Management device and management method

Abstract

This management device is provided with: an acquisition unit which acquires a notification of reception of alert information indicating that alert information has been received from a terminal device; a specification unit which, when the acquisition unit has acquired notifications of reception of alert information from a predetermined number or more of terminal devices belonging to a communication group performing group communication, specifies the communication group as a specified group; and a function transfer unit which transfers a function for managing communication of the communication group to a specified terminal device which is a predetermined terminal device among a plurality of terminal devices belonging to the specified group.

Description

Management device and management method

[0001] The present disclosure relates to a management device and a management method.

[0002] There is disclosed a technique for performing communication by changing a connection destination to a second connection destination when it becomes impossible to communicate with a first connection destination in an emergency (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2019-134377

[0004] For example, when an emergency earthquake warning indicating a large-scale earthquake is transmitted, the base station and the communication network are functioning, but as time passes, the damage spreads and group communication cannot be maintained. It is desirable to form a new communication network before the damage spreads.

[0005] An object of the present disclosure is to provide a management device and a management method capable of forming a new communication network in an emergency.

[0006] The management device of the present disclosure includes an acquisition unit that acquires a notification of reception of notification information indicating that the notification information has been received from a terminal device, and when the acquisition unit acquires the notification of reception of the notification information from a predetermined number or more of the terminal devices belonging to a communication group that performs group communication, a specifying unit that specifies the communication group as a specific group, and a function transfer unit that transfers a function of managing communication of the communication group to a specific terminal device that is a predetermined one of the plurality of terminal devices belonging to the specific group.

[0007] The management device of this disclosure includes: an acquisition unit that acquires location information of a terminal device and a notification of notification information reception indicating that notification information has been received from a terminal device; an evaluation unit that generates an evaluation value for the risk level of the location indicated by the location information based on hazard map information indicating the risk level of each area; an identification unit that identifies the communication group as a specific group when the acquisition unit acquires notification of notification information reception from a predetermined number of terminal devices belonging to a communication group that performs group communication; a determination unit that determines, based on the location information, the terminal device located in the area with the lowest evaluation value among a plurality of terminal devices belonging to the specific group as the specific terminal device; and a function transfer unit that transfers the function of managing the communication of the communication group to the specific terminal device.

[0008] The management device of this disclosure includes: an acquisition unit that acquires location information of a terminal device and a notification of notification information reception indicating that notification information has been received from a terminal device; an identification unit that identifies the communication group as a specific group when the acquisition unit acquires notification of notification information reception from a predetermined number of terminal devices belonging to a communication group that performs group communication; a determination unit that determines a terminal device that has not received the notification information among a plurality of terminal devices belonging to the specific group as a specific terminal device; and a function transfer unit that transfers the function of managing the communication of the communication group to the specific terminal device.

[0009] The management method of this disclosure includes the steps of: obtaining a notification of notification information received from a terminal device; identifying the communication group as a specific group when notification of notification information received is obtained from a predetermined number or more terminal devices belonging to a communication group that performs group communication; and transferring the function of managing the communication of the communication group to a specific terminal device, which is a predetermined terminal device among the multiple terminal devices belonging to the specific group.

[0010] The management method of this disclosure includes the steps of: obtaining location information of a terminal device and a notification of notification information received indicating that notification information has been received from a terminal device; generating an evaluation value for the risk level of the location indicated by the location information based on hazard map information indicating the risk level for each area; identifying the communication group as a specific group when notification of notification information received is obtained from a predetermined number or more of the terminal devices belonging to a communication group that performs group communication; determining the terminal device located in the area with the lowest evaluation value among a plurality of terminal devices belonging to the specific group as the specific terminal device based on the location information; and transferring the function of managing the communication of the communication group to the specific terminal device.

[0011] The management method of this disclosure includes the steps of: obtaining location information of the terminal device and a notification of notification information reception indicating that notification information has been received from the terminal device; identifying the communication group as a specific group when notification of notification information reception is obtained from a predetermined number or more of the terminal devices belonging to a communication group that performs group communication; determining the terminal device that has not received the notification information among the multiple terminal devices belonging to the specific group as a specific terminal device; and transferring the function of managing the communication of the communication group to the specific terminal device.

[0012] According to this disclosure, a new communication network can be formed in times of emergency.

[0013] Figure 1 is a diagram showing an example configuration of a communication system according to an embodiment. Figure 2 is a diagram illustrating the overview of the processing of the communication system according to the first embodiment. Figure 3 is a block diagram showing an example configuration of a terminal device according to the first embodiment. Figure 4 is a block diagram showing an example configuration of a PoC server according to the first embodiment. Figure 5 is a flowchart showing the processing flow of the communication system according to the first example of the first embodiment. Figure 6 is a flowchart showing the authentication processing flow of the core network according to the first example of the first embodiment. Figure 7 is a flowchart showing the authentication processing flow of PoC account information according to the first example of the first embodiment. Figure 8 is a flowchart showing the registration processing flow of global IP address information according to the first example of the first embodiment. Figure 9 is a flowchart showing the registration processing flow of location information of the terminal device according to the first example of the first embodiment. Figure 10 is a flowchart showing the processing flow of the communication system according to the second example of the first embodiment. Figure 11 is a flowchart showing the processing flow for determining whether or not to migrate the server functions according to the first embodiment. Figure 12 is a flowchart showing the function migration processing flow of the PoC server according to the second example of the first embodiment. Figure 13 is a flowchart showing the function migration processing flow of the PoC server according to the second example of the first embodiment. Figure 14 is a flowchart showing the flow of the function migration process of the PoC server according to the second example of the first embodiment. Figure 15 is a flowchart showing the flow of the process in which a specific terminal device determines line setting information according to the second example of the first embodiment. Figure 16 is a diagram showing an example of a line switching destination table according to the first embodiment. Figure 17 is a flowchart showing the flow of the PoC account authentication process between a specific terminal device and a terminal device according to the second example of the first embodiment. Figure 18 is a flowchart showing the flow of the process for operating a local area network communication system according to the second example of the first embodiment. Figure 19 is a flowchart showing the flow of the communication system process according to the third example of the first embodiment. Figure 20 is a flowchart showing the flow of the function migration process of the PoC server according to the third example of the first embodiment. Figure 21 is a flowchart showing the flow of the function migration process of the PoC server according to the third example of the first embodiment.Figure 22 is a flowchart illustrating the flow of the function migration process of a PoC server according to a third example of the first embodiment. Figure 23 is a block diagram illustrating an example configuration of a PoC server according to the second embodiment. Figure 24 is a diagram illustrating the process of determining a specific terminal device according to the second embodiment. Figure 25 is a diagram illustrating the method of calculating an evaluation value according to the second embodiment. Figure 26 is a flowchart illustrating the processing flow of a communication system according to the second embodiment. Figure 27 is a diagram illustrating the method of deriving the boundary line between a broadcast area and an unbroadcast area according to the second embodiment. Figure 28 is a diagram illustrating the process of determining a specific terminal device according to the third embodiment. Figure 29 is a flowchart illustrating the processing flow of a communication system according to the third embodiment. Figure 30 is a diagram illustrating the process of determining a specific terminal device according to a first modification of the third embodiment.

[0014] Embodiments relating to this disclosure will be described in detail below with reference to the attached drawings. However, this embodiment does not limit this disclosure, and in the following embodiments, the same parts are denoted by the same reference numerals to avoid redundant explanations.

[0015] [First Embodiment] (Communication System) An example of the configuration of a communication system according to the first embodiment will be described using Figure 1. Figure 1 is a diagram showing an example of the configuration of a communication system according to the embodiment.

[0016] Communication system 1 includes terminal device 10-1, terminal device 10-2, terminal device 10-3, base station 11, core network device 12, PoC (Push to Talk over Cellular) server 13, and DDNS (Dynamic Domain Name System) server 14. Communication system 1 is a PoC system that performs wireless communication using a mobile phone network.

[0017] Terminal devices 10-1, 10-2, and 10-3 are PoC terminals that perform PoC communication. When there is no need to distinguish between terminal devices 10-1, 10-2, and 10-3, they are collectively referred to as terminal device 10. Terminal device 10 can be implemented, for example, as a business radio or a smartphone. Terminal devices 10-1, 10-2, and 10-3 can communicate with each other via base station 11.

[0018] Base station 11 is a base station of a telecommunications carrier. Base station 11 is, for example, an eNodeB if it supports LTE. Base station 11 includes, for example, a gNodeB if it supports 5G. Base station 11 includes, for example, RRH (Remote Radio Head), BBU (Base Band Unit), RU (Radio Unit), DU (Distributed Unit), CU (Centralized Unit), etc.

[0019] Base station 11 transmits notification information to terminal device 10 in advance to inform of an emergency, such as a major earthquake. The notification information may be, but is not limited to, information from the Earthquake Tsunami Warning System (ETWS).

[0020] The core network device 12 is a device that controls the core network of a telecommunications carrier. The core network includes EPC (Evolved Packet Core), 5GC (5G Core), etc. The core network device 12 may include a gateway device that connects the core network to the internet. If the core network device 12 supports LTE, for example, it may include a P-GW (Packet Gateway). If the core network device 12 supports 5G, for example, it may include a UPF (User Plane Function). As a result, the terminal device 10 can communicate with the PoC server connected to the internet side via the base station 11 and the gateway device of the core network device 12. Connecting via the core network and the gateway device of the core network device 12 in this manner is also referred to as connecting via the core network device 12.

[0021] The PoC server 13 is a server device that manages PoC communication in the communication system 1. The PoC server 13 is also called a management device.

[0022] The DDNS server 14 is a server device that stores the domain information of the terminal device 10 and global IP address information indicating the global IP address. Specifically, the DDNS server 14 stores the dynamically changing global IP address information of the terminal device 10. It may also store the domain information of the PoC server 13 and global IP address information indicating the global IP address.

