CN107980230B

CN107980230B - CSFB (Circuit switched Fall Back) fall result detection method and device and computer storage medium

Info

Publication number: CN107980230B
Application number: CN201780002077.4A
Authority: CN
Inventors: 曾元清
Original assignee: Shenzhen Huantai Technology Co Ltd
Current assignee: Shenzhen Huantai Technology Co Ltd
Priority date: 2017-09-30
Filing date: 2017-09-30
Publication date: 2021-01-19
Anticipated expiration: 2037-09-30
Also published as: CN107980230A; WO2019061482A1

Abstract

The invention discloses a CSFB (Circuit switched Fall Back) result detection method, a CSFB fall result detection device and a computer readable storage medium. The method comprises the following steps: triggering User Equipment (UE) to enter a called CSFB (Circuit switched fallback) process and sending a paging signaling to the UE; the paging signaling at least comprises frequency point information of a first cell of a GSM network; sending information of refusing access of the first cell of the GSM network to the UE so that the UE is in a state that CSFB falls back to the first cell of the GSM network and fails; and detecting whether the UE can initiate an access request to a third cell of the GSM network within a preset time length based on the historical record, and judging whether the CSFB falls back successfully based on the detected result.

Description

CSFB (Circuit switched Fall Back) fall result detection method and device and computer storage medium

Technical Field

The present invention relates to the technical field of Circuit Switched Fallback (CSFB), and in particular, to a method and an apparatus for detecting a CSFB Fallback result, and a computer storage medium.

Background

Since wireless communication between Long Term Evolution (LTE) and 2G/3G dual-mode UE is a single-radio mode (Signal-radio mode), dual-mode or multi-mode UE with LTE and 2G/3G access capability cannot transmit 2G/3G circuit domain service signals when LTE access is used. In order to enable a UE (UE) to perform Circuit domain (CS) services such as voice and the like under LTE access or camping, and to correctly handle Packet domain (PS) services being performed by the UE under LTE access, a CSFB technique has been developed.

In the CSFB procedure, an initiator of a phone call is called a calling party (MO), a receiver of the phone call is called a called party (MT), and the MO and the MT each have their own CSFB signaling flow. For the MT in the CSFB procedure, the occurrence of various abnormal situations will probabilistically cause the CSFB procedure to fail, and thus the call cannot be connected, and how to effectively detect the fall-back result of the CSFB in the abnormal scenario is particularly necessary.

Disclosure of Invention

In order to solve the foregoing technical problem, embodiments of the present invention provide a method and an apparatus for detecting a fallback result of a CSFB, and a computer storage medium.

The embodiment of the invention provides a CSFB fallback result detection method, which comprises the following steps:

triggering User Equipment (UE) to enter a called CSFB (Circuit switched fallback) process and sending a paging signaling to the UE;

the paging signaling at least comprises frequency point information of a first cell of a GSM network;

sending information of refusing access of the first cell of the GSM network to the UE so that the UE is in a state that CSFB falls back to the first cell of the GSM network and fails;

and detecting whether the UE can initiate an access request to a third cell of the GSM network within a preset time length based on the historical record, and judging whether the CSFB falls back successfully based on the detected result.

In the above scheme, the method further comprises:

and configuring a first cell of the GSM network and a second cell of the LTE network as adjacent cells.

In the above scheme, the method further comprises:

triggering the UE to register in a second cell of the LTE network and redirecting to a third cell of the GSM network;

and after the UE completes the preset flow in the third cell of the GSM network, controlling the UE to return to the second cell of the LTE network, and storing the third cell of the GSM network as the historical record of the UE.

In the above scheme, the method further comprises:

sending indication information to the UE to indicate that the UE voice scheme is CSFB through the indication information;

wherein the indication information is carried in an attach accept message sent to the UE.

In the foregoing solution, the determining whether the CSFB fallback is successful based on the result obtained by the detecting includes:

and detecting that the UE cannot initiate an access request to a third cell of the GSM network within a preset time length based on the history record, and determining that the CSFB falls back in failure.

In the foregoing solution, the determining, by the result obtained by the detecting, whether the CSFB falls back successfully includes:

and if the UE is detected to be capable of initiating an access request to a third cell of the GSM network within a preset time length based on the historical record, and the UE successfully establishes the CS voice call, determining that the CSFB falls back successfully.

