WO2024066150A1

WO2024066150A1 - Network fallback method and device and storage medium

Info

Publication number: WO2024066150A1
Application number: PCT/CN2023/074056
Authority: WO
Inventors: 李海波; 薛超; 罗飞; 孟昭
Original assignee: 荣耀终端有限公司
Priority date: 2022-09-26
Filing date: 2023-02-01
Publication date: 2024-04-04
Also published as: CN115297448A; CN115297448B; CN117768856A

Abstract

The present application provides a network fallback method and device and a storage medium. In the method, after a fallback from a first network to a second network occurs and an TAU request is thereby triggered, a terminal device is set to always stay in the second network before receiving a TAU response issued by a core network by means of the second network, so that the success of an EPSFB can be ensured as much as possible by means of adjusting processing logic of the terminal device without modifying a communication protocol followed by the core network and without modifying a communication protocol followed by base stations corresponding to the network side, thereby ensuring the success rate of call services and meeting call requirements of a user.

Description

Network fallback method, device and storage medium

This application claims the priority of the Chinese patent application filed with the China Patent Office on September 26, 2022, with application number 202211172089.0 and invention name “Network Fallback Method, Device and Storage Medium”, all contents of which are incorporated by reference in this application.

Technical Field

The present application relates to the field of communication technology, and in particular to a network fallback method, device and storage medium.

Background technique

At present, some mobile communication networks cannot directly perform call services, such as the Standalone (SA) network of the 5th Generation Mobile Communication Technology (5G). For networks that cannot perform voice calls, terminal devices can use a fallback mechanism, such as the Evolved Packet System Fall Back (EPSFB) mechanism, to fall back to a network that can perform voice calls, such as the 4th Generation Mobile Communication Technology (4G), and then use the Voice over Long-Term Evolution (VoLTE) technology in the 4G network to perform call services. Based on the communication protocol standard corresponding to the EPSFB technology, it is known that after the terminal device falls back from the 5G SA network to the 4G LTE network, it needs to send a Tracking Area Update (TAU) request to the core network, and only after receiving the TAU response can it perform call services on the 4G LTE network.

However, in some abnormal situations, for example, before receiving the TAU response, the service cell of the terminal device changes. Based on the current communication protocol standard, the core network will no longer send a TAU response in this case. Therefore, the terminal device cannot receive the TAU response. In essence, EPSFB is unsuccessful, which will cause the call service to fail.

Summary of the invention

In order to solve the above technical problems, the present application provides a network fallback method, device and storage medium, aiming to improve the success rate of EPSFB, thereby improving the success rate of call services and meeting the call needs of users.

In the first aspect, the present application provides a network fallback method. The method is applied to a terminal device to be used for executing a call service in a first network, including: when the first network cannot execute the call service, falling back from the first network to a second network based on a fallback mechanism, the network types of the first network and the second network are different; sending a first tracking area update TAU request to a core network through the second network; before receiving a first TAU response sent by the core network through the second network, maintaining the current corresponding network, the first TAU response being made by the core network in response to the first TAU request.

Among them, the first network, for example, the 5G SA network mentioned below, can be provided by the 5G base station mentioned below.

Among them, the second network, for example, the 4G LTE network mentioned below, can be provided by the 4G base station mentioned below.

It can be understood that when falling back from the 5G SA network to the 4G LTE network, the specific 4G LTE network to fall back to can be determined based on all 4G LTE networks accessing the core network, the positional relationship between the current terminal device, the signal strength (level strength, quality manifestation) of each 4G LTE network, the transmission power of the 4G base stations corresponding to each 4G LTE network, and the transmission power, signal strength (level strength, quality manifestation) of the terminal device and other parameters.

Exemplarily, in some implementations, for example, the second network to be fallen back to may be determined based on a position relationship. For a specific determination method, please refer to the following, which will not be described in detail here.

Exemplarily, in some other implementations, for example, the second network to fall back to can be determined based on the transmit power. For the specific determination method, please refer to the following and will not be described in detail here.

Exemplarily, in some other implementations, for example, the second network to fall back to can be determined based on signal strength. For specific determination methods, please refer to the following and will not be described in detail here.

Exemplarily, in some other implementations, for example, the second network to fall back to can be determined based on comprehensive consideration of the above three parameters. For specific determination methods, please refer to the following and will not be described in detail here.

Therefore, after falling back from the first network to the second network and triggering the first TAU request, the terminal device is set to always stay in the second network before receiving the first TAU response sent by the core network through the second network. In this way, without modifying the communication protocol followed by the core network or the communication protocol followed by the base station side, by adjusting the processing logic of the terminal device, the success of EPSFB can be guaranteed as much as possible, thereby ensuring the success rate of the call service and meeting the user's call needs.

According to the first aspect, before receiving the first TAU response sent by the core network through the second network, the method also includes: switching from the second network to the third network, the third network having the same network type as the second network; starting a timer; within the timing duration corresponding to the timer, after receiving the first TAU response sent by the core network through the third network, turning off the timer and executing a call service on the third network; when the first TAU response sent by the core network through the third network is not received, after receiving the first TAU request sent by the core network through the third network within the timing duration corresponding to the timer; after receiving the second TAU response sent by the core network through the third network, executing a call service on the third network, the second TAU response being made by the core network in response to the second TAU request.

It can be understood that when the first network is a 5G SA network and the second network is a 4G LTE network, the third network has the same network type as the second network, which is also a 4G LTE network.

Exemplarily, in some implementations, the second network is, for example, the 4G LTE network corresponding to the 4G base station B mentioned below, and the third network is, for example, the 4G LTE network corresponding to the 4G base station C mentioned below.

It is understandable that in other implementations, a calculator may also be used, and this application does not limit this.

Therefore, before receiving the first TAU response, when the 4G LTE network to which the terminal device is connected changes, the timer/calculator is started to count. When the set time is reached, if the first TAU response is still not received, the second TAU request is re-initiated to the core network through the switched 4G LTE network, so that the terminal device can receive the second TAU response issued by the core network through the switched 4G LTE network, thereby ensuring the success of EPSFB and the success of the call service.

According to the first aspect, or any implementation of the first aspect above, the timing duration corresponding to the timer is less than the random access response duration corresponding to the call service.

It can be understood that the random access process is the process in which the terminal device requests access to the system, receives the system's response and allocates an access channel. Generally, data transmission must be performed after the random access is successful. In 4G LTE, each service corresponds to a random access response duration. If no response is received within the response duration, the service fails.

Based on this, by setting the timing duration corresponding to the timer to be shorter than the random access response duration corresponding to the call service, it can be ensured that after the network switch, after the timer reaches the corresponding timing duration, the TAU request is sent through the newly accessed 4G LTE network, and the duration of receiving the TAU response is within the random access response duration, thereby ensuring the success of EPSFB. The timing duration set for the timer must be shorter than the random access response duration corresponding to the call service.

According to the first aspect, or any implementation method of the first aspect above, the timing duration is N times the duration of the TAU process, and the TAU process duration refers to the time taken for the terminal device to send a first TAU request to receive a first TAU response, and N is an integer greater than 0.

According to the first aspect, or any implementation method of the first aspect above, before receiving the first TAU response sent by the core network through the second network, maintaining the current corresponding network, including: before receiving the first TAU response sent by the core network through the second network, suspending the measurement and reporting operation.

The so-called measurement operation refers to the terminal device being used to obtain the MeasurementReport (measurement result/measurement report) corresponding to the accessible 4G LTE network.

Exemplarily, the measurement results obtained through the measurement and reporting operation may include, for example, the transmission power and signal strength of the terminal device, and network information of surrounding accessible networks of the same network type as the second network.

Exemplarily, the aforementioned network information may include, for example, the signal strength of the network (level strength, quality embodiment), the transmission power of the base station corresponding to the network, and the like.

Therefore, the terminal device falls back from the first network to the second network based on EPSFB, and after sending the first TAU request, before receiving the first TAU response to the first TAU request, the terminal device is suppressed from performing measurement operations, so that a 4G LTE network with better transmission power and signal strength than the currently connected 4G LTE network will not be detected, thereby ensuring that the 4G LTE network connected to the terminal device will not change before receiving the first TAU response, and further ensuring that the first TAU response corresponding to the first TAU request sent through the 4G LTE network is received through the currently connected 4G LTE network. In this way, the success of EPSFB can be guaranteed as much as possible, thereby ensuring the success rate of call services and meeting the user's call needs.

According to the first aspect, or any implementation manner of the first aspect above, the method also includes: after receiving a first TAU response sent by the core network through the second network, performing a measurement operation to obtain a measurement result, the measurement result including network information of all fourth networks that the terminal device can switch from the second network and the transmission power and signal strength of the terminal device, and the network type of the fourth network and the second network is the same; reporting the measurement result to the second network; receiving a fifth network determined by the second network according to the measurement result, the fifth network is a fourth network that meets the set requirements and is screened out according to the transmission power, signal strength and network information of all fourth networks of the terminal device; switching from the second network to the fifth network.

It is understandable that in some implementations, the third network, the fourth network and the fifth network can be the same network, that is, a 4G LTE network provided by the same 4G base station corresponding to the same service cell.

For the specific implementation of the measurement and reporting operation, please refer to the existing communication protocol, which will not be repeated here.

Correspondingly, the measurement results obtained through the measurement and reporting operation can also refer to the existing communication protocol, which will not be repeated here.

Therefore, after receiving the first TAU response through the second network that falls back, the suppression of the terminal device is released, even if the terminal device can perform the measurement operation according to the set period or trigger condition, and report the measurement result obtained by the measurement operation to the second network, so that when there is a more suitable terminal device in the measurement result, switching from the second network to the new network can be achieved, thereby ensuring the success rate of EPSFB, the quality of the call corresponding to the call service, and the user experience.

According to the first aspect, or any implementation manner of the first aspect above, the method also includes: before receiving a first TAU response sent by the core network through the second network, suspending the measurement operation, and re-accessing the second network when an abnormality occurs in the wireless link between the core network and the second network.

Therefore, when an abnormality such as Radio Link Failure (RLF) occurs in the wireless link between the wireless link and the second network, the source network, that is, the second network that sends the first TAU request, is rebuilt to ensure that the first TAU response made by the core network for the first TAU request can still be sent to the terminal device through the second network, thereby ensuring the success rate of EPSFB and the success rate of the call service.

According to the first aspect, or any implementation manner of the first aspect above, before re-accessing the second network, the method also includes: determining whether the reference signal received power of the second network satisfies the set reference signal received power threshold, and/or whether the reference signal received quality of the second network satisfies the set reference signal received quality threshold; when the reference signal received power of the second network satisfies the set reference signal received power threshold, and/or the reference signal received quality of the second network satisfies the set reference signal received quality threshold, executing the step of re-accessing the second network; when the reference signal received power of the second network does not satisfy the set reference signal received power threshold, and/or the reference signal received quality of the second network does not satisfy the set reference signal received quality threshold, accessing the sixth network.

