Communication path calculation device

Abstract

The present invention provides a communication path calculation device comprising a path calculation unit. The path calculation unit calculates candidates for communication paths formed from a main path and a redundant path proceeding from a multicast start node to each end node included in an end node set on the basis of physical topology information that represents the nodes that make up a network, edges representing links between nodes, and the failure rate of each edge, said candidates being calculated such that the main path and the redundant path proceeding to the same end node do not contain the same edges. For each of the multiple types of communication path candidates, the path calculation unit calculates an evaluation value representing the impact on a user due to an event in which an edge included in the main path and an edge included in the redundant path fail, and selects a communication path to use from among the plurality of candidates on the basis of the calculated evaluation value.

Description

Communication path calculation device

[0001] The present invention relates to a communication path calculation device.

[0002] Multicast communication is used for multipoint video distribution, etc. The Steiner tree problem is well known for constructing multicast communication routes. This is a problem of finding the tree with the smallest cost that includes all nodes in the source and destination sets. The solution route does not have redundant routes, and does not take into account the impact on users in the event of a failure.

[0003] Meanwhile, there is prior research into providing redundant routes for multicast communication routes (see, for example, Non-Patent Document 1). This prior research provides an optimization method for providing edge-disjoint main and redundant routes connecting a source and destination set, minimizing the cost of the edges used in the main or redundant routes. While this increases reliability, it does not take into account the impact on users when a redundant route fails.

[0004] There is also prior research that takes user impact into account (see, for example, Non-Patent Document 2). This prior research provides an evaluation formula for user impact and an algorithm to minimize its value, taking into account the failure rate of each edge. The expected user impact is calculated as follows:

[0005] "Expected user impact" = (probability of 1st failure and 2nd failure occurrence) x (number of users affected by the failure)

[0006] Although the technology of Non-Patent Document 2 takes into consideration the impact of a failure on users, there is a problem in that even a single failure will cause a disconnection because there are no redundant paths.

[0007] NK Singhal et al., "Provisioning of survivable multicast sessions against single link failures in optical WDM mesh networks", Journal of Lightwave Technology, Vol. 21, No. 11, pp. 2587-2594, 2003. 2018.

[0008] The above-mentioned conventional techniques do not determine the main route and the redundant route in multicast communication while taking into consideration the impact on users.

[0009] In view of the above circumstances, an object of the present invention is to provide a communication path calculation device that can determine a main path and redundant paths in multicast communication while taking into account the impact on users.

[0010] A communication path calculation device according to one aspect of the present invention calculates candidate communication paths consisting of a main path and a redundant path from a multicast start node to each of the end nodes included in a multicast end node set based on information on the nodes that constitute a network, the edges that represent the links between the nodes, and the physical topology that represents the failure rates of each of the edges, such that the main path and the redundant path that lead to the same end node do not include the same edge; calculates an evaluation value for each of the multiple types of candidate communication paths that have been calculated that represents the impact on a user of an event in which an edge included in the main path and an edge included in the redundant path fail; and selects a communication path to use from among the multiple types of candidate communication paths based on the calculated evaluation value.

[0011] According to the present invention, it is possible to determine the main route and the redundant routes in multicast communication while taking into consideration the impact on users.

[0012] FIG. 1 is a configuration diagram of a communication route optimization device according to an embodiment of the present invention. FIG. 2 is a diagram showing whether or not a failure event of an embodiment has an impact on users. FIG. 3 is a flow diagram showing the processing of a communication route optimization device according to an embodiment. FIG. 4 is a diagram showing a comparison between an embodiment and a conventional technique. FIG. 5 is a diagram showing a failure rate used in an experiment of a communication route optimization device according to an embodiment. FIG. 6 is a diagram showing experimental results of a communication route optimization device according to an embodiment. FIG. 7 is a diagram showing an example of a hardware configuration of a communication route optimization device according to an embodiment.

