NETWORK NODE, BASE STATION DEVICE, CONTROL METHOD, AND PROGRAM FOR ENSURING AUTOMATIC ESTABLISHMENT OF Xn INTERFACE

Abstract

To enable automatic establishment of an Xn interface to be surely performed.SOLUTION: When a base station device is adaptable for a plurality of identifiers including a first identifier of the base station device corresponding to a primary network and a second identifier of the base station device corresponding to a non-primary network, a network node functioning as an AMF compliant with a 3GPP cellular communication standard stores the plurality of identifiers in association with the base station device, and when a specified message to be used for acquiring an Internet Protocol (IP) address including one identifier out of a plurality of identifiers corresponding to a second base station device is received from the first base station device, an IP address of the second base station device is provided to the first base station device irrespective of the one identifier being any one of the plurality of identifiers corresponding to the second base station device.SELECTED DRAWING: Figure 8

Description

Technical Field

[0001] The present invention relates to a technique for automatically establishing an Xn interface.

Background Art

[0002] In the 5th generation (5G) cellular communication standard of the Third Generation Partnership Project (3GPP (registered trademark)), an Xn interface is defined as a communication interface for direct communication between base station apparatuses. By using such an interface, high-speed and flexible information exchange between base station apparatuses can be performed, and thereby, for example, the handover of a terminal apparatus can be accelerated.

[0003] The Xn interface can be automatically established, for example, triggered by the handover of a terminal apparatus. In this case, when the terminal apparatus performs a handover from the first base station apparatus to the second base station apparatus, the terminal apparatus acquires the cell global identifier (CGI) of the second base station apparatus and notifies the first base station apparatus. Then, the first base station apparatus uses the Global gNB ID corresponding to the CGI to acquire the IP (Internet Protocol) address of the second base station apparatus from the Access and Mobility Management Function (AMF), and uses the IP address to perform predetermined communication with the second base station apparatus, thereby establishing the Xn interface.

Summary of the Invention

Problems to be Solved by the Invention

[0004] The automatic establishment of the Xn interface is premised on the terminal device being able to obtain the Cell Global Identity (CGI) corresponding to the Global gNB ID of the second base station device stored in the Access and Mobility Management Function (AMF). Therefore, if the terminal device cannot obtain such a CGI, it cannot obtain the IP address of the target base station device for handover, and the automatic establishment of the Xn interface cannot be completed between the source base station device for handover and the target base station device for handover.

Means for Solving the Problem

[0005] The present invention provides a technology that enables reliable execution of the automatic establishment of the Xn interface.

[0006] A network node according to an aspect of the present invention is a network node that functions as an Access and Mobility Management Function (AMF) compliant with the cellular communication standard of the 3rd Generation Partnership Project (3GPP). When one base station device corresponds to a plurality of identifiers including a first identifier of the one base station device corresponding to the primary network and a second identifier of the one base station device corresponding to a non-primary network, storage means for storing the plurality of identifiers in association with the one base station device; and when receiving, from a first base station device, a predetermined message used for obtaining an Internet Protocol (IP) address and including one of the plurality of identifiers corresponding to a second base station device, notification means for notifying the first base station device of the IP address of the second base station device regardless of which of the plurality of identifiers corresponding to the second base station device the one identifier is.

[0007] A base station device according to an aspect of the present invention complies with a cellular communication standard of the 3rd Generation Partnership Project (3GPP) and is a base station device corresponding to a plurality of identifiers including a first identifier corresponding to a primary network and a second identifier corresponding to a non-primary network. When establishing an interface for communication with a network node functioning as an Access and Mobility Management Function (AMF), it has a transmission means for transmitting a notification of the plurality of identifiers to the AMF to store the plurality of identifiers in association with the base station device. When a predetermined message used to obtain an Internet Protocol (IP) address from another base station device including one of the plurality of identifiers is received by the AMF, the IP address of the base station device is notified from the AMF to the other base station device regardless of which one of the plurality of identifiers the one identifier is.

Advantages of the Invention

[0008] According to the present invention, it becomes possible to surely execute the automatic establishment of the Xn interface.

Brief Description of the Drawings

[0009]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Embodiments for Carrying Out the Invention

[0010] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential to the invention. Two or more of the features described in the embodiments may be arbitrarily combined. Also, the same or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0011] (System Configuration) Fig. 1 shows a configuration example of the wireless communication system according to this embodiment. This wireless communication system is a cellular communication system compliant with the cellular communication standards of the fifth generation (5G) or later generations defined in 3GPP (registered trademark). This cellular communication system includes, for example, a base station device 101, a base station device 102, an Access and Mobility Management Function (AMF111), and a terminal device 121. The base station device 101 and the base station device 102 can communicate with the AMF111 by establishing an NG interface with the AMF111, for example, and can also communicate with each other via the AMF111. Note that the NG interface is a general term for each interface such as N1, N2, N3,... between core networks. The interface between the base station device and the AMF is the N2 interface, but in this embodiment, it is called the NG interface. Also, by establishing an Xn interface between the base station device 101 and the base station device 102, direct communication between the base station devices (that is, communication without going through the AMF111) can be performed. The Xn interface can be automatically set, for example, when the terminal device 121 hands over from the cell provided by the base station device 101 to the cell provided by the base station device 102.

