JP2011035728A - Relay device and relay method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To achieve efficient traffic control without blocking a high-priority communication path. <P>SOLUTION: A relay device includes: a priority port to which a high-priority first communication path is connected; another port to which a low-priority second communication path is connected; a transition port to which a third communication path is connected and which relays communication between the first communication path connected to the priority port or the second communication path connected to the another port and the third communication path; and a transition port control unit for performing control so that data input to the priority port from the first communication path is preferentially transmitted from the transition port to the third communication path as compared with data input to the another port from the second communication path. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a technique for relaying data flowing on a communication path.

  Conventionally, a tag VLAN has been proposed as a technique for effectively utilizing network resources. The tag VLAN makes it possible to reduce the number of network switches arranged in the entire network by making one port of the network switch belong to a plurality of VLANs (Virtual Local Area Networks).

  In addition, as a technique for improving network traffic efficiency, a technique for controlling traffic by prioritized switching (see Patent Document 1) and a load balancing technique for switching VLANs according to the load status of each server have been proposed. (See Patent Document 2).

JP 2001-285330 A JP 20032344752

  However, in the technique described in Patent Document 1, communication with a low priority may stagnate communication with a high priority (communication for which a bandwidth is to be secured). In addition, since the priority order cannot be changed dynamically, there is a problem that a network failure with a high priority level has an adverse effect on the entire network. Furthermore, even if priorities are assigned in units of ports, if each port is on the same network, the redundant path will be disconnected by STP (Spanning Tree Protocol) and the increased bandwidth cannot be used. was there.

In the technique described in Patent Document 2, since the VLAN identification number (VID) is converted to switch the VLAN, analysis of the MAC frame is necessary, and layer 2 processing is always necessary. In addition, since the VLAN is converted by detecting the load state of the server, a device for detecting the load is required.
In view of the above circumstances, an object of the present invention is to provide a relay device and a relay method that realize efficient traffic control without interfering with a communication path having a high priority.

  One aspect of the present invention is a relay device, in which a priority port to which a first communication path with a high priority is connected, another port to which a second communication path with a low priority is connected, and a third communication path are The first communication path connected to the priority port or a transition port that relays communication between the second communication path connected to the other port and the third communication path, and the priority from the first communication path A transition port control unit that controls to transmit data entering the port from the transition port to the third communication path with higher priority than data entering the other port from the second communication path.

  One aspect of the present invention is a relay device, wherein an active port to which an active communication path is connected, a redundant port to which a redundant communication path is connected, and a predetermined communication path are connected, and the active port A predetermined communication port that relays communication between the active communication path connected to the redundant communication path connected to the redundant system port and the predetermined communication path and the predetermined communication path until the failure occurs in the active communication path And a port switching control unit that connects the communication port and the working port and connects the predetermined communication port and the redundant port when a failure occurs in the working communication path.

  One aspect of the present invention is a relay method in which a priority port to which a first communication path with a high priority is connected, another port to which a second communication path with a low priority is connected, and a third communication path are A relay device that is connected and includes a first communication path connected to the priority port or a second communication path connected to the other port and a transition port that relays communication between the third communication path, and Monitoring whether data has entered the priority port from one communication path; and when the relay device has entered data to the priority port, the data is input from the second communication path to the other port. And controlling to transmit from the transition port to the third communication path with higher priority than the data.

  One aspect of the present invention is a relay method, in which an active port to which an active communication path is connected, a redundant port to which a redundant communication path is connected, and a predetermined communication path are connected, and the active port A relay device comprising: a working communication path connected to a redundant communication path connected to the redundant system port; and a predetermined communication port that relays communication between the predetermined communication path and a failure occurs in the working communication path. Connecting the predetermined communication port and the active system port until a failure occurs, and the relay device connects the predetermined communication port and the redundant system port when a failure occurs in the active communication path. And a step of.

  According to the present invention, efficient traffic control can be realized without interfering with a communication path having a high priority.

It is a block diagram showing the system configuration | structure of the communication system of 1st embodiment. It is a schematic block diagram showing the function structure of the relay apparatus of 1st embodiment. It is the schematic showing the specific example of operation | movement of the relay apparatus of 1st embodiment. It is a flowchart showing operation | movement of the relay apparatus of 1st embodiment. It is a flowchart showing operation | movement of the relay apparatus of 1st embodiment. It is a block diagram showing the system configuration | structure of the communication system of 2nd embodiment. It is a schematic block diagram showing the function structure of the relay apparatus of 2nd embodiment. It is the schematic showing the specific example of operation | movement of the relay apparatus of 2nd embodiment. It is a flowchart showing operation | movement of the relay apparatus of 2nd embodiment.

