrying the PDU session modification command and sends it to the SMF+PGW-C functional network element.

[0160] Optionally, the reason for rejection may be: the terminal device is executing a switching process.

[0161] S22. The session management network element receives third session management information sent by the first access network device.

[0162] S23. The session management network element determines that the terminal device switches from the first network to the second network.

[0163] Step S23 can be implemented in any one of the methods (1) and (2). Method (1) is to set a timer in the session management network element. When the timer times out, it is determined that the terminal device is switched from the first network to the second network. Method 2 is that when a tunnel modification request (modify bearer request) is received, the session management network element determines that the terminal device is switched from the first network to the second network. The tunnel modification request is used to modify the signaling plane tunnel information of the voice service of the terminal device.

[0164] S24. The session management network element establishes a user plane tunnel for the voice service in the second network according to the cause information.

[0165] In the specific implementation of step S24, when the session management network element determines that the third session management information is cause information or the cause information is that the terminal device is executing a switching process, a user plane tunnel can be established for the voice service in the second network after the terminal device switches from the first network to the second network.

[0166] In method 2, although the network equipment in the first network does not establish a user plane tunnel for the voice service, after determining that the terminal device switches from the first network to the second network, the session management network element establishes a user plane tunnel for the voice service of the terminal device in the second network, thereby allowing the terminal device to perform voice services in the second network.

[0167] Method 2 provides a method for switching networks of a terminal device in a scenario where a first network cannot perform voice services but a second network can perform voice services. When the first access network device receives the first session management information, it can promptly switch the terminal device in the first network to the second network so that the terminal device in the first network can continue to execute the voice call establishment process in the second network. At the same time, the first access network device rejects the establishment of a user plane tunnel for the voice service with the reason that the terminal device is executing the switching process, so as to trigger the user plane gateway to rebuild the user plane tunnel for the voice service after the terminal device successfully switches to the second network (because in this scenario, the second network can perform voice sessions, so that the user plane tunnel can be established successfully), so that the terminal device can perform voice services in the second network.

[0168] Scenario 2: Both the first network and the second network cannot provide voice services.

[0169] In this scenario, the first condition may also include: the second network cannot provide voice services.

[0170] In this scenario, the terminal device can switch networks in any of the following ways: method 3 and method 4.

[0171] Method three: by notifying the session management network element of the reason why the establishment of the user plane tunnel for the voice service is rejected, the session management network element re-establishes the user plane tunnel for the voice service of the terminal device after the terminal device completes the switching from the first network to the second network. When the user plane tunnel is not established successfully, the terminal device falls back to the 2G / 3G network for voice service.

[0172] Method 3 may specifically include:

[0173] S31-S34.

[0174] Steps S31-S34 correspond to steps S21-S24 respectively, that is, step S31 is the same as step S21, step S32 is the same as step S22, step S33 is the same as step S23, and step S34 is the same as step S24. For details, see Fig. 9 .

[0175] When step S34 is implemented specifically, the process of establishing the user plane tunnel can be implemented by any one of the following processes P1 to P4.

[0176] See also Fig.10 , process P1 may include:

[0177] (11) The serving gateway sends a tunnel establishment request (create bearer request) to the second mobility management network element. The tunnel establishment request is used to request to establish a user plane tunnel for the voice service for the terminal device.

[0178] The serving gateway may be SGW, the second mobility management network element may be MME, and the user plane tunnel of the voice service may be a dedicated bearer with QCI=1 (QCI refers to a service quality level identifier, and its full English name is qos class identifier).

[0179] (12) The second mobility management network element receives the tunnel establishment request sent by the serving gateway, and sends a tunnel establishment response (create bearer response) to the serving gateway according to the second condition.

[0180] The tunnel establishment response includes information that the establishment of the user plane tunnel for the voice service of the terminal device is rejected.

[0181] The second condition includes that the second network cannot provide voice services. The second condition may also include that the terminal device is a terminal device switched from the first network to the second network.

[0182] Specifically, when the second mobility management network element determines that the second condition is met, the second mobility management network element refuses to establish a user plane tunnel for the voice service, and includes the information in a tunnel establishment response and sends it to the serving gateway.

[0183] After step (12), the service gateway can inform the IMS network element of the rejection of the user plane tunnel establishment of the voice service through the session management network element and the policy control function network element, so that the IMS network element triggers the circuit switched fallback (CSFB) service of the terminal device. The IMS network element can be a P-CSCF.

[0184] See also Fig.11 , process P2 may include:

[0185] (21) The serving gateway sends a tunnel establishment request to the second mobility management network element. The tunnel establishment request is used to request to establish a user plane tunnel for the voice service for the terminal device.

[0186] (22) The second mobility management network element sends a wireless tunnel establishment request (bearersetup request) to the second access network device, where the wireless tunnel establishment request is used to request to establish a user plane tunnel for the voice service of the terminal device.

[0187] The second access network device may be an eNB, and the user plane tunnel of the voice service may be a dedicated bearer with QCI=1.

[0188] (23) The second access network device receives the wireless tunnel establishment request sent by the second mobility management network element, and sends a wireless tunnel establishment response (bearer setup response) to the second mobility management network element according to the second condition.

[0189] The wireless tunnel establishment response includes information that the user plane tunnel establishment of the voice service is rejected. The second condition includes that the second network cannot perform voice services, and the second condition may also include that the terminal device is a terminal device switched from the first network to the second network.

[0190] Specifically, when the second access network device determines that the second condition is met, the second access network device refuses to establish a user plane tunnel for the voice service, and includes the information in a wireless tunnel establishment response and sends it to the second mobility management network element.

[0191] (24) The second mobility management network element receives the wireless tunnel establishment response sent by the second access network device and sends the tunnel establishment response to the serving gateway according to the second condition.

[0192] The tunnel establishment response includes information that the establishment of the user plane tunnel for the voice service of the terminal device is rejected.

[0193] After step (24), the serving gateway may inform the IMS network element of the rejection of establishing the user plane tunnel for the voice service through the session management network element and the policy control function network element, so that the IMS network element triggers the CSFB service of the terminal device.

[0194] Among them, the policy control function network element can be a PCF+PCRF function network element.

[0195] See also Fig.12 , process P3 may include:

[0196] (31) The serving gateway sends a tunnel establishment request to the second mobility management network element. The tunnel establishment request is used to request to establish a user plane tunnel for the voice service for the terminal device.

[0197] (32) The second mobility management network element receives the tunnel establishment request sent by the service gateway and sends a wireless tunnel establishment request to the second access network device, where the wireless tunnel establishment request is used to request to establish a user plane tunnel for the voice service of the terminal device.

[0198] (33) The second access network device receives the wireless tunnel establishment request sent by the second mobility management network element, and sends a wireless tunnel establishment response to the second mobility management network element according to the second condition.

[0199] The wireless tunnel establishment response includes information that the user plane tunnel establishment of the voice service is rejected. The second condition includes that the second network cannot perform voice services, and the second condition may also include that the terminal device is a terminal device switched from the first network to the second network.

[0200] Specifically, when the second access network device determines that the second condition is met, the second access network device refuses to establish a user plane tunnel for the voice service, and includes the information in a wireless tunnel establishment response and sends it to the second mobility management network element.

[0201] (34) The second mobility management network element receives the wireless tunnel establishment response sent by the second access network device and sends a tunnel establishment response to the serving gateway according to the wireless tunnel establishment response.

[0202] The wireless tunnel establishment response includes information that the user plane tunnel establishment of the voice service of the terminal device is rejected, and the tunnel establishment response includes information that the user plane tunnel establishment of the voice service of the terminal device is rejected.

[0203] After step (34), the serving gateway may inform the IMS network element of the rejection of establishing the user plane tunnel for the voice service through the session management network element and the policy control function network element, so that the IMS network element triggers the CSFB service of the terminal device.

[0204] Since the second network cannot conduct voice conversations in this scenario, the user plane tunnel for voice services cannot be established successfully. In this case, the terminal device can fall back to the 2G / 3G network for voice services, which requires the terminal device to perform CSFB services, and joint registration is a necessary prerequisite for the terminal device to subsequently initiate a CSFB call. The completion of joint registration by the terminal device means that the terminal device completes the joint registration process of the EPS and CS domains. Therefore, in order to ensure that the terminal device successfully initiates a CSFB call, it is necessary to trigger the CSFB service of the terminal device after the terminal device completes the joint registration, which can be achieved in any of the following four ways W1 to W4.

[0205] Method W1:

[0206] See also Fig.10 In process P1, the second mobility management network element determines that the terminal device has completed the joint registration before executing step (12). Specifically, when the second mobility management network element determines that it has received a joint registration completion message from the terminal device, the joint registration completion message may specifically be a tracking area update complete message, and the second mobility management network element determines that the terminal device has completed the joint registration.

[0207] See also Fig.11In process P2, in step (24), after the second mobility management network element determines that the second condition is met and the terminal device completes the joint registration, the second mobility management network element sends a tunnel establishment response to the serving gateway. Specifically, when the second mobility management network element determines that a joint registration completion message is received from the terminal device, the second mobility management network element determines that the terminal device has completed the joint registration.

[0208] See also Fig.12 In process P3, if the second condition is met, the second mobility management network element determines that the terminal device has completed the joint registration before executing step (32). Specifically, when the second mobility management network element determines that a joint registration completion message is received from the terminal device, the second mobility management network element determines that the terminal device has completed the joint registration.

[0209] In this method, since the IMS network element triggers the CSFB service of the terminal device after receiving the information that the user plane tunnel establishment of the voice service is rejected, the second mobility management network element sends a tunnel establishment response to the service gateway after determining that the terminal device has completed the joint registration. As a result, the IMS network element triggers the CSFB service of the terminal device after the terminal device has completed the joint registration, thereby ensuring that the terminal device successfully initiates a CSFB call.

[0210] Method W2:

[0211] In a specific implementation of step S34, the session management network element establishes a user plane tunnel for the voice service in the second network after the first preset time period according to the cause information and the second condition.

[0212] This can be achieved specifically through method m1 and method m2.

[0213] Mode m1 is: the session management network element sends a tunnel establishment request to the service gateway of the second network after a first preset time period according to the cause information and the second condition, and the tunnel establishment request is used to request to establish a user plane tunnel for voice services.

[0214] Specifically, the starting time point of the first preset time period may be the time point when the reason information is received.

[0215] Mode m2 is: the session management network element sends a tunnel establishment request to the service gateway of the second network according to the reason information, the tunnel establishment request is used to request to establish a user plane tunnel for the voice service; the session management network element receives a tunnel establishment response sent by the service gateway, the tunnel establishment response includes information that the user plane tunnel establishment for the voice service is rejected; the session management network element sends a first message to the policy function control network element after a first preset time period according to the second condition, the first message is used to indicate that the user plane tunnel establishment for the voice service fails. The first message may be a credit control request (CCR for short), and the information on the failure to establish the user plane tunnel may be included in the CCR.

[0216] Specifically, the starting time point of the first preset time period may be the time point when the reason information is received.

[0217] In this method, it is considered that when the IMS network element delays the first preset time period to trigger the CSFB service of the terminal device, the terminal device has completed the joint registration. Specifically, the session management network element can be delayed for the first preset time period to send a tunnel establishment request or a first message to cause the IMS network element to delay for the first preset time period to trigger the CSFB service of the terminal device, thereby ensuring that the terminal device successfully initiates a CSFB call.

[0218] Method W3:

[0219] See also Fig.13 , method W3 may include:

[0220] W3-1. The IMS network element receives a request message for establishing a voice service in a packet switching (PS) domain for a terminal device.

[0221] The request message may specifically be an invite message.

[0222] W3-2. The IMS network element determines that a voice service cannot be established in the PS domain of the first network or the second network.

[0223] W3-3. The IMS network element determines that the terminal device completes the joint registration.

[0224] W3-4. The IMS network element triggers the CSFB service of the terminal device.

