Control device, communication system, and control method

Abstract

A control device (20) is provided with a communication unit for communicating with a plurality of transfer devices (30) structuring a ring-like communication network (11), a storage unit for storing, in both a clockwise communication pattern and a counterclockwise communication pattern, a GCL (12) defining a plurality of time slots and a flow having a certain transmission cycle during which a corresponding port is passed through in each of the time slots, and a control unit for creating, upon detecting a failure occurring in a section included in the communication network (11), a GCL (13) in accordance with the failure from a GCL (12R) corresponding to the clockwise communication pattern and from a GCL (12L) corresponding to the counterclockwise communication pattern, and transmits the created GCL (13) to one of the transfer devices (30) having the corresponding port.

Description

Control Device, Communication System, and Control Method

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

[0002] In Non-Patent Document 1, TAS is defined. "TAS" is an abbreviation for time aware shaper.

[0003] IEEE Computer Society, IEEE Std 802.1Qbv-2015, IEEE Standard for Local and metropolitan area networks -- Bridges and Bridged Networks - Amendment 25: Enhancements for Scheduled Traffic, 2016-03-18

[0004] By constructing a network with a plurality of nodes having a TAS function, a network function for guaranteeing the maximum delay and the maximum jitter, that is, deterministic communication can be realized. At this time, it is necessary to allocate a time slot dedicated to deterministic communication to the output ports of all nodes passing through end-to-end.

[0005] The mechanism of TAS is shown in FIG. 15. TAS performs priority control by determining the traffic to be transmitted according to a time-division schedule. Specifically, TAS stores frames in a FIFO queue for each VLAN-CoS or each IP-ToS, and permits transmission from the queue for which the gate is open according to the GCL. "VLAN" is an abbreviation for virtual local area network. "CoS" is an abbreviation for class of service. "IP" is an abbreviation for Internet Protocol. "ToS" is an abbreviation for type of service. "FIFO" is an abbreviation for first in, first out. "GCL" is an abbreviation for gate control list.

[0006] An example of a GCL is shown in Figure 16. The TAS can control best-effort traffic and delay-guaranteed traffic in a superimposed manner. In the example shown in Figure 16, four ST flows and one NST flow are multiplexed. "ST" is an abbreviation for scheduled traffic. "NST" is an abbreviation for non-scheduled traffic. ST flows correspond to delay-guaranteed traffic. NST flows correspond to traffic that is not delay-guaranteed, i.e., best-effort traffic. The GCL shown in Figure 16 specifies that ST with CoS "7" is permitted in time slots 1 and 3, ST with CoS "5" in time slot 2, ST with CoS "4" in time slot 4, and NST with CoS "3" or less in time slot 5. This GCL further specifies that the length of time for which communication is permitted in each time slot from time slot 1 to time slot 4 is 15 microseconds, and the length of time for which communication is permitted in time slot 5 is 100 microseconds.

[0007] To avoid collisions end-to-end, all nodes in the network must be time-synchronized, and the opening and closing timing of the GCL gates at each node must be synchronized. The GCL is either centrally managed by a controller called a CNC, or managed individually at each node. "CNC" is an abbreviation for centralized network configuration. Each node opens its gate considering propagation delay, thus preventing collisions with other communications and enabling communication without queuing delays. The transmitting terminal is also time-synchronized and periodically transmits frames in accordance with the GCL timing, enabling communication without queuing delays.

[0008] One possibility is to construct a ring network using TAS (Transactional Alignment System). In such a ring network, each switch is connected to a CNC (Control Center). A Global Contact Limit (GCL) is configured on each port of each switch, guaranteeing low latency for high-priority flows. However, since the GCL is uniquely determined for any given path, if a path change occurs due to a failure, the GCL needs to be recreated. If the GCL is recreated after a failure, the latency of high-priority flows cannot be guaranteed until the GCL is distributed. Therefore, it is conceivable to apply a multi-GCL method in which GCLs are calculated and maintained for redundant paths in advance of a failure. Since the path of each flow changes depending on the number of failure points in the network, the multi-GCL method requires calculating as many GCLs as there are failure points. In the case of a ring network, the number of failure points is the same as the number of switches that make up the network. For example, in a ring network consisting of five switches, there are five failure points. In the multi-GCL method, it is necessary to create failure GCLs corresponding to these five failure points. As the network size increases and the number of switches that make up the network increases, the number of GCLs required for redundancy, and the corresponding number of calculations, also increase. Because this requires an enormous amount of computation and a vast number of GCLs to be maintained on each port, the application of a multi-GCL scheme is practically difficult.

