Network device, user terminal, and network registration method

Abstract

With respect to a mobile communication system comprising a core network connected to a plurality of wireless access networks, a network device of the present invention is provided to the core network. In the event of a "Multi-access PDU Session" establishment request from a user terminal, the network device includes Secondary PLMN (SPLMN) information, which is to be provided to the user terminal, in a response to the "Multi-access PDU Session" establishment request of the user terminal.

Description

Network device, user terminal and network registration method

[0001] The present invention relates to a network device, a user terminal, and a network registration method.This application claims priority to Japanese Patent Application No. 2024-006279, filed in Japan on January 18, 2024, the contents of which are incorporated herein by reference.

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

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

[0004] 3GPP, TS 23.501, V18.2.0, 2023-063GPP, TS 23.502, V18.2.0, 2023-06

[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) of communication for each 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 realize 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, in conventional 5G systems, a method for notifying the UE of candidates for the second PLMN from the CN is not specified.

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

[0009] One aspect of the present invention is a network device provided in a core network in a mobile communication system having a core network connected to multiple radio access networks, which, when a "Multi-access PDU Session" establishment request is made from a user terminal, 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.

[0010] One aspect of the present invention is a network device provided in a core network in a mobile communication system having a core network connected to multiple radio access networks, which, when a "Service Request" is received from a user terminal, includes SPLMN (Secondary PLMN) information to be provided to the user terminal in a response to the "Service Request" to the user terminal.

[0011] One aspect of the present invention is a user terminal of a mobile communication system having a core network connected to multiple radio access networks, the user terminal having a network registration control unit that, when receiving SPLMN (Secondary PLMN) information from the core network, performs network registration processing for the new radio access network based on the received SPLMN information.

[0012] One aspect of the present invention is a user terminal of a mobile communication system having a core network connected to multiple radio access networks, the user terminal having a network registration control unit that, when SPLMN (Secondary PLMN) information is received 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 to which the user terminal is already connected, executes a network deregistration process for the radio access network to which the user terminal is already connected and which has been registered.

[0013] One aspect of the present invention is a network registration method in a mobile communication system having a core network connected to multiple radio access networks, in which, when a "Multi-access PDU Session" establishment request is received from a user terminal, a network device 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, and 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 to the determined radio access network.

[0014] One aspect of the present invention is a network registration method in a mobile communication system having a core network connected to multiple radio access networks, in which, when a "Service Request" is received from a user terminal, a network device in the core network includes SPLMN (Secondary PLMN) information to be provided to the user terminal in a response to the "Service Request" to the user terminal, and 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 to the determined radio access network.

[0015] One aspect of the present invention is a network registration method in a mobile communication system having a core network connected to multiple radio access networks, in which, when a user terminal receives SPLMN (Secondary PLMN) information from the core network, the user terminal performs network registration processing 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 having a core network connected to multiple radio access networks, in which when a user terminal receives SPLMN (Secondary PLMN) information from the core network, and if the new radio access network determined based on the received SPLMN information is different from the radio access network to which the user terminal is already connected, the user terminal performs a network deregistration process for the radio access network to which the user terminal is already connected and which has been registered.

[0017] According to the present invention, it is possible to obtain the effect of expanding multipath communication.

[0018] FIG. 1 is a block diagram showing an example configuration of a mobile communication system according to an embodiment. FIG. 2 is a diagram showing a schematic configuration of a user equipment (UE) according to an embodiment. FIG. 3 is a diagram showing a schematic configuration of an AM (Access and Mobility) control device according to an embodiment. FIG. 4 is a sequence diagram showing the flow of example 1 of a network registration method according to an embodiment. FIG. 5 is a sequence diagram showing the flow of example 2 of a network registration method according to an embodiment. FIG. 6 is a sequence diagram showing the flow of example 3 of a network registration method according to an embodiment. FIG. 7 is a diagram showing the schematic architecture of a conventional 5G system. FIG. 8 is a diagram showing an example configuration of a conventional "MA PDU Session".

[0019] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing an example of the configuration of a mobile communication system according to an embodiment. In FIG. 1, a UE (user terminal) 10 can be connected to RANs (radio access networks) 30 (30_1, 30_2) that are "3GPP access." RAN 30_1 is a RAN of a first PLMN. RAN 30_2 is a candidate RAN for a second PLMN. The first PLMN and the second PLMN may be the same PLMN (i.e., the same communication carrier) or different PLMNs (i.e., different communication carriers). RAN 30 (30_1, 30_2) is connected to a UPF (user plane function) 60 of a CN (core network) of a mobile communication system 1. Hereinafter, RAN 30_1 and RAN 30_2 will be referred to as RAN 30 when there is no particular need to distinguish them.

