Communication device, communication system, and communication method

Abstract

To implement a communication device that can withstand even a short-time path fault and can suppress a network load.SOLUTION: A communication device included in a plurality of communication devices capable of configuring a mesh type spatial optical communication network includes: a communication unit for transmitting / receiving a packet including transmission information from a terminal and specific information showing a communication device of a call origination source connected to the terminal of the plurality of communication devices and a calling sequence ; and a relay unit that uses the specific information of the received packet and specific information of a packet received from one or more communication devices included in the plurality of communication devices to specify whether or not to relay the received packet to the one or more communication devices of the plurality of communication devices. The communication unit transmits the received packet relayed by the relay unit toward the one or more communication devices.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a communication device, a communication system, and a communication method. [Background technology]

[0002] As a technique for making information paths redundant by connecting each of a plurality of transmitting devices to a plurality of receiving devices via a network, for example, a route redundancy system of Patent Document 1 is known. In the route redundancy system of Patent Document 1, a transmitting device that receives a synchronization signal for synchronously operating a plurality of transmitting devices generates transmission information to be transmitted to a plurality of receiving devices according to the synchronization signal. The transmitting device generates identification information for identifying the transmission information and assigns the identification information to the transmission information. The transmitting device copies the transmission information to which the identification information has been assigned as identification assignment information and transmits the same to each of the plurality of receiving devices. The receiving device receives the plurality of identification assignment information transmitted from each of the plurality of transmitting devices, and acquires the transmission information based on the plurality of identification assignment information. Also, for example, Patent Document 2 provides a method and system for a split optical transport network (OTN) switching system having a step of using a plug-in universal (PIU) module. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2021 / 156918 Specification [Patent Document 2] JP 2018-011289 A Summary of the Invention [Problem to be solved by the invention]

[0004] In the route redundancy system described in Patent Document 1, the sending device performs flooding to deliver data to the receiving device, but there is no mechanism for avoiding broadcast storms. In addition, the system described in Patent Document 2 cannot recover packets lost due to a link failure between the PIU module and the switch. In addition, the system envisioned in Patent Document 2 is based on a wired system, and does not assume that link failures will occur due to disturbances.

[0005] However, in optical space communication, which enables wide-area communication, communication can be interrupted for a very short time due to vibrations or momentary obstacles (such as birds). Although communication interruptions caused by such reasons should be able to be restored immediately, it can be said that protocols such as RSTP (Rapid Spanning Tree Protocol) and OSPF (Open Shortest Path First) have little effect on realizing immediate restoration, even if they have detour routes.

[0006] The present disclosure has been made in consideration of the above problems, and an exemplary objective thereof is to provide a communication device, a communication system, and a communication method that can withstand short-term route failures and reduce network load in an optical space communication network. [Means for solving the problem]

[0007] A communication device according to an exemplary aspect of the present disclosure is a communication device included in a plurality of communication devices capable of constituting a mesh-type free space optical communication network, and includes a communication unit that transmits and receives packets including transmission information from a terminal and identification information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence, and a relay unit that uses the identification information of the received packet and the identification information of the packet that has already been received from one or more communication devices included in the plurality of communication devices to determine whether to relay the received packet to one or more communication devices among the plurality of communication devices, and the communication unit transmits the received packet relayed in the relay unit to the one or more communication devices.

[0008] A communication system according to an exemplary aspect of the present disclosure is a communication system in which terminals transmit and receive information to each other via a mesh-type free-space optical communication network composed of a plurality of communication devices, wherein one or more of the plurality of communication devices include a communication unit that transmits and receives packets including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence, and a relay unit that uses the specific information of the received packet and the specific information of the packet that has already been received from one or more communication devices included in the plurality of communication devices to determine whether to relay the received packet to one or more communication devices among the plurality of communication devices, and the communication unit transmits the received packet relayed in the relay unit to the one or more communication devices.

[0009] A communication method according to an exemplary aspect of the present disclosure is a communication method using the above-mentioned communication device, and includes receiving a packet including transmission information from a terminal and identification information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence, determining whether to relay the received packet to one or more communication devices among the plurality of communication devices using the identification information of the received packet and the identification information of the packet that has already been received from one or more communication devices included in the plurality of communication devices, and if the packet is to be relayed, transmitting the received packet to the one or more communication devices. Effect of the Invention

[0010] According to an exemplary aspect of the present disclosure, it is possible to provide an exemplary effect of providing a communication device, a communication system, and a communication method that can withstand a short-term route failure in an optical space communication network. [Brief description of the drawings]

[0011] [Figure 1] 1 is a block diagram showing a configuration of a communication system according to the present disclosure. [Diagram 2] 1 is a block diagram showing a configuration of a communication device according to the present disclosure. [Diagram 3] 1 is a flow diagram showing the flow of a communication method according to the present disclosure. [Figure 4] FIG. 13 is a block diagram showing another example of the configuration of a communication device according to the present disclosure. [Diagram 5] 4 illustrates a configuration of a packet transmitted and received in a communication device according to the present disclosure. [Figure 6] FIG. 11 is a flow diagram showing the flow of another example of a communication method according to the present disclosure. [Figure 7] FIG. 11 is a flow diagram illustrating the flow of another example of a communication system according to the present disclosure. [Figure 8] 4 illustrates a data configuration of a transmission / reception packet in a communication device according to the present disclosure. [Figure 9]FIG. 1 is a block diagram showing a configuration of a computer that functions as a communication system according to the present disclosure. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] The following are examples of embodiments of the present invention. However, the present invention is not limited to the exemplary embodiments shown below, and various modifications are possible within the scope of the claims. For example, an embodiment obtained by appropriately combining the technical means employed in each of the exemplary embodiments shown below may also be included in the scope of the present invention. In addition, an embodiment obtained by appropriately omitting a part of the technical means employed in each of the exemplary embodiments shown below may also be included in the scope of the present invention. In addition, the effects mentioned in each of the exemplary embodiments shown below are examples of effects expected in the exemplary embodiments, and do not define the scope of the present invention. In other words, an embodiment that does not exhibit the effects mentioned in each of the exemplary embodiments shown below may also be included in the scope of the present invention.