[0009] In particular, when a network consists of multiple ring networks, the total number of fault points in the entire network is the product of the number of fault points in each ring network. For example, in a combination of four ring networks, each consisting of 15 nodes, the total number of fault points in the entire network is 15 ４ This would require pre-calculating approximately 50,000 GCLs, but storing approximately 50,000 GCLs per port is practically impossible.

[0010] In light of these circumstances, the purpose of this disclosure is to expedite the recovery of delay-guaranteed communications in the event of a failure in a ring-shaped communication network.

[0011] A control device according to one embodiment is a control device that sets a plurality of time slots for each port of a plurality of transfer devices that form a ring-shaped communication network capable of communication in both left and right directions, and comprises: a communication unit that communicates with the plurality of transfer devices; a storage unit that stores gate control lists that define the plurality of time slots and flows with a fixed transmission period that pass through the corresponding port in each time slot, for both clockwise and counterclockwise communication patterns; and a control unit that, when it detects a fault occurring in a section included in the communication network, creates a gate control list corresponding to the fault from the gate control list corresponding to the clockwise communication pattern and the gate control list corresponding to the counterclockwise communication pattern stored in the storage unit, and transmits the created gate control list to the transfer device having the corresponding port via the communication unit.

[0012] A control method according to one embodiment includes: a control device that sets a plurality of time slots for each port of a plurality of transfer devices that form a ring-shaped communication network capable of communication in both left and right directions, creating a gate control list for both clockwise and counterclockwise communication patterns that defines the plurality of time slots and a flow with a fixed transmission period that passes through the corresponding port in each time slot; when the control device detects a fault occurring in a section included in the communication network, creating a gate control list corresponding to the fault from the gate control list corresponding to the clockwise communication pattern and the gate control list corresponding to the counterclockwise communication pattern, respectively; and transmitting the gate control list corresponding to the fault to a transfer device having the corresponding port.

[0013] According to this disclosure, it is possible to expedite the recovery of delay-guaranteed communications when a failure occurs in a ring-shaped communication network.

[0014] This figure shows the configuration of a communication system and the operation of GCL distribution according to one embodiment. This figure shows the flow path from node A to node C when no fault occurs. This figure shows the flow path from node A to node C when a fault occurs in section AB. This figure shows the flow path from node A to node C when a fault occurs in section BC. This figure shows the flow path from node A to node C when a fault occurs in section CD. This figure shows the flow path from node A to node C when a fault occurs in section DA. This figure shows a series of operations of the communication system when a fault occurs. This is a block diagram showing the configuration of the control device and each transfer device. This is a flowchart showing the operation of the control device. This figure shows variations of the path when no fault occurs. This figure shows the path when a fault occurs in section CD. This figure shows an example of GCL. This figure shows GCL corresponding to a fault that occurred in section CD, corresponding to the example shown in Figure 12. This figure shows GCL corresponding to a fault that occurred in section BC, corresponding to the example shown in Figure 12. This figure shows the mechanism of TAS. This is a table showing an example of GCL.

[0015] One embodiment will be described below with reference to the figures.

[0016] In each figure, identical or corresponding parts are denoted by the same reference numerals. In the description of this embodiment, the description of identical or corresponding parts will be omitted or simplified as appropriate.

[0017] Referring to Figure 1, the configuration of the communication system 10 according to this embodiment will be described.

[0018] The communication system 10 comprises a control device 20 and a plurality of transfer devices 30. The control device 20 and each transfer device 30 are connected by a control communication network, and can communicate with each other via the control communication network. The plurality of transfer devices 30 form a communication network 11, which is a main signal communication network, and can transfer frames between any user terminals via the communication network 11. The communication network 11 is a ring-shaped network that allows communication in both left and right directions.

[0019] The control device 20 is a computer that monitors and controls each transfer device 30. Each transfer device 30 is a device that accommodates users and transfers frames to a port designated for each destination user terminal. The number of transfer devices 30 is not limited to the four shown in Figure 1, but may be two, three, or five or more. In this embodiment, the control device 20 functions as a CNC, and each transfer device 30 functions as a TAS-compatible switch. Each user terminal is, for example, a terminal such as a mobile device or PC, or a server such as a cloud server. "PC" is an abbreviation for personal computer. Mobile devices may also be IoT devices. "IoT" is an abbreviation for Internet of Things. Each user terminal can be either the start or end point of a flow.