[First embodiment]
FIG. 1 is a configuration diagram showing a system configuration of the first embodiment of the communication system 100. The communication system 100 includes a plurality of communication devices S1 to S4, a network N1, and a relay device 1. The communication devices S1 to S4 are devices that perform communication via the relay device 1, and may be information processing devices such as personal computers and server devices, or may be network devices such as routers and switches. A device such as a printer or a scanner may be used. Further, the communication devices S1 to S3 are directly connected to the relay device 1, and the communication device S4 is connected to the relay device 1 via the network N1. Note that the network configuration shown in FIG. 1 is a specific example, and the relay device 1 may be used in a network having another configuration.

  The relay device 1 includes a plurality of ports, and outputs a packet input from one port from another port, whereby a communication device connected to one port and a communication device connected to another port are connected. Relay communications. The relay device 1 implements a VLAN by a port VLAN (Port Virtual Local Area Network). Hereinafter, the relay apparatus 1 will be described in detail.

  FIG. 2 is a schematic block diagram illustrating a functional configuration of the relay device 1 according to the first embodiment. Note that FIG. 2 shows an example in which the relay device 1 includes eight ports, and the following description describes a case in which the relay device 1 includes eight ports. However, the number of ports provided in the relay device 1 is described. Is not limited to eight.

  The relay device 1 includes a CPU (Central Processing Unit), a memory, an auxiliary storage device, and the like connected by a bus, and by executing a relay program, a plurality of port buffers 2-1 to 2-8 and a plurality of port selectors. It functions as a device including 3-1 to 3-8, the transition port control unit 4, and the general port control unit 5. Note that all or part of the functions of the relay device 1 may be realized using dedicated hardware such as an application specific integrated circuit (ASIC) or a programmable logic device (PLD).

  Each port buffer 2-1 to 2-8 is provided for each port, and accumulates packets received from communication devices connected to each port. For example, each of the port buffers 2-1 to 2-8 is implemented by FIFO (First In First Out). Each port buffer 2-1 to 2-8 has a communication path with each port selector 3-1 to 3-8 in all ports other than the same port. In FIG. 2, the communication path is shown only for the port buffer 2-1 of the port 1 as a representative. However, the port selectors 3-1 to 3-8 are also used for all other ports in the same manner as the port buffer 2-1 of the port 1. Communication path.

  Each port selector 3-1 to 3-8 is provided for each port. Each port selector 3-1 to 3-8 has a communication path to each port buffer 2-1 to 2-8 in all ports other than the same port. In FIG. 7 described later, the communication path is shown only for the port selector 3-1 of the port 1 as a representative. It has a communication path with -8. That is, as shown in FIG. 2, all the port buffers 2-1 to 2-8 have communication paths with the port selectors 3-1 to 3-8 of other ports, thereby substantially showing FIG. Thus, each port selector 3-1 to 3-8 has a communication path with port buffers 2-1 to 2-8 of other ports. The port selectors 3-1 to 3-8 are connected to any of the port buffers 2-1 to 2-8, and themselves provide the packets stored in the connected port buffers 2-1 to 2-8. To the communication device connected to the specified port. The port buffers 2-1 to 2-8 to which the port selectors 3-1 to 3-8 are connected will be described later.

  The transition port control unit 4 controls the transition port connected to the priority port. A priority port is a specific port among the ports provided in the relay apparatus 1, and is a port connected to a communication path with high priority. A packet that reaches the priority port from the communication device is sent out from the transition port. The transition port is a port to which the VLAN to which the self belongs belongs. Specifically, the VLAN to which the priority port belongs (hereinafter referred to as “priority VLAN”) and the VLAN to which the priority port does not belong (hereinafter referred to as “non-priority”). Transition to “priority VLAN”). Then, when the packet is accumulated in the port buffer of the priority port, the transition port control unit 4 connects to the priority VLAN to the port selector of the transition port and sends the packet accumulated in the port buffer of the priority port. Control. The priority VLAN is a communication path with a high priority or a part thereof. A communication path having a higher priority indicates a communication path that should secure a band with priority over other communication paths.