[0225] In this manner, after the IMS network element determines that the terminal device has completed the joint registration, the CSFB service of the terminal device is triggered, thereby ensuring that the terminal device successfully initiates a CSFB call.

[0226] Optionally, after step W3-1, the method may further include: the IMS network element determines that the terminal device is registered in the first network according to the request message for establishing a voice service in the packet switching domain, and further determines that the request message is received in the first network.

[0227] Optionally, W3-2 may specifically include: the IMS network element obtains the voice service establishment failure information from the PS domain of the first network, specifically, when the IMS network element receives the voice service user plane tunnel establishment failure information, it determines that the terminal device is registered in the first network, and determines that the voice service user plane tunnel establishment failure information comes from the PS domain of the first network; or, the IMS network element obtains the voice service establishment failure information from the PS domain of the second network, specifically, when the IMS network element receives the voice service user plane tunnel establishment failure information, it determines that the terminal device is registered in the second network, and determines that the voice service user plane tunnel establishment failure information comes from the PS domain of the second network.

[0228] Voice service establishment failure information can be reported to the IMS network element by other network devices.

[0229] Optionally, W3-3 may specifically include: after the IMS network element determines that it is impossible to establish a voice service in the PS domain of the first network or the second network, the IMS network element determines that the terminal device has completed the joint registration; or, the IMS network element determines that the terminal device has completed the joint registration based on the registration location information of the terminal device obtained from the policy control network element or the home subscriber server (HSS).

[0230] Specifically, the policy control network element or the home subscriber server may actively report the registration location information of the terminal device to the IMS network element, or the IMS network element may query the policy control network element or the home subscriber server.

[0231] When the terminal device is a calling terminal device for a voice service, W3-4 may specifically include: the IMS network element sends a second message to the calling terminal device, where the second message is used to trigger the calling terminal device to initiate a CSFB calling voice service.

[0232] When the terminal device is a called terminal device for a voice service, W3-4 may specifically include: the IMS network element sends a third message to the called domain selection device, and the third message is used to indicate that the establishment of the called voice service in the PS domain of the first network or the second network has failed, so that the called domain selection device triggers the CSFB called voice service of the called terminal device.

[0233] The second message and the third message may be a 500 response message, a 380 response message, or a 503 response message.

[0234] Method 4: The first access network device notifies the session management network element of the rejection of the establishment of the user plane tunnel for the voice service. If the rejection information includes insufficient wireless resources (or resource allocation failure), the session management network element does not establish a user plane tunnel for the voice service of the terminal device after the terminal device completes the switching from the first network to the second network. The information on the unsuccessful establishment of the user plane tunnel is transmitted to the IMS network through the first network, thereby causing the IMS network to trigger the CSFB service of the terminal device.

[0235] Method 4 specifically includes: the first access network device sends fourth session management information to the session management network element, the fourth session management information includes information that establishment of a user plane tunnel for a voice service is rejected, and the information that establishment of a user plane tunnel for a voice service is rejected includes insufficient wireless resources.

[0236] In this method, after the terminal device switches from the first network to the second network, the session management network element does not re-establish the user plane tunnel for the voice service of the terminal device, but makes improvements in the switching process to ensure that the terminal device successfully initiates a CSFB call. This can be achieved through the above W3, and any one of the following methods W4 to W8, among which W5 and W6 are for the case where the terminal device is a calling terminal device.

[0237] Method W4:

[0238] See also Fig.14 , method W4 includes:

[0239] W4-1. The second mobility management network element receives a fourth message sent by the first mobility management network element, where the fourth message is used to confirm that the terminal device has completed relocation.

[0240] The fourth message may specifically be a relocation request complete acknowledgement message, where relocation refers to the process in which the terminal device switches from the first network to the second network, and the mobility management network element corresponding to the terminal device is relocated from the first mobility management network element to the second mobility management network element.

[0241] W4-2. The second mobility management network element determines that the second condition is met and the terminal device completes the joint registration.

[0242] The second condition includes that the second network cannot provide voice services. The second condition may also include that the terminal device is a terminal device switched from the first network to the second network.

[0243] W4-3. The second mobility management network element sends a tunnel modification request to the serving gateway, where the tunnel modification request is used to request modification of the signaling plane tunnel information of the voice service of the terminal device.

[0244] After receiving the tunnel modification request, the service gateway sends the tunnel modification request to the session management network element, which in turn sends the tunnel modification request to the user plane gateway so that the user plane gateway can establish the corresponding signaling plane tunnel of the voice service according to the signaling plane tunnel information of the voice service. The signaling plane tunnel of the voice service here can specifically be a dedicated bearer with QCI=5.

[0245] It should be noted that after the IMS network element learns that the user plane tunnel establishment fails, it can send a second message to the terminal device (the meaning of the second message is the same as mentioned above). The second message needs to be transmitted to the terminal device through the signaling plane tunnel of the voice service (i.e., the dedicated bearer with QCI=5). After receiving the tunnel modification request and completing the establishment of the signaling plane tunnel of the voice service, the user plane gateway will send the second message to the terminal device through the signaling plane tunnel. In this way, the second mobility management network element sends the tunnel modification request to the service gateway only after determining that the terminal device has completed the joint registration, thereby ensuring that the terminal device successfully initiates a CSFB call.

[0246] Method W5:

[0247] See also Fig.15 , method W5 includes:

[0248] W5-1. MME determines that the terminal device has completed the joint registration.

[0249] W5-2. The IMS network element determines that a voice service cannot be established in the PS domain of the first network or the second network.

[0250] W5-3. The IMS network element sends a second message to the terminal device.

[0251] The implementation methods of each step in method W5 can be found above and will not be repeated here.

[0252] In this manner, the IMS network element sends the second message to the terminal device only after the MME determines that the terminal device has completed the joint registration. Therefore, it can be ensured that the terminal device successfully initiates a CSFB call.

[0253] Method W6:

[0254] See also Fig.16 , method W6 includes:

[0255] W6-1. The IMS network element determines that a voice service cannot be established in the PS domain of the first network or the second network.

[0256] W6-2. The IMS network element sends a second message to the user plane gateway.

[0257] W6-3. The user plane gateway caches the second message.

[0258] W6-4. MME determines that the terminal device has completed the joint registration.

[0259] W6-5. MME sends a tunnel modification request to the user plane gateway.

[0260] W6-6. After receiving the tunnel modification request, the user plane gateway sends a second message to the terminal device.

[0261] The implementation method of each step in method W6 and the meaning of related terms can be found above and will not be repeated here.

[0262] In this method, the user plane gateway first caches the second message sent by the IMS network element, and sends the second message to the terminal device after receiving the tunnel modification request. Since the tunnel modification request is sent to the user plane gateway after the MME determines that the terminal device has completed the joint registration, it can be guaranteed that the terminal device successfully initiates a CSFB call.

[0263] Method W7:

[0264] See also Fig.17 , method W7 includes:

[0265] W7-1. The IMS network element determines that the voice service cannot be established in the PS domain of the first network or the second network.

[0266] W7-2. When the terminal device is a calling terminal device, the IMS network element delays the second preset time period to send a second message to the terminal device; when the terminal device is a called terminal device, the IMS network element delays the second preset time period to send a third message to the called domain selected device.

[0267] The implementation method of each step in method W7 and the meaning of related terms can be found above and will not be repeated here.

[0268] In this manner, it is considered that when the IMS network element delays the second preset time period to trigger the CSFB service of the terminal device, the terminal device has completed the joint registration, thereby ensuring that the terminal device successfully initiates a CSFB call.

[0269] The first preset time period and the second preset time period can be preset according to actual network conditions. The first preset time period and the second preset time period can be the same or different. For example, the first preset time period can be 500ms and the second preset time period can be 100ms.

[0270] It should be noted that the 5G network does not deploy a dedicated CS domain like the 2G / 3G network, so it is impossible to provide terminal devices with CS voice services similar to traditional voice. Through methods three and four, the method provided in the embodiment of the present application can also enable the terminal device to perform CS voice services when the IMS voice service cannot be performed.

[0271] The present application also provides the following four embodiments for illustrative purposes of the above method, wherein the application scenarios of embodiment (1) and embodiment (2) are both scenarios where the 5G network cannot provide IMS voice services but the EPS network can provide IMS voice services, and the application scenarios of embodiment (3) and embodiment (4) are both scenarios where the 5G network cannot provide IMS voice services and the EPS network cannot provide IMS voice services. In each embodiment, it can be divided into the calling side and the called side. Unless otherwise specified, the UE and each network element in the method describing the calling side refer to the UE and network element on the calling side, and the UE and each network element in the method describing the called side refer to the UE and network element on the called side.

[0272] Embodiment (1)

[0273] This embodiment provides a method for a calling UE to perform network switching. Fig.18 , the method comprising:

[0274] 1801. UE sends an invite message to P-CSCF. The invite message is used to request to establish an IMS voice service.

[0275] The UE is a UE in a 5G network, and the invitation message is a message for requesting to establish a voice service in the PS domain for the UE in the 5G network.

[0276] 1802. The P-CSCF establishes an IMS voice session for the UE according to the received invitation message sent by the UE.

[0277] The P-CSCF will also send the invitation message to the nodes in the subsequent calling IMS network (such as IMS nodes such as S-CSCF and TAS), and the nodes in the subsequent IMS network will start to process the received invitation message. The called UE may receive the invitation message of the calling UE forwarded by the called IMS network.

[0278] 1803. The P-CSCF sends an authentication authorization request (AAR) to the PCF+PCRF to trigger the establishment of a user plane tunnel for the IMS voice service of the UE.

[0279] AAR may carry the UE user identifier, IMS application layer charging identifier, and media description information of the IMS voice service, etc. The media description information may include at least one of the following information: classifier identifier, bandwidth requirement description information, media type description information, and QoS parameters.

[0280] It should be noted that the P-CSCF may directly send the AAR to the PCF+PCRF, or may send the AAR to the PCF+PCRF after receiving the 183 response message sent by the S-CSCF in the IMS network.

[0281] 1804. PCF+PCRF sends a packet data unit-connectivity access network (PDU-CAN) session modification process request to SMF+PGW-C according to the media description information carried in the AAR sent by P-CSCF to trigger the network element in the 5G network to establish a user plane tunnel for the UE's IMS voice service.

[0282] PDU-CAN session modification carries QoS rules, which include QoS parameter sets (profiles) and packet filters. The QoS parameter set usually consists of one or more of the following QoS key parameters: GBR, ARP, 5QI and MBR.

[0283] Generally speaking, the user plane tunnel in the 5G network usually refers to the QoS flow used to transmit user plane data. The 5QI of the user plane tunnel of the IMS voice service can be equal to 1 or other values. In the embodiment of the present application, the method provided in the embodiment of the present application is exemplified by taking the 5QI=1 of the user plane tunnel of the IMS voice service as an example.

[0284] 1805. After receiving the PDU-CAN session modification process request sent by the PCF+PCRF network element, SMF+PGW-C sends a session management request carrying a PDU session modification command to AMF. The request includes the first SM information, which is the SM information related to the user plane tunnel of the UE's IMS voice service. The first SM information may include QoS parameters of the user plane tunnel, for example, 5QI=1, as well as parameters such as ARP, GBR and MBR. The first SM information may also include other information.

[0285] 1806. AMF sends an N2 session request to NG RAN based on the first SM information sent by the received SMF+PGW-C, wherein the first SM information is transparently transmitted to NG RAN so that NG RAN allocates corresponding wireless resources to the user plane tunnel with 5QI=1 based on the first SM information.

[0286] 1807. The NG RAN determines not to allocate radio resources for the user plane tunnel of the IMS voice service of the UE according to the first SM information and the first condition.

[0287] It should be noted that step 1807 may or may not be executed, and this embodiment of the present application does not specifically limit this.

