Method and apparatus for triggering fallback using RRC establishment cause in a communication system

Abstract

Disclosed are a method and apparatus for triggering a fallback using an RRC establishment cause in a communication system. One aspect of the present disclosure provides a base station of a first wireless communication system, the base station triggering a fallback from the first wireless communication system to a second wireless communication system, the base station comprising: a receiving unit configured to receive an RRC connection request message from a terminal and verify, by using the RRC connection request message, whether the terminal requests a call service; and a fallback triggering unit configured to trigger a fallback to the second wireless communication system when the terminal requests the call service.

Description

Technical Field

[0001] The present disclosure relates to a method and apparatus for triggering a fallback using an RRC establishment cause in a communication system. Background Art

[0002] The description in this section merely provides background information for the present invention and does not constitute prior art.

[0003] As a solution for providing a voice call service in a fifth generation standalone (5GSA) system, there are two main solutions, including a Voice over NR (VoNR) solution for transmitting voice packets based on a New Radio (NR) network, and an Evolved Packet System Fallback (EPS Fallback) solution for transmitting voice packets based on a Long Term Evolution (LTE) network by changing the Radio Access Technology (RAT) to LTE and the core network to the Evolved Packet Core (EPC).

[0004] In the case of VoNR, when a user device moves out of NR coverage, the RAT and core network are changed during a call. This mid-call RAT and core network change causes packet loss, increased latency, and increased jitter, leading to degradation in voice service quality. This degradation in voice service quality creates a negative user experience. Therefore, it is difficult to provide VoNR-based voice call services without quality degradation in situations with insufficient NR coverage, such as in the early stages of 5G commercialization.

[0005] To prevent these connection changes during a call, the EPS fallback solution performs a RAT and core network change when a standalone user equipment (SAUE) initiates or receives a voice call. EPS fallback is suitable for use until NR coverage is expanded nationwide and VoNR quality stabilizes, as it provides the same quality as existing Voice over LTE (VoLTE) after the RAT and core network changes.

[0006] However, the EPS fallback solution has a problem in that the voice call setup time required to connect a voice call is longer than in VoNR. This extended voice call setup time is caused by the EPS fallback triggering process, RAT and core network change process, Tracking Area Update (TAU) process, and bearer establishment process added when using the EPS fallback solution. Therefore, a solution for shortening the voice call setup time in the EPS fallback solution is needed. Summary of the Invention

[0007] Technical issues

[0008] The main object of the present disclosure is to provide a method and apparatus for triggering fallback by using an RRC establishment cause in a communication system, for triggering EPS fallback by detecting a voice call and / or video call service request by using the RRC establishment cause.

[0009] Technical Solution

[0010] One aspect of the present disclosure provides a base station of a first wireless communication system for triggering a fallback from the first wireless communication system to a second wireless communication system, the base station comprising: a receiving unit configured to receive an RRC connection request message from a user equipment and use the RRC connection request message to verify whether the user equipment requests a call service; and a fallback triggering unit configured to trigger the fallback to the second wireless communication system when the user equipment requests the call service.

[0011] Another aspect of the present disclosure provides a method for triggering fallback to a second wireless communication system through a base station of a first wireless communication system, the method comprising the following steps: receiving an RRC connection request message from a user equipment; using the RRC connection request message to verify whether the user equipment requests a call service; and triggering the fallback to the second wireless communication system when the user equipment requests the call service.

[0012] Technical Effects

[0013] As described above, according to the embodiments of the present disclosure, a base station can determine whether EPS fallback is to be triggered by detecting a call service request using an RRC establishment cause. Therefore, the EPS fallback triggering time can be made earlier than in the prior art EPS fallback triggering scheme, and the initial setup time can be shortened. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 FIG. 1 is a flow chart showing the EPS fallback process.

[0015] Figure 2 FIG. 1 is a flow chart illustrating a call setup process using EPS fallback.

[0016] Figure 3 FIG. 1 is a flowchart illustrating a process in which a base station detects a call service request of a user equipment and triggers EPS fallback according to an embodiment of the present disclosure.

[0017] Figure 4 FIG. 1 is a flowchart illustrating a call establishment process using EPS fallback according to the first embodiment of the present disclosure.