It is understandable that in some implementations, the third network, the fourth network, the fifth network and the sixth network can be the same network, that is, a 4G LTE network provided by the same 4G base station corresponding to the same service cell.

Therefore, before rebuilding to the source network, it is determined whether the source network meets the reconstruction conditions through reference information such as the reference signal receiving power (Reference Signal Receiving Power, RSRP) and/or the reference signal receiving quality (Reference Signal Receiving Quality, RSRQ) of the source network. The source network is rebuilt only when the reconstruction conditions are met, such as when the set threshold is met, otherwise it is switched to the sixth network, thereby avoiding the situation where the reconstructed source network still has RLF anomalies, which leads to the failure to receive the first TAU response within the random access response duration.

According to the first aspect, or any implementation of the first aspect above, after accessing the sixth network, the method also includes: starting a timer; within the timing duration corresponding to the timer, after receiving the first TAU response sent by the core network through the sixth network, turning off the timer and executing the call service in the sixth network; when the first TAU response sent by the core network through the sixth network is not received, after receiving the timing duration corresponding to the timer, sending a third TAU request to the core network through the sixth network; after receiving the third TAU response sent by the core network through the sixth network, executing the call service in the sixth network, the third TAU response being made by the core network in response to the third TAU request.

Therefore, in the case where the source network cannot be reestablished, after switching to the sixth network, the sixth network resends the TAU request after receiving it at the timed duration corresponding to the timer, so that the core network can send a TAU response to the newly sent TAU request to the terminal device through the third network, so that the terminal device When the source network cannot be rebuilt, it is still possible to ensure that the TAU process triggered after EPSFB can be successfully completed, thereby ensuring the success rate of EPSFB and further ensuring the success rate of the call service.

According to the first aspect, or any implementation method of the first aspect above, before receiving the first TAU response sent by the core network through the second network, maintaining the current corresponding network, including: before receiving the first TAU response sent by the core network through the second network, when receiving the network switching instruction sent by the second network, suspending the response to the network switching instruction and maintaining the current corresponding network.

Therefore, before waiting for the first TAU response sent by the currently connected second network, the terminal device can be set not to respond to the network switching instruction sent by the second network, or to delay responding to the network switching instruction, thereby avoiding changes in the network to which the terminal device is connected before receiving the first TAU response.

According to the first aspect, or any implementation of the first aspect above, the method also includes: after receiving a first TAU response sent by the core network through the second network, in response to a network switching instruction, switching from the second network to a network indicated by the network switching instruction.

Therefore, after receiving the TAU response sent by the second network, that is, when EPSFB is successful and the call service is already proceeding smoothly, the network switching instruction is responded to, thereby ensuring the success rate of EPSFB and the success rate of the call service.

According to the first aspect, or any implementation of the first aspect above, the method further includes: after receiving a first TAU response sent by the core network through the second network, executing a call service in the second network.

Therefore, after sending the first TAU request through the second network, the terminal device is kept in the second network through any of the above methods, so that the core network can send the first TAU response made for the first TAU request to the terminal device through the second network. After receiving the TAU response, the terminal device can execute the subsequent process of the call service on the second network while still connected to the second network, thereby ensuring that after falling back from the first network to the second network based on EPSFB, the call service can be executed on the second network, thereby meeting the user's call needs.

According to the first aspect, or any implementation of the first aspect above, the first network is a 5G SA network, and the second network is a 4G LTE network.

Since there are two voice call modes supported by 5G SA network, one is the NR voice (Voice over NR, VoNR) service provided based on New Radio (NR) access technology in 5G SA network, and the other is the Long-Term Evolution (VoLTE) service provided based on 4G voice architecture and IP Multimedia Subsystem (IMS) supported by 4G network. Therefore, when 5G SA network cannot perform call services, such as when terminal equipment cannot implement call services based on VoNR in 5G SA network, it can fall back to 4G LTE network, and then implement call services based on VoLTE in 4G LTE network, so as to ensure that call services can be implemented and guarantee the call needs of users.

According to the first aspect, or any implementation of the first aspect above, the fallback mechanism is an evolved packet system fallback EPSFB mechanism.

It can be understood that EPSFB refers to the fallback mechanism that falls back the call service from the 5G SA network to the 4G LTE network when the 5G SA network does not have the VoNR conditions. Based on this fallback mechanism, the call service can be fallen back from the 5G SA network to the 4G LTE network, thereby performing call services based on the VoLTE provided by the 4G LTE network, ensuring the continuity of the voice call service and guaranteeing the user's call needs.

In a second aspect, the present application provides a terminal device. The terminal device includes: a memory and a processor, the memory and the processor are coupled; the memory stores program instructions, and when the program instructions are executed by the processor, the terminal device executes instructions of the method in the first aspect or any possible implementation of the first aspect.

The second aspect corresponds to the first aspect and any implementation of the first aspect. The technical effects corresponding to the second aspect can refer to the technical effects corresponding to the first aspect and any implementation of the first aspect, which will not be repeated here.

In a third aspect, the present application provides a computer-readable medium for storing a computer program, wherein the computer program includes instructions for executing the method in the first aspect or any possible implementation of the first aspect.

The third aspect corresponds to the first aspect and any implementation of the first aspect. The technical effects corresponding to the third aspect can refer to the technical effects corresponding to the first aspect and any implementation of the first aspect, which will not be repeated here.

In a fourth aspect, the present application provides a computer program, comprising instructions for executing the method in the first aspect or any possible implementation of the first aspect.

The fourth aspect corresponds to the first aspect and any implementation of the first aspect. The technical effects corresponding to the fourth aspect can refer to the technical effects corresponding to the first aspect and any implementation of the first aspect, which will not be repeated here.

In a fifth aspect, the present application provides a chip, the chip comprising a processing circuit and a transceiver pin, wherein the transceiver pin and the processing circuit communicate with each other through an internal connection path, and the processing circuit executes the method in the first aspect or any possible implementation of the first aspect to control the receiving pin to receive a signal and control the sending pin to send a signal.

The fifth aspect corresponds to the first aspect and any implementation of the first aspect. The technical effects corresponding to the fifth aspect can refer to the technical effects corresponding to the first aspect and any implementation of the first aspect, which will not be repeated here.

In a sixth aspect, the present application provides a communication system. The system includes a 5G base station, a 4G base station, a core network and the terminal device involved in the second aspect above.

The sixth aspect corresponds to the second aspect, the first aspect, and any implementation of the first aspect. The technical effects corresponding to the sixth aspect can refer to the technical effects corresponding to the second aspect, the first aspect, and any implementation of the first aspect, and will not be repeated here.

BRIEF DESCRIPTION OF THE DRAWINGS

1a to 1d are schematic diagrams of a communication environment in which a terminal device implements a call service;

FIG2 is a timing diagram of the TAU process phase after the network falls back as an example;

FIG3 is a schematic diagram showing a hardware structure of a terminal device;

FIG4 is a flowchart of a network fallback method provided by an embodiment of the present application;

FIG5 is a timing diagram showing one of the interaction processes between entities involved in implementing the network fallback method shown in FIG4 ;

FIG6 is a second timing diagram exemplarily illustrating the interaction process between entities involved in implementing the network fallback method shown in FIG4 ;

FIG. 7 is a third timing diagram exemplarily illustrating the interaction process between the entities involved in implementing the network fallback method shown in FIG. 4 ;

FIG8 is a second flowchart of the network fallback method provided by an embodiment of the present application;

FIG. 9 is a timing diagram exemplarily illustrating the interaction process between entities involved in implementing the network fallback method shown in FIG. 8 .

Detailed ways

The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

The term "and/or" in this article is merely a description of the association relationship of associated objects, indicating that three relationships may exist. For example, A and/or B can mean: A exists alone, A and B exist at the same time, and B exists alone.

The terms "first" and "second" in the description and claims of the embodiments of the present application are used to distinguish different objects rather than to describe a specific order of objects. For example, a first target object and a second target object are used to distinguish different target objects rather than to describe a specific order of target objects.

In the embodiments of the present application, words such as "exemplary" or "for example" are used to indicate examples, illustrations or descriptions. Any embodiment or design described as "exemplary" or "for example" in the embodiments of the present application should not be interpreted as being more preferred or more advantageous than other embodiments or designs. Specifically, the use of words such as "exemplary" or "for example" is intended to present related concepts in a specific way.

In the description of the embodiments of the present application, unless otherwise specified, the meaning of "multiple" refers to two or more than two. For example, multiple processing units refer to two or more processing units; multiple systems refer to two or more systems.

In order to better understand the technical solutions provided by the embodiments of the present application, the communication scenarios to which the technical solutions provided by the embodiments of the present application are applicable are described below.

Specifically, with the continuous development of communication technology, communication networks have evolved from the 4th Generation Mobile Communication Technology (4G) to the 5th Generation Mobile Communication Technology (5G). For 5G networks, they use the New Radio (NR) access technology, but also use the 4G voice architecture and IP Multimedia Subsystem (IMS). Therefore, for 5G networks, they can provide NR-based access technology. It can provide NR voice (Voice over NR, VoNR) services, and can also provide Long-Term Evolution voice bearer (Voice over Long-Term Evolution, VoLTE) services based on the 4G voice architecture and IMS supported by the 4G network.

However, in actual applications, some mobile communication networks cannot directly perform call services, such as 5G standalone (SA). For networks that cannot perform voice calls, terminal devices can use a fallback mechanism, such as the Evolved Packet System Fall Back (EPSFB) mechanism, to fall back to a network that can perform voice calls, such as the 4th Generation Mobile Communication Technology (4G), and then use the Voice over Long-Term Evolution (VoLTE) technology in the 4G network to perform call services. Based on the communication protocol standard corresponding to the EPSFB technology, it is known that after the terminal device falls back from the 5G SA network to the 4G LTE network, it needs to send a Tracking Area Update (TAU) request to the core network, and only after receiving the TAU response can it perform call services on the 4G LTE network.

Exemplarily, referring to FIG. 1a to FIG. 1d , a schematic diagram of a communication environment for a terminal device to implement the above-mentioned call service involving network fallback is provided.

Refer to Figure 1a, where the network accessed by terminal A (calling party) is 4G LTE provided by 4G base station A, and the network accessed by terminal B (called party) is 5G SA network provided by 5G base station, and both 4G base station A and 5G base station are connected to the core network. When terminal A triggers a call service and initiates a call request to terminal B, the call request will be transmitted to the core network through 4G base station A that has established a wireless link with terminal A, and then sent to terminal B through the core network through the 5G base station that has established a wireless link with terminal B.

Through the above description, when the 5G SA network provided by the 5G base station cannot directly perform call services, such as being unable to establish a VoNR call session based on NR, the 5G SA network needs to fall back to the 4G LTE network based on the EPSFB mechanism. As shown in Figure 1b, it is necessary to fall back from the 5G SA network provided by the 5G base station to the 4G LTE network provided by 4G base station B, that is, disconnect the wireless link with the 5G base station and establish a wireless link with 4G base station B.

