Network system and relay device

Abstract

To provide a network system and a relay device capable of securing a relay path for a frame even when a double failure occurs.SOLUTION: A first aware node (ASWB), which is one of aware nodes, includes an aware backup port Pb_a connected to a master backup port Pb_m via a backup line 18, and relays fault monitoring frames DFMm, DFMs received at two aware ports Pa1, Pa2, respectively, to the aware backup port Pb_a. When the master backup port Pb_m does not receive both fault monitoring frames DFMm, DFMs, a master node MN changes the master backup port Pb_m, which is in a blocking state BK, into a forwarding state.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a network system and a relay device. [Background technology]

[0002] Patent Document 1 shows a multi-ring network that can perform appropriate path switching even when multiple failures occur, including a failure in a shared link. In detail, the multi-ring network is based on the ERP (Ethernet (registered trademark) Ring Protection) standard and includes a major ring including a shared link, and sub-rings connected in a ring shape to both ends of the shared link. The multi-ring network detects failures in the shared link and failures in links in the major ring other than the shared link, and switches the sub-rings and the major ring based on the detection results. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2013-157682 A Summary of the Invention [Problem to be solved by the invention]

[0004] For example, various ring networks that operate based on various ring protocols, including the ERP standard as shown in Patent Document 1, are known. Such ring networks are basically composed of multiple nodes arranged in a ring shape and links connecting adjacent nodes. In normal operation, the ring network prevents frame loops by providing a blocking point in one of the multiple nodes. On the other hand, when a failure occurs in one of the multiple links, the ring network opens the blocking point, thereby securing a relay path for frames and preventing frame loops.

[0005] However, in such a ring network, if a failure occurs in one of the multiple links, a relay path for the frame can be secured, but if failures occur in two places, i.e., if a double failure occurs, a relay path for the frame cannot be secured. Specifically, two failures create two relay paths that are separated from each other, and a path connecting the two relay paths cannot be secured.

[0006] The present invention has been made in consideration of the above, and one of its objects is to provide a network system and relay device that can ensure a relay path for frames even when double failures occur.

[0007] The above and other objects and novel features of the present invention will become apparent from the description of this specification and the accompanying drawings. [Means for solving the problem]

[0008] Among the inventions disclosed in this application, a brief outline of a representative embodiment will be described as follows.

[0009] A network system according to an embodiment includes a master node, which is a component of a ring network and is composed of one or more relay devices that relay frames and is responsible for managing the ring network, and one or more aware nodes, which are also components of the ring network and are each composed of a relay device. The master node includes a master port and a slave port connected to the ring network, and a backup port for the master. The master node normally controls a control target port, which is either the master port or the slave port, and a backup port for the master to a blocking state, and changes the control target port to a forwarding state when a fault in the ring network is detected. The master node also periodically transmits a first fault monitoring frame from the master port to the slave port, and periodically transmits a second fault monitoring frame from the slave port to the master port. The aware node includes two aware ports connected to the ring network. Here, the first aware node, which is one of the aware nodes, further includes an aware backup port connected to the master backup port via a backup line, and relays the first fault monitoring frame and the second fault monitoring frame received at each of the two aware ports to the aware backup port. When the master backup port does not receive both the first fault monitoring frame and the second fault monitoring frame, the master node changes the master backup port, which is in a blocking state, to a forwarding state. Effect of the Invention

[0010] To briefly explain the effect obtained by a representative embodiment of the invention disclosed in this application, a frame relay path can be secured even in the event of double failures. [Brief description of the drawings]

[0011] [Figure 1] 1 is a schematic diagram illustrating a configuration example of a network system according to a first embodiment. [Figure 2A]2 is a diagram showing an example of a relay route of a user frame in a normal state in the network system shown in FIG. 1; FIG. [Figure 2B] 2 is a diagram showing an example of a relay route of a user frame in a normal state in the network system shown in FIG. 1; FIG. [Diagram 3] 2 is a diagram illustrating an example of a network management operation during normal operation in the network system illustrated in FIG. 1. FIG. [Figure 4] 4 is a diagram illustrating an example of a network management operation during normal times, which is different from that in FIG. 3. FIG. [Figure 5A] 2 is a diagram showing an example of a relay route of a user frame when a double failure occurs in the network system shown in FIG. 1; FIG. [Figure 5B] 2 is a diagram showing an example of a relay route of a user frame when a double failure occurs in the network system shown in FIG. 1; FIG. [Figure 6A] 2 is a schematic diagram illustrating a detailed operation example in the process in which a double failure occurs in the network system shown in FIG. 1. FIG. [Figure 6B] 2 is a schematic diagram illustrating a detailed operation example in the process in which a double failure occurs in the network system shown in FIG. 1. FIG. [Figure 7] 2 is a schematic diagram illustrating a detailed operation example in the process in which a double failure occurs in the network system shown in FIG. 1. FIG. [Figure 8A] 2 is a schematic diagram illustrating a detailed operation example in the process in which a double failure occurs in the network system shown in FIG. 1. FIG. [Figure 8B] 2 is a schematic diagram illustrating a detailed operation example in the process in which a double failure occurs in the network system shown in FIG. 1. FIG. [Figure 9A] 2 is a schematic diagram illustrating a detailed operation example in the process in which a double failure occurs in the network system shown in FIG. 1. FIG. [Figure 9B] 2 is a schematic diagram illustrating a detailed operation example in the process in which a double failure occurs in the network system shown in FIG. 1. FIG. [Figure 10] 2 is a schematic diagram illustrating a detailed operation example in the process of recovery from a double failure in the network system shown in FIG. 1; FIG. [Figure 11] 2 is a schematic diagram illustrating a detailed operation example in the process of recovery from a double failure in the network system shown in FIG. 1; FIG. [Figure 12] 2 is a schematic diagram illustrating a detailed operation example in the process of recovery from a double failure in the network system shown in FIG. 1; FIG. [Figure 13] FIG. 12 is a diagram showing a path of a flush command frame different from that shown in FIG. 11; [Figure 14] 2 is a diagram showing an example of the configuration of a management frame used in the network system shown in FIG. 1; [Figure 15] 10 is a flow chart showing an example of an operation of transmitting a failure monitoring frame by the master node shown in FIG. 1 in the network system according to the second embodiment. [Figure 16] 13 is a diagram for explaining an example of a method of implementing a fault monitoring frame different from that in FIG. 4 in a network system according to a third embodiment. FIG. [Figure 17] FIG. 13 is a schematic diagram illustrating a configuration example of a network system according to a fourth embodiment. [Figure 18A] 18 is a block diagram showing a schematic configuration example of a main part of a relay device constituting a backup aware node in the network system shown in FIG. 17. [Figure 18B] FIG. 18B is a schematic diagram showing an example of the learning contents of the FDB in FIG. 18A. [Figure 19] 18 is a block diagram showing a schematic configuration example of a main part of a relay device constituting a master node in the network system shown in FIG. 17. [Figure 20A] 20 is a flowchart showing an example of processing contents of a main part in the ring control circuit shown in FIG. 19. [Figure 20B] 20 is a flowchart showing an example of processing contents of a main part in the ring control circuit shown in FIG. 19. [Figure 21]FIG. 13 is a schematic diagram showing an example of a method for monitoring a backup path in a network system according to a fifth embodiment. [Figure 22] 22 is a block diagram showing a schematic configuration example of a main part of a relay device constituting a backup aware node in the network system shown in FIG. 21. FIG. [Diagram 23] 22 is a block diagram showing a schematic configuration example of a main part of a relay device constituting a master node in the network system shown in FIG. 21. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. In all the drawings for explaining the embodiment, the same members are generally designated by the same reference numerals, and the repeated description will be omitted.

[0013] (First embodiment) <Network system configuration> Fig. 1 is a schematic diagram showing a configuration example of a network system according to a first embodiment. The network system shown in Fig. 1 has a master node MN, which is a component of a ring network 15, and one or more aware nodes AN, which are also components of the ring network 15, in this example five aware nodes AN. The master node MN is composed of one or more relay devices that relay frames, and is responsible for managing the ring network 15.