[0018] Figure 5FIG. 1 is a flowchart illustrating a call establishment process using EPS fallback according to a second embodiment of the present disclosure.

[0019] Figure 6 FIG. 1 is a flowchart illustrating a call establishment process using EPS fallback according to a third embodiment of the present disclosure.

[0020] Figure 7 FIG. 4 is a flowchart illustrating a call establishment process using EPS fallback according to a fourth embodiment of the present disclosure.

[0021] Figure 8 FIG. 4 is a configuration block diagram of a base station according to an embodiment of the present disclosure. DETAILED DESCRIPTION

[0022] Hereinafter, some exemplary embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In the following description, the same reference numerals preferably indicate the same elements, even though these elements are shown in different drawings. In addition, in the following description of some embodiments, detailed descriptions of known functions and configurations contained therein will be omitted for the sake of clarity and brevity.

[0023] In addition, various terms such as first, second, A, B, (a), (b), etc. are only used to distinguish one component from another, and do not imply or suggest the substance, order, or sequence of the components. Throughout this specification, when a part "includes" or "contains" a component, it means that the part also includes other components, rather than excluding other components, unless otherwise specifically stated. Terms such as "unit" and "module" refer to one or more units for processing at least one function or operation, which can be implemented by hardware, software, or a combination thereof.

[0024] In this disclosure, a fallback technique for moving a user equipment from a first wireless communication system to a second wireless communication system when a call service request is made will be described. In various embodiments of the present disclosure, an example of the first wireless communication system is a fifth generation new radio (5GNR) communication system, and an example of the second wireless communication system is a long term evolution (LTE) communication system. However, this is for convenience of description, and the present disclosure can be extended to systems other than LTE communication systems and / or 5GNR communication systems.

[0025] Hereinafter, the present disclosure may be described with reference to 3GPP TS 23.502, which is a technical specification related to 5G, but this is for convenience of description and does not limit various embodiments of the present disclosure.

[0026] Figure 1 FIG. 1 is a flow chart showing the EPS fallback process.

[0027] exist Figure 1In (1), the user equipment resides in the next generation radio access network (NG-RAN) of the fifth generation system (5GS), and an IP multimedia system voice session establishment (IMS voice session establishment) is initiated.

[0028] exist Figure 1 In (2), in order to establish a quality of service flow (QoS flow) for voice service, the NW-initiated PDU session modification procedure is initiated. Specifically, the IMS server sends a PDU session resource modification request message including content for setting the 5G QoS indicator (5QI) to 1 to the NG-RAN. In this case, the PDU session resource modification request can be sent to the NG-RAN through the policy control function (PCF), the session management function (SMF), and the access and mobility function (AMF).

[0029] exist Figure 1 In (3), NG-RAN triggers Evolved Packet System Fallback (EPS Fallback).

[0030] exist Figure 1 In (4), NG-RAN sends a PDU session resource modification response message to SMF through AMF, and the PDU session resource modification response message indicates that the PDU session modification is rejected due to EPS fallback.

[0031] exist Figure 1 In (5), the NG-RAN initiates a handover or redirection from 5GS to EPS. The NG-RAN sends an NR RRC release message including the LTE frequency information for the connection of the user equipment to the user equipment.

[0032] exist Figure 1 In (6a), the user equipment changes the radio access technology (RAT) to LTE and initiates a tracking area update (TAU) procedure.

[0033] exist Figure 1 In (7), the PDN connection modification procedure initiated by the NW is initiated to establish a dedicated bearer for voice services in LTE.

[0034] The following is based on Figure 1 The EPS fallback process in the specification will describe the process by which a user equipment in the RRC idle state connects to a 5G base station (NG-RAN node or gNB) to request a call service and the process by which the 5G base station performs EPS fallback.

[0035] Figure 2 FIG. 1 is a flow chart illustrating a voice call establishment process using EPS fallback.

[0036] When a user equipment in the RRC idle state initiates a call (S200), the user equipment sends an RRC connection request message to the 5G base station (S202), and the 5G base station sends an RRC connection establishment message to the user equipment in response to the RRC connection request (S204). After the user equipment receives the RRC connection establishment message, the user equipment transitions from the RRC idle state to the RRC connected state.

