CN115297448B

CN115297448B - Network fallback method, equipment and storage medium

Info

Publication number: CN115297448B
Application number: CN202211172089.0A
Authority: CN
Inventors: 李海波; 薛超; 罗飞; 孟昭
Original assignee: Honor Device Co Ltd
Current assignee: Honor Device Co Ltd
Priority date: 2022-09-26
Filing date: 2022-09-26
Publication date: 2023-01-31
Anticipated expiration: 2042-09-26
Also published as: CN115297448A; CN117768856A; WO2024066150A1

Abstract

The application provides a network fallback method, equipment and a storage medium. After the method falls back from the first network to the second network and further triggers the TAU request, the terminal equipment is set to always stay in the second network before receiving the TAU response sent by the core network through the second network, so that the success of the EPSFB can be ensured as far as possible by adjusting the processing logic of the terminal equipment under the condition of not modifying the communication protocol followed by the core network and not modifying the communication protocol followed by the base station corresponding to the network side, thereby ensuring the success rate of the call service and meeting the call requirement of a user.

Description

Network fallback method, equipment and storage medium

Technical Field

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

Background

Currently, some Mobile Communication networks cannot directly perform call services, such as independent networking (standard, SA) of the fifth Generation Mobile Communication technology (the 5th Generation Mobile Communication technology,5 g). For a network that cannot make a Voice call, the terminal device may employ a fallback mechanism, such as an Evolved Packet System Fallback (EPSFB) mechanism, to Fall Back to a network that can make a Voice call, such as the fourth Generation Mobile Communication technology (4G), and then use a Voice over Long-Term Evolution (Voice over Long-Term Evolution) technology in the 4G network to perform a call service. Based on the communication protocol standard corresponding to the EPSFB technique, it can be known that, after falling back from the 5G SA network to the 4G LTE network, the terminal device needs to send a Tracking Area Update (TAU) request to the core network, and after receiving a TAU response, can execute a call service in the 4G LTE network.

However, in some abnormal situations, for example, before receiving the TAU response, the serving cell of the terminal device changes, and based on the current communication protocol standard, the core network does not issue the TAU response for such a situation, so the terminal device cannot receive the TAU response, and essentially the EPSFB does not succeed, which may cause a call service failure.

Disclosure of Invention

In order to solve the above technical problems, the present application provides a network fallback method, device and storage medium, which aim to improve the success rate of the EPSFB, thereby improving the success rate of the call service and meeting the call requirement of the user.

In a first aspect, the present application provides a network fallback method. The method is applied to the terminal equipment of the call service to be executed in the first network, and comprises the following steps: when the first network can not execute the call service, the call is dropped from the first network to the second network based on a drop-back mechanism, wherein 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 a second network; and before receiving a first TAU response sent by the core network through the second network, keeping the current corresponding network, wherein the first TAU response is made by the core network aiming at the first TAU request.

Wherein the first network is, for example, a 5G SA network, which may be provided by a 5G base station, which is described below.

Wherein the second network is for example a 4G LTE network as described below, which may be provided by a 4G base station as described below.

It can be understood that when a 5G SA network falls back to a 4G LTE network, the specific fallen 4G LTE network may be determined according to parameters such as a position relationship between the current terminal device and all 4G LTE networks accessing a core network, signal strength (level strength, quality manifestation) of each 4G LTE network, transmission power of a 4G base station corresponding to each 4G LTE network, and transmission power and signal strength (level strength, quality manifestation) of the terminal device.

For example, in some implementations, the second network that needs to be dropped back may be determined according to the location relationship, and for a specific determination manner, reference may be made to the following, and details are not described here.

For example, in other implementation manners, the second network to which the fallback needs to be determined according to the transmission power, and for a specific determination manner, reference may be made to the following description, and details of the determination manner are not described herein again.

For example, in other implementation manners, the second network that needs to be dropped may be determined according to the signal strength, and for a specific determination manner, reference may be made to the following description, and details of which are not described herein again.

For example, in other implementation manners, for example, the second network that needs to be dropped back to may be determined according to parameter comprehensive consideration of the above three aspects, and for a specific determination manner, reference may be made to the following description, and details are not described here again.

Therefore, after the first TAU request is triggered after the first TAU request is received from the first network and falls back to the second network, the terminal equipment is set to always stay in the second network before the first TAU response sent by the core network through the second network is received, so that the success of the EPSFB can be ensured as far as possible by adjusting the processing logic of the terminal equipment under the condition that the communication protocol followed by the core network and the communication protocol followed by the base station side are not modified, thereby ensuring the success rate of the call service and meeting the call requirements of users.

According to the first aspect, 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, wherein the third network and the second network have the same network type; starting a timer; within the timing duration corresponding to the timer, after receiving a first TAU response sent by a third network of the core network, closing the timer, and executing a call service in the third network; when a first TAU response sent by a third network of the core network is not received, after a timing duration corresponding to the timer is received, a second TAU request is sent to the core network through the third network; and after receiving a second TAU response sent by the core network through the third network, executing the call service in the third network, wherein the second TAU response is made by the core network for the second TAU request.

It is to be understood that, in the case where the first network is a 5G SA network and the second network is a 4G LTE network, the third network is the same network type as the second network, and is also a 4G LTE network.

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

It is understood that in other implementations, a calculator may be used, and the present application is not limited thereto.

Therefore, before the first TAU response is received, when the 4G LTE network accessed by the terminal equipment is changed, the timer/calculator is started to time, and when the set time length is reached, if the first TAU response is still not received, the second TAU request is sent to the core network again through the switched 4G LTE network, so that the terminal equipment can receive the second TAU response issued by the core network through the switched 4G LTE network, and further the success of the EPSFB and the success of the calling service are ensured.

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

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

Based on this, the timing duration corresponding to the timer is set to be less than the random access response duration corresponding to the call service, so that after network switching is ensured, after the timer reaches the corresponding timing duration, the TAU request is sent through the newly-accessed 4G LTE network, and the duration of the TAU response is received within the random access response duration, thereby ensuring the success of the EPSFB, and the timing duration set for the timer is less than the random access response duration corresponding to the call service.

According to the first aspect, or any one implementation manner of the first aspect, the timing duration is N times of time consumed by the TAU procedure, the TAU procedure time consumed means time consumed from the time when the terminal device sends the first TAU request to the time when the first TAU response is received, and N is an integer greater than 0.

According to the first aspect, or any implementation manner of the first aspect, before receiving a first TAU response issued by a core network through a second network, maintaining a current corresponding network includes: and suspending the execution of the test and report operation before receiving a first TAU response sent by the core network through the second network.

The so-called measurement and report operation means that the terminal device is configured to obtain a MeasurementReport (measurement result/measurement report) corresponding to the accessible 4G LTE network.

The measurement result obtained by the measurement and report operation may include, for example, the transmission power, the signal strength of the terminal device, and the network information of the network that is accessible in the surrounding and has the same type as the second network.

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

Therefore, after the terminal device falls back to the second network from the first network based on the EPSFB, and sends the first TAU request, before receiving the first TAU response aiming at the first TAU request, the terminal device is restrained from executing the measuring and reporting operation, so that the 4G LTE network with better transmitting power and signal intensity than the currently accessed 4G LTE network cannot be detected, the 4G LTE network accessed by the terminal device cannot be changed before receiving the first TAU response, the first TAU response corresponding to the first TAU request sent by the 4G LTE network can be received by the currently accessed 4G LTE network, the success of the EPSFB can be ensured as far as possible, the success rate of the calling service is ensured, and the call requirement of a user is met.

According to a first aspect, or any one of the above implementations of the first aspect, the method further comprises: after receiving a first TAU response sent by a core network through a second network, executing a measuring and reporting operation to obtain a measuring result, wherein the measuring result comprises network information of all fourth networks to which the terminal equipment can be switched from the second network, the transmitting power and the signal intensity of the terminal equipment, and the network types of the fourth networks are the same as the network types of the second network; reporting the measurement result to a second network; receiving a fifth network determined by the second network according to the measurement result, wherein the fifth network is a fourth network which is screened out according to the transmitting power and the signal intensity of the terminal equipment and network information of all fourth networks and meets the set requirement; and switching from the second network to the fifth network.

It can be appreciated that, in some implementations, the third network, the fourth network, and the fifth network may be the same network, i.e., a 4G LTE network provided by the same 4G base station corresponding to the same serving cell.

For the specific implementation of the forecasting operation, reference may be made to the existing communication protocol, which is not described herein again.

Accordingly, the measurement result obtained by the measurement and report operation may also refer to the existing communication protocol, and is not described herein again.

Therefore, after the first TAU response is received through the fallen second network, the inhibition on the terminal equipment is released, even if the terminal equipment can execute the forecast operation according to the set period or the trigger condition, and the measurement result obtained by the forecast operation is reported to the second network, so that the switching from the second network to a new network can be realized under the condition that the measurement result is more suitable for the terminal equipment, the success rate of the EPSFB is ensured, the quality of the call corresponding to the call service is also ensured, and the user experience is ensured.