[0288] The first condition may include the following conditions: (1) the 5G network cannot perform IMS voice services, which means that the 5G network has not deployed IMS voice services, or the current 5G network signal coverage is poor enough to meet the requirements of IMS voice services; (2) the EPS network supports voice services, which can be configured by the operator as a local policy on the NG RAN; (3) the signal quality of the EPS network meets the voice service requirements, and the NG RAN can determine whether the signal quality of the EPS network meets the voice service requirements by instructing the UE to measure and report the signal quality of the surrounding EPS cells; (4) the network equipment (AMF, NG RAN, etc.) and UE of the 5G network support switching between the 5G network and the EPS network, where whether the UE and the AMF support switching between the 5G network and the EPS network can be notified to the NG RAN by the AMF through the N2 message when the UE changes from the idle state to the connected state.

[0289] 1808. NG RAN sends an N2 session response to AMF.

[0290] The N2 session response includes the second SM information, and the second SM information includes information that the establishment of the user plane tunnel of the UE's IMS voice service is accepted.

[0291] 1809. AMF sends a session management response carrying a PDU session modification command to SMF+PGW-C based on the received N2 session response, wherein the second SM information is transparently transmitted to SMF+PGW-C.

[0292] 1810. SMF+PGW-C sends an N4 session modification request to UPF+PGW-U according to the received session management response carrying the PDU session modification command sent by AMF. N4 here means that there is an N4 interface between SMF+PGW-C and UPF+PGW-U, but the embodiment of the present application does not limit the name of the interface, that is, the message name is not limited to N4 session modification request.

[0293] The N4 session modification request carries data detection (packet detection), enforcement rule, reporting rule, core network tunnel information (CN tunnel information), etc. related to the user plane tunnel of 5QI=1, so that UPF+PGW-U can establish a corresponding core network tunnel for the user plane tunnel of 5QI=1.

[0294] 1811. UPF+PGW-U receives the N4 session modification request sent by SMF+PGW-C, and establishes a corresponding core network tunnel for the user plane tunnel with 5QI=1 according to the N4 session modification request.

[0295] It should be noted that the user plane tunnel in the 5G network usually refers to the QoS flow used to transmit user plane data, while the user plane tunnel in the EPS network usually refers to the bearer used to transmit user plane data. After UPF+PGW-U establishes the corresponding user plane tunnel for the user plane tunnel of 5QI=1, the user plane tunnel will also be switched during the process of UE switching from the 5G network to the EPS network, that is, the QoS flow of 5QI=1 is switched to a dedicated bearer of QCI=1. Specifically, SMF+PGW-C can determine that the user plane tunnel of UE's 5QI=1 has been switched from the 5G network to the user plane tunnel of QCI=1 of the EPS network through the tunnel modification request received from the SGW, and the user plane tunnel of QCI=1 has been successfully established. After the UE switches from the 5G network to the EPS network, after the UE receives the relevant signaling of the IMS voice service forwarded by the EPS network, the UE continues the subsequent IMS voice call establishment process in the EPS network, thereby completely establishing the IMS voice session.

[0296] After step 1811, UPF+PGW-U will also send an N4 session modification response to SMF+PGW-C, SMF+PGW-C will send a PDU-CAN session modification to PCF+PCRF, PCF+PCRF will send a re-authentication request (Re-authentication Request, referred to as RAR) to P-CSCF, and P-CSCF will send a credit re-authorization answer (re-authentication answer, referred to as RAA) to PCF+PCRF. From this, P-CSCF can know that the user plane tunnel of the IMS voice service is successfully established.

[0297] 1812. NG RAN sends a switching request to AMF based on the received first SM information and the first condition to trigger the UE to switch from the 5G network to the EPS network.

[0298] Specifically, when the first condition is met, when the NG RAN determines that a user plane tunnel with 5QI=1 needs to be established based on the first SM information, a switching request can be sent to the AMF.

[0299] The handover process of UE switching from 5G network to EPS network can be found in the standard protocol and will not be described here. After UE switches from 5G network to EPS network, after UE receives the relevant signaling of IMS voice service forwarded by EPS network, UE continues the subsequent IMS voice call establishment process in EPS network, thereby completely establishing IMS voice session.

[0300] This embodiment also provides a method for the called UE to perform network switching. Fig.19 , the method comprising:

[0301] 1901. The P-CSCF receives the invitation message sent by the S-CSCF, and establishes an IMS voice session for the UE according to the invitation message.

[0302] The invitation message is used to request the UE of the 5G network to establish a voice service in the PS domain.

[0303] 1902. P-CSCF sends an invite message to UE.

[0304] 1903. The UE receives the invitation message sent by the P-CSCF and replies with a 183 response message to the P-CSCF.

[0305] 1904. The P-CSCF receives the 183 response message sent by the UE, and sends a 183 response message to the S-CSCF.

[0306] The S-CSCF may further send a 183 response message to the calling party's S-CSCF, and the calling party's S-CSCF may further send a 183 response message to the calling party's P-CSCF. If the calling party's P-CSCF receives the 183 response message sent by the calling party's S-CSCF, it may forward the 183 response message to the calling UE.

[0307] 1905-1914.

[0308] Steps 1905-1914 correspond to steps 1803-1812 respectively, that is, step 1905 is the same as step 1803, step 1906 is the same as step 1804, and so on. Step 1914 is the same as step 1812, and similar descriptions below have the same meaning.

[0309] The above embodiment (1) provides a method for terminal equipment to switch networks in a scenario where the 5G network cannot provide IMS voice services but the EPS network can provide IMS voice services. When the NG RAN receives a user plane tunnel establishment request with 5QI=1, it can promptly switch the 5G terminal to the EPS network so that the terminal equipment in the 5G can continue to execute the IMS voice call establishment process in the EPS network.

[0310] Embodiment (2)

[0311] This embodiment provides a method for a calling UE to perform network switching. Fig. 20 , the method comprising:

[0312] 2001-2006.

[0313] Steps 2001-2006 correspond to steps 1801-1806 respectively.

[0314] 2007. NG RAN sends an N2 session response to AMF according to the first SM information and the first condition.

[0315] The NG RAN can determine, based on the first SM information, that the request is to establish a user plane tunnel for the IMS voice service, specifically a user plane tunnel with 5QI=1.

[0316] The N2 session response includes a third SM information, which may include SM information indicating that NG RAN refuses to allocate wireless resources for the user plane tunnel with 5QI=1, and carries the reason information for the rejection, where the reason information is that the UE is performing a switching process. Furthermore, the reason information may be that the UE is performing a switching from the 5G network to the EPS network, so that SMF+PGW-C decides to re-initiate the establishment of the user plane tunnel for the UE's IMS voice service after the UE's switching process is completed based on the reason information.

[0317] The first condition may include the following conditions: (1) the 5G network cannot perform IMS voice services, which means that the 5G network has not deployed IMS voice services, or the current 5G network signal coverage is poor enough to meet the requirements of IMS voice services; (2) the EPS network supports voice services, which can be configured by the operator as a local policy on the NG RAN; (3) the signal quality of the EPS network meets the voice service requirements, and the NG RAN can determine whether the signal quality of the EPS network meets the voice service requirements by instructing the UE to measure and report the signal quality of the surrounding EPS cells; (4) the network equipment (AMF, NG RAN, etc.) and UE of the 5G network support switching between the 5G network and the EPS network. Among them, whether the UE and AMF support switching between the 5G network and the EPS network can be notified to the NG RAN by the AMF through the N2 message when the UE changes from the idle state to the connected state.

[0318] 2008. AMF sends a session management request carrying a PDU session modification command to SMF+PGW-C based on the received N2 session response, wherein the third SM information is transparently transmitted to SMF+PGW-C.

[0319] 2009. SMF+PGW-C determines to re-establish a user plane tunnel for the UE's IMS voice service in the EPS network after the UE switches from the 5G network to the EPS network based on the third SM information in the session management request carrying the PDU session modification command sent by the received AMF.

[0320] It should be noted that re-establishing a user plane tunnel for the IMS voice service of the UE in the EPS network refers to establishing a user plane tunnel with QCI=1.

[0321] During the process of UE switching from 5G network to EPS network, SMF+PGW-C can judge that UE has successfully switched from 5G network to EPS network by receiving the tunnel modification request sent by SGW. In addition, SMF+PGW-C can also set a timer to trigger the timer from the receipt of the third SM information, and judge that UE has successfully switched from 5G network to EPS network when the timer ends.

[0322] 2010. NG RAN sends a switching request to AMF based on the received first SM information and the first condition to trigger the UE to switch from the 5G network to the EPS network.

[0323] Specifically, when the first condition is met, when the NG RAN determines that a user plane tunnel with 5QI=1 needs to be established based on the first SM information, a switching request can be sent to the AMF.

[0324] The switching process of UE from 5G network to EPS network can be found in the standard protocol and will not be repeated here.

[0325] 2011. After the UE handover is completed, SMF+PGW-C sends a tunnel establishment request (create bearerquest) to SGW to trigger the establishment of a user plane tunnel with QCI=1.

[0326] Subsequently, the user plane tunnel of QCI=1 is successfully established in the EPS network, and the EPS network feeds back to the IMS network that the user plane tunnel of the IMS voice service is successfully established. The user plane tunnel establishment process of QCI=1 and the establishment process of the IMS voice session in the EPS network are specifically described in the standard protocol and will not be repeated here.

[0327] This embodiment also provides a method for the called UE to perform network switching. Fig.21 , the method comprising:

[0328] 2101-2113.

[0329] Among them, steps 2101-2104 correspond to steps 1901-1904 respectively, and steps 2105-2113 correspond to steps 2003-2111 respectively.

[0330] The above embodiment (2) provides a method for terminal device to switch networks in a scenario where the 5G network cannot provide IMS voice services but the EPS network can provide IMS voice services. When the NG RAN receives a user plane tunnel establishment request with 5QI=1, it can promptly switch the 5G terminal to the EPS network so that the terminal device in the 5G can continue to execute the IMS voice call establishment process in the EPS network. At the same time, the NG RAN rejects the establishment of the user plane tunnel with 5QI=1 with the reason information that the switching is in progress, so as to trigger the core network gateway to rebuild the user plane tunnel with QCI=1 after the UE successfully switches to the EPS network.

[0331] Embodiment (3)

[0332] This embodiment provides a method for a calling UE to perform network switching. Fig. 22 , the method comprising:

[0333] 2201-2210.

[0334] Steps 2201-2210 correspond to steps 2001-2010 respectively.

[0335] 2211. After the UE switching is completed, SMF+PGW-C sends a tunnel establishment request to SGW to trigger the establishment of a user plane tunnel with QCI=1.

[0336] 2212. SGW forwards the tunnel establishment request to MME.

[0337] After step 2212, the MME receives the tunnel establishment request and executes any one of the following processes: process 1 (including a1), process 2 (including b1-b4) and process 3 (including c1-c4).

[0338] Process 1:

[0339] a1. The MME sends a tunnel establishment response to the SGW according to the second condition, where the tunnel establishment response includes information that establishment of a user plane tunnel for the UE's voice service is rejected.

[0340] In process one, the second condition may include that the second network is unable to perform voice services, and may also include that the UE completes at least one of the joint registrations for the UE switched from the 5G network to the EPS network and the UE, wherein the second network is unable to perform voice services specifically refers to the inability to perform IMS voice services, and the UE completes the joint registration, which means that the UE completes the joint registration process for the EPS and CS domains.

[0341] Specifically, the MME may determine that the UE has completed the joint registration according to a received registration completion message sent by the UE.

[0342] Before a1, the MME may send a wireless tunnel establishment request to the eNB and receive a response message for the IMS voice service, or may not send a wireless tunnel establishment request and receive a response message, which is not limited here.

[0343] Process 2:

[0344] b1. The MME sends a wireless tunnel establishment request to the eNB. The wireless tunnel establishment request is used to request to establish a user plane tunnel for the IMS voice service of the UE. Specifically, the user plane tunnel of the IMS voice service may refer to a dedicated bearer with QCI=1.

