Base station device, base station device switching method, and program

Abstract

To make it possible to provide a communication service that is highly resistant to faults in a transport network.SOLUTION: A base station device of a mobile communication network includes a context holding unit that stores an MM (Mobility Management) context and an SM (Session Management) context for each terminal connected to the base station device, and a context transfer unit that, when a handover of a terminal is detected, transfers the MM context and SM context of the terminal to a base station device that is the target of the handover.SELECTED DRAWING: Figure 12

Description

Technical Field

[0001] The present invention relates to a base station apparatus, a base station apparatus switching method, and a program, and to a base station apparatus, a base station apparatus switching method, and a program that can provide a communication service highly resistant to transport network failures.

Background Art

[0002] With the spread of MEC (Multi-access edge computing), the opportunity for terminals (UEs) to receive the provision of application services on the MEC server is increasing. By using MEC, for example, it becomes possible to reduce the response delay of application services.

[0003] Generally, each terminal in a mobile communication system communicates with an MEC server via a UPF, which is one of the network function parts of the core network. Therefore, for example, when the UPF is located in a specific data center or the like, the advantages of MEC cannot be utilized. Therefore, in the future, it is highly likely that a plurality of UPFs will be arranged in the vicinity of each base station (RAN: Radio Access Network).

[0004] Also, in the MEC architecture, a technique for providing seamless streaming even when a handover occurs has been proposed (see, for example, Patent Document 1). By adopting such an MEC architecture, it becomes possible to stably provide a low-latency network service.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] On the other hand, the current mobile communication system is vulnerable to disconnection between the RAN and the core network due to failures in the transport network. For example, when the communication of the C-plane (N2 interface, SCTP, etc.) is disconnected between the RAN and the core network, the RAN stops the cell.

[0007] In such a situation, for example, if a failure occurs in the transport network connecting the data center where servers corresponding to each network function part of the core network are arranged and the RAN, the terminals accommodated in the cells of the RAN will not be able to communicate. In such a case, for example, even if the communication between the RAN and the UPF is possible, the UE will not be able to receive the application service.

[0008] One aspect of the present invention aims to realize a technology capable of providing a communication service highly resistant to transport network failures.

Means for Solving the Problems

[0009] A base station device according to an aspect of the present invention is a base station device connected to a core network via a transport network. In the base station device of a mobile communication network, a context holding unit that stores an MM (Mobility Management) context and an SM (Session Management) context for each terminal connected to the base station device, and when detecting a handover of a terminal, a context transfer unit that transfers the MM context and the SM context of the terminal to a base station device that is a target of the handover. When a start of a system procedure is requested from the terminal, the CU (Central Unit) of the base station device executes a process corresponding to a process executed by a network function unit of the core network by calling a function for causing a computer to execute a process required in the system procedure. The CU has an SBI (Service Based Interface). When receiving a Registration Request message from the terminal, the CU receives service provision from the UDR (User Data Repository) of the core network via the SBI, and the context holding unit stores the MM context of the terminal.

[0010] A base station apparatus switching method according to an aspect of the present invention is a base station apparatus connected to a core network via a transport network. In a base station apparatus switching method of a mobile communication network, an MM (Mobility Management) context and an SM (Session Management) context are stored for each terminal connected to the base station apparatus. When a handover of the terminal is detected, the MM context and the SM context of the terminal are transferred to a base station apparatus that is the target of the handover. When a start of a system procedure is requested from the terminal, a function for causing a computer to execute processing required in the system procedure is called, so that a CU (Central Unit) of the base station apparatus executes processing corresponding to processing executed by a network function unit of the core network. The CU has an SBI (Service Based Interface). When a Registration Request message is received from the terminal, a service is received from a UDR (User Data Repository) of the core network via the SBI, and the MM context of the terminal is stored.

[0011] Each aspect of the present invention may be implemented by a computer. In this case, a program for causing a computer to execute each step of the above method, and a computer-readable recording medium on which the program is recorded also fall within the scope of the present invention.

Effect of the Invention

[0012] According to an aspect of the present invention, it is possible to realize a technique for providing a communication service highly resistant to a failure of a transport network.

Brief Description of the Drawings

[0013]

Figure 1

Figure 2

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Figure 16

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram for explaining the configuration of a general 5G mobile communication system.

[0015] In the example of FIG. 1, a radio access network (RAN) 12a, which is a base station that performs wireless communication with a terminal (UE: User Equipment) 13 within a cell, is described. Also, similar RANs 12b and 12c are described, and each base station is connected to a core network (CN) 11.

[0016] In the same figure, a router is indicated by an oval symbol. RANs 12a and 12b are connected to Router (router) #a and are connected to the core network 11 via Router #b. RAN 12c is connected to the core network 11 via Router #c. The communication path connecting the base station and the core network 11 is called a backhaul or a transport network (TN).

[0017] (Functional Configuration of Core Network and Base Station Device) FIG. 2 is a block diagram showing a functional configuration example of the core network (CN) 11 and the base station device (RAN) 12 in FIG. 1. Here, the configurations of RANs 12a, 12b, and 12c are shown collectively as the configuration of RAN 12.

[0018] In the example of FIG. 2, the core network 11 is configured to include a Subscriber DB (UDR: User Data Repository) 31, a UPF (User Plane Function) 32, and an AMF (Access and Mobility Management Function) 33.

[0019] UDR31 is a functional block mainly for storing and reading subscriber data, and storing and reading session policies. UPF32 is a functional block mainly for performing session anchor, mobility anchor, packet transfer, access control, etc. AMF33 is a functional block mainly for terminating the N2 interface, terminating the N1 interface, registration management, mobility management, etc.

[0020] In the actual core network 11, in addition to UDR31, UPF32, and AMF33, other network functional units such as SMF (Session Management Function), UDM (Unified Data Management), and PCF (Policy Control Function) are also included. In FIG. 2, the description of other network functional units is omitted.

[0021] Also, in the example of FIG. 2, the base station device 12 is composed of a gNB CU (Central Unit) 61, a gNB DU (Distributed Unit) 62, and a gNB RU (Radio Unit) 63. Note that "gNB" means gNodeB (base station) in the 5G mobile communication network. Each of gNB CU61, gNB DU62, and gNB RU63 will be hereinafter referred to as CU61, DU62, and RU63 as appropriate.