[0014] In this example, the master node MN is configured with two relay devices, a master switch MSW and a slave switch SSW, in other words, a master relay device and a slave relay device. Such a configuration is called a distributed master configuration. However, the master node MN may be configured with one relay device, that is, a switch for the master node. Such a configuration is called a single master configuration.

[0015] The master switch MSW and the slave switch SSW are connected via a normal port and a communication line 16. Unlike the case where a single master configuration is used, the distributed master configuration can achieve load balancing and redundancy in the event of a device failure. In the following, unless there is a particular need, the distributed master configuration and the single master configuration will not be distinguished from each other in the explanation.

[0016] The master node MN includes a master port Pm and a slave port Ps connected to the ring network 15, and an upper port Pul connected to the upper link 10. In addition, the master node MN includes a backup port Pb_m for the master. In detail, the master port Pm is provided in the master switch MSW, and the slave port Ps is provided in the slave switch SSW. In this example, the backup port Pb_m for the master is provided in the master switch MSW, but may be provided in the slave switch SSW.

[0017] In this way, by providing the master port Pm and the slave port Ps, two virtual networks, that is, a master VLAN (Virtual Local Area Network) and a slave VLAN, can be constructed on the ring network 15. Communication on the ring network 15 is performed using the master VLAN or the slave VLAN.

[0018] Under normal circumstances, the master node MN controls the controlled port, either the master port Pm or the slave port Ps, in this example the slave port Ps, for the master VLAN, to the blocking state BK(M), and controls the other port, i.e. the master port Pm, to the forwarding state FW(M). On the other hand, the master node MN controls the controlled port, either the master port Pm or the slave port Ps, in this example the master port Pm, for the slave VLAN, to the blocking state BK(S), and controls the other port, i.e. the slave port Ps, to the forwarding state FW(S).

[0019] Furthermore, under normal circumstances, the master node MN controls the backup port Pb_m to the blocking state BK(M), BK(S) for the master VLAN and the slave VLAN. In this specification, when describing either the master VLAN or the slave VLAN, the forwarding state FW(M), FW(S) is simply called the forwarding state FW, and the blocking state BK(M), BK(S) is simply called the blocking state BK. The forwarding state FW is a state in which frame relay is permitted, and the blocking state BK is a state in which frame relay is prohibited.

[0020] In this example, the upper port Pul is provided in each of the master switch MSW and the slave switch SSW. The upper port Pul is connected to the upper link 10 via a communication circuit 17 that is not included in the ring network 15. For example, the ring network 15 is an in-house network that relays Layer 2 (L2), and the upper link 10 is the Internet that relays Layer 3 (L3).

[0021] In the distributed master configuration, communication with the upper link 10 is distributed between the master switch MSW and the slave switch SSW. This distributes the processing load. Furthermore, even if a failure occurs in either the master switch MSW or the slave switch SSW, a relay path to the upper link 10 can be secured by the other switch.

[0022] Each of the five aware nodes AN is composed of five relay devices, ie, aware switches ASW1 to ASW4, and ASWB. Each of the aware switches ASW1 to ASW4, and ASWB has two aware ports Pa1 and Pa2 connected to the ring network 15, and a user port Pu connected to a user terminal. Although not shown in the figure, the user port Pu may also be provided in the master switch MSW and the slave switch SSW. In this example, user terminals TM1 to TM4, and TMb having MAC (Media Access Control) addresses MA1 to MA4, and MAb are connected to the user ports Pu of the aware switches ASW1 to ASW4, and ASWB, respectively.

[0023] The aware port Pa1 is a port connected to the master port Pm, and the aware port Pa2 is a port connected to the slave port Ps. The aware ports Pa1 and Pa2 are also ring ports connected to the ring network 15 together with the master port Pm and the slave port Ps.

[0024] Here, the awareness switch with backup (first awareness switch) ASWB, which is one of the awareness switches, is different from the awareness switches ASW1 to ASW4 in that it further includes an awareness backup port Pb_a. The awareness backup port Pb_a is connected to the master backup port Pb_m in the master node MN via a backup line 18.

[0025] The relay paths on the ring network 15 are divided into a master side relay path 20 and a slave side relay path 21, with the backup aware switch ASWB as the boundary. The master side relay path 20 is a path from the master port Pm to the aware port Pa1 of the backup aware switch ASWB. The slave side relay path 21 is a path from the slave port Ps to the aware port Pa2 of the backup aware switch ASWB.

[0026] The master side relay path 20 is provided with one or more aware nodes AN according to the scale of the network, for example, two aware switches ASW1 and ASW2 in this example. Similarly, the slave side relay path 21 is provided with one or more aware nodes AN according to the scale of the network, for example, two aware switches ASW3 and ASW4 in this example.

[0027] <Outline of network system operation> Figures 2A and 2B are diagrams showing an example of a relay path of a user frame in a normal state in the network system shown in Figure 1. Figure 2A shows a relay path 25 of a user frame when a master VLAN is used in a ring network 15. A user frame is a normal frame transmitted from a user terminal or the like. Meanwhile, in addition to user frames, management frames for network management are also transmitted on the ring network 15.

[0028] Generally, user frames are relayed based on a Forwarding Database (FDB), whereas management frames are relayed without using the FDB. When a frame is received, the FDB learns the correspondence between the identifier of the port that received the frame and the source MAC address contained in the frame. When relaying a frame, the destination port is determined by searching the FDB using the destination MAC address contained in the received frame.

[0029] 2A, for example, a user frame from each of the user terminals TM1 to TM4, TMb, which is tagged with a master VLAN, is relayed along a relay path 25. As an example, a user frame from the user terminal TMb to the upper link 10 is relayed to the master port Pm in the forwarding state FW(M) via the awareness switches ASWB, ASW2, and ASW1 in this order. The master switch MSW relays the user frame received at the master port Pm to the upper port Pul.

[0030] 2B shows a relay path 26 of a user frame when a slave VLAN is used in the ring network 15. For example, a user frame tagged with a slave VLAN from each of the user terminals TM1 to TM4, TMb is relayed along the relay path 26. As an example, a user frame from the user terminal TMb to the upper link 10 is relayed to the slave port Ps in the forwarding state FW(S) via the awareness switches ASWB, ASW3, and ASW4 in this order. The slave switch SSW relays the user frame received at the slave port Ps to the upper port Pul.

[0031] Fig. 3 is a diagram for explaining an example of a network management operation under normal circumstances in the network system shown in Fig. 1. In a general ring protocol, the master node MN periodically transmits a hello frame, in other words, a continuity monitoring frame, for monitoring the presence or absence of a fault in the ring network 15 from either the master port Pm or the slave port Ps to the other. In the example of Fig. 3, the master node MN transmits a hello frame (first continuity monitoring frame) HLOm from the master port Pm to the slave port Ps at a predetermined transmission interval. The master node MN also transmits a hello frame (second continuity monitoring frame) HLOs from the slave port Ps to the master port Pm at a predetermined transmission interval.

[0032] For example, under normal circumstances, when the master node MN does not receive a hello frame HLOm at the slave port Ps within a predetermined hello time, or when the master port Pm does not receive a hello frame HLOs within a predetermined hello time, it determines that a failure has occurred in the ring network 15. That is, the master node MN detects that a failure has occurred in at least one location in the ring network 15. In this case, the master node MN changes the controlled port in the blocking state BK(M), in this example, the slave port Ps, to the forwarding state FW(M).

[0033] On the other hand, when a fault occurs, if the master node MN receives a hello frame HLOm at the slave port Ps within a predetermined hello time and receives a hello frame HLOs at the master port Pm within a predetermined hello time, it determines that the fault in the ring network 15 has been restored. In this case, the master node MN returns the controlled port that has been changed to the forwarding state FW(M), in this example, the slave port Ps, to the blocking state BK(M).