[0345] b2. The eNB receives the wireless tunnel establishment request and sends a wireless tunnel establishment response to the MME according to the second condition. The wireless tunnel establishment response includes information that the user plane tunnel establishment of the UE's IMS voice service is rejected.

[0346] In process two, the second condition includes that the second network is unable to perform IMS voice services, and may also include that the UE is switched from a 5G network to an EPS network.

[0347] b3. The MME receives the wireless tunnel establishment response sent by the eNB. If the second condition is met, the MME determines that the UE completes the joint registration.

[0348] The wireless tunnel establishment response includes information that the establishment of the user plane tunnel of the IMS voice service of the UE is rejected.

[0349] Specifically, during the specific implementation of step b3, when the MME determines that the registration completion message sent by the UE is received, the MME determines that the UE completes the joint registration.

[0350] b4. The MME sends a tunnel establishment response to the SGW, where the tunnel establishment response includes information that the user plane tunnel establishment of the UE's IMS voice service is rejected.

[0351] Process three:

[0352] c1. If the second condition is met, the MME determines that the UE completes the joint registration.

[0353] Specifically, during the specific implementation of step c1, when the MME determines that the registration completion message sent by the UE is received, the MME determines that the UE completes the joint registration.

[0354] In process three, the second condition includes that the second network is unable to perform IMS voice services, and may also include that the UE is switched from a 5G network to an EPS network.

[0355] c2. The MME sends a wireless tunnel establishment request to the eNB. The wireless tunnel establishment request is used to request to establish a user plane tunnel for the IMS voice service of the UE.

[0356] c3. The eNB receives the wireless tunnel establishment request sent by the MME, and sends a wireless tunnel establishment response to the MME according to the second condition. The wireless tunnel establishment response includes information that the user plane tunnel establishment of the UE's IMS voice service is rejected.

[0357] c4. The MME receives the wireless tunnel establishment response sent by the eNB, and sends a tunnel establishment response to the SGW according to the wireless tunnel establishment response. The tunnel establishment response includes information that the user plane tunnel establishment of the UE's IMS voice service is rejected.

[0358] 2213. SGW receives the tunnel establishment response sent by MME, and sends a tunnel establishment response to SMF+PGW-C.

[0359] 2214. SMF+PGW-C sends CCR to PCF+PCRF.

[0360] The CCR carries an indication of the failure to establish a user plane tunnel with QCI=1, and may also carry information about the cause of the failure to establish the tunnel, which is specifically set with reference to the cause information carried in the tunnel establishment response sent by the SGW. The CCR may also be replaced by messages with other names, which are not limited here, such as an IP-CAN session modification request.

[0361] 2215. PCF+PCRF sends a credit control answer (CCA) to SMF+PGW-C.

[0362] 2216. PCF+PCRF sends RAR to P-CSCF according to CCR. RAR may carry indication information for indicating insufficient wireless resources (or indication information for indicating resource allocation failure).

[0363] 2217. P-CSCF sends RAA to PCF+PCRF.

[0364] 2218. The P-CSCF determines that the IMS voice service of the UE cannot be established in the PS domain based on the acquired indication information of insufficient radio resources (or indication information of resource allocation failure).

[0365] 2219. P-CSCF sends a 500 response message to the UE.

[0366] After step 2219, after the UE receives the 500 response message sent by the P-CSCF, it can reselect the calling domain and initiate a CSFB call. The UE side and the network side cooperate to execute the CSFB process, and finally a voice call may be established in the CS domain.

[0367] After step 2219, if the P-CSCF has received the 183 response message, the P-CSCF may send a cancel message to the S-CSCF and other nodes in the IMS network to cancel the requested IMS voice service related call.

[0368] It should be noted that when the UE switches from the 5G network to the EPS network, the mobility management element serving the UE changes from the AMF to the MME. Therefore, the MME will assign a new globally unique temporary identity (GUTI) to the UE. Fig. 22 After the handover process, the UE sends a tracking area update (TAU) request to the MME. When the MME receives the TAU request sent by the NG RAN, it will bring the allocated new GUTI to the UE through the TAU accept message, so that the UE can reply a TAU completion message (i.e., joint registration completion message) to the MME after receiving the TAU acceptance message carrying the new GUTI.

[0369] In the above description of this embodiment, the purpose of MME sending a tunnel establishment response to SGW after determining that the UE has completed the joint registration process of the EPS and CS domains is to ensure that the message of unsuccessful establishment of the user plane tunnel with QCI=1 reaches the IMS network only after the UE completes the joint registration process of the EPS and CS domains, so that the 500 response message sent by the IMS network can reach the UE only after the UE completes the joint registration process of the EPS and CS domains, ultimately ensuring that the UE successfully initiates a CSFB call.

[0370] In order to ensure that the 500 response message sent by the IMS network can reach the UE after the UE completes the joint registration process of the EPS and CS domains, in addition to making the MME send a tunnel establishment response to the SGW only after determining that the UE has completed the joint registration process of the EPS and CS domains, it can also be implemented in any one of the following methods 1 to 5.

[0371] Method 1: SMF+PGW-C delays the first preset time period to send a tunnel establishment request to SGW according to the second condition.

[0372] In mode 1, the second condition includes that the EPS network cannot perform IMS voice services.

[0373] Mode 2: SMF+PGW-C delays sending CCR to PCF+PCRF for a first preset time period.

[0374] Mode 3: After obtaining the indication information of insufficient radio resources or the indication information of resource allocation failure, the P-CSCF sends a 500 response message to the UE after a second preset time period.

[0375] Method 4: After SMF+PGW-C sends CCR to PCF+PCRF, SMF+PGW-C instructs UPF+PGW-U to cache the data on the user plane tunnel with QCI=5 sent to the UE for a first preset time period. After the first preset time period, UPF+PGW-U can continue to send to the UE.

[0376] Mode 5: After the P-CSCF determines that the UE has completed the joint registration, it sends a 500 response message to the UE.

[0377] Method 5 may include, in specific implementation, that after a second preset time period from when the P-CSCF determines that a voice service cannot be established in the PS domain of the 5G network or the EPS network, the P-CSCF determines that the terminal device has completed the joint registration; or, the P-CSCF determines that the terminal device has completed the joint registration based on the registration location information of the terminal device obtained from the HSS / home location register (HLR).

[0378] The first preset time period and the second preset time period can be set according to actual network communication conditions. For example, both the first preset time period and the second preset time period can be 500 ms.

[0379] This embodiment also provides a method for the called UE to perform network switching. Fig.23 , the method comprising:

[0380] 2301-2304.

[0381] Steps 2301-2304 correspond to steps 1901-1904 respectively.

[0382] 2305-2320.

[0383] Steps 2305-2320 correspond to steps 2203-2218 respectively.

[0384] 2321. After obtaining the indication information of insufficient wireless resources (or the indication information of resource allocation failure), the P-CSCF sends a 500 response message to the TAS in the IMS network through the S-CSCF, where the 500 response message is specifically sent to the called domain selection function module T-ADS in the TAS.

[0385] 2322. After obtaining the indication information of insufficient radio resources (or the indication information of resource allocation failure), the P-CSCF sends a cancellation message to the UE to cancel the requested IMS voice service related session.

[0386] There is no limitation on the order of step 2321 and step 2322.

[0387] After step 2322, the TAS in the IMS network re-selects the called session to the CS domain, and initiates a call to the CS domain call control device (e.g., mobile switching center (MSC)) via the S-CSCF and other devices. The CS domain call control device initiates a call to the MME via the SGs interface. The MME triggers the UE's CSFB process. Through the UE's CSFB process, the UE may eventually establish a voice session in the CS domain. For details of the specific process, see the relevant description in 3GPP TS23.272. It will not be repeated here.

[0388] In the above description of this embodiment, the purpose of MME sending a tunnel establishment response to SGW after determining that the UE has completed the joint registration process of the EPS and CS domains is to ensure that the message of unsuccessful establishment of the user plane tunnel with QCI=1 reaches the IMS network only after the UE completes the joint registration process of the EPS and CS domains, so that the 500 response message sent by the IMS network can reach TAS only after the UE completes the joint registration process of the EPS and CS domains, ultimately ensuring that the IMS call can be converted into a CSFB call and reach the UE.

[0389] In order to ensure that the 500 response message sent by the IMS network can reach the TAS only after the UE completes the joint registration process of the EPS and CS domains, in addition to making the MME send a tunnel establishment response to the SGW only after determining that the UE has completed the joint registration process of the EPS and CS domains, it can also be implemented in any one of the following methods 1 to 5.

[0390] Method 1: SMF+PGW-C delays the first preset time period to send a tunnel establishment request to SGW according to the second condition.

[0391] In mode 1, the second condition includes that the EPS network cannot perform IMS voice services.

[0392] Mode 2: SMF+PGW-C delays sending CCR to PCF+PCRF for a first preset time period.

[0393] Mode 3: After obtaining the indication information of insufficient wireless resources (or the indication information of resource allocation failure), the P-CSCF sends a 500 response message to the TAS after a second preset time period.

[0394] Method 4: After SMF+PGW-C sends CCR to PCF+PCRF, SMF+PGW-C instructs UPF+PGW-U to cache the data on the user plane tunnel with QCI=5 sent to the UE (which can be a cancellation message) for a first preset time period. After the first preset time period, UPF+PGW-U can continue to send to the UE.

[0395] Mode 5: After the P-CSCF determines that the UE has completed the joint registration, it sends a 500 response message to the TAS.

[0396] Method 5 may include, in specific implementation, that after a second preset time period from when the P-CSCF determines that a voice service cannot be established in the PS domain of the 5G network or the EPS network, the P-CSCF determines that the terminal device has completed the joint registration; or, the P-CSCF determines that the terminal device has completed the joint registration based on the registration location information of the terminal device obtained from the HSS / HLR.

[0397] The first preset time period and the second preset time period can be set according to actual network communication conditions. For example, both the first preset time period and the second preset time period can be 500 ms.

[0398] Embodiment (4)

[0399] This embodiment provides a method for a calling UE to perform network switching. Fig.24 , Fig.25 , Fig.26 and Fig. 27 , the method comprising:

[0400] 2401-2406.

[0401] Steps 2401-2406 correspond to steps 1801-1806 respectively.

[0402] Since the scenario in which this embodiment is applied is a scenario in which the 5G network cannot perform IMS voice services and the EPS network cannot perform IMS voice services, in order to ensure that the UE successfully initiates a CSFB call, the 500 response message sent by the IMS network needs to reach the UE after the UE completes the joint registration process of the EPS and CS domains.

[0403] To ensure that the UE successfully initiates a CSFB call, after step 2406, the following process 1 (see Fig.24 ), process 2 (see Fig.25 ), process 3 (see Fig.26 ) and process 4 (see Fig. 27 ) to complete the network switching of the UE.

[0404] Process 1:

[0405] A1. NG RAN sends a switching request to AMF based on the received first SM information and the first condition to trigger the UE to switch from the 5G network to the EPS network.

[0406] In this case, the first condition may include the following conditions: (1) The 5G network cannot perform IMS voice services, which means that the 5G network has not deployed IMS voice services, or the current 5G network signal coverage is not good enough to meet the requirements of IMS voice services; (2) The network equipment (AMF, NG RAN, etc.) and UE of the 5G network support switching between the 5G network and the EPS network. Whether the UE and AMF support switching between the 5G network and the EPS network can be notified to the NG RAN by the AMF through the N2 message when the UE changes from the idle state to the connected state. (3) The EPS network does not support voice services. This condition can be configured by the operator as a local policy on the NG RAN; (4) The signal quality of the EPS network does not meet the requirements of voice services. The NG RAN can determine whether the signal quality of the EPS network meets the requirements of voice services by instructing the UE to measure and report the signal quality of the surrounding EPS cells.