According to the first aspect, or any implementation manner of the first aspect above, the method further includes: and before receiving a first TAU response sent by the core network through the second network, in the process of suspending the execution of the measurement and report operation, when the wireless link between the core network and the second network is abnormal, the core network is accessed into the second network again.

Therefore, when the Radio Link Failure (RLF) and other abnormalities occur in the Radio Link between the core network and the second network, the first TAU response to the first TAU request made by the core network is ensured to be sent to the terminal device through the second network by reconstructing the Radio Link Failure (RLF) to the source network, namely, the second network sending the first TAU request, so that the success rate of the EPSFB and the success rate of the call service are ensured.

According to the first aspect, or any implementation manner of the first aspect above, before re-accessing to the second network, the method further includes: judging whether the reference signal receiving power of the second network meets a set reference signal receiving power threshold value and/or whether the reference signal receiving quality of the second network meets the set reference signal receiving quality threshold value; 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, executing a step of re-accessing the second network; and accessing the sixth 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.

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

Therefore, before the source network is reconstructed, whether the source network meets the reconstruction condition is determined through Reference Signal Receiving Power (RSRP) of the source network and/or Reference Signal Receiving Quality (RSRQ) and other Reference Signal information of the source network, the source network is reconstructed when the reconstruction condition is met, if the set threshold value is met, and otherwise, the source network is switched to a sixth network, so that the situation that the reconstructed source network still has RLF (radio link failure) abnormity and further cannot receive a first TAU response in the random access response duration can be avoided.

According to the first aspect, or any one of the above implementation manners of the first aspect, after accessing the sixth network, the method further includes: starting a timer; within the timing duration corresponding to the timer, after receiving a first TAU response sent by a sixth network of the core network, closing the timer, and executing a call service in the sixth network; when a first TAU response sent by a sixth network of the core network is not received, after a timing duration corresponding to the timer is received, a third TAU request is sent to the core network through the sixth network; and after receiving a third TAU response sent by the core network through the sixth network, executing the call service in the sixth network, wherein the third TAU response is made by the core network aiming at the third TAU request.

Therefore, under the condition that the source network cannot be rebuilt, after the source network is switched to the sixth network and the TAU request is sent again by the sixth network after the source network is switched to the sixth network and the TAU response made to the newly sent TAU request is sent to the terminal equipment through the third network, when the source network cannot be rebuilt by the terminal equipment, the triggered TAU flow can be successfully completed after the EPSFB can still be ensured, the success rate of the EPSFB is ensured, and the success rate of the call service is further ensured.

According to the first aspect, or any implementation manner of the first aspect, before receiving a first TAU response issued by a core network through a second network, maintaining a current corresponding network includes: and before receiving a first TAU response sent by the core network through the second network, when receiving a network switching instruction sent by the second network, suspending responding to the network switching instruction and keeping the current corresponding network.

Therefore, before waiting for the first TAU response issued by the second network accessed currently, the terminal equipment does not respond to the network switching instruction issued by the second network, or delays responding to the network switching instruction, so that the network accessed by the terminal equipment can be prevented from changing before receiving the first TAU response.

According to a first aspect, or any one of the above implementations of the first aspect, the method further comprises: and after receiving a first TAU response sent by the core network through the second network, responding to a network switching instruction, and switching to the network indicated by the network switching instruction from the second network.

Therefore, after receiving the TAU response sent by the second network, namely under the condition that the EPSFB is successful and the call service is successfully carried out, the network switching instruction is responded, so that the success rate of the EPSFB and the success rate of the call service are ensured.

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

Therefore, after the first TAU request is sent through the second network, the terminal device is kept in the second network in any mode, so that the core network can send a first TAU response made for the first TAU request to the terminal device through the second network, and after the terminal device receives the TAU response, the terminal device can execute the subsequent flow of the call service in the second network under the condition that the terminal device is still accessed into the second network, thereby ensuring that the call service can be executed in the second network after the EPSFB falls back to the second network from the first network, and meeting the call requirement of a user.

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

Two Voice call modes supported by the 5G SA network are provided, one is a Voice over NR (Voice over NR) service provided based on a New Radio (NR) access technology in the 5G SA network, and the other is a Voice over Long-Term Evolution (Voice over Long-Term Evolution) service provided based on a 4G Voice architecture and an IP Multimedia Subsystem (IMS) supported by a 4G network. Therefore, when the 5G SA network cannot execute the call service, for example, the terminal equipment cannot realize the call service based on VoNR in the 5G SA network, the call service can be returned to the 4G LTE network, and then the call service can be realized based on VoLTE in the 4G LTE network, so that the realization of the call service is ensured, and the call requirement of the user is ensured.

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

It can be understood that the EPSFB refers to a fallback mechanism for dropping the call service from the 5G SA network to the 4G LTE network when the 5G SA network does not have the VoNR condition, and the call service can be dropped from the 5G SA network to the 4G LTE network based on the fallback mechanism, so that the call service is performed based on the VoLTE provided by the 4G LTE network, thereby ensuring the continuity of the voice call service and guaranteeing the call requirement of the user.

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 coupled; the memory stores program instructions that, when executed by the processor, cause the terminal device to perform the instructions of the first aspect or any possible implementation of the first aspect.

The second aspect corresponds to the first aspect and any one implementation manner of the first aspect. For technical effects corresponding to the second aspect, reference may be made to the first aspect and technical effects corresponding to any implementation manner of the first aspect, and details are not described here again.

In a third aspect, the present application provides a computer readable medium for storing a computer program comprising instructions for performing the method of the first aspect or any possible implementation manner of the first aspect.

The third aspect corresponds to the first aspect and any one of the implementation manners of the first aspect. For technical effects corresponding to the third aspect, reference may be made to the first aspect and technical effects corresponding to any implementation manner of the first aspect, and details are not described here again.

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

A fourth aspect corresponds to the first aspect and any one of the implementation manners of the first aspect. For technical effects corresponding to the fourth aspect, reference may be made to the first aspect and technical effects corresponding to any implementation manner of the first aspect, and details are not described here again.

In a fifth aspect, the present application provides a chip comprising a processing circuit, a transceiver pin. Wherein the transceiver pin and the processing circuit are in communication with each other via an internal connection path, and the processing circuit executes the method of the first aspect or any one of the possible implementations of the first aspect to control the receiving pin to receive a signal and to control the transmitting pin to transmit a signal.

A fifth aspect corresponds to the first aspect and any one of the implementation manners of the first aspect. For technical effects corresponding to the fifth aspect, reference may be made to the first aspect and technical effects corresponding to any implementation manner of the first aspect, and details are not described here again.

In a sixth aspect, the present application provides a communication system. The system comprises a 5G base station, a 4G base station, a core network and the terminal equipment related to the second aspect.

A sixth aspect corresponds to any one of the second, first and first aspects. For technical effects corresponding to the sixth aspect, reference may be made to the technical effects corresponding to any one of the implementation manners of the second aspect, the first aspect, and details are not repeated here.

Drawings

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

FIG. 2 is a timing diagram illustrating the TAU flow phase after network fallback;

fig. 3 is a schematic diagram of an exemplary hardware configuration of a terminal device;

fig. 4 is a flowchart of an exemplary network fallback method provided in an embodiment of the present application;

FIG. 5 is one of the sequence diagrams illustrating the interaction process between the entities involved in implementing the network fall-back method shown in FIG. 4;

FIG. 6 is a second timing diagram illustrating the interaction process between the entities involved in implementing the network fallback method shown in FIG. 4;

FIG. 7 is a third time chart illustrating an interaction process between entities involved in implementing the network fallback method shown in FIG. 4;

fig. 8 is a second flowchart of a network fallback method provided by the embodiment of the present application;

fig. 9 is a sequence diagram illustrating an interaction procedure between entities involved in implementing the network fallback method shown in fig. 8.

Detailed Description

The technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the drawings in the embodiments of the present application, and it is obvious that the described embodiments are some, but not all, embodiments of the present application. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments in the present application without making any creative effort belong to the protection scope of the present application.

The term "and/or" herein is merely an association relationship describing an associated object, and means that there may be three relationships, for example, a and/or B, which may mean: a exists alone, A and B exist simultaneously, and B exists alone.

The terms "first" and "second," and the like, in the description and in the claims of the embodiments of the present application are used for distinguishing between different objects and not for describing a particular order of the objects. For example, the first target object and the second target object, etc. are specific sequences for distinguishing different target objects, rather than describing target objects.

In the embodiments of the present application, words such as "exemplary" or "for example" are used to mean serving as an example, instance, or illustration. Any embodiment or design described herein as "exemplary" or "e.g.," is not necessarily to be construed as preferred or advantageous over other embodiments or designs. Rather, use of the word "exemplary" or "such as" is intended to present relevant concepts in a concrete fashion.

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

In order to better understand the technical solutions provided in the embodiments of the present application, a communication scenario to which the technical solutions provided in the embodiments of the present application are applied is described below.

In particular, with the continuous development of Communication technology, communication networks have evolved from the fourth Generation Mobile Communication technology (4 g) to the fifth Generation Mobile Communication technology (5 g). For 5G networks, it uses New Radio (NR) access technology, but also follows the 4G voice architecture and IP Multimedia Subsystem (IMS). Therefore, for a 5G network, it may provide a Voice over NR (Voice over NR) service based on an NR access technology, and may also provide a Voice over Long-Term Evolution (VoLTE) service based on a 4G Voice architecture and IMS supported by a 4G network.