[0034] The master node MN may determine the presence or absence of a fault in the ring network 15 based on fault notification frames, not limited to these hello frames HLOm and HLOs. As an example, when an aware node AN detects a fault in one of the links connected to the node based on the ring protocol, it transmits a fault notification frame to the other link. The master node MN detects a fault in the ring network 15 by receiving the fault notification frame at the master port Pm or the slave port Ps.

[0035] In one embodiment, the master node MN uses hello frames HLOm, HLOs and a fault notification frame from the aware node AN, specifically, a link down notification frame described later, when detecting a fault in the ring network 15. Specifically, the master node MN determines that a fault has occurred when it does not receive hello frames HLOm, HLOs or receives a fault notification frame. On the other hand, the master node MN uses hello frames HLOm, HLOs or a link up notification frame, which is the opposite of a link down notification frame, when detecting recovery from a fault.

[0036] Fig. 4 is a diagram for explaining an example of a network management operation in normal times, which is different from Fig. 3. In Fig. 4, the master node MN, more specifically, the master switch MSW, periodically transmits a master-side fault monitoring frame (first fault monitoring frame) DFMm via the master-side relay path 20 in the direction from the master port Pm to the slave port Ps.

[0037] Similarly, the master node MN, more specifically, the slave switch SSW, periodically transmits a slave-side fault monitoring frame (second fault monitoring frame) DFMs in the direction from the slave port Ps to the master port Pm via the slave-side relay path 21. Each fault monitoring frame DFMm, DFMs is a management frame. The master node MN regularly transmits each fault monitoring frame DFMm, DFMs, for example, at a preset transmission interval.

[0038] The aware switches ASW1 and ASW2 relay the master side failure monitoring frame DFMm received at one awareness port Pa1 to the other awareness port Pa2. The aware switches ASW4 and ASW3 relay the slave side failure monitoring frame DFMs received at one awareness port Pa2 to the other awareness port Pa1. Meanwhile, the aware switch with backup ASWB relays the master side failure monitoring frame DFMm received at awareness port Pa1 and the slave side failure monitoring frame DFMs received at awareness port Pa2 to the awareness backup port Pb_a.

[0039] The master node MN monitors whether or not each of the fault monitoring frames DFMm, DFMs is received at the master backup port Pb_m. That is, the master node MN monitors whether or not there is a fault in the master side relay path 20 using the master side fault monitoring frame DFMm, and monitors whether or not there is a fault in the slave side relay path 21 using the slave side fault monitoring frame DFMs. In this way, the fault monitoring frames DFMm, DFMs function as double fault monitoring frames. A double fault refers to a situation in which one fault occurs in each of the master side relay path 20 and the slave side relay path 21.

[0040] When the master node MN does not receive both the master side fault monitoring frame DFMm and the slave side fault monitoring frame DFMs at the master backup port Pb_m, it determines that a double fault has occurred and changes the master backup port Pb_m, which is in the blocking state BK, to the forwarding state FW. In detail, when the master node MN does not receive each of the fault monitoring frames DFMm, DFMs at the backup port Pb_m within a predetermined DFM time from the time of transmission, it changes the backup port Pb_m to the forwarding state FW.

[0041] Figures 5A and 5B are diagrams showing an example of a relay path of a user frame when a double failure occurs in the network system shown in Figure 1. Figure 5A shows a relay path 30 of a user frame when a master VLAN is used in a ring network 15. In Figure 5A, unlike the case of Figure 2A, a failure 28a occurs in the link between the two aware switches ASW1 and ASW2 in the master side relay path 20, and a failure 28b occurs in the link between the two aware switches ASW3 and ASW4 in the slave side relay path 21.

[0042] Accordingly, in Fig. 5A, unlike Fig. 2A, the master backup port Pb_m is changed to the forwarding state FW(M). Furthermore, as described in Fig. 3, the slave port Ps is changed to the forwarding state FW(M) when one of the failures 28a, 28b is detected using the hello frames HLOm, HLOs or a failure notification frame.

[0043] 5A, the master backup port Pb_m is controlled to the forwarding state FW(M), so that the relay path 30 for the user frame can be secured even in the event of a double failure. Specifically, if the backup ports Pb_m and Pb_a are not provided, the user terminal TMb cannot communicate with the user terminals TM1 and TM4, for example. On the other hand, by providing the backup ports Pb_m and Pb_a and appropriately controlling the master backup port Pb_m, the user terminal TMb can communicate with the user terminals TM1 and TM4 via the backup line 18.

[0044] Fig. 5B shows a relay path 31 of a user frame when a slave VLAN is used in the ring network 15. In Fig. 5B, a double failure consisting of two failures 28a and 28b occurs, as in Fig. 5A. Accordingly, in Fig. 5B, unlike Fig. 2B, the master backup port Pb_m is changed to the forwarding state FW(S), and the master port Pm is also changed to the forwarding state FW(S).

[0045] As a result, similarly to the case of Fig. 5A, even if a double failure occurs, the relay path 31 of the user frame can be secured. That is, two relay paths that are separated from each other are formed due to a double failure, but a path that connects the two relay paths can be formed by the backup line 18. Note that the relay paths 30, 31 shown in Fig. 5A and Fig. 5B are paths that do not form loops.

[0046] <Details of network system operation> [Operation when a failure occurs] Figures 6A, 6B, 7, 8A, 8B, 9A, and 9B are schematic diagrams for explaining a detailed operation example in the process in which a double failure occurs in the network system shown in Figure 1. First, in Figure 6A, a failure 28a occurs in the link between adjacent aware switches ASW1 and ASW2 in the master side relay path 20 described above.

[0047] When the aware switch ASW1 detects a failure 28a in one aware port Pa2, it transmits a link down notification frame LD from the other aware port Pa1 (step S101a). Similarly, when the aware switch ASW2 detects a failure 28a in one aware port Pa1, it transmits a link down notification frame LD from the other aware port Pa2 (step S101b). The link down notification frame LD is both a management frame and a failure notification frame. The aware switches ASW1 and ASW2 detect the failure 28a, i.e., link down, in the aware ports Pa1 and Pa2 by, for example, monitoring the intensity of an optical signal.

[0048] The link down notification frame LD from the aware switch ASW1 is transmitted to the master node MN, specifically the master switch MSW. On the other hand, the link down notification frame LD from the aware switch ASW2 is relayed by the aware switches ASWB, ASW3, and ASW4 until it reaches the master node MN, specifically the slave switch SSW.

[0049] Here, the aware switches ASW1 and ASW2 that have detected the failure 28a execute FDB flushing on their own FDBs (step S102). Furthermore, the aware switches ASWB, ASW3, and ASW4, the master switch MSW, and the slave switch SSW that have received the link-down notification frame LD also execute FDB flushing on their own FDBs (step S102). The FDB flush erases the learning contents of the FDB. At this time, the learning contents associated with the user port Pu may be excluded from the deletion target.

[0050] Furthermore, the master node MN that has received the link down notification frame LD changes the controlled port in the blocking state BK, in this example the slave port Ps, to the forwarding state FW (step S103). This forms a relay path 35 for user frames as shown in FIG. 6B. Note that the master node MN also changes the controlled port to the forwarding state FW if it does not receive the hello frames HLOm, HLOs as shown in FIG. 3 within a predetermined hello time from the time of transmission. However, the master node MN normally receives the link down notification frame LD before the hello frame times out.

[0051] On the other hand, as described in Fig. 4, the master node MN periodically transmits the fault monitoring frames DFMm and DFMs. When a fault 28a occurs, as shown in Fig. 7, the master node MN receives the slave side fault monitoring frame DFMs at the master backup port Pb_m, but stops receiving the master side fault monitoring frame DFMm (step S104). In this case, the master node MN determines that there is not a double fault, but a fault only in the master side relay path 20, and keeps the master backup port Pb_m in the blocking state BK.

[0052] 8A, a failure 28b occurs in the link between the adjacent aware switches ASW3 and ASW4 also in the slave-side relay path 21. As a result, similar to the case of FIG 6A, the aware switch ASW3 transmits a link down notification frame LD from the aware port Pa1 (step S105a), and the aware switch ASW4 also transmits a link down notification frame LD from the aware port Pa2 (step S105b).