Continuing to refer to Figure 1b, illustratively, after falling back from the 5G SA network to the 4G LTE network based on the EPSFB mechanism, based on the communication protocol related to EPSFB, it can be known that terminal B will send a Tracking Area Update (TAU) request to the core network through the 4G base station B corresponding to the 4G LTE network it falls back to, to inform the core network that the network currently accessed by terminal B is updated from the 5G SA network provided by the 5G base station to the 4G LTE network provided by the 4G base station B, so that the call service can be executed on the 4G LTE network.

Continuing to refer to FIG. 1b, for example, under normal circumstances, that is, when the terminal B does not switch networks, the network it accesses is still the 4G LTE network provided by the 4G base station B, and the wireless links between the core network and the 4G base station B, and between the terminal B and the 4G base station B are normal, the TAU response made by the core network to the TAU request sent by the terminal B through the 4G LTE network provided by the 4G base station B will be sent to the terminal B through the 4G LTE network provided by the 4G base station B. After receiving the TAU response sent by the core network through the 4G LTE network provided by the 4G base station B, if the current time spent does not exceed the random access response time corresponding to the call service after the terminal A initiates the call request, the call response made by the terminal B to the call request will be transmitted to the core network through the 4G LTE network provided by the 4G base station B, and the core network will send the call response to the terminal A through the 4G LTE network of the 4G base station A, as shown in FIG. 1c. In this way, based on the EPSFB mechanism, the network fallback is considered successful, and the subsequent process of the call service can be executed downward.

However, in some abnormal cases, for example, before terminal B receives the TAU response, the serving cell of terminal B, that is, the 4G LTE network accessed, changes, as shown in FIG1d , for example, terminal B is disconnected from the 4G base station. The wireless link between B and 4G base station C has established a wireless link, that is, it has switched to the 4G LTE network provided by 4G base station C. Based on the current communication protocol standard, the core network will no longer send a TAU response in this case, so terminal B cannot receive the TAU response. In essence, the network fallback based on the EPSFB mechanism has not been successful, which will cause the subsequent process of the call service to be unnecessary, and thus cause the call service to fail.

It should be understood that the above description is only an example listed for a better understanding of the technical solution of this embodiment, and is not the only limitation to this embodiment. In practical applications, the base stations that terminal A can access are not limited to the 4G base station A mentioned above, and the base stations that terminal B can access are not limited to the 5G base stations, 4G base stations B, 4G base stations C, etc. mentioned above.

Based on the existing communication protocol, in the communication scenario mentioned above, based on the EPSFB mechanism, after falling back from the 5G SA network to the 4G LTE network, the interaction process between the terminal side and the network side entities in the TAU process stage (sending TAU request and receiving TAU response) is shown in Figure 2.

Referring to Figure 2, it should be noted that in a call service, when a calling party calls a called party, a multimedia session is established with the called party through an INVITE request, and the establishment of the multimedia session is realized through the IMS network. That is, the call request mentioned above can be transmitted from the calling party to the called party in the form of an INVITE request.

In addition, it can be seen from the above communication scenario description that the communication between the caller and the called party needs to be realized through the base station and core network to which they are connected. Therefore, the INVITE request initiated by the caller when triggering the call service will transmit the INVITE request to the core network through the base station to which the caller is connected, and then the core network will establish a multimedia session for the caller with the IMS network, and then the IMS network will transmit the INVITE request to the called party through the core network and the base station to which the called party is connected. The network fallback operation based on the EPSFB mechanism mentioned above is specifically performed when the called party is in the 5G SA network and receives the above-mentioned INVITE request. Therefore, the process shown in Figure 2 takes UE (User Equipment, terminal equipment, also known as: user equipment) as the called party as an example, and explains the scenario in which the INVITE request is directly sent from the IMS network to the called party.

Referring to Figure 2, exemplarily, when the INVITE request initiated by the calling party is sent to the core network through the IMS network, the core network will send the INVITE request to the called party UE through the 5G base station, that is, the core network first sends the INVITE request to the 5G base station accessed by the called party UE, and then the 5G base station sends the INVITE request to the called party UE.

Continuing to refer to Figure 2, for example, based on the Session Initialization Protocol (SIP) corresponding to the call service, it can be known that after receiving the INVITE request, the called party UE will make a temporary response of 100Trying to inform the calling party that the INVITE request has been received. Regarding 100Trying, it is still fed back to the IMS network through the corresponding 5G base station and core network, and then fed back to the calling party by the IMS network, core network and the base station corresponding to the calling party.

Since the technical solutions provided in the embodiments of the present application are mainly aimed at the interaction process between the called party and the base station, the core network, and the IMS network, the subsequent processing flow of the base station and the calling party corresponding to the IMS network, the core network, and the calling party will not be repeated.

Continuing to refer to Figure 2, illustratively, after the called party UE makes 100 Trying, it will also feedback information related to the answering session progress (call status) to the IMS network through the 5G base station and core network. Based on the SIP protocol, it can be known that the information related to the answering session progress (call status) can be reported through 183 Session Progress, for example.

Accordingly, after receiving the information related to the answering session progress (call status) reported by the called party UE through 183 Session Progress, the IMS network will feedback the temporary feedback confirmation message PRACK (Provisional Response Acknowledgement). Since this stage still occurs on the 5G SA network, the PRACK fed back by the IMS will be sent to the called party UE through the core network and 5G base station.

Continuing to refer to Figure 2, based on the communication protocol involved in the 5G bearer establishment process, it can be seen that after completing the above process, the quality of service flow (Quality of Service flow, QOS flow) between the core network and the 5G base station will be set, that is, the Setup QOS flow shown in Figure 2. For detailed information that can be included in the QOS flow between the core network and the 5G base station, please refer to the corresponding communication protocol, which will not be repeated here.

Continuing to refer to Figure 2, illustratively, after completing the Setup QOS flow, when the 5G base station cannot directly perform call services, it will send a switching command to the called party UE. Based on the communication protocol corresponding to the EPSFB mechanism, it can be known that the switching command sent by the 5G base station is, for example, "mobilityFromNRCommand", and through the switching command, the 5G base station will indicate to the called party UE the type of network to be switched. As shown in Figure 2, the "targetRAT-Type:eutra" carried in the command indicates that the network type to be switched by the called party UE is Evolved Universal Terrestrial Radio Access (eutra), that is, the wireless access network architecture of the 4G LTE network.

It should be noted that in actual applications, the 5G base station can also inform the called party UE of the transmission power range, signal strength, etc. of the 4G LTE network to which it can fall back through the switching command, so that the called party UE can select a suitable 4G LTE network to access from multiple accessible 4G LTE networks. For specific implementation methods, please refer to the corresponding communication protocol, which will not be repeated here. This application takes the current 4G LTE network to be accessed as the network corresponding to 4G base station B as an example.

Continuing to refer to Figure 2, illustratively, after the called party UE receives the switching command mobilityFromNRCommand:targetRAT-Type:eutra issued by the 5G base station, when it is determined that the 4G LTE network to be fallen back to is the network provided by 4G base station B, the called party will access 4G base station B, for example, to establish a wireless link with 4G base station B. The specific establishment method can be found in the corresponding communication protocol, which will not be repeated here.

Continuing to refer to FIG. 2, illustratively, after falling back to the 4G LTE network provided by 4G base station B, based on the corresponding communication protocol, the called party UE will send a TAU request (TAU REQ) to the core network through the 4G LTE network provided by 4G base station B. Based on the existing communication protocol, the called party UE will perform measurement and reporting operations in real time or according to a set period, and then obtain the MeasurementReport (measurement result/measurement report) corresponding to the accessible 4G LTE network, and report the obtained measurement results to the currently accessed 4G base station B. Based on the measurement results reported by the called party UE, 4G base station B will select a 4G LTE network with a better transmission power match and better signal quality from the 4G LTE network currently accessible to the called party, and send a network switching instruction to the called party UE to instruct the called party UE to switch to the 4G base station corresponding to the 4G LTE network determined by 4G base station B based on the measurement results, such as 4G base station C shown in FIG. 2.

Exemplarily, the measurement results obtained through the measurement operation may include, for example, the transmission power and signal strength of the called party UE, and network information of the surrounding accessible 4G LTE networks.

Exemplarily, the above-mentioned network information may include, for example, the signal strength (level strength, quality manifestation) of each accessible 4G LTE network in the surrounding area, the transmission power of the base stations corresponding to each 4G LTE network, etc.

Continuing with FIG. 2 , illustratively, in response to a network switching instruction from 4G base station B to switch to 4G base station C, the called UE disconnects the wireless link with 4G base station B, establishes a wireless link with 4G base station C, and thereby accesses the 4G LTE network provided by 4G base station C.

Considering that the core network designed by some manufacturers currently stipulates that TAU is received on the source cell (source 4G LTE network), After the request, if the 4G base station accessed by the called party UE changes, such as when 4G base station B is switched to 4G base station C in Figure 2, the TAU response cannot be fed back to the called party UE through the switched 4G base station C. The called party UE can only feed back the corresponding TAU response through the 4G base station C after resending the TAU request through the switched 4G base station C. Based on the provisions of the communication protocol currently followed, it is known that the timeout period for retransmission of the TAU request is usually 15 seconds, and the random access response duration corresponding to the INVITE request is usually 6 seconds. Obviously, based on the provisions of the communication protocol currently followed, within the random access response duration, the core network cannot process and will not respond to the TAU request previously received through 4G base station B. During the timeout period of waiting for the TAU request to be retransmitted, the caller will have one or more update processes, which will be transmitted to the called party UE by the IMS network through the core network and the 4G base station C currently accessed by the called party, so that the called party UE can know the information used by the caller to reserve resources and update media during the call establishment process.

Continuing to refer to Figure 2, illustratively, when the IMS network transmits the information of the calling party Update process with the called party UE, after the core network determines that the dedicated bearer required for this call service has been established, it will send a request for activating the dedicated bearer to the called party UE through the 4G base station C currently accessed by the called party UE. The request for activating the dedicated bearer sent based on the corresponding communication protocol is, for example, an Activate dedicated EB request.

Continuing to refer to FIG. 2 , illustratively, since the called party UE has not received a TAU response from the core network in response to the TAU request sent by it, it will not respond to the SIP message and the corresponding process message executed by the ESM.

It is understandable that in a mobile communication system, the two core issues to be solved are: "connection" and "mobility". Among them, the Evolved Packet System (EPS) has two corresponding concepts: ESM (EPS Session Management) and EMM (EPS Mobility Management). In this embodiment, when the called party UE does not receive the TAU response made by the core network to the TAU request sent by it, the connection of the session is not completed at this stage, so the corresponding process message executed by ESM is not responded at this stage.

