JP5238755B2 - Transfer device - Google Patents

Description

  Embodiments described herein relate generally to a transfer apparatus that connects redundant networks, for example.

  Non-Patent Document 1 discloses a network redundancy system called High-availability Seamless Ring (HSR).

  In the HSR network, each device is equipped with two communication ports. Each device is connected to two adjacent devices to form a ring network.

  In the HSR network, in order to enable a receiving apparatus to receive a frame without loss even if communication becomes impossible at one place in the network, an apparatus that transmits a frame transmits the same frame from each of two ports.

  The two frames reach the receiving device via the clockwise and counterclockwise paths of the ring.

  Non-Patent Document 1 also discloses a transfer device called QuadBox that connects rings configured as an HSR network.

  QuadBox is equipped with four communication ports. When QuadBox receives a frame from one communication port, it basically copies and transfers the same frame from the other three communication ports.

  Therefore, when connecting rings using two QuadBoxes, there are many patterns of paths through which each frame passes.

  For this reason, it is difficult for the network operator to specify the route followed by the frame. Therefore, when a network failure occurs, it becomes difficult to identify the cause of the failure (identification of the location where the network failure has occurred).

HSR-High Availability Seamless Redundancy, http://lamspeople.epfl.ch/kirrmann/Pubs/IEC_61439-3/IEC_62439-3.5_HSR_Principles_Kirrmann_100327.ppt

  The present invention provides a transfer apparatus that makes it easy to identify a failure factor when a failure occurs in a network.

  According to this embodiment, a transfer device including a first communication port, a second communication port, a third communication port, a fourth communication port, and a transfer unit is provided. Each of the first to fourth communication ports performs frame transmission / reception with a corresponding external communication device. The transfer unit transfers the frame received at the first communication port to the second communication port, transfers the frame received at the second communication port to each of the first and fourth communication ports, The frame received at the third communication port is transferred to the fourth communication port, and the frame received at the fourth communication port is transferred to the second and third communication ports, respectively. The first to fourth communication ports transmit the frames transferred from the transfer unit to the corresponding external communication devices.

1 is a block diagram showing a configuration of a transfer device according to a first embodiment. FIG. 2 is a diagram showing a network system in which two rings are connected using two transfer apparatuses having the configuration of FIG. It is a figure which shows an example of a frame format. It is a flowchart which shows the flow of the transfer process by a transfer part. It is a schematic diagram which shows a mode that the flame | frame received by each communication port is transferred to another communication port. 2 is a flowchart showing the flow of overall processing by the transfer apparatus of FIG. It is a figure which shows the example of the path | route which a flame | frame follows when transmitting / receiving a flame | frame between the apparatuses on two different rings. It is a figure which shows the other example of the path | route which a flame | frame follows, when transmitting / receiving a flame | frame between the apparatuses on two different rings. It is a figure which shows the further another example of the path | route which a frame follows when transmitting / receiving a frame between the apparatuses on two different rings. 18 is a flowchart showing an operation example of the transfer apparatus according to the seventh embodiment. 18 is a flowchart showing another operation example of the transfer device according to the seventh embodiment. FIG. 20 is a diagram showing a network system according to an eighth embodiment.

(First embodiment)
FIG. 1 is a block diagram showing a configuration of a transfer device according to the first embodiment.

  FIG. 2 is a diagram illustrating a network system in which two rings are connected to each other using two transfer apparatuses in FIG.

  First, the details of the transfer device will be described with reference to FIG. 1, and then an example in which a frame transmitted from a transmission device on one ring is transferred to a reception device on the other ring will be shown using FIG.

  The transfer device in FIG. 1 includes a first communication port P1, a second communication port P2, a third communication port P3, and a fourth communication port P4 that transmit and receive frames to and from corresponding external communication devices. The transfer apparatus includes a storage unit 511, a transfer unit 521, and a memory bus 531.