[0012] Here, the flow of the automatic configuration process of the Xn interface will be outlined with reference to FIG. 2. First, in order to establish an NG interface with the AMF 111, the base station device 102 transmits an NG SETUP REQUEST (S201). Here, the base station device 102 includes its own identifier in this message and causes the AMF 111 to store the identifier of the base station device 102 in association with the Internet Protocol (IP) address. In the present embodiment, the term "identifier of the base station device 102" shall indicate the Global gNB ID. The Global gNB ID is represented by a combination of the Public Land Mobile Network Identifier (PLMN-ID) and the base station identifier (gNBID) of the base station device 102. Note that the base station device 102 may notify the AMF 111 of the Cell Global Identifier (CGI) instead of the Global gNB ID. The CGI is composed of the PLMN-ID, the gNBID, and the cell identifier (Cell Identity). That is, the CGI includes the Global gNB ID. In this way, the base station device 102 can notify the AMF 111 of any one identifier that can identify the device itself. When the AMF 111 receives one identifier of the base station device 102, it stores the one identifier of the base station device 102 in association with the IP address and transmits an NG SETUP RESPONSE to the base station device 102 (S202). Thereby, the NG interface between the AMF 111 and the base station device 102 is established. Although not shown in FIG. 2, the NG interface between the base station device 101 and the AMF 111 is established in the same manner.

[0013] In that state, it is assumed that it has been determined that handover of the terminal device 121 connected to the base station device 101 should be performed (S203). In this case, the terminal device 121 transmits, for example, a measurement report of the radio quality regarding the base station device 102 to the base station device in accordance with an instruction from the base station device 101 (S204). At this time, the terminal device 121 specifies, for example, the physical cell identifier (PCI) of the base station device 102 from the synchronization signal transmitted from the base station device 102, and reports the specified PCI to the base station device 101. Here, it is assumed that the base station device 101 does not hold information regarding the PCI. That is, it is assumed that the base station device 101 cannot specify the handover destination base station device (cell) from the received PCI. In this case, in order to acquire more detailed information of the base station device 102 corresponding to the PCI, the base station device 101 instructs the terminal device 121 to report the CGI included in the system information of the base station device 102 (S205). The terminal device 121 decodes system information such as System Information Block (SIB) Type1 (SIB1) transmitted from the base station device 102 in accordance with the instruction, and acquires the CGI of the base station device 102 from the system information (S206). Then, the terminal device 121 notifies the acquired CGI to the base station device 101 (S207).

[0014] The base station device 101 transmits (S208) a message (UPLINK RAN CONFIGURATION TRANSFER) used to obtain the IP address of the base station device corresponding to the identifier, which includes the identifier (Global gNB ID) corresponding to the notified CGI, to the AMF 111. The AMF 111 transmits and receives a predetermined message (DOWNLINK RAN CONFIGURATION TRANSFER / UPLINK RAN CONFIGURATION TRANSFER) (S209, S210) between itself and the base station device 102 that is stored in association with the CGI (or Global gNB ID) specified in the received message. Then, the AMF 111 transmits (S211) a DOWNLINK RAN CONFIGURATION TRANSFER including the IP address of the base station device 102 to the base station device 101. The base station device 101 uses the received IP address to establish a connection of the Stream Control Transmission Protocol (SCTP) between itself and the base station device 102 (S212). Then, the base station device 101 requests the establishment of an Xn interface between itself and the base station device 102 (S213). After that, in response to the request being accepted at the base station device 102 and a response message being transmitted to the base station device 101 (S214), an Xn interface is established between the base station device 101 and the base station device 102.

[0015] In this embodiment, the base station device 101 is configured to be operable in a Stand Alone (SA) mode that operates using only, for example, a 5G communication network (base station device and core network). Note that the base station device 101 may support operation in a Non-Standalone (NSA) mode that provides 5G communication services by at least partially utilizing a Long-Term Evolution (LTE) communication network. Here, in the NSA mode, after the terminal device is connected to the LTE base station device, a connection to the 5G base station device is added. Also, in the SA mode, the terminal device is connected to the 5G base station device without being connected to the LTE base station device. It is assumed that the base station device 102 supports both the SA mode and the NSA mode and can provide communication services to the terminal device via cells corresponding to each mode. When operating in the NSA mode, the base station device does not transmit system information (e.g., SIB1). On the other hand, when operating in the SA mode, the base station device transmits system information. In one example, a base station device that operates only in the NSA mode does not transmit system information, and a base station device that operates in the SA mode (regardless of whether it operates in parallel with the NSA mode) transmits system information. That is, the base station device 102 does not transmit system information in the NSA mode and transmits system information in the SA mode. Therefore, the terminal device 121 acquires the system information transmitted in the SA mode from the base station device 102 and does not acquire the system information in the NSA mode.