[0013] First Exemplary Embodiment A first exemplary embodiment, which is an example of an embodiment of the present invention, will be described in detail with reference to the drawings. This exemplary embodiment is the basic form of each exemplary embodiment described later. The scope of application of each technical means adopted in this exemplary embodiment is not limited to this exemplary embodiment. That is, each technical means adopted in this exemplary embodiment can be adopted in other exemplary embodiments included in this disclosure to the extent that no particular technical obstacle occurs. In addition, each technical means shown in the drawings referred to for explaining this exemplary embodiment can also be adopted in other exemplary embodiments included in this disclosure to the extent that no particular technical obstacle occurs.

[0014] (Communication System Configuration) The configuration of the communication system 1 will be described with reference to Fig. 1. Fig. 1 is a block diagram showing the configuration of the communication system 1. As shown in Fig. 1, the communication system 1 includes a first terminal 100, a second terminal 200, and a plurality of communication devices 10A to 10D that constitute a mesh type free space optical communication network NE.

[0015] In the communication system 1, the first terminal 100 and the second terminal 200 transmit and receive a communication medium via a mesh type free space optical communication network NE. The mesh type free space optical communication network NE refers to a free space optical communication network in which a plurality of meshes are formed by free space optical communication paths. To achieve this, each of the communication devices 10A to 10D is provided with a plurality of links that enable communication of the communication medium between the device itself and other communication devices by free space optical communication. In one example, each of the communication devices 10A to 10D has at least two links and can transmit a received communication medium (packet) to at least one other communication device. Preferably, each of the communication devices 10A to 10D is configured to transmit a received packet to two or more other communication devices. This makes it possible to flood the packet.

[0016] In the communication system 1 shown in FIG. 1, a communication device 10A is connected to a first terminal 100, and the communication device 10A has links with two other communication devices 10B and 10D. The communication device 10B has a link with the communication device 10A, and also has links with the other communication devices 10C and 10D. The communication device 10D has a link with the communication device 10A, and also has a link with the communication device 10B. The communication device 10C has a link with the communication device 10B, and is connected to a second terminal 200.

[0017] Note that communication between the first terminal 100 or the second terminal 200 and the communication devices 10A, 10C connected thereto may be wired or wireless. Also, in Fig. 1, four communication devices 10A to 10D are illustrated as communication devices constituting the mesh-type free space optical communication network NE, but the number is not limited to this. Also, in the example of Fig. 1, a terminal (the first terminal 100, the second terminal 200) is connected to each of the communication devices 10A and 10C, but other terminals may be connected to each of the other communication devices 10B and 10C.

[0018] In other words, the communication medium (packets) transmitted from each of the communication devices 10A to 10D is a directional communication medium. Although a specific example of a directional communication medium is not limited to the illustrative embodiment, an example of the directional communication medium is electromagnetic waves in a high frequency range having a frequency of approximately 10 GHz or more. Electromagnetic waves in this frequency range may include millimeter waves, submillimeter waves, infrared light, visible light, ultraviolet light, and the like. As an example, electromagnetic waves in the above frequency range are directed within a predetermined angle range and sent out, thereby being used for communication as the above-mentioned directional communication medium. As an example, the communication device may be A beamforming antenna that directs and transmits millimeter and sub-millimeter waves within a specified angle range. Collimators for collimating infrared, visible, or ultraviolet light Laser oscillators that generate infrared, visible, or ultraviolet laser light The configuration may include the following.

[0019] (Configuration of communication device) 2 is a block diagram showing the configuration of any one of the communication devices 10A to 10D shown in FIG. 1. For ease of explanation, FIG. 2 will explain the communication device 10B shown in FIG. 1 as an arbitrary communication device 10. As described above, the communication device 10 (10B) shown in FIG. 2 is a communication device included in the multiple communication devices capable of configuring a mesh-type free space optical communication network. The communication device 10 includes a communication unit 20 and a relay unit 30.

[0020] The communication unit 20 receives a packet including transmission information from a terminal and specific information indicating a source communication device connected to the terminal (first terminal 100 in the example of FIG. 1) among a plurality of communication devices and a transmission sequence. The packet is received from another communication device in the mesh type free space optical communication network NE connected to the communication device 10, which is the own device, via a link. In the example shown in FIG. 1, the communication device 10B, which is the own device, can receive a packet from the communication device 10A, the communication device 10D, or the communication device 10C with which it has a link. The communication unit 20 also transmits a packet. With regard to transmission, the packet can also be transmitted to another communication device with a link between the communication device 10, which is the own device.

[0021] A packet includes transmission information from a terminal and specific information. The transmission information is the net data body sent to the other terminal, and is sometimes called a payload.

[0022] The specific information includes, as an example, information for identifying a communication device connected to a terminal (first terminal 100 in the example of FIG. 1) that transmits the transmission information. This communication device is referred to as a source communication device. The example of FIG. 1 shows a mode in which a packet is transmitted from the first terminal 100 to the second terminal 200, and the communication device 10A connected to the first terminal 100 that transmits the transmission information is the source communication device. Therefore, the specific information includes information for identifying the source communication device 10A.

[0023] The specific information includes information that identifies the source communication device, as well as information that indicates a transmission sequence. The information that indicates the transmission sequence is, for example, information that indicates a transmission sequence number of a packet transmitted from the source communication device 10A.

[0024] 1, communication device 10A acquires transmission information to which control information (receiving terminal information) such as a destination is added in advance from first terminal 100, and generates a packet by adding the above-mentioned specific information to the transmission information. The generated packet is flooded from communication device 10A and transmitted to communication device 10B and communication device 10D by spatial optical communication (laser communication).

[0025] The communication unit 20 of the communication device 10B receives the transmitted packet. Here, the communication device 10 can store the received packet. As an example, the communication device 10 may include a storage unit that stores the received packet. The storage unit may be configured as a part of the communication unit 20 or the relay unit 30, or may be realized as a separate component within the communication device 10. In addition, the packet stored by the communication device 10 may be the latest packet of each source communication device. The latest packet can be identified from information indicating the transmission sequence included in the identification information.

[0026] As a specific example of the example shown in Fig. 1, communication device 10B stores a packet including sequence information indicating that it is the 99th packet transmitted from communication device 10A, which is the source of transmission. Although not shown in Fig. 1, another terminal is connected to each of communication device 10C and communication device 10D, and each of them is a source of transmission. Therefore, communication device 10B also stores a packet including sequence information indicating that it is the 150th packet transmitted from communication device 10C, which is the source of transmission, and a packet including sequence information indicating that it is the 200th packet transmitted from communication device 10D, which is the source of transmission.