  The first to fourth communication ports P1 to P4 are each connected to a corresponding external communication device by a communication cable according to the communication standard to be used. The external communication device is, for example, another transfer device, or one of four communication ports of the other transfer device, or a device on the ring, or two ports included in the device on the ring (described later) ).

  The first to fourth communication ports P1 to P4 and the storage unit 511 are connected to the memory bus 531, and the first to fourth communication ports P1 to P4 are configured to be accessible to the storage unit 511 via the memory bus 531. The

  The first communication port P1 includes an input unit 101, a filter 102, a loop frame prevention unit 103, a queue 104, and an output unit 105.

  The second communication port P2 includes an input unit 201, a filter 202, a loop frame prevention unit 203, a queue 204, and an output unit 205.

  The third communication port P3 includes an input unit 301, a filter 302, a loop frame prevention unit 303, a queue 304, and an output unit 305.

  The fourth communication port P4 includes an input unit 401, a filter 402, a loop frame prevention unit 403, a queue 404, and an output unit 405.

  Elements having the same name provided in the first to fourth communication ports P1 to P4 have the same functions. Therefore, in the following, in order to omit redundant description, the description will focus on the fourth communication port P4 unless otherwise specified.

  The input unit 401 receives a frame from the corresponding external communication device via a cable connected to the communication port P4. More specifically, a frame of a digital signal is obtained by receiving a signal from a cable and performing analog / digital conversion on the received signal.

  The filter 402 verifies whether the received frame conforms to a filter rule given in advance, and discards it when it conforms. Filter rules are stored in the storage unit 511 in advance. The filter 402 reads the filter rule from the storage unit 511 via the memory bus 531. The filter 402 verifies the frame based on the read filter rule and the corresponding field in the frame.

  FIG. 3 shows an example of a frame format according to this embodiment.

  The preamble, transmission destination MAC address, transmission source MAC address, EtherType, LSDU, and FCS are fields defined by Ethernet (registered trademark).

  Protocol type, TPID, PCP, CFI, and VID (VLAN-ID) are fields defined by IEEE802.1Q. In particular, the VID represents a broadcast domain or network identifier.

  Path, size, and SequenceNr (sequence number) are fields defined in IEC 62439-3. The sequence number of SequenceNr is incremented by 1 each time the transmitting apparatus transmits a frame.

  In this embodiment, as defined in IEC 62439-3, frames with the same combination of source MAC address and SequenceNr are determined to be the same frame. However, this is merely an example, and the identity of the frame may be determined based on which field.

  The TPID, PCP, CFI, and VID fields defined in IEEE802.1Q may not exist.

  In the description of the present embodiment, the format of FIG. 3 is used, but a frame format of another communication method such as Zigbee, LTE, or proximity wireless can be used alternatively.

  Here, any rule may be used as the filter rule. For example, it may be a condition indicating whether or not a value of a predetermined field is included in a specific range.

  Specifically, it may be a condition indicating whether the value of the transmission source field, the transmission destination field, or the VID (network identifier) is included in a specific range. In this case, the filter 402 determines whether the network identifier, transmission source address, or transmission destination address included in the frame conforms to the filter rule (whether transfer of the frame by the transfer unit is permitted). If the transfer is not permitted, the frame is discarded.

  The filter rule may be a logical product or logical sum of a plurality of conditions.

  The loop frame prevention unit 403 determines whether a frame that has passed through the filter 402 has received the same frame (that is, a frame having the same source address and sequence number) at the same port in the past and has been transferred. Validate. The loop frame prevention unit 403 uses the storage unit 511 for the verification.

  The storage unit 511 stores a set of a transmission source address, a sequence number, and a reception port of a frame transferred in the past in addition to the filter rule described above.

  The loop frame prevention unit 403 checks whether or not the same set as the set of the transmission source address, sequence number, and reception port of the frame is stored in the storage unit 511. Access to the storage unit 511 is performed via the memory bus 531. When the same set is stored, it is determined that the same frame as the frame has been transferred in the past, and otherwise, it is determined that the frame has not been transferred.

  When the loop frame prevention unit 403 determines that the transfer has been completed, the loop frame prevention unit 403 discards the frame.

