Mobile communication system and communication control method

Abstract

To register only a legitimate user terminal in a subscriber database and prevent an illegitimate user terminal from being registered in the subscriber database.SOLUTION: A mobile communication system includes a user terminal and a subscriber database management device that holds a subscriber database for enabling the user terminal to perform mobile communication. The user terminal is configured to acquire GPS location information and transmit a registration request including subscriber identification information and the GPS location information. The subscriber database management device is configured to receive the registration request from the user terminal, determine whether the user terminal can be registered in the subscriber database on the basis of the GPS location information of the user terminal, and register the user terminal in the subscriber database or reject the registration of the user terminal in the subscriber database according to the determination result.SELECTED DRAWING: Figure 7

Description

[Technical field]

[0001] The present invention relates to a mobile communication system and a communication control method. [Background technology]

[0002] In order for user terminals such as mobile phones and smartphones to carry out mobile communications, the subscriber identification information called IMSI, which is usually stored in the SIM card of the user terminal, must be transmitted to a control device on the mobile operator network side and registered. A known phenomenon is clone SIM (or clone mobile phone), where an unauthorized user who has obtained this subscriber identification information illegally accesses the mobile operator network by masquerading as the legitimate user who is the original owner of the subscriber identification information, and intercepts the legitimate user's communications.

[0003] A conventional method for eliminating unauthorized access using cloned SIMs is to check the base station number and AMF number (described later) included in a registration request to a control device on the mobile operator network side, and detect this as unauthorized access if, for example, registration requests using the same subscriber identification information are made from Japan and a foreign country at almost the same time (see, for example, non-patent document 1). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] “Official Document FS.19 - Diameter Interconnect Security Version 4.0”, GSM Association, 3.3.7 Category 3 Filtering on Diameter Message and Location, May 4, 2018 Summary of the Invention [Problem to be solved by the invention]

[0005] However, with the above conventional method, when two registration requests with the same subscriber identification information were made at approximately the same time or at different times within the same or neighboring base station, it was not possible to determine which of the two requests was from a legitimate user. [Means for solving the problem]

[0006] According to one aspect of the present invention, there is provided a mobile communications system comprising a user terminal and a subscriber database management device that holds a subscriber database to enable the user terminal to perform mobile communications, wherein the user terminal is configured to acquire GPS location information and transmit a registration request including subscriber identification information and the GPS location information, and the subscriber database management device is configured to receive the registration request from the user terminal, determine whether the user terminal can be registered in the subscriber database based on the GPS location information of the user terminal, and, depending on the determination result, register the user terminal in the subscriber database or reject registration of the user terminal in the subscriber database.

[0007] According to one aspect of the present invention, the subscriber database management device may be configured to calculate a moving speed of the user terminal based on the received GPS location information, and determine that the user terminal can be registered in the subscriber database if the calculated moving speed is smaller than a threshold value, and determine that the user terminal cannot be registered in the subscriber database if the calculated moving speed is larger than the threshold value.

[0008] Also, according to one aspect of the present invention, the subscriber database management device may be configured to determine that the user terminal is not to be registered in the subscriber database if the received registration request does not include GPS location information.

[0009] Also, according to one aspect of the present invention, the subscriber database management device may be configured to instruct the user terminal to resend the registration request if the received registration request does not include GPS location information.

[0010] In addition, according to one aspect of the present invention, the subscriber database management device may be configured to determine that the user terminal is not to be registered in the subscriber database if GPS location information is not included in the registration request resent from the user terminal.

[0011] According to one aspect of the present invention, the subscriber database management device may be configured to skip registration of the user terminal in the subscriber database based on the registration request if the calculated moving speed is smaller than the threshold value, and to register the user terminal in the subscriber database based on a second registration request received following the registration request.

[0012] In addition, according to one aspect of the present invention, the subscriber database management device may be configured to, when it determines that the user terminal is not registered in the subscriber database, record the source address of the registration request from the user terminal as the address of an unauthorized user terminal.

[0013] According to one aspect of the present invention, there is provided a communication control method in a mobile communication system including a user terminal and a subscriber database management device that holds a subscriber database to enable the user terminal to perform mobile communication, the communication control method including the steps of: the user terminal sending a registration request including subscriber identification information and GPS location information; the subscriber database management device receiving the registration request from the user terminal; the subscriber database management device determining whether the user terminal can be registered in the subscriber database based on the GPS location information of the user terminal; and the subscriber database management device registering the user terminal in the subscriber database or rejecting the registration of the user terminal in the subscriber database depending on the determination result, wherein communication services are provided to user terminals registered in the subscriber database.

