JP2016225890A - Communication device and communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To support the efficient operation and maintenance of an access sub-ring.SOLUTION: A node 16 and a node 20 comprise an AS port 34 used in an access sub-ring. The node 16 autonomously transmits information on an adjacent node on a ring network 102 to the node 20 with which the node 16 is paired on the access sub-ring. The node 20 stores the information on the adjacent node transmitted by the node 16. When the node 20 receives a message to give notice of a failure on the ring network 102, if the transmission source of the message accords with the adjacent node of the node 16, the node 20 switches the AS port 34 to an open state.SELECTED DRAWING: Figure 1

Description

  The present invention relates to data communication technology, and more particularly to a communication apparatus and a communication system.

  A technique relating to an access accommodating node that forms an upper ring with a plurality of relay nodes has been proposed (see, for example, Patent Document 1). In Patent Literature 1, when information on a relay node adjacent to another access accommodation node is set in advance for the access accommodation node, and the access accommodation node receives a message notifying the failure of the upper ring, It is described that the access accommodating port is communicated if the relay node that has notified the message matches the preset relay node.

JP 2013-58863 A

  The access accommodating node of Patent Document 1 is an ITU-T G.264 standard. The present invention can also be applied to the access sub-ring specified by 8032. Here, in the access accommodation node of Patent Document 1, information of a relay node adjacent to another access accommodation node is fixedly set in advance (paragraphs 0041, 0043 to 0045, etc.). The present inventor considered that there is room for improvement in the technique of Patent Document 1 from the viewpoint of realizing efficient operation and maintenance of access sub-rings.

  The present invention has been made on the basis of the above-mentioned problem recognition of the present inventor, and its main object is to provide a technology that supports efficient operation and maintenance of access sub-rings.

  In order to solve the above problems, a communication device according to an aspect of the present invention is an access sub-ring port that is a communication device that forms a ring network together with another relay node, and is a port used in access sub-ring. And an adjacent node information notification unit that autonomously transmits information of adjacent nodes that are adjacent relay nodes in the ring network to a relay node that is paired in the access sub-ring, and a relay node that is paired in the access sub-ring Pair node information storage unit that stores information on adjacent nodes transmitted from the network, and when a message notifying the failure of the ring network is received, the source of the message is the neighbor indicated by the information stored in the pair node information storage unit And a switching unit that switches the access / subring port to an open state if the node matches the node.

  Another aspect of the present invention is a communication system. This communication system includes a plurality of relay nodes constituting a ring network. The plurality of relay nodes include a first relay node and a second relay node that are paired in the access sub-ring. The first relay node is a port used in the access sub-ring, and the information on the access sub-ring port in the open state and the adjacent node that is a relay node adjacent in the ring network is used as the second relay node. And an adjacent node information notifying unit that autonomously transmits to. The second relay node has received a message notifying the failure of the ring network, the access sub-ring port in the blocked state, the pair node information storage unit storing the information of the adjacent node transmitted from the first relay node, and In this case, a switching unit that switches an access / subring port to an open state if the transmission source of the message matches the adjacent node indicated by the information stored in the pair node information storage unit.

  It should be noted that any combination of the above components and the expression of the present invention converted between a method, a program, a recording medium storing the program, and the like are also effective as an aspect of the present invention.

  According to the present invention, efficient operation and maintenance of access subring can be supported.

It is a figure which shows the structure of the communication system of embodiment. It is a figure which shows typically switching of an access sub ring port. It is a figure which shows typically the switching failure of an access sub ring port. FIG. 2 is a block diagram showing a configuration of nodes other than an access sub ring node among a plurality of nodes constituting the ring network of FIG. 1. It is a block diagram which shows the structure of an access sub ring node among the several nodes which comprise the ring network of FIG. It is a figure which shows the pair node information memorize | stored in a pair node information storage part. It is a sequence diagram which shows operation | movement of the communication system of FIG.

  FIG. 1 shows a configuration of a communication system 100 according to the embodiment. The communication system 100 includes a plurality of relay nodes (node 10, node 12, node 14, node 16, node 18, node 20, and node 22) that form the ring network 102. Each of the plurality of relay nodes is a communication device having a layer 2 switch function, and includes a ring port 30 and a ring port 32 which are ports connected to the transmission path of the ring network 102. In the ring network 102, it is necessary to provide a block section (ring protection link). In FIG. 1, the ring port 32 of the node 10 and the ring port 30 of the node 12 are set to a blocked state (ie, a blocking port).