[0027] The relay unit 30 uses the identification information of the newly received packet and the identification information of the packet already received from one or more communication devices included in the multiple communication devices to determine whether or not to relay the newly received packet. In one example, the relay unit 30 compares the identification information of the newly received packet with the identification information of the already received packet, and compares the sequence numbers of the sequence information included in each identification information. Then, it is determined whether the sequence number of the identification information of the newly received packet is the same as the sequence number of the identification information of the already received packet, or a number earlier than the sequence number (i.e., indicating that the packet was transmitted in the past in terms of time series). Then, the relay of the "newly received packet" having the sequence number corresponding to these is blocked and not relayed. On the other hand, the "newly received packet" having the sequence number not corresponding to these is relayed. In the example of FIG. 1, relaying the newly received packet indicates that the communication device 10B passes the packet received from the communication device 10A to a communication channel corresponding to the other communication devices so that the packet can be transmitted (flooded) to the other communication devices 10C and 10D. On the other hand, blocking the relay means that such delivery is not performed. When the relay is blocked, in the example of Fig. 1, this means that the communication device 10B does not transmit (flood) the packet received from the communication device 10A to either the other communication device 10C or the communication device 10D.

[0028] As an example, the relay unit 30 acquires the identification information of the already received packet from the storage unit, and then compares the identification information of the newly received packet with the identification information of the already received packet.

[0029] In the example of FIG. 1, communication device 10B may receive a packet from communication device 10A, which is the source, via two routes. The first route is a route that passes through a link provided between communication device 10A and communication device 10B (this route may be referred to as a direct route). The second route is a route that passes through communication device 10D (this route may be referred to as a redundant route). The packet flooded from communication device 10A is received by communication device 10B via both the direct route and the redundant route. Here, the packet transmission routes will be explained for a case where communication can be performed without problems via both the direct route and the redundant route, and a case where a short-term communication failure (communication interruption) occurs on the direct route.

[0030] (i) When both routes can communicate without problems When both routes can communicate without problems, the packet that has passed through the direct route, which has fewer hops, is delivered earlier to the communication device 10B. Therefore, according to the configuration of this exemplary embodiment, the packet transmitted through the direct route is always flooded, and the packet transmitted through the redundant route is blocked from being relayed at the relay unit 30 of the destination communication device 10B.

[0031] (ii) If a short-term communication failure (disconnection) occurs on the direct route If a short-term communication failure (disconnection) occurs on the direct route, the packet is not delivered from the direct route, and the packet that has passed through the redundant route is received first by the communication device 10B and is flooded. Note that if the communication device 10A recognizes that a communication failure has occurred on the link to the communication device 10B, the communication device 10A discards the packet without waiting for the communication failure to be resolved.

[0032] In this exemplary embodiment, the same packets (packets having the same transmission information) delivered to one communication device (e.g., communication device 10B) with a time difference due to differences in routes may have the same sequence number (e.g., "99") or different sequence numbers (e.g., "100"). Regarding different sequence numbers, it is possible that a sequence number (e.g., "97") earlier than an already received sequence number (e.g., "99") may be received later from another communication device. A time difference due to differences in operation timing of the communication devices may be a cause of later reception of an earlier sequence number. However, this is implementation-dependent, and the more the communication devices operate at the same speed, the more likely it is that this will occur. Another cause of later reception of an earlier sequence number may be that a packet that has passed through the shortest route overtakes a packet flowing through a detour route when a communication failure is restored. Regarding this cause, if this exemplary embodiment is not applied, all packets during the time of the occurrence of a short-term communication failure are lost, whereas by applying this exemplary embodiment, only packets flowing through the network at the moment the communication failure is resolved are lost, so the number of lost packets can be reduced. Therefore, it is sufficient to manage the latest identification information (sequence number) in the storage unit.

[0033] (Effects of communication systems and communication devices) As described above, the communication device 10 (10A to 10D) provided in the communication system 1 is a communication device included in a plurality of communication devices capable of configuring a mesh-type free space optical communication network, and includes a communication unit 20 that transmits and receives a packet including transmission information from a first terminal 100 and specific information indicating a source communication device 10A connected to the first terminal 100 among the plurality of communication devices and a transmission sequence, and a relay unit 30 that uses the specific information of the received packet and the specific information of the packet already received from one or more communication devices included in the plurality of communication devices to determine whether or not to relay the received packet to one or more communication devices among the plurality of communication devices, and the communication unit 20 is configured to transmit the received packet relayed by the relay unit 30 to the one or more communication devices. The received packet relayed by the relay unit 30 is configured to be transmitted to all communication devices that can transmit, thereby realizing so-called flooding, so that even if a communication path is interrupted (failed) for a short time in any link, the packet can be transmitted via another link. In short, it is possible to realize a communication system that can withstand a short-term communication interruption (failure) in the communication path. Also, the relay unit 30 is configured not to relay a packet received later if it receives a packet that has already been received. Therefore, it is possible to reduce the network load on the free-space optical communication network. These effects will be described below together with the explanation of the flow of the communication method.

[0034] (Communication method flow) The flow of a communication method S10 using the communication device 10 in the above-mentioned communication system will be described with reference to Fig. 3. Fig. 3 is a flow diagram showing the flow of the communication method S10. The communication method S10 includes a receiving process S11, a relay process S12, and a transmitting process S13. The communication method S10 will be described below with a focus on the communication device 10B in Fig. 1.

[0035] In the receiving process of step S11, the communication device 10B receives a packet (for convenience of explanation, this packet may be referred to as a "first packet P") from the communication device 10A, which is the sender and connected to the first terminal 100. The packet is received by the communication unit 20. The same first packet P is transmitted from the communication device 10A, which is the sender, to the other communication devices 10B and 10D with which it has a link (flooding). When the communication unit 20 of the communication device 10B receives the first packet P transmitted from the communication device 10A, it proceeds to relay processing (step S12).

[0036] In the relay process of step S12, the relay unit 30 of the communication device 10B determines whether or not to relay the first packet P using the identification information of the first packet P received in the reception process of the previous step S11 and the identification information of packets that have already been received (step S12a). In other words, it determines whether the first packet P received in the reception process of the previous step S11 has already been received. In one example, this is done by comparing the sequence numbers as described above.

