Network device, user terminal, and network registration method

Abstract

To make it possible to expand multipath communication.SOLUTION: In a mobile communication system having a core network connected to a plurality of radio access networks, when a "multi-access PDU session" establishment request is received from a user terminal, a network device provided in the core network includes SPLMN (Secondary PLMN) information to be provided to the user terminal in a response to the "multi-access PDU session" establishment request to the user terminal.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a network device, a user terminal, and a network registration method.

Background Art

[0002] Conventionally, the fifth-generation mobile communication system (5G system) standardized by "3GPP (registered trademark) (3rd Generation Partnership Project)" is known (see, for example, Non-Patent Documents 1 and 2). FIG. 7 is a diagram showing a schematic architecture of the 5G system. In FIG. 7, the 5G system is composed of various NFs (Network Functions) such as UE (User Equipment), RAN (Radio Access Network), UPF (User Plane Function) of CN (Core Network), and the control plane (Control plane: C-plane) of CN. Examples of the NFs in the C-plane of CN include AMF (Access and Mobility Management Function), SMF (Session Management Function), and PCF (Policy Control Function).

[0003] Here, the logical communication path established between the UE and the CN (UPF) for the UE to use the mobile communication service is referred to as a "session". Also, the session established between the UE and the CN (UPF) using multiple radio paths is referred to as a "multi-access session". Non-Patent Documents 1 and 2 define "Multi-access PDU (Packet Data Unit) Session (hereinafter referred to as "MA PDU Session")" as an example of a multi-access session. FIG. 8 is a diagram showing a configuration example of the "MA PDU Session". As shown in FIG. 8, the UE establishes a "MA PDU Session" with the CN (UPF) using a radio path via the RAN which is "3gpp access" and a radio path via a wireless LAN (Local Area Network) such as, for example, "Wi-Fi (registered trademark)" which is "non-3gpp access". "3gpp access" is an access network defined by 3GPP. "non-3gpp access" is an access network other than "3gpp access". The UE uses its "MA PDU Session" to send and receive data to and from a DN (Data Network, data network) such as the Internet outside the 5GC (CN of the 5G system). By using the "MA PDU Session", the UE can obtain the effect of improving communication quality such as expanding the communication bandwidth, reducing communication delay, and ensuring communication path redundancy.

Prior Art Documents

Non-Patent Documents

[0004]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the next generation 5G (Beyond 5G) system and the sixth generation mobile communication system (6G system), multipath communication can be utilized as a means for achieving service requirements such as ultra-high capacity (100 Gbps class) and ultra-low latency (1 ms or less) for communication per user. However, the "MA PDU Session" described in Non-Patent Documents 1 and 2 as a multi-access session for realizing multipath communication is limited to a combination of "one 3GPP access (e.g., 5G base station)" and "one non-3GPP access (e.g., wireless LAN)," and therefore the service area of multipath communication in which a UE can achieve ultra-high capacity communication and ultra-low latency is limited.

[0006] Therefore, if a multi-access session can be established using two arbitrarily selected "3gpp access" (base stations) without limiting the PLMN (Public Land Mobile Network) (i.e., without limiting the communication carrier that manages the base station to which the UE is connected), the service area of multipath communication will be significantly expanded, allowing many users to enjoy the benefits of multipath communication, such as ultra-high capacity communication and ultra-low latency.

[0007] Here, consider a case where a UE performs an initial network registration with a certain PLMN (first PLMN), selects a next PLMN (a PLMN (second PLMN) that may be the same as or different from the first PLMN), and performs a second network registration with the selected second PLMN. It is preferable for the CN to notify the UE which PLMN is appropriate for the UE to select as the second PLMN. However, conventional 5G systems do not specify a method for notifying the UE of candidates for the second PLMN from the CN.

[0008] The present invention has been made in consideration of the above circumstances, and its object is to expand multipath communication. [Means for solving the problem]

[0009] One aspect of the present invention is a network device provided in a core network of a mobile communication system including a core network connected to a plurality of radio access networks, the network device being configured to include, in a response to a "Multi-access PDU Session" establishment request from a user terminal, SPLMN (Secondary PLMN) information provided to the user terminal.

[0010] One aspect of the present invention is a network device provided in a core network of a mobile communication system including a core network connected to a plurality of radio access networks, the network device being configured to include, in a response to a "Service Request" from a user terminal, SPLMN (Secondary PLMN) information provided to the user terminal.