Continuing to refer to FIG. 2 , for example, if the called party UE does not respond to the SIP message and the ESM process message, the calling party will never receive the response made by the called party UE to establish the multimedia session, that is, it will not receive the call response mentioned in FIG. 1c. When the calling party cannot receive the call response, when the IMS detects that the bearer establishment timeout has been reached, such as when the random access response timeout has been reached, it will generate a BYE request to terminate the specified session or the established session, and carry a specific reason, such as a status code 503 indicating a connection error.

Continuing to refer to FIG. 2 , illustratively, a BYE request carrying a 503 status code will be encapsulated as a Cancel as shown in FIG. 2 , and transmitted to the called party UE through the core network and 4G base station C, so that the called party UE performs a hang-up operation in response to the received Cancel.

That is to say, based on the EPSFB mechanism, the 5G SA network provided by the 5G base station falls back to the 4G TLE network provided by the 4G base station B. After the called party UE sends a TAU request to the core network through the 4G TLE network provided by the 4G base station B, and before waiting to receive the TAU response sent by the core network through the 4G TLE network provided by the 4G base station B, if the above-mentioned 4G LTE network switching occurs, such as switching from the 4G TLE network provided by the 4G base station B to the 4G LTE base station provided by the 4G base station C, the network fallback implemented based on the EPSFB mechanism is not truly successful and the call service cannot be carried out.

In view of this, in order to solve the above problems, the embodiment of the present application provides a network fallback method to improve the success rate of EPSFB, thereby improving the success rate of call services and meeting the user's call needs.

In order to better understand the network fallback method provided in the embodiment of the present application, the hardware structure of the terminal device to which the method is applicable is first described in conjunction with Figure 3, and then the process of implementing the network fallback method provided in the embodiment of the present application by the terminal device based on the hardware structure is described in conjunction with Figures 4 to 9.

Referring to FIG. 3 , there is shown a schematic diagram of the hardware structure of a terminal device 100 for implementing the network fallback method provided in an embodiment of the present application.

As shown in Figure 3, the terminal device 100 may include: a processor 110, an external memory interface 120, an internal memory 121, a universal serial bus (USB) interface 130, a charging management module 140, a power management module 141, a battery 142, an antenna 1, an antenna 2, a mobile communication module 150, a wireless communication module 160, an audio module 170, a sensor module 180, a button 190, a motor 191, an indicator 192, a camera 193, a display screen 194, and a subscriber identification module (SIM) card interface 195, etc.

Among them, antenna 1 and antenna 2 are used to transmit and receive electromagnetic wave signals. Each antenna in terminal device 100 can be used to cover a single or multiple communication frequency bands. Different antennas can also be reused to improve the utilization rate of the antenna. For example, antenna 1 can be reused as a diversity antenna of a wireless local area network. In some other embodiments, the antenna can be used in combination with a tuning switch.

It should be noted that, specifically in each embodiment of the present application, the terminal device 100 receives the switching command/instruction, TAU response, INVITE request, PRACK, Update, Activate dedicated EB request and other information sent by the base station (4G base station, 5G base station), and sends 100 Trying, 183 response, TAU request and other information to the base station, all of which are achieved through antenna 1 or antenna 2.

The mobile communication module 150 can provide solutions for wireless communications including 2G/3G/4G/5G applied on the terminal device 100. The mobile communication module 150 may include at least one filter, a switch, a power amplifier, a low noise amplifier (LNA), etc. The wireless communication module 160 can provide solutions for wireless communications including wireless local area networks (WLAN) (such as wireless fidelity (Wi-Fi) network), Bluetooth (BT), global navigation satellite system (GNSS), frequency modulation (FM), near field communication (NFC), infrared technology (IR), etc. applied on the terminal device 100.

In some embodiments, antenna 1 of terminal device 100 is coupled to mobile communication module 150, and antenna 2 is coupled to wireless communication module 160, so that terminal device 100 can communicate with the network and other devices through wireless communication technology.

Continuing to refer to FIG. 3 , illustratively, the audio module 170 of the terminal device 100 includes a speaker 170A, a receiver 170B, a microphone 170C, an earphone interface 170D, and the like.

Exemplarily, the terminal device 100 can implement audio functions such as music playback, recording, and the call services described in the various embodiments of the present application through the speaker 170A, receiver 170B, microphone 170C, headphone interface 170D, and application processor in the audio module 170.

In addition, regarding the sensor module 180 in the terminal device 100, in some embodiments, it may include a pressure sensor, a gyroscope sensor, an air pressure sensor, a magnetic sensor, an acceleration sensor, a distance sensor, a proximity light sensor, a fingerprint sensor, a temperature sensor, a touch sensor, an ambient light sensor, a bone conduction sensor, etc., which are not listed one by one here and this application does not impose any restrictions on this.

In addition, it should be noted that, in some embodiments, the processor 110 may include one or more processing units. Elements, for example: the processor 110 may include an application processor (AP), a modem processor, a graphics processor (GPU), an image signal processor (ISP), a controller, a memory, a video codec, a digital signal processor (DSP), a baseband processor, and/or a neural-network processing unit (NPU), etc.

It is understandable that, in a specific implementation, different processing units may be independent periods or integrated into one or more processors.

In addition, in some embodiments, the controller may be the nerve center and command center of the terminal device 100. The controller may generate an operation control signal according to the instruction operation code and the timing signal to complete the control of fetching and executing instructions.

In addition, the memory in the processor 110 is mainly used to store instructions and data. In some embodiments, the memory in the processor 110 is a cache memory.

In addition, the USB interface 130 shown in Figure 3 is an interface that complies with USB standard specifications, and may specifically be a Mini USB interface, a Micro USB interface, a USB Type C interface, etc.

The charging management module 140 is used to receive charging input from the charger. In addition, the power management module 141 shown in FIG3 is used to connect the battery 142, the charging management module 140 and the processor 110. The power management module 141 receives input from the battery 142 and/or the charging management module 140, and supplies power to the processor 110, the internal memory 121, the external memory, the display screen 194, the camera 193, and the wireless communication module 160. The wireless communication function of the terminal device 100 can be implemented through the antenna 1, the antenna 2, the mobile communication module 150, the wireless communication module 160, the modem processor and the baseband processor.

In addition, the terminal device 100 shown in FIG3 implements a display function through a GPU, a display screen 194, and an application processor. The GPU is a microprocessor for image processing, connecting the display screen 194 and the application processor. The GPU is used to perform mathematical and geometric calculations for graphics rendering. The processor 110 may include one or more GPUs that execute program instructions to generate or change display information.

The display screen 194 is specifically used to display images, videos, etc. The display screen 194 includes a display panel. In some embodiments, the terminal device 100 may include 1 or N display screens 194, where N is a positive integer greater than 1.

In addition, the terminal device 100 can realize the shooting function through ISP, camera 193, video codec, GPU, display screen 194 and application processor.

The camera 193 is used to capture static images or videos. In some embodiments, the terminal device 100 may include 1 or N cameras 193, where N is a positive integer greater than 1.

In addition, FIG. 3 shows that the external memory interface 120 can be used to connect an external memory card, such as a Micro SD card, to expand the storage capacity of the terminal device 100. The external memory card communicates with the processor 110 through the external memory interface 120 to implement a data storage function. For example, files such as music and videos are stored in the external memory card.

3 shows that the internal memory 121 can be used to store computer executable program codes, which include instructions. The processor 110 executes various functional applications and data processing of the terminal device 100 by running the instructions stored in the internal memory 121.

Specifically, the relevant instructions for implementing the network fallback method provided in each embodiment of the present application are pre-stored in the internal memory 121, and the processor 110 executes the instructions stored in the internal memory 121, thereby enabling the terminal device 100 to execute the network fallback method provided in each embodiment of the present application.

In addition, FIG. 3 shows that the motor 191 may be, for example, a vibration motor; and the indicator 192 may be an indicator light.

The SIM card interface 195 is used to connect a SIM card or a USIM card. The SIM card can be connected to or disconnected from the terminal device 100 by inserting the SIM card interface 195 or pulling the SIM card interface 195 out. The terminal device 100 can support 1 or N (N is an integer greater than 1) SIM card interfaces 195. That is, multiple SIM cards or USIM cards can be inserted into the terminal.

The hardware structure of the terminal device 100 is introduced here. It should be understood that the terminal device 100 shown in FIG3 is only an example. In a specific implementation, the terminal device 100 may have more or fewer components than those shown in the figure, may combine two or more components, or may have different component configurations. The various components shown in FIG3 may be implemented in hardware, software, or a combination of hardware and software including one or more signal processing and/or application-specific integrated circuits.

Taking the terminal device with the hardware structure shown in FIG. 3 as an example, the process of implementing the network fallback method provided in the present application by the terminal device is specifically described for the communication environment shown in FIG. 1a to FIG. 1d.

It should be noted that the implementation of the call service needs to be based on the processing implementation of the Modem protocol stack. Therefore, when implementing the network fallback method provided in each embodiment of the present application, the strategy and processing logic followed by the terminal device can be set in the form of a control point in the Modem protocol stack. That is, the network fallback method provided in each of the following embodiments, the operations performed by the terminal device, such as the called party UE, are all completed in the Modem protocol stack.

Referring to FIG. 4 , the network fallback method provided in the embodiment of the present application specifically includes:

S101, when the first network cannot perform a call service, fall back from the first network to the second network based on a fallback mechanism.

Specifically, the second network to which the fallback mechanism falls back is a network that supports call services. From the description of the above communication scenario, it can be seen that in one implementation, the first network is, for example, the 5G SA network mentioned above, and the second network is, for example, the 4G LTE network mentioned above, that is, the network types of the first network and the second network are different.

In addition, from the above description, it can be seen that when the first network is a 5G SA network and the second network is a 4G LTE network, the fallback mechanism followed when falling back from the 5G SA network to the 4G LTE network is specifically the EPSFB mechanism mentioned above.

In addition, it should be noted that regarding the above-mentioned fallback from the first network to the second network based on the fallback mechanism, in actual applications, the specific second network to fall back to can be determined by the called party UE by performing a measurement operation to determine all currently accessible second networks, and the reference information of each determined second network, such as the transmit power, signal strength (level strength, quality embodiment), etc., the called party UE's own transmit power, signal strength (level strength, quality embodiment), etc., and the base station corresponding to each second network, such as the 4G base station B and 4G base station C mentioned above and the position relationship between the called party UE are sent in the form of measurement results to the base station corresponding to the first network, such as the 5G base station mentioned above, and the 5G base station determines the actual fallback to based on this information. The second network.

Exemplarily, in some implementations, the second network to fall back to can be determined based on the location relationship, for example, the 4G LTE network corresponding to the 4G base station closest to the called party UE is determined as the second network to fall back to.

Exemplarily, in other implementations, the second network to fall back to can be determined based on the transmission power. For example, the 4G LTE network corresponding to a 4G base station that matches the transmission power of the called party UE (the same as, or within the range corresponding to the transmission power of the called party UE) is determined as the second network to fall back to.

Exemplarily, in other implementations, the second network to fall back to can be determined based on signal strength, for example, the 4G LTE network corresponding to the 4G base station with the best signal strength can be determined as the second network to fall back to.