[0013] An embodiment of the present invention will be described in detail below with reference to the drawings. Multicast communications, including multipoint video distribution, are commonplace in our daily lives, and many of these communications require high reliability. Because multicast communication paths have a tree structure, a large number of users can be affected depending on the location of a failure. This embodiment relates to a communication path optimization technology that provides redundant paths for high reliability in multicast communications and minimizes the impact on users when the redundant paths also fail (when two failures occur). An impact on users could be, for example, multicast data not reaching users.

[0014] The communication path calculation device of this embodiment determines the main and redundant paths for multicast by optimizing them to minimize the impact on users when two failures occur: one on the main path and one on the redundant path. This improves both the reliability of the communication path and the impact on users. Note that because there is a redundant path, the impact on users due to one failure is zero.

[0015] In this embodiment, when formulating the magnitude of user influence, quadratic terms are eliminated, resulting in a linear programming problem. This makes it possible to obtain a solution relatively quickly. Furthermore, in this embodiment, the magnitude of user influence can be calculated by weighting each multicast endpoint according to its importance, such as the number of users downstream of that endpoint.

[0016] Fig. 1 is a functional block diagram showing the configuration of a communication route optimization device 1 according to one embodiment of the present invention. The communication route optimization device 1 is an example of a communication route calculation device. Fig. 1 shows only functional blocks related to this embodiment. The communication route optimization device 1 can be realized by, for example, a computer device.

[0017] The communication route optimization device 1 is connected to a NW (network) management device 2. The NW management device 2 manages a network 3 in which multicast communication is performed. Each circle in the network 3 represents a node, and the number inside the node represents the node number. The node is, for example, a communication device. A node with node number i (i = 1, 2, ...) is referred to as node #i. According to the communication route information received from the communication route optimization device 1, the NW management device 2 instructs each node in the network 3 which adjacent node will receive multicast data and which adjacent node will be the destination of the received data.

[0018] The communication route optimization device 1 has a database 11 and a route calculation unit 12. The database 11 is a storage unit that stores a physical topology G(V, E, F). The physical topology G(V, E, F) is information that indicates the physical topology of the network 3. V is a set of nodes, E is a set of edges, and F is the failure rate of each edge. An edge is a link between nodes, and corresponds to a data communication path.

[0019] The route calculation unit 12 calculates a multicast communication route in the network 3 based on the communication demand R and information on the physical topology G recorded in the database 11. The communication route consists of a main route and a redundant route. The route calculation unit 12 has an input unit 121, a failure event occurrence probability calculation unit 122, an optimization calculation unit 123, and an output unit 124.

[0020] The input unit 121 acquires information used for calculating a communication path and inputs the acquired information to the path calculation unit 12. The input information is the communication demand R(s, D={d １ ,... ,d ｜Ｄ｜) where s is the starting point, i.e., the node that is the source of the multicast communication. D is a session, i.e., a set of nodes with end points d. For simplicity, the number of users at each end point d is assumed to be 1. The input unit 121 may input information received from another computer device connected via the network to the route calculation unit 12, or may input information read from a computer-readable recording medium to the route calculation unit 12. The input unit 121 may also acquire information input by a user using a keyboard, mouse, touch panel, button, key, or the like.

[0021] The failure event occurrence probability calculation unit 122 calculates all events Y={l=(e １ , e ２ ) | e １ , e ２ ∈E, e １ ≠e ２ Furthermore, the failure event occurrence probability calculation unit 122 calculates the event l=(e １ , e ２ ) occurrence probability q ｌ Hereinafter, the event l of the edge 2 fault will be referred to as edge 2 fault l or fault event l.

[0022] The optimization calculation unit 123 calculates the two-fault on each side l=(e １ , e ２ ) occurrence probability q ｌ Based on this, the main route information P ｅ ｄ and redundant route information B ｅ ｄ This objective function calculates the expected user impact value, which is the magnitude of the impact on users due to the occurrence of edge 2 fault l preventing multicast data from reaching users under destination point d. ｅ ｄ is a binary variable that is 1 if edge e is used in the main path to destination d, and 0 otherwise. ｅ ｄis a binary variable that is 1 if edge e is used in a redundant path to destination d, and 0 otherwise.

