Communication device, communication method, and program

Abstract

This communication device that relays communication between a first other communication device and a second other communication device has: a determination means that determines to disconnect a first link between the communication device and the first other communication device, and a second link between the communication device and the second other communication device; and a transmission means that transmits a disconnect request signal to the first other communication device and the second other communication device.

Description

Communication device, communication method, and program

[0001] The present invention relates to a communication device, a communication method, and a program.

[0002] In recent years, the specifications of 3GPP (Registered Trademark) (3rd Generation Partnership Project)'s LTE (Long Term Evolution) and next generation (NR) have been in progress. Among these, a standard specification called Sidelink communication (hereinafter referred to as Sidelink) has been established. This specification realizes direct wireless communication between terminals (UEs) using an interface called PC5 without going through a mobile communication network (core network).

[0003] Further, in 3GPP, the formulation of Sidelink relay communication, which is a specification for expanding the communication range of Sidelink by means of a Sidelink relay function that relays Sidelink communication via a relay device (UE-to-UE Relay), is in progress. Patent Document 1 discloses that, as a sequence for disconnecting the link between a terminal (UE) and a relay device, the terminal transmits a disconnection request signal to the relay device.

[0004] Japanese Unexamined Patent Application Publication No. 2017-034467

[0005] Conventionally, when ending Sidelink relay communication and disconnecting the link between a terminal and a relay device, it is necessary to transmit a disconnection request signal from the terminal to the relay device. Therefore, there has been a problem that it takes time to disconnect the link between the terminal and the relay device.

[0006] A terminal (UE) according to an embodiment of the present invention is a communication device that relays communication between a first other communication device and a second other communication device, and includes a determination means for determining to disconnect a first link between the first other communication device and the communication device and a second link between the second other communication device and the communication device, and a transmission means for transmitting a disconnection request signal to the first other communication device and the second other communication device.

[0007] When the relay device wants to disconnect the link with the terminal, it becomes possible to transmit a disconnection request signal.

[0008] This figure shows an example of the configuration of a communication system in the first embodiment of the present invention. This figure shows an example of the hardware configuration of a terminal device (UE) and a relay device (UE-to-UE Relay) in the first embodiment of the present invention. This block diagram shows an example of the functional configuration of a terminal device (UE) and a relay device (UE-to-UE Relay) in the first embodiment of the present invention. This figure shows an example of the sequence for disconnecting Sidelink Relay communication in the first embodiment of the present invention. This figure shows an example of the flowchart for determining disconnection of a Sidelink Relay terminal device (UE-to-UE Relay) in the first embodiment of the present invention. This figure shows an example of the message format for Disconnect request in the first embodiment of the present invention. This figure shows an example of the message format for Disconnect response in the first embodiment of the present invention. This figure shows another example of the message format for Disconnect response in the first embodiment of the present invention. This figure shows an example of another sequence for disconnecting Sidelink Relay communication in the first embodiment of the present invention. This figure shows an example of the configuration of the communication system in the second embodiment of the present invention. This figure shows an example of a sequence for disconnecting Sidelink Relay communication in the second embodiment of the present invention. This figure shows an example of the message format of Disconnect request in the second embodiment of the present invention. This figure shows another example of a sequence for disconnecting Sidelink Relay communication in the second embodiment of the present invention.

[0009] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the invention as defined in the claims. While the embodiments describe multiple features, not all of these features are essential to the invention, and the features may be combined in any way. Furthermore, in the attached drawings, identical or similar configurations are given the same reference numerals, and redundant descriptions are omitted.

[0010] [First Embodiment] (System Configuration) Figure 1 is a diagram showing an example configuration of the communication system according to this embodiment. In Figure 1, UE-1 (101) and UE-2 (102) are terminals that comply with the 3GPP standard and have Sidelink communication functionality. UE-to-UE Relay (103) is a terminal that complies with the 3GPP standard, connects to UE-1 (101) and UE-2 (102) via Sidelink communication, and has the function of relaying communication between UE-1 (101) and UE-2 (102) (Sidelink relay function). This terminal is also called a relay device and relay UE. UE-1 (101) and UE-2 (102) communicate using the PC5 interface.

[0011] (Hardware configuration of the device) Figure 2 shows an example of the hardware configuration of UE-1 (101), UE-2 (102), and UE-to-UE Relay (103) according to this embodiment.