[0016] When the NSA mode and the SA mode are used in parallel in the same base station apparatus, the NSA mode network and the SA mode network are treated as separate networks, and different PLMN-IDs can be used. And, as described above, since the CGI includes the PLMN-ID, the CGI will be different when the PLMN-ID is different. That is, since the CGI is composed of a combination of the PLMN-ID and the base station identifier (gNBID), even if the gNBID is common in each CGI, a plurality of CGIs are configured due to different PLMN-IDs. In this case, for example, since the base station apparatus 102 does not transmit system information in the NSA mode, the terminal apparatus 121 cannot obtain the CGI for the NSA mode. Therefore, for example, the CGI that the terminal apparatus 121 can specify in S206 of FIG. 2 is the CGI for the SA mode included in the system information transmitted in the SA mode. Here, the base station apparatus 102 can treat the primary PLMN as the PLMN of the NSA mode and the PLMN of the SA mode as an additional PLMN. In this case, for example, as shown in FIG. 3, when establishing the NG interface, in the AMF111, for the base station apparatus 102, the Global gNB ID (or CGI) corresponding to the primary PLMN, that is, the Global gNB ID (or CGI) for the NSA mode is stored (S301). On the other hand, since the terminal apparatus 121 can only obtain the CGI for the SA mode, the base station apparatus 101 transmits a message used for obtaining the IP address to the AMF111 using the CGI for the SA mode (S302). However, in the AMF111, the Global gNB ID (or CGI) for the NSA mode is stored, but the Global gNB ID (or CGI) for the SA mode is not stored. Therefore, the AMF111 cannot determine that the CGI (or Global gNB ID) specified in the message received from the base station apparatus 101 is related to the base station apparatus 102 (S303).Therefore, AMF 111 cannot notify the base station apparatus 102's IP address to the base station apparatus 101, and the base station apparatus 101 cannot automatically establish an Xn interface with the base station apparatus 102.

[0017] In contrast, for example, the CGI corresponding to the primary PLMN can be notified. On the other hand, when the primary PLMN is used for the NSA mode, in order to prevent the terminal device 121 from connecting to such an NSA-mode cell in the SA mode, a restricted state (Barred state) may be set in the NSA-mode cell. However, for example, since it is necessary to make such a setting individually for a specific PLMN and not to make such a setting for other PLMNs, problems such as the need to add parameters for the setting may occur. Also, when the NSA-mode PLMN for which system information is not notified is primary, the setting can be changed so that the SA-mode PLMN becomes primary. However, it is necessary to reflect the change in the setting throughout the communication carrier's network, and this operation is not always easy.

[0018] In the present embodiment, in view of such a situation, a technique is provided that prevents the IP address of the base station apparatus 102 from being inappropriately notified by AMF 111 by a relatively easy procedure, and ensures that the automatic establishment of the Xn interface is performed.

[0019] In one example, in AMF111, not only the identifier corresponding to the primary PLMN in the base station device 102 (Global gNB ID or CGI, and the same applies to the following identifiers) but also the identifiers corresponding to additional PLMNs are to be stored. That is, AMF111 stores, for example, the Global gNB ID in the SA mode in addition to the Global gNB ID in the NSA mode as the identification information of the base station device 102 and associates it with the IP address of the base station device 102. In this way, AMF111 allows for the existence of multiple global identifiers of the base station device 102 and stores the multiple identifiers in association with the base station device 102. Note that this is just an example. For example, when an identifier other than the Global gNB ID for uniquely identifying the base station device is defined in future specifications, that identifier may be used. Therefore, when there are multiple identifiers that can uniquely identify the base station device, AMF111 can store the multiple identifiers in association with the base station device regardless of the type and name of the identifiers. And when AMF111 receives, for example from the base station device 101, a predetermined message (e.g., DOWNLINK RAN CONFIGURATION TRANSFER message) including any one of the multiple identifiers of the base station device 102, it notifies the base station device 101 of the IP address of the base station device 102. Here, AMF111 transmits the IP address of the base station device 102 to the base station device 101 regardless of which of the multiple identifiers associated with the base station device 102 the received one identifier is. In this way, by storing the multiple identifiers used in the base station device in association with the base station device, AMF111 can return the IP address of the base station device when a predetermined message including an identifier corresponding to an additional PLMN is received, even if a predetermined message including an identifier corresponding to the primary PLMN is not received. As a result, based on the system information transmitted in the SA mode corresponding to a non-primary PLMN from the base station device 102 and received by the terminal device 121, it becomes possible to automatically establish the Xn interface between the base station device 101 and the base station device 102.