Exemplarily, in other implementations, the second network to fall back to can be determined based on a comprehensive consideration of the three parameters mentioned above. For example, the 4G LTE network corresponding to the 4G base station closest to the called party UE, which matches the transmission power of the called party UE and has the best signal strength, is determined as the second network to fall back to.

It should be understood that the above description is merely an example listed for a better understanding of the technical solution of this embodiment, and is not intended to be the sole limitation to this embodiment.

Accordingly, after determining the second network that actually needs to fall back, the 5G base station will send a switching command to the called party UE, such as the "mobilityFromNRCommand:targetRAT-Type:eutra" mentioned above, and indicate the network type of the second network to be switched to and the specific information of the second network in the switching command.

Correspondingly, after the called party UE receives the switching command, it will disconnect the wireless link with the 5G base station in response to the switching command, establish a wireless link with the 4G base station corresponding to the determined second network, and then access the second network.

For the specific process of falling back from the 5G SA network to the 4G LTE network based on the EPSFB mechanism, please refer to the corresponding communication protocol and will not be repeated here.

S102: Send a first tracking area update TAU request to the core network through the second network.

Regarding the specific implementation method of the called party UE sending the first TAU request to the core network through the second network after completing the fallback from the first network to the second network according to the switching command, please refer to the corresponding communication protocol and will not be repeated here.

S103: Before receiving a first TAU response sent by the core network through the second network, maintain the current corresponding network.

It is understandable that since the called party UE falls back from the first network to the second network after responding to the switching command, and sends the first TAU request to the core network through the second network, the above-mentioned maintaining the current corresponding network specifically controls the called party UE to stay in the second network, that is, not switching to other networks, so that the first TAU response made by the core network for the first TAU request can be sent to the called party UE through the network that sent the first TAU request, that is, the second network.

Regarding the implementation method of maintaining the current corresponding network before receiving the first TAU response sent by the core network through the second network, it can be achieved by placing one or more of the following strategies in the control point in the Modem protocol stack corresponding to the called party UE.

Strategy 1: Before receiving the first TAU response sent by the core network through the second network, the called party UE is inhibited from performing the measurement operation, that is, before receiving the first TAU response sent by the core network through the second network, the called party UE is inhibited from performing the measurement operation. The UE of the other party suspends the measurement and reporting operation.

Therefore, the called party UE falls back from the first network to the second network based on EPSFB, and after sending the first TAU request, before receiving the first TAU response to the first TAU request, the called party UE is suppressed from performing measurement operations, so that a 4G LTE network with better transmission power and signal strength than the currently connected 4G LTE network will not be detected, thereby ensuring that the 4G LTE network accessed by the called party UE will not change before receiving the first TAU response, and further ensuring that the first TAU response corresponding to the first TAU request sent through the 4G LTE network is received through the currently connected 4G LTE network. In this way, the success of EPSFB can be guaranteed as much as possible, thereby ensuring the success rate of the call service and meeting the user's call needs.

In addition, it should be noted that in order to ensure the quality of call services, after receiving the first TAU response sent by the core network through the second network, the suppression of the measurement and reporting operation can be released, so that the called party UE can perform the measurement and reporting operation in real time or according to the set period, and obtain measurement results including the above-listed contents.

Accordingly, after obtaining the measurement results including the above-listed contents, the called party UE can report the measurement results to the second network, such as the base station corresponding to the second network, and the base station corresponding to the second network determines a network that is more suitable than the second network, such as a network with better signal strength, a transmission power that is more matched with the called party UE, a network that is closer to the called party UE, and more abundant network bandwidth resources, based on the contents in the received measurement report, and then sends a network switching instruction carrying the determined network to be switched to to the called party UE, so that the called party UE can respond to the network switching instruction and re-determine the network after switching from the second network.

For ease of explanation, the relevant information of multiple networks carried in the measurement report is taken as an example of the fourth network mentioned above, and the network type of the fourth network is the same as that of the second network, such as both are 4G LTE networks.

Accordingly, the new 4G LTE network that needs to be switched to is finally screened out from the measurement report by the 4G base station corresponding to the second network. This is a network in the fourth network that meets the set requirements. For ease of distinction, it can be represented by the fifth network as described above.

Therefore, after receiving the first TAU response through the second network that falls back, the suppression of the called party UE is released, that is, the UE can perform the measurement operation in real time or according to the set period or trigger condition, and report the measurement result obtained by the measurement operation to the second network. In this way, when there is a more suitable terminal device in the measurement result, it is possible to switch from the second network to the new network, thereby ensuring the success rate of EPSFB, the quality of the call corresponding to the call service, and the user experience.

In addition, for the specific implementation process of measurement operations, generating measurement results, and reporting measurement results, please refer to the relevant documents and communication protocols of the "LTE MeasurementReport message", which will not be repeated here.

Strategy 2: before receiving the first TAU response sent by the core network through the second network, when the currently accessed network, such as the second network, has an abnormality such as RLF, reestablish the source network, that is, the second network.

Exemplarily, in some implementations, before receiving the first TAU response sent by the core network through the second network, if the measurement and reporting operation has been suspended, during the process of suspending the measurement and reporting operation, if the second network If the network experiences RLF, network anomalies, insufficient network resources, unstable signals, etc., the user will also reconnect to the second network.

Exemplarily, in some other implementations, before receiving the first TAU response sent by the core network through the second network, if the measurement and reporting operation is not suspended, when an abnormality such as RLF occurs in the second network, strategy 2 can also be followed to re-access the second network.

Therefore, when an abnormality such as RLF occurs in the wireless link between the wireless link and the second network, the source network, that is, the second network that sends the first TAU request, is rebuilt, thereby ensuring that the first TAU response to the first TAU request made by the core network can still be sent to the called party UE through the second network, thereby ensuring the success rate of EPSFB and the success rate of the call service.

In addition, it should be noted that, in actual applications, when anomalies such as RLF occur in the second network, before re-accessing the second network, it can be determined whether the second network meets the re-access conditions.

Exemplarily, in some implementations, it can be determined whether the reference signal receiving power (RSRP) of the second network meets a set reference signal receiving power threshold.

Among them, RSRP is a key parameter that can represent the strength of wireless signals in 4G LTE networks and one of the physical layer measurement requirements. It is the average value of the signal power received on all REs (resource elements) that carry the reference signal within a symbol. Therefore, by judging RSRP, it is possible to determine whether the signal strength and other information of the second network meet the requirements.

Accordingly, when the RSRP of the second network meets the set reference signal received power threshold, the second network is re-accessed, otherwise other networks of the same type as the second network are accessed, which are represented by the sixth network mentioned above for ease of distinction.

It is understandable that the method for determining the sixth network may be the same as the method for determining the fifth network mentioned above, and will not be described in detail here.

In addition, it should be understood that, in some implementations, the sixth network may also be one of the fourth networks mentioned above, which may be a network provided by the same 4G base station as the fifth network. That is, the third network, fourth network, fifth network, and sixth network appearing in this application are to distinguish from the second network, indicating that the network switched from the second network is not the second network, and the third network, fourth network, fifth network, and sixth network may be the same network, that is, a 4G LTE network provided by the same 4G base station corresponding to the same service cell.

Exemplarily, in other implementations, it can be determined whether the reference signal reception quality (RSRQ) of the second network meets a set reference signal reception quality threshold.

Among them, RSRQ is used to identify the reference signal reception quality of the 4G LTE network. This metric is mainly used to sort the candidate cells (4G base stations) corresponding to different 4G LTE networks according to the signal quality, and can be used as an input for handover and cell reselection decisions. Therefore, by judging RSRQ, it can also be determined whether it is necessary to re-access the second network.

Correspondingly, when the RSRQ of the second network meets the set reference signal reception quality threshold, re-access the second network, otherwise access the sixth network representation.

Exemplarily, in some other implementations, it can be determined simultaneously whether the RSRP of the second network meets the set reference signal received power threshold, and whether the RSRQ of the second network meets the set reference signal received quality threshold.

Correspondingly, when the RSRP of the second network meets the set reference signal received power threshold and the RSRQ of the second network meets the set reference signal received quality threshold, re-access the second network, otherwise access the sixth network representation.

Therefore, before rebuilding to the source network, such as the second network mentioned above, it is determined whether the source network meets the reconstruction conditions through reference information such as RSRP and/or RSRQ of the source network. The source network is rebuilt only when the reconstruction conditions are met, such as when the set threshold is met, otherwise it is switched to the sixth network, thereby avoiding the situation where the reconstructed source network still has RLF anomalies, which leads to the situation that the first TAU response cannot be received within the random access response duration.

Further, after accessing the sixth network, in order to avoid the problem in the scenario described in FIG. 2 , the called party UE may start a timer or a counter. This embodiment takes a timer as an example.

Accordingly, after starting the timer, within the timing duration corresponding to the timer, if it is determined that the first TAU response sent by the core network through the sixth network is received, the timer is turned off and the call service is executed on the sixth network; otherwise, after receiving the timing duration corresponding to the timer, the TAU request is resent to the core network through the sixth network. For ease of distinction, it can be represented by the third TAU request described above.

Accordingly, after the called party UE sends the third TAU request to the core network through the sixth network, in order to avoid network switching again, the called party UE can be controlled to remain in the sixth network according to the policy followed in the second network.

Correspondingly, after receiving the third TAU response sent by the core network through the sixth network in response to the third request, the called party UE can execute the call service in the sixth network.

Therefore, in the case where the source network cannot be rebuilt, after switching to the sixth network, the sixth network resends the TAU request after receiving the timing duration corresponding to the timer, so that the core network can send the TAU response made to the newly sent TAU request to the called party UE through the third network, so that when the called party UE cannot rebuild the source network, it can still ensure that the triggered TAU process can be successfully completed after EPSFB, thereby ensuring the success rate of EPSFB, and then ensuring the success rate of the call service. Regarding the implementation process of resending the TAU request within the random access response duration corresponding to the INVITE request using a timer, please refer to the following, which will not be repeated here.

Strategy 3: Before receiving the first TAU response sent by the core network through the second network, do not respond when receiving the network switching instruction sent by the second network. That is, suspend responding to the network switching instruction sent by the second network and keep the current corresponding network, that is, control the called party UE to remain in the second network.

Therefore, before waiting for the first TAU response sent by the currently connected second network, the called party UE is set not to respond to the network switching instruction sent by the second network, or to delay responding to the network switching instruction, so as to avoid changes in the network accessed by the called party UE before receiving the first TAU response.

Further, if after receiving the first TAU response sent by the core network through the second network, the previously received network switching instruction has not timed out, then in response to the network switching instruction, the network can be switched from the second network to the network indicated by the network switching instruction.

It is not difficult to find from the above description that the network fallback method provided in this embodiment, after falling back from the first network to the second network and triggering the first TAU request, sets the terminal device to always stay in the second network before receiving the first TAU response sent by the core network through the second network. In this way, without modifying the communication protocol followed by the core network or the communication protocol followed by the base station side, by adjusting the processing logic of the terminal device, the success of EPSFB can be guaranteed as much as possible, thereby ensuring the success rate of the call service and meeting the user's call needs.