[0023] (Overview of the communication system's processing) The overview of the communication system's processing according to the first embodiment will be explained using Figure 2. Figure 2 is a diagram illustrating the overview of the communication system's processing according to the first embodiment.

[0024] If an emergency such as a major earthquake occurs while communication system 1 is in operation, terminal devices 10-1, 10-2, and 10-3 may be unable to perform group communication. Therefore, in this disclosure, if an emergency is predicted to occur, before the emergency occurs, the PoC server 13 configures communication system 1A by transferring the function for performing group communication to a specific terminal device (for example, terminal device 10-1) belonging to the communication group. The terminal device 10 to which the function for performing group communication is transferred may also be called a specific terminal device. In this embodiment, terminal device 10-1 is described as a specific terminal device. Among multiple terminal devices 10 belonging to the same communication group, the specific terminal device may be predetermined. There may be one specific terminal device or multiple specific terminal devices.

[0025] Communication system 1A includes terminal device 10-1, terminal device 10-2, and terminal device 10-3. In communication system 1A, terminal device 10-1 functions as a PoC server. Terminal devices 10-1 through 10-3 are located in the same area. In other words, communication system 1A can be said to be a PoC system formed in a local area. Because terminal device 10-1 functions as a PoC server in the local area, it is sometimes called a micro PoC server.

[0026] In this disclosure, if an emergency is anticipated, the system switches from communication system 1 to communication system 1A, and terminal device 10-1 functions as a micro PoC server in the local area. Therefore, even after an emergency occurs, terminal devices 10-1 and 10-3 can continue to communicate as a group.

[0027] (Terminal Device) An example of the configuration of a terminal device according to the first embodiment will be described using Figure 3. Figure 3 is a block diagram showing an example of the configuration of a terminal device according to the first embodiment.

[0028] As shown in Figure 3, the terminal device 10 includes an input unit 20, a display unit 22, a microphone 24, a speaker 26, a first communication unit 28, a second communication unit 30, a GNSS receiving unit (Global Navigation Satellite System) 32, a storage unit 34, and a control unit 36.

[0029] The input unit 20 receives various input operations for the terminal device 10. The input unit 20 outputs an operation signal to the control unit 36 ​​corresponding to the received input operation. The input unit 20 includes, for example, a touch panel, buttons, switches, PTT (Push-to-Talk) buttons, etc. When a touch panel is used as the input unit 20, the input unit 20 is arranged on the display unit 22.

[0030] The display unit 22 displays various types of images. The display unit 22 is a display including, for example, a liquid crystal display or an organic EL (Electro-Luminescence) display.

[0031] Microphone 24 is a microphone that detects sounds in the vicinity of the terminal device 10. Microphone 24 detects the voice of the user using the terminal device 10. Microphone 24 converts the detected sound into an audio signal. Microphone 24 outputs the audio signal to the control unit 36.

[0032] Speaker 26 is a speaker that outputs various types of audio. Speaker 26 outputs the voice of the user of the terminal device 10 that is the communication destination.

[0033] The first communication unit 28 is a communication interface that performs communication using a first communication method. The first communication method is a communication method that performs communication via a mobile phone line such as LTE (Long Term Evolution) or 5G (Fifth Generation Mobile Communication System). The first communication unit 28 communicates with the base station 11 using the first communication method, for example.

[0034] The second communication unit 30 is a communication interface that performs communication using a second communication method. The second communication method is a communication method that performs communication using short-range wireless technology such as Wi-Fi® or Bluetooth®. The second communication unit 30 communicates with other terminal devices 10 using, for example, the second communication method.

[0035] The GNSS receiving unit 32 consists of a GNSS receiver and the like that receives GNSS signals from GNSS satellites. The GNSS receiving unit 32 outputs the received GNSS signals to the control unit 36.

[0036] The memory unit 34 stores various types of information. The memory unit 34 stores the calculation contents of the control unit 36 ​​and information such as programs. The memory unit 34 includes at least one of the following: a main memory device such as RAM (Random Access Memory) and ROM (Read Only Memory), or an external memory device such as an HDD (Hard Disk Drive).

[0037] The control unit 36 ​​controls each part of the terminal device 10. The control unit 36 ​​includes, for example, an information processing device such as a CPU (Central Processing Unit) or an MPU (Micro Processing Unit), and a storage device such as RAM or ROM. The control unit 36 ​​executes a program that controls the operation of the terminal device 10 according to the present invention. The control unit 36 ​​may be implemented by an integrated circuit such as an ASIC (Application Specific Integrated Circuit) or an FPGA (Field Programmable Gate Array). The control unit 36 ​​may be implemented by a combination of hardware and software.

[0038] (Management device) An example of the configuration of the PoC server according to the first embodiment will be described using Figure 4. Figure 4 is a block diagram showing an example of the configuration of the PoC server according to the first embodiment.

[0039] As shown in Figure 4, the PoC server 13 comprises a communication unit 40, a storage unit 42, and a control unit 44.

[0040] The communication unit 40 is a communication interface that communicates with external devices. For example, the communication unit 40 communicates with a base station 11 or a terminal device 10.

[0041] The storage unit 42 stores various types of information. The storage unit 42 stores the calculation content of the control unit 44 and information such as programs. The storage unit 42 includes at least one of, for example, a main storage device such as a RAM and a ROM, and an external storage device such as an HDD.

[0042] The control unit 44 controls each part of the PoC server 13. The control unit 44 has, for example, an information processing device such as a CPU or an MPU, and a storage device such as a RAM or a ROM. The control unit 44 executes a program for controlling the operation of the PoC server 13 according to the present invention. The control unit 44 may be realized by an integrated circuit such as an ASIC or an FPGA. The control unit 44 may be realized by a combination of hardware and software.

[0043] The control unit 44 includes an acquisition unit 50, a specification unit 52, a function transfer unit 54, and a notification unit 56.

[0044] The acquisition unit 50 acquires various types of information. The acquisition unit 50 acquires, for example, a notification of reception of notification information indicating that the terminal device 10 has received notification information acquired from the base station 11 from the terminal device 10.

[0045] The acquisition unit 50 acquires, for example, line setting information selected by a specific terminal device as information on a line for the specific terminal device to perform group communication in a specific group from the specific terminal device. [[ID=Z]]

[0046] The specification unit 52 specifies a communication group including a specific terminal device that migrates a function for performing group communication in PoC communication as a specific group. For example, when the acquisition unit 50 acquires a notification of reception of notification information from a predetermined number or more of terminal devices 10 belonging to the communication group, the specification unit 52 specifies that communication group as a specific group.

[0047] The function transfer unit 54 transfers a function for managing PoC communication possessed by the PoC server 13 to a specific terminal device among the terminal devices 10 belonging to the specific group. Specifically, the function transfer unit 54 transfers a group management function and a group communication function for performing group communication by PoC communication to the specific terminal device.

[0048] When the acquisition unit 50 acquires the line setting information, the notification unit 56 transmits, via the communication unit 40, the line setting information acquired by the acquisition unit 50 to the terminal devices 10 other than the specific terminal device among the plurality of terminal devices 10 belonging to the specific group.

[0049] (Processing Contents of Communication System) (First Example) The flow of processing of the communication system according to the first example of the first embodiment will be described using FIG. 5. FIG. 5 is a flowchart showing the flow of processing of the communication system according to the first example of the first embodiment.

[0050] The processing shown in FIG. 5 is the processing in normal times of the communication system 1.

[0051] The control unit 36 of each terminal device 10 connects to the base station 11 (step S10). At this time, the control unit 36 of each terminal device 10 may transmit the position information of its own device to the base station 11. The control unit 36 of each terminal device 10 determines whether or not the authentication of the core network has been completed (step S12).

[0052] FIG. 6 is a flowchart showing the flow of authentication processing of the core network according to the first example of the first embodiment.

[0053] The core network device 12 determines whether or not the position of the terminal device 10 is within a predetermined communication area (step S30). When it is determined that the position of the terminal device 10 is within the predetermined communication area (step S30; Yes), the process proceeds to step S32. When it is determined that the position of the terminal device 10 is not within the predetermined communication area (step S30; No), the process proceeds to step S36.

[0054] When it is determined Yes in step S30, the core network device 12 performs SIM (Subscriber Identity Module) authentication (step S32). Specifically, the core network device 12 performs SIM authentication based on the SIM information of the terminal device 10 and the SIM information stored in the core network device 12.

[0055] Once SIM authentication is complete, communication between the terminal device 10 and the base station 11 begins (step S34). Specifically, the terminal device 10 and the base station 11 can communicate using telecommunications such as LTE or 5G. The control unit 36 ​​of the terminal device 10 becomes able to acquire broadcast information from the core network.

[0056] If the result in step S30 is No, the core network device 12 determines that SIM authentication is unsuccessful (step S36). In this case, communication between the terminal device 10 and the base station 11 is not initiated.

[0057] Return to Figure 5. If it is determined that core network authentication is complete (Step S12; Yes), proceed to Step S14. If it is determined that core network authentication is not complete (Step S12; No), proceed to Step S10.

[0058] If the result in step S12 is determined to be Yes, the control unit 36 ​​of each terminal device 10 performs authentication of the PoC account information (step S14). The control unit 36 ​​of each terminal device 10 determines whether or not the authentication of the PoC account information has been completed (step S16).

[0059] Figure 7 is a flowchart showing the flow of the authentication process for PoC account information according to the first example of the first embodiment.

[0060] The control unit 36 ​​of the terminal device 10 connects to the PoC server 13 via the base station 11 and the core network device 12 (step S40). The control unit 36 ​​of the terminal device 10 performs PoC account authentication with the PoC server 13 (step S42). Specifically, it transmits PoC account information to the PoC server 13 to perform PoC account authentication. The PoC account information includes, for example, an individual ID that can uniquely identify the terminal device 10, a password, and domain information. It is also preferable to include a group ID, which is information for identifying the group to which the user belongs, in the PoC account information. The PoC account information is also called account information.