[0037] The user equipment sends an RRC connection establishment completion message to the 5G base station (S206).

[0038] The 5G base station configures an initial UE message based on the information included in the RRC connection establishment message and sends the initial UE message to the core network (S210). The core network sends an initial context establishment request message to the 5G base station (S212).

[0039] The 5G base station sends an RRC security mode command message to the user equipment (S220), and the user equipment sends an RRC security mode complete message to the 5G base station in response to the RRC security mode command (S222).

[0040] The 5G base station sends an RRC connection reconfiguration message to the user equipment (S224), and the user equipment sends an RRC connection reconfiguration complete message to the 5G base station in response to the RRC connection reconfiguration message (S226).

[0041] The 5G base station sends an initial context establishment completion message to the core network (S230).

[0042] The user equipment sends a SIP INVITE message to the IMS server through the 5G base station (S240). The IMS server initiates an IMS voice session (S242) and sends a PDU session resource modification request including content for setting the 5QI to 1 to the 5G base station (S244). Here, the PDU session resource modification request can be sent to the 5G base station through the PCF, SMF, and AMF.

[0043] The 5G base station determines whether EPS fallback is to be triggered based on the received PDU session resource modification request (S250), and sends a PDU session resource modification response to the core network (or IMS) (S252).

[0044] When the 5G base station determines that EPS fallback is to be triggered, the 5G base station sends an RRC release message including LTE frequency information for fallback to the user equipment (S254).

[0045] The user equipment having received the RRC release message changes the RAT to LTE, and performs Tracking Area Update (TAU) and bearer establishment (S260).

[0046] The core network (or IMS server) sends a SIP Ringing message to the user equipment through the LTE base station (E-UTRAN node or eNB), and the SIP Ringing message indicates that the called user equipment is in a state where the user equipment can receive calls (S270 and S272).

[0047] As mentioned above, in Figure 1 and Figure 2 In the EPS fallback scheme shown in , since the 5G base station can determine whether the EPS fallback is to be triggered only after the 5G base station receives a PDU session resource modification request from the core network (or IMS server), there is the following problem: the voice call establishment time consumed for connecting the voice call is longer than that in the NR bearer voice (VoNR) scheme.

[0048] To solve this problem, the present disclosure proposes a solution for reducing voice call setup time compared to the prior art by detecting a call service request using an RRC establishment cause included in an RRC connection request and triggering EPS fallback.

[0049] Figure 3 FIG. 1 is a flowchart illustrating a process in which a base station detects a call service request of a user equipment and triggers EPS fallback according to an embodiment of the present disclosure.

[0050] When a user equipment in an idle state initiates or receives a call, the 5G base station performs an RRC establishment process (S300) for an RRC connection to the user equipment in an idle state. In this case, the user equipment provides information indicating the reason for the RRC establishment to the 5G base station. For example, in the case of a connection for a voice call, the user equipment sets "mo-VoiceCall" in the RRC establishment cause field in the RRC connection request message and sends an RRC connection request message to the base station. At the same time, in the case of a connection for a video call, the user equipment sets "mo-VideoCall" in the RRC establishment cause field in the RRC connection request message and sends the resulting RRC connection request message to the base station.

[0051] The base station verifies that the RRC establishment cause included in the RRC Connection Request message is "mo-VoiceCall" or "mo-VideoCall" (S310 and S312).

[0052] When the RRC establishment cause is "mo-VoiceCall" or "mo-VideoCall", the base station verifies whether the base station supports VoNR (S320). To this end, a first parameter indicating whether VoNR is supported may be defined in advance in the base station.

[0053] When the base station does not support VoNR, the base station immediately triggers EPS fallback (S330). In this case, the base station triggers EPS fallback by setting the LTE frequency information for the connection of the user equipment in the field "redirectedCarrierInfo" in the RRC release message and sending the RRC release message to the user equipment.

[0054] When the base station supports VoNR, the base station verifies whether the base station is set to provide call service only in the EPS fallback scheme (S340). To this end, a second parameter indicating the call service providing scheme may be defined in advance in the base station.