[0020] In another example, the base station apparatus 102 may transmit, in the system information, information that enables the terminal apparatus 121 to notify the base station apparatus 101 of the CGI using the primary PLMN-ID as the CGI of the base station apparatus 102. For example, in system information such as SIB1, an area for designating the PLMN-ID of the PLMN set primarily in the own apparatus for CGI reporting is provided. The base station apparatus 102 stores and transmits, for example, the value of the NSA mode PLMN-ID in that area of the SIB1 in the SA mode. When receiving this SIB1, the terminal apparatus 121 reports to the base station apparatus 101 a CGI configured by replacing the PLMN-ID of the CGI normally reported to the base station apparatus 101 with the NSA mode PLMN-ID stored in that area. That is, normally, among the list of PLMNs included in the system information, the PLMN-ID described at the top is specified in the CGI. However, in this example, regardless of that description, the terminal apparatus 121 configures the CGI using the PLMN-ID for CGI reporting and notifies the base station apparatus 101 of the configured CGI as the CGI of the base station apparatus 102. Therefore, the NSA mode PLMN-ID set primarily for the base station apparatus 102 as the PLMN-ID for CGI reporting is notified to the terminal apparatus 121 by the system information, so that the CGI including the PLMN-ID and the gNBID is notified to the base station apparatus 101. Then, the base station apparatus 101 notifies the AMF111 of the Global gNB ID configured by the NSA mode PLMN-ID and the gNBID. Here, in the AMF111, the Global gNB ID configured by the NSA mode PLMN-ID and the gNBID is stored in association with the base station apparatus 102. Therefore, the AMF111 can return the IP address of the base station apparatus 102 to the base station apparatus 101. In this way, in this example, even if the information of the Global gNB ID configured by the SA mode PLMN-ID and the gNBID is not held in the AMF111, the IP address of the base station apparatus 102 is notified to the base station apparatus 101.This makes it possible to automatically establish the Xn interface between the base station apparatus 101 and the base station apparatus 102 based on the system information transmitted by the SA method and received by the terminal apparatus 121.

[0021] (Device Configuration) FIG. 4 shows an example of the hardware configuration of each device according to the present embodiment. In one example, each device includes a processor 401, a ROM 402, a RAM 403, a storage device 404, and a communication circuit 405. The processor 401 is a computer including one or more processing circuits such as a general-purpose CPU (Central Processing Unit) or an ASIC (Application Specific Integrated Circuit), and reads and executes programs stored in the ROM 402 and the storage device 404 to execute the overall processing of the device and each of the above-described processes. The ROM 402 is a read-only memory that stores information such as programs related to the processing executed by each device and various parameters. The RAM 403 functions as a workspace when the processor 401 executes a program, and is a random access memory that stores temporary information. The storage device 404 is configured by, for example, a removable external storage device or the like. The communication circuit 405 is configured by, for example, a circuit capable of communicating with other devices. For example, the communication circuit 405 of the terminal apparatus and the base station apparatus includes a baseband circuit, a radio frequency (RF) circuit, an antenna, etc. for providing a radio interface capable of radio communication conforming to the cellular communication standard. In addition, the communication circuit 405 of the base station apparatus includes a circuit for wired or wireless communication that enables communication with other base station apparatuses, network nodes, external devices, etc. In addition, the communication circuit 405 of the AMF includes a circuit that enables communication with the base station apparatus. Note that although one communication circuit 405 is illustrated in FIG. 4, each device may have a plurality of communication circuits.

[0022] FIG. 5 is a diagram showing an example of the functional configuration of a base station apparatus. The base station apparatus includes, for example, an NG establishment processing unit 501, an information notification unit 502, and an Xn establishment processing unit 503. Note that these functions can be implemented, for example, by a processor 401 executing a program stored in a ROM 402 or a storage device 404. However, this is just an example, and the functions in FIG. 5 may be realized by other configurations. Also, the functions shown in FIG. 5 are just an example, and the function blocks shown in FIG. 5 may be implemented integrally with other function blocks, or one function block may be divided into a plurality of function blocks. Also, some functions may be omitted, or additional functions may be added. For example, in FIG. 5, only the functions particularly related to this embodiment among the functions of the base station apparatus are shown, and the base station apparatus naturally has the functions of a base station apparatus in a normal cellular communication system that are not shown in FIG. 5.

