TWI573421B - Relay devices and communication systems - Google Patents

Description

Relay device and communication system

The present invention relates to a relay device and a communication system for detecting a loop in a communication system.

In recent years, the progress of Ethernet (registered trademark) has been seen in the industrial field, and in the manufacturing field, a PLC (Programmable Logic Controller) has been constructed. Industrial network of the communication network of FA (Factory Automation) machines such as inverters and sensors. In the industrial network, in order to improve the processing accuracy, it is extremely important that the time is synchronized by a plurality of FA machines, and the operations are performed in coordination. As means for realizing time synchronization, a master device (Master) belonging to a communication device that outputs an output command is used to transmit its own time information to a slave device (Slave) belonging to a communication device to be controlled, and in the slave device A method in which the received time information is passed through a value corrected by the transfer delay time of the own device, and is updated as its own time information. In the above-described time synchronization method, when the transfer delay time between the master device and the slave device changes with the topology of the network, that is, the change of the connection mode, the time synchronization accuracy between the FA machines is improved. There will be an impact.

On the other hand, connecting multiple FA machines to the second layer of switching In an industrial network constructed by a relay device such as (Layer 2 Switch), a communication path may be erroneously connected due to a human misplaced (Mistake) or the like to form a loop path. When the storm is generated along with the formation of the loop path, it will cause obstacles to the use of the industrial network. The so-called storm refers to the transmission and copy processing of a broadcast frame or a multicast frame, which is repeated indefinitely on the loop path and is pressed to the frequency band of the network.

In order to avoid the above-mentioned storm, it is only necessary to close the port on the loop path by detecting the loop path by the relay device. As a conventional loop detection method, there is known a blocking of a port by STP (Spanning Tree Protocol) disclosed in Non-Patent Document 1. In the STP, the communication path is selected based on the path cost determined from the link speed or the priority order setting of the relay device, and the loop path is released by closing the port on the redundant path.

Further, Patent Document 1 discloses that a test frame (Frame) in which a MAC (Media Access Control) address of a device is stored is transmitted to a transmission destination MAC address by a communication device. And transmitting the source MAC address, and receiving the test frame transmitted by the own device to detect the loop technology. In addition, Patent Document 2 discloses a number of times of update of a receiving port with respect to a MAC address in a transfer table (Table) in which a transmission source MAC address of a received frame is associated with information of a receiving port. The technique of detecting the loop when it is above the set threshold.

[Previous Technical Literature] [Patent Literature]

Patent Document 1: Japanese Laid-Open Patent Publication No. 2012-44384

Patent Document 2: Japanese Patent No. 4879279

[Non-patent literature]

Non-Patent Document 1: IEEE Std 802. ID-2004, "IEEE Standard for Local and Metropolitan Area Networks: Media Access Control (MAC) Bridges" IEEE, 2004, pp. 57-65

In the STP disclosed in Non-Patent Document 1, since the path cost is always the smallest path since the communication path is not fixed, the topology dynamically changes when the new path is connected. When STP is used in an industrial network, the transfer delay time between the master device and the slave device due to the above-described topology change has an influence on the accuracy of the time synchronization and becomes a problem.

On the other hand, in the techniques described in Patent Document 1 and Patent Document 2, although the loop path can be detected, since the communication device does not automatically cancel the loop path, it is necessary to be cut by the network administrator. The problem of the communication path on the loop path.

The present invention has been made in view of the above problems, and an object thereof is to obtain a relay device capable of autonomously releasing a loop path without changing a connection form.

In order to solve the above problems, the relay device of the present invention includes: a plurality of ports; and a loop detecting unit that manages the superiority of each port. Firstly, a loop detection frame having an area for storing port information for displaying the port for transmission and storing priority information for displaying the priority is generated and outputted when receiving the transmission from the device other than the device itself. When loop detection frame, when the priority order of the port is lower than the priority order of the received priority information of the received loop detection frame, the received loop detection frame is updated with the priority order of the port. Priority information, and output a loop detection frame in which the priority information has been updated, and in the case of receiving the loop detection frame transmitted from the own device, according to the stored back from the device The priority information of the circle detection frame and the priority order of each port control whether the port is to be closed. Further, the relay device includes an output control unit that sends a loop detection frame output from the loop detecting unit to the port.

The relay device of the present invention can achieve the effect of autonomously releasing the loop path without changing the connection form.

1, 1-1 to 1-N, 4‧‧‧ relay devices

2‧‧‧Master station installation

3‧‧‧Substation installation

Port 10-1 to 10-N‧‧‧

11‧‧‧FDB Form Memory

12-1 to 12-N‧‧‧ Frame Receiver

13‧‧‧Multi-industry

14‧‧‧Output Control Department

15‧‧‧Circle Detection Department

21‧‧‧Link Monitoring Department

22‧‧‧ Frame Identification Department

23‧‧‧Circle detection frame generation unit

24‧‧‧Transfer Frame Generation Department

25‧‧‧Multi-work

26‧‧‧State Control Department

27‧‧‧Circle Management Form Memory

28‧‧‧Port State Management State Machine

40-1, 40-2, 40-3‧‧‧ ports

100‧‧‧Control circuit

101‧‧‧ Input Department

102‧‧‧Processor

103‧‧‧ memory

104‧‧‧Output Department

200‧‧‧Communication control circuit

300 to 303‧‧ path

400‧‧‧New link

500‧‧‧Communication system

Fig. 1 is a view showing a configuration example of a relay device according to the first embodiment.

Fig. 2 is a view showing a configuration example of a loop detecting unit in the first embodiment.

Fig. 3 is a view showing an example of a hardware configuration of the relay device of the first embodiment.

Fig. 4 is a view showing a configuration example of a control circuit of the first embodiment.

Fig. 5 is a view showing an example of the configuration of an FDB table stored in the FDB (Forwarding Database) table memory unit in the first embodiment.

Fig. 6 is a view showing an example of the configuration of a loop detection frame in the first embodiment.

Fig. 7 is a view showing the definition of the port state in the first embodiment.

Fig. 8 is a view showing a configuration example of a loop management table in the first embodiment.

Fig. 9 is a flowchart (Flowchart) showing an example of the processing procedure when the loop detection frame in the loop detecting unit of the first embodiment is received.

Fig. 10 is a flow chart showing an example of a loop detection frame transmission and a port closing processing procedure in the loop detecting unit of the first embodiment.

Fig. 11 is a view showing a configuration example of a communication system according to the first embodiment.

Fig. 12 is a view showing an example in which the loop path is avoided by the closing process of the first embodiment.