[0053] Also, in Fig. 8A, similarly to the case of Fig. 6A, the aware switches ASW2, ASWB, ASW3, ASW4 and the slave switch SSW execute FDB flush in response to the link down notification frame LD (step S106). Furthermore, the master node MN stops receiving both the fault monitoring frames DFMm and DFMs due to the faults 28a and 28b. The master node MN counts the time during which the frames are not received using the DFM timer (step S107). At this stage, as shown in Fig. 8B, relay paths 36a and 36b of user frames separated from each other are formed.

[0054] Thereafter, the master node MN detects a timeout of the DFM timer and determines that a double failure has occurred. In response to this, the master node MN changes the backup port Pb_m for the master, which is in a blocking state BK, to a forwarding state FW (step S108), as shown in Fig. 9A. Furthermore, the master node MN executes an FDB flush for the FDB of its own node (step S109). As a result, as shown in Fig. 9B, a relay path 30 for user frames including the backup line 18 is formed, as described in Fig. 5A.

[0055] Here, the operation has been described in the case where a failure 28a occurs first in the master side relay path 20, and thereafter a failure 28b occurs in the slave side relay path 21. On the other hand, the operation is similar in the case where a failure 28b occurs first in the slave side relay path 21, and thereafter a failure 28a occurs in the master side relay path 20. However, when a failure 28b occurs first in the slave side relay path 21, the FDB flush (step S109) in the master switch MSW shown in Fig. 9A may be omitted.

[0056] [Operation when recovering from a failure] Figures 10, 11 and 12 are schematic diagrams for explaining a detailed operation example in the process of recovery from a double failure in the network system shown in Figure 1. First, in Figure 10, the failure 28a in the master side relay path 20 shown in Figure 9A etc. is recovered. As a result, the master node MN receives at least one of the two failure monitoring frames DFMm, DFMs, here the master side failure monitoring frame DFMm, at the master backup port Pb_m.

[0057] In response to this, the master node MN determines that the dual failure has been recovered from, and changes the master backup port Pb_m, which is in the forwarding state FW, to the blocking state BK (step S201). Furthermore, the master node MN executes an FDB flush for the FDB of the own node (step S202). At this time, the master node MN may erase only the learning contents associated with the master backup port Pb_m from the FDB.

[0058] Next, the master node MN changes the backup port Pb_m to the blocking state BK in response to recovery from the failure 28a in the master side relay path 20, and therefore transmits a flush command frame FSH from the master port Pm to the master side relay path 20 as shown in Fig. 11 (step S203). The flush command frame FSH is a management frame for requesting the aware node AN to erase the learning contents of the FDB.

[0059] Each of the aware switches ASW1, ASW2, and ASWB sequentially relays the flush command frame FSH to the aware switch ASW3 that has detected the failure 28b. Then, each of the aware switches ASW1, ASW2, ASWB, and ASW3 executes an FDB flush for its own FDB in response to the flush command frame FSH (step S204).

[0060] As a result, a relay path 38 of the user frame that does not include the backup line 18 is formed as shown in Fig. 12. After that, although not shown, the master node MN detects, for example, recovery from the failure 28b based on a general ring protocol, and when recovery from the failure 28b is detected, changes the slave port Ps in the forwarding state FW to the blocking state BK.

[0061] In detail, the master node MN determines whether or not it has recovered from the failure 28b, for example, depending on whether or not it has received the hello frames HLOm, HLOs shown in Fig. 3 within a predetermined hello time from the time of transmission. However, without being limited to this, the master node MN may use a link up notification frame or the like, which is the opposite of the link down notification frame LD shown in Fig. 6A, and determine whether or not it has recovered from the failure 28b depending on whether or not it has received the link up notification frame.

[0062] Here, the operation when the failure 28a in the master side relay path 20 is recovered first has been described. On the other hand, the operation when the failure 28b in the slave side relay path 21 is recovered first is almost the same. However, in this case, the master node MN changes the backup port Pb_m to the forwarding state FW in response to the recovery from the failure 28b in the slave side relay path 21, and therefore transmits a flush command frame using a path different from that in FIG. 11, as shown in FIG. 13.

[0063] Fig. 13 is a diagram showing a route of a flush command frame different from that shown in Fig. 11. As shown in Fig. 13, when the failure 28b is recovered first in the slave side relay route 21, the master node MN transmits a flush command frame FSHa from the master backup port Pb_m. As a result, the flush command frame FSHa is transmitted to the aware switches ASWB, ASW3, and ASW4, and the FDB flush is executed in the aware switches (step S204).

[0064] That is, when the master node MN receives the master side fault monitoring frame DFMm at the master backup port Pb_m but does not receive the slave side fault monitoring frame DFMs, it transmits the flush command frame FSH from the master port Pm as shown in Fig. 11. On the other hand, when the master node MN receives the slave side fault monitoring frame DFMs at the master backup port Pb_m but does not receive the master side fault monitoring frame DFMm, it transmits the flush command frame FSHa from the master backup port Pb_a as shown in Fig. 13.

[0065] [Management Frame Configuration] Fig. 14 is a diagram showing an example of the configuration of management frames used in the network system shown in Fig. 1. Fig. 14 shows examples of the configuration of the above-mentioned hello frames HLOm, HLOs, flush command frame FSH, link down notification frame LD, and fault monitoring frames DFMm, DFMs as management frames. Note that the backup monitoring frames BUM1, BUM2 shown in Fig. 14 will be described in the fifth embodiment.

[0066] The management frame has a header section and a data section. The header section includes a destination MAC address (DA) 40, a source MAC address (SA) 41, a VLAN ID 42, and an Ethertype 43. The data section includes a ring protocol message 45. The ring protocol message 45 includes a type 45a, a message 45b, and a port type 45c.

[0067] In the header section, the destination MAC address 40 is determined to be one of the MAC addresses assigned to the master port Pm, the slave port Ps, the master backup port Pb_m, or the aware backup port Pb_a. Similarly, the source MAC address 41 is determined to be any other of the MAC addresses described above. In this way, in the management frame, unlike the user frame, the MAC address can be determined on a port-by-port basis, not on a device-by-device basis.

[0068] Here, as one of the flush command frames FSH, as shown in FIG. 13, a flush command frame FSHa is shown in which the master backup port Pb_m is set as the source MAC address 41 and the slave port Ps is set as the destination MAC address 40. However, as described above, when the master backup port Pb_m is provided in the slave switch SSW, the destination MAC address 40 is changed to the master port Pm. In the VLAN ID 42, for example, a value assigned to the master VLAN or slave VLAN described above for management purposes is stored. In the Ether type 43, a value identifying the type of ring protocol, in this example, "0x8820", is stored.

[0069] Meanwhile, in the ring protocol message 45 in the data section, the type 45a and the message 45b store values ​​that identify the type of management frame. In this example, a management frame whose type 45a is "0x00" or "0x02" is a hello frame HLOm, HLOs. A management frame whose type 45a is "0x01" is a flush command frame FSH or a link down notification frame LD. The flush command frame FSH and the link down notification frame LD are distinguished by whether the value of the message 45b is "0x00" or "0x01". Also, a management frame whose type 45a is "0x03" is a fault monitoring frame DFMm, DFMs.

[0070] The port type 45c stores a value that identifies the port from which the management frame is transmitted. In detail, the port type 45c stores values ​​that identify the master port Pm, the slave port Ps, the aware ports Pa1 and Pa2, and the backup ports Pb_m and Pb_a.

[0071] In such a configuration, for example, whether a fault monitoring frame is DFMm or DFMs can be identified mainly by the value of the Ethertype 43 and the value of the type 45a. Furthermore, whether a fault monitoring frame is a master side DFMm or a slave side DFMs can be identified by the destination MAC address 40 and the source MAC address 41, or the value of the port type 45c, or a combination of these.