[0023] The NG establishment processing unit 501 executes processing for establishing an NG interface (N2 interface) with the AMF 111. As part of the processing for establishing the NG interface, the NG establishment processing unit 501 transmits an NG SETUP REQUEST message to the AMF 111 and receives an NG SETUP RESPONSE message from the AMF 111. The NG establishment processing unit 501 notifies the AMF 111 of information that enables the identification of its own Global gNB ID in the NG SETUP REQUEST message. For example, in the first processing example described later, the NG establishment processing unit 501 notifies the AMF 111 of the PLMN-ID corresponding to each of a plurality of PLMNs and the gNBID of its base station apparatus. Also, the NG establishment processing unit 501 may notify the AMF 111 of a plurality of Global gNB IDs corresponding to each PLMN. Also, in the second processing example described later, the NG establishment processing unit 501 may notify the AMF 111, for example, of the PLMN-ID and gNBID of a set of primary PLMNs, or one Global gNB ID corresponding to the PLMN-ID. That is, even when a plurality of PLMNs are used, the NG establishment processing unit 501 can notify the AMF 111 of information that enables the identification of one Global gNB ID.

[0024] When the information notification unit 502 operates in the SA mode, it notifies the terminal device 121 of system information such as SIB1. Note that when the information notification unit 502 operates only in the NSA mode and does not operate in the SA mode, it does not notify the system information. In the first processing example described later, the information notification unit 502 notifies normal system information. That is, the system information can include a list of a plurality of PLMNs, and the system information notified in the SA mode has information regarding the PLMN of the SA mode stored at the head of the list of the plurality of PLMNs and is transmitted. On the other hand, in the second processing example described later, the information notification unit 502 notifies the system information including, in addition to the list of the PLMNs, information specifying the PLMN-ID for configuring the CGI. This information may be, for example, a value indicating the PLMN-ID constituting the CGI, or a pointer for pointing to any one of the list of PLMNs. In addition to this, any information capable of specifying the CGI corresponding to the primary PLMN may be notified instead of the information specifying the PLMN-ID for configuring the CGI. That is, the information notification unit 502 includes in the system information any information for enabling the terminal device to configure the CGI using a PLMN different from the PLMN notifying the system information and notifies it.

[0025] The Xn establishment processing unit 503 performs processing for establishing the Xn interface. For example, when the Xn establishment processing unit 503 receives a radio quality measurement report regarding a PCI not registered as the physical cell identifier (PCI) of an adjacent cell from the terminal device, it decodes the system information transmitted from the base station device that is the transmission source of the PCI and instructs to acquire the CGI. Then, when the Xn establishment processing unit 503 acquires the CGI from the terminal device, it notifies the AMF 111 of the Global gNB ID specified by the CGI and acquires the IP address of the base station device corresponding to the CGI. The Xn establishment processing unit 503 uses the acquired IP address to communicate with the base station device corresponding to the CGI and establishes the Xn interface.

[0026] FIG. 6 is a diagram showing a functional configuration example of a network node that functions as an AMF. The network node includes, for example, an information receiving unit 601, an information storage unit 602, and an IP address notification unit 603. Note that these functions can be implemented, for example, by a processor 401 executing a program stored in a ROM 402 or a storage device 404. However, this is just an example, and the functions in FIG. 6 may be realized by other configurations. Also, the functions shown in FIG. 6 are just an example, and the function blocks shown in FIG. 6 may be implemented integrally with other function blocks, or one function block may be divided into a plurality of function blocks. Further, some functions may be omitted, or additional functions may be added. For example, in FIG. 6, only the functions particularly related to this embodiment among the functions of the AMF are shown, and the network node naturally has the functions of the AMF in a normal cellular communication system that are not shown in FIG. 6.

[0027] The information receiving unit 601 receives, from a base station device, information that can identify the Global gNB ID of the base station device. In the first processing example described later, when the base station device uses a plurality of PLMNs, the information receiving unit 601 receives information that can identify the Global gNB ID corresponding to each of the plurality of PLMNs. On the other hand, in the second processing example described later, even when the base station device uses a plurality of PLMNs, the information receiving unit 601 receives information that can identify one Global gNB ID corresponding to the primary PLMN. Also, the information receiving unit 601 receives, from the base station device, information that can identify the Global gNB ID of another base station device in a predetermined message used to obtain the IP address of the other base station device.

[0028] The information storage unit 602 stores the Global gNB ID identified based on the information notified from the base station apparatus in association with that base station apparatus. For example, in the first processing example described later, when a plurality of Global gNB IDs corresponding to a plurality of PLMNs are respectively identified, the information storage unit 602 stores the plurality of Global gNB IDs in association with one base station apparatus. That is, the information storage unit 602 stores not only the identifier corresponding to the primary PLMN but also the identifier corresponding to the additional PLMN. On the other hand, in the second processing example described later, even when there are a plurality of PLMNs that can be used by the base station apparatus, the information storage unit 602 stores only one identifier corresponding to the primary PLMN in association with that base station apparatus. In the second processing example, the information reception unit 601 may receive information that can identify the Global gNB ID corresponding to each of the plurality of PLMNs, but even in this case, the information storage unit 602 stores only the Global gNB ID corresponding to the primary PLMN.