[0022] RU63 is a functional block that controls the antenna and communicates radio waves with the terminal, and also performs controls such as MIMO and beamforming. DU62 is a functional block that performs signal modulation and demodulation, MAC layer communication control, etc. CU61 is a functional block that performs PDCP (Packet Data Convergence Protocol) for controlling DU62 and RU63, connecting to the core network, encrypting packets, etc., and RRC (Radio Resource Control) processing for performing radio resource management of the terminal, etc.

[0023] Furthermore, in the example of FIG. 2, AMF33 includes an N2 processing unit 41, an N1 processing unit 42, a UE N1-MM / SM Context cache 43, an SCTP processing unit 44, and an SBI (Service Based Interface) 45.

[0024] The N2 processing unit 41 is a functional block that terminates the N2 interface, which is a connection interface between the RAN and the AMF, and controls or manages the communication of the N2 interface (for example, the transmission and reception of NGAP messages).

[0025] The N1 processing unit 42 is a functional block that terminates the N1 interface, which is an interface between the UE and the AMF, and controls or manages the communication of the N1 interface (for example, the transmission and reception of NAS messages). Further, the N1 processing unit 42 executes processes related to the generation and update of the Mobility Management Context, which is mobility management information transmitted and received as NAS messages, and the Session Management Context, which is session management information.

[0026] The UE N1-MM / SM Context cache 43 is a cache memory that stores the Mobility Management Context and the Session Management Context transmitted and received as NAS messages.

[0027] The SCTP processing unit 44 is a functional block that terminates and manages the SCTP (Stream Control Transmission Protocol) session in the communication between the core network 11 and the base station device 12.

[0028] The SBI 45 is an interface for calling various network functional units within the core network connected by the service-based architecture.

[0029] Also, in the example of FIG. 2, CU61 includes an SCTP processing unit 71 and a UPF 72. The SCTP processing unit 71 is a functional block that terminates and manages an SCTP session in the communication between the core network 11 and the base station apparatus 12. The UPF 72 is a functional block that implements the functions related to the UPF of the core network 11 in the base station apparatus 12.

[0030] In the example of FIG. 2, for example, considering the case where a terminal receives an application service provided on the MEC server, the base station apparatus 12 includes a UPF 72. A terminal authenticated by the core network can then receive an application service from an MEC server or the like located outside the core network 11 via the UPF 72 included in the CU61 of the base station apparatus 12 without going through the transport network. By doing so, it becomes possible to provide a low-latency communication service as compared with the case of going through the transport network.

[0031] The SCTP processing unit 71 includes an NGAP processing unit 81 and an Xn processing unit 82. The NGAP processing unit 81 is a functional block that performs processes such as generation, encryption, and decryption of NGAP messages. The Xn processing unit is a functional block that controls or manages the communication of the Xn interface, which is an interface for connecting base station apparatuses 12 to each other.

[0032] For example, when a failure occurs in the transport network, the SCTP session between the SCTP processing unit 44 and the SCTP processing unit 71 is disconnected, and NGAP messages cannot be transmitted or received between the N2 processing unit 41 and the NGAP processing unit 81. In this case, the base station apparatus 12 stops transmitting radio waves related to its own cell, and the terminal 13 that has been accommodated in its own cell until then becomes in a state of not being connected to either the core network 11 or the base station apparatus 12.

[0033] On one hand, the CU61 of the base station includes the UPF72. The terminal 13 that has already been authenticated by the core network 11 should then be able to receive application services from an MEC server or the like via the UPF72 of the base station apparatus 12 without going through the transport network. However, in reality, the current base station software, when a failure occurs in the transport network and the SCTP association is disconnected, executes a process to stop transmitting radio waves related to its own cell in the base station apparatus 12. Therefore, even if there is no failure in the base station apparatus 12 itself, the terminal 13 cannot receive application services.

[0034] To avoid such a situation, simply avoiding the stop of radio wave transmission related to the cell is not sufficient. For example, even when a handover occurs, it is necessary to continue communication normally.

[0035] That is, while the conventional mobile communication network attempts to provide low-latency communication services by implementing the function of the UPF in the base station apparatus, there is a problem that its tolerance to transport network failures is low.

[0036] <First Embodiment> FIG. 3 is a block diagram showing a functional configuration example of the core network (CN) 110 and the base station apparatus (RAN) 120 of the 5G mobile communication system according to this embodiment.

[0037] (Functional Configuration of Core Network) The core network 110 shown in the figure includes a Subscriber DB (UDR) 131. Network function parts other than the UDR131, such as the UPF and the AMF, may or may not be included in the core network 110.

[0038] (Functional Configuration of RAN) The base station device 120 in FIG. 3 includes a gNB CU (Central Unit) 161, a gNB DU (Distributed Unit) 162, and a gNB RU (Radio Unit) 163. Hereinafter, the base station device 120 will be appropriately referred to as RAN120, and each of the gNB CU 161, gNB DU 162, and gNB RU 163 will be appropriately referred to as CU161, DU162, and RU163, respectively.

[0039] (CU (Central Unit)) CU161 is a functional block that performs control of the DU162 and RU163 described later, connection to the core network, PDCP (Packet Data Convergence Protocol) for packet encryption, and processing of RRC (Radio Resource Control) for radio resource management of terminals. As an example, the functions of CU161 are realized by software such as a program executed by a computer.

[0040] In the example of FIG. 3, CU161 includes an SBI171, an MM / SM processing unit 172, a C-plane processing unit 173, a context holding unit 174, an SCTP processing unit 175, and a U-Plane processing unit 180.

[0041] As an example, the SBI171, MM / SM processing unit 172, C-plane processing unit 173, context holding unit 174, SCTP processing unit 175, and U-Plane processing unit 180 may be configured as instances generated by calling functions in software that executes processes corresponding to the functions of CU161.

[0042] As described later, each functional block included in CU161 executes various processes corresponding to the AMF, SMF, UPF, etc. That is, in this embodiment, in the conventional 5G mobile communication system, the base station device 120 executes the processes performed by the network function units of the core network such as the AMF, SMF, and UPF.

[0043] (SBI) SBI171 is a functional block similar to SBI45 in FIG. 2 and is an interface for receiving services from various network functional units connected by a service-based architecture. In the example of FIG. 3, SBI171 is connected by the UDR131 of the core network 110 and the service-based architecture.

[0044] (MM / SM processing unit) The MM / SM processing unit 172 is a functional block that executes the same processing as the processing executed by the N1 processing unit 42 in FIG. 2. That is, the MM / SM processing unit 172 terminates the N1 interface and controls or manages the communication of the N1 interface (for example, the transmission and reception of NAS messages). In addition, the MM / SM processing unit 172 executes processing related to the generation and update of the Mobility Management Context, which is mobility management information transmitted and received as a NAS message, and the Session Management Context, which is session management information.