  The general port control unit 5 controls transmission / reception of each port connected to the non-priority VLAN. The general port control unit 5 is a functional unit that performs control related to an existing VLAN, and is realized by an existing technology.

  FIG. 3 is a schematic diagram illustrating a specific example of the operation of the relay device 1 according to the first embodiment. In FIG. 3, port 4 is a priority port and port 8 is a transition port. FIG. 3A shows a configuration of a state in which the transition port belongs to the priority VLAN (hereinafter referred to as “priority state”). In this case, the ports 1 to 3 and 5 to 7 belong to the non-priority VLAN (VLAN 1), and the port 4 (priority port) and the port 8 (transition port) belong to the priority VLAN (VLAN 2). FIG. 3B shows a configuration in a state where the transition port belongs to the non-priority VLAN (hereinafter referred to as “non-priority state”). In this case, the ports 1 to 3 and 5 to 8 belong to the non-priority VLAN (VLAN 1), and the port 4 belongs to the priority VLAN (VLAN 2).

  4 and 5 are flowcharts showing the operation of the relay device 1 of the first embodiment. FIG. 4 is a flowchart showing the priority port monitoring process, and FIG. 5 is a flowchart showing the transition port monitoring process. Hereinafter, the operation of the relay apparatus 1 will be described.

  First, the priority port monitoring process will be described with reference to FIG. The transition port control unit 4 monitors the number of packets (data) stored in the port buffer of the priority port (step S101), and determines whether the number of packets stored in the port buffer of the priority port is zero (step S102).

  When the number of stored port buffers of the priority port is not zero (step S102-NO), that is, when packets are stored in the port buffer of the priority port, the transition port control unit 4 causes the transition port to belong to the priority VLAN. The relay apparatus 1 is set to the priority state. In this case, the port selector of the transition port selects the port buffer of the priority port, and transmits the packet received at the priority port from the transition port (step S103).

  On the other hand, when the accumulated number of port buffers in the priority port is zero (YES in step S102), the transition port control unit 4 causes the transition port to belong to the non-priority VLAN and sets the relay device 1 to the non-priority state. In this case, the port selector of the transition port selects one of the port buffers of the non-priority port according to the control of the general port control unit 5, and transmits the packet received at the non-priority port from the transition port (step S104).

  After step S104, the transition port control unit 4 monitors the number of accumulated port buffers of the priority port (step S105). When the accumulated number of port buffers in the priority port changes from zero to 1 (YES in step S105), the transition port control unit 4 causes the transition port to belong to the priority VLAN and put the relay device 1 in the priority state. In this case, the port selector of the transition port selects the port buffer of the priority port, and transmits the packet received at the priority port from the transition port (step S107). Thereafter, the process of the transition port control unit 4 returns to the process of step S101.

  On the other hand, while the number of stored port buffers in the priority port is zero (step S105—NO), the transition port control unit 4 causes the transition port to belong to the non-priority VLAN and put the relay device 1 in the non-priority state. In this case, the port selector of the transition port selects one of the port buffers of the non-priority port according to the control of the general port control unit 5, and transmits the packet received at the non-priority port from the transition port (step S106).

  Next, transition port monitoring processing will be described with reference to FIG. The transition port control unit 4 monitors the destination of the packet (data) in the port buffer of the transition port (step S201), and determines whether the destination corresponds to the priority port (step S202). The case where the destination corresponds to the priority port means that the destination is a communication device (communication device S3 in FIG. 3) connected to the priority port, or communication connected to the destination network where the destination is connected to the priority port. This is the case of the device.

  When the destination corresponds to the priority port (step S202—YES), the transition port control unit 4 determines whether the relay device 1 is in the priority state (step S203). When the relay device 1 is in the priority state (step S203—YES), the transition port control unit 4 keeps the state as it is and sends out the packet that has reached the transition port from the priority port (step S204). In this case, the port selector of the priority port is connected to the port buffer of the transition port, and transmits the packet accumulated in the port buffer of the transition port from the priority port.