However, in practical applications, some mobile communication networks cannot directly perform call services, such as 5G stand-alone (SA). For a network that cannot make a Voice call, the terminal device may employ a fallback mechanism, such as an Evolved Packet System Fallback (EPSFB) mechanism, to Fall Back to a network that can make a Voice call, such as the fourth Generation Mobile Communication technology (4G), and then use a Voice over Long-Term Evolution (VoLTE) technology in the 4G network to make a call service. Based on the communication protocol standard corresponding to the EPSFB technique, it can be known that, after falling back from the 5G SA network to the 4G LTE network, the terminal device needs to send a Tracking Area Update (TAU) request to the core network, and after receiving a TAU response, can execute a call service in the 4G LTE network.

As an example, referring to fig. 1a to fig. 1d, schematic diagrams of a communication environment in which a terminal device implements the call service related to network fallback are shown.

Referring to fig. 1a, take 4G LTE provided by a network accessed by a terminal a (calling party) for a 4G base station a, a 5G SA provided by a network accessed by a terminal B (called party) for a 5G base station, and both the 4G base station a and the 5G base station are accessed to a core network as an example. When a terminal A triggers a call service and initiates a call request to a terminal B, the call request is specifically transmitted to a core network through a 4G base station A which establishes a wireless link with the terminal A, and then is issued to the terminal B through a 5G base station which establishes a wireless link with the terminal B through the core network.

Through the above description, when the 5G SA network provided by the 5G base station cannot directly perform a call service, for example, the NR-based VoNR call session cannot be established, the 5G SA network can fall back to the 4G LTE network based on the EPSFB mechanism, as shown in fig. 1B, the 5G SA network provided by the 5G base station needs to fall back to the 4G LTE network provided by the 4G base station B, that is, the wireless link with the 5G base station is disconnected, and the wireless link with the 4G base station B is established.

Continuing with fig. 1B, for example, after dropping from the 5G SA network to the 4G LTE network based on the EPSFB mechanism, based on the communication protocol related to the EPSFB, the terminal B may send a Tracking Area Update (TAU) request to the core network through the 4G base station B corresponding to the dropped 4G LTE network, so as to notify the core network that the network to which the terminal B currently accesses 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 in the 4G LTE network.

Continuing with fig. 1B, for example, under a normal condition, that is, when the terminal B does not have a network handover, the accessed network is still the 4G LTE network provided by the 4G base station B, and radio 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 for the terminal B through the TAU request sent by the 4G LTE network provided by the 4G base station B is issued to the terminal B through the 4G LTE network provided by the 4G base station B. And after receiving the TAU response issued by the core network through the 4G LTE network provided by the 4G base station B, if the currently consumed time does not exceed the random access response time corresponding to the call service after the terminal a initiates the call request, the terminal B transmits the call response made to the call request to the core network through the 4G LTE network provided by the 4G base station B, and the core network issues the call response to the terminal a through the 4G LTE network of the 4G base station a, as shown in fig. 1 c. Therefore, based on the EPSFB mechanism, the realized network fallback is successful, and the subsequent flow of the call service can be executed downwards.

However, under some abnormal conditions, for example, before the terminal B receives the TAU response, the serving cell of the terminal B, that is, the accessed 4G LET network, changes, as shown in fig. 1d, for example, the terminal B disconnects the wireless link with the 4G base station B, establishes a wireless link with the 4G base station C, that is, switches to the 4G LTE network provided by the 4G base station C, based on the current communication protocol standard, the core network does not issue the TAU response any more in such a situation, so the terminal B cannot receive the TAU response, and the network fallback realized based on the EPSFB mechanism is essentially unsuccessful, which may cause the subsequent flow of the call service to be unnecessary, and further cause the call service to fail.

It should be understood that the above description is only an example for better understanding of the technical solution of the present embodiment, and is not to be taken as the only limitation of the present embodiment. In practical applications, the base stations accessible to terminal a are not limited to the 4G base station a mentioned above, and the base stations accessible to terminal B are not limited to the 5G base station, 4G base station B, 4G base station C mentioned above, and so on.

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

Referring to fig. 2, it should be noted that, in the 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 implemented through an IMS network. I.e. the call request referred to above, may be transmitted from the calling party to the called party in the form of an INVITE request.

In addition, as can be seen from the above description of the communication scenario, the communication between the calling party and the called party needs to be implemented through the base station and the core network that are accessed by the calling party and the called party. Therefore, an INVITE request initiated when a calling party triggers a call service is transmitted to a core network through a base station accessed by the calling party, a multimedia session facing the calling party between the core network and an IMS network is further established by the core network, and then the INVITE request is transmitted to a called party through the core network and the base station accessed by the called party by the IMS network. The network fallback operation realized based on the EPSFB mechanism is specifically performed when the called party is in the 5G SA network and receives the INVITE request. Therefore, the flow shown in fig. 2 takes UE (User Equipment, terminal Equipment, which may also be referred to as User Equipment) as an example of a called party, and a scenario in which an INVITE request is directly issued from an IMS network to the called party is described.

Referring to fig. 2, for example, after the INVITE request initiated by the calling party is sent to the core network through the IMS network, the core network may 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 sends the INVITE request to the called party UE through the 5G base station.

Continuing with fig. 2, for example, based on a Session initiation Protocol (SIP Protocol) corresponding to the call service, after receiving the INVITE request, the UE of the called party may make a 100Trying temporary response to inform the calling party that the INVITE request is received. Regarding 100Trying, it is still fed back to the IMS network through the corresponding 5G base station and core network, and further fed back to the calling party through the IMS network, core network and base station corresponding to the calling party.

Because the technical solutions provided in the embodiments of the present application mainly aim at the interaction process between the called party and the base station, the core network, and the IMS network, the processing flows of the base station and the calling party corresponding to the IMS network, the core network, and the calling party are not repeated in the following.

Continuing with fig. 2, for example, after the called UE makes 100Trying, it may also feed back information related to the response Session Progress (call state) to the IMS network through the 5G base station and the core network, and based on the SIP protocol, the information related to the response Session Progress (call state) may be reported, for example, through 183 Session Progress.

Accordingly, after receiving the information related to the Response Session Progress (call state) reported by the called UE through 183 Session Progress, the IMS network feeds back a Provisional Response Acknowledgement (PRACK) made for the called UE. Since this stage still occurs in the 5G SA network, the PRACK fed back by the IMS is delivered to the called UE through the core network and the 5G base station.

With reference to fig. 2, based on the communication protocol involved in the 5G bearer establishment process, after the above procedure is completed, quality of Service flow (QOS flow) between the core network and the 5G base station, that is, setup QOS flow shown in fig. 2, is set. For detailed information that can be included in the QOS flow between the core network and the 5G base station, reference may be made to a corresponding communication protocol, which is not described herein again.

Continuing to refer to fig. 2, exemplarily, after completing Setup QOS flow, when the 5G base station cannot directly perform a call service, a handover command is issued to the called party UE, based on a communication protocol corresponding to the EPSFB mechanism, the handover command issued by the 5G base station is, for example, "mobility frontnrcomm command", and through the handover command, the 5G base station indicates to the called party UE a network Type to be handed over, for example, in fig. 2, the network Type to be handed over by the called party UE is Evolved Universal Terrestrial Radio Access (eutra), that is, a Radio Access network architecture of the 4G LTE network, through a "targetRAT-Type: eutra" carried in the command.

It should be noted that, in practical application, the 5G base station may further notify the called party UE of the transmission power range, the signal strength, and the like of the 4G LTE network that can fall back through the handover command, so that the called party UE can select a suitable 4G LTE network from the multiple accessible 4G LTE networks to access. For a specific implementation, reference may be made to a corresponding communication protocol, which is not described herein again. The application takes the example that the currently accessed 4G LTE network is the network corresponding to the 4G base station B at the time of determination.

Continuing to refer to fig. 2, for example, after the called party UE receives the handover command mobilityfrmnrcommand, targetRAT-Type, eutra, issued by the 5G base station, and determines that the 4G LTE network that needs to fall back is the network provided by the 4G base station B, the called party may access the 4G base station B, for example, establish a wireless link with the 4G base station B, and the specific establishment method may refer to a corresponding communication protocol, which is not described herein again.

Continuing with fig. 2, for example, after dropping back to the 4G LTE network provided by the 4G base station B, the called UE may send a TAU request (TAU REQ) to the core network through the 4G LTE network provided by the 4G base station B based on the corresponding communication protocol. Based on the existing communication protocol, the called UE executes a measurement and report operation in real time or according to a set period, so as to obtain a MeasurementReport (measurement result/measurement report) corresponding to the 4G LTE network that can be accessed, and report the obtained measurement result to the currently accessed 4G base station B. And the 4G base station B selects one with better matching transmission power and better signal quality from the 4G LTE network currently accessible by the called party according to the measurement result reported by the called party UE, and sends a network switching instruction to the called party UE to instruct the called party UE to switch to a 4G base station corresponding to the 4G LET network determined by the 4G base station B according to the measurement result, such as the 4G base station C shown in fig. 2.