Fig. 13 is a view showing a configuration example of a communication system of the second embodiment.

Fig. 14 is a flow chart showing an example of the processing procedure in the case where the loop detection frame in the loop detecting unit of the second embodiment is received.

Fig. 15 is a view showing an example of the configuration of a loop management table in the second embodiment.

Fig. 16 is a flow chart showing an example of a loop detection frame transmission and a port closing processing procedure in the loop detecting unit of the second embodiment.

Fig. 17 is a flow chart showing an example of the procedure of the port closure release processing in the third embodiment.

Hereinafter, embodiments of the relay device and communication system of the present invention will be described in detail based on the drawings. Further, the present invention is not limited to the embodiment.

Embodiment 1

Fig. 1 is a view showing a configuration example of the relay device 1 according to the first embodiment of the present invention. The relay device 1 includes a port as a transmission port and as a reception port 10-1 to 10-N. Further, N is an integer of 2 or more. The FDB table storage unit 11 of the relay device 1 is configured to store an FDB (Forwarding Database) table registered in association with the transmission source address of the received frame and the information of the receiving port. The frame receiving units 12-1 to 12-N are connected to corresponding ones of the ports 10-1 to 10-N, and are determined to be sent from the frame received via the connected port according to the transfer destination address. The transmission port of the frame. The multiplexer 13 multiplexes the frames input from the frame receiving units 12-1 to 12-N. The output control unit 14 allocates a frame and transmits a frame according to each transmission destination of the received frame. The loop detecting unit 15 manages the priority order of each port 10-1 to 10-N, and periodically generates port information and display with ports 10-1 to 10-N for storing and displaying the transmission to update the loop. The loop detection frame of the priority order information of the lowest priority port information on the path is outputted, and when receiving the loop detection frame transmitted from the device, the frame is transmitted and received in the frame. When the priority order of the port is lower than the priority order displayed by the priority information of the received loop detection frame, the priority order information of the received loop detection frame is updated with its own priority order, and the output is output. The updated loop detection frame, and in the case of receiving the loop detection frame transmitted from the own device, according to the priority order information stored in the loop detection frame and the priority order of the transmission and reception port of the frame To control whether you want to close the port. In addition, in the first figure, although the port on the receiving side is separated from the port on the receiving side, actually the port 10-i (i=1, ̇ ̇ ̇, N) on the left side of the first figure and the right side are shown. Port 10-i is the same port.

FIG. 2 is a view showing a configuration example of the loop detecting unit 15. The loop detecting unit 15 includes a link monitoring unit 21 for detecting a link establishment and when When it is detected that the connection is established, the output display link is established as a meaningful link detection signal; the frame recognition unit 22 identifies the frame according to the address of the transmission source of the loop detection frame; and the loop detection belonging to the frame generation unit The frame generation unit 23 generates a loop detection frame transmitted from the port in which the connection is established, by causing the connection detection signal to change meaningfully. Further, the loop detecting unit 15 includes a transfer frame generating unit 24 belonging to the transfer unit, and compares the priority order information described later in the loop detecting frame with the priority order of the port of the own device, and is at the port of the own device. In the case where the priority order is lower, the transfer frame belonging to the frame in which the priority order information of the received frame has been updated is output; and the multiplex unit 25 outputs the frame from the transfer frame generating unit 24. The transfer frame and the loop detection frame generated by the loop detection frame generating unit 23 are multiplexed. In addition, the loop detecting unit 15 includes a state control unit 26 that compares the priority order information stored in the received loop detection frame with the priority order of the port of the own device to determine whether the device is the lowest on the loop path. a priority relay device; a loop management table storage unit 27 for storing a loop management table belonging to the loop management information to be described later; and a port state management state machine 28 belonging to the management unit, per port The port status is managed and the priority order corresponding to the port status is managed, thereby managing the priority order of each port.

Fig. 3 is a view showing an example of the hardware configuration of the relay device 1 of the embodiment. As shown in FIG. 3, the relay device 1 is constituted by, for example, ports 10-1 to 10-N belonging to a transmission receiving port and a communication control circuit 200. Ports 10-1 to 10-N are ports 10-1 to 10-N in Fig. 1. Further, in the communication control circuit 200, the FDB table storage unit 11, the frame receiving units 12-1 to 12-N, the multiplex unit 13, the output control unit 14, and the loop shown in Fig. 1 are mounted. Detection unit 15. Each of the components may be mounted as one electronic circuit in the communication control circuit 200, or may be configured as a single electronic circuit in a plurality of constituent elements in the first embodiment.

Further, one or more of the constituent elements shown in FIGS. 1 and 2 may be attached by software. When a component mounted by a software is provided, the component is realized by, for example, a control circuit shown in FIG. Fig. 4 is a view showing a configuration example of the control circuit 100. As shown in FIG. 4, the control circuit 100 includes an input unit 101 belonging to the receiving unit, and receives data (Data) input from the outside of the control circuit 100; a processor 102; a memory 103; And the output unit 104 belonging to the transfer unit transfers the data to the outside. The input unit 101 is an interface circuit that receives data input from the outside of the control circuit 100 and is supplied to the processor 102, and the output unit 104 transmits data from the processor 102 or the memory 103 to the control circuit. Interface circuit of 100 external. When the components shown in FIG. 1 or FIG. 2 are realized by the control circuit 100 shown in FIG. 4, the processor 102 reads a program corresponding to each of the memories 103 and executes it. achieve. Further, the memory 103 is also used as a temporary memory when the processor 102 executes each process.

Next, the operation of the relay device 1 of the present embodiment will be described. Fig. 5 is a view showing an example of the configuration of an FDB table stored in the FDB table storage unit 11. As shown in Figure 5, in the FDB table, the address for storing the address and the port number corresponding to the address are used. The port number indicates the number of the ports 10-1 to 10-N, and in Fig. 5, the port number of the port 10-i is described as the port #i. i is an integer of 1 or more. In addition, the address in this embodiment refers to display transmission. The identification information of the source and the destination device is, for example, a MAC address.

The frame receiving units 12-1 to 12-N extract the address of the transmission source of the received frame when receiving the frame via the connected ports 10-1 to 10-N, and refer to the FDB table for retrieval. Whether there is an address that is consistent with the extracted address, and in the case where there is no address in the FDB table that matches the extracted address, the frame receiving units 12-1 to 12-N will extract the extracted address. The port number of the port that received the frame corresponding to the address is added to the FDB table as the login information (Entry). In this way, the relay device 1 learns the correspondence between the address and the port, and stores the learned result in the FDB table.