[0045] The MM / SM processing unit 172 executes the processing executed by network functional units such as the AMF and SMF in a conventional 5G mobile communication system, instead of the AMF, SMF, etc.

[0046] Note that the MM / SM processing unit 172 may be an instance generated by calling a function for causing a computer to execute the above-described processing. Alternatively, it may be a part of the arithmetic processing executed in the software that realizes the functions of the CU161.

[0047] (C-plane processing unit) The C-plane processing unit 173 is a functional block that executes processing related to procedures such as UE registration and PDU session establishment. As an example, when executing registration, the C-plane processing unit 173 executes processing such as decrypting the SUCI (Subscription Concealed Identifier) and generating an Authentication Request message. Also, when executing PDU session establishment, the C-plane processing unit 173 executes processing such as decrypting the PDU Session Establishment Request message and allocating an IP address.

[0048] The C-plane processing unit 173 executes the processing that is conventionally executed by network function units such as the UDM and PCF in a 5G mobile communication system, instead of the UDM, PCF, etc.

[0049] Note that the C-plane processing unit 173 may be an instance generated by calling a function for causing a computer to execute the above-described processing. Alternatively, it may be a part of a process executed in software that realizes the functions of the CU161.

[0050] (Context holding unit) The context holding unit 174 is a functional block similar to the UE N1-MM / SM Context cache 43 in FIG. 2. That is, the context holding unit 174 is a cache memory that stores the Mobility Management Context and the Session Management Context transmitted and received as NAS messages.

[0051] (SCTP processing unit) The SCTP processing unit 175 is a functional block corresponding to the SCTP processing unit 71 in FIG. 2. The Xn processing unit 191 is a functional block that executes the same processing as the Xn processing unit 82 in FIG. 2. Different from the SCTP processing unit 71 in FIG. 2, the SCTP processing unit 175 in FIG. 3 is not provided with a functional block corresponding to the NGAP processing unit 81. That is, in the 5G mobile communication system according to the present embodiment, there is no need to perform communication via the N2 interface, that is, communication between the RAN 120 and the AMF of the core network 110.

[0052] (U-plane processing unit) The U-plane processing unit 180 is a functional block that executes various processes related to data communication related to UE application services and the like. For example, it may be a functional block that executes the same processing as the UPF 72 in FIG. 2. Note that the U-plane processing unit 180 may be an instance generated by calling a function for causing a computer to execute the same processing as the UPF 72 in FIG. 2. Alternatively, it may be a part of a process executed in the software that realizes the functions of the CU 161.

[0053] (DU (Distributed Unit) and RU (Radio Unit)) Each of the DU 162 and the RU 163 is a functional block similar to the DU 62 and the RU 63 in FIG. 2. That is, the RU 163 is a functional block that controls an antenna and performs radio wave communication with a terminal, and also performs control such as MIMO and beamforming. The DU 162 is a functional block that performs signal modulation and demodulation, MAC layer communication control, and the like.

[0054] Note that in the example of FIG. 3, only the UDR 131 is shown in the core network 110, but the core network 110 may include other network functional units.

[0055] (Detailed configuration of U-plane processing unit) FIG. 4 is a block diagram showing a detailed configuration example of the U-plane processing unit 180 in FIG. 3. In this example, the U-plane processing unit 180 includes a Session Anchor 181, a Mobility Anchor 182, a Packet Forward 183, and an Access Control 184.

[0056] Session Anchor 181 and Mobility Anchor 182 are functional blocks that terminate a PDU session. Packet Forward 182 is a functional block that executes processing related to the transfer of U-plane packets. Access Control 184 is a functional block that performs control related to a session rule described later.

[0057] (Registaraion) Next, the Registaraion in the 5G mobile communication system according to the present embodiment will be described. FIGS. 5 to 8 are diagrams for explaining the processing related to Registaraion among a terminal, a base station, and a core network. FIGS. 5 to 8 show two base stations, RAN 120A (denoted as RAN#A in the figure) and RAN 120B (denoted as RAN#B in the figure). It is assumed that both RAN#A and RAN#B have the functional configuration described above with reference to FIG. 3.

[0058] As shown in FIG. 5, a Registaraion Request message ("reg.req" in the figure) is transmitted from the UE 200 (denoted as UE#1 in the figure), which is a terminal connected to RAN 120A, to RAN 120A. The CU 161A of RAN#A acquires the SUCI (Subscription Concealed Identifier) included in the Registaraion Request message.

[0059] Such processing was executed by the AMF in the conventional 5G mobile communication system, but in the 5G mobile communication system according to the present embodiment, it is executed by the CU 161A of RAN 120A.

[0060] Then, as shown in FIG. 6, CU161A decrypts the SUCI (”decrypt SUCI” in the figure) and queries UDR131 to obtain subscriber information (”get subscriber info” in the figure). CU161A determines whether the user of the UE200 is a registered subscriber based on the obtained subscriber information. If it is determined that the user is a registered subscriber, an Authentication Request message (”auth req” in the figure) is sent to UE200. At this time, the Mobility Management context (MM#1 in the figure) is held in the context holding unit (described as MM / SM Ctx in the figure) 174A of CU161A.

[0061] Note that the Mobility Management context is generated and held for each UE that has sent a Registration Request message. In this embodiment, the subscript ”#1” is used as an indication related to UE#1. In this case, since a Registration Request message has been sent from UE#1, MM#1 is held in the context holding unit.

[0062] Furthermore, as shown in FIG. 7, UE200 sends an Authentication Response message (”auth res” in the figure) to RAN120A. CU161A that has received the Authentication Response message generates a key for encrypting the signal path used in the communication with UE200 and adds the key information to MM#1.

[0063] CU161A sends a Security Mode Command message ( "sec.mod.comm." in the figure) containing information related to key generation to UE200. Based on the received Security Mode Command message, UE200 generates a key for encrypting the signaling path and sends a Security Mode Complete message ( "sec.mod.comp." in the figure) to CU161A.

[0064] After that, as shown in FIG. 8, CU161A of RAN120A updates the information stored in UDR131 of core network 110. That is, the information indicating the state of UE#1 stored in UDR131 is updated to a state where network authentication is completed ( "registered" in the figure).

[0065] Then, CU161A of RAN120A sends a Registration Accept message ( "reg.accept" in the figure) to UE200. UE200 that has received the Registration Accept message sends a Registration Complete message ( "reg.comp." in the figure) to RAN120A. This means that the registration related to UE#1 is completed.