[0020] A ring network has two paths: a clockwise path and a counterclockwise path. Focusing on a single flow, even if there are multiple failure patterns, the path variation is limited to either clockwise or counterclockwise.

[0021] For example, as shown in Figure 1, suppose that multiple transfer devices 30, namely nodes A, B, C, and D, are connected in a ring in this order. Focusing on the flow from node A to node C, as shown in Figure 2, there are two possible paths for this flow: a clockwise path via node B and a counterclockwise path via node D. When no fault occurs, both the clockwise and counterclockwise paths can be used. However, as shown in Figure 3, if a fault occurs in the AB section, only the counterclockwise path can be used. Similarly, as shown in Figure 4, if a fault occurs in the BC section, only the counterclockwise path can be used. On the other hand, as shown in Figure 5, if a fault occurs in the CD section, only the clockwise path can be used. Similarly, as shown in Figure 6, if a fault occurs in the DA section, only the clockwise path can be used.

[0022] By pre-calculating GCLs corresponding to both paths for all flows, it is possible to create GCLs that anticipate all failure patterns. By subtracting the time slots corresponding to each failure point from the GCLs that cover all failure patterns, it is possible to create GCLs that correspond to specific failure points. When creating GCLs, twice the number of time slots are allocated for clockwise and counterclockwise directions, but after a failure occurs, the GCL is executed using only the time slots remaining after the subtraction, thus avoiding the consumption of extra bandwidth.

[0023] The outline of this embodiment will be described with reference to Figures 1 and 7.

[0024] The control device 20 sets multiple time slots for each port of the multiple transfer devices 30. As shown in Figure 1, the control device 20 creates and distributes GCL 12 for both clockwise and counterclockwise communication patterns, which define multiple time slots and a flow with a fixed transmission cycle that passes through the corresponding port in each time slot. The "flow with a fixed transmission cycle" corresponds to the ST flow. The control device 20 sets the multiple time slots defined in GCL 12R to the clockwise communication ports of each transfer device 30 by distributing GCL 12R corresponding to the clockwise communication pattern to each transfer device 30. Similarly, the control device 20 sets the multiple time slots defined in GCL 12L to the counterclockwise communication ports of each transfer device 30 by distributing GCL 12L corresponding to the counterclockwise communication pattern to each transfer device 30.

[0025] As shown in Figure 7, when the control device 20 receives notification from any of the transfer devices 30 of a fault occurring in a section included in the communication network 11, it creates and distributes a GCL 13 corresponding to the fault from GCL 12R corresponding to the clockwise communication pattern and GCL 12L corresponding to the counterclockwise communication pattern. The control device 20 updates the time slot set for the clockwise communication port of each transfer device 30 by distributing the fault-specific GCL 13R corresponding to the clockwise communication pattern to each transfer device 30. Similarly, the control device 20 updates the time slot set for the counterclockwise communication port of each transfer device 30 by distributing the fault-specific GCL 13L corresponding to the counterclockwise communication pattern to each transfer device 30.

[0026] In this embodiment, the control device 20 creates a GCL 13 corresponding to the failure by changing GCL 12 to a GCL in which a time slot that allows the flow passing through the section where the failure occurred is opened among a plurality of time slots. In other words, the control device 20 creates a GCL 13 corresponding to the failure by extracting only those time slots and flow definitions included in GCL 12 that allow bypassing the section where the failure occurred.

[0027] For example, if a failure occurs in the DA section, as shown in Figure 6, the only usable path for the flow from node A to node C is a clockwise path. Therefore, the control device 20 extracts the definition of the time slots assigned to the flow from node A to node C from GCL12R and reflects it in GCL13R, but does not extract it from GCL12L and does not reflect it in GCL13L either. Consequently, in GCL13L, at least the time slots that were assigned to the flow from node A to node C among the multiple time slots defined in GCL12L are released. These released time slots can be used for best-effort traffic.

[0028] Referring to Figure 8, the configurations of the control device 20 and each transfer device 30 according to this embodiment will be described.

[0029] The control device 20 comprises a control unit 21, a storage unit 22, and a communication unit 23.