[0072] 14, there are four types of hello frames, specifically, depending on whether the source is in a blocking state BK or a forwarding state FW, and whether the source is a master port Pm or a slave port Ps. The hello frames with type 45a of "0x00" are hello frames HLO_B1 and HLO_B2 transmitted from a port in a blocking state BK. The hello frame HLO_B1 is transmitted from a slave port Ps in a blocking state BK, and the hello frame HLO_B2 is transmitted from a master port Pm in a blocking state BK.

[0073] On the other hand, the hello frames whose type 45a is "0x02" are hello frames HLO_F1 and HLO_F2 transmitted from a port in the forwarding state FW. The hello frame HLO_F1 is transmitted from a slave port Ps in the forwarding state FW, and the hello frame HLO_F2 is transmitted from a master port Pm in the forwarding state FW. The hello frame HLOm shown in FIG. 3 corresponds to the hello frame HLO_B2 or the hello frame HLO_F2 in FIG. 14. Also, the hello frame HLOs shown in FIG. 3 corresponds to the hello frame HLO_B1 or the hello frame HLO_F1 in FIG. 14.

[0074] <Main Effects of the First Embodiment> As described above, in the method of the first embodiment, a backup port is provided in each of the master node MN and the aware node with backup, which is one of the aware nodes AN, and the backup ports are connected by a backup line. This makes it possible to ensure a relay path for user frames via the backup line even in the event of a double failure. As a result, the availability of the network system is improved.

[0075] In addition, since there is no need to make any particularly complicated changes to an existing general ring network, the availability of the network system can be improved easily or at low cost. Furthermore, the master node MN transmits a fault monitoring frame from each of the master port and the slave port, and the aware node with backup relays the fault monitoring frame to the backup port, thereby making it possible to monitor whether or not there is a double fault.

[0076] (Second embodiment) <Fault monitoring frame transmission operation by the master node> Fig. 15 is a flow diagram showing an example of a transmission operation of a fault monitoring frame by the master node shown in Fig. 1 in a network system according to the second embodiment. In the first embodiment, the master node MN regularly transmits fault monitoring frames DFMm and DFMs periodically. However, since the fault monitoring frames DFMm and DFMs are frames for monitoring double faults as described in the first embodiment, they can also be transmitted periodically only during the necessary period as shown in Fig. 15.

[0077] 15, the master node MN monitors the presence or absence of a fault in the ring network 15 based on a general ring protocol (step S301). Then, the master node MN waits for detection of a fault in the ring network 15 (step S302). Here, when the master node MN detects a fault in the ring network 15 (step S302: Yes), it starts periodic transmission of fault monitoring frames DFMm, DFMs (step S303).

[0078] As a result, for example, after the occurrence of a failure 28a as shown in Fig. 6A, the transmission of failure monitoring frames DFMm, DFMs is started. In detail, in step S302, the master node MN detects a failure in the ring network 15, for example, at the time when the link down notification frame LD shown in Fig. 6A is received or at the time when the hello frames HLOm, HLOs shown in Fig. 3 time out.

[0079] Thereafter, the master node MN waits for recovery from the failure in the ring network 15 (step S304). Here, when the master node MN detects recovery from the failure in the ring network 15 (step S304: Yes), it stops the periodic transmission of the failure monitoring frames DFMm, DFMs (step S305). As a result, for example, when the failure 28b shown in Fig. 12 is recovered from, the transmission of the failure monitoring frames DFMm, DFMs stops. In detail, in step S304, the master node MN detects recovery from the failure in the ring network 15, for example, at the time when the hello frames HLOm, HLOs shown in Fig. 5 are received.

[0080] <Main Effects of the Second Embodiment> As described above, by using the method of the second embodiment, it is possible to obtain the same effects as those described in the first embodiment. Furthermore, unlike the method of the first embodiment, since the fault monitoring frame can be transmitted only during the necessary period, the communication load in the ring network 15 can be reduced.

[0081] (Third embodiment) <How to implement a fault monitoring frame> Fig. 16 is a diagram for explaining an example of a method of implementing a fault monitoring frame different from that in Fig. 4 in a network system according to the third embodiment. In Fig. 16, the master node MN periodically transmits a hello frame (first continuity monitoring frame) HLOm and a hello frame (second continuity monitoring frame) HLOs from the master port Pm and the slave port Ps, respectively, in the same manner as in Fig. 3. The fault monitoring frames DFMm, DFMs shown in Fig. 4 may be implemented using such hello frames HLOm, HLOs.

[0082] 16, the aware switch with backup ASWB copies the hello frames HLOs and HLOm received at the aware ports Pa1 and Pa2. Then, the aware switch with backup ASWB relays the copied hello frames HLOm and HLOs to the aware backup port Pb_a as fault monitoring frames DFMm and DFMs, respectively.

[0083] However, depending on the ring protocol, the hello frames HLOs, HLOm are not always transmitted for the period required to monitor for double faults. For example, in FIG. 1 and the like described above, when a fault occurs in one of the two upper ports Pul, it may be necessary to change the controlled port in the blocking state BK to the forwarding state FW in order to form a relay path using the other upper port. One method for this is to forcibly stop the transmission of hello frames. In this way, when it is not always possible to monitor for double faults using the hello frames HLOm, HLOs, it is advisable to provide fault monitoring frames DFMm, DFMs independent of the hello frames HLOm, HLOs, as in the method of the first embodiment.

[0084] <Main Effects of the Third Embodiment> As described above, by using the method of the third embodiment, it is possible to obtain the same effects as those described in the first embodiment. Furthermore, unlike the method of the first embodiment, since the fault monitoring frame is implemented using a hello frame, the number of types of management frames does not increase, and implementation may be easier.

[0085] (Fourth embodiment) <Network system configuration> Fig. 17 is a schematic diagram showing a configuration example of a network system according to the fourth embodiment. The network system shown in Fig. 17 is a single-master configuration applied, unlike the distributed master configuration network system shown in Fig. 1. Accordingly, the master node MN is configured with one master node switch MNSW, in other words, one master node relay device, unlike the case of Fig. 1.

[0086] The master node switch MNSW has a master port Pm, a slave port Ps, an upper port Pul, and a backup port Pb_m for the master, similar to the case of Fig. 1. However, in this example, unlike the case of Fig. 1, one upper port Pul is provided. The operation of the master node switch MNSW is similar to the operation of the master node MN described in the first embodiment.

[0087] <Repeater details> Fig. 18A is a block diagram showing a schematic configuration example of a main part of a relay device constituting an aware node with backup in the network system shown in Fig. 17. Fig. 18B is a schematic diagram showing an example of the learning contents of the FDB in Fig. 18A. The aware node with backup AN shown in Fig. 18A, in other words, the aware switch with backup ASWB which is a relay device, includes two aware ports Pa1 and Pa2 which are also ring ports, n user ports Pu[1]-Pu[n], and an aware backup port Pb_a.

[0088] 17, two aware ports Pa1 and Pa2 are connected to a ring network 15. User terminals are connected to n user ports Pu[1]-Pu[n] as appropriate. The aware backup port Pb_a is connected to the master backup port Pb_m via a backup line 18.

[0089] 18A includes an interface circuit 50, a frame processing circuit 51, an FDB 52, a processor 53, and a memory 54. The interface circuit 50 includes a link-down monitoring circuit 55, and serves as an interface between a plurality of ports (Pa1, Pa2, Pu[1]-Pu[n], Pb_a) and the frame processing circuit 51 or the processor 53. The link-down monitoring circuit 55 detects a link-down by, for example, monitoring the strength of optical signals at a plurality of ports.

[0090] Furthermore, when the interface circuit 50 receives a frame at any one of the multiple ports, it adds an identifier of the receiving port (called a receiving port ID) to the frame and transmits it to the frame processing circuit 51 or the processor 53. Furthermore, the interface circuit 50 transmits the frame from the frame processing circuit 51 or the processor 53 to any one of the multiple ports based on the destination port ID added to the frame.

[0091] The frame processing circuit 51 includes an FDB processing circuit 57 and a ring control circuit 58. The FDB processing circuit 57 learns and searches the FDB 52 for user frames. Specifically, when learning the FDB 52, when the FDB processing circuit 57 receives a user frame, it learns in the FDB 52 the source MAC address, and more specifically, the VLAN ID, contained in the frame in association with the receiving port ID added to the frame.