[0023] The output unit 124 outputs the main path information P of each edge e calculated by the optimization calculation unit 123. ｅ ｄ and redundant route information B ｅ ｄ The route information indicating the route is recorded in the database 11 and output to the NW management device 2. The NW management device 2 instructs each node of the network 3 to transfer data in accordance with the received route information, thereby opening the main route and redundant route of the network 3 in response to the communication demand.

[0024] In this embodiment, the communication route optimization method is formulated as the following linear programming.

[0025] <Given Information> The following (a1) to (a4) are given.

[0026] (a1) Physical topology G(V, E, F) of a directed simple graph with a given failure rate for each edge. The node set V is a set of nodes that make up the network 3. The edge set E is a set of edges e that represent links between the nodes that make up the network 3. The failure rate F of each edge is the failure rate F of each edge e. ｅ Represents.

[0027] (a2) Communication demand R(s, D={d １ ,... ,d ｜Ｄ｜ ). s is the starting point (source) and D is the set of destination points (session). The starting point is the node that first distributes multicast communication data in network 3. D is the node that is the multicast end point in network 3 and does not forward the received multicast data to other nodes.

[0028] (a3) All events of edge 2 faults Y = {l = (e １ , e ２ ) | e １ , e ２ ∈E, e １ ≠e ２}. Edge 2 fault l = (e １ , e ２ ) is the side e １ Tobe e ２The total event Y of edge 2 failures is calculated based on the physical topology G of the directed simple graph.

[0029] (a4) 2 failures on each side l = (e １ , e ２ ) occurrence probability q ｌ The probability of occurrence of edge 2 fault l is q ｌ is calculated by the following formula (1).

[0030]

[0031] Equation (1) is the side e １ and side e ２ is the probability of occurrence of a failure event in which both ｅ１ Side e １ Failure rate of F ｅ２ Side e ２ Failure rate of F ｅ３ is the edge e among the edges included in the edge set E. １ , side e ２ The side e that is different from ３ is the failure rate.

[0032] <Variable> The variable is the main route information P ｅ ｄ , redundant route information B ｅ ｄ , and communication cutoff information U ｌ ｄ It is. ｅ ｄ , B ｅ ｄ , U ｌ ｄ ∈{0, 1}. Main route information P ｅ ｄ is 1 if edge e is used for the main path to destination d, and is 0 otherwise. ｅ ｄ is 1 if edge e is used in a redundant path to destination d, and is 0 otherwise. ｌ ｄ is 1 if the communication to the destination point d is interrupted due to the edge 2 fault l, and is 0 otherwise. ｌ ｄ is 1 if edge 2 fault l blocks communication to downstream users at destination d, and 0 otherwise.

[0033] <Objective Function> The objective function is expressed by the following formula (2).

[0034]

[0035] In equation (2), the number of downstream users at the end point d is N ｄ The weights of the communication interruption information U ｌ ｄ It may also be used as a coefficient of

[0036] <Constraints> The following (b1) to (b3) are constraints. (b1) Law of conservation of flow rate. At nodes other than the start point and the end point, the amount of data received is equal to the amount of data transmitted. (b2) Edge disjunction condition shown in the following formula (3). That is, for each end point d included in the end point set D, the main route from the start point s to the end point d and the redundant route from the start point s to the end point d do not include a common edge e. However, if the end point set D includes the end point d and the end point d' (d ≠ d'), the main route or redundant route to the end point d and the main route or redundant route to the end point d' may include a common edge e.

[0037]

[0038] (b3) The condition shown in the following formula (4).

[0039]

[0040] According to equation (4), the fault event l=(e １ , e ２ ), communication cutoff information U ｌ ｄ is side e １ is used for the main path to the destination point d, and edge e ２ is used for the redundant path to the destination point d, otherwise it is 0. １ and side e ２ This is to count the number of users affected by the two failures without excess or deficiency, and by using this form, it is possible to avoid the quadratic term in the objective function.