  On the other hand, when the loop frame prevention unit 403 determines that the frame has not been transferred, the loop frame prevention unit 403 stores the set of the transmission source address, sequence number, and reception port of the frame in the storage unit 511. The loop frame prevention unit 403 passes the frame to the transfer unit 521 for transfer.

  Note that the loop frame prevention unit and the filter are not essential elements, and a configuration without one or both of them as described later is also possible.

  The transfer unit 521 is connected to the loop frame prevention unit and the queue of the first to fourth communication ports P1 to P4.

  When receiving a frame from each communication port, the transfer unit 521 determines to which communication port the frame is to be transferred according to the transfer rule, and transfers the frame to the queue of the determined communication port. When there are multiple transfer destination communication ports, the necessary number of frames are copied. The transfer rule is set in the transfer unit 521 in advance.

  FIG. 4 is a flowchart showing the flow of transfer processing performed by the transfer unit 521 in accordance with the transfer rule.

  The transfer unit 521 determines the communication port (input port) that has received the frame (step 11).

  When the communication port that has received the frame is the first communication port P1, the transfer unit 521 transfers the frame to the second communication port P2 (step 12).

  When the communication port that has received the frame is the second communication port P2, the transfer unit 521 transfers the frame to the first communication port P1 and the fourth communication port P4 (step 13).

  When the communication port that has received the frame is the third communication port P3, the transfer unit 521 transfers the frame to the fourth communication port P4 (step 14).

  When the communication port that has received the frame is the fourth communication port P4, the transfer unit 521 transfers the frame to the second communication port P2 and the third communication port P3 (step 15).

  When transferring frames to a plurality of communication ports in steps 13 and 15, the transfer unit 521 copies the frames as described above. At this time, the transfer unit 521 can change fields other than the source MAC address and the SequenceNr field in the copied frame. For example, the Path field of the copied frame may be changed.

  The transfer unit 521 may realize its function by causing a computer such as a CPU to execute a software program, or may be configured by, for example, a crossbar switch or a bus.

  The queue 404 holds the frame passed from the transfer unit 521 until the frame can be output.

  The output unit 405 performs digital / analog conversion on the frame output from the queue 404. The output unit 405 transmits the analog signal frame obtained by the conversion to the corresponding external communication device via the cable connected to the fourth communication port P4.

  FIG. 5 is a schematic diagram specifically showing a state in which a frame received at each communication port is transferred according to the transfer rule described above.

  The frame received at the first communication port P1 is transferred to the second communication port P2 and transmitted from the second communication port to the outside as indicated by the line L1. However, it is assumed that the frame has passed the processing of the filter 102 and the loop frame prevention unit 103 (the same applies hereinafter).

  The frame received at the second communication port P2 is transferred to the first communication port P1 and the fourth communication port P4 and transmitted to the outside from the communication ports P1 and P4 as indicated by a line L2.

  The frame received at the third communication port P3 is transferred to the fourth communication port P4 and transmitted to the outside from the fourth communication port P4 as indicated by a line L3.

The frame received at the fourth communication port P4 is transferred to the second communication port P2 and the third communication port P3 and transmitted to the outside from each communication port P2, P3 as indicated by a line L4.
FIG. 6 is a flowchart showing an overall processing flow by the transfer apparatus of FIG. Here, the flow of processing when a frame is received at the fourth communication port P4 is shown. When a frame is received at the first to third communication ports P1 to P3, processing is performed according to the same procedure.

  The input unit 401 performs analog / digital conversion on an external input signal to obtain a digital frame (step 701).

  Next, the filter 402 determines whether or not the frame obtained in step 701 matches the filter rule stored in the storage unit 511 (step 702).

  If the frame matches the filter rule (YES), the filter 402 discards the frame (step 707).

  On the other hand, when the frame does not conform to the filter rule (NO), the loop frame prevention unit 403 determines whether the same frame as the frame has already been received and transferred (step 703). . Specifically, the loop frame prevention unit 403 verifies whether or not a combination in which the transmission source MAC address, the SequenceNr field value, and the reception port of the frame match is stored in the storage unit 511.