For example, the measurement result obtained by the measurement and report operation may include the transmission power, signal strength of the called UE, and network information of the surrounding accessible 4G LTE network.

For example, the network information may include signal strength (level strength, quality representation) of each 4G LTE network accessible around, transmission power of a base station corresponding to each 4G LTE network, and the like.

Continuing with fig. 2, for example, in response to a network handover instruction issued by the 4G base station B to the 4G base station C, the called UE disconnects the wireless link with the 4G base station B, and establishes a wireless link with the 4G base station C, so as to access the 4G LTE network provided by the 4G base station C.

Considering that after a core network designed by some manufacturers at present specifies that a TAU request is received on a source cell (source 4G LTE network), if a 4G base station accessed by a called party UE changes, for example, after a 4G base station B switches to a 4G base station C in fig. 2, a TAU response cannot be fed back to the called party UE through the switched 4G base station C, and only after the called party UE retransmits the TAU request through the switched 4G base station C, a corresponding TAU response can be fed back through the 4G base station C. As can be seen from the specifications of the currently followed communication protocol, the timeout time for TAU request retransmission is usually 15 seconds, and the random access response duration corresponding to INVITE request is usually 6 seconds. Obviously, based on the current communication protocol, the core network cannot process the TAU request received through the 4G base station B within the random access response duration, and will not respond to the TAU request. And within the timeout time of waiting for the TAU to request to resend, the calling party has one or more Update (Update) processes, and the Update processes are 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 knows the information used for resource reservation and media Update in the call establishment process of the calling party.

Continuing to refer to fig. 2, for example, when the IMS network transmits information in the process of calling party Update with the called party UE, after determining that the dedicated bearer required for the call service is already established, the core network sends a request for requesting activation of the dedicated bearer to the called party UE through the 4G base station C to which the called party UE is currently connected, and the request for activating the dedicated bearer is sent based on a corresponding communication protocol, for example, an active dedicated EB request.

Continuing with fig. 2, for example, since the called UE does not receive the TAU response made by the core network for the TAU request sent by the called UE, it does not respond to the SIP message and the corresponding flow message executed by the ESM.

Understandably, in a mobile communication system, two core problems to be solved are: "connect" and "move". The Evolved Packet System (EPS) has two corresponding concepts: in this embodiment, when the UE of the called party does not receive a TAU response from the core network for the TAU request sent by the core network, the connection of the Session is not completed yet at this stage, so that the corresponding flow message executed by the ESM is not responded at this stage.

Continuing with fig. 2, for example, the called party UE does not respond to the SIP message and the ESM flow message, the calling party always receives no response to establish the multimedia session from the called party UE, i.e. receives no call response as shown in fig. 1 c. When the IMS detects that the bearer establishment time-out, for example, the time length of the random access response time-out is reached, the IMS generates a BYE request for terminating the specified session or the session established by the common sense, and carries a specific reason, for example, a status code 503 indicating a connection error.

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

That is to say, based on the EPSFB mechanism, after dropping from the 5G SA network provided by the 5G base station to the 4G TLE network provided by the 4G base station B, and after sending the TAU request to the core network through the 4G TLE network provided by the 4G base station B, the called party UE waits to receive the TAU response sent by the core network through the 4G TLE network provided by the 4G base station B, and if the handover of the 4G LTE network occurs, for example, when the handover is performed 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 dropping based on the EPSFB mechanism is not really successful, and the call service cannot be performed.

In view of the above, in order to solve the above problem, an embodiment of the present invention provides a network fallback method to improve a success rate of an EPSFB, so as to improve a success rate of a call service and meet a call requirement of a user.

In order to better understand the network fallback method provided in the embodiment of the present application, a hardware structure of a terminal device to which the method is applied is described below with reference to fig. 3, and then a 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 with reference to fig. 4 to 9.

Referring to fig. 3, a schematic diagram of an exemplary hardware structure of a terminal device 100 for implementing the network fallback method according to the embodiment of the present application is shown.

As shown in fig. 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, a Subscriber Identity Module (SIM) card interface 195, and the like.

Wherein the

antennas

1 and 2 are used for transmitting and receiving electromagnetic wave signals. Each antenna in terminal device 100 may be used to cover a single or multiple communication bands. Different antennas can also be multiplexed to improve the utilization of the antennas. For example: the antenna 1 may be multiplexed as a diversity antenna of a wireless local area network. In other embodiments, the antenna may be used in conjunction with a tuning switch.

It should be noted that, specifically, in each embodiment of the present application, the terminal device 100 receives information such as a handover command/instruction, a TAU response, an INVITE request, a PRACK, an Update, an active decoded EB request, and the like, which are sent by a base station (a 4G base station, a 5G base station), and sends information such as a 100Trying, a 183 response, a TAU request, and the like to the base station is implemented by the antenna 1 or the antenna 2.

The mobile communication module 150 may provide a solution including 2G/3G/4G/5G wireless communication 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), and the like. The wireless communication module 160 may provide solutions for wireless communication applied to the terminal device 100, including Wireless Local Area Networks (WLANs) (e.g., wireless fidelity (Wi-Fi) networks), bluetooth (bluetooth, BT), global Navigation Satellite System (GNSS), frequency Modulation (FM), near Field Communication (NFC), infrared (IR), and the like.

In some embodiments, the antenna 1 of the terminal device 100 is coupled to the mobile communication module 150 and the antenna 2 is coupled to the wireless communication module 160 so that the 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 for the terminal device 100 includes a speaker 170A, a headphone 170B, a microphone 170C, an earphone interface 170D, and the like.

Illustratively, the terminal device 100 may implement audio functions, such as music playing, sound recording, call service in the embodiments of the present application, and the like, through the speaker 170A, the receiver 170B, the microphone 170C, the earphone interface 170D, and the application processor in the audio module 170.

In addition, regarding the sensor module 180 in the terminal device 100, in some embodiments, the sensor module may include a pressure sensor, a gyroscope sensor, a barometric 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, and the like, which are not listed here, and the present application is not limited thereto.

Furthermore, it is noted that in some embodiments, processor 110 may include one or more processing units, such as: 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), among others.

It is to be appreciated that in particular implementations, the various processing units may be stand-alone units or may be integrated into one or more processors.

Further, in some embodiments, the controller may be a neural hub and a command center of the terminal device 100. The controller can generate an operation control signal according to the instruction operation code and the timing signal to complete the control of instruction fetching and instruction execution.

In addition, memory in the processor 110 is used primarily for storing instructions and data. In some embodiments, the memory in the processor 110 is a cache memory.

In addition, the USB interface 130 shown in fig. 3 is an interface conforming to the USB standard specification, and may specifically be a Mini USB interface, a Micro USB interface, a USB Type C interface, or the like.

The charging management module 140 is configured to receive charging input from a charger. In addition, the power management module 141 shown in fig. 3 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 charge management module 140 and provides power to the processor 110, the internal memory 121, the external memory, the display 194, the camera 193, the wireless communication module 160, and the like. The wireless communication function of the terminal device 100 may be implemented by the antenna 1, the antenna 2, the mobile communication module 150, the wireless communication module 160, a modem processor, a baseband processor, and the like.

In addition, the terminal device 100 shown in fig. 3 realizes a display function by the GPU, the display screen 194, and the application processor, etc. The GPU is a microprocessor for image processing, and is connected to the display screen 194 and an 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 alter display information.

In this regard, the display screen 194 is specifically used to display images, videos, and the like. The display 194 includes a display panel, and in some embodiments, the terminal device 100 may include 1 or N displays 194, N being a positive integer greater than 1.

In addition, the terminal device 100 can implement a shooting function by the ISP, the camera 193, the video codec, the GPU, the display screen 194, the application processor, and the like.

The camera 193 is used to capture still images or video, and in some embodiments, the terminal device 100 may include 1 or N cameras 193, N being a positive integer greater than 1.

In addition, fig. 3 shows that the external memory interface 120 may be used to connect an external memory card, such as a Micro SD card, to implement the storage capability of the expansion 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, video, etc. are saved in an external memory card.

Furthermore, the internal memory 121 shown in fig. 3 may be used to store computer-executable program code, which includes instructions. The processor 110 executes various functional applications of the terminal device 100 and data processing by executing instructions stored in the internal memory 121.

Specifically, relevant instructions for implementing the network fallback method provided in the embodiments of the present application are stored in the internal memory 121 in advance, and the processor 110 executes the instructions stored in the internal memory 121, so that the terminal device 100 can execute the network fallback method provided in the embodiments of the present application.

Further, the motor 191 shown in fig. 3 may be, for example, a vibration motor; the indicator 192 may be an indicator light.

The SIM card interface 195 is used to connect a SIM card, or USIM card. The SIM card can be brought into and out of contact with the terminal device 100 by being inserted into the SIM card interface 195 or being pulled out of the SIM card interface 195. The terminal device 100 may support 1 or N (N is an integer greater than 1) SIM card interfaces 195. That is, a plurality of SIM cards or USIM cards may be inserted in the terminal.