[0020] Although only two RANs 30 (30_1, 30_2) are shown in FIG. 1 , the mobile communication system 1 may include three or more RANs 30 (30_1, 30_2, 30_3, ...) connected to the UPF 60, and the UE 10 may be connectable to three or more RANs 30 (30_1, 30_2, 30_3, ...). In this case, all of the RANs 30 (30_1, 30_2, 30_3, ...) may or may not be the same PLMN. Furthermore, all of the RANs 30 (30_1, 30_2, 30_3, ...) are connected to the UPF 60 of the mobile communication system 1. Furthermore, although only one UPF 60 is shown in FIG. 1 , the mobile communication system 1 may include multiple UPFs 60, and one RAN 30 may be connected to one or multiple UPFs 60.

[0021] The UE 10 is also 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. In addition, the UE 10 can 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] The present embodiment further aims to enable the UE 10 to establish a multi-access session with the UPF 60 using multiple wireless paths via multiple RANs 30. It also aims to enable two "3gpp access" (base stations) for establishing the multi-access session to be appropriately selected. 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 (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 between the UE 10 and the RAN 30 .

[0027] 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) that calls and executes programs stored in the storage unit 120 to realize various functions.

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

[0030] 2 shows only a conventional NW registration control unit 1101 for addition from the UE 10 as a function of the control unit 110. Similarly, only a conventional NW registration control program 1201 for addition from the UE 10 as a program stored in the storage unit 120.

[0031] The storage unit 120 is configured by a storage medium, such as a hard disk drive (HDD), a flash memory, an electrically erasable programmable read-only memory (EEPROM), a random access read / write memory (RAM), a 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] The display unit 140 includes a display element such as a liquid crystal display or an organic electroluminescence (EL) display, and displays display data output from the control unit 110. The operation unit 150 is configured with an input device such as a numeric keypad, and inputs data in response to user operations. Alternatively, the 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 each PLMN assigned a priority.

[0035] The NW registration control unit 1101 executes a network registration process for the first PLMN and the second PLMN. The network registration process performs network registration of the UE 10.

[0036] Fig. 3 is a diagram showing a schematic configuration of an AM control device according to this embodiment. The AM control device 50 shown in Fig. 3 is a device corresponding to the 5GC AMF. In this embodiment, the AM control device 50 includes, in addition to the functions of the 5GC AMF, an SPLMN control unit 501 as an additional part from the 5GC AMF. Note that Fig. 3 shows only the SPLMN control unit 501 added from the 5GC AMF 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 the appropriate SPLMN information 1202 for the UE 10.

[0038] Next, a network registration method according to this embodiment will be described with some examples.

[0039] (Example 1 of Network Registration Method) Example 1 of the network registration method according to this 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 this embodiment.

[0040] (Step S11) When the power of the UE 10 is turned on or the airplane 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 PLMN to which the UE 10 was previously connected)," 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 its own transfer setting.

[0042] (Step S13) The AM control device 50 performs network registration of the UE 10 in the first PLMN based on the NW registration request received from the base station 30bs_1.

[0043] (Steps S14 and S15) The AM control device 50 transmits a response (Registration complete) message indicating completion of network registration of the UE 10 to the first PLMN to the base station 30bs_1. This response (Registration complete) message is transferred from the base station 30bs_1 to the UE 10.

[0044] (Steps S16 and S17) The NW registration control unit 1101 of the UE 10 transmits a "Multi-access PDU Session" establishment request to the base station 30bs_1. The base station 30bs_1 transfers the "Multi-access PDU Session" establishment request received from the UE 10 to the AM control device 50 based on its own transfer setting.

[0045] (Step S18) When a request for establishing a "Multi-access PDU Session" is received from 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. As a method for selecting this PLMN, for example, the SPLMN control unit 501 may select an available PLMN based on subscriber information of UE 10, location information of UE 10, or the like. Alternatively, when a UPF 60 is determined according to slice information requested by UE 10, the SPLMN control unit 501 may select a PLMN with which the determined UPF 60 can configure a "MA PDU Session" (i.e., a PLMN to which the UPF 60 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 a predetermined priority assignment condition. For example, the priority may be higher if the PLMN has a service area that is closer to the location of UE 10 or has less traffic, making it easier for 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 this 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 even 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 network registration method example 2 according to this embodiment will be described with reference to Fig. 5. Fig. 5 is a sequence diagram showing the flow of a network registration method example 2 according to this embodiment.