[0014] According to one aspect of the present invention, the step of determining whether or not registration is possible may include a step of calculating a moving speed of the user terminal based on the received GPS location information, and a step of determining that the user terminal can be registered in the subscriber database if the calculated moving speed is smaller than a threshold value, and determining that the user terminal cannot be registered in the subscriber database if the calculated moving speed is greater than the threshold value. Effect of the Invention

[0015] According to the present invention, only valid user terminals can be registered in the subscriber database, and unauthorized user terminals can be prevented from being registered in the subscriber database. [Brief description of the drawings]

[0016] [Figure 1] 1 is a diagram showing an example of a network configuration of a mobile communication system according to an embodiment of the present invention; [Diagram 2] FIG. 1 illustrates some unauthorized access routes in a mobile communication system. [Diagram 3] 2 is a block diagram showing a functional configuration of a user terminal in a mobile communication system according to one embodiment of the present invention. [Figure 4] 1 is an exemplary sequence diagram showing a process flow for registering a user terminal in a UDR in a mobile communication system according to an embodiment of the present invention. FIG. [Diagram 5] FIG. 5 is a diagram showing examples of IP packets transmitted in steps 404 to 408 in FIG. [Figure 6] FIG. 2 is a diagram showing an example of a subscriber database held by a UDR in a mobile communication system according to an embodiment of the present invention. [Figure 7] 10 is a flowchart illustrating an example of a process in which a UDR determines whether or not to register a user terminal in a subscriber database in a mobile communication system according to an embodiment of the present invention. [Figure 8] 10 is a flowchart illustrating another example of a process in which the UDR determines whether to register a user terminal in the subscriber database in the mobile communication system according to an embodiment of the present invention. [Figure 9] 10 is a flowchart showing an example of a process for collecting and recording information about unauthorized user terminals in a mobile communication system according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0017] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0018] FIG. 1 is a diagram showing an example of a network configuration of a mobile communication system 10 according to an embodiment of the present invention. The mobile communication system 10 includes a user terminal 100, a plurality of base stations 200, and a core network 300. FIG. 1 illustrates a mobile communication system 10 conforming to a fifth generation (5G) communication standard, and the core network 300 includes nodes of an Access and Mobility Management Function (AMF) 302, a Unified Data Management (UDM) 304, and a Unified Data Repository (UDR) 306. The core network 300 also includes nodes such as a Session Management Function (SMF), a Policy Control Function (PCF), and a User Plane Function (UPF), but these are omitted in FIG. 1. The mobile communication system 10 may be conforming to a fourth generation (4G) communication standard.

[0019] The AMF 302 is a node that provides mobility control functions and performs mobility control such as location registration, paging, and handover. The UDM 304 is a node that manages user contract information and authentication information. The UDR 306 is a node (subscriber database management device) that stores a subscriber database that holds the identification number and location information of user terminals. Each of these nodes is configured as a computer equipped with a processor and memory, and predetermined functions are realized by the processor reading and executing programs stored in the memory.

[0020] As shown in FIG. 1, the UDR 306 has a plurality of UDMs 304 under its control and is communicatively connected to the plurality of UDMs 304. Each UDM 304 has a plurality of AMFs 302 under its control and is communicatively connected to the plurality of AMFs 302. Each AMF 302 has a plurality of base stations 200 under its control and is communicatively connected to the plurality of base stations 200. Each base station 200 forms a base station area (cell) in which wireless communication is possible between the base station 200 and the user terminal 100. The user terminal 100 can be present in a base station area corresponding to any of the base stations 200. The user terminal 100 transmits subscriber identification information (IMSI: International Mobile Subscriber Identity) to the UDR 306 via the AMF 302 and UDM 304 located above the base station 200 in which the user terminal 100 is present, in that order. This subscriber identification information is registered in the UDR 306, and communication services such as voice calls and data communication in the mobile communication system 10 are provided to the user terminal 100.