While the hardware architecture of the terminal device 100 is described herein, it should be understood that the terminal device 100 shown in fig. 3 is merely an example, and in particular implementations, the terminal device 100 may have more or fewer components than shown, may combine two or more components, or may have a different configuration of components. The various components shown in fig. 3 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 a terminal device with a hardware structure shown in fig. 3 as an example, a flow of implementing the network fallback method provided by the present application by the terminal device is specifically described with respect to the communication environments shown in fig. 1a to 1 d.

It should be noted that, the implementation of the call service needs to be implemented based on processing of a Modem protocol stack, so when the network fallback method provided in the embodiments of the present application is implemented, the policy and the processing logic that are followed by the terminal device may be set in the Modem protocol stack in the form of a control point. That is, the network fallback method provided in the following embodiments is implemented by a terminal device, such as a called party UE, all in a Modem protocol stack.

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

s101, when the first network can not execute the call service, the call service is fallen back from the first network to the second network based on a falling back mechanism.

Specifically, the second network to which the fallback based mechanism falls is a network supporting the call service. As can be seen from the above description of the communication scenario, in one implementation, the first network is, for example, the above-mentioned 5G SA network, and the second network is, for example, the above-mentioned 4G LTE network, that is, the network types of the first network and the second network are different.

Two Voice call modes supported by the 5G SA network are Voice over NR (Voice over NR) service provided based on a New Radio (NR) access technology in the 5G SA network, and a Voice over Long-Term Evolution (Voice over Long-Term Evolution) service provided based on a 4G Voice architecture and an IP Multimedia Subsystem (IMS) supported by the 4G network. Therefore, when the 5G SA network cannot execute the call service, for example, the terminal equipment cannot realize the call service based on VoNR in the 5G SA network, the call service can be returned to the 4G LTE network, and then the call service can be realized based on VoLTE in the 4G LTE network, so that the realization of the call service is ensured, and the call requirement of the user is ensured.

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

In addition, it should be noted that, regarding the above-mentioned falling back from the first network to the second network based on the falling back mechanism, in practical application, specifically to which second network the called party UE falls back to, the called party UE may determine all second networks currently accessible by performing a measurement and report operation, and send reference information of each determined second network, such as transmission power, signal strength (level strength, quality embodiment), etc., the transmission power of the called party UE itself, signal strength (level strength, quality embodiment), etc., and the location relationship between each base station corresponding to the second network, such as the above-mentioned 4G base station B, 4G base station C, and the called party UE, to the base station corresponding to the first network in the form of a measurement result, such as the above-mentioned 5G base station, and then the 5G base station determines the second network that the called party UE really falls back to according to the information.

For example, in some implementations, the second network to be dropped may be determined according to the location relationship, for example, a 4G LTE network corresponding to a 4G base station closest to the called party UE is determined as the second network to be dropped.

For example, in other implementations, the second network to be dropped may be determined according to the transmission power, for example, a 4G LTE network corresponding to a 4G base station that matches (is the same as, or within a range corresponding to) the transmission power of the called party UE is determined as the second network to be dropped.

For example, in other implementations, the second network that needs to be dropped may be determined according to the signal strength, for example, the 4G LTE network corresponding to the 4G base station with the best signal strength is determined as the second network that needs to be dropped.

For example, in other implementations, the second network to be dropped may be determined according to the parameter combination of the above three aspects, 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 be dropped, where the signal strength is the best and the transmission power of the called party UE is matched with that of the second network.

It should be understood that the above description is only an example for better understanding of the technical solution of the present embodiment, and is not intended to limit the present embodiment.

Accordingly, after determining the second network really needing to fall back, the 5G base station issues a handover command to the called UE, such as "mobility fromnrmnrcommand: targetRAT-Type: eutra" as described above, and indicates the network Type of the second network needing to be handed over and the specific information of the second network in the handover command.

Correspondingly, after receiving the switching command, the called party UE responds to the switching command, and disconnects the wireless link with the 5G base station, establishes a wireless link with the determined 4G base station corresponding to the second network, and further accesses the second network.

For a specific process of implementing fallback from the 5G SA network to the 4G LTE network based on the EPSFB mechanism, reference may be made to a corresponding communication protocol, which is not described herein again.

S102, a first tracking area update TAU request is sent to a core network through a second network.

For a specific implementation manner that the called UE sends 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 handover command, reference may be made to a corresponding communication protocol, which is not described herein again.

And S103, before receiving a first TAU response sent by the core network through the second network, keeping the current corresponding network.

It can be understood that, after responding to the handover command, the called party UE falls back from the first network to the second network, and sends the first TAU request to the core network through the second network, so that the called party UE is specifically controlled to stay in the second network, that is, not to be handed over to another network, and thus 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 sending the first TAU request, that is, the second network.

Regarding the above-mentioned maintaining the implementation manner of the current corresponding network before receiving the first TAU response issued by the core network through the second network, the implementation manner may be implemented by placing one or more of the following policies in the control point in the Modem protocol stack corresponding to the called UE.

Strategy 1: and before receiving a first TAU response sent by the core network through the second network, inhibiting the called party UE from executing the test and report operation, namely before receiving the first TAU response sent by the core network through the second network, the called party UE suspends the execution of the test and report operation.

Therefore, after the called party UE falls back to the second network from the first network based on the EPSFB, and sends the first TAU request, before receiving the first TAU response aiming at the first TAU request, the called party UE is restrained from executing the measuring and reporting operation, so that the 4G LTE network with better transmitting power and signal strength than the currently accessed 4G LTE network can not be detected, the 4G LTE network accessed by the called party UE can not be changed before receiving the first TAU response, the first TAU response corresponding to the first TAU request sent by the 4G LTE network can be received by the currently accessed 4G LTE network, the success of the EPSFB can be ensured as far as possible, the success rate of the calling service is ensured, and the conversation requirement of the user is met.

In addition, it should be noted that, in order to ensure the quality of the call service, after receiving the first TAU response sent by the core network through the second network, the UE of the called party may release the suppression of the measurement and reporting operation, so that the UE of the called party may perform the measurement and reporting operation in real time or according to a set period, and further obtain the measurement result including the listed content.

Accordingly, after obtaining the measurement result including the content listed above, the called UE may report the measurement result to a second network, such as a base station corresponding to the second network, and then the base station corresponding to the second network determines, according to the content in the received measurement report, a network that is more suitable than the second network, such as a network with better signal strength, better transmission power matching with the called UE, closer to the called UE, and more abundant network bandwidth resources, and further issues a network handover instruction carrying the determined network to be handed over to the called UE, so that the called UE can re-determine the network after being handed over from the second network in response to the network handover instruction.

For convenience of description, the information about the multiple networks carried in the measurement report is taken as the fourth network mentioned above as an example, and the network types of the fourth network and the second network are the same, such as both 4G LTE networks.

Correspondingly, a 4G base station corresponding to the second network finally screens out a new 4G LTE network to which handover is required from the measurement report, that is, a network meeting the set requirements in the fourth network, and for convenience of distinguishing, the network may be represented by the fifth network as described above.

Therefore, after the first TAU response is received through the fallen second network, the inhibition on the called UE is released, even if the UE can execute the test report operation in real time or according to a set period or a trigger condition, and the measurement result obtained by the test report operation is reported to the second network, so that the second network can be switched to a new network under the condition that the measurement result is more suitable for the terminal equipment, the success rate of the EPSFB is ensured, the quality of the call corresponding to the call service is ensured, and the user experience is ensured.

In addition, for the specific implementation flows of the measurement and report operation, the measurement result generation, and the report of the measurement result, reference may be made to documents and communication protocols related to the "LTE measurement report message", and details are not repeated here.

Strategy 2: before receiving a first TAU response sent by the core network through the second network, when the second network is abnormal, such as RLF, the currently accessed network is reestablished to the source network, that is, the second network.

For example, in some implementations, before receiving a first TAU response sent by the core network through the second network, if the execution of the measurement and report operation is already suspended, during the suspension of the measurement and report operation, if an RLF, a network anomaly, a network resource deficiency, a signal instability, and other anomalies occur in the second network, the second network is also re-accessed.

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

Therefore, when the radio link between the core network and the second network is abnormal, such as RLF (radio link failure) and the like, 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 by reestablishing the radio link to the source network, namely the second network sending the first TAU request, so that the success rate of the EPSFB and the success rate of the calling service are ensured.

In addition, it should be noted that, in practical application, when the second network has an abnormality such as RLF, before the second network is re-accessed, it may be determined whether the second network meets the condition of re-access.

For example, in some implementations, it may be determined whether a Reference Signal Receiving Power (RSRP) of the second network satisfies a set Reference Signal Receiving Power threshold.

The RSRP is one of key parameters and physical layer measurement requirements that can represent radio signal strength in a 4G LTE network, and is an average value of signal powers received on all REs (resource elements) that carry reference signals within a certain symbol, so that it can be determined whether information such as signal strength of a second network meets requirements by determining the RSRP.

Correspondingly, 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, and the sixth network is used for distinguishing.

It is understood that the determination manner of the sixth network may be the same as the determination manner of the fifth network, and is not described herein again.