[0051] (Step S31) If UE 10 has been in a non-communication state for a certain period of time, UE 10 transitions from the "RRC-CONCECTED" state to the "RRC-IDLE" state, and the radio resources of UE 10 are released. After that, if new traffic occurs while UE 10 is in the "RRC-IDLE" state, 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 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 PLMN selection method 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 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] (Third Example of Network Registration Method) A third example of a 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 a 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, 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 for which an 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 in accordance with the priority of each PLMN. The NW registration control unit 1101 sends a NW registration request to the determined second PLMN.

[0062] In addition, when UE 10 is already connected to the second PLMN, if the newly determined second PLMN (new second PLMN) is different from the second PLMN (current second PLMN) to which UE 10 is already connected, NW registration control unit 1101 executes a network deregistration process for the current second PLMN with which UE 10 has already registered. 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, NW registration control unit 1101 continues the connection with the current second PLMN.

[0063] In the above-described network registration method examples 1, 2, and 3, the AM control device 50 determines the SPLMN information 1202 of the UE 10, but this is not limiting. For example, the SMF, PCF, or the like may determine the SPLMN information 1202 of the UE 10.

[0064] According to this embodiment, the CN of the mobile communication system 1 can notify the UE 10 of appropriate SPLMN information 1202. This allows the UE 10 to configure an "MA PDU Session" with an appropriate combination of access networks, thereby enabling the expansion of multipath communication.

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

[0066] This will enable, for example, improvements to the overall service quality of mobile communication systems, thereby contributing to Goal 9 of the United Nations-led Sustainable Development Goals (SDGs), which is to "Build resilient infrastructure, promote sustainable industrialization and foster innovation."

[0067] Although an embodiment of the present invention has been described in detail above with reference to the drawings, the specific configuration is not limited to this embodiment, and design changes and the like are also included within the scope that does not deviate from the gist of the present invention.

[0068] Furthermore, a computer program for implementing the functions of each of the above-described devices may be recorded on a computer-readable recording medium, and the program recorded on the recording medium may be read and executed by a computer system. Note that the term "computer system" may also include hardware such as an OS and peripheral devices. Furthermore, the term "computer-readable recording medium" refers to a flexible disk, a magneto-optical disk, a ROM, a writable nonvolatile memory such as a flash memory, a portable medium such as a DVD (Digital Versatile Disc), or a storage device such as a hard disk built into a computer system.

[0069] Furthermore, the term "computer-readable recording medium" also includes a storage medium that stores a program for a certain period of time, such as a volatile memory (e.g., a dynamic random access memory (DRAM)) within a computer system that serves as a server or client when the program is transmitted via a network such as the Internet or a communication line such as a telephone line. The program may also be transmitted from a computer system that stores the program in a storage device or the like to another computer system via a transmission medium or by transmission waves within the transmission medium. Here, the "transmission medium" that transmits the program refers to a medium that has the function of transmitting information, such as a network (communication network) such as the Internet or a communication line (communication line) such as a telephone line. The program may also be a program that realizes part of the aforementioned functions. Furthermore, the program may be a so-called differential file (differential program) that can realize the aforementioned functions in combination with a program already stored in the computer system.

[0070] According to the present invention, it is possible to expand multipath communication.

[0071] 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. 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.

2. 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.

3. A user terminal of a mobile communication system including a core network connected to a plurality of radio access networks, the user terminal comprising a network registration control unit configured to execute a network registration process for a new radio access network based on received SPLMN (Secondary PLMN) information when the SPLMN information is received from the core network.

4. A user terminal of a mobile communication system including a core network connected to a plurality of radio access networks, the user terminal comprising a network registration control unit configured to execute a network deregistration process for a radio access network that is already connected and for which network registration has been performed when the new radio access network determined based on the received SPLMN information is different from the radio access network that is already connected, in a case where the SPLMN (Secondary PLMN) information is received from the core network.

5. In a mobile communication system including 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 Secondary PLMN (SPLMN) 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. A network registration method.

6. In a mobile communication system including a core network connected to a plurality of radio access networks, when a "Service Request" is received from a user terminal, a network device provided in the core network includes Secondary PLMN (SPLMN) 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. A network registration method.

7. In a mobile communication system including a core network connected to a plurality of radio access networks, when a user terminal receives Secondary PLMN (SPLMN) 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. A network registration method.

8. In a mobile communication system including a core network connected to a plurality of radio access networks, when a user terminal receives SPLMN (Secondary PLMN) information from the core network and the new radio access network determined based on the received SPLMN information is different from the radio access network already connected, a network registration cancellation process for the already connected radio access network with which the network is already registered is executed. Network registration method.

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