In addition, the frame receiving units 12-1 to 12-N extract the address of the transmission destination of the received frame, and refer to the FDB table to retrieve whether there is an address in the FDB table that is consistent with the extracted address. The address, in the case where there is an address that coincides with the extracted address, determines the port number corresponding to the address as the port number of the transfer destination. Further, in the case where the FDB table stored in the FDB table storage unit 11 does not have an address matching the address of the extracted transfer destination, the frame receiving sections 12-1 to 12-N are to receive and receive The port number corresponding to all ports except the port of the frame determines the port number to be the destination.

Further, the frame receiving sections 12-1 to 12-N are meaningless, that is, not displayed, by the port closing instruction input from the loop detecting section 15 at the transmission destination port of the receiving frame or the receiving port corresponding to itself. When the loop detecting unit 15 instructs the port to be closed, the port information of the port number of the transfer destination determined by the above display is added to the received frame and transferred to the multiplexer 13. The frame receiving sections 12-1 to 12-N are at the transmission destination port of the receiving frame. Alternatively, the port closing instruction input from the loop detecting unit 15 corresponding to its own receiving port is meaningful, that is, when the loop detecting unit 15 instructs the port to be closed, the receiving frame is abolished. By performing this action, the transmission and reception of the frame relative to the closed port on the loop path can be avoided, and the storm can be avoided.

The multiplexer 13 multiplexes the main signal frame of the frame other than the loop detection frame in the frame of the number of ports input by the frame receiving units 12-1 to 12-N, The multiplexed frame is transferred to the output control unit 14 along with the port information indicating the port number of the transfer destination. Further, the multiplex processing unit 13 transfers the loop detection frame input from the frame receiving units 12-1 to 12-N together with the port information indicating the port number received and the port number of the transmission destination. To the loop detecting unit 15.

The output control unit 14 allocates the main signal frame input from the multiplexing unit 13 and the loop detection frame input from the loop detecting unit 15 according to the port information to each port of the transmission destination, and transmits the signal. The box is output to the ports 10-1 to 10-N of the transfer destination.

In the loop detecting unit 15, the connection monitoring unit 21 shown in FIG. 2 detects whether or not a connection is established for each port, and outputs a meaningful connection detection signal to the loop detection frame at the time of connection establishment. The generating unit 23 and the state control unit 26. Further, although any method can be used for the connection establishment method, for example, the connection monitoring unit 21 monitors the frame to be received, and receives a frame created by the connection of the protocol, thereby detecting the link. The establishment of.

The loop detection frame generating unit 23 changes the value of the connection detection signal to display a meaningful value, and generates a transmission from the port where the connection is established. Loop detection frame. The loop detection frame generating unit 23 outputs the generated loop detection frame together with the port number indicating the transmission destination, that is, the port information indicating the port number of the port on which the connection is established, to the output control. Part 14. Further, the loop detection frame generating unit 23 periodically generates a loop detection frame for periodically checking whether or not there is a loop path after the connection is established for each port.

Fig. 6 is a view showing a configuration example of a loop detection frame. As shown in FIG. 6, the loop detection frame includes: a transmission destination address; a transmission source address; a transmission port information indicating information of a port transmitting the loop detection frame; and a display loop path The priority order information of the priority order of the lowest priority port within the port. In the relay device that transmits the source of the loop detection frame, particularly meaningful information is transmitted without being inserted in the area of the priority order information. Furthermore, the relay device that first receives the loop detection frame stores the priority order of the lower priority port of the receiving port or the transmitting port in the area of the priority order information and transfers the same. Alternatively, the relay device of the transmission source of the loop detection frame may also store the priority order of its own transmission port as the priority order information and transmit it. Further, the configuration example shown in Fig. 6 is an example, and the order of each information is not limited to the example of Fig. 6. Although an arbitrary value can be set in the transfer destination address of the loop detection frame, in the case where the loop path is generated, it is necessary to have a transfer destination address returning to the own device. For example, a multicast address or a broadcast address is used as a transfer destination address of the loop detection frame. Furthermore, when the relay device receives the frame with the multicast address or the broadcast address as the transmission destination, the frame transmits the frame to all ports except the port that received the frame. Therefore, when a loop path is formed, the loop detection signal transmitted by the relay device The box returns to its own device. As described above, in the present embodiment, an area in which the transmission port information and the loop detection frame store the priority order information of the port of the lowest priority order in the loop path is set. The information stored in the transmission port information is information that can be identified by the relay device having the corresponding port. For example, the number unique to the port may be assigned to each port of each relay device, and the number may be used, or the combination of the information of the relay device and the number of the port in the relay device may be used.

The frame identification unit 22 confirms the transmission source address of the received loop detection frame, and if the transmission source address is outside the address of the own device, the received loop detection frame is followed by The information indicating the port receiving the loop detection frame is transferred to the transfer frame generating unit 24, and the received loop detection frame is forwarded in the case where the transmission source address is the address of the own device. To the state control unit 26.

The port state management state machine 28 manages the port state for each port. In the present embodiment, since the ports closed on the loop to be looped are selected, three kinds of port states are defined. The port state management state machine 28 notifies the source of the priority of the corresponding port state when the state control unit 26 and the transfer frame generating unit 24 inquire about the priority order. Fig. 7 is a view showing the definition of the port state in the present embodiment. As shown in Fig. 7, in the present embodiment, the operation belonging to the first state, the main signal filter belonging to the second state, and the three states belonging to the closed state of the third state are defined as ports. Furthermore, the correspondence between these states and the priority order is managed in the order of priority > high signal in the order of operation > main signal filter > closed. In Figure 7, the port status, priority order, main signal transfer, and loop detection frame are displayed. 4 examples. The port status in Fig. 7 shows the three states of the operation, the main signal filter, and the closed operation, and the priority order system displays the priority order corresponding to each state. In addition, the smaller the priority display value is, the higher the priority is. The main signal transmission in Figure 7 shows whether the main signal frame is to be forwarded, Yes indicates that the main signal frame is forwarded, and No indicates that the main signal frame is not forwarded. In the loop detection frame of Figure 7, it is displayed whether the loop detection frame is to be forwarded and whether the loop detection frame is to be transmitted. Yes indicates that the loop detection frame is transferred or transmitted, and the No system display is not transferred or transmitted back. Circle detection frame. In addition, the merits of the ports having the same port state in the relay device are determined by the size of the port number. For example, if the lower number is used as the priority, if the port status of both port 1 and port 2 is used, it is determined that the priority order of port 1 is higher. On the other hand, the merits of the ports having the same port state between the two relay devices are judged by the value inherent to the device such as the MAC address. Along with the above situation, it is possible to determine the merits of the ports in the network, that is, the priority of the ports.