[0407] A2. When the UE switches from the 5G network to the EPS network, after the handover preparation process is completed, the NG RAN sends a handover command to the UE.

[0408] A3. NG RAN sends an N2 session response to AMF according to the first condition. The N2 session response carries the fourth SM information. The fourth SM information includes the information that the establishment of the user plane tunnel of the IMS voice service is rejected. The information that the establishment of the user plane tunnel of the IMS voice service is rejected includes insufficient wireless resources (or resource allocation failure).

[0409] A4. AMF sends a session management response carrying a PDU session modification command to SMF+PGW-C based on the received N2 session response, wherein the fourth SM information is transparently transmitted to SMF+PGW-C.

[0410] A5. After SMF+PGW-C parses the fourth SM information, it sends a PDU-CAN session modification message to PCF+PCRF.

[0411] The PDU-CAN session modification message includes information for indicating the failure of establishing the user plane tunnel of the IMS voice service. The indication information may be indication information of insufficient wireless resources (or indication information of resource allocation failure). In this embodiment, the message name is not limited to the PDU-CAN session modification message, and may be other message names, such as CCR, etc.

[0412] A6. PCF+PCRF sends a RAR to P-CSCF. The RAR may carry information indicating that the user plane tunnel establishment of the IMS voice service has failed.

[0413] A7. The P-CSCF determines that the IMS voice service cannot be established in the PS domain according to the received information indicating the failure of establishing the user plane tunnel.

[0414] A8. P-CSCF sends a 500 response message to the UE, which arrives at UPF+PGW-U.

[0415] The 500 response message is transmitted to the UE through the 5G network tunnel (specifically a QoS flow).

[0416] A9. During the process of UE switching from the 5G network to the EPS network, the MME determines that the UE completes the joint registration.

[0417] A10. MME sends a tunnel modification request for the user plane tunnel of QCI=5 to SMF+PGW-C through SGW, which is used to indicate the downlink SGW user plane address and tunnel information of the QCI=5 dedicated bearer to SMF+PGW-C.

[0418] A11. SMF+PGW-C sends a tunnel modification request to UPF+PGW-U, indicating the downlink SGW user plane address and tunnel information of the dedicated bearer with QCI=5 to UPF+PGW-U. After that, SMF+PGW-C feeds back a tunnel modification response to MME through SGW.

[0419] A12. UPF+PGW-U forwards the user plane data on the dedicated bearer with QCI=5 to the UE, that is, a 500 response message is sent to the UE.

[0420] After step A12, the UE initiates a CSFB calling voice service, and the UE side and the network side cooperate to execute the CSFB process, and eventually a voice call may be established in the CS domain.

[0421] Since the UE has left the 5G network and connected to the EPS network, after the 500 response message reaches UPF+PGW-U, it will be sent to the UE by UPF+PGW-U through the IMS signaling tunnel of the EPS network (user plane tunnel with QCI=5). If the P-CSCF has received the 183 response message, the P-CSCF can send a cancellation message to the S-CSCF and other nodes in the IMS network to cancel the related calls of the requested IMS voice service.

[0422] In process 1, since UPF+PGW-U will send a 500 response message to the UE only after receiving the tunnel modification request, the MME sends a tunnel modification request for the user plane tunnel with QCI=5 to SMF+PGW-C and then to UPF+PGW-U after determining that the UE has completed the joint registration. As a result, the 500 response message sent by the IMS network reaches the UE only after the UE completes the joint registration process of the EPS and CS domains, which provides a guarantee for the UE to successfully initiate a CSFB call.

[0423] Process 2:

[0424] B1. NG RAN sends an N2 session response to AMF according to the first condition. The N2 session response carries the fourth SM information. The fourth SM information includes the information that the establishment of the user plane tunnel of the IMS voice service is rejected. The information that the establishment of the user plane tunnel of the IMS voice service is rejected includes insufficient wireless resources (or resource allocation failure).

[0425] Specifically, NG RAN can determine the fourth SM information based on the first condition.

[0426] In this case, the first condition may include the following conditions: (1) the 5G network cannot perform IMS voice services, which means that the 5G network has not deployed IMS voice services, or the current 5G network signal coverage is poor enough to meet the requirements of IMS voice services; (2) the network equipment (AMF, NG RAN, etc.) and UE of the 5G network support switching between the 5G network and the EPS network. Whether the UE and AMF support switching between the 5G network and the EPS network can be notified to the NG RAN by the AMF through the N2 message when the UE changes from the idle state to the connected state; (3) the EPS network does not support voice services. This condition can be configured by the operator as a local policy on the NG RAN; (4) the signal quality of the EPS network does not meet the voice service requirements. The NG RAN can determine whether the signal quality of the EPS network meets the voice service requirements by instructing the UE to measure and report the signal quality of the surrounding EPS cells.

[0427] B2. AMF sends a session management response carrying a PDU session modification command to SMF+PGW-C based on the received N2 session response, wherein the fourth SM information is transparently transmitted to SMF+PGW-C.

[0428] B3. SMF+PGW-C determines to keep notifying PCF+PCRF, that is, temporarily suspends notifying PCF+PCRF of the information that establishment of the user plane tunnel for the voice service is rejected.

[0429] B4. NG RAN sends a switching request to AMF according to the first condition and the first SM information.

[0430] B5. During the handover process, the MME determines that the UE completes the joint registration.

[0431] B6. MME sends a tunnel modification request for the user plane tunnel with QCI=5 to SMF+PGW-C through SGW, to indicate the downlink SGW user plane address and tunnel information to SMF+PGW-C.

[0432] B7. SMF+PGW-C sends a tunnel modification request to UPF+PGW-U, indicating the downlink SGW user plane address and tunnel information of the dedicated bearer with QCI=5 to UPF+PGW-U. SMF+PGW-C then feeds back a tunnel modification response to MME through SGW.

[0433] B8. SMF+PGW-C sends an IP CAN session modification message to PCF+PCRF.

[0434] The IP-CAN session modification message carries information indicating the failure of establishing the user plane tunnel of the IMS voice service, and the indication information may be indication information of insufficient wireless resources (or indication information of resource allocation failure). In this embodiment, the message name is not limited to the IP-CAN session modification message, and may be other message names, such as CCR, etc.

[0435] B9. PCF+PCRF sends a RAR to P-CSCF. The RAR carries information indicating that establishment of the user plane tunnel of the IMS voice service has failed.

[0436] B10. The P-CSCF determines that the IMS voice service cannot be established in the PS domain according to the received information indicating the failure of establishing the user plane tunnel.

[0437] B11. P-CSCF sends a 500 response message to the UE.

[0438] After step B11, the UE initiates a CSFB calling voice service, and the UE side and the network side cooperate to execute the CSFB process, and eventually a voice call may be established in the CS domain.

[0439] In process 2, since the P-CSCF sends a 500 response message to the UE only after determining that the user plane tunnel establishment of the IMS voice service has failed, by making the MME determine that the UE has completed the joint registration, the PCF+PCRF sends information to the P-CSCF indicating that the user plane tunnel establishment of the IMS voice service has failed, so that the 500 response message sent by the IMS network reaches the UE only after the UE completes the joint registration process of the EPS and CS domains, which provides a guarantee for the UE to successfully initiate a CSFB call.

[0440] Process 3:

[0441] C1. NG RAN sends an N2 session response to AMF according to the first condition. The N2 session response carries the fourth SM information. The fourth SM information includes the information that the establishment of the user plane tunnel of the IMS voice service is rejected. The information that the establishment of the user plane tunnel of the IMS voice service is rejected includes insufficient wireless resources (or resource allocation failure).

[0442] Specifically, NG RAN can determine the fourth SM information based on the first condition.

[0443] In this case, the first condition may include the following conditions: (1) the 5G network cannot perform IMS voice services, which means that the 5G network has not deployed IMS voice services, or the current 5G network signal coverage is poor enough to meet the requirements of IMS voice services; (2) the network equipment (AMF, NG RAN, etc.) and UE of the 5G network support switching between the 5G network and the EPS network. Whether the UE and AMF support switching between the 5G network and the EPS network can be notified to the NG RAN by the AMF through the N2 message when the UE changes from the idle state to the connected state; (3) the EPS network does not support voice services. This condition can be configured by the operator as a local policy on the NG RAN; (4) the signal quality of the EPS network does not meet the voice service requirements. The NG RAN can determine whether the signal quality of the EPS network meets the voice service requirements by instructing the UE to measure and report the signal quality of the surrounding EPS cells.

[0444] C2 and AMF send a session management response carrying a PDU session modification command to SMF+PGW-C based on the received N2 session response, wherein the fourth SM information is transparently transmitted to SMF+PGW-C.

[0445] C3, SMF+PGW-C sends an N4 session modification request to UPF+PGW-U based on the session management response carrying the PDU session modification command sent by AMF.

[0446] The N4 session modification request includes a first command, and the first command is used to instruct the UPF+PGW-U to cache data on the user plane tunnel with 5QI=5.

[0447] C4 and UPF+PGW-U feedback the N4 session modification response to SMF+PGW-C based on the received N4 session modification request.

[0448] C5. SMF+PGW-C sends a PDU CAN session modification message to PCF+PCRF.

[0449] The PDU CAN session modification message carries information indicating that the user plane tunnel establishment of the IMS voice service has failed, and the indication information may be indication information of insufficient wireless resources (or indication information of resource allocation failure). In this embodiment, the message name is not limited to the IP-CAN session modification message, and may be other message names, such as CCR, etc.

[0450] C6. PCF+PCRF sends a RAR to P-CSCF. The RAR carries information indicating that the user plane tunnel establishment of the IMS voice service has failed.

[0451] C7. P-CSCF feeds back RAA to PCF+PCRF.

[0452] C8. The P-CSCF determines that the IMS voice service cannot be established in the PS domain according to the received information indicating the failure of establishing the user plane tunnel.

[0453] C9. P-CSCF sends a 500 response message to the UE, which arrives at UPF+PGW-U.

[0454] C10. UPF+PGW-U caches the data on the user plane tunnel with 5QI=5.

[0455] The data on the user plane tunnel with 5QI=5 may include a 500 response message.

[0456] C11. NG RAN sends a switching request to AMF according to the first condition and the first SM information.

[0457] C12. The MME determines that the UE completes the joint registration.

[0458] C13. MME sends a tunnel modification request (modifybearer request) of the user plane tunnel with QCI=5 to SMF+PGW-C through SGW, which is used to indicate the downlink SGW user plane address and tunnel information to SMF+PGW-C.

[0459] C14. SMF+PGW-C sends a tunnel modification request to UPF+PGW-U, where the tunnel modification request includes a second command, where the second command is used to instruct UPF+PGW-U to stop caching data on QCI=1.

[0460] After step C14, UPF+PGW-U will send a 500 response message to the UE. The UE initiates a CSFB calling voice service. The UE side and the network side cooperate to execute the CSFB process, and may eventually establish a voice call in the CS domain.

[0461] In process 3, the 500 response message sent by the P-CSCF is cached in the UPF+PGW-U through the first command. After the MME determines that the UE has completed the joint registration, the P-CSCF sends the 500 response message to the terminal device through the second command, so that the 500 response message sent by the IMS network reaches the UE only after the UE completes the joint registration process of the EPS and CS domains, which provides a guarantee for the UE to successfully initiate a CSFB call.

[0462] Process 4:

[0463] D1. NG RAN sends an N2 session response to AMF according to the first condition. The N2 session response carries the fourth SM information. The fourth SM information includes the information that the establishment of the user plane tunnel of the IMS voice service is rejected. The information that the establishment of the user plane tunnel of the IMS voice service is rejected includes insufficient wireless resources (or resource allocation failure).

[0464] Specifically, NG RAN can determine the fourth SM information based on the first condition.

