JP5190047B2 - Detour route information creation device and detour route information creation method - Google Patents

Description

  The present invention relates to a failure recovery technique in a network.

  In a network, it is important to perform failure recovery by quickly switching a transfer path in response to an unexpected failure and maintain transfer quality. As a failure recovery method in an IP (Internet Protocol) network, there is a dynamic recovery method using a routing protocol such as OSPF (Open Shortest Path First) (see Non-Patent Document 1).

  In OSPF, a node that detects a failure notifies (floods) failure information to all nodes. The node that has received the failure information can automatically switch the transfer route by calculating a detour route based on the topology database information excluding the failure location. However, in OSPF, a detour route is calculated after a failure occurs, so there is a problem that it takes time in seconds to recover from the failure. Also, failure information notification and detour route calculation increase depending on the network scale.

  As a method for solving such a problem, an IP Fast Reroute (IP-FRR) method has been proposed that realizes fast failure recovery by calculating a detour route in advance (see Non-Patent Document 2). . In the IP-FRR method, backup topology information is created in advance, and when a failure occurs, failure recovery is performed by switching to a transfer path according to backup topology information that protects (bypasses) the corresponding failure location.

  A specific example of the failure recovery method using the backup topology information will be described with reference to FIG.

  First, the detour route information creation device prepares a configuration (preliminary topology information) in preparation for link breakage in advance. For example, the detour route information creation apparatus prepares for a case where the link 1-2 (the link between the node with the node number 1 and the node with the node number 2) is disconnected, and reserves the link 1-2 as a protection link. Create topology information in advance. The link cost of the protect link in the backup topology information is assigned a maximum value that can be set so that the protect link is not selected as a route. Accordingly, when a route is calculated by the minimum cost routing that minimizes the sum of the link costs on the backup topology information, a route that does not use the protected link is calculated. Information indicating this backup topology (backup topology information) is input to all the nodes, and a route according to the backup topology information is calculated in advance (before traffic transfer) for all the nodes.

  Here, a case is considered where a failure of the link 1-2 is detected on a route having the node of node number 1 as src (source node) and the node of node number 5 as dst (destination node). For example, on the normal topology of FIG. 1, (1) when a failure of the link 1-2 is detected, the failure detection node (node of node number 1) transfers the packet according to the backup topology A that protects the failed link. At this time, since the failure detection node knows that the link 1-2 has failed, the failure detection node knows that the failure location can be bypassed using the protection topology information of the protection topology A. However, other nodes cannot grasp the failure location. Therefore, the failure detection node (2) selects the spare topology A to be used, and assigns the spare topology A ID to the header of the packet. When another node (for example, the node with node number 4) on the detour receives the packet, (3) referring to the header of this packet, selects the spare topology information to be used, and selects the selected spare Forward packets according to topology information.

  Here, as a general requirement for failure recovery, it is possible to cope with any single failure in the network. In order to satisfy this requirement, as shown in FIG. 1, if one link is protected by one spare topology information, the number of spare topology information required is the number of links. An increase in the number of spare topology information causes an increase in router memory. Therefore, a method of protecting a plurality of links with one spare topology information has been proposed (see Non-Patent Document 2).

  For example, as shown in FIG. 2, if the following two conditions are satisfied, a plurality of protect links can be arranged in one backup topology information. (1) Even if each protection topology information removes the protection link on the protection topology information, connectivity of all nodes is ensured (a connection graph). (2) The set of protected links in each backup topology information matches the link set of the original topology. The reason for (1) is that reachability of all nodes must be ensured regardless of which link is disconnected. Also, the reason for (2) is that all single link failures in the network must be dealt with.

IETF RFC2328, “OSPF Version 2“ April 1998 A.Kvalbein, A.F.Hansen, T.Cicic, S.Gjessing, and O.Lysne, “Fast IP Network Recovery using Multiple Routing Configurations,” in Proceedings of INFOCOM, Apr.2006 A. Kvalbein, T. Cicic and S. Gjessing, “Post-Failure Routing Performance with Multiple Routing Configurations,” INFOCOM, May 2007

  However, when a backup topology information group is created by the above-described technique, a plurality of links are protected by a single backup topology information, so the number of links that can be used as a detour on each backup topology information is reduced. For this reason, a link connected to a node having a large amount of incoming / outgoing traffic has a high load, and congestion may occur. Here, in the technique described in Non-Patent Document 3, a method is proposed in which a detour path is indirectly optimized and a load is smoothed by optimizing the link cost of the backup topology information. However, as shown in FIG. 2, if the backup topology information (backup topology A) having only one link connected to the high load node is created, the route cannot be optimized, and the load is smoothed. It is not possible. Accordingly, an object of the present invention is to solve the above-described problems and to create a backup topology information group in which the load on the network is smoothed while reducing the number of backup topology information to be prepared.

  In order to solve the above-mentioned problem, the invention according to claim 1 creates detour path information based on backup topology information indicating a link that is disconnected when a node failure or a link failure occurs in the network as a protected link. A detour route information creation device that stores topology information indicating the topology of the network and the link cost of each link, and acquires AC traffic information that is the traffic flow between each node from each node in the network. Referring to the AC traffic acquisition unit stored in the storage unit, the topology information and the AC traffic information, calculate the arrival / departure traffic amount for each node, and designate a node whose calculated arrival / departure traffic amount exceeds a predetermined threshold as a high load node With reference to the high load node selection unit to be selected and the topology information, 1 Initially performing initial information creation processing for creating N pieces of initial information of backup topology information with a maximum of [(maximum number of links connected to each high load node / N) +1] protection links connected to the high load nodes An information creation unit, a connectivity determination unit that determines whether or not a connection between nodes becomes a connection graph when the protected link is removed for all the created N pieces of initial information or spare topology information, and a connectivity determination unit When it is determined that the connection between the nodes becomes a connection graph when the protected links are removed for all the created N initial information, the created N initial information is obtained by the method used for IP-FRR (IP Fast Reroute). For each piece of information, select a process to select a protected link from links other than those already selected as protected links By executing until the set of protected links coincides with the set of links indicated in the topology information, the protection link selection unit for creating N pieces of spare topology information and the created spare topology information The detour route information indicating the detour route detouring the protect link indicated in the backup topology information is created, and the route calculation unit stored in the storage unit and the connectivity determination unit generate one of the N pieces of initial information created When it is determined that the connection between the nodes does not become a connection graph when the protection link is removed, the arrangement of the protection links in the N pieces of initial information is changed, and the connection between the nodes in each of the N pieces of initial information is connected. A protection link arrangement changing unit for searching for initial information to be graphed, Preliminary topology information is created for each of the N pieces of initial information searched by the link arrangement changing unit, and the connection between the nodes in each of the N pieces of initial information becomes the connection graph by the protected link arrangement changing unit. When the information cannot be found, the initial information creation unit increases the value of N and performs the initial information creation process again. The protect link selection unit obtains the N pieces of initial information obtained by the initial information creation process. On the other hand, a detour route information creation device is characterized in that it performs preliminary topology information creation processing.