In the present embodiment, the priority of the port is used to select the port to be closed, thereby avoiding the change of topology. The port state management state machine 28 uses the state of the port as the main signal filter when detecting a new connection establishment based on the connection detection signal input from the state control unit 26. In the port where the port status is the main signal filter, the transfer of the main signal frame is not performed, and the transmission and transfer of the loop detection frame are implemented. In this way, in the case of establishing a new link, it is possible to confirm whether there is a loop path before forwarding the main signal frame. Thereafter, the port state management state machine 28 switches the port state to operation when the state control unit 26 is not notified of the detection of the loop path for a predetermined period of time or more after the connection establishment is detected. In addition, the state control unit 26 is identified by the frame. When the unit 22 inputs the frame and detects the loop path, the information indicating that the loop path has been detected is notified to the port state management state machine 28. The state control unit 26 does not receive the loop detection frame transmitted by the own device over the port 10-i for a certain period of time, or does not receive the transmission from the port 10-i after a certain period of time by the own device. In the case of the circle detection frame, it is determined that the loop path is not detected at the port 10-i, and the content is notified to the port state management state machine 28. Further, the port state management state machine 28 switches the port state to closed when the state control unit 26 notifies that it is closed. Further, the port state management state machine 28 outputs a display portless indication indicating that the port is not closed, for the frame receiving sections 12-1 to 12-N connected to the port whose port state is the port of operation. In addition, the port state management state machine 28 notifies the frame receiving units 12-1 to 12-N of the port status of all the ports, and controls whether the port status is the main signal filter or the closed port does not transmit the main signal. frame.

When receiving the connection detection signal from the connection monitoring unit 21, the state control unit 26 transfers the connection detection signal to the port state management state machine 28. Further, the state control unit 26 stores information corresponding to the transmission port belonging to the port transmitting the loop detection frame and the reception port belonging to the port receiving the loop detection frame as a loop management table. The loop manages the table storage unit 27. Fig. 8 is a view showing a configuration example of a loop management table of the embodiment. As shown in FIG. 8, in the loop management table, according to each transmission port of the transmission loop detection frame, information of the receiving port that has received the frame transmitted from the transmission port is displayed as receiving. Port bitmap (Bitmap) storage. In the receive port bit map, the 0 system shows that it has not been received, and the 1 system shows that it has been received. Therefore, when there is 1 stored, the display is generated in the path corresponding to the combination of 1. Loop path. For example, in the example of Fig. 8, the transmission port is 1, and the combination of the reception port 2 is 1. This shows that the loop detection frame transmitted from port 10-1 has been received at port 10-2. That is, the login information of 1 in the receiving port bit map shown in FIG. 8 is a log information having a loop path, that is, a loop path is generated.

Further, in the loop management table, information indicating whether or not the own device is the lowest priority relay device is stored in the loop path. When the loop detection frame is input from the frame recognition unit 22, the state control unit 26 determines that the loop detection frame transmitted from the own device is received by the own device, and thus determines that the loop detection path has a loop path, that is, a loop is generated. Loop path, and update the loop management table according to the input loop detection frame. Specifically, the corresponding login in the receiving port bit image of the loop management table is updated according to the information of the transmission port stored in the received loop detection frame and the information of the port receiving the loop detection frame. News. Further, in addition to the above, the state control unit 26 inquires of the port state management state machine 28 about the priority order of the transmission/reception port of the received loop detection frame, and obtains the priority order of the port, and based on the obtained priority order, And the priority order information stored in the received loop detection frame, and determining whether the own device is the lowest priority relay device in the loop path, and updating the lowest priority in the loop management table according to the judgment result Follow the device information. Specifically, the state control unit 26 is the port that is acquired from the port state management state machine 28, that is, the priority order of the port that transmits the loop detection frame is stored in the priority position of the received loop detection frame. In the case where the priority displayed by the information is lower, it is determined that the device is the lowest priority in the loop path, that is, the device with low priority. In addition, the state control unit 26 will transmit the office The port of the received loop detection frame and the received port are associated with the information indicating whether the own device is the lowest priority device in the loop path, and are stored in the loop management table.

Further, the state control unit 26 reads the transmission timing of the loop detection frame periodically transmitted by the own device, and reads the login information of the port corresponding to the transmission loop detection frame in the loop management table, and clears ( Clear) This login information for the loop management form. The state control unit 26 determines, based on the read login information, that the own device is the lowest priority device in the loop path, and determines that the highest priority among the ports of the device that constitutes the loop path is closed. The port status management state machine 28 is indicated by a port closure, in addition to the port that displays the port to be closed. The port state management state machine 28 changes the state of the corresponding port to closed based on the instruction. Further, the state control unit 26 and the frame recognition unit 22 of the loop detecting unit 15 are configured to grasp the transfer timing of the loop detection frame for each port. For example, the state control unit 26 may be configured to notify the loop detection frame generation unit 23 and the frame recognition unit 22 of the transmission timing of the loop detection frame of each port, or may be detected by the loop detection frame. The generating unit 23 manages the transmission timing of the loop detection frame for each port, and notifies the state control unit 26 and the frame recognition unit 22. The state control unit 26 does not receive the transmitted loop detection frame during the period of transmitting the next loop detection frame after transmitting the loop detection frame from the port for each port. It is determined that the loop path is not detected.

When receiving the loop detection frame input, the transfer frame generating unit 24 queries the port state management state machine 28 for the port state of the own device to obtain the port state, and compares the own device according to each of the transmission and reception ports of the frame. The port status and the priority information stored in the input loop detection frame. Furthermore, the transfer frame generating unit 24 updates the priority order information of the input frame to the display device according to each of the transmission and reception ports of the frame, when the priority of the port of the device is low. The information of the port, and the frame after the priority order information is updated, is output to the multiplex unit 25 along with the information indicating the port of the transfer destination.

The multiplex unit 25 multiplexes the transfer frame output from the transfer frame generating unit 24 and the loop detection frame generated by the loop detection frame generating unit 23, and multiplexes the multiplexed frame. The frame is output to the output control unit 14 along with the information indicating the port of the transfer destination. In addition, the multiplex means that a plurality of frames are collected in one path.