[0061] The control unit 44 of the PoC server 13 determines whether the PoC account information of the terminal device 10 is correct or not (step S44). Specifically, the control unit 44 of the PoC server 13 determines that the PoC account information of the terminal device 10 is correct if the PoC account information obtained from the terminal device 10 matches the PoC account information stored in the storage unit 42 of the PoC server 13. If the PoC account information is determined to be correct (step S44; Yes), the process proceeds to step S46. If the PoC account information is determined to be incorrect (step S44; No), the process proceeds to step S48.

[0062] If the answer is Yes in step S44, the authentication of the PoC account performed by the terminal device 10 is successful (step S46). Once the authentication of the PoC account is successful, the control unit 36 ​​of the terminal device 10 makes various functions of the PoC available, such as voice calls, messaging, and location information notification.

[0063] If the result in step S44 is determined to be No, the authentication of the PoC account performed by the terminal device 10 will fail (step S48). In this case, the control unit 36 ​​of the terminal device 10 will not be able to use the various functions of the PoC.

[0064] Return to Figure 5. If it is determined that the authentication of the PoC account information is complete (Step S16; Yes), proceed to Step S18. If it is determined that the authentication of the PoC account information is not complete (Step S16; No), proceed to Step S14.

[0065] If the result in step S16 is determined to be Yes, the control unit 36 ​​of the terminal device 10 registers the global IP address information indicating the global IP address of the terminal device 10 with the DDNS server 14 (step S18). However, the process of registering the global IP address information with the DDNS server 14 does not necessarily have to be performed in this step. For example, as shown in Figure 8, the process of registering the global IP address information assigned to the terminal device 10 with the DDNS server 14 may be performed when the terminal device 10 connects to an LTE line. Alternatively, the process of registering the newly assigned global IP address information with the DDNS server 14 may be performed when the global IP address information of the terminal device 10 is changed. The control unit 36 ​​of the terminal device 10 determines whether the registration of the global IP address information has been completed (step S20).

[0066] Figure 8 is a flowchart showing the flow of the global IP address information registration process according to the first example of the first embodiment.

[0067] The control unit 36 ​​of the terminal device 10 connects to the LTE line using the first communication unit 28 (step S50).

[0068] The control unit 36 ​​of the terminal device 10 acquires global IP address information (step S52). Specifically, the terminal device 10 is assigned a local IP address from the core network device 12. In addition, the terminal device 10 is assigned a global IP address from the gateway device of the core network device 12, which is located between the core network and the internet. That is, the control unit 36 ​​of the terminal device 10 acquires global IP address information from the gateway device of the core network device 12.

[0069] The control unit 36 ​​of the terminal device 10 registers terminal information, including global IP address information and domain information, with the DDNS server 14 (step S54). The domain information is the URL (Uniform Resource Locator) registered in the PoC account information. For example, the domain information is "www.micropositorserver.com".

[0070] When the terminal information of terminal device 10 is registered with the DDNS server 14, the operation of communication system 1 begins (step S56).

[0071] The control unit 36 ​​of the terminal device 10 determines whether or not the global IP address has been changed (step S58). If it is determined that the global IP address has not been changed (step S58; No), the process returns to Figure 5. If it is determined that the global IP address has been changed (step S58; Yes), the process proceeds to step S52.

[0072] In other words, if the result in step 58 is determined to be Yes, the processing from step S52 to step S56 is repeated. For example, if the global IP address changes from "10.11.22.121" to "10.11.22.151", the control unit 36 ​​of the terminal device 10 re-registers the terminal information with the DDNS server 14. This allows the control unit 36 ​​of the terminal device 10 to access the device using the same domain information even if the global IP address changes.

[0073] Return to Figure 5. If it is determined that the registration of global IP address information is complete (Step S20; Yes), proceed to Step S22. If it is not determined that the registration of global IP address information is complete (Step S20; No), proceed to Step S18.

[0074] If the result in step S20 is determined to be Yes, the control unit 36 ​​of the terminal device 10 registers the current location information of its device with the PoC server 13 (step S22).

[0075] Figure 9 is a flowchart showing the flow of the terminal device location information registration process according to the first example of the first embodiment.

[0076] The control unit 36 ​​of the terminal device 10 acquires the current location information (step S60). Specifically, the control unit 36 ​​of the terminal device 10 calculates the current location information of the terminal device 10 based on the GNSS signal received by the GNSS receiving unit 32. The control unit 36 ​​of the terminal device 10 may also calculate the current location information of the terminal device 10 using information such as the TAC (Tracking Area Code) or Cell ID of the base station 11.

[0077] The control unit 36 ​​of the terminal device 10 transmits the current location information of the terminal device 10 to the PoC server 13 via the first communication unit 28 (step S62). The control unit 44 of the PoC server 13 stores the location information received from the terminal device 10 in the storage unit 42 (step S64).

[0078] The control unit 36 ​​of the terminal device 10 determines whether or not the location information has been changed (step S66). The control unit 36 ​​of the terminal device 10 determines that the location information has been changed, for example, when the device has moved more than a predetermined distance. The control unit 36 ​​of the terminal device 10 may also determine that the location information has been changed, for example, when the TAC or Cell ID has been updated. If it is determined that the location information has been changed (step S66; Yes), the process proceeds to step S60. If it is determined that the location information has not been changed (step S66; No), the process proceeds to step S68.

[0079] In other words, if the result in step S66 is determined to be Yes, the processing from steps S60 to S64 is repeated. In this case, the control unit 36 ​​of the terminal device 10 sends the latest current location information to the PoC server 13 each time the location changes. Therefore, the location information of the terminal device 10 registered in the PoC server 13 is updated each time the location of the terminal device 10 changes.

[0080] If the result in step S66 is determined to be No, the operation of communication system 1 continues.

[0081] The processing described above, according to the first example of the first embodiment shown in Figures 5 to 9, is the processing of the communication system 1 during normal times when no emergency has occurred.

[0082] (Second Example) The processing flow of the communication system according to the second example of the first embodiment will be explained using Figure 10. Figure 10 is a flowchart showing the processing flow of the communication system according to the second example of the first embodiment.

[0083] The process shown in Figure 10 is the process of transferring the functions of the PoC server 13 to a specific terminal device, terminal device 10-1, when it is determined that an emergency has occurred.

[0084] The notification unit 56 of the PoC server 13 notifies the terminal device 10-1 that it will start the server function migration process (step S80).

[0085] Figure 11 is a flowchart showing the process flow for determining whether or not to migrate the server functions according to the first embodiment.

[0086] When the base station 11 predicts the occurrence of an emergency, it transmits notification information to the terminal device 10 to inform it of the occurrence of an emergency (step S110). The control unit 36 ​​of the terminal device 10 receives the notification information transmitted by the base station 11 (step S112).

[0087] The control unit 36 ​​of the terminal device 10 sends a notification of notification information reception to the PoC server 13 indicating that it has received notification information from the base station 11 (step S114).

[0088] The acquisition unit 50 of the PoC server 13 acquires notification of received notification information from the terminal device 10 (step S116).

[0089] The identification unit 52 of the PoC server 13 determines whether the number of notification of received broadcast information acquired by the acquisition unit 50 is equal to or greater than a threshold (step S118). In other words, the identification unit 52 of the PoC server 13 determines whether the number of terminal devices 10 that have received broadcast information from the base station 11 is equal to or greater than a threshold. Specifically, the identification unit 52 identifies a communication group as a specified group when the acquisition unit 50 has received more than or equal to a threshold number of notification of received broadcast information from multiple terminal devices 10 belonging to the same communication group. If it is determined that the number of received broadcast information notifications acquired is equal to or greater than a threshold (step S118; Yes), the process proceeds to step S120. If it is determined that the number of received broadcast information notifications acquired is not equal to or greater than a threshold (step S118; No), the process proceeds to step S122.

[0090] If the result in step S118 is Yes, the function migration unit 54 of the PoC server 13 notifies terminal device 10-1, which is a specific terminal device among the multiple terminal devices 10 belonging to a specific group, that it will start the server function migration process (step S120).

[0091] If the result in step S118 is determined to be No, the operation of communication system 1 continues (step S122). In this case, the processes from step S110 to step S118 are repeatedly executed.

[0092] Return to Figure 10. Terminal device 10-1 and PoC server 13 begin the process of transferring the functions of PoC server 13 to terminal device 10-1 (step S82).

[0093] Figures 12 to 14 are flowcharts showing the flow of the function migration process of the PoC server according to the second example of the first embodiment.

[0094] The control unit 36 ​​of terminal device 10-1, which is a specific terminal device, sends a notification result to the PoC server 13 regarding the notification to start the server function migration process (step S130). Specifically, the control unit 36 ​​of terminal device 10-1 sends a notification result to the PoC server 13 indicating whether to accept or reject the server function migration.

[0095] The acquisition unit 50 of the PoC server 13 determines whether or not it has acquired a notification result from the terminal device 10-1 (step S132). If it is determined that a notification result has been acquired (step S132; Yes), the process proceeds to step S134. If it is determined that a notification result has not been acquired (step S132; No), the process proceeds to step S136.

[0096] If the result in step S132 is determined to be Yes, the function transition unit 54 of the PoC server 13 determines whether the notification result obtained from the terminal device 10-1 is accepted or not (step S134). If the notification result is determined to be accepted (step S134; Yes), the process proceeds to step S138. If the notification result is determined to be rejected (step S134; No), the process proceeds to step S140.

[0097] If the result is determined to be No in step S132, the control unit 44 of the PoC server 13 requests the terminal device 10-1 to resend the notification result (step S136). In this case, the processing in steps S130 and S132 is repeated.