  According to a fourth aspect of the present invention, there is provided a detour route information creation device for creating detour route information based on backup topology information indicating a link that is disconnected when a node failure or a link failure occurs in a network as a protected link. Acquire AC traffic information that is the traffic flow between each node from each node, and store it in the storage unit, and refer to topology information and AC traffic information indicating the network topology and link cost of each link For each node, calculate the arrival and departure traffic volume of the node, select a node whose calculated arrival and departure traffic volume exceeds a predetermined threshold as a high load node, and refer to the topology information to make one high load node The maximum number of protected links to connect is [( Maximum number of links to be continued / N) +1] a step of performing initial information creation processing for creating initial information of N pieces of spare topology information, and a node when protection links are removed for all the created N pieces of initial information When the connection between the nodes becomes a connection graph, the protected link from the link other than the link already selected as the protected link in each of the N initial information created by the method used for IP-FRR (IP Fast Reroute). The process of selecting N is performed until the selected set of protected links matches the set of links indicated in the topology information, and the created preliminary topology information Each time, detour route information indicating a detour route that detours the protected link indicated in the backup topology information is created. If the connection between the nodes does not become a connection graph when the protection link is removed in any of the N pieces of initial information created and the step of storing in the storage unit, the arrangement of the protection links in the N pieces of initial information is changed. A step of searching for initial information in which a connection between nodes in each of the N pieces of initial information becomes a connection graph, a step of performing preliminary topology information creation processing on each of the searched N pieces of initial information, When the initial information that the connection between the nodes in each of the N pieces of initial information becomes a connection graph cannot be found, the value of N is increased and the initial information creation process is performed again. The detour route information generation is characterized in that a step of performing a preliminary topology information generation process is executed on the N pieces of initial information. It was a method.

  By doing in this way, the detour route information creation apparatus first identifies which node is a high load node using the AC traffic information. Then, referring to the topology information, the number of links connected to each of the high load nodes is specified. Next, based on the value obtained by dividing the maximum number of links connected to the high-load node by the number of backup topology information, the protection link connected to the high-load node per initial information of the backup topology information. Determine the number. For example, if there are three high load nodes and the number of spare topology information to be created is “5”, the maximum number of links connected to this high load node is “4”, “4”, and “5”. The value is “5”. Therefore, a value “1” obtained by dividing “5” by the number of spare topology information “5” is set as the maximum value of the protect link per high load node in one initial information. Then, based on the initial information including the protected link, a protected link is selected by a method used for IP-FRR, and N spare topology information is created. In other words, the detour route information creation device can create a spare topology information group in which the high load node arrival / departure routes (links) are distributed among the spare topology information when creating N pieces of initial information of the spare topology information. Therefore, since the detour route information creation device creates detour route information based on such a backup topology information group, it is possible to smooth the network load when a link failure or node failure occurs in the network.

  According to the second aspect of the present invention, any one of the spare topology information among the N pieces of spare topology information created by the protect link selecting unit by the connectivity determining unit in the detour path information creating device according to the first aspect is provided. If it is determined that the graph does not become a connection graph, the initial information creation unit increases the value of N and performs the initial information creation process again, and the protect link selection unit performs the N pieces of information obtained by the initial information creation process. It is characterized in that preliminary topology information is created for the initial information.

  By doing so, the detour route information creation device can create backup topology information that becomes a connection graph (that is, connectivity between arbitrary nodes in the network is ensured) even if the protection link is removed. Also, the detour route information creation device, after creating the initial information of the backup topology information, increases the number of N if the connection graph is not changed no matter how the protection link of this initial information is changed, Therefore, even if the protection link is removed, it becomes easy to create initial information that becomes a connection graph. Also, starting from the initial value of N and increasing N when the connection between nodes does not become a connection graph, the detour path information creation device can reduce the number of spare topology information as much as possible.

  According to a third aspect of the present invention, there is provided a detour route information creation device for creating detour route information based on backup topology information indicating a link that is disconnected when a node failure or a link failure occurs in a network as a protected link. A storage unit that stores topology information indicating the topology of the network and the link cost of each link, and AC traffic information that is traffic flow between each node in the network is obtained from each node in the network and stored in the storage unit High traffic node selection that refers to topology traffic information and AC traffic information, calculates the incoming and outgoing traffic volume of each node, and selects a node whose calculated traffic volume exceeds a predetermined threshold as a high load node And the method used for IP-FRR When protection links in log information are removed, the connection between nodes becomes a connection graph, and N sets of protection topology information in which the protection link set in each of the backup topology information matches the link set indicated in the topology information. The spare topology information creating unit that selects the spare topology information having the largest number of protected links connected to the high load node from the created N spare topology information, and connects to the high load node in the selected spare topology information One of the protected links to be changed to a normal link, and a protected link exchanging unit that executes a protected link exchanging process for changing the link in the protection topology information other than the selected protection topology information to a protection link, and the protection link After the replacement process, spare Topolo It is determined whether or not the connection between the nodes of the information becomes a connection graph, and when it is determined that the connection between the nodes does not become the connection graph, the protection link and the backup topology not yet selected for the protection link exchange unit For the information, a connectivity determination unit that instructs to execute the protection link replacement processing again, the number of protection links connected to the high-load node of the selected backup topology information after the protection link replacement processing, and other backup topology information The maximum number of protected links connected to each high load node is compared, and the number of protected links connected to the high load node of the selected backup topology information is connected to the high load node of each backup topology information. If the value is less than the maximum number of protected links, protect link replacement Even if the protection link number comparison unit and the protection link exchanging unit that store the group of the protection topology information after processing in the storage unit execute the protection link exchanging process for all combinations of the protection link and the protection topology information, When the connectivity determination unit determines that the connection is not a connection graph, an end determination unit that instructs the protect link switching unit to end the protection link replacement process, and for each backup topology information in the storage unit, The detour route information creating apparatus is characterized by comprising detour route information indicating a detour route that detours the protected link indicated in the information, and a route calculation unit stored in the storage unit.