[0055] When the base station is configured to provide call services only in the EPS fallback scheme, the base station immediately triggers the EPS fallback (S330).

[0056] When the base station is not set to provide call services only in the EPS fallback scheme, the base station verifies whether the user equipment supports VoNR (S350). According to an embodiment of the present disclosure, the base station can verify whether the user equipment supports VoNR by verifying the UE radio capability information in the initial context establishment request message received from the AMF. For example, when the item "VoiceOverNR" in the UE radio capability information is set to "supported", the base station can verify that the user equipment supports VoNR. At the same time, according to another embodiment of the present disclosure, when the UE radio capability is not included in the initial context establishment request message, the base station sends a UE capability query message instructing the user equipment to report the UE radio capability information. Thus, the base station can receive the UE radio capability information from the user equipment and verify whether the item "VoiceOverNR" in the UE radio capability information is set to "supported".

[0057] When the user equipment does not support VoNR, the base station immediately triggers EPS fallback (S330). When the user equipment supports VoNR, the PDU session and bearer establishment process are initiated, and then the base station provides the user equipment with a VoNR-based call service (S362).

[0058] When the RRC establishment cause is not "mo-VoiceCall" or "mo-VideoCall", the PDU session and bearer establishment process is initiated, and then the base station transmits the SIP INVITE sent by the user equipment to the IMS server (S370).

[0059] When the base station receives a PDU session resource modification request including a content for setting the 5QI to 1 from the IMS server, the base station verifies whether the IMS voice session has been initiated (S372). The base station may determine that the IMS voice session has been initiated. That is, when the base station cannot confirm the call service request of the user equipment using the RRC connection request message, for example, when the user equipment does not support RRC establishment causes related to voice calls and / or video calls or when the user equipment in the RRC connected state requests a call service, the core network (or IMS server) instructs the base station to trigger EPS fallback.

[0060] Hereinafter, the process of providing a call service to a user equipment in an idle state according to various embodiments of the present disclosure will be referred to as follows. Figures 4 to 7 Be described. Figure 4 and Figure 6 An example of a case where the base station does not support VoNR is shown, and Figure 5 and Figure 7 An example of a case where a base station supports VoNR is shown. Figures 4 to 7 When, with Figure 2 Detailed description of the same process as in the process is omitted.

[0061] Figure 4 FIG. 1 is a flowchart illustrating a call establishment process using EPS fallback according to the first embodiment of the present disclosure.

[0062] When a user equipment in the RRC idle state initiates a call, the user equipment sends an RRC connection request message "S400" to the 5G base station. In this case, when the user equipment requests RRC for a voice call connection, the user equipment sets the RRC establishment cause field in the RRC connection request message to "mo-VoiceCall". When the user equipment requests RRC for a video call connection, the user equipment sets the RRC establishment cause field in the RRC connection request message to "mo-VideoCall" and sends the RRC connection request message to the 5G base station.

[0063] The 5G base station determines whether EPS fallback is to be triggered based on the RRC establishment cause field in the RRC connection request message (S410). Here, since the 5G base station does not support VoNR, the 5G base station can verify the RRC establishment cause field to detect that the user equipment has requested voice and / or video call services, and then immediately determine whether EPS fallback is to be triggered without an additional confirmation process (e.g., verifying whether the user equipment supports VoNR, etc.).

[0064] Figure 5 FIG. 1 is a flowchart illustrating a call establishment process using EPS fallback according to a second embodiment of the present disclosure.

[0065] When a user equipment in the RRC idle state initiates a call, the user equipment sends an RRC connection request message to the 5G base station (S500). In this case, when the user equipment requests RRC for a voice call connection, the user equipment sets the RRC establishment cause field in the RRC connection request message to "mo-VoiceCall". When the user equipment requests RRC for a video call connection, the user equipment sets the RRC establishment cause field in the RRC connection request message to "mo-VideoCall" and sends the RRC connection request message to the 5G base station.

[0066] The 5G base station configures the initial UE message based on the information establishment completion message included in the RRC connection and sends the initial UE message to the core network (S510). The core network sends an initial context establishment request message to the 5G base station (S512). In this case, the core network can provide the base station with whether the user equipment supports VoNR. For example, Figure 5 An example is shown of a case where the user equipment does not support VoNR, and the core network sets the item "VoiceOverNR" of the UE radio capability information in the initial context establishment request message to "not supported" and sends the initial context establishment request message to the 5G base station.