Furthermore, 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 for the same 4G base station as the fifth network. That is, the third network, the fourth network, the fifth network, and the sixth network are presented in this application to distinguish from the second network, which indicates 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 may be the same network, that is, a 4G LTE network provided by the same 4G base station corresponding to the same serving cell.

For example, in some other implementations, it may be determined whether a Reference Signal Receiving Quality (RSRQ) of the second network meets a set Reference Signal Receiving Quality threshold.

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

Correspondingly, when the RSRQ of the second network meets the set reference signal receiving quality threshold, the second network is accessed again, and otherwise, the sixth network is accessed.

For example, in other implementations, it may be determined whether RSRP of the second network meets a set reference signal received power threshold and RSRQ of the second network meets a set reference signal received quality threshold at the same time.

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, the second network is accessed again, and otherwise, the sixth network representation is accessed.

Therefore, before the source network is reestablished, such as the second network, whether the source network meets the reestablishment condition is determined through reference information such as RSRP and/or reference RSRQ of the source network, the source network is reestablished when the reestablishment condition is met, such as a set threshold value, otherwise, the source network is switched to the sixth network, and therefore the situation that the reestablished source network still has RLF abnormality and further the first TAU response cannot be received within the random access response time length can be avoided.

Further, after accessing the sixth network, in order to avoid the problem in the scenario described in fig. 2, the called UE may start a timer or a calculator, which is taken as an example in this embodiment.

Correspondingly, after the timer is started, within a timing duration corresponding to the timer, if the first TAU response sent by the sixth network of the core network is determined to be received, the timer is closed, and the call service is executed in the sixth network; otherwise, after receiving the timing duration corresponding to the timer, the sixth network resends the TAU request to the core network, which may be represented by the third TAU request for distinguishing.

Accordingly, after the called UE sends the third TAU request to the core network through the sixth network, in order to avoid the network being switched again, the called UE may be controlled to remain in the sixth network according to the policy followed by the second network.

Accordingly, after receiving a third TAU response to the third request issued by the core network through the sixth network, the called UE may execute a call service in the sixth network.

Therefore, under the condition that the source network cannot be reconstructed, after the source network is switched to the sixth network and the core network receives the TAU request through the timing duration corresponding to the timer, the TAU request is sent again by the sixth network, so that the core network can send a TAU response made to the newly sent TAU request to the called UE through the third network, and when the called UE cannot be reconstructed to the source network, the triggered TAU flow can be successfully completed after the EPSFB can be ensured, the success rate of the EPSFB is ensured, and the success rate of the calling service is ensured. For the implementation process of retransmitting the TAU request within the random access response duration corresponding to the INVITE request in the timer manner, reference may be made to the following description, which is not described herein again.

Strategy 3: and before receiving a first TAU response sent by the core network through the second network, when receiving a network switching instruction sent by the second network, not responding. Namely, the response to the network switching instruction sent by the second network is suspended, and the current corresponding network is kept, namely the called party UE is controlled to be still in the second network.

Therefore, before waiting for the first TAU response issued by the second network accessed currently, the UE of the called party does not respond to the network switching instruction issued by the second network or delays responding to the network switching instruction, so that the condition that the network accessed by the UE of the called party is changed before receiving the first TAU response can be avoided.

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

Therefore, after receiving the TAU response sent by the second network, namely under the conditions that the EPSFB succeeds and the calling service is successfully carried out, the network switching instruction is responded, so that the success rate of the EPSFB and the success rate of the calling service are ensured.

It is not difficult to find out through the above description that the network drop-back method provided in this embodiment always stays in the second network by setting the terminal device before receiving the first TAU response issued by the core network through the second network after the first TAU request is dropped from the first network to the second network and then triggers the first TAU request, so that the success of the EPSFB can be ensured as much as possible by adjusting the processing logic of the terminal device without modifying the communication protocol followed by the core network or modifying the communication protocol followed by the base station side, thereby ensuring the success rate of the call service and meeting the call requirement of the user.

In addition, it can be understood that, after receiving the first TAU response issued by the core network through the second network, it indicates that the network fallback based on the EPSFB mechanism is successful, and the fallback to the second network can support the call service, so that after receiving the first TAU response issued by the core network through the second network, the call service can be executed in the second network, and for a specific implementation process of the call service, reference may be made to a corresponding communication protocol, which is not described herein again.

Therefore, after the first TAU request is sent through the second network, the called party UE is kept in the second network in any mode, so that the core network can send a first TAU response made for the first TAU request to the called party UE through the second network, and the called party UE can execute the subsequent flow of the calling service in the second network after receiving the TAU response and under the condition that the called party UE is still accessed to the second network, thereby ensuring that the calling service can be executed in the second network after the EPSFB falls back to the second network from the first network, and meeting the conversation requirement of a user.

In order to better understand the interaction between the called party UE, the 5G base station and the 4G base station on the network side, the core network, and the IMS network when the network fallback method provided by the present application is implemented based on the above three policies, the following description is made with reference to fig. 5 and fig. 6.

Referring to fig. 5, a timing chart for controlling the called party UE to maintain the currently accessed network by using the above policy 1, and further completing the network fallback and executing the call service is exemplarily shown.

As shown in fig. 5, this embodiment still takes the example of receiving an INVITE request sent by an IMS network and the subsequent processing scenario shown in fig. 2 as well. The processing flow before the called UE sends the first TAU request to the core network through the fallback 4G base station B may refer to the description part of fig. 2 above, and is not described here again.

In addition, for convenience of description, the first TAU request is denoted by TAU REQ _1, and accordingly, the first TAU response made by the core network to TAU REQ _1 is denoted by TAU Accept _ 1.

Continuing to refer to fig. 5, exemplarily, after the called party UE sends the 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 and reporting operation based on the policy 1 before receiving the TAU Accept _1, thereby preventing the called party UE from switching the 4G base station.

Continuing to refer to fig. 5, for example, if the called party UE receives the TAU Accept _1 sent by the core network through the 4G base station B during the period of suspending the execution of the measurement and report operation, the control point in the corresponding Modem protocol stack releases the suppression based on the policy 1, so that the called party can execute the measurement and report operation in real time or according to the set period, and further obtain the measurement result. For the called party UE performing the measurement and report operation, obtaining the measurement result, interacting with the 4G base station B, and determining, by the subsequent 4G base station B, the 4G LTE network that can be switched according to the measurement result, for example, the 4G LTE network provided by the 4G base station C, and details of implementing switching from the 4G base station B to the 4G base station C may be referred to above, which is not described herein again.

Continuing to refer to fig. 5, exemplarily, after receiving the TAU Accept _1, if the information in the Update process and the active determined EB request mentioned above are continuously received within the random access response duration corresponding to the INVITE request, the establishment of the multimedia session can be implemented, and then the subsequent flow of the call service is executed. For the information in the Update process, the source of the active decoded EB request in each entry, and the information and functions carried by the request, see above, and are not described herein again.

In addition, it should be noted that, in the scenario shown in fig. 5, the operation of releasing suppression and the information in the process of receiving Update, and the active decoded EB request may not be in a sequential order.

The implementation process of the 4G LTE network provided by the second network or the 4G base station B, which is described above, is introduced to keep the called UE in the currently accessed network by using the method of suppressing the measurement and reporting operation before waiting for the core network to issue the TAU response through the 4G LTE network that sends the TAU request. It should be understood that the above description is only an example for better understanding of the technical solution of the present embodiment, and is not intended to limit the present embodiment.

Referring to fig. 6, a timing diagram for controlling the called UE to maintain the currently accessed network by using the above policy 2, thereby completing the network fallback and executing the call service is exemplarily shown.

As shown in fig. 6, this embodiment still takes the example of receiving the INVITE request sent by the IMS network and the subsequent processing scenario shown in fig. 2 as an example. The processing flow before the called UE sends the first TAU request to the core network through the fallback 4G base station B may refer to the description part of fig. 2 above, and is not described herein again.

In addition, for convenience of description, the first TAU request is denoted by TAU REQ _1, and the first TAU response made by the core network to TAU REQ _1 is denoted by TAU Accept _ 1.

Continuing to refer to fig. 6, for example, after the called party UE sends the TAU REQ _1 to the core network through the 4G base station B, based on the policy 2, before receiving the TAU Accept _1, if it is detected that the radio link between the called party UE and the 4G base station B fails, or the transmission power, the signal strength, and the like of the 4G base station B do not meet the requirements of the called party UE, or the 4G LTE network resources provided by the 4G base station B are insufficient (in this embodiment, an RLF abnormality occurs as an example), and when it is determined that the RSRQ and/or the RSRP of the 4G LTE network provided by the 4G base station B meet the corresponding threshold, the 4G LTE network provided by the 4G base station B is re-accessed to the 4G base station B, so that the TAU Accept _1 made by the core network can be delivered to the called party UE through the 4G LTE network provided by the 4G base station B sending the TAU REQ _ 1.

Continuing to refer to fig. 6, exemplarily, after the called UE is re-established to the source network, that is, re-accesses to the 4G base station B, if the TAU Accept _1 issued by the core network through the 4G base station B is received, if the information in the Update process and the active decoded EB request are continuously received within the random access response duration corresponding to the INVITE request, the establishment of the multimedia session can be realized, and then the subsequent flow of the call service is executed. For the information in the Update process, the source of the activated decrypted EB request in each entry, and the information and functions carried by the request, reference may be made to the above, and details are not repeated here.