  Also by doing in this way, the detour route information creation device can create a backup topology information group in which departure and arrival routes (links) of high load nodes are distributed among the backup topology information. Therefore, the detour route information creation device creates detour route information based on such a backup topology information group, and performs path control based on this detour route information when a link failure or node failure occurs in the network. Can smooth the network load.

  According to the present invention, the detour route information creation device can create a backup topology information group that smoothes the network load while reducing the number of backup topology information to be prepared.

It is the figure which showed the specific example of the failure recovery method using the conventional backup topology information. It is the figure which showed the specific example of the failure recovery method using the conventional backup topology information. It is the figure which showed the example of a network structure in case the detour route information creation apparatus of this Embodiment is implement | achieved by the node. It is a figure explaining the outline | summary of the process of the node of this Embodiment. It is the figure which illustrated the structure of the node of this Embodiment. It is the figure which showed the process sequence of the node of FIG. (A) is the figure which illustrated topology information, (b) is the figure which showed the grouping example of the link connected to the high load node in the topology information of (a). It is the figure which illustrated the initial information of the reserve topology information in this Embodiment. It is the figure which illustrated the backup topology information of this Embodiment. (A) is the figure which illustrated the backup topology information of this Embodiment, (b) is the figure which illustrated the exchange of the protection link in the backup topology information of (a). It is the figure which illustrated the structure of the node of this Embodiment. It is the figure which showed the process sequence of the node of FIG.

  Hereinafter, the embodiments of the present invention will be described by dividing them into a first embodiment and a second embodiment. First, the outline of the process of the detour route information creation device of each embodiment will be described with reference to FIG. The detour route information creation device will be described as being realized by each node 100 of the network as shown in FIG. 3, for example, but the route control signal is transmitted to each node of the network to control the route. You may implement | achieve by the path control management apparatus to perform.

  The node 100 creates spare topology information indicating, as a protected link, a link that is disconnected when a node failure or a link failure occurs in the network. Then, detour route information at the time of occurrence of a failure is created based on the spare topology information. Then, the node 100 transmits to the other node 100 a packet in which the ID of the backup topology used in the detour path information when the failure occurs is added to the header of the packet. Then, when the other node 100 existing on the detour receives the packet, the packet is transferred according to the backup topology information to be used by referring to the header.

  As shown in FIG. 4, in the backup topology information created by the comparative node, there is a possibility that all links except the links connected to the high load node are protected links (FIG. 4). (See (a)). In other words, there is a possibility that one link can be used as a detour on the backup topology information. If detour path information is created based on this, the load may be concentrated. On the other hand, the node 100 according to the present embodiment reduces the number of protected links connected to the high load node as much as possible on the backup topology information, so that the load on each node and link can be smoothed. That is, the node 100 has a topology that avoids the concentration of traffic on a specific link of a high load node when creating the backup topology information. Therefore, if the detour route information is created based on this topology, the load on the network is reduced. Smoothing can be performed (see FIG. 4B).

<First Embodiment>
Next, the configuration of the node 100 according to the first embodiment will be described with reference to FIG. The node 100 is realized by a router or a layer 2 switch, for example. As shown in FIG. 5, the function of the node 100 is roughly divided into an input / output unit 11, a processing unit 12, and a storage unit 13.

  The input / output unit 11 controls input / output of data that is the basis of topology information 131 (described later) and path information 134 with other nodes 100 and packets with other nodes 100. The processing unit 12 performs route control based on the backup topology information and the created backup topology information. The storage unit 13 stores topology information 131 and the like necessary for creating the backup topology information. The input / output unit 11 includes a communication interface for transmitting and receiving packets via a network and an input / output interface. The storage unit 13 includes a storage medium such as a random access memory (RAM), a read only memory (ROM), a hard disk drive (HDD), and a flash memory. The processing unit 12 is realized by a program execution process by a CPU (Central Processing Unit) included in the node 100, a dedicated circuit, or the like. When the node 100 is realized by program execution processing, the storage unit 13 stores a program for realizing the function of the node 100.

  First, the storage unit 13 will be described. The storage unit 13 stores topology information 131 and route information 134. In addition, the storage unit 13 includes an area for storing the backup topology information group 132 generated by the processing unit 12, the AC traffic information 133, the detour route information 135, and the backup topology information management information 136.

  The topology information 131 is information indicating identification information of each node 100 in the network, a link to which each node is connected, a link cost of each link, and the like. The topology information 131 is, for example, information as shown in “normal topology” in FIG. 1 (link cost is omitted in FIG. 1), and each node 100 acquires it by a routing protocol such as OSPF. This topology information 131 is referred to when creating backup topology information and detour route information 135. Note that the topology information 131 uses the same information between the nodes 100.

  The backup topology information group 132 is a set of backup topology information corresponding to all single failures in the network. The spare topology information is information indicating a link that is disconnected when a node failure or a link failure occurs in the network as a protected link. This backup topology information group 132 is created by the backup topology information processing unit 121 and used to create the detour path information 135.

  The AC traffic information 133 is information indicating the amount of traffic flowing between the nodes 100 in the network. This AC traffic information 133 indicates the amount of traffic flowing between the nodes 100 for each combination of the identification information of the node 100 serving as the source node (src) and the identification information of the node 100 serving as the destination node (dst). Information. The AC traffic information 133 is acquired by the AC traffic acquisition unit 127. The AC traffic information 133 is referred to when the backup topology information processing unit 121 selects a high load node.

  The route information 134 is information indicating an interface for outputting the packet for each destination address of the packet.

  The detour path information 135 is information indicating an interface for outputting the packet for each destination address of the packet when a failure of the failure pattern occurs for each failure pattern of the node 100 or the link.

  The spare topology information management information 136 is information in which the spare topology information created by the spare topology information processing unit 121 or the initial information of the spare topology information is recorded as a link selected as a protect link. By referring to this backup topology information management information 136, the backup topology information processing unit 121 covers which link should be selected next as a protected link for a given topology and covers all link failures. It can be determined whether or not such a backup topology information group 132 has been created.

  Next, the processing unit 12 will be described. The processing unit 12 creates a backup topology information group 132. Then, detour path information 135 is created based on the backup topology information group 132, and path control based on the detour path information 135 is performed when a failure occurs. Such a processing unit 12 includes a backup topology information processing unit 121 that creates a backup topology information group 132 and an AC traffic acquisition unit 127 that acquires information that is the basis of the AC traffic information 132 from other nodes 100 in the network. And a route control unit 128 that performs route control of packets transmitted from other nodes 100 with reference to the route information 134 and the detour route information 135.