[0067] The 5G base station determines whether EPS fallback is to be triggered based on the RRC establishment cause field in the RRC connection request message and the UE radio capability information in the initial context establishment request message (S520).

[0068] The 5G base station sends an initial context setup failure message to the core network (or IMS) (S522). In this case, the 5G base station sets the "cause" field in the initial context setup failure message to "ims-voice-eps-fallback-or-rat-fallback-triggered" to notify the core network (or IMS) of the failure caused by EPS fallback.

[0069] As in Figure 6 and Figure 7 As shown in , according to other embodiments of the present disclosure, before sending an RRC release message including LTE frequency information for fallback to the user equipment, the 5G base station is able to perform a security setup process with the user equipment.

[0070] Figure 6 FIG. 1 is a flowchart illustrating a call establishment process using EPS fallback according to a third embodiment of the present disclosure.

[0071] In the description Figure 6 When, with Figure 4 Detailed description of the same process as in the process is omitted.

[0072] The 5G base station determines whether EPS fallback is to be triggered based on the RRC Establishment Cause field in the RRC Connection Request message (S610), and then sends an Initial UE message to the core network (S611). The core network sends an Initial Context Setup Request message to the 5G base station (S612).

[0073] The 5G base station sends a security mode command message to the user equipment (S613), and the user equipment sends a security mode complete message to the 5G base station in response to the security mode command (S614).

[0074] The 5G base station sends an initial context establishment failure message S615 to the core network (or IMS). In this case, the 5G base station sets the field "cause" in the initial context establishment failure message to "ims-voice-eps-fallback-or-rat-fallback-triggered" to notify the core network (or IMS) of the failure caused by EPS fallback.

[0075] After such initial context establishment and security establishment procedures are completed, the 5G base station sends an RRC release message including LTE frequency information for fallback to the user equipment (S616).

[0076] Figure 7 FIG. 4 is a flowchart illustrating a call establishment process using EPS fallback according to a fourth embodiment of the present disclosure.

[0077] In the description Figure 7 When, with Figure 5 Detailed description of the process is omitted.

[0078] The 5G base station determines whether EPS fallback is to be triggered based on the RRC Establishment Cause field in the RRC Connection Request message and the UE radio capability information in the Initial Context Setup Request message (S720), and then sends a Security Mode Command message to the user equipment (S721). In response to the Security Mode Command, the user equipment sends a Security Mode Complete message to the 5G base station (S722).

[0079] After such a security setup process is completed, the 5G base station sends an initial context establishment failure message to the core network (or IMS) (S723) and sends an RRC release message including LTE frequency information for fallback to the user equipment (S724).

[0080] As described above, according to various embodiments of the present disclosure, compared with the EPS fallback triggering scheme according to the prior art, the initial establishment time can be shortened because the base station can directly determine whether EPS fallback is to be triggered based on, for example, the RRC establishment cause and / or UE wireless capability information.

[0081] At the same time, as in Figure 5 and Figure 7 As shown in , since a process of verifying whether the user equipment supports VoNR is required when the base station supports VoNR, the initial establishment time is shorter than that according to Figure 4 and Figure 6 The fallback trigger scheme of the embodiment shown in the embodiment is slightly lengthened, but for user equipment supporting VoNR, the VoNR scheme can be selectively used to implement services, and there is an advantage in that the initial establishment time can still be shortened compared to the EPS fallback trigger scheme according to the prior art.

[0082] Figure 8 FIG. 4 is a configuration block diagram of a base station according to an embodiment of the present disclosure.

[0083] Reference Figure 8 According to an embodiment of the present disclosure, the base station 800 includes all or part of a receiving unit 810, a determining unit 820, and a backoff triggering unit 830. Figure 8 All modules shown in the figure are essential components, and in another embodiment, part of the modules included in the base station 800 may be added, changed or deleted. That is, the components of the base station 800 for detecting a call service request of a user equipment and triggering EPS fallback according to this embodiment are exemplarily shown in FIG. Figure 8 , and it should be appreciated that, in order to implement other functions, the base station 800 may have a configuration with more or fewer components or different components than those shown.