[0012] The storage unit 201 is composed of one or more memories such as ROM and RAM, and stores various information such as computer programs for performing various operations described later, and communication parameters for wireless communication. ROM stands for Read Only Memory. RAM stands for Random Access Memory. In addition to memories such as ROM and RAM, the storage unit 201 may also use storage media such as flexible disks, hard disks, optical disks, magneto-optical disks, CD-ROMs, CD-Rs, magnetic tapes, non-volatile memory cards, and DVDs. Furthermore, the storage unit 201 may have multiple memories.

[0013] The control unit 202 is composed of one or more processors, such as a CPU or MPU, and controls the entire UE-1 (101), UE-2 (102), and UE-to-UE Relay (103) by executing a computer program stored in the memory unit 201. Alternatively, the control unit 202 may control the entire UE-1 (101), UE-2 (102), and UE-to-UE Relay (103) in cooperation with the computer program stored in the memory unit 201 and the OS (Operating System). The control unit 202 also generates data and signals (wireless frames) to be transmitted in communication with other communication devices. Note that CPU stands for Central Processing Unit, and MPU stands for Micro Processing Unit. Alternatively, the control unit 202 may be equipped with multiple processors, such as a multi-core processor, and the multiple processors may control UE-1 (101), UE-2 (102), and the entire UE-to-UE Relay (103).

[0014] Furthermore, the control unit 202 controls the functional unit 205 to perform predetermined processes such as wireless communication, imaging, printing, and projection. The functional unit 205 is hardware for UE-1 (101), UE-2 (102), and UE-to-UE Relay (103) to perform predetermined processes.

[0015] The input unit 203 is a reception device that accepts various user inputs and is used when a user operates the communication device. The output unit 204 presents various information to the outside using functions that enable the output of visually recognizable information such as an LCD (liquid crystal display) or LED (light-emitting diode), or sound output such as a speaker. In other words, the output unit 204 has the function of outputting at least one of visual information or sound information. For example, if the communication device is a smartphone, a touch panel that integrates at least a part of the output unit 204 and the input unit 203 may be used. The communication unit 206 controls wireless communication in accordance with the 3GPP (registered trademark) (3rd Generation Partnership Project) standard. The communication unit 206 also includes an antenna and circuit for sending and receiving wireless signals with other terminals and relay devices. The communication unit 206 controls the antenna to send and receive signals for wireless communication generated by the control unit 202.

[0016] (Functional Configuration of the Device) Next, the functional configuration of the communication device according to this embodiment will be described. Note that the configuration of the functional blocks described below is merely an example.

[0017] Figure 3 is a block diagram showing an example of the functional configuration of UE-1 (101), UE-2 (102), and UE-to-UE Relay (103) in this embodiment.

[0018] The system includes a message generation unit 301, a message analysis unit 302, a disconnection processing unit 303, a UI control unit 304, a communication control unit 305, and a storage processing unit 306. The disconnection processing unit 303 is an example of a determination means. The communication control unit 305 is an example of a transmission means and a reception means.

[0019] The message generation unit 301 generates a message to be transmitted by the communication control unit 305. The message analysis unit 302 analyzes the message received by the communication control unit 305. The content of the wireless control generated by the message generation unit 301 and the content of the wireless control analyzed by the message analysis unit 302 may be based on settings stored in the storage unit 201. These settings may also be changed by user settings via the UI control unit 304. The generated message is sent to the communication control unit 305 and transmitted to the communication partner. The message received by the communication control unit 305 is passed to the message analysis unit 302 and analyzed.

[0020] The disconnection processing unit 303 performs the process of disconnecting the link between the UE and the UE-to-UE Relay. Specifically, the disconnection processing unit 303 determines whether or not to disconnect the link depending on the status of its own terminal and the radio wave environment and distance between it and other terminals. If the disconnection processing unit 303 decides to disconnect the link, it requests the message generation unit 301 to generate a message indicating a disconnection request. The generated message indicating a disconnection request is transmitted by the communication control unit 305. Furthermore, when the disconnection processing unit 303 receives a disconnection request signal from another communication device, it decides whether or not to transmit a disconnection response signal based on the content analyzed by the message analysis unit. If it decides to transmit a disconnection response signal, the disconnection processing unit 303 requests the message generation unit 301 to generate a message indicating a disconnection response. The generated message indicating a disconnection response is transmitted by the communication control unit 305.

[0021] The UI control unit 304 is configured to include a program that controls the input unit 203 and the output unit 204. The UI control unit 304 also has functions for presenting information to the user, such as displaying images or outputting audio.