In addition, it is understandable that after receiving the first TAU response sent by the core network through the second network, it indicates that the network fallback implemented by E based on the EPSFB mechanism has been successful, and the second network that falls back to can support call services. Therefore, after receiving the first TAU response sent by the core network through the second network, the call service can be executed in the second network. For the specific implementation process of the call service, please refer to the corresponding communication protocol, which will not be repeated here.

Therefore, after sending the first TAU request through the second network, the called party UE is kept in the second network through any of the above methods, so that the core network can send the first TAU response made for the first TAU request to the called party UE through the second network. After receiving the TAU response, the called party UE can execute the subsequent process of the call service on the second network while still connected to the second network, thereby ensuring that after falling back from the first network to the second network based on EPSFB, the call service can be executed on the second network, thereby meeting the user's call needs.

In order to better understand the interaction between the called party UE, the 5G base station, the 4G base station on the network side, and the core network and the IMS network when implementing the network fallback method provided in this application based on the above three strategies, the following is explained in conjunction with Figures 5 and 6.

5 , there is shown an exemplary timing diagram of using the above strategy 1 to control the called party UE to maintain the currently accessed network, thereby completing network fallback and executing the call service.

As shown in Figure 5, this embodiment still takes the INVITE request sent by the IMS network as shown in Figure 2 as an example, and the subsequent processing scenario. The processing flow before the called party UE sends the first TAU request to the core network through the 4G base station B that falls back to can refer to the description of Figure 2 above, which will not be repeated here.

In addition, it should be noted that, in order to facilitate the subsequent description, the first TAU request is represented by TAU REQ_1, and the first TAU response made by the core network to TAU REQ_1 is represented by TAU Accept_1.

Continuing to refer to Figure 5, illustratively, after the called party UE sends TAU REQ_1 to the core network through the 4G base station B, the control point in the modem protocol stack corresponding to the called party UE suppresses the measurement operation based on the above strategy 1 before receiving TAU Accept_1, thereby preventing the called party UE from switching the 4G base station.

Continuing to refer to FIG. 5, illustratively, during the period of suspending the measurement and reporting operation, if the called party UE receives TAU Accept_1 sent by the core network through 4G base station B, the control point in the corresponding Modem protocol stack releases the suppression based on the above strategy 1, so that the called party can perform the measurement and reporting operation in real time or according to the set period, and then obtain the measurement result. The implementation details of the called party UE performing the measurement and reporting operation, obtaining the measurement result, interacting with the 4G base station B, and the subsequent 4G base station B determining the 4G LTE network that can be switched according to the measurement result, such as the 4G LTE network provided by the 4G base station C, and switching from the 4G base station B to the 4G base station C can be found in the above text and will not be repeated here.

Continuing to refer to FIG. 5, illustratively, after receiving TAU Accept_1, if the called party UE continues to receive the information in the Update process mentioned above within the random access response duration corresponding to the INVITE request, and Activate dedicated EB request, then the multimedia session can be established, and then the subsequent process of the call service can be executed. For the information in the Update process, the source of each Activate dedicated EB request, and the information and function it carries, please refer to the above, and will not be repeated here.

In addition, it should be noted that in the scenario shown in Figure 5, the order of releasing the suppression operation and receiving the information in the Update process, as well as the Activate dedicated EB request can be ignored.

This is the end of the introduction to the implementation process of keeping the called party UE in the currently accessed network, such as the second network mentioned above, or the 4G LTE network provided by the 4G base station B, before waiting for the core network to send a TAU response through the 4G LTE network that sent the TAU request. It should be understood that the above description is only an example listed for a better understanding of the technical solution of this embodiment, and is not the only limitation to this embodiment.

6 , there is shown an exemplary timing diagram of using the above strategy 2 to control the called party UE to maintain the currently accessed network, thereby completing network fallback and executing the call service.

As shown in Figure 6, this embodiment still takes the INVITE request sent by the IMS network as shown in Figure 2 as an example, and the subsequent processing scenario. The processing flow before the called party UE sends the first TAU request to the core network through the 4G base station B that falls back to can refer to the description of Figure 2 above, which will not be repeated here.

Continuing to refer to Figure 6, illustratively, after the called party UE sends TAU REQ_1 to the core network through 4G base station B, the control point in the Modem protocol stack corresponding to the called party UE is based on the above-mentioned strategy 2. Before receiving TAU Accept_1, if it is detected that the wireless link between the called party UE and 4G base station B fails, or the transmission power, signal strength, etc. of the 4G base station do not meet the needs of the called party UE, or the 4G LTE network resources provided by 4G base station B are insufficient, etc. (this embodiment takes the occurrence of RLF abnormality as an example), when it is determined that the RSRQ and/or RSRP of the 4G LTE network provided by 4G base station B meets the corresponding threshold, it re-accesses to 4G base station B, thereby ensuring that the re-accessed 4G LTE network is still provided by 4G base station B, so that the TAU Accept_1 made by the core network can be sent to the called party UE through the 4G LTE network provided by 4G base station B that sent TAU REQ_1.

Continuing to refer to FIG. 6, illustratively, after the called party UE reestablishes the source network, i.e. re-accesses 4G base station B, if it receives TAU Accept_1 sent by the core network through 4G base station B, and if it continues to receive the information in the Update process mentioned above and the Activate dedicated EB request within the random access response duration corresponding to the INVITE request, then the multimedia session can be established, and then the subsequent process of the call service can be executed. The information in the Update process, the source of the Activate dedicated EB request in each item, and the information and function it carries can be seen above, and will not be repeated here.

In addition, it should be noted that in actual applications, Strategy 2 can be used alone or in combination with Strategy 1, that is, on the basis of the process shown in Figure 6, the process shown in Figure 5 can be integrated. For example, during the period when the called party is controlled to suspend the execution of the measurement and reporting operation or before suppressing the execution of the measurement and reporting operation, if the above-mentioned RLF abnormality occurs, re-access 4G base station B according to the process shown in Figure 6.

Accordingly, after re-accessing the 4G base station B, if the process of suppressing the execution of the measurement and reporting operation has been turned on, the suppression can be released after receiving TAU Accept_1 as shown in Figure 5; if the process of suppressing the execution of the measurement and reporting operation is not turned on, the process can be turned on, and then after receiving TAU Accept_1, the suppression can be released as shown in Figure 5.

This is the end of the introduction to the implementation process of abnormally reconstructing the source network to keep the called party UE in the currently accessed network, such as the second network mentioned above, or the 4G LTE network provided by the 4G base station B, before waiting for the core network to send a TAU response through the 4G LTE network that sent the TAU request. It should be understood that the above description is only an example listed for a better understanding of the technical solution of this embodiment, and is not the only limitation to this embodiment.

7 , there is shown an exemplary timing diagram of using the above strategy 3 to control the called party UE to maintain the currently accessed network, thereby completing network fallback and executing the call service.

As shown in Figure 7, this embodiment still takes the INVITE request sent by the IMS network as shown in Figure 2 as an example, and the subsequent processing scenario. The processing flow before the called party UE sends the first TAU request to the core network through the 4G base station B that falls back to can refer to the description of Figure 2 above, which will not be repeated here.

Continuing to refer to Figure 7, illustratively, after the called party UE sends TAU REQ_1 to the core network through 4G base station B, the control point in the Modem protocol stack corresponding to the called party UE, based on the above strategy 3, does not respond to the network switching instruction before receiving TAU Accept_1 if it receives a network switching instruction from 4G base station B to switch to 4G base station C. This ensures that the called party UE remains on the 4G LTE network provided by 4G base station B, so that the TAU Accept_1 made by the core network can be sent to the called party UE through the 4G LTE network provided by 4G base station B that sends TAU REQ_1.

Continuing to refer to Figure 7, exemplarily, when the called party UE does not respond to the network switching instruction and still remains on the 4G LTE network provided by 4G base station B, if the previously received network switching instruction to switch to 4G base station C has not timed out, it can respond to the network switching instruction and switch from 4G base station B to 4G base station C.

Continuing to refer to FIG. 7, illustratively, after receiving TAU Accept_1, if the called party UE receives TAU Accept_1 sent by the core network through 4G base station B, and if it continues to receive the information in the Update process mentioned above and the Activate dedicated EB request within the random access response duration corresponding to the INVITE request, then the multimedia session can be established, and then the subsequent process of the call service can be executed. The information in the Update process, the source of the Activate dedicated EB request in each item, and the information and function it carries can be seen above, and will not be repeated here.

In addition, it should be noted that in the scenario shown in Figure 7, the operation in response to the previously received network switching instruction and the information received in the Update process, as well as the Activate dedicated EB request may not be sequenced.

In addition, it should be noted that in actual applications, Strategy 3 can be used alone or in combination with Strategy 1 and/or Strategy 2, that is, on the basis of the process shown in Figure 7, it can be integrated into the process shown in Figure 5 and/or Figure 6. The specific coordination logic is not limited in this embodiment and will not be repeated here.

This is the end of the introduction of the implementation process of suspending or not responding to the network switching instruction issued by the network side (the currently accessed 4G base station) before waiting for the core network to send a TAU response through the 4G LTE network that sent the TAU request, so as to keep the called party UE in the currently accessed network, such as the second network mentioned above, or the 4G LTE network provided by the 4G base station B. It should be understood that the above description is only an example listed for a better understanding of the technical solution of this embodiment, and is not the only limitation to this embodiment.

In addition, it should be noted that, in actual applications, the above three implementation methods of keeping the called party UE in the currently accessed network can be arbitrarily combined according to actual business needs, that is, one or several of them are selected as the control point in the Modem protocol stack to control the called party UE to maintain the currently accessed network. The strategy followed, the specific combination method and the order of adjustment of the processing logic will not be repeated here, and this application does not limit this.

Referring to FIG8 , the network fallback method provided in the embodiment of the present application specifically includes:

S201, when the first network cannot perform a call service, fall back from the first network to the second network based on a fallback mechanism.

For example, this embodiment still takes the first network as a 5G SA network, the second network as a 4G LTE network, and the fallback mechanism followed as the EPSFB mechanism as an example. For specific details, please refer to the above and will not be repeated here.

S202: Send a first tracking area update TAU request to the core network through the second network.

It is not difficult to find that step S202 in this implementation is substantially the same as step S102 in the above embodiment. The specific implementation details can be found above and will not be repeated here.

S203: Before receiving a first TAU response sent by the core network through the second network, switching from the second network to the third network.

It is understandable that in some implementations, the third network can be, for example, a 4G LTE network that meets preset conditions and is determined by the 4G base station corresponding to the second network based on the measurement results obtained by the called party UE through the reporting operation, that is, the network type of the third network is the same as that of the second network. When the second network is a 4G LTE network, the third network is also a 4G LTE network, but the service cell/4G base station provided by the third network is not passed. For example, the third network can be provided by the 4G base station C mentioned in this application.