Fig. 9 is a flowchart showing an example of a processing procedure when receiving a loop detection frame in the loop detecting unit 15. Fig. 10 is a flow chart showing an example of the loop detection frame transmission and port closing processing procedure in the loop detecting unit 15. The loop detecting unit 15 periodically transmits a loop detecting frame based on each port in which the link establishment is detected. After the loop detection frame is transmitted, the loop detecting unit 15 performs the processing shown in FIG. The frame recognition unit 22 determines whether or not the loop detection frame is input from the multiplex unit 13, that is, whether or not the loop detection frame has been received (step S1). When the loop detection frame is not received (step S1, No), the frame recognition unit 22 determines whether or not it is the transmission timing of the next loop detection frame (step S2). When it is not the transmission timing of the next loop detection frame (step S2, No), the process returns to step S1. If it is the transmission timing of the next loop detection frame (step S2, Yes), the processing ends.

When receiving the loop detection frame (step S1, Yes), the frame is recognized. The part 22 determines whether the transmission source address in the received loop detection frame is equal to the address of the own device, that is, the own address (step S3). In addition, in FIG. 9, the transmission source address is simply referred to as SA (Source Address). When the transmission source address in the received loop detection frame is equal to the address of the own device, that is, the own device (step S3, Yes), the state control unit 26 updates the loop management table (step S4). Specifically, the loop detection frame is input from the frame recognition unit 22 to the state control unit 26, and the state control unit 26 updates the loop detection signal in the above manner based on the input loop detection frame as described above. frame.

Thereafter, the state control unit 26 determines whether or not it is the transmission timing of the next loop detection frame (step S8). When it is not the transmission timing of the next loop detection frame (No in step S8), the process returns to step S1, and when the transmission timing of the next loop detection frame is (step S8, Yes), the processing ends.

On the other hand, in step S3, when the transmission source address in the received loop detection frame is not equal to the address of the own device, that is, the own address (step S3, No), the transfer frame generating unit 24 It is determined whether the priority port of the port that transmits the loop detection frame is lower than the priority order information stored in the loop detection frame (step S5). Further, as described above, in the present embodiment, since the smaller the priority is, the smaller the value is used as the priority value. Therefore, the smaller the value of the display storage as the priority order, the higher the priority. When the priority order of the own port is lower than the priority order information stored in the loop detection frame (step S5, Yes), the priority order information of the received loop detection frame is updated to display the priority of the port of the own device. The information is in the order (step S6), and proceeds to step S7.

When the priority order of the own port is lower than the priority order information stored in the loop detection frame (step S5, No), the transfer frame generating unit 24 passes the received loop detection frame via the multiplex unit 25 and outputs The control unit 14 performs transfer (step S7), and proceeds to step S8.

Next, the transmission and port closing processing of the loop detection frame will be described using FIG. The loop detecting unit 15 performs the processing of Fig. 10 in accordance with each port to which the connection has been established. The state control unit 26 determines whether or not it is the transfer timing of the loop detection frame (step S11). When it is not the transfer timing of the loop detection frame (step S11, No), the process returns to step S11.

When the transmission timing of the frame is detected (step S11, Yes), the state control unit 26 reads the login information of the transmission port from the loop management table, that is, the login information corresponding to the port transmitting the loop detection frame. And clearing the login information in the loop management table (step S12). Next, the state control unit 26 determines whether or not the transmission port, that is, the port transmitting the loop detection frame is the lowest priority port of the loop path (step S13). Specifically, the state control unit 26 refers to the login information read in step S12, and the state displayed on the receiving port bit map portion, that is, the state in which the own device receives the frame transmitted from the own device. If the field of the lowest priority relay device of the login information is the value of the lowest priority relay device in the loop path, it is determined that the transmission port is the lowest priority port.

When the transmission port is the lowest priority port (Yes in step S13), the loop detecting unit 15 refers to the receiving port bit map read from the loop management table, and in the port of the own device in the loop path. The port other than the highest priority port is closed (step S14). Specifically, the state control unit 26 is Referring to the receiving port bit map read from the loop detection frame, it is determined that the port other than the highest priority port among the ports of the own device in the loop path is closed, and the content is notified to the port status. Management state machine 28. In addition, the highest priority port refers to the port with the highest priority in the determination of the priority order of the above port. In addition, even if the relay device is the lowest priority in the loop path, when the loop path is generated, there are two paths of right turn and left turn, and which one is used. The possibility of the path above. Therefore, in order to not close the port corresponding to the path used for the operation, it is determined that the port immediately after the connection is established as the main signal filter, and the port is not the highest in step S14. The port of the priority port. The port state management state machine 28 updates the managed port state based on the notification from the state control unit 26, and notifies the frame receiving sections 12-1 to 12-N of the port states of all the ports.

Further, the loop detecting unit 15 transmits a loop detecting frame via the output control unit 14 (step S15), and ends the processing. Further, in step S13, when the transfer port is not the lowest priority port (step S13, No), the process proceeds to step S15. The portion shown in A of Fig. 10 becomes a closed process of the closed port.

Further, in the present embodiment, the priority order is determined based on the port state, but the priority order may be changed by the size of the address of each relay device. For example, a weighting according to the priority of the port state is multiplied by the weight according to the address as a priority order. In addition, it is also possible to change the priority order for each port in the same relay device. For example, it is also possible to use a priority number that is determined by the port status to be multiplied by the port number in the own device as a priority order.

Next, an example in which the relay device of the embodiment is applied to a communication system will be described. Fig. 11 is a view showing a configuration example of a communication system of the embodiment. As shown in Fig. 11, the communication system of the present embodiment includes: a master station device 2 that is a master device for time synchronization; and relay devices 1-1 to 1-5 of the relay device 1 of the present embodiment; And the substation device 3 belonging to the slave device that is synchronized at the time. The master station device 2 is connected to the relay device 1-1, the relay device 1-1 is connected to the master station device 2 and the relay device 1-2, and the relay device 1-2 is connected to the relay device 1-1. Relay device 1-3 and relay device 1-5, relay device 1-3 is connected to relay device 1-2 and relay device 1-4, and relay device 1-4 is connected to substation device 3. The relay device 1-4 and the relay device 1-5 are not connected first, and communication using the path 300 and communication using the path 301 are performed, and there is no loop path. It is assumed that in this state, the relay device 1-4 and the relay device 1-5 are connected to establish a new link 400.

Before the loop path is formed, the master station device 2 and the slave station device 3 communicate on the path 300 via the relay devices 1-1 to 1-4, and the time synchronization is also performed on this path. When the loop path is generated by the addition of the new link 400, the relay device 1-4 of the present embodiment detects the connection establishment, and the port state of the port 10-2 of the relay device 1-4 becomes the main signal filter. Device.