  If the matching set is stored, the loop frame prevention unit 403 determines that the same frame as the frame has already been transferred (YES), and discards the frame (step 707).

  On the other hand, when the matched pair is not stored, the loop frame prevention unit 403 determines that the same frame as that frame has not been transferred (NO), and the source MAC address of the frame, the value of the SequenceNr field, and The reception port is stored in the storage unit 511 (step 704).

  Next, the transfer unit 521 determines the transfer destination port of the frame according to the transfer rule, and outputs the frame to the transfer destination port queue (step 705). In this example, since the reception port is the fourth communication port P4, the transfer destination ports are the second and third communication ports P2 and P3 (see FIG. 4).

  Next, the queue in the transfer destination communication port holds (queues) the frame until the frame can be output (step 706).

  Next, the output unit in the transfer destination communication port performs digital / analog conversion on the frame output from the queue, and outputs the analog signal frame from the cable connected to the communication port (step 708).

  Hereinafter, the network system shown in FIG. 2 will be described.

  This network is largely composed of two rings R1 and R2 and two transfer devices 601 and 602.

  Ring R1 comprises devices 611, 615, 616. Each device has two communication ports, and these communication ports are connected by a cable.

  The communication ports of the devices 616 and 611 at both ends are connected to the transfer devices 601 and 602. More specifically, the communication port of the device 616 is cabled to the fourth communication port P4 of the transfer device 601. The communication port of the device 611 is cabled to the second communication port P2 of the transfer device 602.

  Ring R2 comprises devices 612, 613, 614. Each device has two ports, and these communication ports are connected by a cable.

  The communication ports of the devices 612 and 614 at both ends are connected to the transfer devices 601 and 602. More specifically, the communication port of the device 612 is cabled to the second communication port P2 of the transfer device 601. The communication port of the device 614 is cabled to the second communication port P4 of the transfer device 602.

  Also, the third communication port P3 of the transfer device 601 and the first communication port P1 of the transfer device 602 are connected by cable. The first communication port P1 of the transfer device 601 is connected to the third communication port P3 cable of the transfer device 602.

  The devices 611 to 616 each have an equivalent communication function. The devices 611 to 616 are HSR nodes described in Non-Patent Document 1, for example.

  The devices 611 to 616 relay the frame by transmitting the frame received at one port from the other port. However, when the destination address of the frame matches its own address, the frame is taken in and processed, and the frame is not relayed. When a frame having its own address as the transmission source address is received, the frame is discarded and the frame is not relayed.

  An example of the operation of the system in FIG. 2 will be described by taking as an example the case where the device 612 connected to the ring R2 transmits a frame to the device 611 connected to the ring R1. In this case, as shown in FIG. 7, the device 612 is a transmitting device and the device 611 is a receiving device.

The transmission device 612 transmits the same frame from each of the two ports. Frame 1 transmitted from one port of transmission device 612 is transferred to transfer device 602 by devices 613 and 614, and the fourth frame of transfer device 602 is transmitted. Received at communication port P4.

  The transfer device 602 copies one frame 2 received at the fourth communication port P4 and outputs it from the second communication port P2 and the third communication port P3, respectively.

  The frame 2 output from the second communication port P2 is received by the receiving device 611. The frame output from the third communication port P3 is input to the first communication port P1 of the transfer device 601.

  On the other hand, the frame 1 transmitted from the other port of the transmission device 612 is received by the second communication port P2 of the transfer device 601.

  One frame 1 is copied and output from the first communication port P1 and the fourth communication port P4.

  The frame 1 transmitted from the fourth communication port P4 is transferred by the devices 616 and 615 and received by the receiving device 611. That is, the receiving device 611 determines that the destination address of the frame 1 matches the address of its own device, and takes in the frame 1 and processes it.

  Note that the receiving device 611 may process both the received frames 1 and 2, or may process either one and discard the other.

