Communication network management system and method and management computer

A management computer has: a storage unit in which a route information indicating a transfer route of frames in the communication network is stored; and a monitoring unit. The monitoring unit refers to the route information to transmit a frame to the transfer route and performs identification processing that identifies a location of a failure on the transfer route. First to N-th nodes (N is an integer equal to or more than 3) line up in order along the transfer route. The i-th node (i=1 to N−1) forwards a received frame to the (i+1)-th node, and the N-th node forwards a received frame to the management computer. In the identification processing, the monitoring unit sets at least one node between the first node and the N-th node as an insertion node. Then, the monitoring unit transmits a frame to the insertion node each, and identifies the location of the failure based on reception state of a frame from the N-th node.

TECHNICAL FIELD

The present invention relates to a communication network management technique that performs centralized management of a communication network by using a management computer.

BACKGROUND ART

In recent years, a communication network has a significant role as a social infrastructure that provides various services, and failure of the communication network has an incalculable impact on users. Therefore, health-checking of the communication network has become a very important issue.

Patent Literature 1 (International Publication WO2005/048540) discloses a technique that uses a keep-alive frame to detect a failure in a communication network. More specifically, in a communication system in which a plurality of base nodes perform communication through one or more relay node, each base node transmits a keep-alive frame that is broadcasted by the relay node. Here, the plurality of base nodes mutually transmit and receive the keep-alive frame and detect failure by monitoring arrival state of the keep-alive frame transmitted from the other side node. In this case, in order to health-check all physical links in the communication network, it is necessary to configure a plurality of communication routes so as to cover all the physical links and to transmit and receive the keep-alive frame with respect to each communication route. That is, it is required to transmit and receive a large number of keep-alive frames. This causes increase in transmission and reception burden placed on each base node.

Non-Patent Literature 1 (S. Shah and M. Yip, “Extreme Networks' Ethernet Automatic Protection Switching (EAPS) Version 1”, The Internet Society, October 2003; (http://tools.ietf.org/html/rfc3619)) discloses a health-check technique in a communication network that is configured in a ring shape. In this case, a plurality of switches are connected through communication lines to form a ring shape, and one health-check frame is transferred sequentially along the ring. For example, a master switch on the ring transmits the health-check frame from a first port. Another switch forwards the received health-check frame to the next switch. The master switch receives the self-transmitted health-check frame at a second port, and thereby can confirm that no failure occurs. This technique assumes such a ring-shaped network structure and thus is not versatile.

Patent Literature 2 (Japanese Patent No. 3740982) discloses a technique that a management host computer performs health-check of a plurality of host computers. First, the management host computer determines an order of the health-check for the plurality of host computers. Next, the management host computer generates a health-check packet into which a health-check table is incorporated. The health-check table has a plurality of entries respectively related to the plurality of host computers, and the plurality of entries are arranged in the above determined order. Each entry includes an address of the related host computer and a check flag. Then, the management host computer transmits the health-check packet to a first host computer. A host computer that receives the health-check packet searches for the related entry in the health-check table and marks the check flag of the corresponding entry. After that, the host computer refers to the address in the next entry and transmits the health-check packet to the next host computer. Due to repetition of the above-mentioned processing, one health-check packet travels the host computers. Eventually, the management host computer receives the health-check packet that has traveled in this manner. Then, the management host computer determines that a failure occurs in a host computer the corresponding check flag of which is not marked.

According to Patent Literature 3 (Japanese Patent Publication JP-2006-332787), one health-check packet travels a plurality of monitor-target terminals, as in the case of Patent Literature 2. A similar health-check table is incorporated into the health-check packet. However, each entry includes, instead of the above-mentioned check flag, a check list in which such information as a date and time and an operating status is to be written. A monitoring terminal transmits the health-check packet to a first monitor-target terminal. When receiving the health-check packet, the monitor-target terminal judges whether or not itself is operating normally. In a case of a normal operation, the monitor-target terminal searches for the related entry in the health-check table and writes designated information such as the date and time and the operating status in the check list of the corresponding entry. Then, the monitor-target terminal refers to the address in the next entry and transmits the health-check packet to the next monitor-target terminal. Here, if communication with the next monitor-target terminal is impossible, the monitor-target terminal transmits the health-check packet to the monitor-target terminal after the next monitor-target terminal. Due to repetition of the above-mentioned processing, one health-check packet travels the monitor-target terminals. Eventually, the monitoring terminal receives the health-check packet that has traveled in this manner. If the designated information is not written in any check list, the monitoring terminal determines that a failure occurs.

It should be noted that Patent Literature 4 (Japanese Patent Publication JP-2000-48003), Patent Literature 5 (Japanese Patent Publication JP-H8-286920), Patent Literature 6 (Japanese Patent Publication JP-H11-212959) and Patent Literature 7 (Japanese Patent Publication JP-H3-191464) describe a method for solving a traveling salesman problem.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

According to Patent Literature 3 described above, one health-check packet into which the health-check table is incorporated travels a plurality of nodes. When receiving the health-check packet, each node searches for the related entry in the health-check table and writes predetermined information such as the operating status in the corresponding entry. The predetermined information written in the health-check packet is used by the monitoring terminal for identifying location of failure. That is, the monitoring terminal performs identification of location of failure based on the predetermined information written in the health-check packet that comes back after traveling the plurality of nodes.

However, if communication between a node and the next node is not available, the traveling of the health-check packet is not achieved and thus the monitoring terminal cannot receive the health-check packet. That is, the monitoring terminal cannot perform the processing of identifying the location of failure. Therefore, a node that receives the health-check packet investigates whether or not it can communicate with the next node, before forwarding the health-check packet to the next node. More specifically, the node tries to connect a line with the next node for establishing handshake. If communication with the next node is impossible, the node searches for an available communication partner such as a node after the next node. Then, the node transmits the health-check packet to the available communication partner such as the node after the next node. However, such the processing is complicated and places overmuch burden on each node.

An object of the present invention is to provide a technique that can reduce burden placed on each node, when performing centralized management of a communication network including a plurality of nodes by using a management computer.

In an aspect of the present invention, a communication network management system is provided. The communication network management system has: a communication network; and a management computer configured to manage the communication network. The communication network includes a plurality of nodes and a plurality of links connecting between the plurality of nodes. The management computer has: a storage unit in which a route information indicating a transfer route of frames in the communication network is stored; and a monitoring unit. The monitoring unit refers to the route information to transmit a frame to the transfer route and performs identification processing that identifies a location of a failure on the transfer route. First to N-th nodes (N is an integer equal to or more than 3) line up in order along the transfer route. The i-th node (i=1 to N−1) forwards a received frame to the (i+1)-th node, and the N-th node forwards a received frame to the management computer. In the identification processing, the monitoring unit sets at least one node between the first node and the N-th node as an insertion node. Then, the monitoring unit transmits a frame to the insertion node each, and identifies the location of the failure based on reception state of a frame from the N-th node.

In another aspect of the present invention, a management computer that manages a communication network is provided. The communication network includes a plurality of nodes and a plurality of links connecting between the plurality of nodes. The management computer has: a storage unit in which a route information indicating a transfer route of frames in the communication network is stored; and a monitoring unit. The monitoring unit refers to the route information to transmit a frame to the transfer route and performs identification processing that identifies a location of a failure on the transfer route. First to N-th nodes (N is an integer equal to or more than 3) line up in order along the transfer route. The i-th node (i=1 to N−1) forwards a received frame to the (i+1)-th node, and the N-th node forwards a received frame to the management computer. In the identification processing, the monitoring unit sets at least one node between the first node and the N-th node as an insertion node. Then, the monitoring unit transmits a frame to the insertion node each, and identifies the location of the failure based on reception state of a frame from the N-th node.