[0029] The IP address notification unit 603 identifies a second base station apparatus associated with the Global gNB ID specified by the information included in a predetermined message used to obtain the IP address of another base station apparatus, which is received from the first base station apparatus by the information reception unit 601, and obtains the IP address information of the second base station apparatus. For example, the IP address notification unit 603 can obtain the IP address of the second base station apparatus by making an inquiry to the second base station apparatus or another network node. Also, the information storage unit 602 may store the IP address information of the second base station apparatus, and in this case, the IP address notification unit 603 may obtain the IP address of the second base station apparatus by searching the information stored in the information storage unit 602. The IP address notification unit 603 notifies the obtained IP address to the first base station apparatus.

[0030] Note that in the second processing example described below, the AMF only needs to perform its functions as a conventional AMF. On the other hand, in the first processing example described below, the AMF is configured to associate and store a plurality of global identifiers (Global gNB ID) with respect to one base station device, and to return the IP address of the base station device in response to an inquiry accompanied by information specifying any one of the plurality of identifiers.

[0031] FIG. 7 is a diagram showing an example of the functional configuration of a terminal device. The terminal device includes, for example, a system information receiving unit 701 and a CGI notifying unit 702. Note that these functions can be implemented, for example, by a processor 401 executing a program stored in a ROM 402 or a storage device 404. However, this is just an example, and the functions in FIG. 7 may be realized by other configurations. Also, the functions shown in FIG. 7 are just an example, and the functional blocks shown in FIG. 7 may be implemented integrally with other functional blocks, or one functional block may be divided into a plurality of functional blocks. Further, some functions may be omitted, or additional functions may be added. For example, in FIG. 7, only the functions particularly related to the present embodiment among the functions of the terminal device are shown, and the network node naturally has the functions of the terminal device in a normal cellular communication system that are not shown in FIG. 7.

[0032] The system information receiving unit 701 receives system information (e.g., SIB1) transmitted from a candidate base station apparatus of a handover destination in accordance with an instruction from, for example, the connected base station apparatus. The CGI notification unit 702 constructs a CGI from the information included in the system information received by the system information receiving unit 701 and notifies the constructed CGI to the base station apparatus that transmitted the reception instruction of the system information. In the first processing example described later, the CGI notification unit 702 constructs a CGI in the same manner as in the prior art based on the received system information and notifies the constructed CGI to the connected base station apparatus. On the other hand, in the second processing example described later, the CGI notification unit 702 can acquire a PLMN-ID for CGI construction from the system information transmitted from a candidate base station apparatus of a handover destination. Then, the CGI notification unit 702 can construct a CGI in which the PLMN-ID part is replaced using the PLMN-ID for CGI calibration and notify the constructed CGI to the connected base station apparatus.

[0033] (Flow of processing) <Processing example 1> Next, in AMF 111, a first processing example in which a plurality of identifiers (Global gNB ID) of the base station apparatus 102 are stored and the IP address of the base station apparatus 102 is returned in response to any inquiry accompanied by one of those identifiers will be outlined with reference to FIG. 8. In this processing example, the base station apparatus 102 notifies the AMF 111 of a list of PLMN-IDs used by the own apparatus and a base station identifier (gNBID) in an NG SETUP REQUEST message transmitted, for example, when establishing an NG interface with the AMF 111. When the base station apparatus 102 uses a plurality of PLMNs, the base station apparatus 102 notifies the AMF 111 of a plurality of PLMN-IDs corresponding to each of the plurality of PLMNs. Note that the gNBID may be common to a plurality of PLMNs or may be different. That is, information capable of specifying a plurality of Global gNB IDs corresponding to a plurality of PLMNs is notified from the base station apparatus 102 to the AMF 111, and in that regard, the notified information may have any format. For example, a combination of a PLMN-ID and a gNBID may be notified from the base station apparatus 102 to the AMF 111, or a Global gNB ID may be notified. In another example, any information that enables the Global gNB ID to be reproduced based on the information held in the AMF 111 may be notified from the base station apparatus 102 to the AMF 111. Then, the AMF 111 transmits a response message to the base station apparatus 102 to establish an NG interface (S802), and on the other hand, stores the notified plurality of identifiers (Global gNB ID) in association with the base station apparatus 102 (S803).