In addition, it should be noted that, in practical application, policy 2 may be used alone or in combination with policy 1, that is, on the basis of the flow shown in fig. 6, the flow shown in fig. 5 may be merged, for example, during the time when the called party is controlled to suspend the logging operation or before the logging operation is inhibited from being performed, if the RLF is abnormal, the 4G base station B is re-accessed according to the flow shown in fig. 6.

Accordingly, after the 4G base station B is re-accessed, if the flow of suppressing the execution of the measurement and reporting operation is already started, the suppression may be released as shown in fig. 5 after the TAU Accept _1 is received; if the flow for suppressing the execution of the forecast operation is not started, the flow may be started, and then after receiving the TAU Accept _1, the suppression may be released as shown in fig. 5.

It should be understood that the above description is only an example for better understanding of the technical solution of the present embodiment, and is not to be taken as the only limitation of the present embodiment.

Before waiting for the core network to issue the TAU response through the 4G LTE network that sends the TAU request, the method of abnormally reestablishing the source network is used to keep the called UE in the currently accessed network, which is described above as the second network, or the implementation process of the 4G LTE network provided by the 4G base station B is introduced here. It should be understood that the above description is only an example for better understanding of the technical solution of the present embodiment, and is not intended to limit the present embodiment.

Referring to fig. 7, a timing diagram for controlling the called UE to maintain the currently accessed network by using the above policy 3, thereby completing the network fallback and executing the call service is exemplarily shown.

As shown in fig. 7, this embodiment still takes the example of receiving the INVITE request sent by the IMS network and the subsequent processing scenario shown in fig. 2 as an example. The processing flow before the called UE sends the first TAU request to the core network through the fallback 4G base station B may refer to the description part of fig. 2 above, and is not described here again.

Continuing with fig. 7, exemplarily, after the called party UE sends the TAU REQ _1 to the core network through the 4G base station B, based on the policy 3, before receiving the TAU Accept _1, if a network handover instruction for handover to the 4G base station C sent by the 4G base station B is received, the control point in the Modem protocol stack corresponding to the called party UE does not respond to the network handover instruction, so that the called party UE can still be maintained on the 4G LTE network provided by the 4G base station B, and the TAU Accept _1 made by the core network can be sent to the called party UE through the 4G LTE network provided by the 4G base station B sending the TAU REQ _ 1.

Continuing with reference to fig. 7, for example, when the called UE remains on the 4G LTE network provided by the 4G base station B without responding to the network handover command, if the previously received network handover command to the 4G base station C is not timed out, the called UE may handover from the 4G base station B to the 4G base station C in response to the network handover command.

Continuing to refer to fig. 7, exemplarily, after receiving the TAU Accept _1, if the called UE receives the TAU Accept _1 delivered by the core network through the 4G base station B, if the information in the Update process and the active decoded EB request mentioned above are continuously received within the random access response duration corresponding to the INVITE request, the establishment of the multimedia session can be implemented, and then the subsequent flow of the call service is executed. For the information in the Update process, the source of the activated decrypted EB request in each entry, and the information and functions carried by the request, reference may be made to the above, and details are not repeated here.

In addition, it should be noted that, in the scenario shown in fig. 7, the operation responding to the previously received network switching instruction, the information in the Update receiving process, and the active decoded EB request may not be in a sequential order.

In addition, it should be further noted that, in practical application, policy 3 may be used alone, or may be used in combination with policy 1 and/or policy 2, that is, on the basis of the flow shown in fig. 7, the flow shown in fig. 5 and/or fig. 6 may be merged, and a specific combination logic is not limited in this embodiment, and is not described herein again.

Before waiting for the core network to issue the TAU response through the 4G LTE network that sends the TAU request, the called UE is maintained in the currently accessed network in a manner of suspending or not responding to the network switching instruction issued by the network side (the currently accessed 4G base station), and the implementation process of the 4G LTE network provided by the second network or the 4G base station B is introduced here. It should be understood that the above description is only an example for better understanding of the technical solution of the present embodiment, and is not to be taken as the only limitation of the present embodiment.

In addition, it should be noted that, in practical application, the three implementation manners for maintaining the called party UE in the currently accessed network may be arbitrarily combined according to actual service requirements, that is, one or more of them are selected, and when the three implementation manners are used as a control point in a Modem protocol stack to control the called party UE to maintain the currently accessed network, the policy followed, the specific combination manner, and the order adjustment of the processing logic are not described herein again, and this application is not limited thereto.

Referring to fig. 8, a network fallback method provided in the embodiment of the present application specifically includes:

s201, when the first network cannot execute the call service, dropping from the first network to the second network based on a dropping mechanism.

For example, in this embodiment, the first network is still a 5G SA network, the second network is a 4G LTE network, and the fallback mechanism is an EPSFB mechanism, which may be referred to above for specific details, and is not described herein again.

S202, sending a first tracking area update TAU request to the core network through the second network.

It is to be understood that step S202 in this embodiment is substantially the same as step S102 in the above embodiment, and details of the implementation may be referred to above, which are not described herein again.

S203, before receiving the first TAU response sent by the core network through the second network, the core network is switched from the second network to the third network.

It is understood that, in some implementations, the third network may be, for example, a 4G LTE network that satisfies the preset condition and is determined by the 4G base station corresponding to the second network according to the measurement result obtained by the callee UE through the measurement and report operation, that is, the network types of the third network and the second network are the same, and in the case that the second network is the 4G LTE network, the third network is also the 4G LTE network, except that the serving cell/provided 4G base station corresponding to the third network does not pass through, for example, the third network may 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 presented above, and is mainly used to distinguish from the second network, which indicates that the network to which the second network is handed over is not the second network, and the third network, the fourth network, the fifth network, and the sixth network may be the same network, that is, a 4G LTE network provided by the same 4G base station corresponding to the same serving cell. For the determination of the third network, see above, it is not described here.

In addition, it should be noted that, considering that there may be movement in the process of using the terminal device to perform a call service, which may cause different access base stations and core networks, distribution maps of the core networks provided by different manufacturers and the base stations corresponding to each core network may be built into the terminal device in advance, so that the terminal device may implement optimization of network handover based on the location according to built-in base station maps corresponding to different core networks.

And S204, starting a timer.

It can be understood that in practical applications, the method can also be implemented by using a calculator, and the present embodiment takes a timer as an example.

And S205, whether the TAU response is received within the timing duration or not.

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

And S206, whether the timing time is reached.

Specifically, if not, that is, the timing task of the timer has not been ended, step S205 is continuously executed; otherwise, step S207 is executed to resend the TAU request to the core network through the third network, which is referred to as a third TAU request for convenience of differentiation. Accordingly, the TAU answer made by the core network for the third TAU request is referred to as a third TAU answer.

For example, in some implementations, the time duration set for the timer is N times (N is an integer greater than 0) of the time taken for sending the TAU request to receiving the TAU response when the TAU procedure is performed, that is, when network handover, network abnormality, or the like does not occur.

As can be seen from the above description, the random access response duration of the INVITE request is usually 6 seconds, while the normal time consumption of the TAU procedure is about 0.3 seconds. Therefore, in order to ensure that the TAU request can be reinitiated by the newly switched network even if the network switching occurs within the random access response duration, and the TAU response is received within the random access response duration, N may be 3.

It should be understood that the above description is only an example for better understanding of the technical solution of the present embodiment, and is not to be taken as the only limitation of the present embodiment. In practical applications, the terminal device may also multiply the learned normal time consumption of the TAU procedure in different networks by a specific N according to the set historical time period.

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

S207, sending the second TAU request to the core network through the third network, and receiving that the core network passes through the third network. And executing the call service in the third network after the issued second TAU response.

For example, in some implementation manners, after the second network is switched to the third network and the second TAU request is sent to the core network through the third network, during the period of waiting for the second TAU which is issued by the core network through the third network to be due, any one or more of the above-mentioned policy 1, policy 2 and policy 3 may also be adopted to control the called party UE to stay in the third network, and the specific implementation manner may refer to the above, and is not described herein again.

And S208, closing the timer, and executing the call service in the third network.

Therefore, in the network fallback method provided in this embodiment, before the first TAU response is received, when the 4G LTE network accessed by the terminal device changes, the timer/calculator is started to time, and when the set duration 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 the EPSFB and the success of the call service.

In order to better understand the interaction between the called party UE, the 5G base station and the 4G base station on the network side, and the core network and the IMS network when the network fallback method provided by the present application is implemented based on the timer, the following description is made with reference to fig. 9.

Referring to fig. 9, an exemplary timing chart shows that a timer is used to set a timing duration, and after a TAU response is not received after timeout, a newly switched network initiates a TAU request again, so as to complete network fallback and execute a call service.

As shown in fig. 9, this embodiment still takes the example of receiving the INVITE request sent by the IMS network and the subsequent processing scenario shown in fig. 2 as an example. The processing flow before the called UE sends the first TAU request to the core network through the fallback 4G base station B may refer to the description part of fig. 2 above, and is not described here again.