[0037] If the first packet P is determined not to be an already received packet (NO in step S12a), the process proceeds to step S12b. In step S12b, the relay unit 30 relays the first packet P to the communication unit 20 so that the first packet P is transmitted to the other communication devices 10C, 10D with which the communication device B has formed a link. Upon receiving the first packet P relayed by the relay unit 30, the communication unit 20 transmits the first packet P (flooding) to all other communication devices 10C, 10D with which it has links (step S13).

[0038] On the other hand, if it is determined in step S12a that the first packet P is the same as a packet that has already been received (YES in step S12a), the first packet P is not relayed (step S12c). As an example, in this case, the first packet P is discarded by the relay unit 30.

[0039] (Effect of communication method) According to the above communication method S10, first, communication device 10A transmits (floods) the same packet (first packet P) to communication device 10B and communication device 10D. Therefore, even if a momentary failure (communication interruption) occurs in the communication between communication device 10A and communication device 10B, for example, the first packet P transmitted from communication device 10A is delivered to communication device 10B via communication device D. As a result, the first packet P is received by the second terminal 200 on the other side via communication device 10C.

[0040] Furthermore, by providing relay unit 30 and configuring it so as not to relay packets that have already been received, it is possible to suppress the network load that would be a concern if flooding were simply introduced.

[0041] Furthermore, when a momentary failure (communication interruption) between the communication device 10A and the communication device 10B is eliminated and communication resumes, even if the first packet P is transmitted directly from the communication device 10A to the communication device 10B, it can be understood that the relay unit 30 of the communication device 10B has received the first packet P from the communication device 10D first. In other words, the first packet P has been received from the communication device 10D first and has already been transmitted to the communication device 10C, that is, has been relayed. Therefore, even if the first packet P is received directly from the communication device 10A later than that, the relay unit 30 blocks the relay of this first packet P (step S12c). This prevents the first packet P from being transmitted in duplicate.

[0042] Furthermore, if flooding is realized between communication devices that can form a looped network, packets may continue to circulate around the loop, resulting in a so-called broadcast storm. However, by providing the relay unit 30, received packets are not transmitted, and received packets are not relayed, so packets do not continue to circulate.

[0043] Second Exemplary Embodiment A second exemplary embodiment, which is an example of an embodiment of the present invention, will be described in detail with reference to the drawings. Components having the same functions as those described in the above exemplary embodiment will be given the same reference numerals, and their description will be omitted as appropriate. The scope of application of each technical means adopted in this exemplary embodiment is not limited to this exemplary embodiment. That is, each technical means adopted in this exemplary embodiment can be adopted in other exemplary embodiments included in this disclosure, as long as no particular technical hindrance occurs. In addition, each technical means shown in each drawing referred to for explaining this exemplary embodiment can be adopted in other exemplary embodiments included in this disclosure, as long as no particular technical hindrance occurs.

[0044] (Communication System Configuration) The configuration of the communication system of this exemplary embodiment is similar to that already described with reference to FIG. 1, and therefore will not be described here.

[0045] (Configuration of communication device) The configuration of each of the communication devices 10A to 10D included in the communication system of this exemplary embodiment will be described with reference to Fig. 4. Fig. 4 is a block diagram showing the configuration of an arbitrary communication device among a plurality of communication devices capable of configuring a mesh-type free space optical communication network of the communication system of this exemplary embodiment. Note that, similar to Fig. 2, Fig. 4 takes up the communication device 10C connected to the second terminal 200 as an arbitrary communication device 10 among the plurality of communication devices shown in Fig. 1. Note that the other communication devices 10A, 10B, and 10D have the same configuration.

[0046] 4 is a communication device included in a plurality of communication devices capable of configuring a mesh-type free space optical communication network, as described above. The communication device 10 includes a communication unit 20, a relay unit 30, and a switch unit 40 (switch unit, providing unit).

[0047] The communication unit 20 includes a plurality of communication channels 22a, 22b. Each of these communication channels 22a, 22b forms a link with a communication channel of a communication unit of another communication device. Each of the communication channels 22a, 22b can transmit and receive packets to and from the communication channel to which it is linked by spatial optical communication. Note that, although FIG. 4 illustrates an example in which two communication channels 22a, 22b are provided, the number is not limited to this.

[0048] As for packets, they are directional communication media as described in the first exemplary embodiment, so their description will be omitted here. The communication unit 20 includes multiple communication channels 22a and 22b, and is configured to transmit packets received on one communication channel from another communication channel. This causes the packets to be flooded.

[0049] A packet received by the communication unit 20 is acquired by the relay unit 30. The packet acquired by the relay unit 30 can be relayed to the communication unit 20. Note that a packet itself received by a certain communication channel 22a of the communication unit 20 from another communication device 10 may be acquired by the relay unit 30, and if relaying is possible, the packet may be sent from the relay unit 30 to another communication channel 22b of the communication unit 20. However, this is not the only possible embodiment. As another embodiment, a packet may be delivered between communication channels, a packet acquired from another communication device on a certain communication channel 22a is copied, the copied packet is acquired by the relay unit 30 to determine whether or not to relay it, and the copied packet may be sent from the certain communication channel 22a to the other communication channel 22b.

[0050] Here, the configuration of a packet will be described with reference to Fig. 5. Each packet transmitted and received between communication devices includes transmission information (payload), which is the net data body sent from the transmitting terminal (the first terminal 100 in the example of Fig. 1) to the other terminal. Furthermore, the packet includes specific information. As described in the first exemplary embodiment, this specific information includes information (originating device ID in Fig. 5) that identifies the communication device 10A connected to the terminal that transmits the transmission information (the first terminal 100 in the example of Fig. 1). Furthermore, the specific information includes information that indicates a transmission sequence in addition to information that identifies the originating communication device. The information that indicates a transmission sequence is information that indicates a transmission sequence number of a packet transmitted from the originating communication device 10A (sequence number in Fig. 5).

[0051] The switch unit 40 (addition unit) shown in Fig. 4 is configured to add the information for identifying the communication device and the information indicating the transmission sequence to transmission information (payload) to which control information such as the destination has been added in advance. Since the communication device 10 (10C) shown in Fig. 4 is a communication device connected to the second terminal 200 shown in Fig. 1, when a packet is transmitted from the second terminal 200, the switch unit 40 shown in Fig. 4 adds the information for identifying the communication device 10C and the information indicating the transmission sequence to the transmission information (payload to which control information has been added in advance).