  The backup topology information processing unit 121 includes a high load node selection unit 122, an initial information creation unit 123, a connectivity determination unit 1213, a protection link selection unit 124, a protection link arrangement change unit 125, and backup topology information output processing. Part 126.

  The high load node selection unit 122 refers to the topology information 131 and the AC traffic information 133 and calculates the amount of incoming and outgoing traffic for each of the nodes 100 in the network. Then, the node 100 whose calculated traffic volume exceeds a predetermined threshold is selected as a high load node. The selection of the high load node may be performed by selecting the upper predetermined number of nodes 100 in descending order of the amount of incoming / outgoing traffic for the nodes 100 whose amount of incoming / outgoing traffic exceeds a predetermined threshold.

The initial information creation unit 123 refers to the topology information 131 and creates N pieces of initial information of backup topology information including a maximum of M protect links connected to each high load node selected by the high load node selection unit 122. . M is a number that satisfies the following formula (1).
M = [(D / N) +1] (1)
Here, D is the maximum value of the number of links connected to each of the high load nodes, and [] indicates a maximum integer smaller than the value in []. N is assumed to have an initial value determined by the scale of the network. When the protect link arrangement changing unit 125, which will be described later, cannot find the initial information in which the connection between the nodes in each of the generated N pieces of initial information becomes a connection graph, the initial information generating unit 123 sets the value of N The initial information creation process is performed again.

  For example, in the topology shown in FIG. 7A, when N (number of spare topology information) = 5 and high load node = node number “0, 6, 9”, the link group connected to this high load node is , Grouped into three groups as shown in FIG. That is, grouping is performed such as Group 1 (solid line), Group 2 (two-dot chain line), and Group 3 (dashed line). Here, since the maximum value of the number of links connected to each of the high load nodes is “5”, M = [(5/5) +1] = 1. Therefore, initial information as shown in # 1 to # 5 in FIG. 8 including at most one link of each group is created as a protect link (up to one for # 1 to # 5 in FIG. 8). As a result, the initial information creation unit 123 can create an initial information group of standby topology information in which protected links connected to high load nodes are dispersed as much as possible between the initial information of each backup topology information. The information of the link that is a protected link in this initial information is recorded in the backup topology information management information 136.

  The connectivity determination unit 1213 in FIG. 5 removes the protection links from the N pieces of initial information created by the initial information creation unit 123 and the backup topology information created by the protection link selection unit 124 and the protection link placement change unit 125. Even if the connection between the nodes becomes a connection graph, it is determined. That is, it is determined whether the connectivity between all the nodes is secured even if the protect link is removed in the backup topology information and the initial information.

  When the connectivity determination unit 1213 determines that the connection between nodes becomes a connection graph even if the protection link in the N pieces of initial information is removed, the protect link selection unit 124 uses the N pieces of initial information as a base. As described above, N pieces of spare topology information are created by a method used in IP-FRR (see Non-Patent Document 2). That is, the protected link selection unit 124 refers to the backup topology information management information 136 and selects a protected link from links other than links already selected as protected links in each of the N pieces of initial information. This selection is performed until the selected set of protected links matches the set of links indicated in the topology information 131. For example, the protected link selection unit 124 selects the protected link based on the initial information shown in # 1 to # 5 in FIG. 8 until the set of protected links is the same as the link set of the original topology. Thus, a preliminary topology information group as shown in # 1 to # 5 of FIG. 9 is created. Details of the processing procedure here will be described later with reference to FIG.

  The protect link arrangement changing unit 125 in FIG. 5 uses the connectivity determination unit 1213 to change the connection between the nodes and the connection graph when the protect link is removed in any of the N pieces of initial information created by the initial information creation unit 123. If there is one node 100 that cannot secure the connectivity, the arrangement of the protection links in the N pieces of initial information is changed, and each of the N pieces of initial information is changed. The initial information group in which the connection between nodes becomes a connection graph is searched. For example, if any of the initial information shown in # 1 to # 5 in FIG. 8 does not result in a connection graph between nodes when the protect link is removed, the protect link arrangement changing unit 125 selects “6” in the initial information of # 1. The -1 protect link is changed to “6-2”, and the protect link “9-3” is changed to “9-4”. In addition, the protect link “6-2” in the initial information # 2 is changed to “6-4”, and the protect link “9-4” is changed to “9-8”. Such processing is also executed for # 3 to # 5. That is, the protect link arrangement changing unit 125 changes the combination of the protect links between the pieces of initial information, and searches for an initial information group in which the connection between the nodes becomes a connection graph even if the protect link is removed. Here, when the protect link arrangement changing unit 125 finds an initial information group in which the connection between the nodes becomes a connection graph even if the protect link is removed, the protect link arrangement changing unit 125 manages the protection link arrangement in the initial information group. Record in information 136. Then, the protect link selection unit 124 creates N pieces of spare topology information based on the initial information group in which the connection between the nodes becomes a connection graph.

  When the protect link arrangement changing unit 125 cannot find the initial information group in which the connection between the nodes in each of the N pieces of initial information becomes a connection graph, the initial information creating unit 123 increases the value of N, The initial information creation process is performed again. Then, the protect link selection unit 124 performs a preliminary topology information creation process on the N pieces of initial information obtained by the initial information creation process. For example, if there is at least one spare topology information that does not become a connection graph in the spare topology information of # 1 to # 5 shown in FIG. 9, the number of N is increased from five to one, and six pieces of initial information are created. Based on these six pieces of initial information, six pieces of preliminary topology information are created.

  The backup topology information output processing unit 126 uses the backup topology information processing unit 121 to (1) a connection between nodes is a connection graph, and (2) a set of protected links in each backup topology information in the topology information 131. When a backup topology information group that matches the set of links is created, this backup topology information group is stored in the storage unit 13 as a backup topology information group 132.

  The AC traffic acquisition unit 127 acquires information indicating the amount of traffic flowing between the nodes 100 from each node 100 in the network via the input / output unit 11.

  The route control unit 128 includes a route calculation unit 129 and a packet transfer unit 130. The route calculation unit 129 calculates a transfer route (a bypass route) based on the topology information 131 and the backup topology information group 132, and creates the route information 134 and the bypass route information 135.