  Among the plurality of relay nodes, the node 16 and the node 20 are ITU-T G.264. An access sub-ring defined by 8032 (also called “access redundancy”) is formed. In FIG. 1, the node 16, the node 20, and the L2SW 24 that is a layer 2 switch form the access sub-ring 104. In the access sub-ring 104, the ITU-T G. An R-APS message for controlling ring protection defined in 8032 is not transmitted. The L2SW 24 may be a device that does not support ring protection.

  The nodes 16 and 20 are communication devices installed at the boundary between the ring network 102 and the access sub-ring 104, and are also referred to as “access sub-ring nodes” in the embodiment. The access sub-ring node corresponds to the access accommodation node in Patent Document 1 and can be said to be an access redundancy accommodation node. The nodes 16 and 20 include an access sub-ring port (AS port 34) that is a port connected to the transmission path of the access sub-ring 104.

  In the access sub-ring 104, in order to prevent occurrence of a frame loop, when one AS port 34 of the node 16 and the node 20 is in an open state, the other AS port 34 needs to be closed. The open state of the AS port 34 can be said to be a state where communication of the frame is possible, and it can also be said to be a state where reception of the frame is not rejected. The blocked state of the AS port 34 can be said to be a state in which frame communication is impossible and a state in which frame communication (reception) is refused.

  In the initial state of the communication system 100, it is assumed that the AS port 34 of the node 16 is opened and the AS port 34 of the node 20 is closed. For example, the L2SW 24 transfers the user frame transmitted from the user terminal 26 to both the node 16 and the node 20 (if there is no learning information). In this case, the node 16 receives the user frame, but the node 20 does not receive the user frame because the AS port 34 of the node 20 is in the blocked state.

  As another example, when the user frame received by the node 16 at a port (not shown) is forwarded to the node 20 by flooding, the user frame output from the ring port 30 of the node 16 is discarded at the ring port 30 of the node 12. The user frame output from the AS port 34 is discarded at the AS port 34 of the node 20. Therefore, the user frame output from the ring port 32 of the node 16 is received by the node 20. In this way, the access sub-ring 104 can be said to make the communication path between the L2SW 24 (user terminal 26) and the ring network 102 redundant, and the communication path between the node 16 and the node 20 made redundant. I can say that.

  Next, the problem of conventional access subring will be described. FIG. 2 schematically shows switching of the access / subring port. The paired nodes (node 16 and node 20) in the access sub-ring store each other's node information. When a failure occurs in the AS port 34 of the node 16, the node 16 transmits an R-APS (SF) message from its own ring port 30 and ring port 32.

  The node 20 receives the R-APS (SF) message transmitted by the node 16 at the ring port 30 and the ring port 32. Since the source address of the R-APS (SF) is the node 16 paired in the access sub-ring 104, the node 20 switches its AS port 34 from the blocked state to the opened state. In other words, the state in which the AS port 34 refuses to receive a frame is terminated, and the AS port 34 is switched to a state in which the frame can be communicated. The process of FIG. 8032.

  FIG. 3 schematically shows an access / subring port switching failure. This figure shows a situation in which a fatal problem has occurred in the node 16 and the node 16 has become unable to communicate with the outside. The node 14 detects an abnormality in communication with the node 16 at the ring port 32 (for example, link down or LOC (Loss Of Continuity)), and transmits an R-APS (SF) message from the ring port 30. Similarly, the node 18 detects a communication abnormality with the node 16 at the ring port 30 and transmits an R-APS (SF) message from the ring port 32.

  The node 20 receives the R-APS (SF) message (the source address is the node 18) at the ring port 30 and receives the R-APS (SF) message (the source address is the node 14) at the ring port 32. However, since the source of the R-APS (SF) message is not the paired node 16 in the access sub-ring 104, the node 20 recognizes this message as a ring port switching notification, and switches the AS port 34. do not do. That is, when the access sub-ring node cannot transmit R-APS (SF) due to its own failure, switching of the AS port 34 does not operate in the paired access sub-ring node.

  In the communication system 100 according to the embodiment, the ITU-T G. The conventional access sub-ring problem is solved by using the transmission of the ring switching R-APS (SF) based on the detection of an adjacent node abnormality defined in 8032. Specifically, the access sub-ring node according to the embodiment autonomously notifies the pair node, which is a pair of nodes in the access sub-ring 104, of information on adjacent nodes that are adjacent in the ring network 102. . When a message indicating a failure of the ring network 102 (typically R-APS (SF)) is received, if the source of the message is an adjacent node of the pair node, the AS port 34 of the own node is blocked. Switch from open to open.