[0022] The communication control unit 305 is configured to include a program for controlling the communication unit 206. The communication control unit 305 performs communication control related to the PC5 interface based on the message generated by the message generation unit 301 in accordance with the 3GPP standard. In addition to the 3GPP standard, the communication control unit 305 may also control wireless communication in accordance with the IEEE 802.11 series standard, or wired communication such as wired LAN.

[0023] The memory processing unit 306 performs the process of storing the programs and data on which UE-1 (101), UE-2 (102), and UE-to-UE Relay (103) operate in the memory unit 201.

[0024] (Processing Example) Using Figures 4 and 5, the process by which Sidelink Relay (103) disconnects the link in communication between UE-1 (101) and UE-2 (102) via Sidelink Relay (103) in an embodiment of this present invention will be explained.

[0025] In Figure 4, the UE-to-UE Relay (103) decides to disconnect the link between UE-1 (101) and UE-2 (102) based on predetermined conditions. Having decided to disconnect the link, the UE-to-UE Relay (103) transmits a Disconnect Request signal to UE-2 (102) at F401. UE-2 (102) receives the Disconnect Request signal and, in response, transmits a Disconnect Response signal at F402. As signals are transmitted and received at F401 and F402, the link between the UE-to-UE Relay and UE-2 is disconnected.

[0026] Furthermore, F403 of the UE-to-UE Relay transmits a Disconnect Request signal to UE-1 (101). UE-1 (101) receives the Disconnect Request signal and, in response, transmits a Disconnect Response signal at F404. As signals are transmitted and received at F403 and F404, the link between the UE-to-UE Relay and UE-1 is disconnected.

[0027] In Figure 4, Sidelink Relay (103) initially disconnects the link between UE-to-UE Relay and UE-2 (102), but it is not limited to this; it may also disconnect the link with UE-1 (101) first.

[0028] Next, the process by which UE-to-UE Relay (103) decides to disconnect the link will be explained using Figure 5.

[0029] In Figure 5, at S501, the UE-to-UE Relay (103) determines whether an operation has been performed via the UI input unit 203 to instruct the user to disconnect the link. For example, it determines whether an operation to instruct disconnection has been performed by the user manually pressing a predetermined button displayed on the output unit 204 via the input unit 203. If an operation to instruct disconnection has been performed, the process proceeds to S506; otherwise, the process proceeds to S502.

[0030] In S502, the UE-to-UE Relay (103) determines whether the signal strength between it and the currently connected UE-1 (101) or UE-2 (102) has decreased. If the signal strength has decreased, it proceeds to S506; otherwise, it proceeds to S503. More specifically, the UE-to-UE Relay (103) measures the received signal strength of the radio signals received from UE-1 (101) and UE-2 (102), respectively. The UE-to-UE Relay (103) may determine that the received signal strength has decreased if the received signal strength of at least one of them is below a threshold, and then proceed to S506. Indicators that represent signal strength may include, for example, RSRP (Reference Signal Received Power), RSRQ (Reference Signal Received Quality), RSSI (Received Signal Strength Indicator), and SINR (Signal-to-Noise Ratio).

[0031] In S503, UE-to-UE Relay(103) determines whether the distance between it and the currently connected UE-1(101) or UE-2(102) has increased. If the distance has increased, it proceeds to S506; otherwise, it proceeds to S503. More specifically, UE-to-UE Relay(103) may calculate the distance between it and UE-1(101) and UE-2(102) based on the current positions obtained from UE-1(101) and UE-2(102) and its own measured current position. UE-to-UE Relay(103) may also determine that the distance has increased and proceed to S506 if at least one of the distances between it and UE-1(101) or between it and UE-2(102) is greater than or equal to a threshold.

[0032] In S504, UE-to-UE Relay (103) is a process that determines whether the amount of traffic being transmitted and received in communication with other devices (e.g., base stations or other UEs) is increasing or is expected to increase. If it is increasing or is expected to increase, the process proceeds to S506; otherwise, it proceeds to S503. More specifically, UE-to-UE Relay (103) may determine that the amount of traffic it transmits and receives is increasing or is expected to increase if it is above a threshold, and then proceed to S506.

[0033] In S505, the UE-to-UE Relay (103) determines whether it has enough battery power remaining to continue the Sidelink relay function. If it determines that it cannot continue the relay function, it proceeds to S506; if it determines that it can continue the relay function, it proceeds to S501. More specifically, if the UE-to-UE Relay (103) has less than a threshold of battery power remaining, it may determine that it does not have enough battery power remaining to continue the Sidelink relay function and proceed to S506.