[0030] The control unit 21 includes at least one processor, at least one programmable circuit, at least one dedicated circuit, or any combination thereof. The processor is a general-purpose processor such as a CPU or GPU, or a dedicated processor specialized for a specific process. "CPU" is an abbreviation for central processing unit. "GPU" is an abbreviation for graphics processing unit. The programmable circuit is, for example, an FPGA. "FPGA" is an abbreviation for field-programmable gate array. The dedicated circuit is, for example, an ASIC. "ASIC" is an abbreviation for application specific integrated circuit. The control unit 21 controls each part of the control device 20 and executes processes related to the operation of the control device 20. The control unit 21 has functions such as a full pattern GCL creation function 24, a GCL distribution function 25, a fault information reception function 26, and a fault GCL creation function 27.

[0031] The storage unit 22 includes at least one semiconductor memory, at least one magnetic memory, at least one optical memory, or any combination thereof. The semiconductor memory is, for example, RAM, ROM, or flash memory. "RAM" is an abbreviation for random access memory. "ROM" is an abbreviation for read-only memory. The RAM is, for example, SRAM or DRAM. "SRAM" is an abbreviation for static random access memory. "DRAM" is an abbreviation for dynamic random access memory. The ROM is, for example, EEPROM. "EEPROM" is an abbreviation for electrically erasable programmable read-only memory. The flash memory is, for example, SSD. "SSD" is an abbreviation for solid-state drive. The magnetic memory is, for example, HDD. "HDD" is an abbreviation for hard disk drive. The storage unit 22 functions, for example, as main memory, auxiliary memory, or cache memory. The memory unit 22 stores information used for the operation of the control device 20 and information obtained through the operation of the control device 20. The memory unit 22 stores the GCL 12, and when a failure occurs, it also stores the GCL 13 corresponding to the failure.

[0032] The communication unit 23 includes at least one communication module. The communication module is, for example, a module compatible with a LAN communication standard such as Ethernet®. "LAN" is an abbreviation for local area network. The communication unit 23 communicates with each transfer device 30. The communication unit 23 receives information used for the operation of the control device 20 and transmits information obtained through the operation of the control device 20.

[0033] The functions of the control device 20 are realized by executing the program according to this embodiment on the processor acting as the control unit 21. In other words, the functions of the control device 20 are realized by software. The program causes the computer to perform the operations of the control device 20, thereby causing the computer to function as the control device 20. That is, the computer functions as the control device 20 by performing the operations of the control device 20 according to the program.

[0034] The program can be stored on a non-temporary computer-readable medium. Examples of non-temporary computer-readable mediums include flash memory, magnetic recording devices, optical discs, magneto-optical recording media, or ROM. The program can be distributed, for example, by selling, transferring, or lending portable media such as SD cards, DVDs, or CD-ROMs containing the program. "SD" is an abbreviation for Secure Digital. "DVD" is an abbreviation for digital versatile disc. "CD-ROM" is an abbreviation for compact disc read-only memory. The program may also be distributed by storing it in server storage and transferring it from the server to other computers. The program may also be provided as a program product.

[0035] A computer, for example, stores a program stored on a portable medium or a program transferred from a server in its main memory. Then, the computer reads the program stored in the main memory with its processor and executes the processing according to the read program. The computer may also read a program directly from the portable medium and execute the processing according to the program. The computer may also execute the processing according to the received program sequentially each time a program is transferred to it from a server. Processing may also be performed by a so-called ASP type service, which does not transfer programs from the server to the computer, but realizes its function only through execution instructions and result acquisition. "ASP" is an abbreviation for application service provider. A program includes information used for processing by an electronic computer that is equivalent to a program. For example, data that is not a direct instruction to the computer but has the nature of defining the computer's processing falls under "equivalent to a program".

[0036] Some or all of the functions of the control device 20 may be implemented by a programmable circuit or dedicated circuit as the control unit 21. In other words, some or all of the functions of the control device 20 may be implemented by hardware.

[0037] Each transfer device 30 has functions such as a GCL receiving function 31, a GCL execution function 32, and a fault information transmission function 33.

[0038] Referring to Figure 9, the operation of the control device 20 according to this embodiment will be described. The operation described below corresponds to the control method according to this embodiment. That is, the control method according to this embodiment includes at least the steps S1 to S5 shown in Figure 9.