Fig. 12 is a view showing an example in which the loop path is avoided by the closing process of the embodiment. Since the port status of the port connected to the new connection 400 of the relay device 1-4 and the relay device 1-5 is the main signal filter, the priority order is lower than the path in the application, and the loop detection signal is detected by the loop. The transmission and reception processing of the frame closes the relay device 1-4 and the port on the lower side of the priority of the relay device 1-5. Therefore, the path after the port is closed becomes the path 302, and becomes the same as The state of Fig. 11, that is, the same path as before the loop path is formed. On the other hand, in the case where the loop avoidance path is assumed by STP, when the path cost of the path 303 is smaller than the path 302, the path after the loop is avoided becomes the path 303. In the path 303, the transfer delay time varies with the topology change between the primary station device 2 and the secondary station device 3, and affects the time synchronization accuracy. On the other hand, in the present embodiment, since the priority of the port in the operating state is set to be high and the port with the lower priority is closed, the port used for the operation before the loop path is formed is not closed. Instead, the port that is connected to the new link 400 with the lower priority is closed. Therefore, in the present embodiment, the path after the loop between the primary station device 2 and the substation device 3 is prevented from being the same as the path before the loop path is formed, and between the primary station device 2 and the secondary station device 3 The topology does not change, so it does not affect the timing synchronization accuracy. Further, the manager does not need to perform path switching for canceling the loop path, and the relay device 1 can autonomously cancel the loop path.

As described above, in the present embodiment, when the relay device 1 manages the port state and establishes a connection according to each port, even if the port state is switched to the main signal filter, the loop detection frame is transmitted and received, and the connection is not performed. The status of the transfer of the main signal frame, and after detecting the loop detection frame transmitted from the own device, after receiving the loop detection frame transmitted from the own device for a certain period of time or more, the port state is converted into operation. And the information indicating the port transmitting the loop detection frame to be transmitted from the own device and the priority order determined according to the port status are stored as the priority order information. Furthermore, when receiving a loop detection frame from a relay device other than the own device, when the priority of the port of the own device is low, the priority is updated with the port corresponding to the port of the own device. The priority information of the received frame is forwarded and forwarded. In addition, according to the received loop detection frame, the relay port storing the loop detection frame transmitted from the own device and the relay port and the loop path indicating whether the device is the lowest priority are updated. The loop management form of the information. Further, when the own device is the lowest priority relay device according to the loop management table, the port of the own device is closed. Therefore, the loop path can be released autonomously without changing the connection form.

Embodiment 2

Fig. 13 is a view showing a configuration example of a communication system 500 according to the second embodiment of the present invention. As shown in FIG. 13, the communication system 500 of the present embodiment includes the relay devices 1-1 and 1-2 having the same configuration as the relay device 1 described in the first embodiment; and does not have an embodiment. The relay device 4 of the function of the relay device 1 described in 1. In the present embodiment, the additional relay devices 1-1 and 1-2 are stored in the information of the loop management table storage unit 27 shown in FIG. 2, and the relay device of the present embodiment is added to determine whether or not the relay device is present. The operation of the processing on the loop path, but the operations and configurations other than the above are the same as those in the first embodiment. Points different from the first embodiment will be described below. In addition, since the configuration of the relay devices 1-1 and 1-2 of the present embodiment is the same as that of the first embodiment, the same components as those of the first embodiment will be described. symbol.

In the relay device according to the first embodiment, the loop path is detected by not changing the topology before the path formation, and the port on the loop path is closed, and the loop path is released. However, there are cases where a relay device having such a function is mixed with a relay device not including such a function. E.g, In the case of the configuration shown in Fig. 13, since the relay device 4 cannot detect the loop path autonomously, when the path including the relay device 4 is formed, there is no implementation and implementation in the loop path. In the case of the relay device of the same form 1, the path cannot be detected. In the present embodiment, the path detection processing in such a configuration will be described.

As shown in Fig. 13, the relay device 4 has ports 40-1, 40-2, and 40-3. The port 40-1 of the relay device 4 is connected to the port 10-2 of the relay device 1-2. A loop path is formed between the port 40-2 of the relay device 4 and the port 40-3. In this case, it is necessary to detect the loop by the relay device 1-2 closest to the loop path to close the port 10-2 instead of the relay device 4 having no loop detecting portion 15. Further, in the relay device 1-1 in which the relay device 1-2 exists between the loop path and the loop, even if the loop is detected at the extension destination, it is necessary to control not to be closed to the relay device 1-2. Port 10-1. Hereinafter, the relay devices 1-1, 1-2 and the like having the loop detecting unit 15 are referred to as a relay device having a loop detecting unit, a relay device of the present embodiment, or a relay device capable of updating a priority order. Further, the relay device 4 is referred to as a relay device having no loop detecting portion.

In the present embodiment, when the transmission port of the loop detection frame transmitted by the own device is the same as the reception port, it is determined whether or not the own device is the relay closest to the loop path among the relay devices having the loop detection unit. The device uses the priority information stored in the loop path of the loop detection frame. Since the priority order information in the updateable loop path is only the relay device having the loop detection unit, whether or not there is a loop detection unit in the extension destination can be determined by whether or not there is update of the priority order information. Following the device.

Therefore, the loop detection of the relay devices 1-1 and 1-2 of the present embodiment When receiving the loop detection frame transmitted by the own device, the state control unit 26 of the measuring unit 15 refers to the priority order information of the loop detection frame and determines whether the priority order information has been updated. Further, the loop detecting unit 15 holds the priority order information set when the loop detecting frame transmitted by the own device is transmitted. Alternatively, information other than the priority order of the first embodiment may be stored as priority information, and information indicating whether or not the information has been updated may be stored.

Fig. 14 is a flow chart showing an example of the processing procedure at the time of receiving the loop detection frame in the loop detecting unit 15 of the present embodiment. As shown in Fig. 14, the same as Fig. 9 of the first embodiment except that step S4 is replaced with step S4a. In step S4a, when the loop management table is updated, the state control unit 26 performs the same update as step S4 of the first embodiment, and also updates based on whether or not the priority ranking information of the received loop detection frame is updated. It is displayed whether or not the relay device of the present embodiment can update the information of the relay device of the priority order information. Fig. 15 is a view showing an example of the configuration of a loop management table of the present embodiment. As shown in Fig. 15, in the loop management table of the present embodiment, it is added whether or not the field of the relay device of the present embodiment is displayed, that is, whether or not there is a loop detecting portion on the loop path. Information about the relay device.