  The packet transfer unit 130 refers to the route information 134 or the detour route information 135 based on the destination address of the received packet, selects an output interface of the packet, and outputs the packet from the selected output interface. Here, when a failure occurs, the packet transfer unit 130 refers to the detour route information 135 and selects an output interface of the packet. The detour route information 135 to be used is determined by the failure information input to the node 100. Judgment based on.

<Processing procedure>
Next, the processing procedure of the node 100 will be described using FIG. 6 with reference to FIG. First, the AC traffic acquisition unit 127 of the node 100 acquires AC traffic information (information that is the basis of the AC traffic information 133) from the node 100 of the network (S1), and stores this information as AC traffic information 133 in the storage unit 13. To remember. Then, the high load node selection unit 122 refers to the topology information 131 and the AC traffic information 133, calculates the arrival / departure traffic amount for each node 100, and selects the node 100 whose calculated arrival / departure traffic amount exceeds a predetermined threshold value. Select as a high load node (S2).

  Next, the initial information creation unit 123 refers to the topology information 131 and sets the initial information of the backup topology information including up to [(D / N) +1] links as protected links for one high load node as N. This is created (S3). The information of the link that is a protected link in this initial information is recorded in the backup topology information management information 136. Next, the connectivity determination unit 1213 determines whether or not the connection between the nodes becomes a connection graph when the protected link is removed for all the created N pieces of initial information (S4). Here, if the connection between the nodes is the connection graph for all the initial information (Yes in S4), the protect link selection unit 124 uses the N pieces of initial information created in S3 as a base for IP-FRR. The preliminary topology information is created by a method (see Non-Patent Document 2). In other words, the protected link selection unit 124 uses a method other than the link already selected as the protected link by the method used for IP-FRR (see Non-Patent Document 2) in each of the N pieces of initial information created in S3. By selecting a protect link (S8), spare topology information is created. Information on the selected protect link is recorded in the backup topology information management information 136. If the set of selected protected links matches the set of links indicated in the topology information 131 (Yes in S9), the protected link selecting unit 124 ends the selection of the protected link. On the other hand, if the set of selected protected links does not match the set of links indicated in the topology information 131, the process returns to S8. Then, when the answer is Yes in S9, it is determined whether or not the connection between the nodes from which the protection link in each of the backup topology information is removed is a connection graph (S10). Here, when the connectivity determination unit 1213 determines that the connection graph is formed (Yes in S10), the backup topology information output processing unit 126 stores the created backup topology information (backup topology information group) in the storage unit. 13 (S11). That is, the created backup topology information is stored in the storage unit 13 as the backup topology information group 132. Then, the route calculation unit 129 creates detour route information 135 based on the backup topology information group 132 (S12) and stores it in the storage unit 13. Thereafter, when the node 100 detects a node failure or link failure in the network, the route control unit 128 reads the detour route of this failure location from the detour route information 135, and the packet transfer unit 130 is based on the read detour route. Perform packet transfer.

  On the other hand, in S4, the connectivity determination unit 1213 determines that the connection between the nodes is not a connection graph when the protected link is removed in any of the N pieces of initial information created by the initial information creation unit 123. In the case where the protection link is changed (No in S4), the protection link arrangement changing unit 125 changes the arrangement of the protection links in the N pieces of initial information, and between the nodes from which the protection links are removed in each of the N pieces of initial information. Initial information (initial information group) in which the connection becomes a connection graph is searched (S5). Here, when initial information (initial information group) serving as a connection graph can be found (Yes in S6), the protect link arrangement changing unit 125 stores the information of the protect link in the initial information group in the backup topology information management information 136. Record and proceed to S8. On the other hand, no matter how the protect link arrangement changing unit 125 changes the arrangement of the protect links in the N pieces of initial information, when the initial information group in which all the N pieces of initial information become connection graphs cannot be found ( The initial information creation unit 123 increases the value of N (S7) and proceeds to S3. For example, when the protect link arrangement changing unit 125 attempts to change the arrangement of all the protect links for four pieces of initial information, but cannot find an arrangement that becomes a connection graph, N is incremented by one, and the initial information creating unit 123. Creates five pieces of initial information. And the process after S4 is performed.

  In S10, when the connectivity determination unit 1213 determines that the connection between the nodes is not in the connection graph when the protected link is removed in any of the N spare topology information created in S8. (No in S10), the initial information creation unit 123 increases the value of N (S7) and proceeds to S3.

  In this way, each node 100 in the network can take a detour route in which traffic to a specific link of a high load node is less likely to concentrate when a failure occurs.

  Next, with reference to FIG. 5, a specific example of a procedure for creating backup topology information in the present embodiment will be described with reference to FIGS. Here, the topology shown in FIG. 7A is given as the topology information 131, and the high-load node selected by the high-load node selection unit 122 is the node 100 with the node number “0, 6, 9”. A case where = 5 will be described as an example.

  First, the initial information creation unit 123 of the node 100 refers to the topology information 131 and groups the link group connected to the high load node for each high load node to be connected. For example, as shown in FIG. 7B, Group1 (link group connected to node number “0”), Group2 (link group connected to node number “6”), and Group3 (link connected to node number “9”) Group). Next, the initial information creation unit 123 creates N pieces of initial information of spare topology information including a maximum of M links connected to each high load node based on the above-described equation (1). Here, since N = 5 and D = 5, M = 1. Therefore, each high load node creates initial information including a maximum of two protect links (see # 1 to # 5 in FIG. 8). Here, there are various methods for selecting the protect link in each initial information. For example, a unique node number as shown in FIG. 8 is assigned to each node 100 constituting the topology. Then, the links connected to the node 100 having the smallest node number among the links connected to the high load node are selected in order.

  For example, in the case of # 1 in FIG. 8, the initial information creation unit 123 sets the link (link 0-1) to the smallest node number among the links connected to the high load node having the node number “0” as the protected link. select. Similarly, link 6-1 is selected as the protect link to be connected to the high load node with node number “6”, and link 9-3 is selected as the protect link to be connected to the high load node with node number “9”. select. Similarly, in # 2, the link (link 0-2) to the second smallest node number among the links connected to the high load node of node number “0” is selected as the protect link. Similarly, the link 6-2 is selected as the protect link connected to the high load node having the node number “6”, and the link 9-4 is selected as the protect link connecting to the high load node having the node number “9”. select. The initial information creation unit 123 executes such processing for # 3 to # 5, and creates initial information as indicated by # 1 to # 5 in FIG. Here, the case of N = 5 has been described, but when N = 4, the protect link (link 6-10) in # 5 is arranged in # 1.