[0041] The key points in the above formulation are explained below. Figure 2 shows the edge 2 fault l = (e １ , e ２) is a diagram showing whether or not the user at the end point d is affected by the edge 2 fault l. When the number of users affected by the edge 2 fault l is used as the objective function, it is expressed as the following equation (5).

[0042]

[0043] Equation (5) includes the quadratic term P ｅ１ ｄ B ｅ２ ｄ On the other hand, in this embodiment, the number of users affected by two faults on each side is counted by P ｅ１ ｄ B ｅ２ ｄ Instead of the above, a new variable, communication cutoff information U, is obtained by the constraints (b1) to (b3). ｌ ｄ Communication cutoff information U ｌ ｄ is expressed as P as shown in FIG. ｅ１ ｄ B ｅ２ ｄ As in equation (2), by eliminating the quadratic term from the objective function and linearizing it, it becomes possible to find a solution relatively quickly.

[0044] Next, a description will be given of the processing of the communication route optimization device 1. FIG.

[0045] When a communication demand R occurs in the network 3, the NW management device 2 notifies the communication route optimization device 1 of the communication demand R. For example, communication demand R (s=7, D={6, 19, 22}) starting from node #7 and ending at nodes #6, #19, and #22 is notified. The input unit 121 of the communication route optimization device 1 inputs the communication demand R notified from the NW management device 2 to the route calculation unit 12 (step S1).

[0046] The failure event occurrence probability calculation unit 122 reads out information on the physical topology G of the network 3 from the database 11 (step S2). Based on the physical topology G, the failure event occurrence probability calculation unit 122 calculates all events Y={l=(e １ , e２ ) | e １ , e ２ ∈E, e １ ≠e ２} is calculated, and then, using equation (1), １ , e ２ ) occurrence probability q ｌ (Step S3). The failure event occurrence probability calculation unit 122 calculates the calculated occurrence probability q ｌ is written to the database 11.

[0047] The optimization calculation unit 123 uses the physical topology G to calculate communication route candidates (hereinafter referred to as communication route candidates) consisting of a set of main routes and redundant routes from the node of the starting point s indicated by the communication demand R to the nodes of each end point d, in accordance with constraints (b1) and (b2). FIG. 3 shows an example of main routes and redundant routes of communication routes starting from node #7 indicated by the communication demand R and ending at nodes #6, #19, and #22. p_d(i,j) is the main route information P of the edge e between node #i and node #j (j is a positive number other than i). ｅ ｄ =P （ｉ，ｊ） ｄ b_d(i, j) represents the redundant path information B of the edge e between node #i and node #j. ｅ ｄ =B （ｉ，ｊ） ｄ Represents.

[0048] Furthermore, the optimization calculation unit 123 calculates the main route information P ｅ ｄ and redundant route information B ｅ ｄ Using the equation (4) of the constraint (b3), the communication interruption information U ｌ ｄ The optimization calculation unit 123 calculates the value of the objective function of the communication path candidate based on the occurrence probability q ｌ and the communication cutoff information U calculated according to the constraint (b3). ｌ ｄ and are calculated using equation (2).

[0049] The optimization calculation unit 123 calculates the value of the objective function for each of the multiple different communication path candidates, and selects the communication path candidate with the smallest objective function value as the communication path to be used for the communication demand R (step S4).

[0050] The output unit 124 writes the route information indicating the selected communication route to the database 11 and outputs it to the NW management device 2 (step S5). ｅ ｄ and redundant route information B for each node ｅ ｄ The NW management device 2 sets routing information of the main route and the redundant route in each node of the network 3 according to the received route information. As a result, a path for the communication demand R is opened in the network 3.

[0051] Fig. 4 compares this embodiment with the prior art. As shown in Fig. 4, in the Steiner tree problem, redundant paths are not set, and the impact on users in the event of a failure is not taken into consideration. In Non-Patent Document 1, redundant paths are set, but the impact on users in the event of a failure is not taken into consideration. The objective function used in Non-Patent Document 1 is Equation (6).