[0052] As shown in FIG. 4, the relay unit 30 includes a determination unit 31 and a storage unit 33. The storage unit 33 stores packets that have already been received. The packets stored in the storage unit 33 may be the latest packets of the communication devices that are the source of transmission. The latest packets can be identified from information indicating the transmission sequence included in the identification information. The embodiment is not limited to storing packets, and may be, for example, a form in which only the identification information of the received packets is stored in a database. The storage unit 33 is configured as a part of the relay unit 30, but is not limited thereto. For example, the storage unit 33 may be configured as a part of the communication unit 20, or may be realized as a separate component within the communication device 10.

[0053] FIG. 6 shows a schematic diagram of a database stored in the storage unit 33 as an example. FIG. 6 shows the database DB in the storage unit 33 of the communication device 10B shown in FIG. 1. The database DB is associated with the sequence number of the latest packet among packets received by each source communication device. As shown in FIG. 6, when a packet with a sequence number "100" is received from the source communication device 10A, the sequence number corresponding to the communication device 10A is updated from "99" to "100" in the database DB stored in the storage unit 33. The database DB shown in FIG. 6 shows that the packet with the sequence number "150" is the latest packet received from the communication device 10C. The database DB shown in FIG. 6 shows that the packet with the sequence number "200" is the latest packet received from the communication device 10D. The sequence number starts from "1" and increases with the number, indicating that the packet is more recently transmitted.

[0054] In this exemplary embodiment, when the sequence number "99" is stored in the database DB for the communication device 10A, all packets with the previous sequence numbers "1" to "98" are considered to have been received by the communication device itself (communication device 10B).

[0055] The determination unit 31 acquires a received packet, and compares the packet's identification information with the database DB to determine whether the sequence number included in the identification information of the packet is the same as the sequence number of the communication device of the same source on the database DB, a number earlier than the sequence number, or a number later than the sequence number of the communication device of the same source on the database DB. If the sequence number of the packet is a number later than the sequence number of the communication device of the same source on the database DB, the determination unit 31 relays the packet to another communication channel. On the other hand, if the sequence number of the packet is the same as the sequence number of the communication device of the same source on the database DB, or a number earlier than the sequence number, the relay is blocked. When the relay is blocked, the relay unit 30 discards the received packet.

[0056] In other words, the relay unit 30 stores sequence information for each communication device, and if the sequence number of a received packet is later than the sequence number stored for the communication device that has the same source as the packet, the relay unit 30 relays and floods the packet.

[0057] In this exemplary embodiment, a plurality of communication devices are connected to each other via a plurality of links in the mesh type free space optical communication network NE. Therefore, as described above, the same packet (a packet having the same specific information) is delivered to a certain communication device via different routes. If every delivered packet were flooded, the network load would be undesirably high, and communication failure or system failure may occur. However, by providing the relay unit 30, flooding is prevented when a packet identical to a packet that has already been received, in other words, already flooded, is received. This makes it possible to suppress the network load while performing flooding.

[0058] According to one example, by providing the relay unit 30 as in this exemplary embodiment, a packet is duplicated for the number of links in the network, but is not duplicated any more than that, thereby suppressing bandwidth congestion.

[0059] For example, in the communication system shown in FIG. 1, there is a slight difference between the timing of a packet delivered from the communication device 10A connected by forming a link to the communication device 10B and the timing of the packet delivered from the communication device 10A to the communication device 10B via a redundant path via the communication device 10D, and the packet is delivered slightly later via the redundant path. Therefore, if there is no communication interruption between the communication device 10A and the communication device 10B, the packet delivered to the communication device 10B via the redundant path is discarded without being relayed. On the other hand, if a short communication interruption occurs in the link between the communication device 10A and the communication device 10B, the packet that passed through the redundant path is delivered to the communication device 10B first and flooded. If the communication device 10A recognizes that a communication failure has occurred in the link to the communication device 10B, the communication device 10A discards the packet without waiting for the communication failure to be resolved.

[0060] The switch unit 40 acquires the packet relayed by the relay unit 30. Then, based on destination information included in the packet, that is, receiving terminal information indicating the terminal at which the transmission information should be received, the switch unit 40 determines whether or not the terminal (second terminal 200) to which the own device (communication device 10 (10C)) is connected is the terminal indicated by the receiving terminal information. If the terminal (second terminal 200) to which the own device (communication device 10 (10C)) is connected is the terminal indicated by the receiving terminal information, the switch unit 40 removes the identifying information from the packet and transmits the transmission information included in the packet to the terminal (second terminal 200).

[0061] (Communication method flow) The flow of the communication method S10 using the communication device 10 in the above-mentioned communication system will be described with reference to FIG. 7. FIG. 7 is a flow diagram showing the flow of the communication method S20. The communication method S20 includes the reception process S11 and relay process S12 described in the first exemplary embodiment. Furthermore, the communication method S20 includes the transmission process S13, the destination determination process S14, the removal process S15, and the transfer process S16. Hereinafter, the communication method S20 will be described with attention to the communication device 10C in FIG. 1. Note that the reception process S11 has been described in the first exemplary embodiment, so the description here will be omitted.

[0062] In the relay process of step S12, it is determined whether the packet (first packet P) received in the previous reception process of step S11 has already been received. As described above, whether the first packet P received in the previous reception process of step S11 is the same as an already received packet is determined by comparing the identification information given to each packet with the identification information in the database stored in the storage unit 33. This has been described in the present exemplary embodiment, so a description thereof will be omitted here.

[0063] If the first packet P received in the receiving process of step S11 is not identical to a packet that has already been received (NO judgment in step S12a), the relay unit 30 relays the first packet P to the communication unit 20 so that the first packet P is transmitted to another communication device with which the own device (communication device 10C) has formed a link (step S12b).

[0064] The communication channel of the communication unit that has received the relay of the first packet P in step S12b (eg, communication channel 22a) transmits the first packet P to another communication device having a link (transmission process S13).

[0065] Furthermore, when the first packet P is relayed in step S12b, the relay unit 30 transmits the first packet P to the switch unit 40 as well.