[0034] In S506, the UE-to-UE Relay (103) transmits Disconnect Request signals to UE-1 (101) and UE-2 (102).

[0035] Figure 6 shows an example of the message format of a Disconnect Request transmitted by UE-to-UE Relay (103). The Disconnect Request may include, as Information Element, a Request message identity 601 indicating the type of message and a Sequence number 602 indicating the sequence number. The Disconnect Request may also include an Operation code 603, QoS Flow descriptions 604, and QoS rule 605. Furthermore, the Disconnect Request may include Relay UE info 606, which indicates the User Info of a UE-to-UE Relay, and Source end UE info 607, which indicates the User Info of UE-1 (101). The Disconnect Request may also include Target end UE info 608, which indicates the User Info of UE-2 (102), and Security information 609, which indicates security-related information. Also, Figure 6 is merely an example, and some of the information shown in Figure 6 may be omitted. Security-related information may include, for example, information such as encryption methods, encryption keys, public keys, and passcodes, as well as identifiers such as time information and data numbers to prevent replay attacks. Request message identity 601 may store an identifier indicating that the message is a Disconnect Request.

[0036] The identifier may be, for example, 8 bits long. Specifically, it may be "00101000".

[0037] Figures 7 and 8 show examples of message formats for Disconnect Responses sent by UE-1 (101) and UE-2 (102). The Disconnect Response may have different message formats depending on whether the disconnection request is permitted or not, as shown in Figures 7 and 8, for example. Figure 7 is an example of a message format when the disconnection request is permitted, and Figure 8 is an example of a message format when the disconnection request is not permitted. The difference from the Disconnect Request in Figure 6 is the Accept message identity 701, which indicates the message type, and the Reject message identity 801 in Figure 8. Accept message identity 701 may store an identifier indicating that the message is an Accept message. This identifier may be, for example, 8 bits long. Specifically, it may be "00101001". Reject message identity 801 may store an identifier indicating that the message is a Reject message. This identifier may be, for example, 8 bits long. Specifically, it may be "00101010".

[0038] Figure 9 is a sequence diagram showing another example of the process by which Sidelink Relay (103) disconnects a link. The UE may disconnect the link according to the sequence shown in Figure 9, not limited to the process shown in Figure 4. At F901, UE-to-UE Relay (103) sends a Disconnect Request message to both UE-1 (101) and UE-2 (102). Next, at F902, UE-2 (102) sends a Disconnect Response message to UE-to-UE Relay (103). Also at F903, UE-1 (101) sends a Disconnect Response message to UE-to-UE Relay (103).

[0039] In the example shown in Figure 4, the UE-to-UE Relay (103) disconnects the link with UE-1 (101) and then disconnects the link with UE-2 (102).

[0040] In other words, UE-to-UE Relay(103) sends a Disconnect Request message to the other UE after receiving a Disconnect Response message from one UE. On the other hand, in the example in Figure 9, UE-to-UE Relay(103) sends a Disconnect Request message to both UEs. In other words, UE-to-UE Relay(103) sends a Disconnect Request message to the other UE before receiving a Disconnect Response message from one UE.

[0041] This operation sequence makes it possible to shorten the time until disconnection compared to the sequence in Figure 4. Furthermore, at this time, the Disconnect Request message may include information on which terminal, UE-1 (101) or UE-2 (102), will send the Disconnect Response message first. For example, UE-to-UE Relay (103) may include information in the Disconnect Request message indicating the time from receiving the message to sending the Disconnect Response message. Alternatively, UE-to-UE Relay (103) may set different times for each UE. This results in a staggered timing for each UE sending Disconnect Response messages, making it possible to avoid collisions between Disconnect Response messages sent from both UEs.

[0042] [Second Embodiment] FIG. 10 is a diagram showing a configuration example of a communication system according to this embodiment. In FIG. 10, UE-1 (101) and UE-2 (102) are terminals each having a Sidelink communication function, similar to FIG. 1. UE-to-UE Relay1 (1001) and UE-to-UE Relay2 (1002) are devices that relay communication between UE-1 (101) and UE-2 (102). In the first embodiment, only one relay device was arranged between UE-1 (101) and UE-2 (102), but in this embodiment, two relay devices are arranged.

[0043] Note that the hardware configuration and functional configuration of UE-1 (101), UE-2 (102), UE-to-UE Relay1 (1001), and UE-to-UE Relay2 (104) are the same as those shown in FIGS. 2 and 3. Also, PC5 in FIG. 10 means a PC5 interface.