[0098] If the result in step S134 is determined to be Yes, the function transfer unit 54 of the PoC server 13 issues a token and transmits the token to the terminal device 10-1 (step S138). In this embodiment, the token is a certificate containing information such as a timestamp, an electronic signature, and a unique identifier of the terminal device 10-1. The unique identifier of the terminal device 10-1 is, for example, the MAC (Media Access Control) address and the IMEI (International Mobile Equipment Identity) number.

[0099] If the result is determined to be No in step S134, the transfer process of the functions of the PoC server 13 from the PoC server 13 to the terminal device 10-1 will fail (step S140). In this case, the process will terminate.

[0100] After step S138, the control unit 36 ​​of the terminal device 10-1 determines whether or not it has received a token from the PoC server 13 (step S142). If it is determined that a token has been received (step S142; Yes), the process proceeds to step S144. If it is determined that a token has not been received (step S142; No), the process proceeds to step S146.

[0101] If the result in step S142 is determined to be Yes, the control unit 36 ​​of the terminal device 10-1 sends a token reception completion notification to the PoC server 13 (step S144).

[0102] If the result in step S142 is determined to be No, the control unit 36 ​​of the terminal device 10-1 requests the PoC server 13 to resend the token (step S146). In this case, the processing in steps S138 and S142 is repeated.

[0103] After step S144, the function transfer unit 54 of the PoC server 13 transmits account information for a specific group to the terminal device 10-1 (step S148). The account information includes information necessary for PoC authentication and PoC communication. For example, it includes an individual ID that can uniquely identify the terminal device 10, a password, and domain information. The account information may also include a group ID, which is information to identify the group to which the user belongs.

[0104] The control unit 36 ​​of the terminal device 10-1 determines whether or not it has received account information from the PoC server 13 (step S150). If it is determined that account information has been received (step S150; Yes), the process proceeds to step S152. If it is determined that account information has not been received (step S150; No), the process proceeds to step S154.

[0105] If the answer is Yes in step S150, the control unit 36 ​​of the terminal device 10-1 sends a notification to the PoC server 13 indicating that the account information has been received (step S152).

[0106] If the result in step S150 is determined to be No, the control unit 36 ​​of the terminal device 10-1 requests the PoC server 13 to resend the account information (step S154). In this case, the processing in steps S148 and S150 is repeated.

[0107] After step S152, the control unit 36 ​​of the terminal device 10-1 determines the line configuration information (step S156). The line configuration information is information necessary for the operation of the PoC system on the local area network. The line configuration information includes, for example, the wireless access technology to which the local area network line is switched, the information necessary to connect to the wireless access technology, and the location information of the terminal device 10-1. If the wireless access technology is Wi-Fi, the information necessary to connect to the wireless access technology is, for example, SSID and password information. If the wireless access technology is LTE or local 5G, it is SIM information. The PoC server 13, for example, in random access during the initial connection of each wireless access technology, determines the location of the terminal device 10-1 in advance using the location information and connects.

[0108] Figure 15 is a flowchart showing the process flow for determining line setting information by a specific terminal device according to a second example of the first embodiment.

[0109] The control unit 36 ​​refers to the line switching destination table stored in the storage unit 34 (step S200). Figure 16 is a diagram showing an example of a line switching destination table according to the first embodiment. The line switching destination table T1 includes items such as "priority" and "line". The line switching destination table T1 is information that associates priority with line. Lines with higher priority are more likely to be selected. Although the line switching destination table T1 shows three priority levels from "1" to "3", this disclosure is not limited to these.

[0110] The control unit 36 ​​selects a line with priority "1" based on the line switching destination table T1 (step S202).

[0111] The control unit 36 ​​determines whether the line with priority "1" is valid or not (step S204). If it is determined that the line with priority "1" is valid (step S204; Yes), the process proceeds to step S206. If it is determined that the line with priority "1" is not valid (step S204; No), the process proceeds to step S208.

[0112] If the answer in step S204 is Yes, the control unit 36 ​​sets the switch to the line with priority "1" (step S206). Specifically, the control unit 36 ​​determines the "Local 5G" line with priority "1" as the switch destination based on the line switching destination table T1.

[0113] If the result in step S204 is determined to be "No", the control unit 36 ​​selects a line with priority "2" based on the line switching destination table T1 (step S208).

[0114] The control unit 36 ​​determines whether the line with priority "2" is valid or not (step S210). If it is determined that the line with priority "2" is valid (step S210; Yes), the process proceeds to step S212. If it is determined that the line with priority "2" is not valid (step S210; No), the process proceeds to step S214.

[0115] If the answer is Yes in step S210, the control unit 36 ​​sets the switch to the line with priority "2" (step S212). Specifically, the control unit 36 ​​determines "Wi-Fi" with priority "2" as the switch destination based on the line switching destination table T1.

[0116] If the result in step S210 is determined to be "No", the control unit 36 ​​selects a line with priority "3" based on the line switching destination table T1 (step S214).

[0117] The control unit 36 ​​determines whether the line with priority "3" is valid or not (step S214). If it is determined that the line with priority "3" is valid (step S214; Yes), the process proceeds to step S218. If it is determined that the line with priority "3" is not valid (step S216; No), the process proceeds to step S202.

[0118] If the result in step S216 is determined to be Yes, the control unit 36 ​​sets the switch to the line with priority "3" (step S218). Specifically, the control unit 36 ​​determines the "Private LTE" line with priority "3" as the switch destination based on the line switching destination table T1.

[0119] Once the destination line is determined, the process proceeds to Figure 13.

[0120] The control unit 36 ​​of the terminal device 10-1 sends a notification to the PoC server 13 indicating that the account information has been received and a notification of the line setting information (step S160).

[0121] The acquisition unit 50 of the PoC server 13 determines whether or not it has received a notification of completion of receiving account information and a notification of line setting information from the terminal device 10-1 (step S162). If it is determined that it has received the notification of completion of receiving account information and the notification of line setting information (step S162; Yes), the process proceeds to step S164. If it is determined that it has not received the notification of completion of receiving account information and the notification of line setting information (step S162; No), the process proceeds to step S166.

[0122] If the result in step S162 is determined to be No, the control unit 44 of the PoC server 13 requests the terminal device 10-1 to resend a notification of completion of receiving account information and a notification of line setting information (step S166). In this case, the processing in steps S160 and S162 is repeated.

[0123] If the result in step S162 is determined to be Yes, the control unit 44 of the PoC server 13 receives the line configuration destination (step S164). The control unit 44 of the PoC server 13 sends a response to the terminal device 10-1 acknowledging receipt of the line configuration destination (step S168).

[0124] The control unit 36 ​​of the terminal device 10-1 determines whether or not it has received a confirmation from the PoC server 13 that the line configuration destination has been received (step S170). If it is determined that a confirmation from the line configuration destination has been received (step S170; Yes), the process proceeds to Figure 14. If it is determined to be No in step S170, the control unit 36 ​​of the terminal device 10-1 requests the PoC server 13 to resend the confirmation from the line configuration destination (step S172). In this case, the processes of steps S168 and S170 are repeated.

[0125] If the result in step S170 is determined to be Yes, the control unit 36 ​​of the terminal device 10-1 performs line configuration (step S174). Specifically, the control unit 36 ​​of the terminal device 10-1 switches the line in order to perform PoC communication in the local area.

[0126] The notification unit 56 of the PoC server 13 sends line configuration information and a notification of the start of the migration to terminal devices 10 other than the specific terminal device belonging to the specific group (step S176).

[0127] The control unit 36 ​​of the terminal device 10 other than the specific terminal device belonging to the specific group performs line configuration (step S178). Specifically, the control unit 36 ​​of the terminal device 10 other than the specific terminal device belonging to the specific group switches the line in order to perform PoC communication in the local area.

[0128] Terminal devices 10 other than the specific terminal device belonging to the specific group send a notification of completion of line setup to the PoC server 13 (step S180).

[0129] The acquisition unit 50 of the PoC server 13 determines whether or not it has received a line configuration completion notification from a terminal device 10 other than the specific terminal device belonging to the specific group (step S182). If it is determined that a line configuration completion notification has been received (step S182; Yes), the process proceeds to step S184. If it is determined that a line configuration completion notification has not been received (step S182; No), the process proceeds to step S186.

[0130] If the result in step S182 is determined to be Yes, the control unit 44 of the PoC server 13 stores the account information of the terminal device 10 that has completed the line switching in the storage unit 42 (step S184). Then, the process returns to the process shown in Figure 10.

[0131] If the result in step S182 is determined to be No, the control unit 44 of the PoC server 13 requests the terminal devices 10 other than the specific terminal device belonging to the specific group to resend the line setup completion notification (step S186). In this case, the processing in steps S180 and S182 is repeated.

[0132] Return to Figure 10. The control unit 44 of the PoC server 13 determines whether the migration of the functions of the PoC server 13 has been completed (step S84). If it is determined that the migration of the functions of the PoC server 13 has been completed (step S84; Yes), proceed to step S86. If it is determined that the migration of the functions of the PoC server 13 has not been completed (step S84; No), proceed to step S82, and the migration of the functions of the PoC server 13 continues.

[0133] If the result in step S84 is determined to be Yes, the control unit 36 ​​of terminal device 10-1 (specific terminal device) and the control unit 36 ​​of terminal devices 10 other than the specific terminal device belonging to the specific group perform PoC account authentication (step S86).

[0134] Figure 17 is a flowchart showing the flow of the authentication process for a PoC account between a specific terminal device and another terminal device, relating to a second example of the first embodiment.

[0135] The control unit 36 ​​of terminal device 10-1 (specific terminal device) uses the first communication unit 28 or the second communication unit 30 to determine whether or not it is possible to connect to the Internet (step S230). If it is determined that it is possible to connect to the Internet (step S230; Yes), the process proceeds to step S232. If it is determined that it is not possible to connect to the Internet (step S230; No), the process proceeds to step S234.