[0021] FIG. 2 is a diagram showing some unauthorized access routes in the mobile communication system 10. An unauthorized user terminal 100A possessed by an unauthorized user may be present in any base station area, similar to the user terminal 100, and may masquerade as the user terminal 100 by using the subscriber identification information of the user terminal 100 obtained illegally, and may perform unauthorized access to the UDR 306 via the base station 200. In addition, unauthorized access may be performed directly to the core network 300 without going through the base station 200. For example, the unauthorized user terminal 100B may perform unauthorized access to the UDR 306 by transmitting the subscriber identification information of the user terminal 100 obtained illegally to the AMF 302. Similarly, the unauthorized user terminal 100C may perform unauthorized access to the UDR 306 by transmitting the subscriber identification information obtained illegally to the UDM 304. Furthermore, the unauthorized user terminal 100D may perform unauthorized access by directly transmitting the subscriber identification information obtained illegally to the UDR 306.

[0022] In the mobile communication system 10 according to an embodiment of the present invention, the user terminal 100 transmits its own GPS location information to the UDR 306, and the UDR 306 decides whether or not to register the subscriber identification information (IMSI) of the user terminal 100 in the subscriber database based on the received GPS location information. By controlling whether or not to register the subscriber identification information using the GPS location information of the user terminal 100, it is possible to prevent unauthorized access from unauthorized user terminals (e.g., 100A, 100B, 100C, 100D).

[0023] 3 is a block diagram showing a functional configuration of a user terminal 100 in a mobile communication system 10 according to an embodiment of the present invention. The user terminal 100 is a wireless communication device such as a mobile phone terminal or a smartphone. The user terminal 100 includes at least an identification information storage unit 102, a GPS position information acquisition unit 104, a registration request creation unit 106, and a wireless communication unit 108.

[0024] The identification information storage unit 102 may be, for example, a SIM card. The identification information storage unit 102 may be a combination of a SIM card and an information storage means (memory) other than a SIM card. The SIM card stores identification information such as a subscriber identification information (IMSI) and a telephone number (MSISDN). The subscriber identification information is information that uniquely identifies a subscriber and is issued by a mobile phone carrier when a communication service contract is made and is linked to a SIM card. The information storage means other than a SIM card stores, for example, an International Mobile Equipment Identity (IMEI), which is device-specific identification information of the user terminal 100.

[0025] The GPS position information acquisition unit 104 receives GPS signals from GPS satellites and generates GPS position information indicating the location of the user terminal 100. The GPS position information may be three-dimensional position coordinates consisting of latitude, longitude, and altitude.

[0026] The registration request creation unit 106 creates a registration request for registering the user terminal 100 in the UDR 306, and transmits the created registration request to the base station 200 in which the user terminal 100 is located via the wireless communication unit 108. The registration request includes at least the subscriber identification information read from the identification information storage unit 102 and the current GPS location information of the user terminal 100 created by the GPS location information acquisition unit 104. The registration request may include other information in addition to the subscriber identification information and GPS location information of the user terminal 100, for example, the terminal identification information (IMEI) of the user terminal 100 read from the identification information storage unit 102. The creation and transmission of the registration request by the registration request creation unit 106 may be triggered, for example, by the user terminal 100 being turned on, or by the user terminal 100 moving out of the base station area, or by the GPS function of the user terminal 100 being enabled, or periodically (for example, multiple times per minute).

[0027] 4 is an exemplary sequence diagram showing a process flow for registering the user terminal 100 in the UDR 306 in the mobile communication system 10 according to an embodiment of the present invention. In step 402, the user terminal 100 transmits a registration request including the subscriber identification information and GPS location information of the user terminal 100 to the base station 200 in the base station area in which the user terminal 100 is located, as described above. In step 404, the base station 200 (the base station 200 corresponding to the base station area in which the user terminal 100 is located) receives the registration request from the user terminal 100 and transfers the received registration request to the AMF 302, which is an upper node. Similarly, in step 406, the AMF 302 that receives the registration request from the base station 200 transfers the received registration request to the UDM 304, which is its upper node, and in the following step 408, the UDM 304 further transfers the registration request transferred from the AMF 302 to the UDR 306.

[0028] The core network 300 of the mobile communication system 10 is configured as an IP (Internet Protocol) network, and the registration request is transmitted from the base station 200 to the UDR 306 in the form of an IP packet. Fig. 5 is a diagram showing examples of IP packets transmitted in each of steps 404 to 408. As shown in Fig. 5, each IP packet transmitted in steps 404 to 408 includes the subscriber identity (IMSI) and GPS location information, which are the contents of the registration request, and the destination IP address and source IP address, which are header information.