[0084] The receiving unit 810 detects a call service request of the user equipment based on a message received from the user equipment and / or the IMS server.

[0085] The receiving unit 810 according to an embodiment of the present disclosure detects a call service request of the user equipment using an RRC connection request message received from the user equipment. Specifically, the receiving unit 810 can detect the call service request of the user equipment based on whether the RRC establishment cause field in the RRC connection request message is set to a value related to the call service request of the user equipment. Here, the value related to the call service request of the user equipment can be "mo-VoiceCall" or "mo-VideoCall".

[0086] According to another embodiment of the present disclosure, the receiving unit 810 uses the PDU session resource modification request message received from the IMS server to detect the call service request of the user equipment. Specifically, the receiving unit 810 can detect the call service request of the user equipment based on whether the 5QI included in the PDU session resource modification request message is set to 1.

[0087] The determining unit 820 determines whether the capability of the base station or the capability of the user equipment meets a preset fallback triggering condition.

[0088] According to an embodiment of the present disclosure, the determination unit 820 verifies whether the base station supports VoNR. To this end, a first parameter indicating whether the base station supports VoNR may be pre-defined in the determination unit 820. When the base station does not support VoNR, the determination unit 820 determines whether the capability of the base station satisfies a pre-set fallback trigger condition.

[0089] According to an embodiment of the present disclosure, the determination unit 820 verifies whether the base station is configured to provide call services only using the EPS fallback scheme. To this end, a second parameter indicating the call service provision scheme may be predefined in the base station. When the base station is configured to provide call services only using the EPS fallback scheme, the determination unit 820 determines whether the base station's capabilities meet a pre-defined fallback trigger condition.

[0090] According to an embodiment of the present disclosure, the determination unit 820 verifies whether the user equipment supports VoNR. The determination unit 820 can verify whether the user equipment supports VoNR by verifying the UE radio capability information in the initial context setup request message received from the AMF. For example, when the item "VoiceOverNR" in the UE radio capability information is set to "supported", the determination unit 820 can verify that the user equipment supports VoNR. At the same time, when the UE radio capability is not included in the initial context setup request message, the determination unit 820 sends a UE capability query message to the user equipment instructing the user equipment to report the UE radio capability information. Thus, the base station can receive the UE radio capability information from the user equipment and verify whether the item "VoiceOverNR" in the UE radio capability information has been set to "supported".

[0091] When the user equipment does not support VoNR, the determining unit 820 determines whether the capability of the user equipment meets a preset fallback trigger condition.

[0092] When the user equipment requests a call service and / or when the capabilities of the base station or the user equipment meet a pre-set fallback trigger condition, the fallback trigger unit 830 triggers EPS fallback. The fallback trigger unit 830 sets the LTE frequency information for the user equipment's connection in the "redirectedCarrierInfo" field in the RRC release message and sends the RRC release message to the user equipment.

[0093] Although reference has been Figures 1 to 7 The case where each process is performed in sequence is described, but this is only an example of the technical idea of ​​the embodiment of the present disclosure. In other words, since ordinary technicians in the technical field of the embodiment of the present disclosure can Figures 1 to 7 Various changes or modifications can be applied, as the process may be performed in an order altered from the order described in the foregoing, or one or more of the processes may be performed in parallel without departing from the essential features of the embodiments of the present disclosure. Figures 1 to 7 Not limited to chronological order.

[0094] The various implementation examples of the system and scheme described herein can be implemented by digital electronic circuits, integrated circuits, field programmable gate arrays (FPGAs), application specific integrated circuits (ASICs), computer hardware, firmware, software and / or combinations thereof. Various implementation examples can include the implementation of one or more computer programs executable on a programmable system. A programmable system includes at least one programmable processor (which can be a special-purpose processor or a general-purpose processor), at least one input device, and at least one output device connected to receive data and instructions from a storage system and send data and instructions to the storage system. A computer program (also referred to as a program, software, software application, or code) includes instructions for a programmable processor and is stored on a "computer-readable recording medium."