Fig. 16 is a flow chart showing an example of a loop detection frame transmission and a port closing processing procedure in the loop detecting unit 15 of the present embodiment. In the loop detecting frame transmission and port closing processing in the loop detecting unit 15 of the present embodiment, the step S12 is replaced with the step S12a, and the steps S21, S22, and S23 are added, and the back of the first embodiment is performed. The loop detection frame transmission and the port closing processing in the circle detecting unit 15 are the same. In step S12a, Similarly, in the first embodiment, the loop detection unit 15 reads the login information of the transmission port and clears the login information in the loop management table, but at this time, as described above, it is also read whether or not the loop is displayed on the loop path. The information of the relay device of this embodiment. After step S12a, in step S21, the state control unit 26 determines whether the transmission port of the loop detection frame is identical to the reception port based on the received port bit map of the read login information (step S21). In addition, in step S21, the transmission port of the loop detection frame is the same as the receiving port, and refers to the port that receives the loop detection frame transmitted from the own device and the port that transmits the loop detection frame. the same. In addition, the transmission port information indicating the port transmitting the loop detection frame is stored in the loop detection frame, and the information can be used to identify the transmitted port.

When the transmission port of the loop detection frame is the same as the reception port (Yes in step S21), the state control unit 26 determines whether or not the relay device 1 of the present embodiment is on the loop path read from the loop management table. The login information is judged (step S22). When the relay device 1 of the present embodiment is provided on the loop path (step S22, Yes), the process proceeds to step S15. When the relay device 1 of the present embodiment is not provided in the loop path (step S22, No), the loop detecting unit 15 closes the transmission port of the loop detection frame (step S23), and proceeds to step S15. In step S23, specifically, the state control unit 26 determines that the transmission port of the loop detection frame is closed, and notifies the port state management state machine 28 of the content thereof. Thereafter, the port state management state machine 28 updates the managed port state based on the notification from the state control unit 26, and closes the display port to a meaningful port close indication to the frame receiving portion 12 corresponding to the port to be closed. -1 to 12-N. Thereby, the port becomes closed.

When the transmission port of the loop detection frame is different from the reception port (step S21, No), the process proceeds to step S13.

In summary, whether or not there is an update of the priority information stored in the loop detection frame determines whether the relay device of the embodiment exists on the loop path, and the present embodiment does not exist on the loop path. The port relay processing according to the priority order information according to the first embodiment is performed when the port of the relay device of the form receives the loop detection frame transmitted from the own device and the port that transmits the loop detection frame. . Therefore, the same effect as in the first embodiment is obtained, and even in the case where the relay device of the present embodiment does not exist in the loop path, the relay that is closest to the loop path in the relay device of the present embodiment can be obtained. The device is closed to the port.

Embodiment 3

Next, the relay device of the third embodiment will be described. The configuration of the relay device 1 of the present embodiment is the same as that of the relay device 1 of the first embodiment. Points different from the first embodiment will be described below. In the first embodiment and the second embodiment, the processing of the closed port has been described. However, it is also conceivable to cancel the loop path after the port is closed. At this time, in a case where the closed port is not received for a certain period of time, the port is closed by switching the port into an operation without receiving the loop detection frame transmitted by the own device, so that the unnecessary port is closed. The status does not occur.

Fig. 17 is a flow chart showing an example of the procedure of the port closing release processing in the embodiment. As shown in Fig. 17, the state control unit 26 of the loop detecting unit 15 determines whether or not the loop detection frame transmitted from the own device has not been received in the closed port for a certain period of time (step S31). After the port is closed, the closed port is not received for loop detection transmitted from its own device for a certain period of time. At the time of the frame (Yes in step S31), the port state of the closed port is changed to the operation (step S32), and the processing ends. After the port is closed, the loop is closed until the loop detection frame transmitted from the own device is received until a certain period of time has elapsed (step S31, No), and the processing is terminated. The operation and configuration of this embodiment other than the above are the same as those of the first embodiment. Further, in the relay device of the second embodiment, the operation of the above-described embodiment described above may be added.

The configuration shown in the above embodiment is an example of the present invention, and may be combined with other known techniques, and a part of the configuration may be omitted or changed without departing from the gist of the present invention.

Port 10-1 to 10-N‧‧‧

11‧‧‧FDB Form Memory

12-1 to 12-N‧‧‧ Frame Receiver

13‧‧‧Multi-industry

14‧‧‧Output Control Department

15‧‧‧Circle Detection Department

Claims (24)