[0011] One aspect of the present invention is a user terminal of a mobile communication system including a core network connected to a plurality of radio access networks, the user terminal including a network registration control unit configured to execute a network registration process for a new radio access network based on received SPLMN information when the SPLMN (Secondary PLMN) information is received from the core network.

[0012] One aspect of the present invention is a user terminal of a mobile communication system including a core network connected to a plurality of radio access networks. When receiving SPLMN (Secondary PLMN) information from the core network, if a new radio access network determined based on the received SPLMN information is different from the radio access network that is already connected, a network registration control unit executes a network deregistration process for the already connected radio access network for which network registration has been completed. The user terminal includes the network registration control unit.

[0013] One aspect of the present invention is a network registration method in a mobile communication system including a core network connected to a plurality of radio access networks. When there is a "Multi-access PDU Session" establishment request from a user terminal, a network device provided in the core network includes SPLMN (Secondary PLMN) information provided to the user terminal in a response to the "Multi-access PDU Session" establishment request to the user terminal. The user terminal determines a radio access network to be next connected based on the SPLMN information included in the response, and makes a network registration request for the determined radio access network.

[0014] One aspect of the present invention is a network registration method in a mobile communication system including a core network connected to a plurality of radio access networks. When there is a "Service Request" from a user terminal, a network device provided in the core network includes SPLMN (Secondary PLMN) information provided to the user terminal in a response to the "Service Request" to the user terminal. The user terminal determines a radio access network to be next connected based on the SPLMN information included in the response, and makes a network registration request for the determined radio access network.

[0015] One aspect of the present invention is a network registration method in a mobile communication system including a core network connected to a plurality of radio access networks, wherein when a user terminal receives SPLMN (Secondary PLMN) information from the core network, the user terminal executes a network registration process for a new radio access network based on the received SPLMN information.

[0016] One aspect of the present invention is a network registration method in a mobile communication system including a core network connected to a plurality of radio access networks, wherein when a user terminal receives SPLMN (Secondary PLMN) information from the core network, and when a new radio access network determined based on the received SPLMN information is different from the radio access network that is already connected, the user terminal executes a network deregistration process for the already connected radio access network for which network registration has been completed.

Advantages of the Invention

[0017] According to the present invention, an effect of expanding multi-path communication can be obtained.

Brief Description of the Drawings

[0018]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0019] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration example of a mobile communication system according to an embodiment. In FIG. 1, a UE (User Equipment) 10 can be connected to a RAN (Radio Access Network) 30 (30_1, 30_2) which is "3gpp access". RAN30_1 is the RAN of the first PLMN. RAN30_2 is a candidate RAN of the second PLMN. The first PLMN and the second PLMN may be the same PLMN (that is, the same communication carrier) or different PLMNs (that is, different communication carriers). RAN30 (30_1, 30_2) is connected to a UPF (User Plane Function) 60 of the CN (Core Network) of the mobile communication system 1. Hereinafter, when RAN30_1 and RAN30_2 are not particularly distinguished, they are referred to as RAN30.

[0020] Note that only two RAN30s (30_1, 30_2) are shown in FIG. 1, but the mobile communication system 1 may include three or more RAN30s (30_1, 30_2, 30_3, ···) connected to the UPF60, and the UE10 may be connectable to three or more RAN30s (30_1, 30_2, 30_3, ···). In this case, all the RAN30s (30_1, 30_2, 30_3, ···) may be the same PLMN or not. Also, all the RAN30s (30_1, 30_2, 30_3, ···) are connected to the UPF60 of the mobile communication system 1. Also, only one UPF60 is shown in FIG. 1, but the mobile communication system 1 may include a plurality of UPF60s, and one RAN30 may be connected to one or more UPF60s.

[0021] Furthermore, the UE 10 is connectable to a wireless LAN 80 that is "non-3gpp access." The wireless LAN 80 is connected to the UPF 60 of the mobile communication system 1. The wireless LAN 80 is an example of a wireless access network that is "non-3gpp access."

[0022] The UPF 60 is connected to a DN (data network) such as the Internet outside the CN of the mobile communication system 1.