[0066] In this way, RAN120A is connected to the core network via the transport network, has an SBI (Service Based Interface) 171 in CU (Central Unit) 161, and when receiving a Registration Request message from UE200, receives service provision from UDR (User Data Repository) 131 of core network 110 via SBI171, and the context holding unit 174 stores the MM context of UE200.

[0067] (PDU Session Establishment) Next, the PDU Session Establishment in the 5G mobile communication system according to this embodiment will be described. FIGS. 9 and 10 are diagrams for explaining the processes related to PDU Session Establishment among a terminal, a base station, and a core network. FIGS. 9 and 10 show two base stations, RAN120A and RAN120B.

[0068] As shown in FIG. 9, from the UE200 for which Registration has been completed, a PDU Session Establishment Request message ("PDU sess.estab.req" in the figure) is transmitted to RAN120A. The PDU Session Establishment Request message contains an MM / SM message, and the CU161A of RAN#A refers to the SM (Session Management) message of the MM / SM message to obtain the session policy of UE#1 from the UDR131 ("get session policy" in the figure).

[0069] Such processing was executed by the SMF in the conventional 5G mobile communication system, but in the 5G mobile communication system according to this embodiment, it is executed by the CU161A of RAN120A.

[0070] The CU161A that has obtained the session policy of UE#1 generates the session rule of UE#1 based on the session policy by the U-plane processing unit ("insert sess.rule" in the figure). As a result, the U-plane data of UE#1 will be transmitted based on this session rule. Also, at this time, the Session Management context (SM#1 in the figure) is held in the context holding unit of the CU161A, and it means that the PDU session for UE#1 (for example, PDU#001) has been established.

[0071] In this way, when RAN120A receives a PDU session establishment request message from UE200, it receives service provision from the UDR of the core network via SBI171, and the context retention unit 174 stores the SM context of UE200.

[0072] After this, as shown in FIG. 10, UE200 can transmit and receive data with a DN (Data Network) using PDU#001. That is, UE200 can receive the provision of an application service from a server or the like on the DN.

[0073] As described above, since the CU161A of RAN120A includes the U-plane processing unit 180 described above with reference to FIGS. 3 and 4, UE200 can transmit and receive data with the DN without passing through the core network 110. It is assumed that RAN120A is connected to an MEC server, an Internet eXchange, a satellite communication system, or the like. That is, it is assumed that RAN120A having the U-plane processing unit 180 is connected to a connection interface with the DN.

[0074] In this way, CU161A executes a process corresponding to the process executed by the UPF (User Plane Function) which is a network function unit of the core network, and RAN120A is connected to a connection interface with the DN (Data Network).

[0075] As a result, for example, as shown in FIG. 11, even when a failure occurs in the transport network, the UE 200 can continue to transmit and receive data to and from the DN. In the example of FIG. 11, the symbol “X” in the figure indicates that a failure has occurred in the transport network connecting RAN 120A and RAN 120B. Thus, in the 5G mobile communication system according to the present embodiment, even when the communication between the RAN and the core network is disconnected due to a failure in the transport network, the UE that has already completed the Registration can continue to receive the application service.

[0076] (Handover) Next, the handover in the 5G mobile communication system according to the present embodiment will be described. FIG. 12 is a diagram for explaining the handover of the UE 200 performed between RAN 120A and RAN 120B.

[0077] As shown in the figure, it is assumed that the connection destination of the UE 200 has been switched from RAN #A to RAN #B due to the movement of the UE 200. In this case, an Xn handover is performed between RAN #A and RAN #B. Note that the RAN #A, which is the base station apparatus before the switching, is referred to as the Source base station apparatus, and the RAN #B, which is the base station apparatus after the switching, is referred to as the Target base station apparatus.

[0078] As described above, in the 5G mobile communication system according to the present embodiment, a context holding unit is provided in the CU of the base station apparatus. In the current case, the Mobility Management context (MM #1) and the Session Management context (SM #1) of UE #1 are held in the context holding unit 174A of the CU 161A of RAN 120A.

[0079] Therefore, when performing an Xn handover of UE#1 from RAN#A to RAN#B, it is necessary to transmit MM#1 and SM#1 from RAN#A to RAN#B. The transmission and reception of MM#1 and SM#1 between RAN#A and RAN#B are performed using the Xn interface. That is, contexts such as MM#1 and SM#1 are transmitted and received between RAN120A and RAN120B without going through the core network 110.

[0080] Since RAN120B has the same configuration as RAN120A, the context transmitted from RAN120A is held in the context holding unit 174B of CU161B of RAN120B. MM#1 and SM#1, which are the contexts of UE#1 held in the context holding unit 174A of RAN120A, are invalidated (described as expired in the figure).

[0081] In RAN#B, PDU#0001, which is the PDU session established for UE#1, is continuously used to provide a communication path between UE#1 and the DN. That is, based on SM#1 transmitted from RAN#A, data related to the U-Plane communication of UE#1 is transmitted using PDU#0001, and the data is transmitted based on the session rule.

[0082] In this way, the base station device 120A according to the present embodiment stores the MM (Mobility Management) context and the SM (Session Management) context for each terminal connected to the base station device 120, and when detecting a handover of a terminal (for example, UE200), transfers the MM context and the SM context of UE200 to the base station device 120B that is the target of the handover.

[0083] Thus, for example, even when a failure occurs in the transport network as shown in FIG. 12, handover can be performed. In the example of FIG. 12, it is shown that a failure has occurred in the transport network connecting RAN120A and RAN120B to the core network 110 by the symbol "X" in the figure. Also, the UE200 can continue to transmit and receive data with the DN at the target base station (RAN#B).

[0084] In this way, in the 5G mobile communication system according to this embodiment, even when the communication between the RAN and the core network is disconnected due to a failure in the transport network, the UE that has already completed the Registaraion can continue to receive the application service. At this time, even if a handover occurs due to the movement of the UE or the like, the UE can continue to receive the application service.

[0085] (Registaration Sequence) Next, the Registaration sequence, which is one of the system procedures executed in the 5G mobile communication system according to this embodiment, will be described. FIG. 13 is an arrow chart for explaining the Registaration sequence.

[0086] In this arrow chart, as entities that execute each step, the UE200 (UE#1), CU161A, CN-C170A, the context holding unit 174A, and the UDR131 are shown. CU161A, CN-C170A, and the context holding unit 174A are included in RAN120A. CN-C170A is an entity corresponding to the MM / SM processing unit 172 and the C-plane processing unit 173 described above with reference to FIG. 3, and may be, for example, an instance generated by CU161A calling a predetermined function.