[0029] The destination IP address and source IP address of each IP packet in the example of Fig. 5 show an example in which a registration request is transmitted to UDR 306 via base station #111, AMF #11, and UDM #1 (see Fig. 1) in this order. Specifically, IP packet 502 in the example of Fig. 5 is transferred from base station #111 to AMF #11 in step 404, IP packet 504 is transferred from AMF #11 to UDM #1 in step 406, and IP packet 506 is transferred from UDM #1 to UDR 306 in step 408. Each of these IP packets, or at least the source IP address and subscriber identification information among the information contained in each IP packet, is recorded in a reception log together with reception time information at the receiving node of the IP packet.

[0030] For example, in the example of Fig. 5, the reception log of AMF#11 records at least the time when a registration request (IP packet) was received from base station #111, which is a lower node, the source IP address of the IP packet, i.e., the IP address of base station #111, and the subscriber identification information included in the registration request, based on IP packet 502 received by AMF#11. Similarly, the reception log of UDM#1 records at least the time when a registration request was received from AMF#11, the IP address of AMF#11, and the subscriber identification information, based on IP packet 504 received by UDM#1, and the reception log of UDR306 records at least the time when a registration request was received from UDM#1, the IP address of UDM#1, and the subscriber identification information, based on IP packet 506 received by UDR306. A method of using the reception logs recorded in each of these nodes will be described later with reference to Fig. 9.

[0031] 4, in step 410, the UDR 306 determines whether or not to register the user terminal 100 (subscriber identification information of the user terminal 100) that has sent the registration request in its subscriber database based on the GPS location information included in the received registration request, and in the following step 412, the UDR 306 performs or rejects the registration depending on the result of the determination. After that, in step 414, the UDR 306 transmits a notification based on the registration result to the user terminal 100 via the UDM 304, the AMF 302, and the base station 200 in that order.

[0032] Next, a method of determining whether or not registration in the subscriber database in the UDR 306 is possible (details of the above steps 410 to 414) will be described with reference to Figs. 6 to 8. Fig. 6 is a diagram showing an example of a subscriber database held by the UDR 306 in the mobile communication system 10 according to an embodiment of the present invention. As shown in Fig. 6, the subscriber database records, for each user terminal 100 (i.e., for each subscriber identification information), at least a timestamp indicating the time when the UDR 306 received a registration request from the UDM 304, the subscriber identification information that is the target of the registration request, and the GPS location information of the user terminal 100 included in the registration request. In the example of Fig. 6, an example is shown in which the user terminal 100 having the subscriber identification information IMSI#1 and located at GPS location coordinates (X1, Y1, Z1) has already been determined to be a valid user terminal (registration possible) at least once by the determination process of Fig. 7 described later and has been registered in the subscriber database. In the following, a description will be given assuming a case where the UDR 306 receives a new registration request starting from this state.

[0033] In addition, the subscriber database may further record information (e.g., identification information of a base station and / or an AMF) for identifying the network location of the user terminal 100 on the communication network (core network 300 and radio access network) of the mobile communication system 10 as additional registration information. For example, the base station 200 and / or the AMF 302 may add their own base station identification information or AMF identification information to the IP packet when forwarding the registration request (IP packet) in each step 404, 406 of FIG. 4, or, if the user terminal 100 already knows the base station identification information and / or AMF identification information of the connection destination before step 402, the user terminal 100 may create a registration request including the base station identification information and / or AMF identification information from the beginning in step 402 and transmit it to the base station 200. Then, these base station identification information and / or AMF identification information may be recorded in the subscriber database in the UDR 306 together with the subscriber identification information.

[0034] Let us return to the explanation of the method for determining whether or not to register in the subscriber database. FIG. 7 is a flowchart showing an example of a process in which the UDR 306 determines whether or not to register the user terminal 100 in the subscriber database in the mobile communication system 10 according to an embodiment of the present invention. In step 702, the UDR 306 receives a registration request from the UDM 304. This step corresponds to step 408 in the sequence diagram of FIG. 4. Next, in step 704, the UDR 306 checks whether or not the received registration request includes GPS location information. If the registration request includes GPS location information, the process proceeds to step 706.