[0023] The UE 10 can establish a session with the UPF 60 using a wireless path via the RAN 30 or the wireless LAN 80, and can transmit and receive data to and from the DN using the established session. The UE 10 can also establish a multi-access session with the UPF 60 using a wireless path via the RAN 30 and a wireless path via the wireless LAN 80, and can transmit and receive data to and from the DN using the established multi-access session.

[0024] This embodiment also aims to enable the UE 10 to establish a multi-access session with the UPF 60 using multiple radio paths via each of multiple RANs 30. It also aims to enable appropriate selection of two "3gpp access" (base stations) for establishing the multi-access session. To this end, the UE 10 is enabled to select a next PLMN (a PLMN (second PLMN) that may be the same as or different from the first PLMN) after performing an initial network registration with a first PLMN, and perform a second network registration with the selected second PLMN.

[0025] The AM (Access and Mobility) control device 50 is a network device that realizes one NF (Network Function) of the control plane (C-plane) of the mobile communication system 1. The AM control device 50 is a network device that realizes an NF corresponding to the AMF of, for example, 5GC (the CN of the 5G system). However, in this embodiment, the AM control device 50 is a network device that realizes a new additional NF in addition to the AMF of 5GC.

[0026] The AM control device 50 performs C-plane communication with the UE 10 and the RAN 30.

[0027] FIG. 2 is a diagram showing a schematic configuration of a UE according to this embodiment. In FIG. 2, the UE 10 includes a control unit 110, a storage unit 120, a communication unit 130, a display unit 140, and an operation unit 150.

[0028] The control unit 110 is a CPU (Central Processing Unit), and realizes various functions by calling and executing a program stored in the storage unit 120.

[0029] As its function, the control unit 110 includes a network registration control unit (NW registration control unit) 1101. The NW registration control unit 1101 is realized by the CPU executing an NW registration control program 1201 stored in the storage unit 120.

[0030] Note that FIG. 2 shows only the additional NW registration control unit 1101 from the conventional UE 10 as a function of the control unit 110. Similarly, as a program stored in the storage unit 120, only the additional NW registration control program 1201 from the conventional UE 10 is shown.

[0031] The storage unit 120 is configured by a storage medium, such as a hard disk drive (HDD), flash memory, electrically erasable programmable read-only memory (EEPROM), random access read / write memory (RAM), read-only memory (ROM), or any combination of these storage media. The storage unit 120 stores various programs, such as a NW registration control program 1201, executed by the control unit 110 (CPU), and various data.

[0032] The communication unit 130 connects to a base station of the RAN 30 and performs wireless communication via the connected base station. The communication unit 130 also connects to an access point of the wireless LAN 80 and performs wireless communication via the connected access point.

[0033] Display unit 140 includes a display element such as a liquid crystal display or organic EL (Electro Luminescence) display, and displays display data output from control unit 110. Operation unit 150 is configured with an input device such as a numeric keypad, and inputs data in response to user operations. Alternatively, UE 10 may include a touch panel that can both input and display data.

[0034] The storage unit 120 stores SPLMN (Secondary PLMN) information 1202. The SPLMN information 1202 is information indicating PLMNs that are candidates for the second PLMN. The SPLMN information 1202 is provided by the CN of the mobile communication system 1. The SPLMN information 1202 may be, for example, information in the form of a list including multiple PLMNs. When the SPLMN information 1202 includes multiple PLMNs, a predetermined priority is set for each PLMN. Alternatively, the SPLMN information 1202 may be information that is a list of multiple PLMNs, with a priority assigned to each PLMN.

[0035] The NW registration control unit 1101 executes network registration processes for the first PLMN and the second PLMN. Through the network registration processes, the network registration of the UE 10 is performed.

[0036] FIG. 3 is a diagram showing a schematic configuration of the AM control device according to the present embodiment. The AM control device 50 shown in FIG. 3 is a device corresponding to the AMF of the 5GC. In the present embodiment, in addition to the functions of the AMF of the 5GC, the AM control device 50 further includes an SPLMN control unit 501 as an additional part from the AMF of the 5GC. Note that in FIG. 3, only the additional SPLMN control unit 501 from the AMF of the 5GC is shown as a function of the AM control device 50.

[0037] The SPLMN control unit 501 provides the SPLMN information 1202 to the UE 10. The SPLMN control unit 501 determines appropriate SPLMN information 1202 for the UE 10.