  FIG. 4 is a block diagram showing a configuration of a node other than the access / sub-ring node among a plurality of nodes constituting the ring network 102. Specifically, FIG. 1 shows the configuration of the node 10, the node 12, the node 14, the node 18, and the node 22 that do not have the AS port 34. Hereinafter, the configuration of the node 18 will be described as a representative.

  Each block shown in the block diagram of the present specification can be realized by hardware such as a computer CPU, memory, FPGA (Field-Programmable Gate Array), and the like, and can be realized by software. Although realized by a computer program or the like, here, functional blocks realized by their cooperation are depicted. Therefore, those skilled in the art will understand that these functional blocks can be realized in various forms by a combination of hardware and software. The same applies to the subsequent block diagrams.

  The node 18 includes a ring port 30, a ring port 32, an adjacent node information storage unit 40, a failure detection unit 44, a control information transmission / reception unit 46, a ring port control unit 48, an own node information notification unit 50, and an adjacent node information reception unit 52. Prepare. In addition, since the function to transfer a user frame or a monitoring frame between the ring port 30 and the ring port 32, the function to determine the route of the frame, and the like are known, the description thereof is omitted.

  The failure detection unit 44 detects the occurrence of a failure in the ring network 102 by a known method. For example, the state of communication with an adjacent node in the ring network 102 is determined by CCM (Continuity Check Message), R-APS (NS), R-APS (NR) of Ethernet (registered trademark) OAM (Operations, Administration, and Maintenance). ) Etc. to check regularly. When a communication abnormality (link down, LOC, etc.) with an adjacent node occurs, the fact is detected.

  The control information transmission / reception unit 46 is an ITU-T G. Controls transmission / reception of an R-APS message, which is a frame for controlling ring protection defined in 8032. Specifically, the R-APS message received at one ring port is transferred to the other ring port and output. The control information transmission / reception unit 46 outputs an R-APS (SF) message from the ring port 30 and the ring port 32 when the failure detection unit 44 detects a failure of the ring network 102, for example, a communication abnormality with an adjacent node. .

  The ring port control unit 48 controls the communication state of frames in the ring port 30 and the ring port 32 in accordance with an operation of a maintenance person input from a maintenance terminal (not shown) or ring protection. For example, when a failure in communication with an adjacent node connected via a specific ring port is detected by the failure detection unit 44, the specific ring port may be switched from an open state to a blocked state. The control information transmitting / receiving unit 46 and the ring port control unit 48 are ITU-T G. A known ring protection process defined in 8032 is executed.

  The own node information notifying unit 50 sends an LLDP (Link Layer discovery protocol) frame defined by IEEE802.1AE to an adjacent node in response to the link up of the ports (ie, the ring port 30 and the ring port 32) for which ring setting has been made. Send. In the case of the node 18, the LLDP frame is transmitted from the ring port 30 and the ring port 32, the LLDP frame transmitted from the ring port 30 reaches the node 16, and the LLDP frame transmitted from the ring port 32 reaches the node 20.

  In the embodiment, “1” is set in the TTL (Time To Live) field of the LLDP frame. By setting the TTL of the LLDP frame to “1”, the notification destination of the local node information can be limited to the adjacent node, in other words, the local node information can be limited not to be transmitted beyond the adjacent node.

  The adjacent node information storage unit 40 is a storage area that holds information on relay nodes adjacent to the own node in the ring network 102. The adjacent node information receiving unit 52 receives the LLDP frame via the ring port 30 or the ring port 32. When the TTL of the received LLDP frame is “1”, it is recognized as the node information notification from the adjacent node, and the information of the transmission source node indicated by the LLDP frame is stored in the adjacent node information storage unit 40 as the adjacent node information. Thereafter, the received LLDP frame may be discarded.

  In the embodiment, the adjacent node information receiving unit 52 records the MAC address set as the transmission source address of the LLDP frame in the adjacent node information storage unit 40 as adjacent node information. As a modified example, identification information (various addresses, IDs, etc.) of adjacent nodes set in a predetermined area (data area, etc.) of the LLDP frame other than the transmission source address is recorded in the adjacent node information storage unit 40 as adjacent node information. May be. Since there are two adjacent nodes for one node in the ring network 102, information of two adjacent nodes is recorded in the adjacent node information storage unit 40.