In addition, for convenience of description, the first TAU request is denoted by TAU REQ _1, the first TAU response made by the core network to TAU REQ _1 is denoted by TAU Accept _1, the second TAU request is denoted by TAU REQ _2, and the second TAU response made by the core network to TAU REQ _2 is denoted by TAU Accept _2.

Continuing with fig. 9, exemplarily, after the called party UE sends TAU REQ _1 to the core network through the 4G base station B, if the policy 1 is not adopted to suppress the execution of the measurement and report operation, the called party UE may execute the measurement and report operation in real time according to a set period, and report the measurement result obtained through the measurement and report operation to the 4G base station B. And the 4G base station B selects a new base station meeting the current scene according to the measurement result, and if the new base station needing to be switched is determined to be the 4G base station C, the network switching instruction for indicating the new base station to be switched to the 4G LTE network provided by the 4G base station C is issued by the UE of the lower called party. Accordingly, the called party UE will access the 4G base station C in response to the instruction, and then complete network handover.

For the called party UE performing the measurement and report operation, obtaining the measurement result, interacting with the 4G base station B, and determining, by the subsequent 4G base station B, the 4G LTE network that can be switched according to the measurement result, for example, the 4G LTE network provided by the 4G base station C, and details of implementing switching from the 4G base station B to the 4G base station C may be referred to above, which is not described herein again.

With reference to fig. 9, for example, when the called UE is handed over from the 4G bs B to the 4G bs C, the control point in the corresponding Modem protocol stack starts a timer or a calculator (the timer is taken as an example in this embodiment), and further, according to the processing manners of the step S205 and the step S206, it is determined whether to receive the TAU Accept _1 within the timing duration, and whether to reach the timing duration.

Continuing to refer to fig. 9, for example, if the timer is closed if the TAU Accept _1 is received within the timing duration, and the above-mentioned information in the Update process and the active decoded EB request are continuously received within the random access response duration corresponding to the INVITE request, the establishment of the multimedia session may be implemented, and then the subsequent flow of the call service is executed. For the information in the Update process, the source of the active decoded EB request in each entry, and the information and functions carried by the request, see above, and are not described herein again.

Continuing with fig. 9, exemplarily, if the TAU Accept _1 is not received within the timing duration, the called UE regenerates a TAU request, such as TAU REQ _2, and sends the TAU REQ _2 to the core network through the 4G base station C, and waits for the TAU Accept _2 sent by the core network through the 4G base station C.

Continuing to refer to fig. 9, exemplarily, after receiving the TAU Accept _2, if the information in the Update process and the active determined EB request mentioned above are continuously received within the random access response duration corresponding to the INVITE request, the establishment of the multimedia session can be implemented, and then the subsequent flow of the call service is executed. For the information in the Update process, the source of the activated decrypted EB request in each entry, and the information and functions carried by the request, reference may be made to the above, and details are not repeated here.

Before waiting for the core network to issue the TAU response through the 4G LTE network that sends the TAU request, the 4G base station to which the called UE accesses changes, and the TAU response is not received within the timing duration, and the implementation process of the called UE resending the TAU request to the core network through the switched 4G base station is introduced here. It should be understood that the above-mentioned handover between the 4G base station B and the 4G base station C is only an example listed for better understanding of the technical solution of the present embodiment, and is not meant to be the only limitation to the present embodiment.

In addition, it should be noted that, in practical application, the policy for controlling the called UE to maintain the currently accessed network given in the above embodiments may be implemented according to actual service requirements, and after network handover occurs, a TAU response is not received within a timing duration, and the called UE retransmits a TAU request to the core network through the switched 4G base station to perform any combination, so as to better ensure the success rate of the EPSFB, and further ensure the success rate of the call service.

Furthermore, it is understood that the terminal device comprises corresponding hardware and/or software modules for performing the respective functions in order to implement the above-described functions. The present application can be realized in hardware or a combination of hardware and computer software in connection with the exemplary algorithm steps described in connection with the embodiments disclosed herein. Whether a function is performed as hardware or computer software drives hardware depends upon the particular application and design constraints imposed on the solution. Skilled artisans may implement the described functionality in varying ways for each particular application, in conjunction with the embodiments, but such implementation decisions should not be interpreted as causing a departure from the scope of the present application.

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

In addition, an embodiment of the present application further provides a computer-readable storage medium, where the computer-readable storage medium stores computer instructions, and when the computer instructions are executed on a terminal device, the terminal device is caused to execute the relevant method steps to implement the network fallback method in the foregoing embodiment.

In addition, an embodiment of the present application further provides a computer program product, which when running on a terminal device, causes the terminal device to execute the above related steps, so as to implement the network fallback method in the above embodiment.

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

In addition, as can be seen from the foregoing description, the terminal device, the computer readable storage medium, the computer program product, or the chip provided in the embodiments of the present application are all configured to execute the corresponding method provided above, and therefore, the beneficial effects achieved by the terminal device, the computer readable storage medium, the computer program product, or the chip may refer to the beneficial effects in the corresponding method provided above, which are not described herein again.

The above embodiments are only used for illustrating the technical solutions of the present application, and not for limiting the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those of ordinary skill in the art that: the technical solutions described in the foregoing embodiments may still be modified, or some technical features may be equivalently replaced; and the modifications or the substitutions do not make the essence of the corresponding technical solutions depart from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A network fallback method is applied to a terminal device to execute a call service in a first network, and includes:

when the first network cannot execute the call service, the call service is dropped from the first network to a second network based on a drop-back mechanism, wherein 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 issued by the core network through the second network, keeping the current corresponding network, wherein the first TAU response is made by the core network for the first TAU request;

before receiving a first TAU response issued by the core network through the second network, the method further includes:

the second network is switched to a third network, and the type of the third network is the same as that of 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, closing the timer, and executing the call service in 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;

and after receiving a second TAU response sent by the core network through the third network, executing the call service in the third network, wherein the second TAU response is made by the core network aiming at the second TAU request.

2. The method of claim 1, wherein a timing duration corresponding to the timer is less than a random access response duration corresponding to the call service.

3. The method of claim 2, wherein the timing duration is N times of a TAU procedure time consumption, the TAU procedure time consumption refers to a time consumption from the terminal device sending the first TAU request to receiving the first TAU response, and N is an integer greater than 0.

4. The method of claim 1, wherein before receiving a second TAU response sent by the core network via the third network, the method further comprises:

and suspending the execution of the test and report operation before receiving a second TAU response sent by the core network through the third network.

5. The method of claim 4, further comprising:

after receiving the second TAU response sent by the core network through the third network, executing the measurement and report operation to obtain a measurement result, wherein the measurement result comprises network information of all fourth networks to which the terminal device can be switched from the third network, the transmission power and the signal strength of the terminal device, and the network types of the fourth network and the third network are the same;

reporting the measurement result to the third network;

receiving a fifth network determined by the third network according to the measurement result, wherein the fifth network is a fourth network which is screened out according to the transmitting power, the signal intensity and the network information of all the fourth networks and meets the set requirement;

switching from the third network to the fifth network.

6. The method of claim 4, further comprising:

and re-accessing the third network when the wireless link between the core network and the third network is abnormal in the process of suspending the execution of the forecast operation before receiving a second TAU response sent by the core network through the third network.

7. The method of claim 6, wherein prior to the re-accessing the third network, the method further comprises:

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

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

and accessing a sixth network when the reference signal receiving power of the third network does not meet the set reference signal receiving power threshold and/or the reference signal receiving quality of the third network does not meet the set reference signal receiving quality threshold.

8. The method of claim 7, wherein after the accessing a sixth network, the method further comprises:

starting a timer;

within the timing duration corresponding to the timer, after receiving the second TAU response issued by the core network through the sixth network, closing the timer, and executing the call service in the sixth network;

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

and after receiving a third TAU response sent by the core network through the sixth network, executing the call service in the sixth network, wherein the third TAU response is made by the core network for the third TAU request.

9. The method of claim 1, wherein before receiving a second TAU response sent by the core network via the third network, the method further comprises:

and when a network switching instruction sent by the third network is received before a second TAU response sent by the core network through the third network is received, the response to the network switching instruction is suspended, and the current corresponding network is maintained.

10. The method of claim 9, further comprising:

and after receiving the second TAU response sent by the core network through the third network, responding to the network switching instruction, and switching to the network indicated by the network switching instruction from the third network.

11. The method of any one of claims 1 to 10, further comprising:

and after receiving the first TAU response sent by the core network through the second network, executing the call service in the second network.

12. The method according to any of claims 1 to 10, wherein the first network is a 5G SA network and the second network is a 4G LTE network.

13. The method of claim 12, wherein the fallback mechanism is an evolved packet system fallback EPSFB mechanism.

14. A terminal device, characterized in that the terminal device comprises: a memory and a processor, the memory and the processor coupled; the memory stores program instructions that, when executed by the processor, cause the terminal device to perform the network fallback method according to any one of claims 1 to 13.

15. A computer-readable storage medium, characterized by comprising a computer program which, when run on a terminal device, causes the terminal device to perform the network fallback method according to any one of claims 1 to 13.