[0035] In step 706, UDR 306 reads out from the subscriber database GPS location information corresponding to the subscriber identification information in the registration request received in step 702, and calculates the moving speed of the user terminal 100 based on the read GPS location information and the GPS location information included in the registration request received in step 702. For example, in response to a registration request from a user terminal 100 having subscriber identification information IMSI#1, UDR 306 can calculate the moving speed V of the user terminal 100 according to the following equation using the GPS location coordinates (X1, Y1, Z1) read out from the subscriber database and the GPS location coordinates (X2, Y2, Z2) in the registration request received in step 702.

[0036]

number

[0037] Here, ΔT is the time difference (ΔT=T2-T1) between the time T1 recorded in the subscriber database when the registration request was last received from the user terminal 100 and the time T2 when the registration request is newly received in step 702.

[0038] In the next step 708, the UDR 306 calculates the moving speed V by dividing the moving speed V by a predetermined threshold speed V thBy comparing with the threshold speed V, it is possible to identify whether the sender of the registration request received in step 702 is a user terminal that legitimately possesses the subscriber identification information, or an unauthorized user terminal that has illegally obtained the subscriber identification information. If the sender of the registration request in step 702 is a legitimate user terminal, it is considered that the GPS position coordinates included in the registration request will not differ significantly from the previous GPS position coordinates of the user terminal that are already recorded in the subscriber database. Even if the user terminal is moving, its moving speed should be limited to the speed possible for the actual means of transportation (e.g., walking, car, train, etc.). Therefore, if the moving speed V calculated in step 706 is less than the threshold speed V th , it is possible to identify the sender of the registration request in step 702 as a legitimate user terminal. On the other hand, if the sender of the registration request in step 702 is an unauthorized user terminal, the GPS location coordinates included in the registration request will be far away (e.g., in a different country or city) from the actual GPS location coordinates of the legitimate user terminal recorded in the subscriber database, and therefore the moving speed V calculated in step 706 will be a value that far exceeds the speed possible as a real means of transportation. Therefore, if the moving speed V calculated in step 706 is greater than the threshold speed V th If the threshold speed V is greater than 0, it is possible to identify the sender of the registration request in step 702 as an unauthorized user terminal. th can be set to an appropriate speed (for example, 500 km / h) that is faster than the maximum speed that a real means of transportation can achieve.

[0039] Therefore, the moving speed V calculated in step 706 is equal to the threshold speed V thIf the difference is smaller than , the process proceeds to step 710, where UDR 306 identifies the user terminal 100 that sent the registration request in step 702 as a legitimate user terminal, determines that registration of the user terminal 100 in the subscriber database based on the registration request (updating of the subscriber database) is permitted, and carries out the registration. As a result, the subscriber identification information and GPS location information of the user terminal 100 contained in the registration request received in step 702, as well as the reception time of the registration request, are registered in the subscriber database (the subscriber database is updated). Also, if the moving speed V calculated in step 706 is smaller than the threshold speed V th If it is greater than , the process proceeds to step 712, where UDR 306 identifies the sender of the registration request in step 702 as an unauthorized user terminal, determines that registration in the subscriber database based on the registration request (updating of the subscriber database) is not permitted, and rejects the registration. As a result, the subscriber database is not updated based on a registration request sent from an unauthorized user terminal that contains the same subscriber identification information as a legitimate user terminal, and the subscriber database maintains the subscriber identification information, etc., of the legitimate user terminal. In this way, only legitimate user terminals can be registered in the subscriber database, and unauthorized user terminals can be prevented from being registered in the subscriber database.

[0040] Also, in the above-mentioned step 704, if the registration request received in step 702 does not include GPS location information, the process proceeds to step 714, where UDR 306 instructs the user terminal that transmitted the registration request to resend the registration request including GPS location information. In the following step 716, UDR 306 checks whether the resent registration request includes GPS location information as instructed. If the resent registration request includes GPS location information, the process proceeds to step 706, where the moving speed of the user terminal is calculated, and thereafter, in the same manner as described above, whether or not to register the user terminal in the subscriber database is determined based on the calculated moving speed. If the resent registration request does not include GPS location information, the process proceeds to step 712, where registration in the subscriber database is rejected. Since it is assumed that an unauthorized user terminal does not include GPS location information in a registration request, the flow proceeds in the order of step 714 to step 716 to step 712, and it is possible to prevent an unauthorized user terminal that does not transmit GPS location information from being registered in the subscriber database.