[0034] Thereafter, assume that a message used to acquire an IP address, which specifies an identifier (Global gNB ID) corresponding to the SA mode PLMN of the base station apparatus 102, is transmitted from the base station apparatus 101 to the AMF 111 (S804). For example, when the terminal apparatus 121 connected to the base station apparatus 101 sets the base station apparatus 102 as a handover destination candidate and acquires the CGI of the base station apparatus 102 and notifies the base station apparatus 101 of the CGI, the base station apparatus 101 may transmit this message to the AMF 111. The base station apparatus 101 transmits a message to the AMF 111 in order to acquire the IP address of the base station apparatus 102 corresponding to the identifier by specifying the identifier corresponding to the CGI notified from the terminal apparatus 121. The terminal apparatus 121 receives, for example, system information transmitted in the SA mode from the base station apparatus 102, specifies the CGI based on the PLMN-ID corresponding to the SA mode, and transmits the CGI to the base station apparatus 101. The base station apparatus 101 specifies the Global gNB ID corresponding to the CGI and transmits a message including the Global gNB ID to the AMF 111. When the PLMN corresponding to the SA mode is not the primary PLMN, the conventional AMF cannot return the IP address corresponding to the base station apparatus 102. On the other hand, in this processing example, in S803, the Global gNB ID corresponding to an additional PLMN that is not the primary PLMN is also stored in the AMF 111 in association with the base station apparatus 102. Therefore, the AMF 111 can identify that the specified Global gNB ID corresponds to the base station apparatus 102 based on the information, and can notify the base station apparatus 101 of the IP address of the base station apparatus 102 based on the identification result (S805). Note that in FIG. 8, for simplicity of explanation, an example is shown in which the AMF 111 receives the message of S804 and then returns the IP address to the base station apparatus 101 without performing any communication with the base station apparatus 102, but the present invention is not limited to this. That is, in this processing example as well, the same processing as S209 and S210 in FIG. 2 may be performed.

[0035] <Processing Example 2> Next, with reference to FIG. 9, a second processing example will be outlined in which the base station apparatus 102 notifies the system information including the PLMN-ID to be used for configuring the CGI when reporting the CGI, and the terminal apparatus 121 configures the CGI using the PLMN-ID and reports it to the base station apparatus 101. Since this processing is the processing in which the processing of S206 and S207 in FIG. 2 is changed as compared with the conventional case, FIG. 9 shows a part corresponding to the processing in FIG. 2 extracted, and steps performing the same processing as in FIG. 2 are denoted by the same reference numerals.

[0036] This processing example is performed to identify the Global gNB ID of the primary PLMN of the base station device 102 at the base station device 101 based on the CGI reported from the terminal device 121. The base station device 102 includes, in the AMF 111, the value of the PLMN-ID corresponding to the Global gNB ID stored in association with its own device as the PLMN-ID for configuring the CGI in the system information, and notifies the system information (S901). When the terminal device 121 receives this system information, it configures a CGI in which the PLMN-ID part of the conventionally reported CGI is replaced with the PLMN-ID for configuring the CGI, and reports the CGI to the base station device 101 (S902). That is, conventionally, a CGI including the first PLMN-ID (for example, related to the PLMN of the system information transmitter) described at the head of the PLMN list and the gNB ID is configured and reported. However, in this processing example, regardless of the PLMN list, a CGI including the second PLMN-ID for configuring the CGI and the gNB ID is configured and reported. In one example, the base station device 102 notifies system information of the SA mode including the PLMN-ID for the NSA mode PLMN, which is the primary PLMN, as the PLMN-ID for configuring the CGI. The terminal device 121 normally reports a CGI including the SA mode PLMN-ID and the gNB ID to the base station device 101. However, in this processing example, without using the SA mode PLMN-ID, a CGI including the NSA mode PLMN-ID and the gNB ID is reported to the base station device 101. Thus, according to this processing example, the terminal device 121 can configure and report to the base station device 101 a CGI corresponding to the NSA mode PLMN for which the system information is not notified.

[0037] When the base station device 101 receives this CGI, it specifies a Global gNB ID consisting of a PLMN-ID for the primary PLMN and a gNB ID, and transmits a message used for obtaining an IP address to the AMF 111 (S208). Here, even if the AMF 111 stores only the Global gNB ID corresponding to the primary PLMN for the base station device 102, due to the processes of S901 and S902, in S208, that Global gNB ID will be specified. Therefore, the AMF 111 can identify the IP address of the base station device 102 and notify the base station device 101 of that IP address (S208 to S210).

[0038] In addition, in Processing Example 2, an example in which system information including the PLMN-ID for configuring the CGI is notified from the base station device 102 has been described, but it is not limited to this. For example, instead of the PLMN-ID for configuring the CGI, a Global gNB ID or the CGI itself may be specified within the system information as information for reporting the CGI. Note that the information for configuring or reporting the CGI can be set in the base station device 102 so that the CGI corresponding to the Global gNB ID stored in association with the base station device 102 in the AMF 111 is reported from the terminal device 121. When, as in Processing Example 1, the AMF 111 stores Global gNB IDs corresponding to two or more of the plurality of PLMNs that the base station device 102 can use, the information specified in the system information can be set so that a CGI corresponding to any one of the two or more Global gNB IDs is configured. That is, Processing Example 1 and Processing Example 2 can also be used in combination.