[0087] In practice, various messages transmitted from the UE200 are actually obtained by the CU161A via the DU162A of the RAN120A. Similarly, various messages transmitted from the CU161A to the RAN120A are actually transmitted via the DU162A. Here, for simplicity of explanation, the description of the processing executed by the DU162 is omitted.

[0088] In the figure, first, a system procedure called RRCSetup is executed between the UE200 and the RAN120A. Thereafter, the Registaration is actually started (“begin Registaration”).

[0089] In step S111, the UE200 transmits a Registration Request message to the RAN120A, and in step S131, this is received by the CU161A of the RAN120A.

[0090] In step S132, the CU161A calls a function for executing various processes related to the MM / SM processing unit 172 and the C-plane processing unit 173. Here, a function call (func.call) is executed with the SUCI#1 as an argument, and in step S161, for example, the CN-C170A as an instance corresponding to the MM / SM processing unit 172 and the C-plane processing unit 173 is generated.

[0091] In step S162, the CN-C170A executes the HTTP method “GET Subsc.Info of UE#1”. As a result, in step S191, the UDR131 searches for the subscriber information of the UE#1.

[0092] In step S192, the UDR131 provides the subscriber information (Sub#1) of the UE#1 to the CN-C170, and in step S163, this is obtained by the CN-C170A.

[0093] In step S164, CN-C170A executes "Store UE#1 context" using the protocol specified by the context holding unit 174A. As a result, the Mobility Management context of UE#1 is held by the context holding unit 174A in step S181.

[0094] In step S165, CN-C170A generates "Authentication Request" as the return value for the function call in step S132, and in step S133, this is acquired by CU161A.

[0095] In step S134, CU161A transmits the Authentication Request message to UE200, and in step S112, this is received by UE200.

[0096] In step S113, UE200 transmits the Authentication Response message to RAN120A, and in step S135, this is received by CU161A.

[0097] In step S136, CU161A calls a function for executing various processes related to the MM / SM processing unit 172 and the C-plane processing unit 173. Here, a function call (func.call) is executed with AMF-UE-NGAP-ID#1 as an argument, and in step S166, for example, CN-C170A is generated as an instance corresponding to the MM / SM processing unit 172 and the C-plane processing unit 173. Then, after that, a system procedure called Authentication is executed, and UE#1 is authenticated.

[0098] In step S167, CN-C170A generates "Security mode command" as the return value for the function call in step S136, and in step S137, this is acquired by CU161A.

[0099] In step S138, CU161A sends a Security mode command message to UE200, and in step S114, this is received by UE200.

[0100] In step S115, UE200 sends a Security mode complete message to RAN120A, and in step S139, this is received by CU161A.

[0101] In step S140, CU161A calls a function for executing various processes related to the MM / SM processing unit 172 and the C-plane processing unit 173. Here, a function call (func.call) is executed with AMF-UE-NGAP-ID#1 as an argument, and in step S168, for example, CN-C170A as an instance corresponding to the MM / SM processing unit 172 and the C-plane processing unit 173 is generated.

[0102] In step S182, the context holding unit 174A executes "Load UE#1 context" using a specified protocol. Thereby, in step S169, the context related to UE#1 held by the context holding unit 174 is read into CN-C170A.

[0103] In step S170, CN-C170A executes the handle Registaraion request process. Thereby, the location information of UE# is obtained.

[0104] In step S171, CN-C170A executes "Update the state of UE#1" using the protocol specified by the context holding unit 174A. Thereby, in step S193, the subscriber information of UE#1 is updated in UDR131.

[0105] Also, in step S172, CN-C170A executes "Store UE#1 context" using the protocol specified by the context holding unit 174A. As a result, the Mobility Management context of UE#1 updated in step S183 is held by the context holding unit 174A.

[0106] In step S173, CN-C170A generates "Registration Accept" as the return value for the function call in step S140, and in step S141, this is acquired by CU161A.

[0107] In step S142, CU161A transmits a Registration Accept message to UE200, and in step S116, this is received by UE200.

[0108] In step S117, UE200 transmits a Registration complete message to RAN120A, and in step S143, this is received by CU161A.

[0109] In step S144, CU161A calls a function for executing various processes related to the MM / SM processing unit 172 and the C-plane processing unit 173. Here, a function call (func.call) is executed with AMF-UE-NGAP-ID#1 as an argument, and in step S174, for example, CN-C170A is generated as an instance corresponding to the MM / SM processing unit 172 and the C-plane processing unit 173.

[0110] In step S175, CN-C170A executes the handle Registaraion complete process. As a result, for example, a predetermined timer used at the time of registration of UE#1 is stopped.

[0111] In step S176, CN-C170A generates a return value for the function call in step S144, and in step S145, this is acquired by CU161A. Note that in the current case, for example, the return value may be Null.

[0112] Then, Registaration is terminated (“end Registaration”).

[0113] In the 5G mobile communication system according to this embodiment, Registaration as a system procedure is executed in this way.

[0114] (Sequence of PDU Session Establishment) Next, the sequence of PDU Session Establishment, which is one of the system procedures executed in the 5G mobile communication system according to this embodiment, will be described. FIG. 14 is an arrow chart for explaining the sequence of PDU Session Establishment.

[0115] In this arrow chart, as entities that execute each step, UE200 (UE#1), CU161A, CN-C170A, context holding unit 174A, U-Plane processing unit 180A, and UDR131 are shown. CU161A, CN-C170A, context holding unit 174A, and U-Plane processing unit 180A are included in RAN120A.

[0116] CN-C170A is an entity corresponding to the MM / SM processing unit 172 and C-plane processing unit 173 described above with reference to FIG. 3, and may be, for example, an instance generated by CU161A calling a predetermined function. Also, the U-Plane processing unit 180A is an entity corresponding to the U-Plane processing unit 180 described above with reference to FIG. 3, and may be, for example, an instance generated by CU161A calling a predetermined function.

[0117] In practice, various messages transmitted from the UE 200 are acquired by the CU 161A via the DU 162A of the RAN 120A. Similarly, various messages transmitted from the CU 161A to the RAN 120A are actually transmitted via the DU 162A. Here, for simplicity of explanation, the description of the processing executed by the DU 162 is omitted.