[0052]

[0053] In addition, c ｅ is the cost of edge e. ｅ is 1 if edge e is used in a primary or redundant path to any destination d, and is 0 otherwise.

[0054] Conversely, in Non-Patent Document 2, no redundant paths are set up, but the impact on users in the event of a failure is taken into consideration. The objective function used in Non-Patent Document 2 is shown in Equation (7).

[0055]

[0056] Here, LT is a light tree network, and LP is a point-to-point path. U(e) is the number of users downstream of edge e. In Non-Patent Document 2, a tree that minimizes LIFPMS is obtained by a greedy heuristic.

[0057] In this embodiment, redundant paths are set and the impact on users in the event of a failure is also taken into consideration. Furthermore, the amount of calculation is reduced by using the objective function of equation (2).

[0058] Next, the effects of this embodiment will be described. In the evaluation experiment, a directed simple graph of the Japanese network with 25 vertices and 43 edges was used as the physical topology G=(V, E, F), and the communication demand R(s, D) was set as a set of randomly selected start and end points.

[0059] Fig. 5 shows the failure rate F used in the evaluation experiment. In the evaluation experiment, the MTTR / MTBF value of "Optical Fiber" shown in Table 1 of the reference document was randomly assigned as the failure rate F of each edge d from among Optimistic, Nominal, and Conservative.

[0060] (Reference) J. Segovia et al., “Topology-focused availability analysis of basic protection schemes in optical transport networks”, Journal of Optical Networking, Vol. 7, No. 4, pp. 351-364, 2008

[0061] Fig. 6 shows the expected value of the impact on users with respect to the number of end nodes when using the present embodiment and the technology of Non-Patent Document 1. Fig. 6 shows the results of implementation for end points of 1 to 11. As shown in Fig. 6, the impact on users due to two failures is improved in this embodiment compared to the method of Non-Patent Document 1 (cost minimization).

[0062] 7 is a diagram illustrating an example of the hardware configuration of the communication route optimization device 1. The communication route optimization device 1 includes a processor 71, a storage unit 72, a communication interface 73, and a user interface 74.

[0063] The processor 71 is a central processing unit that performs calculations and control. The processor 71 is, for example, a CPU (central processing unit) or a GPU (graphics processing unit). The processor 71 reads and executes programs from the storage unit 72. The storage unit 72 further has a work area and the like when the processor 71 executes various programs. The communication interface 73 is connected to other devices so as to be able to communicate with them. The user interface 74 is an input device such as a keyboard, a pointing device (a mouse, a tablet, etc.), a button, a touch panel, etc., and a display device such as a display. Human operations are input via the user interface 74.

[0064] At least some of the functions of the route calculation unit 12 of the communication route optimization device 1 are realized by the processor 71 reading and executing a program from the storage unit 72. The program of the communication route optimization device 1 may be recorded on a computer-readable recording medium. Examples of the computer-readable recording medium include portable media such as flexible disks, optical magnetic disks, ROMs, and CD-ROMs, and storage devices such as hard disks built into computer systems. The program of the communication route optimization device 1 may be transmitted via a telecommunications line. At least some of the functions of the communication route optimization device 1 may be realized using hardware such as an ASIC (Application Specific Integrated Circuit), a PLD (Programmable Logic Device), or an FPGA (Field Programmable Gate Array). The database 11 is realized using the storage unit 72.

[0065] The failure event occurrence probability calculation unit 122 of the communication route optimization device 1 calculates in advance the number of two failures on each side l=(e １ , e ２ ) occurrence probability q ｌ , and write it into the database 11. As a result, instead of step S3 of the processing flow of FIG. 3, the optimization calculation unit 123 of the communication route optimization device 1 can obtain the occurrence probability q ｌIn addition, the previously calculated two-fault on each side l = (e １ , e ２ ) occurrence probability q ｌ may be stored in the database 11. In this case, the communication route optimization device 1 does not need to include the failure event occurrence probability calculation unit 122.