In still another aspect of the present invention, a communication network management method that manages a communication network by using a management computer is provided. The communication network includes a plurality of nodes and a plurality of links connecting between the plurality of nodes. The communication network management method includes: transmitting a frame from the management computer to a transfer route of frames in the communication network. Here, first to N-th nodes (N is an integer equal to or more than 3) line up in order along the transfer route. The i-th node (i=1 to N−1) forwards a received frame to the (i+1)-th node, and the N-th node forwards a received frame to the management computer. The communication network management method further includes: identifying, by the management computer, a location of a failure on the transfer route. The identifying includes: setting at least one node between the first node and the N-th node as an insertion node; transmitting a frame to the insertion node each; and identifying the location of the failure based on reception state of a frame from the N-th node.

In still another aspect of the present invention, a management program recorded on a tangible computer-readable medium that, when executed, causes a management computer to perform management processing of a communication network is provided. The communication network includes a plurality of nodes and a plurality of links connecting between the plurality of nodes. The management processing includes: storing a route information indicating a transfer route of frames in the communication network in a storage device; and transmitting a frame to the transfer route by referring to the route information. Here, first to N-th nodes (N is an integer equal to or more than 3) line up in order along the transfer route. The i-th node (i=1 to N−1) forwards a received frame to the (i+1)-th node, and the N-th node forwards a received frame to the management computer. The management processing further includes: identifying a location of a failure on the transfer route. The identifying includes: setting at least one node between the first node and the N-th node as an insertion node; transmitting a frame to the insertion node each; and identifying the location of the failure based on reception state of a frame from the N-th node.

According to the present invention, it is possible to reduce burden placed on each node, when performing centralized management of a communication network including a plurality of nodes by using a management computer.

DESCRIPTION OF EMBODIMENTS

FIG. 1schematically shows a configuration example of a communication network management system100according to an exemplary embodiment of the present invention. In the communication network management system100, centralized management of a communication network is performed by a management computer. That is, the communication network management system100is provided with a communication network NET and a management computer1that manages the communication network NET, as shown inFIG. 1.

The communication network NET includes a plurality of nodes2to5and a plurality of physical links71to75connecting between the nodes2to5. The physical link71is a signal line that bi-directionally connects the node2and the node4. The node2and the node4can communicate bi-directionally through the physical link71. The physical link72is a signal line that bi-directionally connects the node4and the node5. The node4and the node5can communicate bi-directionally through the physical link72. The physical link73is a signal line that bi-directionally connects the node5and the node2. The node5and the node2can communicate bi-directionally through the physical link73. The physical link74is a signal line that bi-directionally connects the node2and the node3. The node2and the node3can communicate bi-directionally through the physical link74. The physical link75is a signal line that bi-directionally connects the node3and the node5. The node3and the node5can communicate bi-directionally through the physical link75.

A control link62is a signal line that bi-directionally connects the management computer1and the node2. A control link63is a signal line that bi-directionally connects the management computer1and the node3. A control link64is a signal line that bi-directionally connects the management computer1and the node4. A control link65is a signal line that bi-directionally connects the management computer1and the node5. The management computer1and the nodes2to5can communicate bi-directionally through the control links62to65, respectively.

The management computer1transmits a frame for health-check (hereinafter referred to as a “check frame FR”) to the communication network NET. The check frame FR goes through a certain transfer route PW in the communication network NET and comes back to the management computer1. The transfer route PW of the check frame FR may be appropriately determined by the management computer1or may be fixed.

As an example, a transfer route PW along which the check frame FR travels in an order of “node2-4-5-2-3-5” is shown inFIG. 1. In this case, the management computer1transmits the check frame FR to the node2through the control link62. The node2forwards the received check frame FR to the subsequent node4through the physical link71. The node4forwards the received check frame FR to the subsequent node5through the physical link72. The node5forwards the received check frame FR to the subsequent node2through the physical link73. The node2forwards the received check frame FR to the subsequent node3through the physical link74. The node3forwards the received check frame FR to the subsequent node5through the physical link75. In this manner, each node, when receiving the check frame FR, forwards the received check frame FR along the transfer route PW. Lastly, the node5forwards the received check frame FR to the management computer1.

FIG. 2shows in an easy-to-understand manner the travelling of the check frame FR shown inFIG. 1. N nodes line up in order on the transfer route PW of the check frame FR. The N is an integer equal to or more than 3. Hereinafter, the N nodes are respectively referred to as “first to N-th nodes” in an order along the transfer route PW. The first to N-th nodes may include a physically identical node for plural times. In the example shown inFIG. 2, N=6, the first node is the node2, the second node is the node4, the third node is the node5, the fourth node is the node2, the fifth node is the node3, and the sixth node is the node5.

At normal times, the management computer1transmits a check frame FR to the first node being a start-point of the transfer route PW. The i-th node (i=1 to N−1) on the transfer route PW, when receiving the check frame FR, forwards the received check frame FR to the (i+1)-th node. The N-th node, when receiving the check frame FR, forwards the received check frame FR to the management computer1. In this manner, the travelling of the check frame FR is achieved.

Here, let us consider a case where a failure is occurring at some node on the transfer route PW. In this case, the management computer1carries out identification of location of the failure on the transfer route PW. More specifically, the management computer1transmits a check frame FR to at least one node in the middle of the transfer route PW. Such the node is hereinafter referred to as an “insertion node”. That is, the management computer1sets at least one node between the first node and the N-th node on the transfer route PW as the “insertion node”. Then, the management computer1transmits the check frame FR to each insertion node. As an example,FIG. 2shows a case where the third node is selected as the insertion node.

After that, each node performs the processing of forwarding the check frame FR in a similar way. If the management computer1receives the check frame FR from the N-th node, it means that the check frame FR has been transferred from the insertion node to the N-th node without being lost. Therefore, the management computer1can judge that the links after the insertion node are healthy and there exists the failure in the transfer route PW before the insertion node. On the other hand, if the management computer1does not receive the check frame FR from the N-th node, it means that the check frame FR has not been transferred from the insertion node to the N-th node. Therefore, the management computer1can judge that there exists the failure in the transfer route PW after the insertion node. By appropriately change the insertion node and repeating the same processing, the management computer1can identify the location of failure on the transfer route PW. That is, the management computer1, which transmits the check frame FR to the insertion node, can identify the location of failure based on reception state of the check frame FR from the N-th node.

According to the present exemplary embodiment, each node on the transfer route PW just needs to forward the received check frame FR also in the failure location identification processing, as in the case of normal times. There is no need to change the setting of each node for identifying the location of failure. Also, each node needs not to write health-check information and the like to the check frame FR. Furthermore the complicated processing such as required in Patent Literature 2 or Patent Literature 3 is not necessary for identifying the location of failure. For example, such processing as described in Patent Literature 3 that each node investigates whether or not it can communicate with the next node is not necessary. Consequently, burden placed on each node is greatly reduced. According to the present exemplary embodiment, it is possible to identify the location of failure on the transfer route PW with simple processing and to reduce burden placed on each node.

It should be noted that although the term “frame” is used in the above description, the same applies to a case of “packet (IP packet etc.)”.