[0039] In this way, by means of at least one of the above-described Processing Example 1 and Processing Example 2, the CGI corresponding to the Global gNB ID stored in association with the base station apparatus 102 in the AMF 111 can be reported from the terminal apparatus 121 to the base station apparatus 101. As a result, the AMF 111 can surely notify the base station apparatus 101 of the information on the IP address of the base station apparatus 102, and the automatic establishment of the Xn interface can be more surely completed. Therefore, it becomes possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, "Build resilient infrastructure, promote inclusive and sustainable industrialization and foster innovation."

[0040] The invention is not limited to the above-described embodiments, and various modifications and changes are possible within the scope of the gist of the invention.

Claims

1. A network node that functions as an Access and Mobility Management Function (AMF) compliant with the cellular communication standard of the 3rd Generation Partnership Project (3GPP), storage means for storing the plurality of identifiers including a first identifier of the one base station device corresponding to the primary network and a second identifier of the one base station device corresponding to a non-primary network in association with the one base station device when the one base station device corresponds to the plurality of identifiers; notification means for notifying the first base station device of the IP address of the second base station device regardless of which of the plurality of identifiers corresponding to the second base station device the one identifier included in the received predetermined message for obtaining an Internet Protocol (IP) address from the first base station device to the second base station device is; A network node characterized by comprising the above.

2. The network node according to claim 1, wherein in the primary network, system information is not notified by the second base station device, and in the non-primary network, system information is notified by the second base station device.

3. The predetermined message is transmitted from the first base station device to the network node in response to the terminal device connected to the first base station device receiving information on a cell identifier corresponding to the second identifier included in the system information notified from the second base station device when the terminal device hands over to the second base station device and the terminal device notifying the first base station device of the cell identifier. The network node according to claim 2, characterized by the above.

4. The storage means according to claim 1, wherein when establishing an interface for communication between the one base station device and the network node, the storage means obtains and stores information on the plurality of identifiers used in the one base station device from the one base station device. The network node according to claim 1, characterized by the above.

5. The plurality of identifiers each include a different Public Land Mobile Network Identifier (PLMN-ID) and a common base station identifier for identifying a base station device that uses the plurality of identifiers, and the network node according to claim 1 is characterized in that.

6. A base station device corresponding to a plurality of identifiers including a first identifier corresponding to a primary network and a second identifier corresponding to a non-primary network, which complies with the cellular communication standard of the 3rd Generation Partnership Project (3GPP). When establishing an interface for communication with a network node functioning as an Access and Mobility Management Function (AMF), there is a transmission means for transmitting a notification of the plurality of identifiers for storing the plurality of identifiers in association with the base station device to the AMF. When a predetermined message used to obtain an Internet Protocol (IP) address from another base station device including one of the plurality of identifiers is received by the AMF, regardless of which of the plurality of identifiers the one identifier is, the AMF notifies the other base station device of the IP address of the base station device, and the base station device is characterized in that.

7. In the primary network, system information is not notified by the base station device, and in the non-primary network, system information is notified by the base station device, and the base station device according to claim 6 is characterized in that.

8. The plurality of identifiers each include a different Public Land Mobile Network Identifier (PLMN-ID) and the base station identifier of the common base station device, and the base station device according to claim 6 is characterized in that.

9. A control method executed by a network node functioning as an Access and Mobility Management Function (AMF) compliant with the cellular communication standard of the 3rd Generation Partnership Project (3GPP). When one base station device corresponds to a plurality of identifiers including a first identifier of the one base station device corresponding to a primary network and a second identifier of the one base station device corresponding to a non-primary network, storing the plurality of identifiers in association with the one base station device; When receiving, from a first base station device, a predetermined message used for obtaining an Internet Protocol (IP) address including one identifier of the plurality of identifiers corresponding to a second base station device, notifying the first base station device of the IP address of the second base station device regardless of which of the plurality of identifiers the one identifier corresponds to; A control method characterized by including the above.

10. A control method executed by a base station device corresponding to a plurality of identifiers including a first identifier corresponding to a primary network and a second identifier corresponding to a non-primary network, compliant with the cellular communication standard of the 3rd Generation Partnership Project (3GPP), When establishing an interface for communication with a network node functioning as an Access and Mobility Management Function (AMF), transmitting, to the AMF, a notification of the plurality of identifiers for storing the plurality of identifiers in association with the base station device, When a predetermined message used for obtaining an Internet Protocol (IP) address from another base station device including one identifier of the plurality of identifiers is received by the AMF, the IP address of the base station device is notified from the AMF to the other base station device regardless of which of the plurality of identifiers the one identifier is, A control method characterized by the above.

11. A program for causing a computer to function as each means of the network node according to any one of Claims 1 to 5.

12. A program for causing a computer to function as each means of the base station device according to any one of Claims 6 to 8.

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