An embodiment of the present invention provides a device for detecting a fallback result of a CSFB, where the device includes:

the control unit triggers the UE to enter a called CSFB flow and sends a paging signaling to the UE; the paging signaling at least comprises frequency point information of a first cell of a GSM network; sending information of refusing access of the first cell of the GSM network to the UE so that the UE is in a state that CSFB falls back to the first cell of the GSM network and fails;

the detection unit is used for detecting whether the UE can initiate an access request to a third cell of the GSM network within a preset time length based on the historical record;

and the judging unit is used for judging whether the CSFB falls back successfully or not based on the detected result.

In the above scheme, the control unit configures a first cell of a GSM network and a second cell of an LTE network as neighboring cells.

In the above scheme, the control unit triggers the UE to register in a second cell of the LTE network and to redirect to a third cell of the GSM network; and after the UE completes the preset flow in the third cell of the GSM network, controlling the UE to return to the second cell of the LTE network, and storing the third cell of the GSM network as the historical record of the UE.

In the foregoing solution, the control unit sends indication information to the UE, so as to indicate that the UE voice scheme is CSFB through the indication information;

In the foregoing solution, the determining unit detects that the UE cannot initiate an access request to a third cell of a GSM network within a preset time based on a history, and determines that the CSFB fallback fails.

In the foregoing solution, the determining unit determines that the CSFB fallback is successful if it detects that the UE can initiate an access request to a third cell of the GSM network within a preset time based on the history, and the UE successfully establishes the CS voice call.

An embodiment of the present invention further provides a device for detecting a fallback result of a CSFB, including: a processor and a memory configured to store a computer program capable of running on the processor,

wherein the processor is configured to perform the steps of any of the above methods when executing the computer program.

Embodiments of the present invention further provide a computer-readable storage medium, on which a computer program is stored, where the computer program, when executed by a processor, implements the steps of any of the above methods.

According to the technical scheme provided by the embodiment of the invention, whether the UE can initiate access to a third cell accessed once within a preset time length based on a historical record when the UE is detected to be in a called state and a network side rejects the first cell of the UE access request is detected, so that whether CSFB fallback is successful is verified, the feasibility and the stability of a CSFB optimization scheme under the condition that the network side rejects a GSM cell access anomaly can be obtained, the optimization scheme can be further perfected to improve the success probability of the CSFB process, and the call experience of a user is improved.

Drawings

Fig. 1 is a schematic flow chart of a method for detecting a fallback result of a CSFB according to an embodiment of the present invention 1;

fig. 2 is a flowchart illustrating a method for detecting a fallback result of a CSFB according to an embodiment of the present invention 2;

FIG. 3 is a diagram of an emulation code of an embodiment of the present invention 1;

FIG. 4 is a schematic diagram of emulation code of an embodiment of the present invention 2;

FIG. 5 is a schematic structural diagram of a fall-back result detection apparatus of a CSFB according to an embodiment of the present invention;

fig. 6 is a schematic diagram illustrating a hardware structure of a fall-back result detection apparatus of a CSFB according to an embodiment of the present invention.

Detailed Description

So that the manner in which the features and aspects of the embodiments of the present invention can be understood in detail, a more particular description of the embodiments of the invention, briefly summarized above, may be had by reference to the embodiments, some of which are illustrated in the appended drawings.

Under normal conditions, the terminal with the CSFB function can search the LTE network when being started, complete the joint registration of the LTE/2G network and carry out voice calling and called.

The CSFB procedure comprises three phases: 1) the UE initiates a call (corresponding to MO) in the LTE network or receives a paging (corresponding to MT); 2) the UE falls back under the guidance of an LTE network and searches a proper GSM cell/WCDMA cell for access; 3) the UE reads the GSM cell/WCDMA cell system broadcast message and establishes a voice call.

With the continuous expansion of the LTE base station scale and the network quitting and re-cultivation of some old GSM/TDSCDMA base stations, the configuration of the original network deployment on the signaling side of the base station is not updated in real time, and the configuration information issued by the network to the UE is inconsistent with the actual deployment situation, so that various abnormal situations, such as unavailable connection, failed repeated connection, etc., occur in the voice call across systems (inter rat) such as CSFB.