The present invention can be applied to health-check of nodes and physical links on a LAN of companies, data centers, universities and the like and health-check of communication equipments and physical links of telecommunication carriers.

2. Concrete Example

Hereinafter, an exemplary embodiment of the present invention will be described in more detail. Various methods are possible as a method for achieving the traveling of the check frame FR along a predetermined transfer route PW in the communication network NET. In the following description, for example, each node is provided with a “forwarding table” in order to achieve the traveling of the check frame FR. The forwarding table is a table that indicates a correspondence relationship between input sources and forwarding destinations of the check frames FR. Each node can forward the check frame FR received from an input source to a designated forwarding destination, by referring to the forwarding table.

Contents of the forwarding table of each node are set up by each node in accordance with an instruction from the management computer1. More specifically, the management computer1uses the control link (62,63,64,65) to instruct each node (2,3,4,5) to set up the forwarding table. Here, the management computer1instructs each node to set up the forwarding table such that the check frames FR are forwarded along the transfer route PW. Each node sets up the contents of the forwarding table in accordance with the instruction from the management computer1.

Various interfaces are possible as an interface between the management computer and the nodes for achieving the processing described above. For example, Openflow (refer to http://www.openflowswitch.org/) is applicable. In this case, an “Openflow Controller” serves as the management computer1and an “Openflow Switch” serves as each of the nodes2to5. It is possible to set up the forwarding table by using “Secure Channel” of the Openflow. Alternatively, GMPLS (Generalized Multi-Protocol Label Switching) also is applicable. In this case, the management computer instructs a GMPLS switch to set up the forwarding table. Alternatively, VLAN (Virtual LAN) also is applicable. In this case, the management computer can control VLAN setting of each switch by using an MIB (Management Information Base) interface.

In the following description, let us consider a case where the Openflow is used as the interface between the management computer and the nodes.

FIG. 3is a block diagram showing a configuration example of the communication network management system100according to the present exemplary embodiment. A management host1(Openflow Controller) inFIG. 3is equivalent to the management computer1inFIG. 1. Switches2to5(Openflow Switch) inFIG. 3are equivalent to the nodes2to5inFIG. 1, respectively.

The management host1has a storage unit10, a topology management unit11, a route designing unit12, an entry control unit13, a monitoring unit14, a node communication unit15and a display unit16. The node communication unit15is connected to the switches2to5through the control links62to65, respectively. The management host1can communicate bi-directionally with the switches2to5by using the node communication unit15and the control links62to65.

The storage unit10is a storage device such as a RAM and an HDD. A topology table TPL, a route table RTE, an insertion switch table INS and the like are stored in the storage unit10. The topology table TPL (topology information) indicates the above-mentioned physical topology of the communication network NET, namely, a connection relationship between the switches2to5. The route table RTE (route information) indicates the transfer route PW of the check frames FR in the communication network NET. The insertion switch table INS indicates information on an “insertion switch” to which the check frame FR is transmitted at failure location identification processing.

The topology management unit11creates the topology table TPL and stores it in the storage unit10. Moreover, the topology management unit11receives from the node communication unit15a topology change notification that is transmitted from each switch. Here, the topology change notification is information indicating change in the physical topology of the communication network NET and includes new switch connection information, up-down notification of a physical link and so forth. The topology management unit11updates the topology table TPL in accordance with the received topology change notification.

The route designing unit12refers to the topology table TPL stored in the storage unit10to determine (design) the transfer route PW of the check frame FR in the communication network NET. Then, the route designing unit12stores the route table RTE indicating the determined transfer route PW in the storage unit10.

The entry control unit13instructs each switch (2,3,4,5) to set up the forwarding table (22,32,42,52). More specifically, the entry control unit13refers to the topology table TPL and the route table RTE stored in the storage unit10. Then, the entry control unit13instructs each switch (2,3,4,5) to set up the forwarding table (22,32,42,52) such that the check frames FR are forwarded along the transfer route PW indicated by the route table RTE. The entry control unit13transmits a table setup command indicating the instruction to each switch (2,3,4,5) through the node communication unit15and the control links (62,63,64,65).

The monitoring unit14performs, based on the route table RTE stored in the storage unit10, transmission and reception of the check frames FR to and from the communication network NET. The transmission and reception of the check frame FR to and from the switch2is performed through the node communication unit15and the control link62. The transmission and reception of the check frame FR to and from the switch3is performed through the node communication unit15and the control link63. The transmission and reception of the check frame FR to and from the switch4is performed through the node communication unit15and the control link64. The transmission and reception of the check frame FR to and from the switch5is performed through the node communication unit15and the control link65. Moreover, as will be described later in detail, the monitoring unit14detects a failure occurrence in the transfer route PW and performs processing of identifying a location of the failure.

It should be noted that the topology management unit11, the route designing unit12, the entry control unit13and the monitoring unit14described above can be realized by a processor executing a computer program.

The display unit16is a display device such as a liquid crystal display device. The display unit16displays various information. For example, the display unit16displays the connection state between the switches indicated by the topology table TPL and a state of failure occurrence that will be described below.

The switch2has a table storage unit20, a forwarding processing unit21, a host communication unit23, a table setup unit24, a port27, a port28and a port29. The host communication unit23corresponds to the “Secure Channel” of the “Openflow Switch”. The host communication unit23is connected to the management host1through the control link62, and the switch2can communicate bi-directionally with the management host1by using the host communication unit23and the control link62. Moreover, each port (communication interface) is connected to another switch through the physical link, and the switch2can communicate bi-directionally with another switch by using the port and the physical link.

The table storage unit20is a storage device such as a RAM and an HDD. The forwarding table22that indicates a correspondence relationship between input sources and forwarding destinations of the check frames FR is stored in the table storage unit20.

The forwarding processing unit21receives the check frame FR from the host communication unit23(i.e. management host1). Alternatively, the forwarding processing unit21receives the check frame FR from any port (i.e. another switch). Then, by referring to the forwarding table22stored in the table storage unit20, the forwarding processing unit2forwards the check frame FR received from an input source to a forwarding destination (host communication unit23or port) designated by the forwarding table22. In a case where a plurality of forwarding destinations are designated, the forwarding processing unit21copies the check frame FR and forwards them respectively to the plurality of forwarding destinations.

The table setup unit24receives from the host communication unit23the above-mentioned table setup command transmitted from the management host1. Then, in accordance with the table setup command, the table setup unit24sets (add, delete, change) the contents of the forwarding table22stored in the table storage unit20.

Other switches3to5each has a similar configuration to that of the switch2. That is, the switch3has a table storage unit30, a forwarding processing unit31, a host communication unit33, a table setup unit34, a port37, a port38and a port39. A forwarding table32is stored in the table storage unit30. The switch4has a table storage unit40, a forwarding processing unit41, a host communication unit43, a table setup unit44, a port47, a port48and a port49. A forwarding table42is stored in the table storage unit40. The switch5has a table storage unit50, a forwarding processing unit51, a host communication unit53, a table setup unit54, a port57, a port58and a port59. A forwarding table52is stored in the table storage unit50. Each component and processing are the same as in the case of the switch2, and description thereof is omitted.

In the example shown inFIG. 3, the physical topology of the communication network NET, namely, the connection relationship between the switches2to5is as follows. The port27of the switch2and the port47of the switch4are connected bi-directionally through the physical link71. The port49of the switch4and the port57of the switch5are connected bi-directionally through the physical link72. The port58of the switch5and the port28of the switch2are connected bi-directionally through the physical link73. The port29of the switch2and the port37of the switch3are connected bi-directionally through the physical link74. The port39of the switch3and the port59of the switch5are connected bi-directionally through the physical link75.