  In the initial information created in this way (for example, # 1 to # 5 in FIG. 8), since the connection between the nodes when the protection link is removed is a connection graph, the protection link selection unit 124 Based on the technology described in Non-Patent Document 2, based on the initial information of # 1 to # 5, preliminary topology information shown in # 1 to # 5 of FIG. 9 is created. For example, the protect link selection unit 124 selects an unselected link as a protect link from links connected to the node 100 in the order of node numbers. Specifically, it is created as follows.

  First, the protect link selection unit 124 pays attention to the node 100 having the youngest node number (node number “0”) in # 1 of FIG. 8 and protects the link connected to the node 100 having the node number “0”. Look for links not selected as links. However, the link connected to the node 100 with the node number “0” is not selected because it has already been selected as a protected link in # 2 to # 5. Since the processing related to the node 100 with the node number (node number “0”) is completed, the process proceeds to # 2.

  In # 2, paying attention to the node 100 of the next node number (node number “1”), from the links connected to this node 100, unselected links 1-2, 1- # 1 in # 1, # 3- # 5. 7 is selected as the protect link. Next, the process proceeds to # 3.

  In # 3, paying attention to the node 100 of the next node number (node number “2”), the unselected links 2-3, 2-5 are selected as protected links in # 1, # 2, # 4, and # 5. To do. Next, the process proceeds to # 4.

  In # 4, paying attention to the node 100 of the next node number (node number “3”), unselected links 3-4 and 3-5 are selected as protect links in # 1 to # 3 and # 5. Next, the process proceeds to # 5.

  In # 5, paying attention to the node 100 of the next node number (node number “4”), the unselected link 4-8 is selected as the protect link in # 1 to # 4. Next, the process returns to # 1.

  In # 1, paying attention to the node 100 of the next node number (node number “5”), the unselected links 5-7 and 5-8 are selected as protected links in # 2 to # 5. Next, the process proceeds to # 2.

  In # 2, attention is paid to the node 100 of the next node number (node number “6”), but in # 1, # 3 to # 5, all the links connected to this node 100 have been selected as protected links. The process proceeds to # 3.

  In # 3, paying attention to the node 100 of the next node number (node number “7”), the unselected links 7-8 and 7-10 are selected as protect links in # 1, # 2, # 4, and # 5. To do. Next, the process proceeds to # 4.

  In # 4, paying attention to the node 100 of the next node number (node number “8”), the unselected link 8-10 is selected as the protected link in # 1 to # 3 and # 5. Next, the process proceeds to # 5.

  In # 5, attention is paid to the node 100 of the next node number (node number “9”). However, since all the links connected to this node in # 1 to # 4 have been selected as protect links, the processing in # 1 is performed. Return.

  In # 1, attention is paid to the node 100 of the next node number (node number “10”), but in # 2 to # 5, all links connected to this node have been selected as protected links. Now, since the processing of the node 100 with the node numbers “1 to 10” is completed, the protect link selection processing is terminated.

  The spare topology information group created in this way covers all the links indicated in the topology information 131, and the connection between nodes when the protected link is excluded is also a connection graph. Therefore, the backup topology information output processing unit 126 stores this backup topology information group in the storage unit 13 as the backup topology information group 132.

  The backup topology information group 132 created by the above-described procedure has protection links distributed between the backup topology information. Therefore, the node 100 creates the detour path information 135 based on the backup topology information group 132, so that even when a node failure or link failure occurs in the network, the load is not concentrated on a specific node or link. Such a detour route can be taken.

<Second Embodiment>
Next, a second embodiment will be described. When the node 100A according to the second embodiment creates N pieces of spare topology information by the technique described in Non-Patent Document 2, and then finds the spare topology information in which the protection links are concentrated on the high load node, The protection link in this backup topology information is changed as a protection link of another backup topology information.

  For example, when the node 100A creates the three backup topology information (x, y1, y2) shown in FIG. 10A and the high load node is the node 100A with the node number “7”, the node in the backup topology information x Of the four links connected to the node 100A with the number “7”, only one link can be used, so that the load may be concentrated. Therefore, as shown in FIG. 10B, the node 100A changes the link 6-7 connected to the high load node of the backup topology information x from the protected link to the normal link, and instead, the link in the backup topology information y2 Change 6-7 to a protected link. Further, the node 100A changes the link 4-7 connected to the high load node 100A of the backup topology information x from the protected link to the normal link, and changes the link 4-7 in the backup topology information y1 to the protected link instead. . In this way, the node 100A can create the backup topology information group 132 in which the protection links are distributed and arranged between the backup topology information. Therefore, the node 100A creates the detour path information 135 based on the backup topology information group 132, so that even when a node failure or link failure occurs in the network, the load is not concentrated on a specific node or link. Such a detour route can be taken.

  Next, the configuration of such a node 100A will be described with reference to FIG. Constituent elements similar to those of the above-described embodiment are denoted by the same reference numerals and description thereof is omitted. As illustrated in FIG. 11, the processing unit 12 of the node 100A includes a backup topology information processing unit 121A. The backup topology information processing unit 121A includes a high load node selection unit 122, a backup topology information creation unit 1211, a protect link exchange unit 1212, a connectivity determination unit 1213A, a protect link number comparison unit 1214, and an end determination unit. 1215 and a backup topology information output processing unit 126.

  The backup topology information creation unit 1211 uses the technique described in Non-Patent Document 2 to (1) when the protection link in the backup topology information is removed, the connection between the nodes becomes a connection graph, and (2) in each of the backup topology information N pieces of spare topology information in which a set of protected links matches a set of links indicated in the topology information 131 are created.

  The protect link exchanging unit 1212 selects spare topology information having the largest number of protect links connected to the high load node among the N pieces of spare topology information created by the spare topology information creating unit 1211. Then, one of the protected links connected to the high load node in the selected backup topology information is changed to a normal link, and the backup topology information other than the selected backup topology information for the link changed to the normal link. Change to a protected link at. That is, the protection link exchange process is performed.

  The connectivity determination unit 1213A determines whether the connection between the nodes in the backup topology information becomes a connection graph after the protection link exchange process. Then, when the connection between the nodes does not become the connection graph, the connectivity determination unit 1213A performs the protection link exchange process again for the protection link exchange unit 1212 with the combination of the protection link and the backup topology information not yet selected. Instruct to run.