[0038] Next, several examples of the network registration method according to the present embodiment will be described.

[0039] (Example 1 of network registration method) Example 1 of the network registration method according to the present embodiment will be described with reference to FIG. 4. FIG. 4 is a sequence diagram showing the flow of Example 1 of the network registration method according to the present embodiment.

[0040] (Step S11) When the power of the UE 10 is turned on or the in-aircraft mode is turned off, the NW registration control unit 1101 of the UE 10 connects to the base station (BS) 30bs_1 of the first PLMN, which is the "Registered PLMN (the previously connected PLMN)", and transmits a network registration request (NW registration request) to the connected base station 30bs_1.

[0041] (Step S12) The base station 30bs_1 transfers the NW registration request received from the UE 10 to the AM control device 50 based on the transfer settings it has.

[0042] (Step S13) Based on the NW registration request received from base station 30bs_1, the AM control device 50 performs network registration of UE10 to the first PLMN.

[0043] (Steps S14, S15) The AM control device 50 transmits a response (Registration complete) message indicating the completion of network registration of UE10 to the first PLMN to base station 30bs_1. This response (Registration complete) message is transferred from base station 30bs_1 to UE10.

[0044] (Steps S16, S17) The NW registration control unit 1101 of UE10 transmits a "Multi-access PDU Session" establishment request to base station 30bs_1. Based on its own transfer settings, base station 30bs_1 transfers the "Multi-access PDU Session" establishment request received from UE10 to the AM control device 50.

[0045] (Step S18) When there is a "Multi-access PDU Session" establishment request from UE10, the SPLMN control unit 501 of the AM control device 50 selects a PLMN to be included in the SPLMN information 1202 of the UE10. As a method for selecting this PLMN, for example, the SPLMN control unit 501 may select an available PLMN based on the subscriber information of UE10, the location information of UE10, etc. Or, when the UPF60 is determined according to the slice information requested by UE10, the SPLMN control unit 501 may select a PLMN for which the determined UPF60 can configure a "MA PDU Session" (that is, the UPF60 can be connected in terms of the network configuration).

[0046] The SPLMN control unit 501 may also assign a priority to each PLMN included in the SPLMN information 1202. The SPLMN control unit 501 determines the priority of a PLMN according to predetermined priority conditions. For example, the priority may be higher if the PLMN has a service area that is closer to the location of the UE 10 or has less traffic, making it easier for the UE 10 to use. The priority of each PLMN is included in the SPLMN information 1202.

[0047] (Steps S19 and S20) The SPLMN control unit 501 of the AM control device 50 includes SPLMN information 1202 indicating the PLMN selected in step S18 in a response to the "MA PDU Session" establishment request and transmits the response to the base station 30bs_1. This response (including the SPLMN information 1202) is transferred from the base station 30bs_1 to the UE 10.

[0048] (Step S21) The NW registration control unit 1101 of the UE 10 stores the SPLMN information 1202 included in the response (including the SPLMN information 1202) in the storage unit 120. The NW registration control unit 1101 determines a second PLMN based on the SPLMN information 1202 stored in the storage unit 120, and sends a NW registration request to the determined second PLMN.

[0049] Note that UE 10 can make a "MA PDU Session" establishment request when it has only performed network registration with one access network (first PLMN). Even when UE 10 has established a session with only one access network (first PLMN), if the session is established as a "MA PDU Session," the session is treated as a "MA PDU Session." After completing network registration with a second access network (second PLMN), UE 10 sends a session establishment request to the second access network (second PLMN) using the same session identifier (session ID) as the established "MA PDU Session." This allows the CN to recognize that the session establishment request is for configuring a "MA PDU Session."

[0050] (Network registration method example 2) A second example of the network registration method according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a sequence diagram showing the flow of the second example of the network registration method according to this embodiment.

[0051] (Step S31) If the UE 10 has been in a non-communication state for a certain period of time, the UE 10 transitions from the "RRC-CONCECTED" state to the "RRC-IDLE" state, and the radio resources of the UE 10 are released. After that, if new traffic occurs while the UE 10 is in the "RRC-IDLE" state, the UE 10 transmits a "Service Request" message to the base station (BS) 30bs_1 of the first PLMN to re-establish the radio resources of the UE 10.