[0136] If the result in step S230 is Yes, the control unit 36 ​​of the terminal device 10 other than the specific terminal device belonging to the specific group uses the first communication unit 28 or the second communication unit 30 to determine whether or not it is possible to connect to the Internet (step S232). If it is determined that it is possible to connect to the Internet (step S232; Yes), the process proceeds to step S236. If it is determined that it is not possible to connect to the Internet (step S232; No), the process proceeds to step S242.

[0137] If the result in step S230 is No, then terminal devices 10 other than the specific terminal device belonging to the specific group will be unable to connect to terminal device 10-1 (specific terminal device) (step S234).

[0138] The control unit 36 ​​of a terminal device 10 other than the specified terminal device belonging to the specified group confirms the global IP address associated with the domain information of terminal device 10-1 (specified terminal device) with the DDNS server 14 (step S236). The control unit 36 ​​of a terminal device 10 other than the specified terminal device belonging to the specified group obtains global IP address information from the DDNS server 14 that indicates the global IP address confirmed in step S236 (step S238).

[0139] The control unit 36 ​​of terminal devices 10 other than the specific terminal device belonging to the specific group connects to terminal device 10-1 via the internet based on the global IP address information obtained in step S238 (step S240).

[0140] If the result is No in step S232, or after step S234, the control unit 36 ​​of the terminal device 10 other than the specified terminal device belonging to the specified group searches for the location of terminal device 10-1 (specified terminal device) (step S242). For example, the control unit 36 ​​of the terminal device 10 other than the specified terminal device belonging to the specified group searches for terminal device 10-1 (specified terminal device) by short-range wireless communication using the second communication unit 30.

[0141] The control unit 36 ​​of a terminal device 10 other than the specific terminal device belonging to the specific group determines whether or not it has detected terminal device 10-1 (the specific terminal device) (step S244). If it is determined that terminal device 10-1 (the specific terminal device) has been detected (step S244; Yes), the process proceeds to step S246. If it is determined that terminal device 10-1 (the specific terminal device) has not been detected (step S244; No), the process proceeds to step S242. In this case, the processing of steps S242 and S244 is repeated.

[0142] If Yes is determined in step S244, the control unit 36 ​​of the terminal device 10 other than the specific terminal device belonging to the specific group connects to terminal device 10-1 (specific terminal device) via short-range wireless communication (step S246).

[0143] After step S240 or step S246, the control unit 44 of the specified terminal device initiates PoC authentication (step S248). Specifically, the control unit 44 of the specified terminal device performs PoC authentication using authentication information including the domain information and password of terminal devices 10 other than the specified terminal device belonging to the specified group.

[0144] The control unit 44 of the specific terminal device determines whether the authentication information is correct or not (step S250). For example, the control unit 44 of the specific terminal device determines that the authentication information is correct if the authentication information stored in the storage unit 42 matches the authentication information obtained from terminal devices 10 other than the specific terminal device belonging to the specific group. If the authentication information is determined to be correct (step S250; Yes), the process proceeds to step S252. If the authentication information is determined to be incorrect (step S250; No), the process proceeds to step S254.

[0145] If the answer in step S250 is Yes, then PoC authentication is successful (step S252). Then, PoC authentication is completed (step S256).

[0146] If the result in step S250 is determined to be No, then PoC authentication fails (step S254). In this case, PoC communication on the local area network does not start.

[0147] Return to Figure 10. The control unit 44 of the specific terminal device determines whether or not PoC account authentication has been completed (step S88). If it is determined that PoC account authentication has been completed (step S88; Yes), proceed to step S90. If it is determined that PoC account authentication has not been completed (step S88; No), proceed to step S86, and the PoC account authentication process continues.

[0148] If the answer in step S88 is Yes, then communication system 1 switches to communication system 1A, which is a Proof of Concept (PoC) system of the local area network (step S90).

[0149] Figure 18 is a flowchart showing the process flow for operating a local area network communication system according to a second example of the first embodiment.

[0150] The control unit 36 ​​of terminal devices 10 other than the specific terminal device belonging to the specific group connects to terminal device 10-1 (specific terminal device) via the internet (step S260).

[0151] The control unit 36 ​​of the terminal device 10 other than the specific terminal device belonging to the specific group determines whether or not there is a response to the connection from terminal device 10-1 (the specific terminal device) (step S262). If it is determined that there is a response (step S262; Yes), the process proceeds to step S260. In this case, the connection between terminal device 10-1 (the specific terminal device) and the terminal device 10 other than the specific terminal device belonging to the specific group continues via the Internet. If it is determined that there is no response (step S262; No), the process proceeds to step S264.

[0152] The processes from step S264 to step S268 are the same as the processes from step S242 to step S246 shown in Figure 17, so their explanation will be omitted.

[0153] The control unit 36 ​​of a terminal device 10 other than the specific terminal device belonging to the specific group requests a connection to terminal device 10-1 (the specific terminal device) via the local area network (step S270).

[0154] The control unit 36 ​​of terminal device 10-1 (specific terminal device) determines whether its own device has had its functions transferred from PoC server 13 and is operating as a PoC server in the local area (step S272). If it is determined that it is not operating as a PoC server (step S272; No), the process proceeds to step S274. If it is determined that it is operating as a PoC server (step S272; Yes), the process proceeds to step S276.

[0155] If the result in step S272 is No, then the connection between terminal device 10-1 (specific terminal device) and terminal devices 10 other than the specific terminal device belonging to the specific group will not be established on the local area network (step S274).

[0156] If the answer is Yes in step S272, the control unit 36 ​​of terminal device 10-1 (specific terminal device) assigns a private IP address to terminal devices 10 other than the specific terminal device belonging to the specific group (step S276). The control unit 36 ​​of terminal device 10-1 (specific terminal device) records the domain information and private IP address of the terminal devices 10 other than the specific terminal device belonging to the specific group in the PoC account information (step S278). Then, operation of the communication system 1A, which is a PoC system, in the local area network is started (step S280).

[0157] (Third Example) The processing flow of the communication system according to the third example of the first embodiment will be explained using Figure 19. Figure 19 is a flowchart showing the processing flow of the communication system according to the third example of the first embodiment.

[0158] The process shown in Figure 19 represents the process of returning the functions that were transferred from the PoC server 13 to the terminal device 10-1 (specific terminal device) back to the PoC server 13 when predetermined conditions are met.

[0159] The control unit 36 ​​of terminal device 10-1 (specific terminal device) continues to operate the communication system 1A in the local area (step S290).

[0160] The control unit 36 ​​of terminal device 10-1 (specific terminal device) determines whether the connection conditions to PoC server 13 are met (step 292). For example, the control unit 36 ​​of terminal device 10-1 (specific terminal device) determines that the connection conditions are met when the emergency situation is resolved and stable communication with PoC server 13 is possible. If it is determined that the connection conditions to PoC server 13 are met (step S292; Yes), the process proceeds to step S294. If it is determined that the connection conditions to PoC server 13 are not met (step S292; No), the process proceeds to step S290, and the operation of communication system 1A continues.

[0161] If the result in step S292 is determined to be Yes, the control unit 36 ​​of terminal device 10-1 (specific terminal device) performs a transfer of the PoC server's functions to the PoC server 13 (step S294).

[0162] Figures 20 to 22 are flowcharts showing the flow of the function migration process of the PoC server according to the third example of the first embodiment.

[0163] The control unit 36 ​​of terminal device 10-1 (specific terminal device) sends a Ping to PoC server 13 via base station 11 and core network device 12 (step S300). Sending a Ping means executing a ping command and sending a packet called an echo request to a specified IP address using a network control message protocol called ICMP (Internet Control Message Protocol). If the receiving device is functioning normally, an echo reply packet will be returned.

[0164] The control unit 36 ​​of terminal device 10-1 (specific terminal device) determines whether or not there is a response (echo response) to the Ping from the PoC server 13 (step S302). If it is determined that there is a response (echo response) to the Ping (step S302; Yes), the process proceeds to step S304. If it is determined that there is no response (echo response) to the Ping (step S302; No), the process proceeds to step S300. In this case, the processing of steps S300 and S302 is repeated.

[0165] If the result in step S302 is Yes, the control unit 36 ​​of terminal device 10-1 (specific terminal device) determines whether the response condition satisfies the threshold (step S304). The response condition may be, for example, the number of responses to Ping, the response time, or a combination of the number of responses and the response time. The threshold may be set arbitrarily. If it is determined that the response condition satisfies the threshold (step S304; Yes), the process proceeds to step S306. If it is determined that the response condition does not satisfy the threshold (step S304; No), the process proceeds to step S300. In this case, the process from step S300 to step S304 is repeated.

[0166] If the result in step S304 is determined to be Yes, the control unit 36 ​​of terminal device 10-1 (specific terminal device) sends a token and a notification of the PoC server's function transition request to PoC server 13 (step S306).

[0167] The control unit 44 of the PoC server 13 determines whether to approve the function migration request of the PoC server (step S308). If it determines to approve the function migration request of the PoC server (step S308; Yes), the process proceeds to step S310. If it determines to deny the function migration request of the PoC server (step S308; No), the process proceeds to step S314.

[0168] If the result in step S308 is determined to be Yes, the control unit 44 of the PoC server 13 sends a notification to the terminal device 10-1 (specific terminal device) granting permission to transfer the functions of the PoC server (step S310).

[0169] The control unit 36 ​​of terminal device 10-1 (specific terminal device) receives a notification of permission to transfer the functions of the PoC server (step S312). Then, it proceeds to the process shown in Figure 21.

[0170] The control unit 44 of the PoC server 13 determines whether the token is legitimate or not (step S314). If the token is determined to be legitimate (step S314; Yes), the process proceeds to step S300 and the above process is repeated. If the token is determined to be illegitimate (step S314; No), the process proceeds to step S316.