3. Detection of Failure Occurrence

FIG. 4is a flow chart showing a communication network management method according to the present exemplary embodiment. The communication network management processing according to the present exemplary embodiment will be described in detail with reference toFIGS. 3 and 4as appropriate. It should be noted that management processing by the management host1is realized by the management host1executing a management program. Also, frame forwarding processing by each switch is realized by the each switch executing a frame forwarding program.

The topology management unit11creates the topology table TPL and stores it in the storage unit10. Moreover, the topology management unit11receives the topology change notification from each switch and updates the topology table TPL in accordance with the topology change notification.

Here, let us consider a case where the physical topology of the communication network NET is as shown inFIG. 3.FIG. 5shows an example of the topology table TPL in that case. The topology table TPL has a plurality of entries that are respectively related to a plurality of physical links71to75. In the case where the physical link is bi-directional, the entry is created with respect to each direction. Each entry indicates a source switch, a source port, a destination switch, a destination port and a status flag with regard to the related physical link. The source switch is a switch as a start-point of the physical link, and the source port is a port of the source switch. The destination switch is a switch as an end-point of the physical link, and the destination port is a port of the destination switch. For example, the first entry “source switch=2, source port=27, destination switch=4, destination port=47” inFIG. 5is related to the physical link71from the switch2toward the switch4. The same applies to the other entries.

The status flag included in each entry indicates whether the related physical link is available or not. If validity of a physical link is confirmed, the status flag of the entry related to the physical link is set to “1 (available)” On the other hand, if validity of a physical link is not yet confirmed or a failure is occurring at the physical link, the status flag of the entry related to the physical link is set to “0 (not available)”. In the example shown inFIG. 5, the status flags of all the entries are “1”.

The route designing unit12refers to the physical topology indicated by the above-mentioned topology table TPL to determine (design) the transfer route PW of the check frame FR. Then, the route designing unit12creates the route table RTE indicating the determined transfer route PW and stores it in the storage unit10.

Here, the route designing unit12may determine the transfer route PW such that all of the physical links71to75is traversable by the transfer route PW. When determining the traversable route, an algorithm for solving the traveling salesman problem (for example, refer to Patent Literature 4, Patent Literature 5, Patent Literature 6 and Patent Literature 7) can be used. In this case, each physical link corresponds to a “destination to visit by a salesman in the traveling salesman problem”.

Moreover, the transfer route PW may not be a complete traversable route. The transfer route PW may be determined such that the check frame FR travels as many physical links as possible. Alternatively, all the physical links71to75may be covered by combining a plurality of traversable routes. In this case, successive route IDs such as “00”, “01”, “02” are given to the respective traversable routes.

FIG. 6shows an example of the transfer route PW with which the physical links71to75are traversable. In the case of the transfer route PW shown inFIG. 6, the switch2(first switch), the physical link71, the switch4(second switch), the physical link72, the switch5(third switch), the physical link73, the switch2(fourth switch), the physical link74, the switch3(fifth switch), the physical link75and the switch5(sixth switch) are connected in this order. The check frame FR is transferred along this transfer route PW.

FIG. 7shows an example of the route table RTE in the case of the transfer route PW shown inFIG. 6. The route table RTE has a plurality of entries that indicate in order the transfer route PW shown inFIG. 6. Each entry indicates the route ID, a sequence, a stopover switch and an output port. The route ID is an ID that is given with respect to each transfer route PW. The sequence indicates a sequence number of each switch. In the present example, there exist first to sixth switches in this order along the transfer route PW. The stopover switch indicates a switch associated with the sequence number. The output port is a port connected to the next sequence number switch and indicates an output destination of the check frame FR. If the output destination is the host communication unit (i.e. management host1), the output port is expressed by “HOST”.

FIG. 8is a conceptual diagram showing an example of the check frame FR. The check frame FR has information on a destination MAC address (MAC DA), a source MAC address (MAC SA), the route ID and a sequence number A. In the present exemplary embodiment, the destination MAC address is used for distinguishing the check frame FR. The setting of the destination MAC address is arbitrary as long as the check frame FR can be distinguished. For example, the destination MAC address is set to “00-00-4c-00-aa-00”. The source MAC address is set to a MAC address “00-00-4c-00-12-34” of the management host1. The route ID is an ID that is given with respect to each transfer route PW, as described above. The sequence number A indicates the sequence number of a destination switch to which the check frame FR is transmitted from the management host1. For example, in a case where a check frame FR is transmitted from the management host1to the first switch, the sequence number A of the check frame FR is set to “1” according to the route table RTE shown inFIG. 7.

The entry control unit13of the management host1instructs the table setup unit of each of the switches2to5to set up each forwarding table. At this time, the entry control unit13refers to the topology table TPL and the route table RTE stored in the storage unit10. Then, the entry control unit13determines contents of the instruction such that the check frame FR is forwarded along the transfer route PW indicated by the route table RTE. The table setup command indicating the instruction is transmitted from the entry control unit13to each switch (2,3,4,5) through the node communication unit15and the control link (62,63,64,65).

In the switch2, the table setup unit24receives the table setup command from the host communication unit23. Then, the table setup unit24sets, in accordance with the table setup command, the contents of the forwarding table22stored in the table storage unit20.FIG. 9shows an example of the forwarding table22in the case of the transfer route PW shown inFIG. 6. The forwarding table22indicates an input port, the destination MAC address (MAC DA), the source MAC address (MAC SA) and an output port.

The input port indicates the input source (port or host communication unit23) to which the check frame FR is input. If the input source is any port (i.e. another switch), the input port is expressed by its port number. If the input source is the host communication unit23(i.e. the management host1), the input port is expressed by “HOST”.

The output port indicates the forwarding destination (port or host communication unit23) to which the check frame FR is forwarded. If the forwarding destination is any port (i.e. another switch), the output port is expressed by its port number. If the forwarding destination is the host communication unit23(i.e. management host1), the output port is expressed by “HOST”. It should be noted that a plurality of output ports may be set with respect to one entry. In this case, the check frame FR is output to the respective output ports.

The destination MAC address in the forwarding table22is the same as the above-mentioned destination MAC address in the check frame FR. In the present example, the destination MAC address is “00-00-4c-00-aa-00”. Moreover, the source MAC address in the forwarding table22is the same as the above-mentioned source MAC address in the check frame FR. In the present example, the source MAC address is the MAC address “00-00-4c-00-12-34” of the management host1. It should be noted that the source MAC address may be omitted if only one management host1is used.

As described above, the forwarding table22includes the input source (input port), the forwarding destination (output port) and header information (MAC DA, MAC SA and the like) regarding the check frame FR. In other words, the forwarding table22indicates a correspondence relationship between the input source, the header information and the forwarding destination with regard to the check frame FR. By referring to such the forwarding table22, the forwarding processing unit21is able to forward the received check frame FR to the designated forwarding destination. At this time, the input port and the header information (MAC DA, MAC SA) are used as a search keyword for the associated output port. As an example, let us consider a case where the forwarding processing unit21receives the check frame FR (MAC DA=00-00-4c-00-aa-00, MAC SA=00-00-4c-00-12-34) from the host communication unit23(input port=HOST). In this case, the first entry in the forwarding table22becomes a hit entry. Therefore, the forwarding processing unit21forwards the check frame FR to the output port27indicated by the hit entry. That is, the check frame FR transmitted from the management host1is output to the physical link71connected to the output port27and thus forwarded to the switch4. In this manner, the forwarding of the check frame FR is achieved.