[0465] In this case, the first condition may include the following conditions: (1) The 5G network cannot perform IMS voice services, which means that the 5G network has not deployed IMS voice services, or the current 5G network signal coverage is not good enough to meet the requirements of IMS voice services; (2) The network equipment (AMF, NG RAN, etc.) and UE of the 5G network support switching between the 5G network and the EPS network. Whether the UE and AMF support switching between the 5G network and the EPS network can be notified to the NG RAN by the AMF through the N2 message when the UE changes from the idle state to the connected state. (3) The EPS network does not support voice services. This condition can be configured by the operator as a local policy on the NG RAN; (4) The signal quality of the EPS network does not meet the requirements of voice services. The NG RAN can determine whether the signal quality of the EPS network meets the requirements of voice services by instructing the UE to measure and report the signal quality of the surrounding EPS cells.

[0466] D2. AMF sends a session management response carrying a PDU session modification command to SMF+PGW-C based on the received N2 session response, wherein the fourth SM information is transparently transmitted to SMF+PGW-C.

[0467] D3. SMF+PGW-C sends a PDU CAN session modification message to PCF+PCRF. In this embodiment, the message name is not limited to the IP-CAN session modification message, and can be other message names, such as CCR.

[0468] The PDU CAN session modification message carries information for indicating failure in establishing the user plane tunnel of the IMS voice service. The indication information may be indication information of insufficient radio resources (or indication information of resource allocation failure).

[0469] D4. PCF+PCRF sends a RAR to P-CSCF. The RAR carries information indicating that the user plane tunnel establishment of the IMS voice service has failed.

[0470] D5. The P-CSCF determines that the IMS voice service cannot be established in the PS domain according to the received information indicating the failure of establishing the user plane tunnel.

[0471] D6. P-CSCF feeds back RAA message to PCF+PCRF.

[0472] D7. The P-CSCF determines to delay sending the 500 response message for a second preset time period.

[0473] D8. NG RAN sends a switching request to AMF based on the received first SM information and the first condition to trigger the UE to switch from the 5G network to the EPS network.

[0474] After step D8, the UE executes the handover process. After the handover process is completed, the P-CSCF sends a 500 response message to the UE. The UE initiates a CSFB calling voice service. The UE side and the network side cooperate to execute the CSFB process, and finally a voice call may be established in the CS domain.

[0475] In process 4, the P-CSCF delays sending the 500 response message for a second preset time period, so that the 500 response message sent by the IMS network reaches the UE only after the UE completes the joint registration process of the EPS and CS domains, thereby ensuring that the UE successfully initiates a CSFB call.

[0476] This embodiment also provides a method for the called UE to perform network switching. Since this embodiment is applied in the scenario where the 5G network cannot perform IMS voice services and the EPS network cannot perform IMS voice services, in order to ensure that the UE successfully initiates a CSFB call, the 500 response message sent by the IMS network needs to reach the TAS after the UE completes the joint registration process of the EPS and CS domains, so that the TAS can reselect the called domain of the UE to the CS domain to ensure the success of the CSFB call. Fig.28 , the method comprising:

[0477] 2801-2808.

[0478] Steps 2801-2808 correspond to steps 1901-1908 respectively.

[0479] 2809-2814.

[0480] Steps 2809-2814 correspond to the same as steps D1-D6 respectively.

[0481] 2815. The P-CSCF sends a 500 response message to the TAS after a second preset time period is delayed. The 500 response message is specifically sent to the called domain selection function module T-ADS in the TAS.

[0482] The P-CSCF delays sending the 500 response message for the second preset time period, so that the 500 response message sent by the P-CSCF reaches the TAS only after the UE completes the joint registration process of the EPS and CS domains, which ensures the success of the CSFB call.

[0483] The network switching method provided in Example (3) and Example (4) can enable the 5G terminal device to switch to the EPS network during the IMS voice session establishment phase, and then use the CSFB technology in the EPS network to make the UE fall back to the 2G / 3G network, and finally initiate a voice call in the CS domain of the 2G / 3G network. This application uses the EPS network as a springboard and reuses the traditional 2G / 3G network architecture to provide a method for terminal devices in the 5G network to provide voice services in scenarios where both the 5G network and the EPS network cannot provide IMS voice services.

[0484] The 500 response message in the above-mentioned embodiments (1) to (4) may also be a 380 response message or a 503 response message, and the RAR message may also be an abort-session-request (ASR) message. In this case, the RAA message may be an abort-session-answer (ASA) message.

[0485] The present application also provides a network registration method, such as Fig.28A As shown, the method includes:

[0486] 2801A. The first mobility management network element receives a registration request from a terminal device, where the registration request is used to request that the terminal device be registered in a first network.

[0487] Among them, the first mobility management network element can be an AMF, and the first network can be a 5G network.

[0488] 2802A. If the third condition is met, the first mobility management network element sends first indication information to the terminal device, where the first indication information is used to indicate that the voice service in the PS domain is supported.

[0489] The third condition may include: the first network supports moving the terminal device to the second network. The first network supports moving the terminal device to the second network, which may mean that the first network supports moving the terminal device to the second network by switching, redirecting or other means.

[0490] Optionally, the first network supports moving the terminal device to the second network, which may include: a first access network device in the first network supports accessing the terminal device to the second network upon receiving first session management information from a session management network element, the first session management information being used to request establishment of a user plane tunnel for a voice service of the terminal device. The first access network device may be an NG RAN, and the session management network element may be an SMF+PGW-C functional network element.

[0491] Exemplarily, the first indication information may be carried in a registration acceptance message, the voice service may be an IMS voice service, and the terminal device may specifically be a terminal device that initiates a calling or called voice service.

[0492] Specifically, the first mobility management network element may determine whether the third condition is met by any one of the following methods or other methods:

[0493] (1) During the process of the terminal device registering in the first network, the first mobility management network element determines whether the third condition is met by obtaining whether the access network device and / or the core network element device where the current terminal device is located has the ability to move the terminal device to the second network.

[0494] (2) The first mobility management network element determines whether the third condition is met through its own configuration conditions, wherein the configuration conditions configure whether the access network device and / or the core network element device where the terminal device is located can move the terminal device to the second network.

[0495] Optionally, the core networks of the first network and the second network are the same, but the access standards are different; or, the core networks and the access standards of the first network and the second network are different.

[0496] When the core networks and access standards of the first network and the second network are different, the second network can be an EPS network. When the core networks of the first network and the second network are the same but the access standards are different, the first network and the second network can both be 5G networks. The difference is that the access standards of the first network and the second network are different.

[0497] Specifically, the first access network device can connect the terminal device to the second network by sending a switching request to the first mobility management network element to switch the terminal device from the first network to the second network. It should be noted that the first access network device connects the terminal device to the second network only when the terminal device initiates a PS domain voice service. The terminal device can be a terminal device that initiates a calling PS domain voice service or a terminal device that initiates a called PS domain voice service.

[0498] Optionally, the third condition may further include: the first network and the second network support handover interoperability. In this case, the first network supports moving the terminal device to the second network through handover.

[0499] Optionally, the first network and the second network support handover interoperability, including: a handover interoperability interface exists between the first network and the second network. Exemplarily, the handover interoperability interface may be an N26 interface.

[0500] Optionally, the second network may support the PS domain voice service or may not support the PS domain voice service. If the second network is limited to support the PS domain voice service, the third condition may further include: the second network can support the PS domain voice service.

[0501] Optionally, before step 2803A, the method may further include: the first mobility management network element determines that the terminal device is a terminal device mainly providing voice services. Since the terminal device mainly providing data services is irrelevant to the voice services, this optional method can distinguish the terminal type, and the terminal device mainly providing data services does not need to execute this solution, that is, it does not need to determine whether the third condition is met, and it does not need to send the first indication information.

[0502] Optionally, the method may also include: the terminal device generates a registration request, the registration request carries indication information that the terminal device is a terminal device mainly providing voice services; the terminal device sends a registration request to a first mobility management network element; in this case, the first mobility management network element determines that the terminal device is a terminal device mainly providing voice services, including: the first mobility management network element determines that the terminal device is a terminal device mainly providing voice services based on the registration request.

[0503] In this case, the terminal device carries indication information that the terminal device is a terminal device mainly providing voice services through a registration request, so there is no need to send separate signaling to inform the first mobility management network element of the indication information, thereby saving signaling overhead.

[0504] Optionally, before step 2803A, the method may further include: the first mobility management network element determines that the terminal device supports the process of moving from the first network to the second network and continuing the process of initiating the voice service through the second network during the process of initiating the voice service. Since the above method can only be implemented if the terminal device supports the process of moving from the first network to the second network and continuing the process of initiating the voice service through the second network during the process of initiating the voice service, the information can be determined in advance to avoid affecting the terminal device that cannot support the process of moving from the first network to the second network and continuing the process of initiating the voice service through the second network during the process of initiating the voice service.

[0505] Optionally, the registration request also carries indication information that the terminal device supports moving from the first network to the second network and continuing the voice service initiation process through the second network during the voice service initiation process. The first mobility management network element determines that the terminal device supports moving from the first network to the second network and continuing the voice service initiation process through the second network during the voice service initiation process, including: the first mobility management network element determines, based on the registration request, that the terminal device supports moving from the first network to the second network and continuing the voice service initiation process through the second network.

[0506] In this case, the terminal device carries indication information through a registration request that the terminal device supports moving from the first network to the second network during the voice service initiation process and continuing the voice service initiation process through the second network, thereby eliminating the need to send separate signaling to inform the first mobility management network element of the indication information, thereby saving signaling overhead.

[0507] It should be noted that the method provided in this embodiment can be executed in Fig.28 Before any of the above methods. In addition, the first mobility management network element may also send the first indication information to the terminal device under other conditions instead of the third condition.

[0508] The method provided in this embodiment, regardless of whether the first network supports the voice service of the terminal device, as long as the first network has the ability to fall back the terminal device to a network that can provide voice services by switching or other means when the terminal device initiates a voice service, then when the terminal device registers with the first network, the first mobility management network element indicates that the voice service of the PS domain of the terminal device is supported, thereby ensuring that the terminal device registers and resides in the first network without reselecting to other networks, saving network resources, and ensuring that the terminal device normally executes the PS domain voice service registration process and initiates the PS domain voice call process through the first network.

[0509] The present application also provides a network registration method, such as Fig.28B As shown, it is used for Fig.28AThe method shown is specifically described, and the method includes:

[0510] 2801B. UE sends a registration request to AMF.

[0511] Specifically, the registration request is used to request that the UE be registered in the first network. The UE can send a registration request to the NG RAN, and the NG RAN forwards the registration request to the AMF.

[0512] The registration request may carry indication information that the UE is a UE that mainly provides voice services and indication information that the UE supports moving from the first network to the second network during the voice service initiation process and continuing the voice service initiation process through the second network.

[0513] 2802B. AMF receives a registration request from the UE.

[0514] 2803B. The AMF determines, based on the registration request, that the UE supports moving from the first network to the second network during the voice service initiation process and continuing the voice service initiation process through the second network.

[0515] 2804B. AMF determines that the UE is a UE mainly used for voice services based on the registration request.

[0516] There is no particular order in which step 2803B and step 2804B are executed.

[0517] 2805B. AMF determines whether the third condition is met.

[0518] If yes, execute step 2806B. The third condition includes: the first network supports moving the UE to the second network, and the second network can support voice services in the PS domain. Fig.28B The AMF is used as an example to determine that the third condition is met.

[0519] 2806B. AMF sends first indication information to the UE, where the first indication information is used to indicate that the voice service in the PS domain is supported.

[0520] The first indication information may be carried in the registration acceptance message.

[0521] After step 2806B, the UE continues with subsequent procedures.

[0522] The above mainly introduces the solution provided by the embodiment of the present application from the perspective of the interaction between various network elements. It can be understood that in order to realize the above functions, each of the above network devices includes a hardware structure and / or software module corresponding to the execution of each function. Those skilled in the art should easily realize that, in combination with the units and algorithm steps of each example described in the embodiments disclosed in this document, the present application can be implemented in the form of hardware or a combination of hardware and computer software. Whether a function is executed in the form of hardware or computer software driving hardware depends on the specific application and design constraints of the technical solution. Professional and technical personnel can use different methods to implement the described functions for each specific application, but such implementation should not be considered to exceed the scope of this application.