[0066] In step S14 of Fig. 7, the switch unit 40 acquires the receiving terminal information from the identification information of the first packet P, and judges whether the receiving terminal is a terminal to which the device is connected. If the receiving terminal is a terminal to which the device is connected, the process proceeds to step S15. If the receiving terminal is not a terminal to which the device is connected, the process ends.

[0067] In step S15, the switch unit 40 removes the specific information from the packet as described above.

[0068] In step S16, switch section 40 transfers the transmission information that has been removed in step S15 to second terminal 200. This completes a series of flows.

[0069] (Modification of relay section) The relay unit 30 may be configured to send information (signal) indicating that the packet will not be relayed to a communication device that has transmitted a packet that was not relayed.

[0070] (Effects of communication devices) As described above, in the communication device 10, the relay unit 30 compares the identification information of the received packet with the identification information of the packet already received from one or more communication devices included in the multiple communication devices. Then, it compares and judges whether the sequence number included in the identification information of the received packet is the same as the sequence number of the communication device of the same source on the database DB, a number earlier than the sequence number, or a number later than the sequence number of the communication device of the same source on the database DB. If the sequence number included in the identification information of the received packet is the same as the sequence number of the communication device of the same source on the database DB, or a number earlier than the sequence number, the received packet is discarded. Therefore, according to the communication device 10, in addition to the effects achieved in the first exemplary embodiment described above, the data capacity of the communication device is not exceeded by packets delivered by flooding, and communication failure due to this does not occur, and a good spatial optical communication environment can be provided.

[0071] Here, an example of the effect achieved by the communication system (communication device) in this exemplary embodiment will be described with reference to Fig. 8. Note that this effect also applies to the first exemplary embodiment described above.

[0072] Fig. 8 shows an example of a packet in the communication system shown in Fig. 1. In Fig. 8, it is assumed that the links connecting the communication devices communicate packets at the same packet communication speed.

[0073] The first terminal 100 shown in FIG. 8 transmits transmission information (data in FIG. 8) to the communication device 10A connected to the first terminal 100. The communication device 10A that receives the transmission information assigns specific information by the switch unit 40 (FIG. 4). The specific information includes information for identifying the communication device of the sender described above (A in FIG. 8) and a transmission sequence number (100 in FIG. 8). In FIG. 8, a packet to which these are assigned is indicated by "P". The communication device 10A transmits the packet P to the communication device 10B and the communication device 10D having a link, and the communication device 10B and the communication device 10D each receive the packet P at approximately the same timing. Here, for convenience of explanation, it is assumed that the communication device 10B and the communication device 10D relay the packet P received from the communication device 10A. At this time, the packet P or the specific information of the packet P is stored in each of the communication device 10B and the communication device 10D. Then, a packet P is flooded from each of the communication device 10B and the communication device 10D. Specifically, the packet P flooded from the communication device 10B is directed to the communication device 10C and the communication device 10D. Also, the packet P flooded from the communication device 10D is directed to the communication device 10B. At this time, the packet P directed from the communication device 10D to the communication device 10B is the same as the packet P (already received packet) directly transmitted from the communication device 10A to the communication device 10B. This is identified by the relay unit 30 of the communication device 10B based on the sequence number, and the packet P directed from the communication device 10D to the communication device 10B is discarded and is not flooded. Also, the packet P directed to the communication device 10D among the packets flooded from the communication device 10B to the communication device 10C and the communication device 10D is the same as the packet P (already received packet) directly delivered from the communication device 10A to the communication device 10D. The relay unit 30 of the communication device 10D identifies this based on the sequence number, and the packet P sent from the communication device 10B to the communication device 10D is discarded and is not flooded.

[0074] Here, as described above, whether or not the packet P is a packet that has already been received is judged by the judgment unit 31 of the relay unit 30. That is, the judgment unit 31 is configured to check the sequence number of the received packet against the sequence number of a packet that has already been received for each source communication device. This makes it possible to obtain the effect of being able to judge whether or not flooding is possible without the need for complex judgment processing.

[0075] This is because each communication device 10 includes a switch unit 40 (addition unit) that adds identification information indicating the device itself and sequence information indicating a sequence number to transmission information sent from a terminal connected to the device itself, which allows the determination unit 31 to make a determination based on the sequence number.

[0076] Further, each communication device 10 is provided with the above-mentioned switch unit 40. As a result, when the terminal to which the device is connected is the terminal indicated by the receiving terminal information included in the packet P, the specific information is removed from the packet P and the transmission information is transmitted to the terminal. Explaining the example of FIG. 8, the communication device 10C receives the packet P from the communication device 10B. The receiving terminal information in the packet P indicates that the communication device 10C is the communication device 10C. In this case, the switch unit 40 of the communication device 10C removes the specific information from the packet P and transfers the transmission information (data) to the second terminal 200. As a result, the transmission information is delivered from the first terminal 100 to the second terminal 200.

[0077] [Software implementation example] Some or all of the functions of the communication device 10 (hereinafter also referred to as "each of the above-mentioned units") may be realized by hardware such as an integrated circuit (IC chip), or may be realized by software.

[0078] In the latter case, each of the above units is realized, for example, by a computer that executes instructions of a program, which is software that realizes each function. An example of such a computer (hereinafter, referred to as computer C) is shown in Fig. 9. Fig. 9 is a block diagram showing the hardware configuration of computer C that functions as each of the above units.

[0079] The computer C includes at least one processor C1 and at least one memory C2. The memory C2 stores a program P for causing the computer C to operate as each of the above-mentioned parts. In the computer C, the processor C1 reads and executes the program P from the memory C2, thereby realizing the functions of each of the above-mentioned parts.

[0080] The processor C1 may be, for example, a central processing unit (CPU), a graphic processing unit (GPU), a digital signal processor (DSP), a micro processing unit (MPU), a floating point number processing unit (FPU), a physics processing unit (PPU), a tensor processing unit (TPU), a quantum processor, a microcontroller, or a combination thereof. The memory C2 may be, for example, a flash memory, a hard disk drive (HDD), a solid state drive (SSD), or a combination thereof.

[0081] The computer C may further include a RAM (Random Access Memory) for expanding the program P during execution and for temporarily storing various data. The computer C may further include a communication interface for transmitting and receiving data to and from other devices. The computer C may further include an input / output interface for connecting input / output devices such as a keyboard, a mouse, a display, and a printer.