[0039] In S1, the control unit 21 of the control device 20 uses the full-pattern GCL creation function 24 to create GCLs 12 for both clockwise and counterclockwise communication patterns, defining multiple time slots and flows with a fixed transmission period that pass through the corresponding ports in each time slot, and stores them in the storage unit 22. That is, the control unit 21 creates GCL 12R corresponding to the clockwise communication pattern and GCL 12L corresponding to the counterclockwise communication pattern and stores them in the storage unit 22. Known methods can be used to create the GCLs 12. Information necessary for creating the GCLs 12, such as the configuration of the communication network 11 and the requirements of each flow, can also be collected using known methods. As one modification, instead of the control device 20 creating the GCLs 12, another device may create the GCLs 12, and the control device 20 may obtain the GCLs 12 from the other device.

[0040] In S2, the control unit 21 of the control device 20 transmits the GCL 12 stored in the storage unit 22 to the transfer device 30 having the corresponding port via the communication unit 23 using the GCL distribution function 25. That is, the control unit 21 distributes GCL 12R and GCL 12L to each transfer device 30 via the communication unit 23. Each transfer device 30 receives GCL 12R and GCL 12L using the GCL receiving function 31. Then, each transfer device 30 uses the GCL execution function 32 to perform ST flow communication, or ST flow and NST flow communication, according to GCL 12R and GCL 12L.

[0041] When a fault occurs in a section included in the communication network 11, the transfer device 30 at one end of that section uses the fault information transmission function 33 to create fault information indicating the section where the fault occurred and transmits it to the control device 20. Known methods can be used to create the fault information. In S3, the control unit 21 of the control device 20 detects the fault by receiving fault information via the communication unit 23 using the fault information reception function 26.

[0042] In S4, the control unit 21 of the control device 20 creates a GCL 13 corresponding to a failure from the GCL 12 stored in the storage unit 22 by means of the failure-time GCL creation function 27, and stores it in the storage unit 22. That is, the control unit 21 creates, from the GCL 12R and GCL 12L stored in the storage unit 22, a GCL 13R corresponding to a failure and corresponding to a clockwise communication pattern, and a GCL 13L corresponding to a failure and corresponding to a counterclockwise communication pattern, respectively, and stores them in the storage unit 22. As a method for creating the GCL 13, a method can be used in which each of the GCL 12R corresponding to the clockwise communication pattern and the GCL 12L corresponding to the counterclockwise communication pattern is changed to a GCL in which a time slot through which a flow passing through a section where a failure has occurred among a plurality of time slots is released.

[0043] In S5, the control unit 21 of the control device 20 transmits, by means of the GCL distribution function 25, the GCL 13 corresponding to a failure, which is stored in the storage unit 22, to the transfer device 30 having a corresponding port via the communication unit 23. That is, the control unit 21 distributes the GCL 13R and GCL 13L corresponding to a failure to each transfer device 30 via the communication unit 23. Each transfer device 30 receives the GCL 13R and GCL 13L by means of the GCL reception function 31. Then, each transfer device 30 performs communication of the ST flow, or communication of the ST flow and the NST flow, according to the GCL 13R and GCL 13L instead of the GCL 12R and GCL 12L by means of the GCL execution function 32.

[0044] As described above, in the present embodiment, paying attention to failure patterns at the time of failure for two paths, clockwise and counterclockwise, of the ring network, a GCL assuming all failure patterns is created by calculating GCLs corresponding to both paths in advance for all flows. A GCL corresponding to a failure point is created by subtracting time slots related to the path corresponding to each failure point from the created GCL. When a failure occurs, the GCL is executed only for the time slots remaining after the subtraction. By this method, it is possible to reduce the calculation cost of creating a GCL for each failure point in a large-scale ring network without consuming extra bandwidth.

[0045] For example, for nodes A, B, C, and D, as shown in Figure 10, if no failure occurs, there are two paths for all flows heading to other nodes: clockwise and counterclockwise. However, as shown in Figure 11, if a failure occurs in section C and D, it becomes necessary to bypass section C and D, leaving one of either a clockwise or counterclockwise path for each flow.

[0046] As an example of a GCL12R that corresponds to a clockwise communication pattern, let's assume that one like the one shown in Figure 12 has been created. In this example, time slots for clockwise paths are set for all flows from Node A, Node B, Node C, and Node D to other nodes. These time slots are set with time staggered in the order of transit for Node A's clockwise communication port 1, Node B's clockwise communication port 2, Node C's clockwise communication port 3, and Node D's clockwise communication port 4. For example, after the time slot for the flow from Node A to Node D, a time slot for the flow from Node A to Node B is set after a gap. After that, a time slot for the flow from Node C to Node B is set after a relatively long gap. After that, a time slot for the flow from Node A to Node C is set after a relatively short gap. After that, the remaining time slots are set, such as the time slots for the flow from Node D to Node B, and the time slots for the flow from Node D to Node C.