[0118] Prior to the execution of PDU Session Establishment, the Registration described above with reference to FIG. 13 is executed. After the completion of Registration, a system procedure called PFCP (Packet Forwarding Control Protocol) Association Setup is executed. After the completion of PFCP Association Setup, the process of step S201 is executed.

[0119] In step S201, the UE 200 executes Gen.PDU Session ID processing. As a result, the ID of the PDU Session to be used by itself (for example, ID#1) is generated.

[0120] In step S202, the UE 200 transmits a PDU session establishment request message to the RAN 120A, and this is received by the CU 161A of the RAN 120A in step S221.

[0121] In step S222, the CU 161A calls a function for executing various processes related to the MM / SM processing unit 172 and the C-plane processing unit 173. Here, a function call (func.call) is executed with the AMF-UE-NGAP-ID#1 as an argument, and in step S241, for example, the CN-C170A as an instance corresponding to the MM / SM processing unit 172 and the C-plane processing unit 173 is generated.

[0122] In step S271, the context holding unit 174A executes "Load UE#1 context" using the specified protocol. As a result, in step S242, the context related to UE#1 held by the context holding unit 174A is read by the CN-C170A.

[0123] In step S243, the CN-C170A executes the handle PDU session establishment request process. In this process, the CN-C170A obtains the session policy of UE#1 from the UDR131. As a result, it is determined whether the establishment of the Uplink PDU session is possible. Here, it is assumed that it is determined that the establishment of the Uplink PDU session is possible.

[0124] Thereafter, a system procedure called PFCP session establishment is executed. As a result, an Uplink session rule is inserted into the U-Plane processing unit 180A of the CU161A.

[0125] In step S244, the CN-C170A executes "Store UE#1 context" using the protocol specified by the context holding unit 174A. As a result, in step S181, the Session Management context (SM#1) of UE#1 is held by the context holding unit 174A.

[0126] In step S245, the CN-C170A generates "PDU session establishment accept" as the return value for the function call in step S222, and in step S223, this is obtained by the CU161A.

[0127] In step S224, CU161A sends a PDU session establishment accept message to UE200, and in step S203, this is received by UE200.

[0128] In step S204, UE200 sends First Uplink Data to U-plane processing unit 180A, and in step S291, this is received by U-plane processing unit 180A.

[0129] In step S225, CU161A calls a function for executing various processes related to MM / SM processing unit 172 and C-plane processing unit 173. Here, a function call (func.call) is executed with AMF-UE-NGAP-ID#1 as an argument, and in step S246, for example, CN-C170A as an instance corresponding to MM / SM processing unit 172 and C-plane processing unit 173 is generated.

[0130] In step S273, context holding unit 174A executes "Load UE#1 context" using a specified protocol. Thereby, the context related to UE#1 held by context holding unit 174A is read into CN-C170A.

[0131] In step S248, CN-C170A executes a handle PDU session resource setup request process. Thereby, it is determined whether the establishment of the Downlink PDU session is possible. Here, it is assumed that the establishment of the Downlink PDU session is determined to be possible.

[0132] Thereafter, a system procedure called PFCP session modification is executed. Thereby, a Downlink session rule is inserted into U-Plane processing unit 180A of CU161A.

[0133] In step S249, CN-C170A executes "Store UE#1 context" using the protocol specified by the context holding unit 174A. As a result, in step S274, the Session Management context of UE#1 updated along with the execution of PFCP session modification is held by the context holding unit 174A.

[0134] In step S250, CN-C170A generates "PDU session resource setup response" as the return value for the function call in step S225, and in step S226, this is acquired by CU161A.

[0135] In step S292, the U-plane processing unit 180A transmits First Downlink Data to UE200, and in step S205, this is received by UE200.

[0136] In the 5G mobile communication system according to this embodiment, PDU Session Establishment as a system procedure is executed in this way.

[0137] (Sequence of handover) Next, the sequence of Xn Handover, which is the process related to the handover of the base station executed in the 5G mobile communication system according to this embodiment, will be described. FIG. 15 is an arrow chart for explaining the sequence of Xn Handover.

[0138] In this flowchart, the entities that execute each step are shown as UE200 (UE#1), CU161A, U-Plane processing unit 180A, CU161B, CN-C170B, context holding unit 174B, and U-Plane processing unit 180B. CU161A and U-Plane processing unit 180A are included in RAN120A. CU161B, CN-C170B, context holding unit 174B, and U-Plane processing unit 180B are included in RAN120B.

[0139] CN-C170B is an entity corresponding to the MM / SM processing unit 172 and C-plane processing unit 173 described above with reference to FIG. 3, and may be, for example, an instance generated by CU161B calling a predetermined function. Also, U-Plane processing unit 180A and U-Plane processing unit 180B are entities corresponding to the U-Plane processing unit 180 described above with reference to FIG. 3, and may be, for example, instances generated by CU161A and CU161B calling a predetermined function.

[0140] In actuality, various messages transmitted from UE200 are acquired by CU161A via DU162A of RAN120A. Similarly, various messages transmitted from CU161A to RAN120A are actually transmitted via DU162A. Here, for simplicity of explanation, the description of the processing executed by DU162A is omitted.

[0141] When it is detected that the base station to which UE200 is connected has switched from RAN120A to RAN120B, a system procedure called Handover preparation is executed between RAN120A and RAN120B. Thereafter, the actual Xn Handover is started (“begin Xn Handover”).

[0142] In step S331, CU161A transmits an RRC Reconfiguration message to UE200, and this is received by UE200 in step S301.

[0143] In step S312, CU161A performs buffer downlink data processing. As a result, data (Downlink data) transmitted from the DN to UE#1 while UE#1 is currently in communication is buffered.

[0144] In step S313, CU161A transmits an SN (Serial Number) to RAN120B (SN status Transfer in the figure), and this is received by CU161B of RAN120B in step S331.

[0145] In step S314, CU161A transfers the context of UE#1 held in the context holding unit 174A, that is, the Session Management context and the Mobility Management context, to CU161B, and this is acquired by CU161B in step S331. At this time, the transfer of the context of UE#1 may be performed using the Xn interface, or may be transferred by other methods. As an example, the transfer of the context of UE#1 may be performed using gRPC (Remote Procedure Calls).

[0146] In step S333, CU161B performs Associate UE context processing. As a result, the SN status received in step S331 and the context of UE#1 acquired in step S332 are associated with each other.

[0147] In step S334, CU161B calls functions for performing various processes related to the MM / SM processing unit 172 and the C-plane processing unit 173. Here, CP A function call (func.call) is executed with UE Context Handover as an argument, and in step S361, for example, a CN-C170B is generated as an instance corresponding to the MM / SM processing unit 172 and the C-plane processing unit 173.