In order to solve the call problem caused by the incompatible situation of network deployment, various optimization means are adopted by terminal manufacturers to improve the call experience, and in order to verify the rationality of the CSFB optimization scheme, it is necessary to detect the CSFB process in an abnormal scene so as to improve the CSFB optimization scheme in a targeted manner.

The CSFB fallback scheme adopts a 3GPP R8 redirection fallback scheme, and during a CSFB deployment process, a CSFB procedure is probabilistically abnormal due to a problem of parameter configuration. Therefore, the embodiment of the invention provides a weak signal access failure of a GSM cell designated by a network side, and a mobile phone completes CSFB according to the LU record of the previous GSM strong signal cell to verify the validity and rationality of a call optimization scheme at the mobile phone side.

Fig. 1 is a schematic flow chart of a method for detecting a fallback result of a CSFB provided in an embodiment of the present invention, and as shown in fig. 1, the method for detecting a fallback result of a CSFB includes the following steps:

step 101: triggering User Equipment (UE) to enter a called CSFB (Circuit switched fallback) process and sending a paging signaling to the UE; the paging signaling at least comprises frequency point information of a first cell of a GSM network;

step 102: sending information of refusing access of the first cell of the GSM network to the UE so that the UE is in a state that CSFB falls back to the first cell of the GSM network and fails;

step 103: and detecting whether the UE can initiate an access request to a third cell of the GSM network within a preset time length based on the historical record, and judging whether the CSFB falls back successfully based on the detected result.

Here, the execution subject corresponding to the present embodiment may be a device capable of having a network environment simulation function, that is, a device having the above function simulates an environment capable of simulating at least one network, and for example, may include at least one network environment of GSM, CDMA, TSCDMA, WCDMA, LTE, and 5G, NR.

In practical application, a network environment applied to the embodiment of the invention can be constructed in a laboratory simulation mode, that is, the scene where the UE is located in the embodiment of the invention is obtained in a simulation mode, so that on one hand, a worker does not need to go to a field for detection, and therefore, the cost of the worker can be reduced; on the other hand, the scene of the site may include other factors, so as to affect the detection result, so that the simulation network according to the embodiment of the present invention can stably reproduce the CSFB abnormal scene occurring in the scene of the site, and can eliminate the influence of other factors on the detection result in the scene described in the embodiment of the present invention. Based on this, in some embodiments, a voice call state of the UE in the GSM network in the emulated network environment is detected.

Further, before the step 101 is executed, the first cell of the GSM network and the second cell of the LTE network may be configured as neighboring cells in advance.

It should be understood that the network side does not pre-configure the UE with a third cell in the GSM network. The specific configuration information may include information such as networks, frequency points, bandwidths, and the like of each cell, which is not described herein again; the mode of issuing the configuration information may be determined by the SI information, specifically, by the SIB placed in the SIB, according to a preset policy with the UE, for example, the mode may be determined to be in the SIB8, or other configuration situations may also exist, which is not exhaustive here.

The foregoing sending, to the UE, information that the first cell of the GSM network denies access, so that the UE is in a state where CSFB falls back to the first cell of the GSM network and fails, where the existing triggering manner includes: triggering UE to initiate access to a first cell of a GSM network; that is to say, since the paging is initiated to the UE, the UE can initiate an access request to the network side based on the frequency point information of the first cell in the paging.

And before performing step 101, the method may comprise:

Thus, the UE side accesses the third cell in advance, so that the third cell exists in the history record of the UE, and the record may include the identification information and the frequency point information of the third cell of the GSM.

Correspondingly, the paging signaling sent to the UE may further include identification information of the first cell of the GSM network.

Wherein the redirection may be an RRC redirection.

The preset process may include: location Update (LU) and GMM RAU (route update) flows.

After the controlling the UE to return to the LTE cell, the method further comprises:

sending indication information to the UE to indicate that the UE voice scheme is CSFB through the indication information; the indication information is carried in an attach accept message sent by the LTE base station to the UE. After the UE returns to the LTE cell, the UE is issued to the UE in the LTE attachment request receiving Attach Accept, and the voice scheme is designated as CSFB; the issuing mode can be as shown in fig. 3.

Judging whether the CSFB falls back successfully or not based on the detected result, comprising the following steps:

Alternatively, the first and second electrodes may be,

And the UE is detected to be capable of initiating an access request to a third cell of the GSM network within a preset time length based on the historical record, and meanwhile, the UE is required to carry a preset reason value in the access request.