[0041] Fig. 8 is a flowchart showing another example of the process in which the UDR 306 determines whether or not to register the user terminal 100 in the subscriber database in the mobile communication system 10 according to an embodiment of the present invention. The example in Fig. 8 is the same as the example in Fig. 7, except that it has additional steps 718 to 722 between steps 708 and 710. In the following, a description of the overlapping steps will be omitted.

[0042] In step 708 of the flowchart in FIG. 8, the moving speed V calculated in step 706 is equal to or lower than the threshold speed V thIf the temporary memory is smaller than the current value, the process proceeds to step 718. In step 718, the UDR 306 checks whether the temporary memory is empty. It is assumed that the temporary memory is empty in the initial state. If the temporary memory is empty, the process proceeds to step 720, where the UDR 306 stores the contents of the registration request received in step 702 in the temporary memory. Thereafter, the process proceeds to step 702, where the UDR 306 receives the next registration request (second registration request) from the UDM 304. When the process proceeds from step 702 to step 704, 706, and 708 in this order for the next registration request, and then to step 718, the previous registration request (first registration request) is now stored in the temporary memory, so the process proceeds to step 722. In step 722, the UDR 306 clears the temporary memory. Next, the process proceeds to step 710, where the UDR 306 performs registration in the subscriber database based on the current registration request (i.e., the second registration request). In the above, the contents of the registration request itself are stored in temporary memory. Alternatively, a predetermined flag may be set to 1 in step 720, the flag may be cleared to 0 in step 722, and the flag may be checked to see whether it is 0 or 1 in step 718.

[0043] The method of determining whether or not to register in the example of FIG. 8 is effective when an unauthorized user terminal is relatively close to a legitimate user terminal (for example, in the same base station area). When an unauthorized user terminal that is close to a legitimate user terminal transmits a registration request, the moving speed V calculated in step 706 is greater than or equal to the threshold speed V th , which is smaller than the threshold speed V. Therefore, it is not desirable to immediately register the user in the subscriber database in step 710 based on the comparison result in step 708. Here, since both the legitimate user terminal and the unauthorized user terminal periodically transmit registration requests, the UDR 306 receives registration requests from the legitimate user terminal and the unauthorized user terminal alternately. Therefore, as in the method according to the example of FIG. 8, if the moving speed V calculated in step 706 is smaller than the threshold speed V thIf the first registration request is smaller than this, registration in the subscriber database based on the first registration request is skipped, and registration in the subscriber database is performed based on the next second registration request, thereby more effectively preventing unauthorized user terminals from being registered in the subscriber database.

[0044] FIG. 9 is a flowchart showing an example of a process for collecting and recording information on unauthorized user terminals in the mobile communication system 10 according to an embodiment of the present invention. The series of processes in FIG. 9 is performed following step 712 in the flowchart in FIG. 7 or FIG. 8. As described above, the UDR 306 holds a reception log that records information on the IP packet 506 (registration request) received in step 408 in FIG. 4. In step 902, the UDR 306 refers to the reception log to identify the source IP address of the registration request that was rejected for registration in the subscriber database in step 712 in FIG. 7 or FIG. 8. Here, the UDR 306 stores the IP addresses of multiple UDMs 304 under its control. In the following step 904, the UDR 306 checks whether the source IP address of the registration request identified in step 902 is the IP address of any of the UDMs 304 under its control. If the source IP address of the registration request is not the IP address of any of the UDMs 304 under its control, the UDR 306 records the IP address in the unauthorized terminal list as the IP address of an unauthorized user terminal in step 906. If the source IP address of the registration request is the IP address of a UDM 304 under its control, the process proceeds to step 908.