[0092] When searching the FDB, the FDB processing circuit 57 searches the FDB 52 using the destination MAC address included in the received user frame as a search key, and obtains the corresponding port ID, i.e., the port ID of the hit entry. The FDB processing circuit 57 then adds the obtained port ID to the user frame as the destination port ID, and transmits it to the interface circuit 50.

[0093] FIG. 18B shows an example of the learning contents of the FDB 52, taking the network system shown in FIG. 17 as an example. In the FDB 52, the correspondence between the MAC address, the VLAN ID, and the port ID is learned for each entry. For example, the combination of the MAC addresses MA1 and MA2 and the master VLAN identifier "VIDm" is associated with the port ID {Pa1} of the aware port Pa1. The combination of the MAC addresses MA3 and MA4 and "VIDm" is associated with the port ID {Pa2} of the aware port Pa2. On the other hand, the combination of the MAC address MAb and "VIDm" is associated with the port ID {Pu[1]} of the user port Pu[1].

[0094] The ring control circuit 58 includes a fault monitoring frame relay circuit 61 in addition to a protocol control circuit 60 that performs control based on a predetermined ring protocol. The protocol control circuit 60 includes, for example, a link down notification circuit 65 and a flush execution circuit 66. When a link down is detected by the link down monitoring circuit 55, the link down notification circuit 65 transmits a link down notification frame LD as shown in Fig. 6A. The flush execution circuit 66 executes an FDB flush in response to the link down notification frame LD as shown in Fig. 6A, or an FDB flush in response to a flush command frame FSH as shown in Fig. 11.

[0095] As shown in Fig. 3 etc., the fault monitoring frame relay circuit 61 detects fault monitoring frames DFMm, DFMs from various frames received at the aware ports Pa1, P2, and relays the fault monitoring frames DFMm, DFMs to the aware backup port Pb_a. The detection of the fault monitoring frames DFMm, DFMs is performed based on various information within the frames, as described in Fig. 14.

[0096] The processor 53 manages and controls the entire relay device by executing programs stored in the memory 54. As one example, the processor 53 may perform control based on a predetermined ring protocol in cooperation with the protocol control circuit 60 based on a control program for a ring protocol stored in the memory 54.

[0097] The interface circuit 50 is realized, for example, by an ASIC (Application Specific Integrated Circuit). The frame processing circuit 51 is realized, for example, by an FPGA (Field Programmable Gate Array) or an ASIC. The FDB 52 is implemented, for example, in a CAM (Content Addressable Memory). The memory 54 is configured by a combination of a volatile memory and a non-volatile memory. However, the specific implementation form of each part is not limited to this, and may be hardware, software, or a combination of these.

[0098] Fig. 19 is a block diagram showing a schematic configuration example of a main part of a relay device constituting a master node in the network system shown in Fig. 17. The master node MN shown in Fig. 19, in other words, the master node switch MNSW which is a relay device for the master node, includes a master port Pm and a slave port Ps which are also ring ports, an upper port Pul, and a backup port Pb_m for the master.

[0099] 17, the master port Pm and the slave port Ps are connected to a ring network 15. The upper port Pul is connected to the upper link 10 via a communication circuit 17 that is not included in the ring network 15. The backup port Pb_m for the master is connected to the backup port Pb_a for the awareness via a backup line 18.

[0100] Moreover, the master node switch MNSW shown in Fig. 19 includes an interface circuit 70, a frame processing circuit 71, an FDB 72, a processor 73, and a memory 74. The interface circuit 70 includes a link down monitoring circuit 75, and operates in the same manner as the interface circuit 50 shown in Fig. 18A. Moreover, the FDB 72, the processor 73, and the memory 74 are also the same as the FDB 52, the processor 53, and the memory 54 shown in Fig. 18A.

[0101] The frame processing circuit 71 includes an FDB processing circuit 77 similar to that in Fig. 18A, and a ring control circuit 78 different from that in Fig. 18A. The ring control circuit 78 includes a protocol control circuit 80 that performs control based on a predetermined ring protocol, as well as a fault monitoring frame transmitting circuit 81, a fault monitoring frame receiving circuit 82, and a backup port control circuit 83.

[0102] The protocol control circuit 80 includes a ring port control circuit 85, a flush execution circuit 86, a hello frame transmission circuit 88, and a flush command transmission circuit 87. The ring port control circuit 85 controls the states of the master port Pm and the slave port Ps. In detail, the ring port control circuit 85 normally controls a controlled port, which is either the master port Pm or the slave port Ps, to a blocking state BK.

[0103] Furthermore, when the ring port control circuit 85 detects a failure in the ring network 15, it changes the controlled port from the blocking state BK to the forwarding state FW. Furthermore, after changing the controlled port to the forwarding state FW, when the ring port control circuit 85 detects recovery from the failure in the ring network 15, it changes the controlled port from the forwarding state FW to the blocking state BK.

[0104] 6A, the flush execution circuit 86 erases the learning contents of the FDB 72 when a link down notification frame LD is received, or when the state of the controlled port is changed by the ring port control circuit 85. In addition, the flush execution circuit 86 also erases the learning contents of the FDB 72 when the master backup port Pb_m is changed to the forwarding state FW or to the blocking state BK, as shown in FIGS.

[0105] The flush command transmission circuit 87 transmits a flush command frame to the relay device for the aware node to request erasure of the learning contents of the FDB when, for example, the state of the controlled port is changed by the ring port control circuit 85. In addition, the flush command transmission circuit 87 transmits flush command frames FSH, FSHa to the relay device for the aware node even when the backup port Pb_m for the master is changed to the blocking state BK as shown in Fig. 11 and Fig. 13. Note that in a single-master configuration, the master node switch MNSW may transmit the flush command frame from the slave port Ps instead of the backup port Pb_m for the master in Fig. 13.

[0106] The hello frame transmission circuit 88 transmits a hello frame (continuity monitoring frame) from either the master port Pm or the slave port Ps to the other to monitor the presence or absence of a fault in the ring network 15. In detail, as shown in Fig. 3, the hello frame transmission circuit 88 transmits a hello frame HLOm from the master port Pm to the slave port Ps, and transmits a hello frame HLOs from the slave port Ps to the master port Pm.

[0107] 4, the fault monitoring frame transmitting circuit 81 transmits a master side fault monitoring frame (first fault monitoring frame) DFMm from the master port Pm to the ring network 15, and transmits a slave side fault monitoring frame (second fault monitoring frame) DFMs from the slave port Ps to the ring network 15. Then, the fault monitoring frame transmitting circuit 81 causes the relay device for the aware node to relay the fault monitoring frames DFMm, DFMs to the aware backup port Pb_a.

[0108] The fault monitoring frame receiving circuit 82 monitors whether the fault monitoring frames DFMm, DFMs are received at the master backup port Pb_m within a predetermined DFM time. The backup port control circuit 83 controls the state of the master backup port Pb_m based on the monitoring results by the fault monitoring frame receiving circuit 82. In detail, the backup port control circuit 83 controls the master backup port Pb_m to the blocking state BK during normal times when no fault is detected by the protocol control circuit 80.

[0109] Furthermore, if the master backup port Pb_m does not receive both of the fault monitoring frames DFMm, DFMs, the backup port control circuit 83 changes the master backup port Pb_m, which is in the blocking state BK, to the forwarding state FW. After that, if the master backup port Pb_m receives at least one of the fault monitoring frames DFMm, DFMs, the backup port control circuit 83 changes the master backup port Pb_m, which is in the forwarding state FW, to the blocking state BK.

[0110] <Operation of the main parts of the ring control circuit> Figures 20A and 20B are flow diagrams showing an example of the processing contents of the main parts of the ring control circuit shown in Figure 19. In Figure 20A, the fault monitoring frame transmitting circuit 81 transmits fault monitoring frames DFMm, DFMs (step S401). In addition, the fault monitoring frame receiving circuit 82 starts a DFM timer in response to the transmission of the fault monitoring frames DFMm, DFMs (step S402).