  The number of protected links comparison unit 1214 determines the number of protected links connected to the high load node of the selected backup topology information after the protection link replacement process and the number of protected links connected to the high load node of each of the other backup topology information. Compare the maximum value. When the number of protected links connected to the high load node of the selected backup topology information is smaller than the maximum value of the number of protected links connected to the high load node of each backup topology information, the backup topology information output processing unit Instruct 126 to output the protection topology information group after the protection link exchange processing to the storage unit 13 as the protection topology information group 132.

  The end determination unit 1215 has a connectivity determination unit 1213A if the connection between the nodes does not become a connection graph even if the protection link exchange unit 1212 executes the protection link exchange process for all combinations of the protection link and the backup topology information. Is determined, the protect link exchanging unit 1212 is instructed to end the protect link exchanging process.

<Processing procedure>
Next, the processing procedure of the node 100A will be described with reference to FIG. Since S21 and S22 are the same processing as S1 and S2 of FIG. 6, description is abbreviate | omitted and it demonstrates from S23.

  The backup topology information creation unit 1211 of the node 100A creates N pieces of backup topology information based on the technique described in Non-Patent Document 2 (S23). In the backup topology information created here, the connection between nodes becomes a connection graph when the protection link in the protection topology information is removed, and the set of protection links in each protection topology information is a set of links indicated in the topology information. Is consistent with The spare topology information creation unit 1211 creates, for example, three pieces of spare topology information shown in FIG.

  Next, the protect link exchanging unit 1212 selects spare topology information having the largest number of protect links connected to the high load node from the N pieces of spare topology information created in S23 (S24). For example, the protect link exchange unit 1212 selects the backup topology information x from the backup topology information group illustrated in FIG.

  Then, the protect link exchanging unit 1212 replaces the protect link connected to the high load node in the selected backup topology information with a link in other backup topology information (S25). That is, the protect link exchange unit 1212 executes a protect link exchange process. For example, as shown in FIG. 10B, the protect link exchanging unit 1212 changes the protect link (link 6-7) connected to the high load node of the backup topology information x to a normal link. Further, the link 6-7 in the backup topology information y2 is changed from a normal link to a protected link. The protect link exchange unit 1212 records the result of such protect link exchange processing in the backup topology information management information 136. Here, the case where there is one high load node has been described as an example, but if there are a plurality of high load nodes, the protect link exchange processing is performed for the protect links connected to all the high load nodes.

Then, the connectivity determination unit 1213A determines whether the connection between the nodes in all the backup topology information becomes a connection graph even if the protection link is removed (S26). If the connection between the nodes in all the backup topology information is a connection graph even if the protection link is removed (Yes in S26), the process of S29 is executed. That is, the protected link number comparison unit 1214 has a higher load of the backup topology information selected in S24 than the maximum value of the number of protected links connected to the high load node in each backup topology information other than the backup topology information selected in S24. It is determined whether or not the number of protected links connected to the node is smaller (S29). That is, the protected link number comparison unit 1214 determines whether or not the number of protected links connected to the high load node is distributed among the backup topology information as a result of the protected link exchange process. Here, the number of protected links connected to the high load node of the selected backup topology information is larger than the maximum number of protect links connected to the high load node in each of the backup topology information other than the backup topology information selected in S24. If there are few (Yes in S29), the node 100A executes the backup topology information output process in S30 and the detour path information creation process in S31. Since S30 and S31 are the same as S11 and S12 of FIG.

  For example, after the protection link exchange process, when the protection link arrangement of the backup topology information x, y1, y2 is as shown in FIG. 10B, the high load node (node number “ The number of protected links to be connected to the node 100A) of “7” is “1”. The number of protect links connected to the high load node (node 100A with node number “7”) in the backup topology information y1 is “1”, and the high load node (node 100A with node number “7” in the backup topology information y2). ) Is “2”. Therefore, the number of protected links connected to the high load node of the selected backup topology information x (“1”) is larger than the maximum value (“2”) of the number of protected links connected to the high load node in the backup topology information y1, y2. ) Is less, the process proceeds to S30.

  On the other hand, when it is determined in S26 that the connection between the nodes of the backup topology information does not become a connection graph even if the protection link is removed (No in S26), and the connection is made to the high load node of the selected backup topology information. When the number of protected links is equal to or greater than the maximum number of protected links connected to the high load node in each of the other backup topology information (No in S29), the process proceeds to S27. Then, the end determination unit 1215 determines the end of the protect link exchange process. That is, the end determination unit 1215 refers to the backup topology information management information 136 and determines whether or not the protection link exchange unit 1212 has executed the protection link replacement processing for all combinations of protection links and backup topology information. If the protection link exchange processing has already been executed for all combinations of the protection link and the backup topology information (Yes in S27), N is increased (S32), and the process returns to S23. That is, when the arrangement of the connection graph cannot be found no matter how the protection links are exchanged between the backup topology information, the node 100A increases the number of backup topology information, and performs the processes after S23. Run.

  On the other hand, when the protect link exchanging unit 1212 determines that there is a combination that has not yet executed the protect link exchanging process among the combinations of all the protect links and the backup topology information (No in S27). The protect link exchanging unit 1212 selects another combination of the protect link and the backup topology information (S28), and returns to S25.

  In this way, the node 100A can create the backup topology information group 132 in which the protection links are distributed and arranged between the backup topology information. Therefore, the node 100A creates the detour path information 135 based on the backup topology information group 132, so that even when a node failure or link failure occurs in the network, the load is not concentrated on a specific node or link. Such a detour route can be taken.