The preset cause value may be obtained by pre-negotiating between the network side and the UE, for example, as long as both sides can know that the UE initiates an access request to the tecscdma cell based on the preset cause value.

The method provided by the embodiment of the invention can detect whether the UE can initiate access to a third cell accessed once within a preset time length based on the historical record when the UE is in a called state and the network side rejects the first cell of the UE access request, thereby verifying whether CSFB fallback is successful, and thus, the feasibility and the stability of a CSFB optimization scheme under the condition that the network side rejects the GSM cell access abnormity can be obtained, thereby further perfecting the optimization scheme to improve the success probability of the CSFB process and improving the call experience of a user.

In addition, the voice call state of the UE in the GSM network under the simulation network environment is detected, a simulation mode is adopted, workers do not need to go to the site, and other factors influencing detection can be removed, so that the personnel cost can be greatly reduced, and meanwhile, the influence of other factors on the detection result under the scene described by the embodiment of the invention can be eliminated.

The invention is described in more detail below with reference to an application example.

In the embodiment of the application, a network environment is constructed through a simulation platform, and the network environment comprises a Frequency Division Duplex (FDD) -LTE cell, a WCDMA cell and a GSM cell; the LTE SIB is configured with WCDMA1 as neighbor cell information, the GSM cell is configured as a neighbor cell, and the LTE neighbor cell information is configured in WCDMASIB 18.

The application embodiment provides a CSFB abnormal scenario: the GSM cell network appointed by the network side refuses access, the mobile phone completes CSFB according to the previous GSM cell LU record, and the validity and the rationality of the mobile phone side conversation optimization scheme are verified.

Firstly, a network side configures UE (user equipment), and configures a first cell of a GSM (global system for mobile communications) network as a cell adjacent to a second cell of an LTE (long term evolution) network;

specifically, the method comprises the following steps: the simulation network constructs a network environment comprising TDD-LTE/TDSCDMA/GSM cells, wherein GSM 1 is configured in LTE SIB as the information of the cells in the adjacent cells, and GSM 0 cells are not configured. And configuring LTE (Long term evolution) neighbor cell information in GSM SI.

As shown in fig. 2, the method for detecting a CSFB fallback result in the present application embodiment includes the following steps:

step 200: triggering UE to register to an LTE second cell, and RRC redirecting to a third cell of a GSM network to enable the UE to complete LU and GMM RAU processes on the GSM third cell, and then returning to the LTE second cell;

step 201: after the UE returns to the LTE cell, the UE is issued to the UE in the LTE attachment request receiving Attach Accept, and the voice scheme is designated as CSFB;

specifically, the UE is an MT, and after the UE is powered on, an Evolved Packet System (EPS) and International Mobile Subscriber Identity (IMSI) attach procedure is first performed.

In the process, the method comprises the steps of triggering the UE to send an attachment Request message (Attach Request) to the LTE base station and receiving an attachment acceptance message (Attach Accept) sent by the LTE base station, wherein the attachment acceptance message carries indication information used for indicating the UE to adopt a preset CSFB optimization scheme to carry out voice service. Fig. 3 is a first schematic diagram of an emulation code according to an embodiment of the present invention, where: IMS voice over PS (V) ═ Not supported (0), and represents the instruction information.

Step 202: the network side triggers the MT CSFB process, and the LTE network sends a Paging signaling to the UE so that the UE starts the CSFB process; the paging signaling may include frequency point information of a target GSM 1 cell (i.e., a first cell).

In the LTE _ RRCConnectionRelease signaling, frequency point information of a target GSM cell is included; for example, as shown in FIG. 4;

here, in practical application, the MO needs to initiate a call to the MT first, and then the MT receives the paging message sent by the network side.

Specifically, after receiving an initial address REQUEST (IAM) incoming message, a Mobile Switching Center (MSC) in the network sends an SGsAP-PAGING-REQUEST message to an Mobility Management Entity (MME) according to existing SGs association and MME information, where the SGsAP-PAGING-REQUEST message carries the following information: IMSI, Temporary Mobile Subscriber Identity (TMSI), Service identifier (Service indicator), calling number, location area information.