[0523] The embodiment of the present application can divide the functional modules of each network device according to the above method example. For example, each functional module can be divided according to each function, or two or more functions can be integrated into one processing module. The above integrated module can be implemented in the form of hardware or in the form of software functional modules. It should be noted that the division of modules in the embodiment of the present application is schematic and is only a logical function division. There may be other division methods in actual implementation.

[0524] Exemplarily, a functional module division method of the network device provided in an embodiment of the present application is given below as an example.

[0525] The present application embodiment also provides a network device 290, see Fig.29 , including a processing unit 2901 and a transceiver unit 2902.

[0526] The network device may be a first access network device, a session management network element, a second mobility management network element, a second access network device, an IMS network element or a first mobility management network element.

[0527] Specifically, when Fig.29 When the schematic diagram of the first access network device is shown, the processing unit 2901 is used to receive the first session management information from the session management network element through the transceiver unit 2902, and the first session management information is used to request to establish a user plane tunnel for the voice service of the terminal device; through the transceiver unit 2902, a switching request is sent to the first mobility management network element according to the first session management information and the first condition, and the switching request is used to switch the terminal device from the first network to the second network, and the first condition includes: the first network cannot provide voice services.

[0528] Optionally, the first condition also includes: the second network supports voice services, the signal quality of the second network meets the voice service requirements, and the network equipment and terminal equipment of the first network support at least one of switching between the first network and the second network.

[0529] Optionally, the processing unit 2901 is further configured to send second session management information to the session management network element through the transceiver unit 2902, where the second session management information includes information that establishment of the user plane tunnel for the voice service is accepted.

[0530] Optionally, the processing unit 2901 is further configured to determine not to allocate radio resources for the user plane tunnel of the voice service according to the first session management information and the first condition.

[0531] Optionally, the processing unit 2901 is further configured to send third session management information to the session management network element through the transceiver unit 2902, where the third session management information includes information that establishment of a user plane tunnel for the voice service is rejected.

[0532] Optionally, the information that establishment of the user plane tunnel for the voice service is rejected includes reason information for the rejection.

[0533] Optionally, the reason information is that the terminal device is executing a switching process.

[0534] Optionally, the first condition also includes: the second network is unable to perform voice services, and the processing unit 2901 is also used to send fourth session management information to the session management network element through the transceiver unit 2902, and the fourth session management information includes information that the establishment of the user plane tunnel of the voice service is rejected, and the information that the establishment of the user plane tunnel of the voice service is rejected includes insufficient wireless resources.

[0535] When the terminal device in the first network performs voice service, the network device 290 can switch the terminal device to the second network so that the terminal device can perform voice service in the second network, thereby solving the problem that the terminal device in the first network cannot perform voice service.

[0536] when Fig.29 When the schematic diagram of the session management network element is shown, the processing unit 2901 is used to receive the third session management information sent by the first access network device through the transceiver unit 2902, and the third session management information includes the reason information that the establishment of the user plane tunnel of the voice service of the terminal device is rejected; determine that the terminal device switches from the first network to the second network; and establish a user plane tunnel for the voice service in the second network according to the reason information.

[0537] Optionally, the reason information is that the terminal device is executing a switching process.

[0538] Optionally, the processing unit 2901 is specifically configured to establish a user plane tunnel for the voice service in the second network after a first preset time period according to the cause information and a second condition, wherein the second condition includes that the second network cannot perform the voice service.

[0539] Optionally, the processing unit 2901 is specifically used to send a tunnel establishment request to the service gateway of the second network after the first preset time period through the transceiver unit 2902 according to the reason information and the second condition, and the tunnel establishment request is used to request establishment of a user plane tunnel for the voice service.

[0540] Optionally, the processing unit 2901 is specifically used to send a tunnel establishment request to the service gateway of the second network through the transceiver unit 2902 according to the reason information, and the tunnel establishment request is used to request to establish a user plane tunnel for the voice service; receive a tunnel establishment response sent by the service gateway through the transceiver unit 2902, and the tunnel establishment response includes information that the establishment of the user plane tunnel for the voice service is rejected; send a first message to the policy function control network element after the first preset time period according to the second condition through the transceiver unit 2902, and the first message is used to indicate that the establishment of the user plane tunnel for the voice service has failed.

[0541] When a terminal device in the first network switches from the first network to the second network, the network device 290 establishes a user plane tunnel for the voice service in the second network according to the reason information. If the second network can provide voice services, the user plane tunnel can be established successfully, so that the terminal device can provide voice services in the second network, solving the problem that the terminal device in the first network cannot provide voice services.

[0542] when Fig.29 When the schematic diagram shown is a second mobility management network element, the network device 290 may perform the following action one, action two, action three or action four.

[0543] Action 1: The processing unit 2901 is used to receive a tunnel establishment request sent by the service gateway through the transceiver unit 2902, where the tunnel establishment request is used to request to establish a user plane tunnel for a voice service for a terminal device; and send a tunnel establishment response to the service gateway through the transceiver unit 2902 according to a second condition, where the tunnel establishment response includes information that establishment of a user plane tunnel for the voice service of the terminal device is rejected, and the second condition includes that the second network cannot perform the voice service.

[0544] Optionally, the second condition also includes: the terminal device is a terminal device switched from the first network to the second network.

[0545] Optionally, the processing unit 2901 is further used to determine whether the terminal device has completed the joint registration.

[0546] The processing unit 2901 is specifically configured to determine whether a joint registration completion message is received from the terminal device.

[0547] When the second network cannot provide voice services, the network device 290 sends a tunnel establishment response to the service gateway, so that the service gateway transmits the information that the user plane tunnel establishment is rejected to the IMS network, thereby enabling the IMS network to trigger the CSFB service of the terminal device, and then enabling the terminal device to provide CS voice services.

[0548] Action 2: The processing unit 2901 is used to send a wireless tunnel establishment request to the second access network device through the transceiver unit 2902, and the wireless tunnel establishment request is used to request to establish a user plane tunnel for the voice service of the terminal device; receive a wireless tunnel establishment response sent by the second access network device through the transceiver unit 2902, and the wireless tunnel establishment response includes information that the user plane tunnel establishment for the voice service of the terminal device is rejected; send a tunnel establishment response to the service gateway through the transceiver unit 2902 according to the second condition, and the tunnel establishment response includes information that the user plane tunnel establishment for the voice service of the terminal device is rejected, and the second condition includes that the second network cannot perform the voice service.

[0549] Optionally, the second condition also includes: the terminal device is a terminal device switched from the first network to the second network.

[0550] Optionally, the processing unit 2901 is specifically used to determine that the second condition is met and the terminal device completes the joint registration; and send a tunnel establishment response to the service gateway through the transceiver unit 2902.

[0551] Optionally, the processing unit 2901 is specifically configured to determine whether a registration completion message is received from the terminal device.

[0552] The network device 290 sends the user plane tunnel establishment rejection information to the service gateway, so that the service gateway transmits the user plane tunnel establishment rejection information to the IMS network, thereby causing the IMS network to trigger the CSFB service of the terminal device, thereby causing the terminal device to perform the CS voice service.

[0553] Action three, the processing unit 2901 is used to receive a tunnel establishment request sent by the service gateway through the transceiver unit 2902, and the tunnel establishment request is used to request to establish a user plane tunnel for the voice service for the user equipment terminal device; if the second condition is met, it is determined that the terminal device has completed the joint registration, and the second condition includes that the second network cannot perform the voice service; send a wireless tunnel establishment request to the second access network device through the transceiver unit 2902, and the wireless tunnel establishment request is used to request to establish a user plane tunnel for the voice service of the terminal device; receive a wireless tunnel establishment response sent by the second access network device through the transceiver unit 2902, and the wireless tunnel establishment response includes information that the user plane tunnel establishment for the voice service of the terminal device is rejected; send a tunnel establishment response to the service gateway through the transceiver unit 2902 according to the wireless tunnel establishment response, and the tunnel establishment response includes information that the user plane tunnel establishment for the voice service of the terminal device is rejected.

[0554] Optionally, the second condition also includes: the terminal device is a terminal device switched from the first network to the second network.

[0555] Optionally, the processing unit 2901 is specifically configured to determine whether a registration completion message sent by the terminal device is received.

[0556] After the network device 290 determines that the terminal device has completed the joint registration, it sends the information that the user plane tunnel establishment is rejected to the service gateway, so that the service gateway transmits the information that the user plane tunnel establishment is rejected to the IMS network, thereby allowing the IMS network to trigger the CSFB service of the terminal device, and then allowing the terminal device to perform CS voice service, and can also ensure that the terminal device successfully initiates a CSFB call.

[0557] Action four, the processing unit 2901 is used to receive the fourth message sent by the first mobility management network element through the transceiver unit 2902, and the fourth message is used to confirm that the terminal device has completed the relocation; through the transceiver unit 2902, a tunnel modification request is sent to the service gateway according to the second condition, and the tunnel modification request is used to modify the signaling plane tunnel information of the voice service of the terminal device, and the second condition includes that the second network cannot perform the voice service.

[0558] Optionally, the processing unit 2901 is specifically used to determine that the second condition is met and the UE completes the joint registration; and send the tunnel modification request to the service gateway through the transceiver unit 2902.

[0559] When the second network is unable to provide voice services, the network device 290 sends a tunnel modification request to the service gateway, and the service gateway forwards the tunnel modification request to the session management network element. Since the session management network element will send a message for triggering the terminal device to initiate a CSFB call (i.e., the second message mentioned above) to the terminal device only after receiving the tunnel modification request, the network device 290 can trigger the terminal device to initiate a CSFB call when the second network is unable to provide voice services, thereby enabling the terminal device to perform CS voice services.

[0560] when Fig.29 When the schematic diagram shown is a second access network device, the processing unit 2901 is used to receive a wireless tunnel establishment request sent by the second mobility management network element through the transceiver unit 2902, and the wireless tunnel establishment request is used to request the second access network device to establish a user plane tunnel for the voice service for the terminal device; through the transceiver unit 2902, a wireless tunnel establishment response is sent to the second mobility management network element according to the second condition, and the wireless tunnel establishment response includes information that the user plane tunnel establishment of the voice service is rejected, and the second condition includes that the second network cannot perform the voice service.

[0561] Optionally, the second condition also includes: the terminal device is a terminal device switched from the first network to the second network.

[0562] When the second network cannot perform voice services, the network device 290 refuses to allocate wireless resources for the user plane tunnel, and carries the information that the establishment of the user plane tunnel for the voice service is rejected in the wireless tunnel establishment response and sends it to the second mobility management network element. The second mobility management network element can pass the information that the establishment of the user plane tunnel is rejected to the IMS network, so that the IMS network triggers the CSFB service of the terminal device, and then enables the terminal device to perform CS voice services.

[0563] when Fig.29 When the schematic diagram of the IMS network element is shown, the processing unit 2901 is used to receive a request message for establishing a voice service for a terminal device in a packet switching PS domain through the transceiver unit 2902; determine that the voice service cannot be established in the PS domain of the first network or the second network; determine that the terminal device completes the joint registration; and trigger the circuit domain switching fallback CSFB service of the terminal device.

[0564] Optionally, the processing unit 2901 is further used to determine that the terminal device is registered in the first network.

[0565] Optionally, the processing unit 2901 is specifically used to obtain the voice service establishment failure information from the first network PS domain; or, to obtain the voice service establishment failure information from the second network PS domain.

[0566] Optionally, the processing unit 2901 is specifically used to determine that the terminal device has completed the joint registration after a second preset time period from the time when the voice service cannot be established in the PS domain of the first network or the second network; or, to determine that the terminal device has completed the joint registration based on the registration location information of the terminal device obtained from the policy control network element or the home user server.