DESCRIPTION OF SYMBOLS 11 Input / output part 12 Processing part 13 Storage part 100,100A Node 121,121A Backup topology information processing part 122 High load node selection part 123 Initial information creation part 124 Protect link selection part 125 Protect link arrangement change part 126 Backup topology information output process Unit 127 AC traffic acquisition unit 128 route control unit 129 route calculation unit 130 packet transfer unit 131 topology information 132 spare topology information group 133 AC traffic information 134 route information 135 detour route information 136 spare topology information management information 1211 spare topology information creation unit 1212 Protect link exchange unit 1213, 1213A Connectivity determination unit 1214 Protect link number comparison unit 1215 End determination unit

Claims (4)

A detour route information creation device that creates detour route information based on backup topology information indicating a link that is disconnected when a node failure or a link failure occurs in a network,
A storage unit for storing topology information indicating a topology of the network and a link cost of each link;
An AC traffic acquisition unit that acquires AC traffic information that is a traffic flow between the nodes from each node in the network, and stores the AC traffic information in the storage unit;
A high load node selection unit that refers to the topology information and the AC traffic information, calculates a traffic amount for each node, and selects a node having the calculated traffic amount exceeding a predetermined threshold as a high load node; ,
Referring to the topology information, initial information of the backup topology information with a maximum of [(maximum number of links connected to each of the high load nodes / N) +1] protect links connected to one of the high load nodes An initial information creation unit for performing initial information creation processing for creating N pieces of information,
A connectivity determination unit that determines whether or not a connection between nodes becomes a connection graph when the protected link is removed for all of the created N pieces of initial information or backup topology information;
A method used for IP-FRR (IP Fast Reroute) when the connectivity determination unit determines that the connection between nodes becomes a connection graph when the protected links are removed for all the created N pieces of initial information Thus, in each of the created N pieces of initial information, a process of selecting the protected link from links other than those already selected as the protected link is performed. A protected link selection unit that performs processing for creating the N pieces of spare topology information by executing until the set of links shown in FIG.
For each of the created backup topology information, creating a bypass path information indicating a bypass path that bypasses the protected link indicated in the backup topology information, and storing the path calculation unit in the storage unit;
When the connectivity determination unit determines that the connection between nodes does not become a connection graph when the protected link is removed in any of the created N pieces of initial information, A protection link arrangement changing unit that changes the arrangement of the protection links and searches for initial information in which the connection between the nodes in each of the N pieces of initial information becomes a connection graph;
The protect link selection unit performs the preliminary topology information creation processing for each of the N pieces of initial information searched by the protect link arrangement change unit,
When the protect link arrangement changing unit cannot find the initial information in which the connection between the nodes in each of the N pieces of initial information becomes a connection graph, the initial information creating unit increases the value of N, Perform the initial information creation process again,
The detour path information creation device, wherein the protect link selection unit performs the backup topology information creation process on the N pieces of initial information obtained by the initial information creation process. When it is determined by the connectivity determination unit that any one of the N backup topology information created by the protected link selection unit is not a connection graph,
The initial information creation unit increases the value of N, performs the initial information creation process again,
2. The detour path information creation device according to claim 1, wherein the protection link selection unit performs the spare topology information creation process on the N pieces of initial information obtained by the initial information creation process. . A detour route information creation device that creates detour route information based on backup topology information indicating a link that is disconnected when a node failure or a link failure occurs in a network,
A storage unit for storing topology information indicating a topology of the network and a link cost of each link;
An AC traffic acquisition unit that acquires AC traffic information that is traffic flow between each node in the network from each node in the network, and stores the AC traffic information in the storage unit;
A high load node selection unit that refers to the topology information and the AC traffic information, calculates the arrival and departure traffic amount of each of the nodes, and selects a node having the calculated traffic amount exceeding a predetermined threshold as a high load node;
When the protected link in the backup topology information is removed by the method used for IP-FRR, the connection between the nodes becomes a connection graph, and a set of protected links in each of the backup topology information is a link indicated in the topology information. A standby topology information creating unit for creating N pieces of spare topology information that matches the set of
Of the created N pieces of protection topology information, the protection topology information having the largest number of protection links connected to the high load node is selected, and the protection links connected to the high load node in the selected protection topology information are selected. One of them is changed to a normal link, and a protected link exchanging unit that executes a protected link exchanging process for changing the link in the backup topology information other than the selected backup topology information to a protected link;
After the protection link exchange process, it is determined whether or not the connection between the nodes in the backup topology information becomes a connection graph. When it is determined that the connection between the nodes does not become a connection graph, the protection link exchange unit On the other hand, for the protected link and backup topology information that have not yet been selected, a connectivity determination unit that instructs to perform the protected link replacement process again,
After the protection link replacement processing, the number of protection links connected to the high load node of the selected backup topology information is compared with the maximum number of protection links connected to the high load node of each other backup topology information. When the number of protected links connected to the high load node of the selected backup topology information is smaller than the maximum value of the number of protected links connected to the high load node of each of the backup topology information, the protection link exchange process A protection link number comparison unit for storing a subsequent backup topology information group in the storage unit;
Even if the protect link exchanging unit executes the protect link exchanging process for all combinations of the protect link and the backup topology information, the connectivity determining unit determines that the connection between the nodes does not become a connection graph. An end determining unit that instructs the protect link exchanging unit to end the protect link exchanging process;
For each spare topology information in the storage unit, a detour route information indicating a detour route that detours the protect link indicated in the spare topology information is created, and a route calculator that stores the detour route information in the memory unit is provided. Detour route information creation device. A detour route information creation device that creates detour route information based on backup topology information indicating a link that is disconnected when a node failure or link failure occurs in the network as a protected link,
Acquiring AC traffic information, which is traffic flow between the nodes, from each node in the network, and storing the information in a storage unit;
Referring to the topology information indicating the topology of the network and the link cost of each link and the AC traffic information, for each node, the traffic volume of the node is calculated, and the calculated traffic volume is a predetermined threshold value. Selecting a node that exceeds A as a high load node;
Referring to the topology information, initial information of the backup topology information with a maximum of [(maximum number of links connected to each of the high load nodes / N) +1] protect links connected to one of the high load nodes Performing initial information creation processing for creating N pieces,
When the connection between nodes becomes a connection graph when the protected link is removed for all the created N pieces of initial information, the created pieces of N pieces of initial information are obtained by a method used for IP-FRR (IP Fast Reroute). In each, the process of selecting the protected link from links other than those already selected as the protected link is executed until the set of the selected protected links matches the set of links indicated in the topology information. Performing a process of creating N pieces of spare topology information;
For each of the created backup topology information, creating detour path information indicating a detour path that bypasses the protected link indicated in the backup topology information, and storing the detour path information in the storage unit;
If the connection between nodes does not become a connection graph when the protection link is removed in any of the created N pieces of initial information, the arrangement of the protection links in the N pieces of initial information is changed, and the N Searching for initial information in which the connection between the nodes in each of the initial information becomes a connection graph;
Performing the preliminary topology information creation process for each of the searched N pieces of initial information;
When the initial information that the connection between the nodes in each of the N pieces of initial information becomes a connection graph cannot be found, the value of N is increased, and the initial information creation process is performed again;
A detour route information creating method, comprising: performing the preliminary topology information creating process on the N pieces of initial information obtained by the initial information creating process.

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