After receiving the message, the MME sends a Paging message to the base station, and the base station initiates a Paging flow of an air interface. UE establishes connection and sends Extended Service Request message to MME, MME sends SGsAP-Service-Request message to MSC, MSC receives the message, and MSC does not resend paging Request message to MME. In order to avoid the overlong waiting time of the calling party in the call connection process, the MSC receives the SGs Service Request message containing the idle state indication and firstly informs the calling party that the calling party is in the connection process. The MME sends an Initial UE Context Setup message to a base station, wherein the Initial UE Context Setup message carries a CS feedback Indicator, and the CS feedback Indicator is used for indicating that the base station UE needs to fall back to a UMTS Terrestrial Radio Access Network (UTRAN) or a GSM/EDGE Radio Access Network (GERAN, GSM EDGE Radio Access Network) due to CSFB service.

In the attach procedure, the UE receives an LTE _ RRCConnectionRelease signaling, i.e., a redirection command, sent by the LTE base station. The redirection command carries the wrong frequency point information of the designated WCDMA cell. As shown in fig. 4, the base station issues an R8 redirection command (rrcConnectionRelease _ R8(0)) to the UE, but the command carries the wrong frequency point information of the target WCDMA cell, and such an abnormal scenario cannot direct the terminal to fall back to the target GSM cell.

Step 203: the network simulates a GSM 1(GSM first cell) to send a locationUpdateReject and simulates CSFB to fall back to a scene that the access of a target cell is rejected;

step 204: detecting whether UE can initiate a power scan to a frequency point of GSM 0 (a third cell of a GSM network) within a specified timer to initiate an access Request Channel Request according to the previous history record and carrying a correct access Request reason value; if so, executing step 205, otherwise, the UE cannot initiate a GSM 0 access Request Channel Request within the specified timer, and judging that the optimization scheme fails;

step 205: the network side starts the CSFB subsequent flow at the GSM layer, checks that the mobile phone can successfully establish the CS voice call, and shows that the scheme is successfully optimized.

In order to implement the method according to the embodiment of the present invention, an embodiment of the present invention further provides a device for detecting a fallback result of a CSFB, where as shown in fig. 5, the device includes:

a control unit 51, configured to trigger a UE to enter a called CSFB procedure, and send a paging signaling to the UE; the paging signaling at least comprises frequency point information of a first cell of a GSM network; sending information of refusing access of the first cell of the GSM network to the UE so that the UE is in a state that CSFB falls back to the first cell of the GSM network and fails;

a detecting unit 52, configured to detect whether the UE can initiate an access request to a third cell of the GSM network within a preset time based on the history;

and a judging unit 53 for judging whether the CSFB falls successfully based on the detected result.

Further, the control unit 51 may configure the first cell of the GSM network and the second cell of the LTE network as neighboring cells in advance.

And the control unit 51, triggering the UE to register to the second cell of the LTE network, and redirecting to the third cell of the GSM network;

Wherein the redirection may be an RRC redirection.

A control unit 51, configured to send indication information to the UE, so as to indicate that the UE voice scheme is CSFB through the indication information; wherein the indication information is carried in an attach accept message sent to the UE. After the UE returns to the LTE cell, the UE is issued to the UE in the LTE attachment request receiving Attach Accept, and the voice scheme is designated as CSFB; the issuing mode can be as shown in fig. 3.

And the judging unit is used for detecting that the UE can not initiate an access request to a third cell of the GSM network within a preset time length based on the history record, and determining that the CSFB falls back to fail.

Alternatively, the first and second electrodes may be,

It should be noted that: in the CSFB fallback result detection apparatus according to the above embodiment, when performing the CSFB fallback result detection, only the above-mentioned division of the program modules is taken as an example, and in practical applications, the above-mentioned processing may be distributed to different program modules according to needs, that is, the internal structure of the apparatus may be divided into different program modules to complete all or part of the above-mentioned processing. In addition, the fall-back result detection apparatus of the CSFB and the fall-back result detection method of the CSFB provided in the above embodiments belong to the same concept, and specific implementation processes thereof are detailed in the method embodiments and are not described herein again.

Based on the above hardware implementation of each unit in the CSFB fallback result detection apparatus, in order to implement the embodiment of the present invention, an embodiment of the present invention further provides a CSFB fallback result detection apparatus, as shown in fig. 6, where the apparatus 60 includes: a processor 61 and a memory 62 configured to store computer programs capable of running on the processor,

wherein the processor 61 is configured to perform the method steps of the previous embodiments when running the computer program.