  FIG. 5 is a block diagram showing a configuration of an access sub-ring node among a plurality of nodes constituting the ring network 102. Specifically, the configuration of the node 16 and the node 20 in FIG. 1 is shown. Hereinafter, the configuration of the node 20 will be described as a representative.

  The node 20 includes all functional blocks of nodes other than the access / subring node described in FIG. Further, the node 20 includes an AS port 34, a pair node information storage unit 42, an adjacent node information notification unit 54, a pair node information reception unit 56, and an AS port control unit 58, which are shown as an access / subring (AS) processing unit.

  It can be said that the AS processing unit is a function that is effective when an access / sub-ring is set for a relay node constituting the ring network 102. Nodes other than the access / subring node may also include an AS processing unit, and the AS processing unit may function effectively when the access / subring is set for the node. Hereinafter, the configuration of the AS processing unit will be described.

  The pair node information storage unit 42 is another node that forms a pair in the access sub-ring 104, and is a storage area that holds information of a pair node including the AS port 34 among a plurality of nodes constituting the ring network 102. The pair node for node 20 is node 16. FIG. 6 shows pair node information stored in the pair node information storage unit 42. The pair node information includes information items “pair node” and “pair adjacent node”. In the information item “pair node”, identification information of the pair node in the access sub-ring 104 is recorded. The identification information in the embodiment is the MAC address of the pair node (node 16).

  Further, in the information item “pair adjacent node”, identification information of adjacent nodes (node 14 and node 18) adjacent to the pair node in the ring network 102 is held. The identification information in the embodiment is the MAC address of each of the nodes 14 and 18. Note that the value of the information item “pair node” is set in advance by the maintenance person. On the other hand, the value of the information item “Pair Adjacent Node” is automatically set as will be described later, regardless of the maintenance person's work.

  Returning to FIG. 5, the adjacent node information notification unit 54 autonomously notifies the information on the adjacent node in the ring network 102 to the pair node (node 16) in the access sub-ring 104. That is, the adjacent node information is automatically transmitted from the ring port 30 and the ring port 32 to the pair node without depending on the maintenance person's hand and without depending on the instruction of the maintenance person.

  Specifically, the adjacent node information notification unit 54 receives the LLDP frame of TTL “1” from two adjacent nodes, and the adjacent node information reception unit 52 identifies the two adjacent nodes to the adjacent node information storage unit 40. When it is detected that the information is stored, identification information of two adjacent nodes is transmitted to the pair node. For example, the update status of the adjacent node information storage unit 40 may be monitored, and the transmission process may be executed when two MAC addresses are newly recorded in the adjacent node information storage unit 40. In the case of the node 20, the identification information of the two adjacent nodes is the MAC addresses of the node 18 and the node 22.

  Further, the adjacent node information notifying unit 54 transmits the adjacent node information to the pair node using an Ethernet OAM loopback message (LBM). At this time, the MAC address of the pair node (node 16) is set as the transmission destination address of the LBM, the MAC address of the own node (node 20) is set as the transmission source address, and the nodes 18 and 22 are stored in the data area defined as the Don't care area. Set the MAC address.

  Since the LBM can set a data field having an arbitrary length as the Don't care area, it is suitable for notification of adjacent node information. Further, by receiving a loopback reply (LBR) returned by the pair node that has received the LBM, it can be confirmed that the pair node has received the adjacent node information. When the LBR is not received from the pair node within a predetermined time, the adjacent node information notification unit 54 may retransmit the LBM in which the adjacent node information is set, or notify the maintenance person terminal of an alert.

  The pair node information receiving unit 56 receives the LBM via the ring port 30 or the ring port 32. When the transmission source address of the LBM matches the MAC address of the pair node stored in the pair node information storage unit 42, the pair node information reception unit 56 sets the adjacent node set in the Don't care area (data area) of the LBM. The information is stored in the item “pair adjacent node” of the adjacent node information storage unit 40. When the pair node information receiving unit 56 succeeds in storing the adjacent node information, the pair node information receiving unit 56 may transmit an LBR indicating that fact to the pair node.

  The control information transmission / reception unit 46 is a message for notifying the failure of the ring network 102. Specifically, every time an R-APS (SF) message is received, the control information transmission / reception unit 46 transfers the message to the AS port control unit 58. The AS port control unit 58 compares the transmission source of the R-APS (SF) message with the pair node information stored in advance in the pair node information storage unit 42. Specifically, the MAC address set as the source address of the R-APS (SF) message is compared with the MAC address stored in each of the pair node and pair adjacent node of the pair node information storage unit 42.