  On the other hand, when the relay device 1 is not in the priority state (step S203—NO), the transition port control unit 4 causes the transition port to belong to the priority VLAN and sets the relay device 1 in the priority state (step S205). Next, the transition port control unit 4 causes a packet that has reached the transition port to be transmitted from the priority port (step S206). In this case, the port selector of the priority port is connected to the port buffer of the transition port, and transmits the packet accumulated in the port buffer of the transition port from the priority port. When the process of step S206 is completed, that is, when the process of transmitting the packet corresponding to the priority port from the priority port is completed, the transition port control unit 4 causes the transition port to belong to the non-priority VLAN, The priority state is restored (step S207). Thereafter, the process of the transition port control unit 4 returns to the process of step S201, and the transition port belonging to the non-priority VLAN operates according to the control of the general port control unit 5.

  In the process of step S202, when the destination does not correspond to the priority port (step S202—NO), the transition port control unit 4 determines whether or not the relay device 1 is in the priority state (step S208). When the relay device 1 is not in the priority state (step S208—NO), the transition port control unit 4 notifies the general port control unit 5 to perform control. Upon receiving this notification, the general port control unit 5 sends out the packet that has arrived at the transition port from the predetermined port according to the control related to the existing VLAN (step S209).

  On the other hand, when the relay apparatus 1 is in the priority state (step S208—YES), the transition port control unit 4 keeps the packet stored in the port buffer of the transition port until the number of stored port buffers of the priority port becomes zero. Waiting for transmission (step S210-NO). When the accumulated number of port buffers in the priority port becomes zero (step S210-YES), the transition port control unit 4 causes the transition port to belong to the non-priority VLAN and puts the relay device 1 in the non-priority state (step S211). Next, the transition port control unit 4 notifies the general port control unit 5 to perform control. Upon receiving this notification, the general port control unit 5 causes the packet that has reached the transition port to be sent out from the predetermined port according to the control related to the existing VLAN (step S212). Thereafter, the process of the transition port control unit 4 returns to the process of step S201.

The transition port control unit 4 always executes the processing shown in FIGS. 4 and 5 to control the transition port.
By providing the above configuration, the relay device 1 has the following effects. First, the transition port control unit 4 monitors the accumulation state of the port buffer of the priority port, and only makes the transition port belong to the non-priority VLAN when there is no accumulation. Therefore, all packets related to communication on a communication path with a higher priority (priority VLAN) are transmitted from the transition port with priority over packets on a communication path with a lower priority (non-priority VLAN). Further, when communication does not occur on a communication path with a high priority, it is possible to transmit a packet related to communication on a communication path with a low priority from the transition port. Therefore, it is possible to effectively use network resources and perform efficient traffic control without interfering with communication on a communication path with a high priority.

  Second, regarding the priority port monitoring process, the transition port control unit 4 monitors whether or not packets are accumulated in the port buffer of the priority port, so it is necessary to analyze the contents of the packet (for example, a MAC frame). There is no. Therefore, the determination in the transition port control unit 4 can be realized with low latency.

<Modification>
In the priority VLAN in the priority state, the port 4 and the port 8 may be connected by pass-through. In this case, the communication device S3 can occupy the communication path of the port 8. On the other hand, since the port 8 belongs to the non-priority VLAN in the non-priority state, the communication device S1 and the communication device S2 share the communication path of the port 8, and the communication device S3 cannot use the communication path.

  In the relay device 1, STP (Spanning Tree Protocol) may be invalidated. This is because port 5 and port 8 are connected to the same network N1, and therefore either path may be disconnected when the STP operates. The broadcast received by the port 5 in the relay device 1 may be set not to be transmitted from the port 8 in advance, or the broadcast received by the port 8 may be set not to be transmitted from the port 5. By setting in this way, broadcast storms can be prevented.

[Second Embodiment]
FIG. 6 is a configuration diagram illustrating a system configuration of the communication system 100a according to the second embodiment. In the communication system 100a in the second embodiment, the relay device 1a is connected to the network N1 and the network N2. The network N1 is an active network, and the network N2 is a redundant network for the network N1. In a normal state, the communication devices S1 and S2 can be connected only to the network N1 via the relay device 1a, and cannot be connected to the network N2. On the other hand, when a failure occurs in the network N1, the communication devices S1 and S2 can be connected to the network N2 via the relay device 1a. Hereinafter, a specific configuration and operation of the relay apparatus 1a will be described.

  FIG. 7 is a schematic block diagram illustrating a functional configuration of the relay device 1a according to the second embodiment. FIG. 7 shows an example in which the relay device 1a includes eight ports. In the following description, the case where the relay device 1a includes eight ports is described. However, the number of ports provided in the relay device 1a is described. Is not limited to eight.