In the switch3, the table setup unit34receives the table setup command from the host communication unit33. Then, the table setup unit34sets, in accordance with the table setup command, the contents of the forwarding table32stored in the table storage unit30.FIG. 10shows the forwarding table32in the present example.

In the switch4, the table setup unit44receives the table setup command from the host communication unit43. Then, the table setup unit44sets, in accordance with the table setup command, the contents of the forwarding table42stored in the table storage unit40.FIG. 11shows the forwarding table42in the present example.

In the switch5, the table setup unit54receives the table setup command from the host communication unit53. Then, the table setup unit54sets, in accordance with the table setup command, the contents of the forwarding table52stored in the table storage unit50.FIG. 12shows the forwarding table52in the present example.

After the Step S13is completed, the monitoring unit14of the management host1periodically performs transmission of the check frame FR. The forwarding processing unit of each switch, when receiving the check frame FR, forwards the check frame FR.FIG. 13shows transmission and forwarding processing of the check frame FR at normal times. InFIG. 13, dashed arrows indicate communications by using the control links62to65, and solid arrows indicate communications by using the physical links71to75.

First, the monitoring unit14generates a check frame FR as shown inFIG. 8. Subsequently, the monitoring unit14refers to the route table RTE shown inFIG. 7to transmit the check frame FR to the first switch on the transfer route PW, i.e. the switch2(first switch). At this time, the sequence number A of the check frame FR for transmission is set to “1”. Moreover, the monitoring unit14starts a first timer TM1and a second timer TM2at the same time as the transmission of the check frame FR. The first timer TM1is used for performing the periodical transmission of the check frame FR. That is, the monitoring unit14performs the transmission of the check frame FR at a predetermined interval counted by the first timer TM1. The second timer TM2is used for processing of detecting failure occurrence which will be described later. A set time of the second timer TM2is substantially longer than a set time of the first timer TM1.

The check frame FR is transmitted from the node communication unit15of the management host1through the control link62to reach the host communication unit23of the switch2(first switch). The forwarding processing unit21receives the check frame FR from the host communication unit23. The forwarding processing unit21refers to the forwarding table22shown inFIG. 9to forward the received check frame FR to the port27(i.e. switch4).

The check frame FR is transmitted from the port27of the switch2through the physical link71to reach the port47of the switch4(second switch). The forwarding processing unit41receives the check frame FR from the port47. The forwarding processing unit41refers to the forwarding table42shown inFIG. 11to forward the received check frame FR to the port49(i.e. switch5).

The check frame FR is transmitted from the port49of the switch4through the physical link72to reach the port57of the switch5(third switch). The forwarding processing unit51receives the check frame FR from the port57. The forwarding processing unit51refers to the forwarding table52shown inFIG. 12to forward the received check frame FR to the port58(i.e. switch2).

The check frame FR is transmitted from the port58of the switch5through the physical link73to reach the port28of the switch2(fourth switch). The forwarding processing unit21receives the check frame FR from the port28. The forwarding processing unit21refers to the forwarding table22shown inFIG. 9to forward the received check frame FR to the port29(i.e. switch3).

The check frame FR is transmitted from the port29of the switch2through the physical link74to reach the port37of the switch3(fifth switch). The forwarding processing unit31receives the check frame FR from the port37. The forwarding processing unit31refers to the forwarding table32shown inFIG. 10to forward the received check frame FR to the port39(i.e. switch5).

The check frame FR is transmitted from the port39of the switch3through the physical link75to reach the port59of the switch5(sixth switch). The forwarding processing unit51receives the check frame FR from the port59. The forwarding processing unit51refers to the forwarding table52shown inFIG. 12to forward the received check frame FR to the host communication unit53(i.e. management host1).

The check frame FR is transmitted from the host communication unit53of the switch5(sixth switch) through the control link65to reach the node communication unit15of the management host1. In this manner, the transfer (travel) of the check frame FR along the transfer route PW is achieved.

The monitoring unit14of the management host1monitors arrival of the check frame FR. In the case of the example shown inFIG. 13, the check frame FR returns back to the management host1from the switch5(sixth switch) without being lost on the way. In this case, the monitoring unit14receives the check frame FR before the sufficiently long second timer TM2expires. That is, the monitoring unit14receives the check frame FR from the sixth switch within a predetermined period of time counted by the second timer TM2after transmitting the check frame FR to the first switch. In this case, the monitoring unit14resets the second timer TM2and determines that no failure is occurring on the transfer route PW (Step S20; No).

After that, when the first timer TM1expires, the monitoring unit14transmits a new check frame FR. Then, the Steps S14and S15are repeated. In this manner, at normal times, the check frame FR periodically travels the transfer route PW and whether or not a failure is occurring is judged every travel.

FIG. 14shows a case where a failure is occurring at a part of the transfer route PW. As an example, let us consider a case where a failure occurs at the physical link72between the switch4and the switch5and the bi-directional communication there becomes impossible. As in the case ofFIG. 13, the monitoring unit14periodically transmits the check frame FR. However, since the failure occurs at the physical link72, the check frame FR is not transferred from the switch4to the switch5. Therefore, the second timer TM2expires without the monitoring unit14receiving the check frame FR. That is, the monitoring unit14does not receive the check frame FR from the sixth switch within a predetermined period of time counted by the second timer TM2after transmitting the check frame FR to the first switch. In this case, the monitoring unit14determines that a failure is occurring somewhere on the transfer route PW (Step S20; Yes).

In this manner, the monitoring unit14can detect failure occurrence on the transfer route PW by monitoring reception state of the check frame FR. When the failure occurrence is detected, the monitoring unit14instructs the display unit16to display that effect. The display unit16displays the physical topology indicated by the topology table TPL, the transfer route PW indicated by the route table RTE and the failure occurrence on the transfer route PW. If the failure occurrence is detected by the monitoring unit14, the processing proceeds to identification of location of the failure (Step S100).

4. Identification of Location of Failure (Step S100)

The failure location identification processing according to the present exemplary embodiment will be described hereinafter. Let us consider a case where the location of failure is the physical link72from the second switch (switch4) toward the third switch (switch5). Various algorithms for identifying the location of failure are possible as follows.

4-1. First Example

FIG. 15is a flow chart showing a first example of Step S100.FIG. 16shows an insertion switch table INS used in Step S100. In the present example, the insertion switch table INS indicates the sequence number i of the insertion switch.FIG. 17conceptually shows forwarding of the check frame FR in the present example.

First, the monitoring unit14refers to the route table RTE to initialize the insertion switch table INS stored in the storage unit10. In the present example, a switch whose sequence number is immediately before the final sequence number in the transfer route PW indicated by the route table RTE is set as an initial insertion switch. That is, the initial insertion switch is set to the fifth switch immediately before the end-point (N-th switch) of the transfer route PW. The monitoring unit14sets the sequence number i in the insertion switch table INS to “5 (=N−1)”.

Next, the monitoring unit14refers to the insertion switch table INS and the route table RTE to transmit a check frame FR to the insertion switch (Step S111). More specifically, the monitoring unit14reads the sequence number i of the insertion switch from the insertion switch table INS, and reads the “stopover switch” and the “output port” associated with the sequence number i from the route table RTE. Then, the monitoring unit14transmits the check frame FR to the stopover switch (i.e. the insertion switch) with specifying the output port. At this time, the sequence number A of the transmitted check frame FR is set to be equal to the sequence number i of the insertion switch. Moreover, the monitoring unit14starts the second timer TM2at the same time as the transmission of the check frame FR to the insertion switch.