[0044] (Processing Example) Using FIG. 11, the process of disconnecting the link in the communication between UE-1 (101) and UE-2 (102) via UE-to-UE Relay1 (1001) and UE-to-UE Relay2 (1002) will be described. Note that FIG. 11 is a sequence example when UE-to-UE Relay1 (1001) determines to disconnect the link.

[0045] First, UE-to-UE Relay1 (1001) determines to disconnect the links with UE-1 (101) and UE-to-UE Relay2 (1002) based on the flowchart shown in FIG. 5.

[0046] In F1101, the UE-to-UE Relay1 (1001) transmits a Disconnect Request signal to the UE-to-UE Relay2 (1002). The UE-to-UE Relay2 (1002) receives the Disconnect Reqst signal and, in response, transmits a Disconnect Response signal in F1102. By transmitting and receiving signals in F1101 and F1102, the link between the UE-to-UE Relay1 (1001) and the UE-to-UE Relay2 (1002) is disconnected.

[0047] Furthermore, in F1103, the UE-to-UE Relay1 (1001) transmits a Disconnect Request signal to the UE-1 (101). The UE-1 (101) receives the Disconnect Request signal and, in response, transmits a Disconnect Response signal to the UE-to-UE Relay1 (1001) in F1104. By transmitting and receiving signals in F1103 and F1104, the link between the UE-to-UE Relay1 (1001) and the UE-1 (101) is disconnected. As a result, the two links connected by the UE-to-UE Relay1 (1001) are disconnected.

[0048] Next, in F1102, the UE-to-UE Relay2 (1002) that transmitted the Disconnect Response signal determines to disconnect the link with the UE-2 (102) and transmits a Disconnect Request signal to the UE-2 (102) in F1105.

[0049] Here, UE-to-UE Relay2 (1002) may decide to disconnect the link with UE-2 (102) based on the flow in Figure 5. Alternatively, UE-to-UE Relay2 (1002) may decide to disconnect the link with UE-2 (102) because it has received a Disconnect Request signal from UE-to-UE Relay1 (1001). Alternatively, UE-to-UE Relay2 (1002) may decide to disconnect the link with UE-2 (102) because it has sent a Disconnect Response signal to UE-to-UE Relay1 (1001). In other words, a UE-to-UE Relay may decide to sever the link between itself and the UEs it is connected to if the link between it and other UE-to-UE Relays is severed.

[0050] UE-2 (102) receives a Disconnect Request signal and, in response, transmits a Disconnect Response signal to UE-to-UE Relay2 (1002) via F1106. The transmission and reception of signals via F1105 and F1106 disconnects the link between UE-to-UE Relay2 (1002) and UE-2 (102).

[0051] In the example shown in Figure 11, UE-to-UE Relay1 (1001) initially disconnects the link with UE-to-UE Relay2 (1002), but it is not limited to this; it may also initially disconnect the link with UE-1 (101).

[0052] Figure 12 shows an example of the message format for a Disconnect Request sent by UE-to-UE Relay 1 (1001). The message format shown in Figure 12 is the same as the message format in Figure 6, but with the addition of Hop Limit 1201 indicating the upper limit of the number of relay hops, Hop count 1202 indicating the current number of relay hops, and Relay Indication 1203 indicating a request to relay this message.

[0053] In Figure 11, if the UE transmitting the Disconnect Request signal is a relay device, the Disconnect Request signal transmitted to the relay device by UE-to-UE Relay 1 (1001) may include information indicating a request for relaying and / or information indicating an upper limit on the number of relay hops. That is, the Disconnect Request signal transmitted to UE-to-UE Relay 2 (1002) by UE-to-UE Relay 1 (1001) may include Relay Indication 1203 and / or Hop Limit 1201.

[0054] UE-to-UE Relay2 (1002) may, based on the fact that the Disconnect Request signal received by F1101 includes a Relay Indication 1203, send a Disconnect Request to UE-2 (102) at F1105. In this case, the Relay Indication 1203 may be set to indicate a request for a relay, for example, when the value "1" is set. In other words, if the Relay Indication 1203 of the Disconnect Request signal received by F1101 is set to "1", UE-to-UE Relay2 (1002) may send a Disconnect Request to the UE with which it has established a link.