  The relay device 1a includes a CPU, a memory, an auxiliary storage device, and the like connected by a bus, and by executing a relay program, a plurality of port buffers 2-1 to 2-8 and a plurality of port selectors 3-1 to 3 are provided. −8, functions as a device including the port switching control unit 6 and the general port control unit 5. Note that all or part of the functions of the relay device 1 may be realized using dedicated hardware such as an ASIC or a PLD.

The configurations of the port buffers 2-1 to 2-8, the port selectors 3-1 to 3-8, and the general port control unit 5 are the same as the configurations in the first embodiment, and thus description thereof is omitted.
The port switching control unit 6 controls switching between the active port and the redundant port. The working port is a port to which the working network (working communication path) N1 is connected. The redundant port is a port to which a redundant network (redundant communication path) N2 is connected. Only one of the active port and the redundant port belongs to a predetermined VLAN to which the other port belongs. The port switching control unit 6 monitors the communication status of the working port, and when the remaining capacity of the port buffer of the working port becomes zero, an abnormal situation such as a broadcast storm has occurred in the working network N1. Judge. When determining that an abnormal state has occurred in the active network N1, the port switching control unit 6 disconnects the active port from the predetermined VLAN and adds a redundant port to the predetermined VLAN.

  Thereafter, the port switching control unit 6 monitors the communication status of the redundant system port. When the remaining capacity of the port buffer of the redundant port becomes zero, the port switching control unit 6 determines that an abnormal situation such as a broadcast storm has occurred in the redundant network N2. When the port switching control unit 6 determines that an abnormal state has occurred in the redundant network N2, the port switching control unit 6 disconnects the redundant port from the predetermined VLAN and adds the working port to the predetermined VLAN.

  FIG. 8 is a schematic diagram illustrating a specific example of the operation of the relay device 1a according to the second embodiment. In FIG. 8, port 5 is an active port and port 8 is a redundant port. FIG. 8A shows a configuration in a state where the working port belongs to a predetermined VLAN (hereinafter referred to as “working system state”). In this case, the ports 1 to 3 and 5 to 7 belong to a predetermined VLAN, and the ports 4 and 8 (redundant ports) do not belong to the predetermined VLAN. FIG. 8B shows a configuration in a state in which the redundant port belongs to a predetermined VLAN (hereinafter referred to as “redundant state”). In this case, the ports 1 to 3 and 6 to 8 belong to a predetermined VLAN, and the ports 4 and 5 (active ports) do not belong to the predetermined VLAN.

  FIG. 9 is a flowchart showing the operation of the relay device 1a of the second embodiment. The port switching control unit 6 monitors the accumulated number of packets (data) in the port buffer of the active port (step S301), and determines whether the accumulated number exceeds the capacity of the port buffer and overflows (step S302). ).

  If it has not overflowed (NO in step S302), the port switching control unit 6 continues the relay process of the relay device 1a while maintaining the active port. In this case, the port selector of each port (ports 1 to 3, 6 and 7 in the case of FIG. 8) belonging to the predetermined VLAN is in accordance with the control of the general port controller 5 (port 5 in the case of FIG. 8). ) Port buffer. The port selector of the active port selects and connects the port buffer of any one of the ports belonging to the predetermined VLAN under the control of the general port control unit 5. As a result, the communication devices S1 and S2 communicate with the network N1. Thereafter, the process of the port switching control unit 6 returns to the process of step S301.

  On the other hand, if it has overflowed (YES in step S302), the port switching control unit 6 disconnects the active port from the predetermined VLAN and adds a redundant port to the predetermined VLAN. In this case, each port belonging to the predetermined VLAN (ports 1 to 3, 6, and 7 in the case of FIG. 8) selects a redundant port (port 8 in the case of FIG. 8) (step S304). In this case, the port selector of each port (ports 1 to 3, 6 and 7 in the case of FIG. 8) belonging to a predetermined VLAN is a redundant system port (port 8 in the case of FIG. 8) under the control of the general port control unit 5. ) Port buffer. The port selector of the redundant port selects and connects the port buffer of any one of the ports belonging to the predetermined VLAN under the control of the general port control unit 5. As a result, the communication devices S1 and S2 communicate with the network N2. After the redundant system port belongs to the predetermined VLAN, the process of reversing the redundant system and the active system in FIG. 9 is executed. Therefore, when the port buffer of the redundant port overflows, the port switching control unit 6 again causes the working port to belong to the predetermined VLAN.