[0111] Next, if the master backup port Pb_m is controlled to the blocking state BK (step S403: Yes), the fault monitoring frame receiving circuit 82 judges whether or not both the fault monitoring frames DFMm, DFMs have been received by the master backup port Pb_m within the time of the DFM timer (step S404). If at least one of the fault monitoring frames DFMm, DFMs has been received (step S404: No), the master backup port Pb_m is maintained in the blocking state BK.

[0112] On the other hand, if neither of the fault monitoring frames DFMm, DFMs has been received (step S404: Yes), the backup port control circuit 83 changes the backup port Pb_m from the blocking state BK to the forwarding state FW (step S405).Then, the flush execution circuit 86 executes an FDB flush to erase the learning contents of the FDB 72 (step S406).

[0113] Also, in step S403, if the master backup port Pb_m is controlled to the forwarding state FW (if "No"), the process shown in Fig. 20B is executed. In Fig. 20B, the fault monitoring frame receiving circuit 82 judges whether or not at least one of the fault monitoring frames DFMm, DFMs is received by the master backup port Pb_m within the time of the DFM timer (step S501). Here, if neither of the fault monitoring frames DFMm, DFMs is received (step S501: No), the master backup port Pb_m is maintained in the forwarding state FW.

[0114] On the other hand, if at least one of the fault monitoring frames DFMm, DFMs is received (step S501: Yes), the backup port control circuit 83 changes the backup port Pb_m, which is in the forwarding state FW, to the blocking state BK (step S502). Then, the flush execution circuit 86 erases the learning contents of the FDB 72 by executing an FDB flush (step S503). Furthermore, the flush command transmission circuit 87 transmits a flush command frame to the aware node AN via the ring network 15 (step S504).

[0115] <Main Effects of the Fourth Embodiment> As described above, by using the method of the fourth embodiment, it is possible to obtain the same effects as those described in the first embodiment. Note that the method of the fourth embodiment can be combined with the method of the second embodiment or the method of the third embodiment.

[0116] (Fifth embodiment) <How to monitor backup routes> Fig. 21 is a schematic diagram showing an example of a method for monitoring a backup path in a network system according to the fifth embodiment. Fig. 21 also shows the control states of the master port Pm, the slave port Ps, and the master backup port Pb_m in the case of using the master VLAN in Fig. 17 as an example.

[0117] In the first to fourth embodiments, it is assumed that no failure occurs in the backup path, that is, the backup ports Pb_m, Pb_a and the backup line 18. On the other hand, if a failure occurs in the backup path, the master node MN does not receive both of the failure monitoring frames DFMm, DFMs at the backup port Pb_m for the master, and therefore may erroneously determine that a double failure has occurred.

[0118] 21, the master node MN periodically transmits a backup monitoring frame (first backup monitoring frame) BUM1 from the master backup port Pb_m to the aware backup port Pb_a. Similarly, the aware switch with backup ASWB periodically transmits a backup monitoring frame (second backup monitoring frame) BUM2 from the aware backup port Pb_a to the master backup port Pb_m.

[0119] The backup monitoring frames BUM1 and BUM2 are distinguished from other management frames by storing "0x04" in the type 45a as shown in Fig. 14. Furthermore, the destination MAC address 40 and the source MAC address 41 are swapped between the backup monitoring frames BUM1 and BUM2.

[0120] When the master node MN does not receive the backup monitoring frame BUM2 at the master backup port Pb_m within a specified BUM time, it determines that a failure has occurred on the backup path. On the other hand, when the backup aware switch ASWB does not receive the backup monitoring frame BUM1 at the aware backup port Pb_a within a specified BUM time, it stops sending the backup monitoring frame BUM2. As a result, the master node MN can detect that a failure has occurred on at least one of the paths from "Pb_m" to "Pb_a" or the path in the reverse direction.

[0121] When a failure in the backup path is detected in this manner, the master node MN stops monitoring for double failures using the failure monitoring frames DFMm, DFMs, i.e., stops monitoring the failure monitoring frames DFMm, DFMs at the master backup port Pb_m. This makes it possible to prevent erroneous detection of double failures. In addition, the master node MN controls the backup line 18 not to be used by maintaining the master backup port Pb_m in a blocking state BK.

[0122] <Repeater details> Fig. 22 is a block diagram showing a schematic configuration example of a main part of a relay device constituting a backup aware node in the network system shown in Fig. 21. The backup aware node AN shown in Fig. 22, in other words, the backup aware switch ASWB which is a relay device, differs from the configuration example shown in Fig. 18A in the following points. That is, the ring control circuit 58 further includes a backup (also abbreviated as BU) monitoring frame transmitting circuit 90 and a BU monitoring frame receiving circuit 91.

[0123] The BU monitoring frame transmission circuit 90 periodically transmits a backup monitoring frame (second backup monitoring frame) BUM2 from the aware backup port Pb_a to the master backup port Pb_m at a predetermined transmission interval. The BU monitoring frame reception circuit 91 receives a backup monitoring frame BUM1 from the master node MN by identifying various information in the management frame as shown in Fig. 14. If the BU monitoring frame reception circuit 91 does not receive the backup monitoring frame BUM1 at the aware backup port Pb_a within a predetermined BUM time, it causes the BU monitoring frame transmission circuit 90 to stop transmitting the backup monitoring frame BUM2.

[0124] Fig. 23 is a block diagram showing a schematic configuration example of a main part of a relay device constituting a master node in the network system shown in Fig. 21. The master node MN shown in Fig. 23, in other words, the master node switch MNSW which is a relay device for the master node, differs from the configuration example shown in Fig. 19 in the following points. That is, the ring control circuit 78 further includes a BU monitoring frame transmitting circuit 95 and a BU monitoring frame receiving circuit 96.

[0125] The BU monitoring frame transmitting circuit 95 periodically transmits a backup monitoring frame (first backup monitoring frame) BUM1 from the master backup port Pb_m to the aware backup port Pb_a at a predetermined transmission interval. The BU monitoring frame receiving circuit 96 receives a backup monitoring frame BUM2 from the aware switch ASWB with backup by identifying various information in the management frame as shown in Fig. 14. Then, if the BU monitoring frame receiving circuit 96 does not receive the backup monitoring frame BUM2 at the master backup port Pb_m within a predetermined BUM time, it determines that a failure has occurred in the backup path.

[0126] When a failure in the backup path is detected in this manner, the BU monitoring frame receiving circuit 96 notifies the failure detection to the failure monitoring frame transmitting circuit 81, the failure monitoring frame receiving circuit 82, and the backup port control circuit 83. In response to the failure detection notification, the failure monitoring frame transmitting circuit 81 stops transmitting the failure monitoring frames DFMm and DFMs. In addition, the failure monitoring frame receiving circuit 82 stops monitoring for double failures, i.e., monitoring the failure monitoring frames DFMm and DFMs at the master backup port Pb_m. Furthermore, the backup port control circuit 83 maintains the master backup port Pb_m in the blocking state BK.

[0127] <Main Effects of the Fifth Embodiment> As described above, the use of the method of the fifth embodiment can also provide the same effects as those described in the fourth embodiment. Furthermore, it is possible to detect a failure in a backup path and prevent erroneous detection of a double failure. The method of the fifth embodiment can also be combined with the method of the first embodiment, the method of the second embodiment, or the method of the third embodiment.