In addition, it should be noted that the third network in this embodiment is similar to the fourth network, the fifth network and the sixth network mentioned above, mainly to distinguish it from the second network, indicating that the network switched from the second network is not the second network, and the third network, the fourth network, the fifth network and the sixth network can be the same network, that is, the 4G LTE network provided by the same 4G base station corresponding to the same service cell. For the determination method of the third network, please refer to the above, which will not be repeated here.

In addition, it should be noted that, taking into account that users may move when using terminal devices for call services, which may result in different base stations and core networks being accessed, the distribution maps of core networks provided by different manufacturers and the base stations corresponding to each core network can be pre-built into the terminal devices, so that the terminal devices can optimize network switching based on location according to the built-in maps of base stations corresponding to different core networks.

S204, start the timer.

It is understandable that in practical applications, this can also be achieved by means of a calculator. This embodiment takes a timer as an example.

S205: Whether a TAU response is received within the timing period.

Specifically, if received, step S208 is directly executed to close the timer and perform the call service in the switched third network; otherwise, step S206 is executed to further determine whether the timing time set for the timer is reached.

S206: Whether the timing time has been reached.

Specifically, if it is not reached, that is, the timer task has not ended, then continue to execute step S205; otherwise, execute step S207, resend the TAU request to the core network through the third network, and for the sake of distinction, it is called the third TAU request. Correspondingly, the TAU response made by the core network to the third TAU request is called Third TAU response.

It can be understood that the random access process is the process in which the terminal device requests access to the system, receives the system's response and allocates an access channel. General data transmission must be preceded by successful random access. In 4G LTE, each service corresponds to a random access response duration. If no response is received within the response duration, the service fails.

Exemplarily, in some implementations, the timing duration set for the timer is N times (N is an integer greater than 0) the time taken to send a TAU request and receive a TAU response when there is no network switching, network anomaly, etc.

From the above description, we can know that the random access response time of INVITE request is usually 6 seconds, and the normal TAU process takes about 0.3 seconds. Therefore, in order to ensure that within the random access response time, even if a network switch occurs, the TAU request can be re-initiated through the newly switched network and the TAU response can be received within the random access response time, N can be set to 3.

It should be understood that the above description is only an example listed for a better understanding of the technical solution of this embodiment, and is not the only limitation to this embodiment. In practical applications, the terminal device may also multiply the normal time consumption of the TAU process under different networks learned by itself within a set historical time period by a specific N.

In addition, the value of N may be adjusted according to the congestion level of uplink and downlink data transmission, that is, to stagger the congestion.

S207: Send a second TAU request to the core network through the third network, and after receiving a second TAU response sent by the core network through the third network, execute a call service in the third network.

Exemplarily, in some implementations, when switching from the second network to the third network and sending a second TAU request to the core network through the third network, while waiting for the second TAU request to be sent by the core network through the third network, any one or more of the above-mentioned strategies 1, 2 and 3 can also be adopted to control the called party UE to stay in the third network. The specific implementation method can be found above and will not be repeated here.

S208, close the timer and execute the call service in the third network.

Therefore, the network fallback method provided in this embodiment, before receiving the first TAU response, when the 4G LTE network to which the terminal device accesses changes, starts a timer/calculator to count, and when the set time is reached, if the first TAU response is still not received, a second TAU request is re-initiated to the core network through the switched 4G LTE network, so that the terminal device can receive the second TAU response issued by the core network through the switched 4G LTE network, thereby ensuring the success of EPSFB and the success of the call service.

In order to better understand the interaction between the called party UE, the 5G base station, 4G base station on the network side, and the core network and IMS network when implementing the network fallback method provided in this application based on the above-mentioned timer, the following is an explanation in conjunction with Figure 9.

Referring to FIG. 9 , there is shown an exemplary timing diagram of setting a timing duration through a timer, re-initiating a TAU request from the newly switched network after no TAU response is received within a timeout, and then completing network fallback and executing a call service.

As shown in Figure 9, this embodiment still takes the INVITE request sent by the IMS network as shown in Figure 2 as an example, and the subsequent processing scenario. The called party UE sends the first TAU to the core network through the 4G base station B to which it falls back. The processing flow before the request can be found in the description of FIG. 2 above, which will not be repeated here.

In addition, it should be noted that, for the convenience of subsequent description, the first TAU request is represented by TAU REQ_1, and the first TAU response made by the core network to TAU REQ_1 is represented by TAU Accept_1. The second TAU request is represented by TAU REQ_2, and the second TAU response made by the core network to TAU REQ_2 is represented by TAU Accept_2.

Continuing to refer to FIG. 9 , illustratively, after the called party UE sends TAU REQ_1 to the core network through 4G base station B, if the above-mentioned strategy 1 is not adopted to suppress the execution of the measurement and reporting operation, the called party UE will perform the measurement and reporting operation in real time according to the set period, and report the measurement results obtained through the measurement and reporting operation to 4G base station B. 4G base station B will select a new base station that meets the current scenario based on the measurement results. For example, if it is determined that the new base station to be switched to is 4G base station C, the called party UE will be issued a network switching instruction to instruct it to switch to the 4G LTE network provided by 4G base station C. Accordingly, the called party UE will access 4G base station C in response to the instruction, thereby completing the network switching.

Regarding the implementation details of the called party UE performing measurement operations, obtaining measurement results, interacting with 4G base station B, and subsequent 4G base station B determining the 4G LTE network that can be switched based on the measurement results, such as the 4G LTE network provided by 4G base station C, and switching from 4G base station B to 4G base station C, please refer to the above and will not be repeated here.

Continuing to refer to Figure 9, illustratively, when the called party UE switches from 4G base station B to 4G base station C, the control point in the corresponding Modem protocol stack will start a timer or calculator (this embodiment takes the timer as an example), and then according to the processing method of the above steps S205 and S206, it is determined whether TAU Accept_1 is received within the timing duration and whether the timing time is reached.

Continuing to refer to FIG. 9, for example, if TAU Accept_1 is received within the timing duration, the timer is turned off, and the information in the Update process mentioned above and the Activate dedicated EB request are continued to be received within the random access response duration corresponding to the INVITE request, then the multimedia session can be established, and then the subsequent process of the call service can be executed. The information in the Update process, the source of the Activate dedicated EB request in each item, and the information and function it carries can be seen above, and will not be repeated here.

Continuing to refer to Figure 9, illustratively, if TAU Accept_1 is not received within the timing period, the called party UE regenerates a TAU request, such as TAU REQ_2, and sends TAU REQ_2 to the core network through 4G base station C, waiting for TAU Accept_2 sent by the core network through 4G base station C.

Continuing to refer to FIG. 9, illustratively, after receiving TAU Accept_2, if the called party UE continues to receive the information in the Update process mentioned above and the Activate dedicated EB request within the random access response duration corresponding to the INVITE request, the multimedia session can be established, and then the subsequent process of the call service can be executed. The information in the Update process, the source of the Activate dedicated EB request in each item, and the information and function it carries can be seen above, and will not be repeated here.

This is the introduction to the implementation process of the called party UE resending the TAU request to the core network through the switched 4G base station when the 4G base station connected to the called party UE changes before the core network sends the TAU response through the 4G LTE network that sent the TAU request, and the TAU response is not received within the timing period. It should be understood that the above switching between 4G base station B and 4G base station C is only an example listed for a better understanding of the technical solution of this embodiment, and is not the only limitation to this embodiment.

In addition, it should be noted that in actual applications, the strategy of controlling the called party UE to maintain the currently accessed network given in the above embodiment and the timing after the network switching occurs can be changed according to actual business needs. If no TAU response is received within the time period, the called party UE resends the TAU request strategy to the core network through the switched 4G base station, and makes any combination to better ensure the success rate of EPSFB and thus ensure the success rate of the call service.

In addition, it is understood that in order to implement the above functions, the terminal device includes hardware and/or software modules corresponding to the execution of each function. In combination with the algorithm steps of each example described in the embodiments disclosed herein, 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. Those skilled in the art can use different methods to implement the described functions for each specific application in combination with the embodiments, but such implementation should not be considered to be beyond the scope of this application.

In addition, it should be noted that the network fallback method provided in the above embodiments implemented by the terminal device in the actual application scenario can also be executed by a chip system included in the terminal device, wherein the chip system may include a processor. The chip system can be coupled to the memory so that the chip system calls the computer program stored in the memory when it is running to implement the steps executed by the above terminal device. The processor in the chip system can be an application processor or a processor other than an application processor.

In addition, an embodiment of the present application also provides a computer-readable storage medium, which stores computer instructions. When the computer instructions are executed on a terminal device, the terminal device executes the above-mentioned related method steps to implement the network fallback method in the above-mentioned embodiment.

In addition, an embodiment of the present application also provides a computer program product. When the computer program product runs on a terminal device, the terminal device executes the above-mentioned related steps to implement the network fallback method in the above-mentioned embodiment.

In addition, an embodiment of the present application also provides a chip (which may also be a component or module), which may include one or more processing circuits and one or more transceiver pins; wherein the transceiver pins and the processing circuit communicate with each other through an internal connection path, and the processing circuit executes the above-mentioned related method steps to implement the network fallback method in the above-mentioned embodiment, so as to control the receiving pin to receive the signal, so as to control the sending pin to send the signal.

In addition, it can be seen from the above description that the terminal device, computer-readable storage medium, computer program product or chip provided in the embodiments of the present application are all used to execute the corresponding methods provided above. Therefore, the beneficial effects that can be achieved can refer to the beneficial effects in the corresponding methods provided above, and will not be repeated here.