  The frame 1 transmitted from the first communication port P1 of the transfer device 601 is received by the third communication port P3 of the transfer device 602.

  The transfer device 601 transfers the frame 2 from the transfer device 602 received at the first communication port P1 from the communication port P2 to the transmission device 612. For example, as described in Non-Patent Document 1, the transmission apparatus 612 discards the frame 2 transferred from the transfer apparatus 601 because the transmission source MAC address of the frame 2 is the address of the transmission apparatus 612. The mark “x” in the figure means that the frame is discarded by the corresponding transfer device or device.

  On the other hand, the transfer device 602 transfers the frame received from the transfer device 601 at the third communication port P3 to the device 614 from the communication port P4. The frame 2 transferred from the communication port P4 of the transfer device 602 is received by the transmission device 612 via the device 614 and the device 613. The transmission apparatus 612 discards the frame 1 because the transmission source MAC address of the frame 1 transferred from the apparatus 613 is the address of the transmission apparatus 612.

  Here, it is possible that the frame 1 goes around the ring R2 for some reason, and the transfer device 601 receives again at the communication port P2. For example, the transmission device 612 may fail to discard frame 1. The frame flow in this case is as shown in FIG.

  That is, when frame 1 received once in the past by transfer apparatus 601 is received again at the same communication port P2, transfer apparatus 601 discards frame 1.

  On the other hand, there is a possibility that the frame 2 makes a round in the ring R2 for some reason, and the transfer device 602 receives again at the communication port P4. The frame flow in this case is as shown in FIG.

  That is, when the transfer device 602 receives the frame 2 once received in the past again at the same communication port P4, the transfer device 602 discards the frame 2.

  As can be understood from the above description, the path followed by the frame received by the receiving apparatus 611 is limited to two paths at the maximum. Therefore, when a failure occurs in the network (for example, when the receiving apparatus cannot receive one or both of the frames), it is possible to easily identify the cause of the failure such as an abnormal portion of the cable.

(Second embodiment)
In the first embodiment, the storage unit 511 is provided in common for each loop frame prevention unit of the communication ports P1 to P4, and stores a set of a transmission source MAC address, a SequenceNr field value (sequence number), and a reception port. However, a storage area for storing the set may be secured for each loop frame prevention unit. In this case, since the storage area is not shared by a plurality of communication ports, there is no resource contention, so there is an advantage that it is possible to eliminate waiting until the contention resource can be used and to reduce the processing time. The flow of frames in the present embodiment is the same as that shown in the first embodiment.

(Third embodiment)
In the present embodiment, a case where each communication port does not include one or both of the loop frame prevention unit and the filter is shown.

  When no filter is installed, it is not necessary to store the filter rule, so that the amount of installed memory can be reduced.

  When the loop frame prevention unit is not provided, it is not necessary to store the transmission source MAC address, sequence number, and reception port pair of the transferred frame in the storage unit 511, so that the amount of installed memory can be reduced.

  When the loop frame prevention unit is not provided, it is preferable to add a Hop limit field for limiting the number of hops to the frame format shown in FIG. The Hop limit field is defined at any position between the protocol type of the frame format and the LSDU.

  All devices and transfer devices shown in FIG. 2 decrement the Hop limit field value by 1 when transferring a frame, and discard the frame when the Hop limit field value is 0. Thereby, it is possible to prevent the frame from being transferred infinitely when there is no device having the destination address.

  When the loop frame prevention unit is not provided according to the present embodiment, the basic flow of the frame is the same as that shown in the first embodiment.

(Fourth embodiment)
The arrangement locations of the loop frame prevention unit and the filter shown in FIG. 1 are merely examples, and these can be arranged at other locations.

  For example, the loop frame prevention unit may be disposed between the queue and the transfer unit, between the queue and the output unit, or between the filter and the input unit. When the loop frame prevention unit is arranged between the queue and the transfer unit, or between the queue and the output unit, the loop frame prevention unit is not the same frame received in the same port in the past, but from the same port in the past. When the same output frame is detected, the frame is discarded.