[0128] The invention made by the present inventor has been specifically described above based on the embodiments, but the present invention is not limited to the above-mentioned embodiments and can be modified in various ways without departing from the gist of the invention. For example, the above-mentioned embodiments have been described in detail to easily explain the present invention, and the present invention is not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0129] 15: ring network, 18: backup line, 28a, 28b: fault, 52, 72: FDB, 80: protocol control circuit, 81: fault monitoring frame transmission circuit, 82: fault monitoring frame reception circuit, 83: backup port control circuit, 86: flush execution circuit, 87: flush command transmission circuit, 95: backup monitoring frame transmission circuit, 96: backup monitoring frame reception circuit, AN: aware node, ASW: aware switch, ASWB: aware switch with backup, BK: blocking state, BUM1, BUM2: backup monitoring frame, DFMm, DFMs: fault monitoring frame, FSH: flush command frame, FW: forwarding state, HLOm, HLOs: hello frame (connectivity monitoring frame), LD: link down notification frame, MN: master node, MNSW: switch for master node, Pa: aware port, Pb_m, Pb_a: backup port, Pm: master port, Ps: slave port

Claims

1. A master node is a component of a ring network, and is configured of one or more relay devices that relay frames, and is responsible for managing the ring network; One or more aware nodes, each of which is a component of the ring network and is configured with the relay device; A network system having: The master node, a master port and a slave port connected to the ring network, and a backup port for the master; under normal circumstances, a controlled port, which is either the master port or the slave port, is controlled to a blocking state in which relay of user frames is prohibited, and when a fault is detected in the ring network, the controlled port in the blocking state is changed to a forwarding state in which relay of the user frames is permitted; During the normal period, the backup port for the master is controlled to be in the blocking state; periodically transmitting a first fault monitoring frame in a direction from the master port to the slave port, and periodically transmitting a second fault monitoring frame in a direction from the slave port to the master port; The aware node comprises two aware ports connected to the ring network; A first aware node, which is one of the aware nodes, In addition to the two aware ports, a backup port for awareness is provided, which is connected to the backup port for the master via a backup line, relaying the first fault monitoring frame received at one of the two aware ports and the second fault monitoring frame received at the other of the two aware ports to the backup port for awareness; when the master node does not receive both the first fault monitoring frame and the second fault monitoring frame at the backup port for the master, the master node changes the backup port for the master, which is in the blocking state, to the forwarding state. Network system.

2. 2. The network system according to claim 1, The master node periodically transmits a continuity monitoring frame from one of the master port and the slave port to the other to monitor the presence or absence of a fault in the ring network. Network system.

3. 2. The network system according to claim 1, The master node and the aware node each have an FDB in which a correspondence relationship between an identifier of a port that receives the user frame and a source MAC address included in the user frame is learned; When the master node changes the backup port for the master to the forwarding state, the master node erases the learning contents of the FDB of the own node. Network system.

4. 2. The network system according to claim 1, the master node periodically transmits a first continuity monitoring frame from the master port to the slave port for monitoring the presence or absence of a fault in the ring network, and periodically transmits a second continuity monitoring frame from the slave port to the master port for monitoring the presence or absence of a fault in the ring network; the first aware node copies the first continuity monitoring frame and the second continuity monitoring frame received at the two aware ports, and relays the copied first continuity monitoring frame and the copied second continuity monitoring frame to the aware backup port as the first fault monitoring frame and the second fault monitoring frame; Network system.

5. 2. The network system according to claim 1, when the master node receives at least one of the first fault monitoring frame or the second fault monitoring frame at the backup port for the master after changing the backup port for the master to the forwarding state, the master node changes the backup port for the master in the forwarding state to the blocking state; Network system.

6. 6. The network system according to claim 1, the master node changes the control target port from the forwarding state to the blocking state when detecting recovery from a failure in the ring network after changing the control target port to the forwarding state; Network system.

7. 6. The network system according to claim 5, The master node and the aware node each have an FDB in which a correspondence relationship between an identifier of a port that receives the user frame and a source MAC address included in the user frame is learned; When the master node changes the backup port for the master to the blocking state, the master node erases the learning contents of the FDB of the own node, and transmits a flush command frame to the aware node to request the erasure of the learning contents of the FDB. Network system.

8. 8. The network system according to claim 7, The master node, receiving the first fault monitoring frame at a backup port for the master, and transmitting the flush command frame from the master port when the second fault monitoring frame is not received; receiving the second fault monitoring frame at a backup port for the master, and transmitting the flush command frame from the backup port for the master if the first fault monitoring frame is not received; Network system.

9. 2. The network system according to claim 1, the master node starts transmitting the first fault monitoring frame and the second fault monitoring frame after detecting a fault in the ring network; Network system.

10. 2. The network system according to claim 1, the master node periodically transmits a first backup monitoring frame from the backup port for the master to the backup port for the aware; the first aware node periodically transmits a second backup monitoring frame from the aware backup port to the master backup port; When the first aware node does not receive the first backup monitoring frame at the aware backup port within a predetermined time, the first aware node stops transmitting the second backup monitoring frame; when the master node does not receive the second backup monitoring frame at the backup port for the master within a predetermined time, the master node stops monitoring the first fault monitoring frame and the second fault monitoring frame at the backup port for the master; Network system.

11. 2. The network system according to claim 1, Between the master port and the first aware node, and between the slave port and the first aware node, one or more aware nodes are provided that do not have a backup port for the awareness. Network system.

12. A relay device for a master node, which is a component of a ring network and is responsible for managing the ring network and relaying frames, a master port and a slave port connected to the ring network; a backup port for master connected via a backup line to a backup port for awareness of a relay device for an aware node, which is a component of the ring network; a protocol control circuit that normally controls a controlled port, which is one of the master port or the slave port, to a blocking state in which relaying of frames is prohibited, and when a fault is detected in the ring network, changes the controlled port in the blocking state to a forwarding state in which relaying of frames is permitted; a fault monitoring frame transmitting circuit that transmits a first fault monitoring frame from the master port to the ring network and transmits a second fault monitoring frame from the slave port to the ring network, and relays the first fault monitoring frame and the second fault monitoring frame to a backup port for the aware node in a relay device for the aware node; a fault monitoring frame receiving circuit that monitors whether the first fault monitoring frame and the second fault monitoring frame are received by a backup port for the master; a backup port control circuit that controls the backup port for the master to the blocking state during the normal operation, and changes the backup port for the master in the blocking state to the forwarding state when neither the first fault monitoring frame nor the second fault monitoring frame is received by the backup port for the master; Equipped with Relay device.

13. The relay device according to claim 12, the protocol control circuit transmits a continuity monitoring frame from one of the master port and the slave port to the other, for monitoring the presence or absence of a fault in the ring network; Relay device.

14. The relay device according to claim 12, an FDB for learning a correspondence relationship between an identifier of a port that has received the user frame and a source MAC address included in the user frame; a flush execution circuit for erasing the learning contents of the FDB when the backup port for the master is changed to the forwarding state; Equipped with Relay device.

15. The relay device according to claim 12, the backup port control circuit changes the backup port for the master in the forwarding state to the blocking state when at least one of the first fault monitoring frame or the second fault monitoring frame is received by the backup port for the master after changing the backup port for the master to the forwarding state; Relay device.

16. 16. The relay device according to claim 12, the protocol control circuit, after changing the state of the controlled port to the forwarding state, changes the state of the controlled port from the forwarding state to the blocking state when recovery from a failure in the ring network is detected; Relay device.

17. 16. The relay device according to claim 15, the relay device for the master node and the relay device for the aware node each have an FDB in which a correspondence relationship between an identifier of a port that has received the user frame and a source MAC address included in the user frame is learned; The relay device for the master node includes: a flush execution circuit that erases the learning contents of the FDB of the node when the backup port for the master is changed to the blocking state; a flush command transmission circuit that transmits a flush command frame to a relay device for the aware node when the backup port for the master is changed to the blocking state, the flush command frame being for requesting erasure of learned contents of the FDB; Equipped with Relay device.

18. The relay device according to claim 12, the fault monitoring frame transmission circuit starts transmitting the first fault monitoring frame and the second fault monitoring frame after detecting a fault in the ring network. Relay device.

19. The relay device according to claim 12, a backup monitoring frame transmission circuit that periodically transmits a first backup monitoring frame from the master backup port to the aware backup port; a backup monitoring frame receiving circuit that receives a second backup monitoring frame periodically transmitted from a relay device for the aware node at the backup port for the master, and when the second backup monitoring frame is not received within a predetermined time, causes the fault monitoring frame receiving circuit to stop monitoring the first fault monitoring frame and the second fault monitoring frame; Equipped with Relay device.

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