A relay device includes: a plurality of ports; a loop detection unit that manages a priority order of each of the ports, and periodically generates a port order information for storing a port for display transmission and a priority order for storing a display priority The loop detection frame of the information area is outputted. When receiving the loop detection frame transmitted from the device, the priority order of the port is displayed as the priority information of the received loop detection frame. If the priority is lower, the priority information of the received loop detection frame is updated with the priority of the port, and the loop detection frame that has updated the priority information is output, and is received. In the case of the loop detection frame transmitted by the own device, it is controlled whether to close the port according to the priority order information stored in the loop detection frame transmitted from the device and the priority order of each port. And an output control unit that sends the loop detection frame output from the loop detecting unit to the port. According to the relay device of claim 1, wherein the loop detecting unit determines that the loop path has been generated and receives the loop detection frame after receiving the loop detection frame transmitted from the own device. If the priority of the port of the circle detection frame is lower than the priority order of the priority information stored in the received loop detection frame, it is determined that the device is low priority in the loop path. Device, and the received loop detection frame is received to transmit the aforementioned port and received The port and the information indicating whether the own device is associated with the information of the low priority device are stored as the loop management information, and the device is determined to be the low priority device according to the loop management information. Next, the aforementioned port in the aforementioned loop path is closed. According to the relay device of claim 1, wherein the loop detecting unit determines that the loop path has been generated, and receives the loop detecting frame transmitted from the own device, according to the storage. And determining, by the received priority information of the loop detection frame, whether there is a relay device that can update the priority information in the loop path, and receiving a loop detection signal transmitted from the device The port of the frame is the same as the port that transmits the loop detection frame, and in the case that there is no relay device in the loop path that can update the priority information, the aforementioned detection of the loop detection frame is closed. port. The relay device according to claim 2, wherein the loop detecting unit determines that the loop path has been generated, and receives the loop detecting frame transmitted from the own device, according to the storage. And determining, by the received priority information of the loop detection frame, whether there is a relay device that can update the priority information in the loop path, and receiving a loop detection signal transmitted from the device The port of the frame is the same as the port that transmits the loop detection frame, and in the case that there is no relay device in the loop path that can update the priority information, the aforementioned detection of the loop detection frame is closed. port. The relay device according to any one of claims 1 to 4, wherein the aforementioned loop detecting portion is not received after a certain period of time from the closing of the aforementioned port In the case of the loop detection frame transmitted by the own device, the closing of the aforementioned port is released. The relay device according to any one of claims 1 to 4, wherein the loop detecting unit manages the state of the port as a first state for performing transmission and reception of all frames according to each of the ports. The detection and reception of the loop detection frame does not transmit which of the second state of the frame other than the loop detection frame and the third state of the closed state, and manages the state of the port and the priority order correspond. The relay device according to claim 5, wherein the loop detecting unit manages the state of the port as a first state for transmitting and receiving all frames and performing a loop detection frame according to each of the ports. The second state of the frame other than the loop detection frame and the third state belonging to the closed state are transmitted and received, and the state of the port and the priority order are managed. According to the relay device of claim 6, wherein the priority order corresponding to the first state is higher than the priority order corresponding to the second state, and the priority order corresponding to the second state corresponds to the aforementioned The priority of the third state is high. According to the relay device of claim 7, wherein the priority order corresponding to the first state is higher than the priority order corresponding to the second state, and the priority order corresponding to the second state corresponds to the aforementioned The priority of the third state is high. According to the relay device of claim 6, wherein the loop detecting unit causes the port to be detected when the connection is established according to each of the ports described above. Converting to the second state, after the conversion to the second state, the loop detection frame transmitted by the own device is not received at the port for a certain period of time, or the device does not receive the port from the port after a certain period of time When the loop detection frame is transmitted, the port is switched to the first state. The relay device according to claim 7, wherein the loop detecting unit converts the port to the second state when the connection establishment is detected, and after converting to the second state, When the loop detection frame transmitted by the own device is not received at the port for a certain period of time, or when the loop detection frame transmitted from the port is not received by the device for a certain period of time, the port is converted into the foregoing The first state. According to the relay device of the eighth aspect of the invention, the loop detection unit converts the port to the second state when the connection establishment is detected, and after converting to the second state, When the loop detection frame transmitted by the own device is not received at the port for a certain period of time, or when the loop detection frame transmitted from the port is not received by the device for a certain period of time, the port is converted into the foregoing The first state. The relay device according to claim 9, wherein the loop detecting unit converts the port to the second state when the connection is established, and after converting to the second state, When the loop detection frame transmitted by the own device is not received at the port for a certain period of time, or when the loop detection frame transmitted from the port is not received by the device for a certain period of time, the port is converted into the foregoing The first state. The relay device according to any one of claims 1 to 4, wherein the foregoing relay device belongs to a transmission source of the aforementioned loop detection frame In the case where the information of the priority information of the loop detection frame to be transmitted is inserted, meaningful information is inserted and transmitted, and in the case of the relay device that originally received the loop detection frame, The priority order of the port storing the lower priority of the receiving port or the transmitting port is forwarded to the loop detection frame as the priority order information. According to the relay device of claim 5, in the case of the aforementioned relay device belonging to the transmission source of the aforementioned loop detection frame, the priority information of the aforementioned loop detection frame to be transmitted is not present. The area is inserted with meaningful information for transmission, and in the case of the aforementioned relay device that originally received the aforementioned loop detection frame, the priority order of the port of the lower priority order in the storage port or the transmission port is stored as the priority. The loop detection frame is forwarded by the information. According to the relay device of claim 6, wherein in the case of the aforementioned relay device belonging to the transmission source of the aforementioned loop detection frame, the priority information of the aforementioned loop detection frame to be transmitted is not present. The area is inserted with meaningful information for transmission, and in the case of the aforementioned relay device that originally received the aforementioned loop detection frame, the priority order of the port of the lower priority order in the storage port or the transmission port is stored as the priority. The loop detection frame is forwarded by the information. According to the relay device of claim 7, wherein in the case of the foregoing relay device belonging to the transmission source of the aforementioned loop detection frame, the priority information of the aforementioned loop detection frame to be transmitted is not present. The area is inserted with meaningful information for transmission, and in the case of the aforementioned relay device that originally received the aforementioned loop detection frame, the storage receiving port or The priority order of the lower priority port in the transmit port is forwarded to the loop detection frame as the priority order information. According to the relay device of claim 8, wherein in the case of the relay device belonging to the transmission source of the loop detection frame, the priority information of the loop detection frame to be transmitted is not The area is inserted with meaningful information for transmission, and in the case of the aforementioned relay device that originally received the aforementioned loop detection frame, the priority order of the port of the lower priority order in the storage port or the transmission port is stored as the priority. The loop detection frame is forwarded by the information. According to the relay device of claim 9, wherein in the case of the relay device belonging to the transmission source of the loop detection frame, the priority information of the loop detection frame to be transmitted is not The area is inserted with meaningful information for transmission, and in the case of the aforementioned relay device that originally received the aforementioned loop detection frame, the priority order of the port of the lower priority order in the storage port or the transmission port is stored as the priority. The loop detection frame is forwarded by the information. According to the relay device of claim 10, in the case of the aforementioned relay device belonging to the transmission source of the aforementioned loop detection frame, the priority information of the aforementioned loop detection frame to be transmitted is not present. The area is inserted with meaningful information for transmission, and in the case of the aforementioned relay device that originally received the aforementioned loop detection frame, the priority order of the port of the lower priority order in the storage port or the transmission port is stored as the priority. The loop detection frame is forwarded by the information. According to the relay device of claim 11 of the scope of the patent application, which belongs to the aforementioned In the case of the relay device of the transmission source of the detection frame, the meaningful information is not transmitted in the region of the priority information of the loop detection frame to be transmitted, and the transmission is initially received. In the case of the aforementioned relay device of the circle detection frame, the priority order of the port of the lower priority order in the storage receiving port or the transmission port is transferred to the loop detection frame as the priority order information. According to the relay device of claim 12, in the case of the aforementioned relay device belonging to the transmission source of the aforementioned loop detection frame, the priority information of the aforementioned loop detection frame to be transmitted is not present. The area is inserted with meaningful information for transmission, and in the case of the aforementioned relay device that originally received the aforementioned loop detection frame, the priority order of the port of the lower priority order in the storage port or the transmission port is stored as the priority. The loop detection frame is forwarded by the information. According to the relay device of claim 13, wherein in the case of the aforementioned relay device belonging to the transmission source of the aforementioned loop detection frame, the priority information of the aforementioned loop detection frame to be transmitted is not The area is inserted with meaningful information for transmission, and in the case of the aforementioned relay device that originally received the aforementioned loop detection frame, the priority order of the port of the lower priority order in the storage port or the transmission port is stored as the priority. The loop detection frame is forwarded by the information. A communication system comprising a plurality of relay devices of any one of claims 1 to 23; and comprising: a master station device; and a slave station device, performing the foregoing plurality of relay devices with the master station device communication.