  The filter may be disposed between the queue and the transfer unit, between the queue and the output unit, and between the transfer unit and the loop frame prevention unit.

(Fifth embodiment)
In the first embodiment, the storage unit 511 is arranged as a common storage device for each communication port, but instead, the communication ports P1 to P4 may each include a storage device.

  In this case, the filter rule is stored in the storage device for each communication port. A set of a transmission source address, a sequence number, and a reception port is also stored in a storage device for each communication port.

  The flow of frames in the present embodiment is the same as that shown in the first embodiment.

(Sixth embodiment)
The loop frame prevention unit of each communication port may include a cache memory for the storage unit 511.

  As a result, memory access can be performed at high speed, and faster frame transfer and filtering can be performed.

(Seventh embodiment)
In each of the embodiments described above, if the connection method between the ring and the transfer device is wrong, proper operation of each embodiment cannot be obtained. As an incorrect connection, for example, there is a case where the transfer device 601 in FIG. 2 is connected to the ring while being rotated 180 degrees in parallel with the paper surface. That is, the fourth communication port P4 of the transfer device 601 and the third communication port P3 of the transfer device 602, the third communication port P3 and device 612 of the transfer device 601, the second communication port P2 of the transfer device 601 and the second of the transfer device 602. This is a case where the communication port P1 and the first communication port P1 of the transfer device 601 and the device 615 are connected.

  In order to prevent such an artificial connection error, after the user connects the ring and the transfer device, the transfer device determines which of the first to fourth communication ports P1 to P4 to set each communication port. An example is shown in which the determination is automatically made and each communication port is set to one of the first to fourth communication ports P1 to P4 according to the determination result.

  FIG. 10 shows an operation flow of the transfer apparatus 601 according to the present embodiment, and FIG. 11 shows an operation flow of the transfer apparatus 602.

  The transfer device 601 transmits a notification message from the four communication ports at the time of activation (step 1101 in FIG. 10). The notification message is a message including a description indicating that the own device is a transfer device. The destination address of the notification message may be a special address that can only reach the neighboring device.

  The transfer device 602 receives the notification message transmitted from the transfer device 601 at two communication ports (step 1201 in FIG. 11). The communication port that has received the notification message or the transfer unit of the transfer device 602 returns a response message from the communication port from which the notification message has been received (step 1202). Each device on the ring is configured not to return a response message even when a notification message is received, or to return a different type of message.

  The transfer device 602 sets the two communication ports that have received the notification message as the first and third communication ports (step 1203). Either communication port may be set as the first communication port, and any communication port may be set as the third communication port.

  The transfer device 602 sets the remaining two communication ports that did not receive the notification message as the second and fourth communication ports (step 1204). More specifically, of the remaining two communication ports, one communication port associated with the first communication port in advance is set as the second communication port, and the other communication port is set as the fourth communication port.

  That is, in the transfer device 602, the four communication ports are divided into two pairs, and the two communication ports are combined. The same applies to the transfer apparatus 601. When the operator connects the transfer devices to each other by cable, the transfer device is connected using one port of one pair and one port of the other pair for each transfer device.

  The transfer device 602 stores setting information indicating the contents set as described above in an internal buffer (step 1205). The transfer device 602 refers to the setting information, identifies each communication port, and performs a transfer process as shown in FIG.

  On the other hand, the transfer device 601 receives the response message from the transfer device 602 via two communication ports (step 1102), and sets the two communication ports as the first and third communication ports (step 1103). Either communication port may be set as the first communication port, and any communication port may be set as the third communication port.

  The transfer apparatus 601 sets the remaining two communication ports that have not received the response message as the second and fourth communication ports (step 1104). More specifically, of the remaining two communication ports, one communication port previously associated with the first communication port is set as the second communication port, and the other communication port is set as the fourth communication port.

  The transfer device 601 stores setting information indicating such setting contents in an internal buffer (step 1105). The transfer device 601 refers to the setting information, identifies each communication port, and performs the transfer process shown in FIG.