[0171] If the result in step S314 is determined to be No, the migration of the PoC server's functions will not be completed (step S316). Then, the process ends.

[0172] After step S312, the control unit 36 ​​of the terminal device 10-1 (specific terminal device) transmits the call record from the communication system 1A to the PoC server 13 (step S318).

[0173] When the control unit 36 ​​of terminal device 10-1 (specific terminal device) completes the transmission of the call record in the communication system 1A, it sends a notification of completion of call record transmission to the PoC server 13 (step S320).

[0174] The acquisition unit 50 of the PoC server 13 determines whether or not it has received notification of the completion of transmission of the call record (step S322). If it is determined that it has received notification of the completion of transmission of the call record (step S322; Yes), the process proceeds to step S324. If it is determined that it has not received notification of the completion of transmission of the call record (step S322; No), the process proceeds to step S332.

[0175] If the answer is Yes in step S322, the control unit 44 of the PoC server 13 sends a call record receipt notification to the terminal device 10-1 (specific terminal device) (step S324).

[0176] The control unit 44 of the PoC server 13 sends a connection request notification to terminal device 10-1 (specific terminal device) to allow terminal devices 10 other than the specific terminal device belonging to the specific group to connect to the PoC server 13 (step S326).

[0177] The control unit 36 ​​of terminal device 10-1 (specific terminal device) determines whether or not it has received a connection request notification from the PoC server 13 (step S328). If it is determined that a connection request notification has been received (step S328; Yes), the process proceeds to step S330. If it is determined that a connection request notification has not been received (step S328; No), the process proceeds to step S338.

[0178] If the result in step S328 is determined to be Yes, the control unit 36 ​​of terminal device 10-1 (specific terminal device) sends a connection request notification to terminal devices 10 other than the specific terminal device belonging to the specific group (step S330). Then, the process proceeds to Figure 22.

[0179] If the result is determined to be No in step S322, the control unit 44 of the PoC server 13 sends a retransmission of the call record transmission completion notification to the terminal device 10-1 (specific terminal device) (step S332).

[0180] The control unit 44 of the PoC server 13 determines whether the number of requests for retransmission of the call record transmission completion notification has exceeded a threshold (step S334). For example, the control unit 44 of the PoC server 13 determines that the number of requests for retransmission of the call record transmission completion notification has exceeded a threshold if the number of requests exceeds a predetermined number. If it is determined that the number of requests for retransmission of the call record transmission completion notification has exceeded a threshold (step S334; Yes), the process proceeds to step S336. If it is determined that the number of requests for retransmission of the call record transmission completion notification is below the threshold (step S334; No), the process proceeds to step S332. In this case, the processing of steps S332 and S334 is repeated.

[0181] If the result in step S334 is Yes, the migration of the PoC server's functions will not be completed (step S336). Then the process will end.

[0182] If the result is determined to be No in step S328, the control unit 36 ​​of terminal device 10-1 (specific terminal device) sends a retransmission of the connection request notification to the PoC server 13 (step S338).

[0183] The control unit 36 ​​of terminal device 10-1 (specific terminal device) determines whether the number of retransmission requests for connection request notifications has exceeded a threshold (step S340). For example, the control unit 36 ​​of terminal device 10-1 (specific terminal device) determines that the number of retransmission requests for connection request notifications has exceeded a threshold if the number of retransmission requests for connection request notifications exceeds a predetermined number. If it is determined that the number of retransmission requests for connection request notifications has exceeded a threshold (step S340; Yes), the process proceeds to step S342. If it is determined that the number of retransmission requests for connection request notifications is below the threshold (step S340; No), the process proceeds to step S338. In this case, the processing of steps S338 and S340 is repeated.

[0184] If the result in step S340 is Yes, the migration of the PoC server's functions will not be completed (step S342). Then the process ends.

[0185] After step S330, the control units 36 of terminal devices 10 other than the specific terminal device belonging to the specific group start connecting to the base station 11 (step S346).

[0186] The control unit 36 ​​of a terminal device 10 other than the specified terminal device belonging to the specified group determines whether or not it has received a connection request notification from terminal device 10-1 (the specified terminal device) (step S348). If it is determined that a connection request notification has been received (step S348; Yes), the process proceeds to step S350. If it is determined that a connection request notification has not been received (step S348; No), the process proceeds to step S360.

[0187] If the result in step S348 is determined to be Yes, the control unit 36 ​​of the terminal device 10 other than the specific terminal device belonging to the specific group sends a connection request notification to the PoC server 13 (step S350).

[0188] The acquisition unit 50 of the PoC server 13 determines whether or not it has received a connection request notification from a terminal device 10 other than a specific terminal device belonging to a specific group (step S352). If it is determined that a connection request notification has been received (step S352; Yes), the process proceeds to step S354. If it is determined that a connection request notification has not been received (step S352; No), the process proceeds to step S366.

[0189] If the result in step S352 is determined to be Yes, the control unit 44 of the PoC server 13 sends a connection approval notice to terminal device 10-1 (specific terminal device) and terminal devices 10 other than the specific terminal device belonging to the specific group (step S354). Terminal device 10-1 (specific terminal device) and terminal devices 10 other than the specific terminal device belonging to the specific group receive the connection approval notice from the PoC server 13.

[0190] Then, the communication system is started by the PoC server 13 (step S358). Then, the process ends.

[0191] If the result in step S348 is determined to be No, the control unit 36 ​​of the terminal device 10 other than the specified terminal device belonging to the specified group sends a retransmission of the connection request notification to terminal device 10-1 (specified terminal device) (step S360).

[0192] The control unit 36 ​​of a terminal device 10 other than a specific terminal device belonging to a specific group determines whether the number of requests for retransmission of connection request notifications has exceeded a threshold (step S362). For example, the control unit 36 ​​of a terminal device 10 other than a specific terminal device belonging to a specific group determines that the number of requests for retransmission of connection request notifications has exceeded a threshold if the number of requests for retransmission of connection request notifications exceeds a predetermined number. If it is determined that the number of requests for retransmission of connection request notifications has exceeded a threshold (step S362; Yes), the process proceeds to step S364. If it is determined that the number of requests for retransmission of connection request notifications is below the threshold (step S362; No), the process proceeds to step S360. In this case, the processing of steps S360 and S362 is repeated.

[0193] If the result in step S362 is Yes, the migration of the PoC server's functions will not be completed (step S364). Then the process will end.

[0194] If the result in step S352 is determined to be No, the control unit 44 of the PoC server 13 sends a retransmission of the connection request notification to a terminal device 10 other than the specific terminal device belonging to the specific group (step S366).

[0195] The control unit 44 of the PoC server 13 determines whether the number of requests to resend connection request notifications exceeds a threshold (step S368). For example, the control unit 44 of the PoC server 13 determines that the number of requests to resend connection request notifications exceeds a threshold if the number of requests exceeds a predetermined number. If it is determined that the number of requests to resend connection request notifications exceeds a threshold (step S368; Yes), the process proceeds to step S370. If it is determined that the number of requests to resend connection request notifications is below the threshold (step S368; No), the process proceeds to step S366. In this case, the processing in steps S366 and S368 is repeated.

[0196] If the result in step S368 is Yes, the migration of the PoC server's functions will not be completed (step S370). Then the process will end.

[0197] As described above, in the first embodiment, when an emergency is predicted to occur, the function of the PoC server that controls PoC communication is transferred to a specific terminal device among multiple terminal devices. As a result, in the first embodiment, even if an emergency such as a major earthquake occurs and communication between the terminal device and the PoC server becomes impossible, a PoC communication system can be formed in the local area and PoC communication can be performed.

[0198] [Second Embodiment] An example of the configuration of a PoC server according to the second embodiment will be described using Figure 23. Figure 23 is a block diagram showing an example of the configuration of a PoC server according to the second embodiment.

[0199] As shown in Figure 23, the PoC server 13A differs from the PoC server 13 shown in Figure 4 in that its control unit 44A includes a determination unit 58 and an evaluation unit 60.

[0200] The acquisition unit 50A acquires location information of each terminal device 10 managed by the PoC server 13A via the communication unit 40. The acquisition unit 50A may, for example, acquire the location information of each terminal device 10 at predetermined intervals.

[0201] The determination unit 58 determines a specific terminal device from among multiple terminal devices 10 belonging to the same communication group to which the functions of the PoC server 13A will be transferred. For example, based on the location information acquired by the acquisition unit 50, the determination unit 58 determines the terminal device 10 located in the area with the lowest evaluation value by the evaluation unit 60 as the specific terminal device.

[0202] For example, if there are multiple terminal devices 10 located in the area with the lowest evaluation value, the determination unit 58 may identify the terminal device 10 closest to the terminal device 10 located in the area with the lowest evaluation value that is managed by the PoC server 13A and has not received notification information as the specified terminal device.

[0203] The determination unit 58 derives, for example, a boundary line to be drawn between the notification area of ​​the notification information and the unnotified area of ​​the notification information. In this case, the determination unit 58 may identify the terminal device 10 closest to the boundary line from among the multiple terminal devices 10 belonging to the specific group identified by the identification unit 52 as the specified terminal device.

[0204] The determination unit 58 may, for example, determine as a specified terminal device a terminal device 10 that has not received notification information from among a plurality of terminal devices 10 belonging to a specified group identified by the identification unit 52.

[0205] For example, if there are multiple terminal devices 10 belonging to a specific group identified by the identification unit 52 that have not received notification information, the determination unit 58 calculates the distance between each of the multiple terminal devices 10 that have not received notification information and each terminal device that has received notification information, and then calculates a total value by summing up the calculated distances. In this case, the determination unit 58 may determine the terminal device 10 with the largest total value as the specific terminal device.