  When the source node of the R-APS (SF) message matches the pair node, the AS port control unit 58 switches the AS port 34 from the closed state to the open state. The AS port control unit 58 also switches the AS port 34 from the blocked state to the opened state even when the source node of the R-APS (SF) message matches the pair adjacent node. The AS port control unit 58 can also be said to be a switching unit that switches a frame communication state in the AS port 34.

  According to the access sub-ring node of the embodiment, the AS port 34 can be switched even when the pair node fails and the pair node cannot notify the failure. Further, at the time of link-up operation such as when the node is activated, the adjacent node information is exchanged and stored between the pair nodes autonomously. The configuration of the access sub-ring 104 (pair node and adjacent node) can be changed in the operation and maintenance of the communication system 100. However, each time this change is made, information on the adjacent node of the pair node can be set by an external operation such as a maintenance person. It becomes unnecessary. As a result, it is possible to reduce the burden of operation and maintenance of the access sub-ring and realize efficient operation and maintenance.

  The AS port control unit 58 accepts an R-APS (SF) transmitted from one of the two adjacent nodes for the pair node, and accepts an R-APS (SF) transmitted from the other adjacent node. If not, switching the AS port 34 to the open state is suppressed. That is, the closed state of the AS port 34 is maintained. In other words, the AS port control unit 58 performs switching of the AS port 34 on condition that the R-APS (SF) message is received from both of the two adjacent nodes. As a result, when R-APS (SF) is received except for a pair node failure in the access sub-ring 104, switching of the AS port 34 can be suppressed, that is, inappropriate switching of the AS port 34 can be avoided.

The operation of the communication system 100 configured as above will be described.
FIG. 7 is a sequence diagram showing an operation of the communication system 100 of FIG. In the initial state, as shown in FIG. 1, it is assumed that the AS port 34 of the node 16 is set to an open state and the AS port 34 of the node 20 is set to a closed state.

  In parallel with each other, the nodes 22, 18, and 14 autonomously transmit LLDP frames (TTL = 1) indicating their own node information from the ring port 30 and the ring port 32 at the time of link-up. The LLDP frame is autonomously provided to both adjacent nodes (S10, S12, S14, S16). Although not shown, the node 20 also notifies its own node information to both adjacent nodes (node 22, node 18), and the node 16 also notifies its own node information to both adjacent nodes (node 18, node 14).

  The node 20 stores the node information notified from each of the node 22 and the node 18 as adjacent node information, and autonomously transmits the LBM including the adjacent node information to the predetermined node 16 as a pair node (S18). In parallel, the node 16 stores the node information notified from each of the node 18 and the node 14 as adjacent node information, and autonomously transmits the LBM including the adjacent node information as a pair node to the predetermined node 20 ( S20).

  The node 18 stores the adjacent node information transmitted in S18 in association with the node 20, and the node 20 stores the adjacent node information transmitted in S20 in association with the node 16. That is, both nodes automatically set the pair adjacent node information in the pair node information storage unit 42. The node 22, node 18, and node 14 also store adjacent node information notified from adjacent nodes, but these nodes are not access / subring nodes, and therefore do not execute adjacent node information notification to external nodes.

  Here, it is assumed that a failure occurs in the node 16 and the node 16 is in a state where information cannot be transmitted / received to / from an adjacent node, in other words, a state where the R-APS (SF) message cannot be transmitted autonomously (S22). When the node 14 detects a communication failure with the node 16 at the ring port 32, the node 14 switches the ring port 32 to the blocked state and transmits an R-APS (SF) message from the ring port 30 (S24). In parallel, when detecting a communication failure with the node 16 at the ring port 30, the node 18 switches the ring port 30 to the blocked state and transmits an R-APS (SF) message from the ring port 32 (S26). Although not shown in the drawing, the R-APS (SF) message transmitted from the node 14 and the node 18 causes a blockage period in the ring network 102 so far (in FIG. 1, the period from the ring port 32 of the node 10 to the ring port 30 of the node 12). ) Is released.

  The R-APS (SF) message transmitted from the ring port 30 of the node 14 reaches the node 20 via the node 12, the node 10, and the node 22, and the node 20 receives the R-APS (SF) message ( S28). Further, the R-APS (SF) message transmitted from the ring port 32 of the node 18 reaches the adjacent node 20, and the node 20 receives the R-APS (SF) message (S30). The AS port control unit 58 of the node 20 determines whether or not an R-APS (SF) message has been received from both the node 14 and the node 18 that are pair adjacent nodes. When it is detected that the R-APS (SF) message is received from both of the pair adjacent nodes, the AS port 34 of the own node is switched from the blocked state to the opened state (S32).