[0045] In step 908, UDR 306 queries UDM 304 corresponding to the source IP address of the registration request for the IP address of the node that transmitted the registration request to the UDM 304. As described above, UDM 304 also holds a reception log that records information of IP packet 504 (registration request) received in step 406 of Fig. 4. Similarly to UDR 306, UDM 304 stores the IP addresses of multiple AMFs 302 under its control. In step 910, UDM 304 refers to the reception log to identify the source IP address of the registration request that is the subject of the query from UDR 306 (i.e., the registration request that has been rejected for registration in the subscriber database), and checks whether the source IP address is the IP address of any of the AMFs 302 under its control. If the source IP address of the query is not the IP address of the subordinate AMF 302, in step 912, the UDM 304 responds to the UDR 306 with the IP address as the IP address of the unauthorized user terminal, and the UDR 306 records it in the unauthorized terminal list. If the source IP address of the query is the IP address of the subordinate AMF 302 of the UDM 304, the process proceeds to step 914.

[0046] In steps 914 to 918, similarly to steps 908 to 912, the IP address of the unauthorized user terminal that transmitted the registration request to the AMF 302 is identified and recorded in the unauthorized terminal list. In this way, information (IP address) of the unauthorized user terminal that illegally obtains the subscriber identification information of the user terminal and attempts to register it in the UDR 306 can be collected as the unauthorized terminal list.

[0047] Although the embodiment of the present invention has been described above, the present invention is not limited to this, and various modifications are possible without departing from the spirit and scope of the present invention. [Explanation of symbols]

[0048] 10 Mobile communication systems 100 user terminals 102 Identification information storage unit 104 GPS position information acquisition section 106 Registration Request Creation Department 108 Wireless Communication Division 200 base stations 300 Core Network 302 AMF 304 UDM 306 UDR

Claims

1. A mobile communication system comprising: a user terminal; and a subscriber database management device that holds a subscriber database for enabling the user terminal to perform mobile communication, The user terminal, Acquire GPS location information, sending a registration request including a subscriber identification and said GPS location information; It is configured as follows: The subscriber database management device includes: receiving the registration request from the user terminal; determining whether or not the user terminal can be registered in the subscriber database based on the GPS location information of the user terminal; Depending on the result of the determination, registering the user terminal in the subscriber database or refusing to register the user terminal in the subscriber database; It is configured as follows: Mobile communication systems.

2. The subscriber database management device includes: Calculating a moving speed of the user terminal based on the received GPS location information; When the calculated moving speed is smaller than a threshold value, it is determined that the user terminal can be registered in the subscriber database, and when the calculated moving speed is larger than the threshold value, it is determined that the user terminal cannot be registered in the subscriber database. The mobile communication system according to claim 1 , configured to:

3. The mobile communication system according to claim 1 , wherein the subscriber database management device is configured to determine that the user terminal is not to be registered in the subscriber database if the received registration request does not include GPS location information.

4. The mobile communication system according to claim 1 , wherein the subscriber database management device is configured to instruct the user terminal to resend a registration request if the received registration request does not include GPS location information.

5. The mobile communication system according to claim 4, wherein the subscriber database management device is configured to determine that the user terminal is not to be registered in the subscriber database if the registration request resent from the user terminal does not include GPS location information.

6. 3. The mobile communication system of claim 2, wherein the subscriber database management device is configured to skip registration of the user terminal in the subscriber database based on the registration request if the calculated moving speed is less than the threshold, and to register the user terminal in the subscriber database based on a second registration request received following the registration request.

7. A mobile communication system as claimed in any one of claims 1 to 6, wherein the subscriber database management device is configured to, when determining that the user terminal is not to be registered in the subscriber database, record the source address of the registration request from the user terminal as the address of an unauthorized user terminal.

8. A communication control method in a mobile communication system including a user terminal and a subscriber database management device that holds a subscriber database for enabling the user terminal to perform mobile communication, comprising: the user terminal sending a registration request including a subscriber identity and GPS location information; the subscriber database management device receiving the registration request from the user terminal; a step of the subscriber database management device determining whether or not the user terminal can be registered in the subscriber database based on the GPS location information of the user terminal; a step in which the subscriber database management device registers the user terminal in the subscriber database or rejects the registration of the user terminal in the subscriber database according to the result of the determination, and a communication service is provided to the user terminal registered in the subscriber database; A communication control method comprising:

9. The step of determining whether or not registration is possible includes: Calculating a moving speed of the user terminal based on the received GPS location information; determining that the user terminal can be registered in the subscriber database when the calculated moving speed is smaller than a threshold value, and determining that the user terminal cannot be registered in the subscriber database when the calculated moving speed is larger than the threshold value; The communication control method according to claim 8 , comprising:

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