(Eighth embodiment)
In the first embodiment, a configuration in which two rings are connected by two transfer devices is shown, but it is also possible to interconnect three or more rings.

  FIG. 12 shows a network system in which four rings R11 to R14 are interconnected.

  Three pairs of transfer devices are used to connect the rings R11 to R14. A pair of transfer devices 901 and 902 connects the rings R11 and R12, a pair of transfer devices 903 and 904 connects between the rings R12 and R13, and a pair of transfer devices 905 and 906 connects between the rings R12 and R14. Is connected.

  Devices 801, 802, 803, and 804 are connected to the ring R11. Devices 805, 806, and 807 are connected to the ring R12. Devices 808, 809, 810, 811 are connected to the ring R13. Devices 812, 813, 814, and 815 are connected to the ring R14.

  Even when three or more rings are connected in this way, the path followed by the frame is limited by the operation shown in Fig. 4 by each transfer device, and if a failure occurs, the cause can be easily identified. Can do.

  Each embodiment mentioned above is not limited as it is, but can be embodied by modifying the constituent elements without departing from the scope of the invention in the implementation stage. In addition, various inventions can be formed by appropriately combining a plurality of components disclosed in the embodiment. For example, some components may be deleted from all the components shown in the embodiment. Furthermore, constituent elements over different embodiments may be appropriately combined.

  The transfer device shown in FIG. 1 can also be realized by using, for example, a general-purpose computer device as basic hardware. That is, it is possible to realize the operation of each element by causing a computer to execute a program that describes a process to be performed by each element included in the apparatus of FIG. At this time, the transfer device may be realized by installing the above-described program in a computer device in advance, or may be stored in a storage medium such as a hard disk, a memory device, an optical disk, or the above-mentioned program via a network. You may implement | achieve by distributing and installing this program in a computer apparatus suitably.

Claims (3)

The transfer device in a network system for connecting networks with a plurality of transfer devices,
A first communication port, a second communication port, a third communication port, and a fourth communication port that transmit and receive frames to and from corresponding external communication devices;
Forwarding the frame received at the first communication port to the second communication port;
Forwarding the frames received at the second communication port to the first and fourth communication ports,
Forwarding the frame received at the third communication port to the fourth communication port;
Transferring frames received at the fourth communication port to the second and third communication ports, respectively.
A transfer section;
A storage unit;
A loop frame prevention unit,
The first to fourth communication ports transmit frames transferred from the transfer unit to the corresponding external communication devices,
The storage unit stores a transmission source address of a frame, a sequence number, and a communication port that has received the frame or a communication port that is an output destination of a frame received by the communication port as a set,
The loop frame prevention unit includes a transmission source address of a frame received at at least one of the first to fourth communication ports, a sequence number, and a communication port that has received the frame or a frame received at the communication port. Check whether a pair with the same communication port as the output destination exists in the storage unit, and if it does not exist, receive at the communication port that received the frame or the communication port that received the frame A set of communication ports to be output destinations of the received frames are stored in the storage unit;
The transfer unit includes a transmission source address, a sequence number of a frame received at at least one of the first to fourth communication ports, and an output destination of a frame received at the communication port or the communication port The transfer apparatus is characterized in that the frame is not transferred when the same set as the set of communication ports to be present exists in the storage unit . The transfer unit
Send notification messages from the four communication ports,
Each of the four communication ports receives a response message for the notification message at two communication ports,
The communication port that has received the response message is set to the first communication port and the third communication port,
Of the remaining two communication ports that did not receive the response message, one communication port previously associated with the first communication port is set as the second communication port, and the other communication port is set as the fourth communication port. 2. The transfer device according to claim 1, wherein Based on a network identifier, a transmission source address, or a transmission destination address included in a frame received by at least one of the first to fourth communication ports, it is determined whether to permit transfer of the frame by the transfer unit, and permission 3. The transfer apparatus according to claim 1, further comprising: a filter that discards the frame when it is determined not to do so.

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