  By providing the above configuration, the relay device 1a can improve the availability against the failure because the active network where the failure has occurred is disconnected from the VLAN and the redundant network is added to the VLAN.

  Further, since the port switching control unit 6 of the relay device 1a is configured to monitor whether or not the packet overflows in the active port, it is not necessary to analyze the contents of the packet (for example, a MAC frame). Therefore, the determination in the port switching control unit 6 can be realized with low latency.

  Further, since the relay device 1a switches between the active network and the redundant network by switching the port, the active network in which the failure has occurred can be instantaneously switched to the redundant network. Therefore, it is not necessary to construct a redundant network configuration in the communication devices S1 and S2. For example, in order to construct a redundant network configuration in the communication devices S1 and S2, the communication devices S1 and S2 need to be provided with two systems of NICs, LAN cables, etc., and the monitoring load is also imposed on the processors of the communication devices S1 and S2. Accompany. However, by using the relay device 1a, it becomes possible to construct a redundant configuration in the network switch (relay device 1a) directly connected to the communication devices S1 and S2, thereby reducing the construction cost of the redundant network configuration and the communication device S1. And the processing load of S2 can also be suppressed.

<Modification>
When switching to the redundant network, the port switching control unit 6 may be configured to stop the monitoring process and stop switching between the active system and the redundant system until the relay device 1a is reset.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

DESCRIPTION OF SYMBOLS 1,1a ... Relay device, S1-S4 ... Communication device, N1 ... Network (working system network), N2 ... Redundant network, 2-1-2-8 ... Port buffer, 3-1-3-8 ... Port selector , 4 ... Transition port control unit, 5 ... General port control unit, 6 ... Port switching control unit

Claims (6)

A priority port to which the first communication path with a higher priority is connected;
Other ports to which the second communication path with low priority is connected,
A third communication path is connected, a transition port that relays communication between the first communication path connected to the priority port or the second communication path connected to the other port and the third communication path;
Transition that controls data that has entered the priority port from the first communication path to be transmitted from the transition port to the third communication path with priority over data that has entered the other port from the second communication path. A port controller;
A relay device comprising: A control unit that constructs a priority virtual network including the first communication path and another virtual network including the second communication path by controlling a path in units of ports, and blocks communication between the priority virtual network and the other virtual network. Further comprising
The transition port control unit controls the transition port to belong to the priority virtual network when data enters the priority port from the first communication path, and data is transferred from the first communication path to the priority port. 2. The relay apparatus according to claim 1, wherein, when there is no entry, the transition port is controlled to belong to the other virtual network. The working port to which the working communication path is connected;
A redundant port to which the redundant communication path is connected;
A predetermined communication path connected to the active communication path connected to the active port or a redundant communication path connected to the redundant port and a predetermined communication port that relays communication between the predetermined communication path;
The predetermined communication port and the active port are connected until a failure occurs in the active communication path, and the predetermined communication port and the redundant port are connected when a failure occurs in the active communication path A port switching control unit,
A relay device comprising:   The port switching unit determines that a failure has occurred in the active communication path when the amount of buffers entering the active port from the active communication path exceeds the buffer capacity of the active port. 4. The relay apparatus according to claim 3, wherein switching between the system port and the redundant system port is performed. A priority port to which the first communication path having a higher priority is connected, another port to which the second communication path having a lower priority is connected, and a first communication to which the third communication path is connected and connected to the priority port Whether or not a relay device comprising a path or a transition port that relays communication between the second communication path connected to the other port and the third communication path enters data from the first communication path to the priority port. Monitoring step,
When data enters the priority port, the relay device transmits the data from the transition port to the third communication path with higher priority than data that enters the other port from the second communication path. Step to control, and
A relay method comprising: An active port to which an active communication path is connected, a redundant port to which a redundant communication path is connected, an active communication path to which a predetermined communication path is connected and connected to the active port or the redundant port A relay device comprising a redundant communication path connected to a predetermined communication port for relaying communication between the predetermined communication path and
Connecting the predetermined communication port and the working port until a failure occurs in the working communication path;
The relay device connecting the predetermined communication port and the redundant system port when a failure occurs in the active communication path;
A relay method comprising:

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