As described above, the above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

A network fallback method, characterized in that it is applied to a terminal device to be used for executing a call service in a first network, and the method comprises:

When the first network cannot perform the call service, fall back from the first network to a second network based on a fallback mechanism, and the network types of the first network and the second network are different;

Sending a first tracking area update TAU request to the core network through the second network;

Before receiving a first TAU response sent by the core network through the second network, the current corresponding network is maintained, where the first TAU response is made by the core network in response to the first TAU request.
The method according to claim 1, characterized in that before receiving the first TAU response sent by the core network through the second network, the method further comprises:

Switching from the second network to a third network, where the third network is of the same network type as the second network;

Start the timer;

Within the timing duration corresponding to the timer, after receiving the first TAU response sent by the core network through the third network, turning off the timer and executing the call service on the third network;

When the first TAU response sent by the core network through the third network is not received, after receiving the timing duration corresponding to the timer, sending a second TAU request to the core network through the third network;

After receiving a second TAU response sent by the core network through the third network, the call service is performed on the third network, where the second TAU response is made by the core network in response to the second TAU request.
The method according to claim 2 is characterized in that the timing duration corresponding to the timer is less than the random access response duration corresponding to the call service.
The method according to claim 3 is characterized in that the timing duration is N times the time consumed by the TAU process, and the time consumed by the TAU process refers to the time consumed from the terminal device sending the first TAU request to receiving the first TAU response, and N is an integer greater than 0.
The method according to claim 1, wherein before receiving the first TAU response sent by the core network through the second network, maintaining the current corresponding network comprises:

Before receiving a first TAU response sent by the core network through the second network, suspending the measurement and reporting operation.
The method according to claim 5, characterized in that the method further comprises:

After receiving the first TAU response sent by the core network through the second network, performing the measurement operation to obtain a measurement result, the measurement result including network information of all fourth networks that the terminal device can switch from the second network and the transmit power and signal strength of the terminal device, and the fourth network and the second network have the same network type;

Reporting the measurement result to the second network;

receiving a fifth network determined by the second network according to the measurement result, where the fifth network is a fourth network that meets set requirements and is screened out according to the transmit power and signal strength of the terminal device and network information of all fourth networks;

Switch from the second network to the fifth network.
The method according to claim 5, characterized in that the method further comprises:

Before receiving the first TAU response sent by the core network through the second network, during the process of suspending the measurement and reporting operation, when an abnormality occurs in the radio link with the second network, re-accessing the second network.
The method according to claim 7, characterized in that before re-accessing the second network, the method further comprises:

Determining whether a reference signal received power of the second network meets a set reference signal received power threshold, and/or whether a reference signal received quality of the second network meets a set reference signal received quality threshold;

When the reference signal received power of the second network meets the set reference signal received power threshold, and/or the reference signal received quality of the second network meets the set reference signal received quality threshold, performing the step of re-accessing the second network;

When the reference signal received power of the second network does not meet the set reference signal received power threshold, and/or the reference signal received quality of the second network does not meet the set reference signal received quality threshold, access the sixth network.
The method according to claim 8, characterized in that after accessing the sixth network, the method further comprises:

Start the timer;

Within the timing duration corresponding to the timer, after receiving the first TAU response sent by the core network through the sixth network, turning off the timer and executing the call service on the sixth network;

When the first TAU response sent by the core network through the sixth network is not received, after receiving the timing duration corresponding to the timer, sending a third TAU request to the core network through the sixth network;

After receiving a third TAU response sent by the core network through the sixth network, the call service is performed on the sixth network, wherein the third TAU response is made by the core network in response to the third TAU request.
The method according to claim 1, wherein before receiving the first TAU response sent by the core network through the second network, maintaining the current corresponding network comprises:

Before receiving the first TAU response sent by the core network through the second network, when receiving the network switching instruction sent by the second network, suspend responding to the network switching instruction and maintain the current corresponding network.
The method according to claim 10, characterized in that the method further comprises:

After receiving the first TAU response sent by the core network through the second network, in response to the network switching instruction, switching from the second network to the network indicated by the network switching instruction.
The method according to any one of claims 1 to 11, characterized in that the method further comprises:

After receiving the first TAU response sent by the core network through the second network, the call service is executed in the second network.
The method according to any one of claims 1 to 11 is characterized in that the first network is a 5G SA network and the second network is a 4G LTE network.
The method according to claim 13 is characterized in that the fallback mechanism is an Evolved Packet System Fallback EPSFB mechanism.
A terminal device, characterized in that the terminal device includes: a memory and a processor, the memory and the processor are coupled; the memory stores program instructions, and when the program instructions are executed by the processor, the terminal device executes the network fallback method as described in any one of claims 1 to 14.
A computer-readable storage medium, characterized in that it includes a computer program, and when the computer program is executed on a terminal device, the terminal device executes the network fallback method as described in any one of claims 1 to 14.
A network fallback method, characterized in that it is applied to a terminal device to be used for executing a call service in a first network, and the method comprises:

When the first network cannot perform the call service, fall back from the first network to a second network based on a fallback mechanism, and the network types of the first network and the second network are different;

Sending a first tracking area update TAU request to the core network through the second network;

Before receiving a first TAU response sent by the core network through the second network, maintaining the current corresponding network, wherein the first TAU response is made by the core network in response to the first TAU request;

Before receiving the first TAU response sent by the core network through the second network, the method further includes:

Switching from the second network to a third network, where the third network is of the same network type as the second network;

Start the timer;

Within the timing duration corresponding to the timer, after receiving the first TAU response sent by the core network through the third network, turning off the timer and executing the call service on the third network;

When the first TAU response sent by the core network through the third network is not received, after receiving the timing duration corresponding to the timer, sending a second TAU request to the core network through the third network;

After receiving a second TAU response sent by the core network through the third network, the call service is performed on the third network, where the second TAU response is made by the core network in response to the second TAU request.
The method according to claim 17 is characterized in that the timing duration corresponding to the timer is less than the random access response duration corresponding to the call service.
The method according to claim 18 is characterized in that the timing duration is N times the time consumed by the TAU process, and the time consumed by the TAU process refers to the time consumed from the terminal device sending the first TAU request to receiving the first TAU response, and N is an integer greater than 0.
The method according to claim 17, characterized in that before receiving the second TAU response sent by the core network through the third network, the method further comprises:

Before receiving the second TAU response sent by the core network through the third network, suspending the measurement and reporting operation.
The method according to claim 20, characterized in that the method further comprises:

After receiving the second TAU response sent by the core network through the third network, performing the measurement operation to obtain a measurement result, the measurement result including network information of all fourth networks that the terminal device can switch from the third network and the transmit power and signal strength of the terminal device, and the fourth network and the third network have the same network type;

Reporting the measurement result to the third network;

receiving a fifth network determined by the third network according to the measurement result, where the fifth network is a fourth network that meets set requirements and is screened out according to the transmit power and signal strength of the terminal device and network information of all fourth networks;

Switch from the third network to the fifth network.
The method according to claim 20, characterized in that the method further comprises:

Before receiving the second TAU response sent by the core network through the third network, during the process of suspending the measurement and reporting operation, when an abnormality occurs in the radio link with the third network, re-accessing the third network.
The method according to claim 22, characterized in that before re-accessing the third network, the method further comprises:

Determining whether a reference signal received power of the third network meets a set reference signal received power threshold, and/or whether a reference signal received quality of the third network meets a set reference signal received quality threshold;

When the reference signal received power of the third network meets the set reference signal received power threshold, and/or the reference signal received quality of the third network meets the set reference signal received quality threshold, performing the step of re-accessing the third network;

When the reference signal received power of the third network does not meet the set reference signal received power threshold, and/or the reference signal received quality of the third network does not meet the set reference signal received quality threshold, accessing the sixth network.
The method according to claim 23, characterized in that after accessing the sixth network, the method further comprises:

Start the timer;

Within the timing duration corresponding to the timer, after receiving the second TAU response sent by the core network through the sixth network, turning off the timer and executing the call service on the sixth network;

When the second TAU response sent by the core network through the sixth network is not received, after receiving the timing duration corresponding to the timer, sending a third TAU request to the core network through the sixth network;

After receiving a third TAU response sent by the core network through the sixth network, the call service is performed on the sixth network, wherein the third TAU response is made by the core network in response to the third TAU request.
The method according to claim 17, characterized in that before receiving the second TAU response sent by the core network through the third network, the method further comprises:

Before receiving the second TAU response sent by the core network through the third network, when receiving the network switching instruction sent by the third network, suspend responding to the network switching instruction and maintain the current corresponding network.
The method according to claim 25, characterized in that the method further comprises:

After receiving the second TAU response sent by the core network through the third network, in response to the network switching instruction, switching from the third network to the network indicated by the network switching instruction.
The method according to any one of claims 17 to 26, characterized in that the method further comprises:

After receiving the first TAU response sent by the core network through the second network, the call service is executed in the second network.
The method according to any one of claims 17 to 26 is characterized in that the first network is a 5G SA network and the second network is a 4G LTE network.
The method according to claim 28 is characterized in that the fallback mechanism is an evolved packet system fallback EPSFB mechanism.
A network fallback method, characterized in that it is applied to a terminal device to be used for executing a call service in a first network, and the method comprises:

When the first network cannot perform the call service, fall back from the first network to a second network based on a fallback mechanism, and the network types of the first network and the second network are different;

Sending a first tracking area update TAU request to the core network through the second network;

Before receiving a first TAU response sent by the core network through the second network, suspending the measurement and reporting operation, where the first TAU response is made by the core network in response to the first TAU request.
The method according to claim 30, characterized in that the method further comprises:

After receiving the first TAU response sent by the core network through the second network, performing the measurement operation to obtain a measurement result, the measurement result including network information of all fourth networks that the terminal device can switch from the second network and the transmit power and signal strength of the terminal device, and the fourth network and the second network have the same network type;

Reporting the measurement result to the second network;

receiving a fifth network determined by the second network according to the measurement result, where the fifth network is a fourth network that meets set requirements and is screened out according to the transmit power and signal strength of the terminal device and network information of all fourth networks;

Switch from the second network to the fifth network.
The method according to claim 30, characterized in that the method further comprises:

Before receiving the first TAU response sent by the core network through the second network, during the process of suspending the measurement and reporting operation, when an abnormality occurs in the radio link with the second network, re-accessing the second network.
The method according to claim 32, characterized in that before re-accessing the second network, the method further comprises:

Determining whether a reference signal received power of the second network meets a set reference signal received power threshold, and/or whether a reference signal received quality of the second network meets a set reference signal received quality threshold;

When the reference signal received power of the second network meets the set reference signal received power threshold, and/or the reference signal received quality of the second network meets the set reference signal received quality threshold, performing the step of re-accessing the second network;

When the reference signal received power of the second network does not meet the set reference signal received power threshold, and/or the reference signal received quality of the second network does not meet the set reference signal received quality threshold, access the sixth network.
The method according to claim 33, characterized in that after accessing the sixth network, the method further comprises:

Start the timer;

Within the timing duration corresponding to the timer, after receiving the first TAU response sent by the core network through the sixth network, turning off the timer and executing the call service on the sixth network;

When the first TAU response sent by the core network through the sixth network is not received, after receiving the timing duration corresponding to the timer, sending a third TAU request to the core network through the sixth network;

After receiving a third TAU response sent by the core network through the sixth network, the call service is performed on the sixth network, wherein the third TAU response is made by the core network in response to the third TAU request.
The method according to claim 30, characterized in that the method further comprises:

Before receiving the first TAU response sent by the core network through the second network, the measurement operation is suspended. When a network switching instruction sent by the second network is received, the response to the network switching instruction is suspended to maintain the current corresponding network.
The method according to claim 35, characterized in that the method further comprises:

After receiving the first TAU response sent by the core network through the second network, in response to the network switching instruction, switching from the second network to the network indicated by the network switching instruction.
The method according to any one of claims 30 to 36, characterized in that the method further comprises:

After receiving the first TAU response sent by the core network through the second network, the call service is executed in the second network.
The method according to any one of claims 30 to 36 is characterized in that the first network is a 5G SA network and the second network is a 4G LTE network.
The method according to claim 38 is characterized in that the fallback mechanism is an evolved packet system fallback EPSFB mechanism.