[0206] If there are multiple terminal devices 10 belonging to a specific group identified by the identification unit 52 that have not received notification information, the determination unit 58 may determine the terminal device 10 closest to the terminal device 10 that is managed by the PoC server 13A and does not belong to the specific group as the specific terminal device.

[0207] The determination unit 58 may determine the terminal device 10 that is located in the area with the lowest evaluation value from the evaluation unit 60 among the multiple terminal devices 10 belonging to a specific group, and which has not received notification information.

[0208] The evaluation unit 60 generates an evaluation value for the risk level of the location indicated by the location information of the terminal device 10, based on hazard map information that shows the risk level for each area. The hazard map information may be stored in advance in the storage unit 42, for example. The evaluation unit 60 may also acquire hazard map information provided by local governments, etc., via the communication unit 40, for example.

[0209] (Determination process for specific device) The determination process for a specific terminal device according to the second embodiment will be explained using Figure 24. Figure 24 is a diagram for explaining the determination process for a specific terminal device according to the second embodiment.

[0210] Figure 24 shows terminal devices 10-1 to 10-8. Terminal devices 10-1 to 10-8 belong to communication group G1.

[0211] Base station 11-1 transmits broadcast information to broadcast area 61. Base station 11-2 transmits broadcast information to broadcast area 62. Base station 11-3 transmits broadcast information to broadcast area 63. Base station 11-4 transmits broadcast information to broadcast area 64.

[0212] Terminal devices 10-1 and 10-2 are located within the broadcast area 61. Terminal devices 10-1 and 10-2 receive broadcast information from base station 11-1.

[0213] Terminal devices 10-3 and 10-4 are located within the broadcast area 62. Terminal devices 10-3 and 10-4 receive broadcast information from base station 11-2.

[0214] Terminal devices 10-5 and 10-6 are located within the broadcast area 63. Terminal devices 10-5 and 10-6 receive broadcast information from base station 11-3.

[0215] Terminal devices 10-7 and 10-8 are located within the broadcast area 64. Terminal devices 10-7 and 10-8 receive broadcast information from base station 11-4.

[0216] In other words, in the example shown in Figure 24, all terminal devices 10-1 through 10-8 belonging to communication group G1 have received the notification information. Each of terminal devices 10-1 through 10-8 sends a notification indicating that it has received the notification information, along with its location information, to the PoC server 13.

[0217] The evaluation unit 60 generates an evaluation value for the degree of risk for each area in which terminal devices 10-1 to 10-8 are located.

[0218] Figure 25 is a diagram illustrating a method for calculating evaluation values ​​according to the second embodiment. The evaluation unit 60 sets areas 71 to 78 in the hazard map M, for example. The evaluation unit 60 calculates evaluation values ​​for each of the areas 71 to 78, for example. The evaluation unit 60 calculates the evaluation value for area 71 as "70%". The evaluation unit 60 calculates the evaluation value for area 72 as "50%". The evaluation unit 60 calculates the evaluation value for area 73 as "20%". The evaluation unit 60 calculates the evaluation value for area 74 as "40%". The evaluation unit 60 calculates the evaluation value for area 75 as "50%". The evaluation unit 60 calculates the evaluation value for area 76 as "30%". The evaluation unit 60 calculates the evaluation value for area 77 as "70%". The evaluation unit 60 calculates the evaluation value for area 77 as "60%". The higher the number, the more dangerous the situation.

[0219] The determination unit 58 determines the terminal device 10 located in the area with the lowest risk among the areas 71 to 78 where the terminal device 10 is located as the specified terminal device. In the example shown in Figure 25, for example, if the terminal devices 10 are located in areas 72 to 74 respectively, the determination unit 58 determines the terminal device 10 located in area 73 as the specified terminal device.

[0220] (Processing details of the communication system) The processing flow of the communication system according to the second embodiment will be explained using Figure 26. Figure 26 is a flowchart showing the processing flow of the communication system according to the second embodiment.

[0221] The control units 36 of all terminal devices 10 transmit the current location information to the PoC server 13A (step S400). The control units 36 of all terminal devices 10 receive notification information from the base station 11 (step S402).

[0222] The control units 36 of all terminal devices 10 send notification of receipt of notification information to the PoC server 13A (step S404). The PoC server 13A receives the notification of receipt of notification information (step S406).

[0223] The evaluation unit 60 of the PoC server 13A refers to the risk assessment results that show the evaluation value of the area where each terminal device 10 is located (step S408).

[0224] The determination unit 58 determines whether or not multiple terminal devices 10 exist in an area of ​​the same risk level (step S410). If it is determined that multiple terminal devices 10 exist in an area of ​​the same risk level (step S410; Yes), the process proceeds to step S412. If it is determined that multiple terminal devices 10 do not exist in an area of ​​the same risk level (step S410; No), the process proceeds to step S414.

[0225] If the answer is Yes in step S410, the determination unit 58 compares the location information of all terminal devices 10 with the location information of the terminal devices 10 that have received notification information from the base station 11 (step S412).

[0226] If the result in step S410 is No, the determination unit 58 determines a specific terminal device based on the risk assessment result (step S414). Specifically, the determination unit 58 determines the terminal device 10 located in the area with the lowest risk assessment result among the areas where terminal devices 10 are located as the specific terminal device.

[0227] After step S412, the boundary line between the broadcast area and the unbroadcast area of ​​the broadcast information is derived (step S416).

[0228] Figure 27 is a diagram illustrating a method for deriving the boundary line between the broadcast area and the unbroadcast area according to the second embodiment. In the example shown in Figure 27, base stations 11-1 to 11-4 transmit broadcast information. Base stations 11-5 to 11-7 do not transmit broadcast information. Terminal devices 10-1 to 10-8 are located in the broadcast area where they receive broadcast information. Terminal devices 10-9 to 10-14 are located in the unbroadcast area where they do not receive broadcast information.

[0229] The determination unit 58 derives the boundary line 81 between the notification area and the unnotified area based on the location information from terminal devices 10-1 to 10-14.

[0230] Returning to Figure 26, the determination unit 58 determines a specific terminal device based on the boundary line 81 (step S418). Specifically, the determination unit 58 determines the terminal device 10 closest to the boundary line 81 from among terminal devices 10-1 to 10-8 belonging to communication group G1 as the specific terminal device. For example, the determination unit 58 determines the terminal device 10-8 closest to the boundary line 81 as the specific terminal device.

[0231] The function transfer unit 54 of the PoC server 13A transfers the functions of the PoC server 13A to a specific terminal device (step S420). Then, the process shown in Figure 26 is completed.

[0232] As described above, the second embodiment determines a specific terminal device to which the PoC server functions will be transferred based on the risk assessment results of the area where the terminal device is located. This allows the second embodiment to transfer the PoC server functions to a safer terminal device in the event of an emergency such as a major earthquake.

[0233] [Third Embodiment] (Specific Device Determination Process) The specific terminal device determination process according to the third embodiment will be explained using Figure 28. Figure 28 is a diagram for explaining the specific terminal device determination process according to the third embodiment. The PoC server according to the third embodiment is the same as the PoC server 13A shown in Figure 23, so its explanation will be omitted.

[0234] The example shown in Figure 28 differs from Figure 24 in that terminal devices 10-7 and 10-8 do not receive broadcast information from base station 11-4. In the third embodiment, if there are terminal devices 10 that do not receive broadcast information within the same communication group G1, a specific terminal device is determined from among the terminal devices 10 that do not receive broadcast information.

[0235] Base station 11-1 transmits broadcast information to broadcast area 61. Base station 11-2 transmits broadcast information to broadcast area 62. Base station 11-3 transmits broadcast information to broadcast area 63. Base station 11-4 does not transmit broadcast information to broadcast area 64.

[0236] (Processing details of the communication system) The processing flow of the communication system according to the third embodiment will be explained using Figure 29. Figure 29 is a flowchart showing the processing flow of the communication system according to the third embodiment.

[0237] The control unit 36 ​​of all terminal devices 10 transmits the current location information to the PoC server 13A (step S430). The control unit 36 ​​of the terminal device 10 receives notification information from the base station 11 (step S432).

[0238] The control unit 36 ​​of the terminal device 10, upon receiving the notification information, sends a notification information reception notification to the PoC server 13A (step S434). The PoC server 13A receives the notification information reception notification (step S436).

[0239] The determination unit 58 determines whether or not there are any terminal devices in the same communication group that did not receive the notification information (step S438). Specifically, the determination unit 58 determines that terminal devices 10 that did not send a notification of receipt of notification information are terminal devices that did not receive the notification information. If it is determined that there are terminal devices in the same communication group that did not receive the notification information (step S438; Yes), the process proceeds to step S440. If it is determined that there are no terminal devices in the same communication group that did not receive the notification information (step S438; No), the process proceeds to step S442. Here, the PoC server 13A may determine that terminal devices 10 managed by the PoC server 13A that have not sent a notification of receipt of notification information even after a predetermined time has elapsed since receiving the notification of receipt of notification information are terminal devices that did not receive the notification information.

[0240] If the result in step S438 is Yes, the determination unit 58 determines whether there are multiple terminal devices that did not receive the notification information (step S440). If it is determined that there are multiple terminal devices that did not receive the notification information (step S440; Yes), the process proceeds to step S444. If it is determined that there are not multiple terminal devices that did not receive the notification information (step S440; No), the process proceeds to step S448.

[0241] If the result in step S438 is determined to be No, the determination unit 58 determines the predetermined terminal device 10 to be the specific terminal device (step S442).

[0242] If the result in step S440 is determined to be Yes, the determination unit 58 calculates the sum of the distances between each terminal device that did not receive the notification information and each terminal device 10 that did receive the notification information (step S444). In the example shown in Figure 28, terminal devices 10-7 and 10-8 are terminal devices that did not receive the notification information. In this case, the determination unit 58 calculates the distance between terminal device 10-7 and each of terminal devices 10-1 through 10-6, and then calculates the sum of the calculated distances. The determination unit 58 calculates the distance between terminal device 10-8 and each of terminal devices 10-1 through 10-6, and then calculates the sum of the calculated distances.