[0052] (Step S32) The base station 30bs_1 transfers the "Service Request" message received from the UE 10 to the AM control device 50 based on its own transfer setting.

[0053] (Step S33) When a "Service Request" is received from the UE 10, the SPLMN control unit 501 of the AM control device 50 selects a PLMN to be included in the SPLMN information 1202 of the UE 10. This method of selecting a PLMN is the same as the example 1 of the network registration method described above.

[0054] (Steps S34 and S35) The SPLMN control unit 501 of the AM control device 50 includes the SPLMN information 1202 indicating the PLMN selected in step S33 in a response to the "Service Request" and transmits the response to the base station 30bs_1. This response (including the SPLMN information 1202) is transferred from the base station 30bs_1 to the UE 10.

[0055] (Step S36) The NW registration control unit 1101 of the UE 10 stores the SPLMN information 1202 included in the response (including the SPLMN information 1202) in the storage unit 120. The NW registration control unit 1101 determines a second PLMN based on the SPLMN information 1202 stored in the storage unit 120, and sends a NW registration request to the determined second PLMN.

[0056] (Network registration method example 3) A third example of the network registration method according to this embodiment will be described with reference to Fig. 6. Fig. 6 is a sequence diagram showing the flow of the third example of the network registration method according to this embodiment.

[0057] (Step S51) When a predetermined SPLMN selection trigger is detected, the SPLMN control unit 501 of the AM control device 50 proceeds to step S52. The SPLMN selection trigger is, for example, an update of the subscriber information of the UE 10, an update of the location information of the UE 10, etc. Updates of the subscriber information and location information of the UE 10 are detected by messages from the UE 10 or the RAN 30, or by processing within the CN of the mobile communication system 1, etc.

[0058] (Step S52) The SPLMN control unit 501 of the AM control device 50 selects a PLMN to be included in the SPLMN information 1202 of the UE 10 in which the SPLMN selection trigger has been detected. This PLMN selection method is the same as the example 1 of the network registration method described above.

[0059] (Steps S53 and S54) The SPLMN control unit 501 of the AM control device 50 transmits SPLMN information 1202 indicating the PLMN selected in step S52 to the base station 30bs_1, addressed to the UE 10 that is the target of the SPLMN information 1202. This SPLMN information 1202 is transferred from the base station 30bs_1 to the UE 10.

[0060] (Step S55) The NW registration control unit 1101 of the UE 10 stores the SPLMN information 1202 received from the base station 30bs_1 in the storage unit 120.

[0061] The NW registration control unit 1101 executes network registration processing for a new radio access network (second PLMN) based on the SPLMN information 1202 stored in the storage unit 120. When the SPLMN information 1202 includes multiple PLMNs, the NW registration control unit 1101 determines the second PLMN from among the PLMNs in the SPLMN information 1202 according to the priority of each PLMN. The NW registration control unit 1101 sends a NW registration request to the determined second PLMN.

[0062] If the UE 10 is already connected to a second PLMN, and the newly determined second PLMN (new second PLMN) is different from the second PLMN (current second PLMN) to which the UE 10 is already connected, the NW registration control unit 1101 executes a network deregistration process for the current second PLMN that has been registered in the network. The NW registration control unit 1101 sends a NW registration request to the new second PLMN. On the other hand, if the new second PLMN is the same as the current second PLMN, the NW registration control unit 1101 continues the connection to the current second PLMN.

[0063] In the above Examples 1, 2, and 3 of the network registration method, the AM control device 50 determines the SPLMN information 1202 of the UE 10, but it is not limited to this. For example, the SMF, PCF, etc. may determine the SPLMN information 1202 of the UE 10.

[0064] According to this embodiment, the appropriate SPLMN information 1202 can be notified from the CN of the mobile communication system 1 to the UE 10. Thereby, the UE 10 can configure the "MA PDU Session" with an appropriate combination of access networks, so that it is possible to promote the expansion of multipath communication.

[0065] The above-described embodiments are applicable to mobile communication systems such as 5G systems, B5G systems, and 6G systems.

[0066] Note that, thereby, for example, since it is possible to improve the overall service quality in the mobile communication system, it is possible to contribute to Goal 9 of the Sustainable Development Goals (SDGs) led by the United Nations, "Build resilient infrastructure, promote sustainable industrialization, and foster innovation."