[0082] Furthermore, the program P can be recorded on a non-transitory tangible recording medium M that can be read by the computer C. Such a recording medium M can be, for example, a tape, a disk, a card, a semiconductor memory, or a programmable logic circuit. The computer C can obtain the program P via such a recording medium M. Furthermore, the program P can be transmitted via a transmission medium. Such a transmission medium can be, for example, a communication network or broadcast waves. The computer C can also obtain the program P via such a transmission medium.

[0083] [Additional Note 1] This disclosure includes the techniques described in the following appendices. However, the present invention is not limited to the techniques described in the following appendices, and various modifications are possible within the scope of the claims.

[0084] (Appendix 1) A communication device included in a plurality of communication devices capable of configuring a mesh type free space optical communication network, a communication unit that transmits and receives packets including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence; a relay unit that uses the identification information of the received packet and the identification information of the packet already received from one or more communication devices included in the plurality of communication devices to determine whether or not to relay the received packet to one or more communication devices among the plurality of communication devices; Including, The communication unit transmits the received packet relayed by the relay unit to the one or more communication devices. Communications equipment.

[0085] (Appendix 2) the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; the relay unit discards the received packet when the sequence number indicated in the sequence information of the received packet is the same as or an earlier sequence number than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the plurality of communication devices; 2. The communication device of claim 1.

[0086] (Appendix 3) the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; The relay unit includes: a determination unit for determining, for each of the source communication devices, the sequence number of a received packet and the sequence number of a previously received packet; the relay unit, when, as a result of the comparison and determination by the determination unit, (I) the sequence number indicated in the sequence information of the received packet is a number later than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices, relays the received packet to one or more communication devices among the multiple communication devices, and (II) when the sequence number indicated in the sequence information of the received packet is the same as or an earlier number than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices, blocks the relay. 3. A communication device according to claim 1 or 2.

[0087] (Appendix 4) The terminal is connected to the device itself, and the device includes an assigning unit that assigns identification information indicating the device itself and sequence information indicating a sequence number to transmission information transmitted from the terminal. 4. A communication device according to any one of claims 1 to 3.

[0088] (Appendix 5) the packet includes receiving terminal information indicating a terminal at which the transmission information is to be received; a switch unit that, when a terminal to which the device itself is connected is a terminal indicated by the receiving terminal information of the packet received by the communication unit, removes the specific information from the packet and transmits the transmission information included in the packet to the terminal; 5. A communication device according to any one of claims 1 to 4.

[0089] (Appendix 6) A communication system for transmitting and receiving data between terminals via a mesh-type free space optical communication network composed of a plurality of communication devices, One or more of the plurality of communication devices, a communication unit that transmits and receives packets including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence; a relay unit that uses the identification information of the received packet and the identification information of the packet already received from one or more communication devices included in the plurality of communication devices to determine whether or not to relay the received packet to one or more communication devices among the plurality of communication devices; Including, The communication unit transmits the received packet relayed by the relay unit to the one or more communication devices. Communication systems.

[0090] (Appendix 7) the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; the relay unit discards the received packet when the sequence number indicated in the sequence information of the received packet is the same as or an earlier sequence number than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the plurality of communication devices; 7. The communication system of claim 6.

[0091] (Appendix 8) the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; The relay unit includes: a determination unit for determining, for each of the source communication devices, the sequence number of a received packet and the sequence number of a previously received packet; the relay unit, when, as a result of the comparison and determination by the determination unit, (I) the sequence number indicated in the sequence information of the received packet is a number later than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices, relays the received packet to one or more communication devices among the multiple communication devices, and (II) when the sequence number indicated in the sequence information of the received packet is the same as or an earlier number than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices, blocks the relay. 8. The communication system of claim 6 or 7.

[0092] (Appendix 9) The terminal is connected to the device itself, and the device includes an assigning unit that assigns identification information indicating the device itself and sequence information indicating a sequence number to transmission information transmitted from the terminal. 9. A communication system according to any one of claims 6 to 8.

[0093] (Appendix 10) the packet includes receiving terminal information indicating a terminal at which the transmission information is to be received; a switch unit that, when a terminal to which the device itself is connected is a terminal indicated by the receiving terminal information of the packet received by the communication unit, removes the specific information from the packet and transmits the transmission information included in the packet to the terminal; 10. A communication system according to any one of claims 6 to 9.

[0094] (Appendix 11) A communication method using a communication device according to any one of claims 1 to 5, receiving a packet including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence; determining whether to relay the received packet to one or more communication devices among the plurality of communication devices, using the identification information of the received packet and the identification information of the packet already received from one or more communication devices included in the plurality of communication devices; if the packet is to be relayed, transmitting the received packet towards the one or more communication devices; Including, Communication methods.

[0095] (Appendix 12) A program for causing a computer to operate as the communication device according to any one of claims 1 to 5, the program causing the computer to function as each of the units.

[0096] [Additional Note 2] This disclosure includes the techniques described in the following appendices. However, the present invention is not limited to the techniques described in the following appendices, and various modifications are possible within the scope of the claims.

[0097] (Appendix 1) A communication device included in a plurality of communication devices capable of configuring a mesh type free space optical communication network, A communication unit and at least one processor, the communication unit transmits and receives a packet including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence; The at least one processor: executes a process of determining whether or not to relay the received packet to one or more communication devices among the plurality of communication devices, using the identification information of the received packet and the identification information of the packet already received from one or more communication devices included in the plurality of communication devices; The communication unit transmits the received packet relayed in the identifying process to the one or more communication devices. Communications equipment.

[0098] The communication device may further include a memory, and the memory may store a program for causing the at least one processor to execute each of the processes.

[0099] (Appendix 2) the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; The at least one processor: in the identifying process, if the sequence number indicated in the sequence information of the received packet is equal to or an earlier sequence number than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the plurality of communication devices, a process of discarding the received packet is further executed. 2. The communication device according to claim 1 ,

[0100] (Appendix 3) the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; The at least one processor: In the process of identifying, a process of comparing and determining the sequence number of the received packet with the sequence number of the already-received packet is executed for each of the communication devices of the source; In the identifying process, the at least one processor, as a result of the comparison and determination in the determining process, (I) relays the received packet to one or more of the multiple communication devices if the sequence number indicated in the sequence information of the received packet is later than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices, and (II) blocks the relay if the sequence number indicated in the sequence information of the received packet is the same as or an earlier sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices. 3. A communication device according to claim 1 or 2.