[0148] In step S362, CN-C170B executes "Restore UE context of source CN-C" using the protocol specified by the context holding unit 174B. From this, in step S381, the context of UE#1 is held by the context holding unit 174B.

[0149] In step S363, CN-C170B generates "CP UE Context Handover response" as the return value for the function call in step S334, and in step S335, this is acquired by CU161B.

[0150] In step S336, CU161B calls a function for executing various processes related to the MM / SM processing unit 172 and the C-plane processing unit 173. Here, A function call (func.call) is executed with UE Context Handover as an argument, and in step S391, for example, a U-Plane processing unit 180B is generated as an instance.

[0151] In step S392, the U-Plane processing unit 180B executes the Insert session rule process. As a result, a Downlink session rule is inserted into the U-Plane processing unit 180B of CU161B.

[0152] In step S393, the U-Plane processing unit 180B generates "UP UE Context Handover response" as the return value for the function call in step S336, and in step S337, this is acquired by CU161B.

[0153] In step S338, CU161B sends a UE Context Handover response message to RAN120A, and in step S315, this is received by CU161A of RAN120A.

[0154] In step S316, CU161A sends the Downlink data buffered by the processing in step S312 to RAN120B, and in step S339, this is received by CU161B of RAN120B.

[0155] In steps S302 and S340, a Random Access Procedure is executed by UE200 and CU161B of RAN120B.

[0156] Then, the Xn Handover is completed ("end Xn Handover").

[0157] In the 5G mobile communication system according to this embodiment, the Xn Handover is executed in this way.

[0158] (Effect of the First Embodiment) As described above, according to this embodiment, since the RAN120 includes the U-plane processing unit 180, the UE200 can perform data transmission and reception with the DN without going through the core network 110.

[0159] In this embodiment, during registration, in addition to communicating with the UDR 131 for obtaining and updating subscriber information, there is no need to communicate between the RAN 120 and the core network 110. Also, for the process related to PDU Session Establishment, in addition to communicating with the UDR 131 for obtaining the session policy, there is no need to communicate between the RAN 120 and the core network 110.

[0160] Therefore, according to this embodiment, even when the communication between the RAN and the core network is disconnected due to a transport network failure, a UE for which registration has already been completed can continue to receive application service provision. Thus, for example, the advantages of MEC can be fully utilized.

[0161] Furthermore, according to this embodiment, all the processes related to Xn handover are also executed by the RAN 120. Therefore, according to this embodiment, even when the communication between the RAN and the core network is disconnected due to a transport network failure, the UE can be freely moved.

[0162] Also, in this embodiment, as described above, there is no need to perform communication via the N2 interface, that is, communication between the RAN 120 and the AMF of the core network 110. For this reason, for example, when many UEs resume communication simultaneously due to the occurrence of a transport network failure, it is possible to avoid an increase in the processing load of the core network due to the concentration of N2 interface communication to the AMF of the core network. That is, it is possible to suppress the occurrence of congestion due to an increase in the processing load of the core network accompanying the occurrence of a transport network failure, which has been a conventional problem.

[0163] In this way, according to this embodiment, it is possible to realize a technology that enables the provision of a communication service with high resistance to transport network failures.

[0164] <Second Embodiment> As described above, in RAN120, in a conventional 5G mobile communication system, the processing executed by network function units of a core network such as AMF, SMF, and UPF can be executed by CU161. Therefore, the functional division between the base station device and the core network can be determined flexibly.

[0165] That is, in the above-described first embodiment, among the network function units of the core network 110, only UDR131 is configured to be called from RAN120 via SBI171, but other network function units may be further configured to be called from RAN120 via SBI171.

[0166] For example, among the network function units of the core network 110, in addition to UDR131, UDM (Unified Data Management) may be called from RAN120 via SBI171. Also, for example, all of the processing executed by network function units of the core network other than UDR can be executed by CU161.

[0167] Alternatively, for example, a network function unit that processes highly confidential information such as a user's personal information may be arranged in the core network 110 and called from RAN120 via SBI171, and the processing related to other network function units may be executed by CU161.

[0168] Alternatively, UPF may be provided separately from RAN120. For example, a server used as UPF may be arranged in the building where RAN120 is arranged, and RAN120 and UPF may be connected by a LAN or the like. In this case, the U-Plane processing unit 180 may not be included in the CU161 of RAN120.

[0169] <Example of Realization by Software> The base station apparatus 120 described above is a program for causing a computer to function, and can be realized by a program for causing a computer to function as the base station apparatus 120. In this case, the base station apparatus 120 includes a computer having at least one control device (for example, a processor) and at least one storage device (for example, a memory) as hardware for executing the above program. An example of such a computer is shown in FIG. 16.

[0170] The computer 500 includes at least one processor 501 and at least one memory 502. A program 520 for operating the computer 500 as the base station apparatus 120 is recorded in the memory 502. In the computer 500, the processor 501 reads and executes this program 520 from the memory 502, whereby each function of the base station apparatus 120 is realized.

[0171] As the processor 501, for example, a CPU (Central Processing Unit), GPU (Graphic Processing Unit), DSP (Digital Signal Processor), MPU (Micro Processing Unit), FPU (Floating point number Processing Unit), PPU (Physics Processing Unit), a microcontroller, or a combination thereof can be used.

[0172] As the memory 502, for example, a flash memory, HDD (Hard Disk Drive), SSD (Solid State Drive), or a combination thereof can be used.

[0173] Note that the computer 500 may further include a RAM (Random Access Memory) for expanding the program 520 during execution or temporarily storing various data. The computer 500 may further include a communication interface for transmitting and receiving data to and from other devices. The computer 500 may further include an input / output interface for connecting input / output devices such as a keyboard, a mouse, a display, and a printer.

[0174] Also, the program 520 for operating the computer 500 as the base station device 120 can be recorded on a non-transitory tangible recording medium 530 readable by the computer 500. As such a recording medium 530, for example, a tape, a disk, a card, a semiconductor memory, or a programmable logic circuit can be used. The computer 500 can acquire the program 520 via such a recording medium 530.

[0175] Also, the program 520 for operating the computer 500 as the base station device 120 can be transmitted via a transmission medium. As such a transmission medium, for example, a communication network or a broadcast wave can be used. The computer 500 can also acquire the program 520 via such a transmission medium.