[0055] Note that the link may be disconnected using the operation sequence shown in Figure 13 instead of the operation sequence shown in Figure 11. In Figure 13, at F1301, UE-to-UE Relay1 (1001) sends a Disconnect Request message to both UE-1 (101) and UE-to-UE Relay2 (1002). Next, at F1302, UE-to-UE Relay2 (1002) sends a Disconnect Response message to UE-to-UE Relay1 (1001). Furthermore, at F1303, UE-1 (101) sends a Disconnect Response message to UE-to-UE Relay1 (1001). This sequence makes it possible to shorten the time until the link is disconnected compared to the sequence in Figure 11. The disconnection of the link between UE-to-UE Relay2 (1002) and UE-2 is the same as in Figure 11, so the explanation is omitted.

[0056] In the second embodiment, the case where there are two relay devices was described, but the same applies when three or more devices are arranged.

[0057] [Other Embodiments] The present invention provides a program that implements one or more of the functions of the above-described embodiments to a system or device via a network or storage medium. It can also be implemented by a process in which one or more processors in the computer of the system or device read and execute the program. Furthermore, it can also be implemented by a circuit (e.g., ASIC) that implements one or more functions.

[0058] Please understand that each feature described in the detailed explanation above, as well as each feature shown in the attached drawings, can be considered an independent element with its own unique technical contribution. While these features may work synergistically within the context of the detailed explanation above, they are not limited to such combinations and may be individually extracted and used independently to address specific challenges or enhance specific functions.

[0059] Furthermore, the specific embodiments presented in the above-mentioned detailed description may include many variations. These embodiments are illustrative and do not limit the scope, applicability, control, or configuration of this disclosure. Rather, the above-mentioned detailed description provides a guide for a technically familiar person to implement the feasible embodiments, and it should be understood that various modifications may be made to the operations, methods, steps, means, and schemes described in the above-mentioned detailed description without departing from the scope of the appended claims.

[0060] Therefore, those skilled in the art will understand that the various operations, methods, steps, means, and schemes in the flowcharts described herein may be substituted, modified, combined, or deleted. Furthermore, other steps, means, and schemes in the various operations, methods, and processes already described herein may also be substituted, modified, rearranged, disassembled, combined, or deleted.

[0061] The present invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of the invention public.

[0062] This application claims priority based on Japanese Patent Application No. 2025-018858, filed on 7 February 2025, and all of its contents are incorporated herein by reference.

Claims

1. A communication device that relays communication between a first other communication device and a second other communication device, comprising: a determination means for determining to disconnect a first link between the first other communication device and the communication device, and a second link between the second other communication device and the communication device; and a transmission means for transmitting disconnection request signals to the first other communication device and the second other communication device.

2. The communication device according to claim 1, characterized in that it has receiving means for receiving disconnection response signals from the first other communication device and the second other communication device.

3. The communication device according to claim 1, characterized in that the determination means decides to disconnect the first link and the second link based on instructions from the user.

4. The communication device according to claim 1, characterized in that the determination means determines to disconnect the first link and the second link based on the received signal strength of the signal received from the first other communication device, or the received signal strength of the signal received from the second other communication device.

5. The communication device according to claim 1, characterized in that the determination means determines to disconnect the first link and the second link based on the remaining battery level of the communication device.

6. The communication device according to claim 1, characterized in that the transmitting means transmits a disconnection request signal to the first other communication device, and transmits another disconnection request signal to the second other communication device before receiving a response signal to the disconnection request signal from the first other communication device.

7. The communication device according to claim 1, characterized in that the first other communication device or the second other communication device is a communication device capable of operating as a relay device compliant with the 3GPP (3rd Generation Partnership Project) standard.

8. The communication device according to claim 1, characterized in that the disconnection request signal transmitted by the transmitting means includes information related to security.

9. The communication device according to claim 7, characterized in that, when the first other communication device operates as a relay device, the disconnection request signal transmitted by the transmitting means to the first other communication device includes information indicating a request to relay.

10. The communication device according to claim 7, characterized in that, when the first other communication device operates as a relay device, the disconnection request signal transmitted by the transmitting means to the first other communication device includes information indicating an upper limit on the number of relay hops.

11. A control method for controlling a communication device that relays communication between a first other communication device and a second other communication device, comprising: a step of deciding to disconnect a first link between the first other communication device and the communication device, and a second link between the second other communication device and the communication device; and a transmission step of transmitting disconnection request signals to the first other communication device and the second other communication device.

12. A program for causing the computer of a communication device that relays communication between a first other communication device and a second other communication device to execute: a process of deciding to disconnect a first link between the first other communication device and the communication device, and a second link between the second other communication device and the communication device; and a transmission process of sending disconnection request signals to the first other communication device and the second other communication device.

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