[0101] (Appendix 4) The at least one processor: execute a process of adding identification information indicating the own device and sequence information indicating a sequence number to transmission information transmitted from a terminal connected to the own device; 4. A communication device according to any one of claims 1 to 3.

[0102] (Appendix 5) The packet includes receiving terminal information indicating a terminal at which the transmission information is to be received, The at least one processor: based on the receiving terminal information of the packet received by the communication unit, when the terminal to which the device itself is connected is the terminal indicated by the receiving terminal information, remove the identifying information from the packet, and execute a switching process of transmitting the transmission information included in the packet to the terminal. 5. A communication device according to any one of claims 1 to 4.

[0103] (Appendix 6) A communication system for transmitting and receiving data between terminals via a mesh-type free space optical communication network composed of a plurality of communication devices, One or more of the plurality of communication devices, A communication unit and at least one processor, the communication unit transmits and receives a packet including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence; The at least one processor: executes a process of determining whether or not to relay the received packet to one or more communication devices among the plurality of communication devices, using the identification information of the received packet and the identification information of the packet already received from one or more communication devices included in the plurality of communication devices; The communication unit transmits the received packet relayed in the identifying process to the one or more communication devices. Communication systems.

[0104] (Appendix 7) the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; The at least one processor: in the identifying process, if the sequence number indicated in the sequence information of the received packet is equal to or an earlier sequence number than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the plurality of communication devices, a process of discarding the received packet is further executed. 7. The communication system of claim 6.

[0105] (Appendix 8) the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; The at least one processor: In the process of identifying, a process of comparing and determining the sequence number of the received packet with the sequence number of the already-received packet is executed for each of the communication devices of the source; The at least one processor: In the identifying process, as a result of the comparison and determination in the determining process, (I) if the sequence number indicated in the sequence information of the received packet is a number later than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices, relay the received packet to one or more communication devices of the multiple communication devices, and (II) if the sequence number indicated in the sequence information of the received packet is the same as or an earlier number than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices, block the relay. 8. The communication system of claim 6 or 7.

[0106] (Appendix 9) The at least one processor: execute a process of adding identification information indicating the own device and sequence information indicating a sequence number to transmission information transmitted from a terminal connected to the own device; 9. A communication system according to any one of claims 6 to 8.

[0107] (Appendix 10) The packet includes receiving terminal information indicating a terminal at which the transmission information is to be received, The at least one processor: based on the receiving terminal information of the packet received by the communication unit, when the terminal to which the device itself is connected is the terminal indicated by the receiving terminal information, remove the identifying information from the packet, and execute a switching process of transmitting the transmission information included in the packet to the terminal. 10. A communication system according to any one of claims 6 to 9.

[0108] (Appendix 11) A communication method using a communication device according to any one of claims 1 to 5, receiving a packet including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence; determining whether to relay the received packet to one or more communication devices among the plurality of communication devices, using the identification information of the received packet and the identification information of the packet already received from one or more communication devices included in the plurality of communication devices; if the packet is to be relayed, transmitting the received packet towards the one or more communication devices; Including, Communication methods. [Explanation of symbols]

[0109] 1. Communication Systems 10, 10A, 10B, 10C, 10D...Communication device 20. Communications Department 30 Relay section 31... Judgment section 33...Storage section 40 Switch section (applying section) 100···1st Terminal 200: Second terminal (receiving terminal) NE: Mesh-type free space optical network P... Packet

Claims

1. A communication device included in a plurality of communication devices capable of configuring a mesh type free space optical communication network, a communication unit that transmits and receives packets including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence; a relay unit that uses the identification information of the received packet and the identification information of the packet already received from one or more communication devices included in the plurality of communication devices to determine whether or not to relay the received packet to one or more communication devices among the plurality of communication devices; Including, The communication unit transmits the received packet relayed by the relay unit to the one or more communication devices. Communications equipment.

2. the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; the relay unit discards the received packet when the sequence number indicated in the sequence information of the received packet is the same as or an earlier sequence number than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the plurality of communication devices; The communication device according to claim 1 .

3. the specific information includes identification information indicating a source communication device connected to the terminal and sequence information indicating a sequence number of the transmission information; The relay unit includes: a determination unit for determining, for each of the source communication devices, the sequence number of a received packet and the sequence number of a previously received packet; The relay unit, when, as a result of the comparison and determination by the determination unit, (I) the sequence number indicated in the sequence information of the received packet is a number later than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices, relays the received packet to one or more communication devices among the multiple communication devices, and (II) blocks the relaying if the sequence number indicated in the sequence information of the received packet is the same as or an earlier number than the sequence number indicated in the sequence information of the packet already received from one or more communication devices included in the multiple communication devices. The communication device according to claim 1 .

4. The terminal is connected to the device itself, and the device includes an assigning unit that assigns identification information indicating the device itself and sequence information indicating a sequence number to transmission information transmitted from the terminal. The communication device according to claim 1 .

5. The packet includes receiving terminal information indicating a terminal at which the transmission information is to be received, a switch unit that, when a terminal to which the device itself is connected is a terminal indicated by the receiving terminal information of the packet received by the communication unit, removes the specific information from the packet and transmits the transmission information included in the packet to the terminal; The communication device according to claim 1 .

6. A communication system for transmitting and receiving data between terminals via a mesh-type free space optical communication network composed of a plurality of communication devices, One or more of the plurality of communication devices, a communication unit that transmits and receives packets including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence; a relay unit that uses the identification information of the received packet and the identification information of the packet already received from one or more communication devices included in the plurality of communication devices to determine whether or not to relay the received packet to one or more communication devices among the plurality of communication devices; Including, The communication unit transmits the received packet relayed by the relay unit to the one or more communication devices. Communication systems.

7. A communication method using the communication device according to any one of claims 1 to 5, receiving a packet including transmission information from a terminal and specific information indicating a source communication device connected to the terminal among the plurality of communication devices and a transmission sequence; determining whether or not to relay the received packet to one or more communication devices among the plurality of communication devices, using the identification information of the received packet and the identification information of the packet already received from one or more communication devices included in the plurality of communication devices; if the packet is to be relayed, transmitting the received packet towards the one or more communication devices; Including, Communication methods.

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