The initial insertion switch is the fifth switch (i=5). Therefore, the monitoring unit14reads “stopover switch=3” and “output port=39” from the route table RTE. Then, the monitoring unit14transmits the check frame FR (A=5) to the switch3(fifth switch) with specifying “output port=39”. The switch3, when receiving the check frame FR from the management host1, outputs the check frame FR from the specified “output port=39”. That is, the check frame FR is forwarded to the switch5(sixth switch). The switch5forwards the received check frame FR to the management host1, as in the case of the normal time.

The monitoring unit14monitors arrival of the transmitted check frame FR (Step S112). In the case where the insertion switch is the fifth switch (i=5), the monitoring unit14receives the check frame FR from the sixth switch before the second timer TM2expires (Step S113; Yes). In this case, the monitoring unit14resets the second timer TMs and rewrites the insertion switch table INS to change the insertion switch. More specifically, the monitoring unit14decreases the sequence number i of the insertion switch by 1 (Step S114). In other words, the monitoring unit14changes the insertion switch to the preceding one along the transfer route PW. After that, the processing returns back to Step S111.

In the case where the insertion switch is the fourth switch (i=4), the processing is carried out in a similar way and the monitoring unit14receives the check frame FR from the sixth switch (Step S113; Yes). As a result, the insertion switch is changed to the third switch (i=3). Also in the case where the insertion switch is the third switch (i=3), the processing is carried out in a similar way and the monitoring unit14receives the check frame FR from the sixth switch (Step S113; Yes). As a result, the insertion switch is changed to the second switch (i=2).

In the case where the insertion switch is the second switch (i=2), the monitoring unit14transmits the check frame FR (A=2) to the switch4(second switch) with specifying “output port=49”. The switch4, when receiving the check frame FR from the management host1, outputs the check frame FR from the specified “output port=49”. However, the failure is occurring between the switch4and the switch5and thus the check frame FR does not reach the switch5(third switch). In this case, the monitoring unit14fails to receive the check frame FR from the sixth switch before the second timer TM2expires (Step S113; No).

The second timer TM2expires while the monitoring unit14does not receive the check frame FR. At this time, the sequence number i of the insertion switch indicated by the insertion switch table INS is “2”. The monitoring unit14refers to the insertion switch table INS and determines that the failure is occurring between the second switch (i=2) and the subsequent third switch (i=3). Further, the monitoring unit14can convert the second switch (i=2) and the third switch (i=3) to the switch4and the switch5, respectively, by referring to the route table RTE. That is, the monitoring unit14can determine that the failure is occurring between the switch4and the switch5.

When the location of failure is identified, the monitoring unit14updates the status flag in the topology table TPL stored in the storage unit10. More specifically, the status flag of the entry “source switch=4, source port=49, end-point switch=5, end-point port=57” associated with the physical link72from the switch4to the switch5is updated to “0 (not available)”.

The monitoring unit14instructs the display unit16to display the identified location of failure. The display unit16refers to the topology table TPL and displays the link whose status flag is “0” as the location of failure.

According to the first example, as described above, the monitoring unit14searches for the location of failure in a linear manner from the end-point of the transfer route PW toward the upstream. More specifically, the monitoring unit14changes the insertion switch in turn from the (N−1)-th switch towards the first switch until the monitoring unit14fails to receive the check frame FR from the N-th switch. The insertion switch when the monitoring unit14fails to receive the check frame from the N-th switch is a k-th switch. In this case, the monitoring unit14determines that the failure is occurring between the k-th switch and the (k+1)-th switch. When a total of N switches exist along the transfer route PW, the number of links on the transfer route PW is N−1. Therefore, the monitoring unit14can identify the location of failure by the frame transmission for (N−1)/2 times on average and N−1 times at a maximum.

4-2. Second Example

In a second example, the monitoring unit14searches for the location of failure from the start-point of the transfer route PW toward the downstream, which is the opposite to the case of the first example.FIG. 18andFIG. 19respectively show a flow chart and forwarding of the check frame FR in the second example. The insertion switch table INS used in the present example is the same as that in the first example (refer toFIG. 16). An overlapping description with the first example will be omitted as appropriate.

First, the monitoring unit14refers to the route table RTE to initialize the insertion switch table INS stored in the storage unit10. In the present example, a switch whose sequence number is immediately after the initial sequence number in the transfer route PW indicated by the route table RTE is set as an initial insertion switch. That is, the initial insertion switch is set to the second switch immediately after the start-point (first switch) of the transfer route PW. The monitoring unit14sets the sequence number i in the insertion switch table INS to “2”.

Next, the monitoring unit14refers to the insertion switch table INS and the route table RTE to transmit a check frame FR to the insertion switch (Step S121). Moreover, the monitoring unit14monitors arrival of the transmitted check frame FR (Step S122). The transmission and forwarding of the check frame FR are the same as those in Step S111in the first example.

In the case where the insertion switch is the second switch (i=2), the monitoring unit14transmits the check frame FR (A=2) to the switch4(second switch) with specifying “output port=49”. The switch4, when receiving the check frame FR from the management host1, outputs the check frame FR from the specified “output port=49”. However, the failure is occurring between the switch4and the switch5and thus the check frame FR does not reach the switch5(third switch). In this case, the monitoring unit14fails to receive the check frame FR from the sixth switch before the second timer TM2expires (Step S123; No). In this case, the monitoring unit14rewrites the insertion switch table INS to change the insertion switch. More specifically, the monitoring unit14increases the sequence number i of the insertion switch by 1 (Step S124). In other words, the monitoring unit14changes the insertion switch to the subsequent one along the transfer route PW. After that, the processing returns back to Step S121.

In the case where the insertion switch is the third switch (i=3), the check frame FR is forwarded from the third switch to the sixth switch in order and returns back to the management host1. That is, the monitoring unit14receives the check frame FR from the sixth switch before the second timer TM2expires (Step S123; Yes).

When the monitoring unit14receives the check frame FR, the sequence number i of the insertion switch indicated by the insertion switch table INS is “3”. The monitoring unit14refers to the insertion switch table INS and determines that the failure is occurring between the third switch (i=3) and the preceding second switch (i=2). Further, the monitoring unit14can convert the second switch (i=2) and the third switch (i=3) to the switch4and the switch5, respectively, by referring to the route table RTE. That is, the monitoring unit14can determine that the failure is occurring between the switch4and the switch5.

When the location of failure is identified, the monitoring unit14updates the status flag in the topology table TPL as in the case of the first example. Moreover, the monitoring unit14instructs the display unit16to display the identified location of failure. The display unit16refers to the topology table TPL and displays the link whose status flag is “0” as the location of failure.

According to the second example, as described above, the monitoring unit14searches for the location of failure in a linear manner from the start-point of the transfer route PW toward the downstream. More specifically, the monitoring unit14changes the insertion switch in turn from the second switch towards the N-th switch until the monitoring unit14receives the check frame FR from the N-th switch. The insertion switch when the monitoring unit14receives the check frame from the N-th switch is a k-th switch. In this case, the monitoring unit14determines that the failure is occurring between the (k−1)-th switch and the k-th switch. An efficiency of identifying the location of failure is the same as in the case of the first example.