[0243] The determination unit 58 determines a specific terminal device based on the sum of the calculated distances (step S446). In the example shown in Figure 28, this is the sum of the distances between the terminal that did not receive the notification information and the terminal device 10 that received the notification information. Therefore, a larger sum of the calculated distances means that the terminal is located further away from the terminal device 10 that received the notification information. Conversely, a smaller sum of the calculated distances means that the terminal is located closer to the terminal device 10 that received the notification information. In the example in Figure 28, the determination unit 58 determines the terminal device with the larger sum of calculated distances between terminal device 10-7 and terminal device 10-8 as the specific terminal device. Alternatively, the determination unit 58 can also determine the terminal device with the smaller sum of calculated distances between terminal device 10-7 and terminal device 10-8 as the specific terminal device.

[0244] If the result in step S440 is determined to be No, the determination unit 58 determines that the terminal device that did not receive the notification information is the specified terminal device (step S448).

[0245] The process in step S450 is the same as the process in step S420 shown in Figure 26, so its explanation is omitted.

[0246] As described above, the third embodiment determines a specific terminal device to which the PoC server functions will be transferred from among terminal devices belonging to the same communication group that have not received notification information. This allows the third embodiment to transfer the PoC server functions to a more secure terminal device in the event of an emergency such as a major earthquake.

[0247] [Modification of the Third Embodiment] (First Modification) The process for determining a specific terminal device according to the first modification of the third embodiment will be explained using Figure 30. Figure 30 is a diagram for explaining the process for determining a specific terminal device according to the first modification of the third embodiment.

[0248] Figure 30 shows communication group G1 and communication group G2 adjacent to communication group G1. Communication group G1 includes terminal devices 10-1 to 10-8. Communication group G2 includes terminal devices 10-9 to 10-14.

[0249] In communication group G1, terminal devices 10-1 through 10-6 receive the notification information. Terminal devices 10-7 and 10-8 do not receive the notification information. In communication group G2, terminal devices 10-9 through 10-14 do not receive the notification information.

[0250] In the example shown in Figure 30, the determination unit 58 determines that the terminal device 10-7 and terminal device 10-8 belonging to the specific group, communication group G1, is closer to the terminal device 10 belonging to a different communication group G2, and designates the latter as the specific terminal device. For example, the determination unit 58 determines that the terminal device 10-7 and terminal device 10-8 that is closer to the terminal device 10-9, which is closest to communication group G1 within communication group G2, is the specific terminal device. As a result, in the first modification of the third embodiment, among multiple terminal devices 10 that have not received notification information within the specific group, the terminal device 10 closest to the communication group that has not received notification information can be determined as the specific terminal device, and the functions of the PoC server can be transferred to a more secure terminal device 10.

[0251] (Second Modification) A second modification of the third embodiment will now be described. In the second modification of the third embodiment, in the example shown in Figure 30, the determination unit 58 may determine the specific terminal device from among terminal devices 10-7 and 10-8 based on the evaluation results of the area in which terminal devices 10-7 and 10-8 are located by the evaluation unit 60. In this case, the determination unit 58 determines, for example, the terminal device located in the area with the lower risk evaluation result from among terminal devices 10-7 and 10-8 as the specific terminal device. As a result, the second modification of the third embodiment can determine the terminal device 10 located in the area with the lowest risk evaluation result among multiple terminal devices 10 that have not received notification information within a specific group as the specific terminal device, and thus the function of the PoC server can be transferred to a safer terminal device 10.

[0252] Each component of the illustrated device is a functional concept and does not necessarily have to be physically configured as shown. In other words, the specific forms of distribution and integration of each device are not limited to those shown, and all or part of them can be functionally or physically distributed and integrated in any unit according to various loads and usage conditions. Furthermore, this distribution and integration configuration may be performed dynamically.

[0253] While embodiments of the present disclosure have been described above, the present disclosure is not limited by the content of these embodiments. Furthermore, the aforementioned components include those that are readily conceivable to those skilled in the art, those that are substantially identical, and those that fall within the so-called equivalent range. Moreover, the aforementioned components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the embodiments described above.

[0254] The management device, management method, and program can be used in a PoC system that performs PoC communication.

[0255] 1, 1A Communication System 10, 10-1, 10-2, 10-3, 10-4, 10-5, 10-6, 10-7, 10-8, 10-9, 10-10, 10-11, 10-12, 10-13, 10-14 Terminal Device 11, 11-1, 11-2, 11-3, 11-4, 11-5, 11-6, 11-7 Base Station 12 Core Network Device 13, 13A PoC Server 14 DDNS Server 20 Input Unit 22 Display Unit 24 Microphone 26 Speaker 28 First Communication Unit 30 Second Communication Unit 32 GNSS Receiving Unit 34, 42 Storage Unit 36, 44, 44A Control Unit 40 Communication Unit 50, 50A Acquisition Unit 52 Identification Unit 54 Function transition unit 56 Notification unit 58 Decision unit 60 Evaluation unit

Claims

1. A management device comprising: an acquisition unit that acquires notification of notification information received from a terminal device; an identification unit that identifies the communication group as a specific group when the acquisition unit acquires notification of notification information received from a predetermined number or more terminal devices belonging to a communication group that performs group communication; and a function transfer unit that transfers the function of managing the communication of the communication group to a specific terminal device, which is a predetermined terminal device among the multiple terminal devices belonging to the specific group.

2. The management device according to claim 1, comprising: an acquisition unit that acquires line setting information, which is information about the line used for group communication of the communication group, from the specified terminal device; and a notification unit that, when the acquisition unit has acquired the line setting information, transmits the line setting information to the terminal devices other than the specified terminal device among the plurality of terminal devices belonging to the communication group.

3. A management method comprising: a step of obtaining a notification of notification information reception indicating that notification information has been received from a terminal device; a step of identifying the communication group as a specific group when notification of notification information reception is obtained from a predetermined number or more terminal devices belonging to a communication group that performs group communication; and a step of transferring the function of managing the communication of the communication group to a specific terminal device, which is a predetermined terminal device among the multiple terminal devices belonging to the specific group.

4. A management device comprising: an acquisition unit that acquires location information of a terminal device and a notification of notification information reception indicating that notification information has been received from a terminal device; an evaluation unit that generates an evaluation value for the risk level of the location indicated by the location information based on hazard map information indicating the risk level for each area; an identification unit that identifies the communication group as a specific group when the acquisition unit acquires notification of notification information reception from a predetermined number of terminal devices belonging to a communication group that performs group communication; a determination unit that determines, based on the location information, the terminal device located in the area with the lowest evaluation value among a plurality of terminal devices belonging to the specific group as the specific terminal device; and a function transfer unit that transfers the function of managing the communication of the communication group to the specific terminal device.

5. The management device according to claim 4, wherein, if there are multiple terminal devices located in the area with the lowest evaluation value, the determination unit determines the terminal device closest to the terminal device managed by the device and that does not receive the notification information, among the multiple terminal devices located in the area with the lowest evaluation value, as the specified terminal device.

6. The management device according to claim 4, wherein the determination unit derives a boundary line drawn between the notification area of ​​the notification information and the unnotified area of ​​the notification information, and determines the terminal device closest to the boundary line among a plurality of terminal devices belonging to the specific group as the specific terminal device.

7. A management method comprising: acquiring location information of a terminal device and a notification of notification information reception indicating that notification information has been received from a terminal device; generating an evaluation value for the risk level of the location indicated by the location information based on hazard map information indicating the risk level for each area; identifying the communication group as a specific group when notification of notification information reception is acquired from a predetermined number or more terminal devices belonging to a communication group that performs group communication; determining the terminal device located in the area with the lowest evaluation value among a plurality of terminal devices belonging to the specific group as the specific terminal device based on the location information; and transferring the function of managing the communication of the communication group to the specific terminal device.

8. A management device comprising: an acquisition unit that acquires location information of a terminal device and a notification of notification information reception indicating that notification information has been received from a terminal device; an identification unit that identifies the communication group as a specific group when the acquisition unit acquires notification of notification information reception from a predetermined number of terminal devices belonging to a communication group that performs group communication; a determination unit that determines a terminal device that has not received the notification information among a plurality of terminal devices belonging to the specific group as a specific terminal device; and a function transfer unit that transfers the function of managing the communication of the communication group to the specific terminal device.

9. The management device according to claim 8, wherein, if there are multiple terminal devices belonging to the specified group that have not received the notification information, the determination unit calculates the distance between each of the multiple terminal devices that have not received the notification information and each of the terminal devices that have received the notification information, calculates a total value by summing these distances, and determines the terminal device with the largest total value as the specified terminal device.

10. The management device according to claim 8, wherein, if there are multiple terminal devices belonging to the specified group that have not received the notification information, the determination unit determines the terminal device closest to the terminal device managed by the device and not belonging to the specified group among the multiple terminal devices that have not received the notification information as the specified terminal device.

11. The management device according to claim 8, comprising an evaluation unit that generates an evaluation value for the degree of risk of the location indicated by the location information based on hazard map information indicating the degree of risk for each area, wherein the determination unit determines as a special terminal device a terminal device among a plurality of terminal devices belonging to the specific group that has not received the notification information and is located in the area with the lowest evaluation value.

12. A management method comprising: the steps of: obtaining location information of a terminal device and a notification of notification information reception indicating that notification information has been received from a terminal device; identifying the communication group as a specific group when notification of notification information reception is obtained from a predetermined number or more terminal devices belonging to a communication group that performs group communication; determining a terminal device that has not received the notification information among a plurality of terminal devices belonging to the specific group as a specific terminal device; and transferring the function of managing the communication of the communication group to the specific terminal device.

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