[0567] Optionally, the terminal device is a calling terminal device of the voice service, and the processing unit 2901 is specifically used to send a second message to the calling terminal device through the transceiver unit 2902, and the second message is used to trigger the calling terminal device to initiate a CSFB calling service.

[0568] Optionally, the terminal device is the called terminal device of the voice service, and the processing unit 2901 is specifically used to send a third message to the called domain selection device through the transceiver unit 2902, and the third message is used to indicate that the establishment of the called voice service in the PS domain of the first network or the second network has failed, so that the called domain selection device triggers the CSFB called voice service of the called terminal device.

[0569] When the network device 290 determines that it is impossible to establish a voice service in the PS domain of the first network or the second network and the terminal device completes the joint registration, it triggers the CSFB service of the terminal device. Since the completion of the joint registration by the terminal device is a necessary condition for the terminal device to initiate a CSFB call, it can ensure that the terminal device successfully initiates the CSFB call, thereby enabling the terminal device to perform CS voice service.

[0570] when Fig.29 When the schematic diagram of the first mobility management network element is shown, the processing unit 2901 is used to receive a registration request from the terminal device through the transceiver unit 2902, and the registration request is used to request that the terminal device be registered in the first network; the processing unit 2901 is also used to determine that a third condition is met, and the third condition includes: the first network supports moving the terminal device to the second network, and the second network can support voice services in the PS domain; the processing unit 2901 is also used to send a first indication information to the terminal device through the transceiver unit 2902, and the first indication information is used to indicate that the voice service in the PS domain is supported.

[0571] Optionally, the core networks of the first network and the second network are the same, but the access standards are different; or, the core networks and the access standards of the first network and the second network are different.

[0572] Optionally, the first network supports moving the terminal device to the second network, including: a first access network device in the first network supports connecting the terminal device to the second network upon receiving first session management information from a session management network element, the first session management information being used to request establishment of a user plane tunnel for a voice service of the terminal device.

[0573] Optionally, the third condition also includes: the first network and the second network support switching interoperability.

[0574] Optionally, the first network and the second network support handover interoperability, including: a handover interoperability interface exists between the first network and the second network.

[0575] Optionally, the processing unit 2901 is further configured to determine that the terminal device is a terminal device mainly providing voice services.

[0576] Optionally, the registration request carries indication information that the terminal device is a terminal device mainly providing voice services, and the processing unit 2901 is specifically configured to determine, based on the registration request, that the terminal device is a terminal device mainly providing voice services.

[0577] Optionally, the processing unit 2901 is further configured to determine whether the terminal device supports moving from the first network to the second network during the voice service initiation process and continuing the voice service initiation process through the second network.

[0578] Optionally, the registration request also carries indication information that the terminal device supports the process of moving from the first network to the second network and continuing the voice service initiation process through the second network during the voice service initiation process. The processing unit 2901 is specifically used to determine, based on the registration request, that the terminal device supports the process of moving from the first network to the second network and continuing the voice service initiation process through the second network during the voice service initiation process.

[0579] Regardless of whether the first network supports the voice service of the terminal device, as long as the first network has the ability to switch the terminal device back to a network that can provide voice services through switching or other means when the terminal device initiates voice services, when the terminal device registers with the first network, the first mobility management network element will instruct the terminal device that the voice service of the PS domain is supported, thereby ensuring that the terminal device registers and resides in the first network without reselecting to other networks, saving network resources, and ensuring that the terminal device normally executes the PS domain voice service registration process and initiates the PS domain voice call process through the first network.

[0580] The present application embodiment also provides a terminal device 290A, see Fig.29A, including a processing unit 2901A and a transceiver unit 2902A. The processing unit 2901A is used to generate a registration request, the registration request is used to request that the terminal device be registered in the first network, and the registration request carries indication information that the terminal device is a terminal device mainly providing voice services; the processing unit 2901A is also used to send the registration request to the first mobility management network element through the transceiver unit 2902A.

[0581] Optionally, the registration request also includes indication information that the terminal device supports moving from the first network to the second network during the voice service initiation process and continuing the voice service initiation process through the second network.

[0582] Optionally, the core networks of the first network and the second network are the same, but the access standards are different; or, the core networks and the access standards of the first network and the second network are different.

[0583] When the first network has the ability to fall back the terminal device to a network that can provide voice services by switching or other means when the terminal device initiates a voice service, the terminal device registers and resides in the first network instead of reselecting to other networks based on the first indication information sent by the received first mobility management network element, thereby saving network resources and ensuring that the terminal device normally executes the PS domain voice service registration process and initiates the PS domain voice call process through the first network.

[0584] The embodiment of the present application also provides a network device, including: a memory, a processor and a communication interface; the memory is used to store computer-executable instructions, the processor executes the computer-executable instructions stored in the memory, and the network device implements the method corresponding to the instruction through the communication interface. The structural diagram of the network device can be seen in Figure 6 .

[0585] The network device may be a first access network device, a session management network element, a second mobility management network element, a second access network device, an IMS network element or a first mobility management network element. Figure 6 and Fig.29 When the schematic diagram of the first access network device is shown, the processing unit 2901 may be the processor 601, and the transceiver unit 2902 may be the communication interface 604; Figure 6 and Fig.29 When the diagram shown is a schematic diagram of a session management network element, the processing unit 2901 may be the processor 601, and the transceiver unit 2902 may be the communication interface 604; Figure 6 and Fig.29 When the schematic diagram of the second mobility management network element is shown, the processing unit 2901 may be the processor 601, and the transceiver unit 2902 may be the communication interface 604; Figure 6 and Fig.29When the schematic diagram of the second access network device is shown, the processing unit 2901 may be the processor 601, and the transceiver unit 2902 may be the communication interface 604; Figure 6 and Fig.29 When the schematic diagram of the IMS network element is shown, the processing unit 2901 may be the processor 601, and the transceiver unit 2902 may be the communication interface 604; Figure 6 and Fig.29 When the schematic diagram shown is a first mobility management network element, the processing unit 2901 may be the processor 601 , and the transceiver unit 2902 may be the communication interface 604 .

[0586] The present application also provides a terminal device, including: a memory, a processor and a communication interface; the memory is used to store computer-executable instructions, the processor executes the computer-executable instructions stored in the memory, and the terminal device implements the method corresponding to the instruction through the communication interface. The structural diagram of the terminal device can be seen in Fig. 6A The processing unit 2901A may be the processor 601A, and the transceiver unit 2902A may be the communication interface 604A.

[0587] The embodiment of the present application also provides a computer-readable storage medium, including instructions, which, when executed on a computer, enable the computer to execute the above method.

[0588] The embodiment of the present application also provides a computer program product including instructions, which, when executed on a computer, enables the computer to execute the above method.

[0589] In the above embodiments, it can be implemented in whole or in part by software, hardware, firmware or any combination thereof. When implemented using a software program, it can be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, the process or function described in the embodiment of the present application is generated in whole or in part. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions may be stored in a computer-readable storage medium, or transmitted from one computer-readable storage medium to another computer-readable storage medium. For example, the computer instructions may be transmitted from a website site, computer, server or data center by wired (e.g., coaxial cable, optical fiber, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) mode to another website site, computer, server or data center. The computer-readable storage medium may be any available medium that a computer can access or may include one or more servers, data centers and other data storage devices that can be integrated with the medium. The available medium may be a magnetic medium (eg, a floppy disk, a hard disk, a magnetic tape), an optical medium (eg, a DVD), or a semiconductor medium (eg, a solid state disk (SSD)).

[0590] Although the present application is described herein in conjunction with various embodiments, in the process of implementing the claimed application, those skilled in the art may understand and implement other variations of the disclosed embodiments by viewing the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other components or steps, and "one" or "an" does not exclude multiple situations. A single processor or other unit may implement several functions listed in a claim. Certain measures are recorded in different dependent claims, but this does not mean that these measures cannot be combined to produce good results.

[0591] Although the present application has been described in conjunction with specific features and embodiments thereof, it is obvious that various modifications and combinations may be made thereto without departing from the spirit and scope of the present application. Accordingly, this specification and the drawings are merely exemplary illustrations of the present application as defined by the appended claims, and are deemed to have covered any and all modifications, variations, combinations or equivalents within the scope of the present application. Obviously, those skilled in the art may make various modifications and variations to the present application without departing from the spirit and scope of the present application. Thus, if these modifications and variations of the present application fall within the scope of the claims of the present application and their equivalents, the present application is also intended to include these modifications and variations.

Claims

1. A network switching method, characterized in that: include: The session management network element sends first session management information to the first access network device, where the first session management information is used to request to establish a user plane tunnel for the voice service of the terminal device; The first access network device sends a switching request to the first mobility management network element according to the first session management information and a first condition, wherein the switching request is used to switch the terminal device from the first network to the second network, and the first condition includes: the first network cannot perform the voice service.

2. The method according to claim 1, characterized in that The first condition also includes at least one of: the second network supports the voice service, the signal quality of the second network meets the voice service requirements, and the network equipment of the first network and the terminal equipment support switching between the first network and the second network.

3. The method according to claim 1 or 2, characterized in that: The method further comprises: The first access network device sends second session management information to the session management network element, where the second session management information includes information that establishment of the user plane tunnel of the voice service is accepted.

4. The method according to claim 3, characterized in that Before the first access network device sends the second session management information to the session management network element, the method further includes: The first access network device determines not to allocate wireless resources for the user plane tunnel of the voice service according to the first session management information and the first condition.

5. The method according to claim 1 or 2, characterized in that: The method further comprises: The first access network device sends third session management information to the session management network element, where the third session management information includes information that establishment of the user plane tunnel of the voice service is rejected.

6. The method according to claim 5, characterized in that The information that establishment of the user plane tunnel of the voice service is rejected includes rejection reason information.

7. The method according to claim 6, characterized in that The reason information is: the terminal device is executing a switching process.

8. The method according to claim 1, characterized in that The first condition further includes: the second network cannot perform the voice service, and the method further includes: The first access network device sends fourth session management information to the session management network element, where the fourth session management information includes information that establishment of the user plane tunnel of the voice service is rejected, and the information that establishment of the user plane tunnel of the voice service is rejected includes insufficient wireless resources.

9. The method according to any one of claims 5 to 7, characterized in that: The method further comprises: The session management network element determines, according to the third session management information, that the terminal device switches from the first network to the second network; After the terminal device switches from the first network to the second network, the session management network element establishes a user plane tunnel for the voice service in the second network according to the cause information.

10. The method according to claim 9, characterized in that The session management network element determines that the terminal device switches from the first network to the second network, including: The session management network element triggers a timer when receiving the third session management information sent by the access network device; If the timer expires, the session management network element determines that the terminal device switches from the first network to the second network.

11. The method according to claim 9, characterized in that The session management network element determines that the terminal device switches from the first network to the second network, including: The session management network element receives a tunnel modification request from a serving gateway in the second network; The session management network element determines, based on the tunnel modification request, that the terminal device switches from the first network to the second network.

12. The method according to claim 9, characterized in that The session management network element establishes a user plane tunnel for the voice service in the second network, including: The session management network element sends a tunnel establishment request to the service gateway of the second network, where the tunnel establishment request is used to request establishment of a user plane tunnel for the voice service.

13. The method according to any one of claims 1 to 12, characterized in that: The session management network element is a network element having a packet data network gateway-control plane and a session management function.

14. The method according to any one of claims 1 to 12, characterized in that: The first network is a 5G network, and the second network is a 4G network.

15. The method according to any one of claims 1 to 12, characterized in that: The first network and the second network have the same core network but different access standards; or, the first network and the second network have different core networks and different access standards.

16. A communication system comprising: A first access network device, configured to execute the method according to any one of claims 1 to 15, and A session management network element, configured to execute the method as described in any one of claims 1 to 15.

Images