[0095] Computer-readable recording media include various recording devices that store data that can be read by a computer system. Computer-readable recording media can be non-volatile or non-transitory media such as ROMs, CD-ROMs, magnetic tapes, floppy disks, memory cards, hard disks, magneto-optical disks, and storage devices, and can also include temporary media such as data transmission media. Furthermore, computer-readable recording media can be distributed across computer systems connected via a network, and computer-readable code can be stored and executed in a decentralized manner.

[0096] Various implementation examples of the systems and solutions described herein can be implemented by programmable computers. Here, the computer includes a programmable processor, a data storage system (including volatile memory, non-volatile memory, other types of storage systems or combinations thereof) and at least one communication interface. For example, the programmable computer can be one of a server, a network device, a set-top box, an embedded device, a computer expansion module, a personal computer, a laptop computer, a personal digital assistant (PDA), a cloud computing system, and a mobile device.

[0097] Although the exemplary embodiments of the present disclosure have been described for illustrative purposes, it will be understood by those skilled in the art that various modifications, additions, and substitutions are possible without departing from the spirit and scope of the claimed invention. Therefore, the exemplary embodiments of the present disclosure have been described for the sake of brevity and clarity. The scope of the technical concept of the present embodiment is not limited by the description. Therefore, it will be understood by those skilled in the art that the scope of the claimed invention is not limited by the embodiments explicitly described above, but is defined by the claims and their equivalents.

[0098] (reference numerals)

[0099] 800: Base station 810: Receiving unit

[0100] 820: Determining unit 830: Backoff triggering unit

[0101] CROSS-REFERENCE TO RELATED APPLICATIONS

[0102] This application claims priority from Patent Application No. 10-2020-0140494 filed in South Korea on October 27, 2020, which is hereby incorporated by reference in its entirety.

Claims

1. A base station of a first wireless communication system for triggering a fallback from a first wireless communication system to a second wireless communication system, the base station comprising: a receiving unit configured to receive an RRC connection request message from a user equipment and to verify whether the user equipment requests a call service using the RRC connection request message; as well as a fallback triggering unit, configured to trigger a fallback to the second wireless communication system when the user equipment requests the call service, The fallback triggering unit is configured to trigger the fallback to the second wireless communication system before an IP Multimedia System (IMS) voice session for the user equipment is initiated.

2. The base station according to claim 1, wherein The receiving unit verifies whether an RRC establishment cause field in the RRC connection request message is set to a value related to a call service request of the user equipment.

3. The base station according to claim 2, wherein: The value associated with the call service request of the user equipment is mo-VoiceCall or mo-VideoCall.

4. The base station according to claim 1, further comprising: a determining unit configured to determine whether the capability of the base station or the capability of the user equipment meets a preset condition, The fallback triggering unit triggers the fallback to the second wireless communication system when the user equipment requests the call service and the capability of the base station or the capability of the user equipment requesting the call service meets the preset condition. The base station according to claim 4 , wherein: The determination unit verifies whether the user equipment supports the call service using the first wireless communication system based on an initial context establishment request message received from a core network of the first wireless communication system. The base station according to claim 5 , wherein: The determining unit requests the user equipment to provide the information related to whether the user equipment supports the call service using the first wireless communication system when the information related to whether the user equipment supports the call service using the first wireless communication system is not included in the initial context establishment request message.

7. The base station according to claim 1, wherein The fallback triggering unit sends an RRC release message including information about the second wireless communication system to the user equipment. The base station according to claim 7 , wherein: After the security setup procedure for the user equipment is completed, the RRC release message is sent to the user equipment.

9. A method for triggering fallback to a second wireless communication system by a base station of a first wireless communication system, the method comprising the following steps: receiving an RRC connection request message from a user equipment; verifying whether the user equipment requests a call service using the RRC connection request message; as well as triggering a fallback to the second wireless communication system when the user equipment requests the call service, The fallback to the second wireless communication system is triggered before an IP Multimedia System (IMS) voice session for the user equipment is initiated.

10. The method according to claim 9, wherein: The step of verifying whether the user equipment requests a call service comprises the following steps: verifying whether an RRC establishment cause field in the RRC connection request message is set to a value related to the call service request of the user equipment.

Images