[0067] As described above, the embodiments of the present invention have been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment, and design changes and the like within the scope not departing from the gist of the present invention are also included.

[0068] Also, a computer program for realizing the functions of each of the above-described apparatuses may be recorded on a computer-readable recording medium, and the program recorded on this recording medium may be read into a computer system and executed. Here, the "computer system" may include hardware such as an OS and peripheral devices. Further, the "computer-readable recording medium" refers to a writable non-volatile memory such as a flexible disk, a magneto-optical disk, a ROM, a flash memory, a portable medium such as a DVD (Digital Versatile Disc), and a storage device such as a hard disk built into a computer system.

[0069] Furthermore, the "computer-readable recording medium" includes a volatile memory (for example, DRAM (Dynamic Random Access Memory)) inside a computer system that becomes a server or a client when a program is transmitted via a network such as the Internet or a communication line such as a telephone line, and that holds the program for a certain period of time. Also, the above program may be transmitted from a computer system storing the program in a storage device or the like to another computer system via a transmission medium or by a transmission wave in the transmission medium. Here, the "transmission medium" for transmitting the program refers to a medium having a function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication wire) such as a telephone line. Also, the above program may be for realizing a part of the above-described functions. Further, it may be a so-called difference file (difference program) that can realize the above-described functions in combination with a program already recorded in a computer system.

Description of Reference Numerals

[0070] 1... Mobile communication system, 10... UE, 30... RAN, 50... AM control device, 60... UPF, 70... DN, 80... Wireless LAN, 110... Control unit, 120... Storage unit, 130... Communication unit, 140... Display unit, 150... Operation unit, 1101... Network registration control unit, 501... SPLMN control unit

Claims

1. In a mobile communication system including a core network connected to a plurality of radio access networks, a network device provided in the core network, when a "Multi-access PDU Session" establishment request is received from a user terminal, includes Secondary Public Land Mobile Network (SPLMN) information provided to the user terminal in a response to the "Multi-access PDU Session" establishment request to the user terminal, a network device.

2. In a mobile communication system including a core network connected to a plurality of radio access networks, a network device provided in the core network, when a "Service Request" is received from a user terminal, includes Secondary Public Land Mobile Network (SPLMN) information provided to the user terminal in a response to the "Service Request" to the user terminal, a network device.

3. A user terminal in a mobile communication system including a core network connected to a plurality of radio access networks, when receiving Secondary Public Land Mobile Network (SPLMN) information from the core network, includes a network registration control unit that executes a network registration process for a new radio access network based on the received SPLMN information, a user terminal including the same.

4. A user terminal in a mobile communication system including a core network connected to a plurality of radio access networks, when receiving Secondary Public Land Mobile Network (SPLMN) information from the core network, and when the new radio access network determined based on the received SPLMN information is different from the radio access network that is already connected, includes a network registration control unit that executes a network deregistration process for the already connected radio access network for which network registration has been completed, a user terminal including the same.

5. In a mobile communication system including a core network connected to a plurality of radio access networks, When a network device provided in the core network receives a "Multi-access PDU Session" establishment request from a user terminal, the SPLMN (Secondary PLMN) information provided to the user terminal is included in the response to the "Multi-access PDU Session" establishment request to the user terminal. The user terminal determines the radio access network to connect to next based on the SPLMN information included in the response, and makes a network registration request for the determined radio access network. Network registration method.

6. In a mobile communication system including a core network connected to a plurality of radio access networks, When a network device provided in the core network receives a "Service Request" from a user terminal, the SPLMN (Secondary PLMN) information provided to the user terminal is included in the response to the "Service Request" to the user terminal. The user terminal determines the radio access network to connect to next based on the SPLMN information included in the response, and makes a network registration request for the determined radio access network. Network registration method.

7. In a mobile communication system including a core network connected to a plurality of radio access networks, When the user terminal receives SPLMN (Secondary PLMN) information from the core network, it executes network registration processing for a new radio access network based on the received SPLMN information. Network registration method.

8. In a mobile communication system including a core network connected to a plurality of radio access networks, When the user terminal receives SPLMN (Secondary PLMN) information from the core network, and when the new radio access network determined based on the received SPLMN information is different from the radio access network that is already connected, it executes network registration cancellation processing for the already connected radio access network for which network registration has been completed. Network registration method.

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