[0176] Also, part or all of each function of the base station device 120 can be realized by a logic circuit. For example, an integrated circuit in which a logic circuit functioning as each of the above control blocks is formed is also included in the scope of the present invention. In addition to this, for example, it is also possible to realize the functions of each of the above control blocks by a quantum computer.

[0177] Furthermore, in each of the above-described embodiments, an example of applying the present invention to a 5G communication system has been described. However, the present invention can be similarly applied to a communication system configured in NF units even in a communication system after 6G.

[0178] According to each aspect of the present invention described above, by achieving the above-described operational effects, it is possible to contribute to the achievement of Goal 9, "Build the infrastructure for industry and innovation," of the Sustainable Development Goals (SDGs).

[0179] Note that the present invention is not limited to the above-described embodiments, and various modifications are possible within the scope indicated in the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0180] 〔Summary〕 The base station apparatus according to Aspect 1 of the present invention is a base station apparatus of a mobile communication network, and includes a context holding unit that stores an MM (Mobility Management) context and an SM (Session Management) context for each terminal connected to the base station apparatus, and a context transfer unit that transfers the MM context and the SM context of the terminal to a base station apparatus that is a target of handover when a handover of the terminal is detected.

[0181] The base station apparatus according to Aspect 2 of the present invention is, in the above Aspect 1, when a start of a system procedure is requested from the terminal, the CU (Central Unit) of the base station apparatus executes a process corresponding to a process executed by a network function unit of a core network by calling a function for causing a computer to execute a process required in the system procedure.

[0182] The base station apparatus according to Aspect 3 of the present invention is, in the above Aspect 2, the CU of the base station apparatus executes a process corresponding to a process executed by a UPF (User Plane Function) that is a network function unit of a core network, and the base station apparatus is connected to a connection interface with a DN (Data Netwaork).

[0183] The base station device according to aspect 4 of the present invention is connected to a core network via a transport network in the above aspect 2 or 3, has an SBI (Service Based Interface) in the CU, and when receiving a Registration Request message from the terminal, receives service provision from a UDR (User Data Repository) of the core network via the SBI, and the context holding unit saves the MM context of the terminal.

[0184] The base station device according to aspect 5 of the present invention is, in the above aspect 4, when receiving a PDU session establishment request message from the terminal, receives service provision from the UDR of the core network via the SBI, and the context holding unit saves the SM context of the terminal.

[0185] The base station device according to aspect 6 of the present invention is, in any of the above aspects 1 to 4, the handover is an Xn handover.

[0186] The base station device according to aspect 7 of the present invention is, in the above aspect 6, the context transfer unit transfers the MM context and the SM context of the terminal to the base station device that is the target of the handover using gRPC.

[0187] A method for switching a base station device according to aspect 8 of the present invention is a method for switching a base station device in a mobile communication network, which saves an MM (Mobility Management) context and an SM (Session Management) context for each terminal connected to the base station device, and when detecting a handover of the terminal, transfers the MM context and the SM context of the terminal to the base station device that is the target of the handover.

[0188] The program according to aspect 9 of the present invention causes a computer to function as a base station device in a mobile communication network, the base station device including a context holding unit that stores an MM (Mobility Management) context and an SM (Session Management) context for each terminal connected to the base station device, and a context transfer unit that transfers the MM context and the SM context of the terminal to a base station device that is a target of handover when handover of the terminal is detected.

Explanation of Signs

[0189] 110 Core Network 120 Base Station Device 131 UDR 161 CU 162 DU 163 RU 170 CN-C 171 SBI 172 MM / SM Processing Unit 173 C-Plane Processing Unit 174 Context Holding Unit 175 SCTP Processing Unit 180 U-Plane Processing Unit 181 Session Anchor 182 Mobility Anchor 183 Packet Forward 184 Access Control

Claims

1. A base station device of a mobile communication network connected to a core network via a transport network, a context holding unit that stores an MM (Mobility Management) context and an SM (Session Management) context for each terminal connected to the base station device; a context transfer unit that transfers an MM context and an SM context of the terminal to a base station device that is a target of the handover when a handover of the terminal is detected; When the start of a system procedure is requested from the terminal, a function for causing a computer to execute a process required in the system procedure is called, so that a CU (Central Unit) of the base station device executes a process corresponding to a process executed by a network function unit of a core network; The CU has a Service Based Interface (SBI), When a Registration Request message is received from the terminal, a service is provided from a User Data Repository (UDR) of a core network via the SBI, and the context holder stores the MM context of the terminal. Base station equipment.

2. The CU of the base station device executes a process corresponding to a process executed by a UPF (User Plane Function), which is a network function unit of a core network; The base station device is connected to a connection interface with a DN (Data Network). The base station device according to claim 1 .

3. When a PDU session establishment request message is received from the terminal, a service is provided from the UDR of the core network via the SBI, and the context maintenance unit stores the SM context of the terminal. The base station device according to claim 1 .

4. The handover is an Xn handover. The base station device according to claim 1 .

5. The context transfer unit transfers the MM context and the SM context of the terminal to a base station device that is a target of handover by using gRPC. The base station device according to claim 4.

6. A base station device switching method for a mobile communication network, comprising: A mobility management (MM) context and a session management (SM) context are stored for each terminal connected to the base station device; When a handover of a terminal is detected, the MM context and the SM context of the terminal are transferred to a base station device that is a target of the handover; When the start of a system procedure is requested from the terminal, a function for causing a computer to execute a process required in the system procedure is called, so that a CU (Central Unit) of the base station device executes a process corresponding to a process executed by a network function unit of a core network; The CU has a Service Based Interface (SBI), When a Registration Request message is received from the terminal, the service is provided from a User Data Repository (UDR) of the core network via the SBI, and the MM context of the terminal is stored. A base station device switching method.

7. Computer, A base station device of a mobile communication network connected to a core network via a transport network, a context holding unit that stores an MM (Mobility Management) context and an SM (Session Management) context for each terminal connected to the base station device; a context transfer unit that transfers an MM context and an SM context of the terminal to a base station device that is a target of the handover when a handover of the terminal is detected; When the start of a system procedure is requested from the terminal, a function for causing a computer to execute a process required in the system procedure is called, so that a CU (Central Unit) of the base station device executes a process corresponding to a process executed by a network function unit of a core network; the base station device is connected to a core network via a transport network; The CU has a Service Based Interface (SBI), When a Registration Request message is received from the terminal, the base station device receives a service from a User Data Repository (UDR) of a core network via the SBI, and the context holding unit functions as a base station device that stores the MM context of the terminal. program.

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