[0047] When a failure occurs in the CD section, from GCL12R, as GCL13R corresponding to the right-turn communication pattern and corresponding to the failure, something like that shown in FIG. 13 is created. In this example, among all the flows from nodes A, B, C, and D to other nodes, for only the flows that can communicate by bypassing the CD section even in the right turn, time slots for the right-turn path are set. For example, the time slot for the flow from node A to node D is released and can be used for the NST flow. The time slot for the flow from node C to node B is also released and can be used for the NST flow. In addition, several other time slots are released.

[0048] When a failure occurs in the BC section, from GCL12R, as GCL13R corresponding to the right-turn communication pattern and corresponding to the failure, something like that shown in FIG. 14 is created. In this example, among all the flows from nodes A, B, C, and D to other nodes, for only the flows that can communicate by bypassing the BC section even in the right turn, time slots for the right-turn path are set. For example, the time slot for the flow from node A to node C is released and can be used for the NST flow. The time slot for the flow from node D to node C is also released and can be used for the NST flow. In addition, several other time slots are released.

[0049] According to this embodiment, the calculation cost of creating GCL for each failure point in the ring network can be reduced to the cost of creating two types of GCL. For example, in the combination of four ring networks each composed of 15 nodes, 2 ４ = 16 pre-calculations of GCL are required, but it is realistically quite possible to store 16 GCL for each port. Therefore, delay guarantee can be achieved except for the jitter generated during switching. That is, according to this embodiment, the recovery of delay-guaranteed communication when a failure occurs in the ring-shaped communication network 11 can be accelerated.

[0050] This disclosure is not limited to the embodiments described above. For example, two or more blocks shown in the block diagram may be combined, or one block may be divided. Instead of executing two or more steps shown in the flowchart in chronological order as described, they may be executed in parallel or in a different order, depending on the processing capacity of the device performing each step, or as necessary. Other modifications are possible without departing from the spirit of this disclosure.

[0051] 10 Communication system 11 Communication network 12, 12R, 12L, 13, 13R, 13L GCL 20 Control device 21 Control unit 22 Storage unit 23 Communication unit 24 All pattern GCL creation function 25 GCL distribution function 26 Fault information reception function 27 Fault GCL creation function 30 Transfer device 31 GCL receiving function 32 GCL execution function 33 Fault information transmission function

Claims

1. A control device for setting multiple time slots for each port of multiple transfer devices that form a ring-shaped communication network capable of bidirectional communication, comprising: a communication unit that communicates with the multiple transfer devices; a storage unit that stores gate control lists defining the multiple time slots and flows with a fixed transmission period that pass through the corresponding ports in each time slot, for both clockwise and counterclockwise communication patterns; and a control unit that, upon detecting a fault occurring in a section included in the communication network, creates a gate control list corresponding to the fault from the gate control list corresponding to the clockwise communication pattern and the gate control list corresponding to the counterclockwise communication pattern stored in the storage unit, and transmits the created gate control list to the transfer device having the corresponding port via the communication unit.

2. The control device according to claim 1, wherein the control unit creates a gate control list corresponding to the fault by changing each of the gate control list corresponding to the clockwise communication pattern and the gate control list corresponding to the counterclockwise communication pattern to a gate control list in which a time slot that allows a flow passing through the section in which the fault occurred is opened among the plurality of time slots.

3. A communication system comprising a control device according to claim 1 or claim 2, and a plurality of transfer devices, wherein when a fault occurs, the plurality of transfer devices transmit fault information indicating the section in which the fault occurred to the control device, and the control unit of the control device detects the fault by receiving the fault information via the communication unit.

4. A control method comprising: a control device that sets multiple time slots for each port of multiple transfer devices that form a ring-shaped communication network capable of bidirectional communication, creating gate control lists for both clockwise and counterclockwise communication patterns that define the multiple time slots and flows with a fixed transmission period that pass through the corresponding port in each time slot; when the control device detects a fault occurring in a section included in the communication network, creating a gate control list corresponding to the fault from the gate control list corresponding to the clockwise communication pattern and the gate control list corresponding to the counterclockwise communication pattern, respectively; and transmitting the gate control list corresponding to the fault to a transfer device having the corresponding port.

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