4-3. Third Example

In a third example, a “search range” in which the location of failure is searched for is defined. The search range can be said be to an interval where the failure is considered to be occurring. By gradually narrowing the search range, the location of failure can be identified. A start-point switch and an end-point switch of the search range are hereinafter referred to as a “range start switch” and a “range end switch”, respectively. When the sequence number on the transfer route PW is used, the range start switch is expressed as a s-th switch, and the range end node is expressed as a e-th switch. Here, the “s” is in a range from 1 to N−1. The “e” is in a range from 2 to N and is larger than “s”.

FIG. 20is a flow chart in the third example. FIG.21shows the insertion switch table INS used in the third example. In the present example, the insertion switch table INS indicates the sequence numbers (s, e) of the range start switch and the range end switch in addition to the sequence number m of the insertion switch.FIG. 22conceptually shows forwarding of the check frame FR in the present example. An overlapping description with the first example will be omitted as appropriate.

First, the monitoring unit14refers to the route table RTE to initialize the insertion switch table INS stored in the storage unit10. More specifically, the monitoring unit14initially sets the start-point (first switch) and the end-point (sixth switch) of the transfer route PW as the range start switch and the range end switch, respectively (s=1, e=6). This is equivalent to the maximum search range.

Moreover, the monitoring unit14sets any switch (intermediate switch=m-th switch) between the range start switch (s-th switch) and the range end switch (e-th switch) as the insertion switch. Here, any switch can be selected as long as it exists between the range start switch and the range end switch. However, from a viewpoint of the efficiency of identifying the location of failure, it is preferable that a switch located at nearly middle of the range start switch and the range end switch is set as the insertion switch. In this case, the “m” is a maximum natural number not more than (s+e)/2, which can be expressed by the following Equation (1).
m=INT((s+e)/2)  Equation (1)

This is equivalent to the binary search. In the initial setting stage, s=1, e=6, and m is set to 3. That is, the insertion switch is set to the third switch.

Next, the monitoring unit14refers to the insertion switch table INS and the route table RTE to transmit a check frame FR to the insertion switch (Step S131). Moreover, the monitoring unit14monitors arrival of the transmitted check frame FR (Step S132). The transmission and forwarding of the check frame FR are the same as those in Step S111in the first example.

In the case where the insertion switch is the third switch (m=3), the monitoring unit14transmits the check frame FR (A=3) to the switch5(third switch) with specifying “output port=58”. The check frame FR is forwarded from the third switch to the sixth switch in order and returns back to the management host1. That is, the monitoring unit14receives the check frame FR from the sixth switch before the second timer TM2expires (Step S133; Yes). In this case, the monitoring unit14determines that the transfer route after the current insertion switch is normal and newly sets the current insertion switch (intermediate switch) as the range end switch (Step S134). That is, the monitoring unit14updates the “e” in the insertion switch table INS to the current m=3. Furthermore, the monitoring unit14recalculates the “m” in accordance with the above-mentioned Equation (1) (Step S136). As a result, the insertion switch is changed from the third switch (m=3) to the second switch (m=2). If “m” and “s” are different from each other (Step S137; No), the processing returns back to Step S131.

In the case where the insertion switch is the second switch (m=2), the monitoring unit14transmits the check frame FR (A=2) to the switch4(second switch) with specifying “output port=49”. The switch4, when receiving the check frame FR from the management host1, outputs the check frame FR from the specified “output port=49”. However, the failure is occurring between the switch4and the switch5and thus the check frame FR does not reach the switch5(third switch). In this case, the monitoring unit14fails to receive the check frame FR from the sixth switch before the second timer TM2expires (Step S133; No). In this case, the monitoring unit14determines that the failure exists after the current insertion switch and newly sets the current insertion switch (intermediate switch) as the range start switch (Step S135). That is, the monitoring unit14updates the “s” in the insertion switch table INS to the current m=2. Furthermore, the monitoring unit14recalculates the “m” in accordance with the above-mentioned Equation (1) (Step S136). As a result, the “m” becomes 2.

Here, the “m” and the “s” both become 2. If the and the “s” are equal to each other (Step S137; Yes), it means that there is no switch between the range start switch and the range end switch. In other words, the search range is narrowed to the limit. Therefore, the monitoring unit14can determine that the failure is occurring between the current range start switch and the current range end switch. That is, the monitoring unit14refers to the current insertion switch table INS and determines that the failure is occurring between the second switch (s=2) and the third switch (e=3). Further, the monitoring unit14can convert the second switch (s=2) and the third switch (e=3) to the switch4and the switch5, respectively, by referring to the route table RTE. That is, the monitoring unit14can determine that the failure is occurring between the switch4and the switch5.

When the location of failure is identified, the monitoring unit14updates the status flag in the topology table TPL as in the case of the first example. Moreover, the monitoring unit14instructs the display unit16to display the identified location of failure. The display unit16refers to the topology table TPL and displays the link whose status flag is “0” as the location of failure.

According to the third example, as described above, the monitoring unit14searches for the location of failure by gradually narrowing the search range. In the case of the binary search, the monitoring unit14can identify the location of failure by the frame transmission for log 2(N−1) times on average and log 2(N−1)+1 times at a maximum. Therefore, the efficiency is improved as compared with the case of the first example. The present example is particularly preferable in a case where the total number N of the switches on the transfer route PW is large.

4-4. Fourth Example

In the fourth example, the search range is defined, as in the case of the third example. Although one intermediate switch within the search range is set as the insertion switch in the case of the third example, a plurality of intermediate switches within the search range are concurrently set as the insertion switches in the case of the fourth example. Therefore, the check frame FR is concurrently transmitted to the plurality of insertion switches (intermediate switches).

FIG. 23is a flow chart in the fourth example.FIG. 24shows the insertion switch table INS used in the fourth example. In the present example, the insertion switch table INS indicates the sequence numbers mj (j=1 to n; n is an integer equal to or more than 2) of the n insertion switches and the sequence numbers (s, e) of the range start switch and the range end switch.FIG. 25conceptually shows forwarding of the check frame FR in the present example. An overlapping description with the first example will be omitted as appropriate.

First, the monitoring unit14refers to the route table RTE to initialize the insertion switch table INS stored in the storage unit10. More specifically, the monitoring unit14initially sets the start-point (first switch) and the end-point (sixth switch) of the transfer route PW as the range start switch and the range end switch, respectively (s=1, e=6). This is equivalent to the maximum search range.

Moreover, the monitoring unit14sets n intermediate switches (m1-th to mn-th switches) between the range start switch (s-th switch) and the range end switch (e-th switch) as the insertion switches. Here, any switch can be selected as long as it exists between the range start switch and the range end switch. However, from a viewpoint of the efficiency of identifying the location of failure, it is preferable that the n intermediate switches are so selected as to divide the search range into (n+1) sections at substantially regular intervals. In this case, mj (j=1 to n) is a maximum natural number not more than ((n+1−j)×s+j×e)/(n+1), which can be expressed by the following Equation (2).
mj=INT(((n+1−j)×s+j×e)/(n+1))  Equation (2)

Hereinafter, let us consider a case where n=2. In this case, two intermediate switches (m1-th switch, m2-th switch) become the insertion switches at the same time. In the initial setting stage, s=1, e=6, and the “m1” and the “m2” are respectively calculated to be 2 and 4 according to the Equation (2). That is, the insertion switches are set to the second switch (first intermediate switch) and the fourth switch (second intermediate switch).