  The present invention has been described based on the embodiments. This embodiment is an exemplification, and it will be understood by those skilled in the art that various modifications can be made to combinations of the respective constituent elements and processing processes, and such modifications are also within the scope of the present invention. is there.

  In the communication system 100 of the above embodiment, the nodes other than the access / sub-ring node among the plurality of nodes constituting the ring network 102 also hold the adjacent node information in the adjacent node information storage unit 40. In operation and maintenance of the communication system 100, a node that has not configured an access subring until then may be changed to a node that configures an access subring.

  The adjacent node information notification unit 54 of the node whose setting is newly changed to configure the access sub-ring (also referred to as “setting change node A”) inputs an operation for instructing to configure the access sub-ring. May be detected. In this operation, a pair node to be paired in the access sub-ring may be designated and stored in the pair node information storage unit 42. The adjacent node information notifying unit 54 of the setting change node A is notified from the adjacent node in advance when the adjacent node is linked up, and the adjacent node information stored in advance in the adjacent node information storage unit 40 is triggered by the detection of the above operation. You may transmit to the designated pair node.

  In this case, the setting change that designates the setting change node A as a new pair node is also made to the node that is paired with the setting change node A (referred to as “setting change node B”). The adjacent node information notifying unit 54 of the setting change node B detects the above-described setting change operation based on the adjacent node information previously notified from the adjacent node when the adjacent node is linked up and stored in the adjacent node information storage unit 40 in advance. As an opportunity, it may be transmitted to a new pair node (that is, setting change node A). According to this aspect, when the access sub-ring is changed during the operation of the communication system 100, the adjacent node information is autonomously exchanged between the pair nodes. Reduction and efficient operation and maintenance can be realized.

  It should also be understood by those skilled in the art that the functions to be fulfilled by the constituent elements described in the claims are realized by the individual constituent elements shown in the embodiments and the modification examples or by their cooperation.

  30 ring port, 32 ring port, 34 AS port, 42 pair node information storage unit, 54 adjacent node information notification unit, 56 pair node information reception unit, 58 AS port control unit, 100 communication system, 102 ring network, 104 access sub-ring .

Claims (5)

A communication device that forms a ring network together with other relay nodes,
An access subring port, which is a port used in access subring;
An adjacent node information notifying unit that autonomously transmits information of adjacent nodes that are adjacent relay nodes in the ring network to a relay node that is paired in the access sub-ring;
A pair node information storage unit for storing information of the adjacent node transmitted from a relay node paired in the access sub-ring;
When a message notifying the failure of the ring network is received, the access sub-ring port is released if the transmission source of the message matches the adjacent node indicated by the information stored in the pair node information storage unit A switching unit for switching to a state;
A communication apparatus comprising:   When the LLDP (Link Layer Discovery Protocol) frame in which TTL (Time To Live) is set to 1 is received, the adjacent node information notification unit displays information on the transmission source node of the LLDP frame as information on the adjacent node. The communication apparatus according to claim 1, wherein the communication apparatus transmits to the pair of relay nodes.   The adjacent node information notification unit transmits information of the adjacent node to the paired relay node using a loopback message of Ethernet (registered trademark) OAM (Operations, Administration, and Maintenance). The communication device according to claim 1 or 2. The adjacent node information includes information on two adjacent nodes adjacent to the pair of relay nodes in the ring network,
The switching unit receives the message transmitted from one adjacent node of the two adjacent nodes, and if the message transmitted from another adjacent node is not received, the access sub-ring port 4. The communication device according to claim 1, wherein switching to an open state is suppressed. 5. A plurality of relay nodes constituting a ring network are provided,
The plurality of relay nodes include a first relay node and a second relay node that are paired in an access sub-ring,
The first relay node is
A port used in the access sub-ring, and an open access sub-ring port;
An adjacent node information notifying unit that autonomously transmits information on an adjacent node that is an adjacent relay node in the ring network to the second relay node, and
The second relay node is
A blocked access sub-ring port;
A pair node information storage unit for storing information of the adjacent node transmitted from the first relay node;
When a message notifying the failure of the ring network is received, the access sub-ring port is released if the transmission source of the message matches the adjacent node indicated by the information stored in the pair node information storage unit And a switching unit that switches to a state.

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