In practice, of course, the various components of the device 60 are coupled together by a bus system 63, as shown in FIG. 6. It will be appreciated that the bus system 63 is used to enable communications among the components. The bus system 63 includes a power bus, a control bus, and a status signal bus in addition to the data bus. For clarity of illustration, however, the various buses are labeled as bus system 63 in FIG. 6.

In an exemplary embodiment, the present invention further provides a computer-readable storage medium, such as a memory 62 comprising a computer program, which is executable by a processor 61 of the fall back result detection apparatus 60 of the CSFB to complete the steps of the foregoing method. The computer-readable storage medium may be a magnetic random access Memory (FRAM), a Read Only Memory (ROM), a Programmable Read-Only Memory (PROM), an Erasable Programmable Read-Only Memory (EPROM), an Electrically Erasable Programmable Read-Only Memory (EEPROM), a Flash Memory (Flash Memory), a magnetic surface Memory, an optical disk, or a Compact Disc Read-Only Memory (CD-ROM), among other memories.

The technical schemes described in the embodiments of the present invention can be combined arbitrarily without conflict.

In the embodiments provided in the present invention, it should be understood that the disclosed method and intelligent device may be implemented in other ways. The above-described device embodiments are merely illustrative, for example, the division of the unit is only a logical functional division, and there may be other division ways in actual implementation, such as: multiple units or components may be combined, or may be integrated into another system, or some features may be omitted, or not implemented. In addition, the coupling, direct coupling or communication connection between the components shown or discussed may be through some interfaces, and the indirect coupling or communication connection between the devices or units may be electrical, mechanical or other forms.

The units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, that is, may be located in one place, or may be distributed on a plurality of network units; some or all of the units can be selected according to actual needs to achieve the purpose of the solution of the embodiment.

In addition, all the functional units in the embodiments of the present invention may be integrated into one second processing unit, or each unit may be separately regarded as one unit, or two or more units may be integrated into one unit; the integrated unit can be realized in a form of hardware, or in a form of hardware plus a software functional unit.

The above description is only for the specific embodiments of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can easily conceive of the changes or substitutions within the technical scope of the present invention, and all the changes or substitutions should be covered within the scope of the present invention.

Industrial applicability

Claims

1. A method for detecting a fallback result of a Circuit Switched Fallback (CSFB), the method comprising:

triggering User Equipment (UE) to enter a called CSFB (Circuit switched fallback) process and sending a paging signaling to the UE; the paging signaling at least comprises frequency point information of a first cell of a GSM network;

2. The method of claim 1, further comprising:

3. The method of claim 2, further comprising:

4. The method of claim 3, further comprising:

5. The method according to any of claims 1-4, wherein the determining whether the CSFB falls successfully based on the detected result comprises:

6. The method according to any of claims 1-4, wherein the detecting determines whether the CSFB falls successfully comprises:

7. A fallback result detecting apparatus of a CSFB, the apparatus comprising:

8. The apparatus of claim 7, wherein the control unit configures a first cell of a GSM network and a second cell of an LTE network as neighboring cells.

9. The apparatus of claim 8, wherein the control unit is configured to trigger the UE to register with a second cell of an LTE network and to redirect to a third cell of a GSM network; and after the UE completes the preset flow in the third cell of the GSM network, controlling the UE to return to the second cell of the LTE network, and storing the third cell of the GSM network as the historical record of the UE.

10. The apparatus of claim 9, wherein the control unit is configured to send indication information to the UE to indicate that the UE voice scheme is CSFB;

11. The apparatus according to any one of claims 7-10, wherein the determining unit detects that the UE is unable to initiate an access request to a third cell of a GSM network within a preset time period based on a history record, and determines that the CSFB fallback fails.

12. The apparatus according to any one of claims 7-10, wherein the determining unit determines that the CSFB fallback is successful if it is detected that the UE can initiate an access request to a third cell of a GSM network within a preset time period based on a history record, and the UE successfully establishes a CS voice call.

13. A fallback result detecting apparatus of a CSFB, the apparatus comprising: a processor and a memory configured to store a computer program capable of running on the processor,

wherein the processor is configured to perform the steps of the method of any one of claims 1 to 6 when running the computer program.

14. A computer-readable storage medium, on which a computer program is stored which, when being executed by a processor, carries out the steps of the method of any one of claims 1 to 6.