Next, the monitoring unit14refers to the insertion switch table INS and the route table RTE to transmit a check frame FR concurrently to the respective insertion switches (Step S141). Moreover, the monitoring unit14monitors arrival of the transmitted check frame FR (Step S142). The transmission and forwarding of the check frame FR are the same as those in Step S111in the first example.

The monitoring unit14transmits a check frame FR (A=4) whose sequence number A is set to “4” to the fourth switch (m2=4). The check frame FR (A=4) is forwarded from the fourth switch to the sixth switch in order and returns back to the management host1. That is, the monitoring unit14receives the check frame FR (A=4) from the sixth switch before the second timer TM2expires (Step S143; Yes). In this case, the monitoring unit14determines that the transfer route after the fourth switch (m2=4) is normal and newly sets the fourth switch as the range end switch (Step S144). That is, the monitoring unit14updates the “e” in the insertion switch table INS to the current m2=4.

Also, the monitoring unit14transmits a check frame FR (A=2) whose sequence number A is set to “2” to the second switch (m1=2). The check frame FR (A=2) is not transferred from the second switch to the third switch and does not return back to the management host1. That is, the monitoring unit14fails to receive the check frame FR (A=2) from the sixth switch before the second timer TM2expires (Step S143; No). In this case, the monitoring unit14determines that the failure exists after the second switch (m1=2) and newly sets the second switch as the range start switch (Step S145). That is, the monitoring unit14updates the “s” in the insertion switch table INS to the current m1=2.

When the second timer TM2expires, the monitoring unit14recalculates the “m” in accordance with the above-mentioned Equation (2) (Step S146). Currently s=2 and e=4, and the “m1” and the “m2” are respectively calculated to be 2 and 3 according to the Equation (2). That is, the insertion switches are set to the second switch and the third switch. If any of the “m1” and “m2” is different from the “s” (Step S147; No), the processing returns back to Step S141.

The monitoring unit14transmits a check frame FR (A=3) whose sequence number A is set to “3” to the third switch (m2=3). The check frame FR (A=3) is forwarded from the third switch to the sixth switch in order and returns back to the management host1. That is, the monitoring unit14receives the check frame FR (A=3) from the sixth switch before the second timer TM2expires (Step S143; Yes). In this case, the monitoring unit14determines that the transfer route after the third switch (m2=3) is normal and newly sets the third switch as the range end switch (Step S144). That is, the monitoring unit14updates the “e” in the insertion switch table INS to the current m2=3.

The second switch (m1=2) as the other insertion switch is the same as the range start switch (s=2). In this case, the monitoring unit14needs not to transmit the check frame FR to the second switch. It should be noted that the check frame FR has been already transmitted to the second switch in the previous processing and it has been confirmed that the check frame FR does not return back.

When the second timer TM2expires, the monitoring unit14recalculates the “m” in accordance with the above-mentioned Equation (2) (Step S146). Currently s=2 and e=3, and the “m1” and the “m2” both are calculated to be 2 according to the Equation (2).

Here, the “m1”, the “m2” and the “s” all become 2. If the “m1”, the “m2” and the “s” are equal to each other (Step S147; Yes), it means that there is no switch between the range start switch and the range end switch. In other words, the search range is narrowed to the limit. Therefore, the monitoring unit14can determine that the failure is occurring between the current range start switch and the current range end switch. That is, the monitoring unit14refers to the current insertion switch table INS and determines that the failure is occurring between the second switch (s=2) and the third switch (e=3). Further, the monitoring unit14can convert the second switch (s=2) and the third switch (e=3) to the switch4and the switch5, respectively, by referring to the route table RTE. That is, the monitoring unit14can determine that the failure is occurring between the switch4and the switch5.

When the location of failure is identified, the monitoring unit14updates the status flag in the topology table TPL as in the case of the first example. Moreover, the monitoring unit14instructs the display unit16to display the identified location of failure. The display unit16refers to the topology table TPL and displays the link whose status flag is “0” as the location of failure.

According to the fourth example, the efficiency is further improved as compared with the case of the third example. The present example is particularly preferable in a case where the total number N of the switches on the transfer route PW is large.

The present exemplary embodiment provides a technique of performing centralized management of the communication network NET by using the management host1. In the communication network management processing, the management host1makes the check frame FR travel along a predetermined transfer route PW. Here, each switch (each node) in the communication network is provided with the forwarding table. The contents of the forwarding table are set up in accordance with the instruction from the management host1such that the check frame FR is forwarded along the predetermined transfer route PW. Therefore, each switch just needs to refer to the forwarding table to forward the received check frame FR to a designated forwarding destination. Thus, the traveling of the check frame FR along the predetermined transfer route PW is achieved. The management host1can detect whether or not a failure is occurring on the transfer route PW based on whether or not it receives the check frame FR within a predetermined period of time.

According to the present exemplary embodiment, there is no need to incorporate the health-check table including information of the transfer route, the check list and the like (see Patent Literature 2, Patent Literature 3) into the check frame FR. Therefore, each switch needs not to search for the related entry in the health-check table. In particular, even in a case of a large number of switches, there is no need to search for the related entry from a large number of entries, and thus a processing time in each switch is prevented from increasing. Moreover, each switch needs not to refer to the next entry following the related entry in order to forward the check frame FR to the next node. As a result, burden placed on each switch is reduced.

Moreover, according to the present exemplary embodiment, it is possible to identify the location of failure on the transfer route PW by simple processing. In the failure location identification processing, each switch on the transfer route PW just needs to forward the received check frame FR, as in the case of normal times. There is no need to change the setting of each switch for identifying the location of failure. Also, each switch needs not to write health-check information and the like to the check frame FR. Furthermore the complicated processing such as required in Patent Literature 2 or Patent Literature 3 is not necessary for identifying the location of failure. For example, such processing as described in Patent Literature 3 that each node investigates whether or not it can communicate with the next node is not necessary. Consequently, burden placed on each node is greatly reduced. According to the present exemplary embodiment, it is possible to identify the location of failure on the transfer route PW with simple processing and to reduce burden placed on each node.

Particularly, in a case where the node in the communication network is a switch with a simple configuration, the complicated processing such as required in Patent Literature 2 or Patent Literature 3 is substantially impossible. The present exemplary embodiment can be applied to the case where the node in the communication network is a switch.

Moreover, in the case where the transfer route PW of the check frame FR is a traversable route, health-checking of a large number of physical links is possible by only transmitting one check frame FR. It is therefore possible to reduce the number of check frames FR that the management host1needs to transmit and receive. As a result, burden placed on the management host1is reduced, which is preferable. Furthermore, since the burden placed on the management host1is reduced, it is possible to increase a transmission frequency of the check frame FR. As a result, it is possible to quickly detect failure occurrence on the transfer route PW.

Moreover, according to the present exemplary embodiment, a ring-shaped network structure is not assumed for achieving the traveling of the check frame FR. The present exemplary embodiment can be applied to a case where the physical topology of the communication network NET is not a ring shape. There is no constraint on the physical topology of the communication network NET.

While the exemplary embodiments of the present invention have been described above with reference to the attached drawings, the present invention is not limited to these exemplary embodiments and can be modified as appropriate by those skilled in the art without departing from the spirit and scope of the present invention.

This application is based upon and claims the benefit of priority from Japanese patent application No. 2009-043112, filed on Feb. 25, 2009, the disclosure of which is incorporated herein in its entirely by reference.