[0066] Furthermore, the communication route optimization device 1 may not have the database 11 inside, but the database 11 may be provided in another device connected to the communication route optimization device 1 .

[0067] Furthermore, the communication route optimization device 1 may be realized by a plurality of computer devices connected to a network. In this case, it is possible to arbitrarily determine which of the plurality of computer devices each functional unit of the communication route optimization device 1 is realized by. For example, the database 11 and the path calculation unit 12 may be realized by different computer devices, and the failure event occurrence probability calculation unit 122 and the optimization calculation unit 123 may be realized by different computer devices. Furthermore, the same functional unit may be realized by a plurality of computer devices. For example, the optimization calculation unit 123 may be realized by a plurality of computer devices, and the processing of step S4 may be performed in parallel.

[0068] According to the above-described embodiment, the communication path calculation device includes a path calculation unit. The communication path calculation device corresponds, for example, to the communication path optimization device 1 of the embodiment. The path calculation unit calculates candidate communication paths consisting of a main path and a redundant path from a multicast start node to each of the end nodes included in a multicast end node set based on information on the nodes constituting the network, the edges representing the links between the nodes, and the failure rate of each edge, such that the main path and the redundant path leading to the same end node do not include the same edge. For each of the multiple types of calculated candidate communication paths, the path calculation unit calculates an evaluation value representing the impact on a user of an event in which an edge included in the main path and an edge included in the redundant path fail, and selects a communication path to be used from the multiple types of candidate communication paths based on the calculated evaluation value. For example, the path calculation unit selects the communication path with the evaluation value that has the smallest impact on the user.

[0069] The communication path calculation device may further include a storage unit that stores information about the physical topology. The storage unit corresponds to, for example, the database 11 in the embodiment. The storage unit may store all two-failure events in which both edges of a combination of two edges fail, calculated from the information about the physical topology, and their occurrence probabilities. The storage unit may also store information about the communication paths (main path and redundant path) calculated by the path calculation unit. Upon receiving a communication demand, the path calculation unit reads the information about the physical topology and all two-failure events and their occurrence probabilities stored in the storage unit, and calculates a main path and redundant path that minimizes the expected impact on users due to the occurrence of two failures.

[0070] The route calculation unit calculates routes based on the formulation into a linear programming problem shown in the communication route optimization method described above. The following points are important in the formulation. One is to improve both the reliability of the communication route and the impact on users by finding the main route and redundant route through optimization that minimizes the impact on users when two failures occur. The other is to reduce the problem to a linear programming problem by formulating the problem in a form that does not include quadratic terms. Furthermore, by using a similar formulation, it is possible to calculate the number of downstream users N at each end point. ｄ This can also be extended to cases where weighting is performed as above.

[0071] The path calculation unit may include a failure event occurrence probability calculation unit and a calculation unit. The failure event occurrence probability calculation unit calculates a failure event occurrence probability q ｌ The calculation unit corresponds to, for example, the optimization calculation unit 123 in the embodiment. The calculation unit calculates a plurality of types of communication path candidates based on information on the physical topology. For each communication path candidate, the calculation unit calculates communication cutoff information U which takes a value of 1 if the condition that one edge of the edge 2 fault l is included in the main path leading to the end node and the other edge of the edge 2 fault l is included in the redundant path leading to the end node is satisfied, and takes a value of 0 if the condition is not satisfied. ｌ The value ΣU obtained by adding the above for the end node set ｌ The probability of failure event occurrence q of side 2 failure l ｌMultiply by the partial evaluation value q ｌ ΣU ｌ Calculate the partial evaluation value q of all edge 2 faults l in the network. ｌ ΣU ｌ The calculation unit calculates an evaluation value by adding the above values. The calculation unit selects a communication path to be used from among multiple types of candidate communication paths based on the calculated evaluation value. For example, the calculation unit selects a communication path with an evaluation value that has the smallest impact on the user.

[0072] The calculation unit calculates the communication cutoff information U ｌ may be weighted by the number of downstream users of the end node. ｌ takes a positive finite value if the condition that one edge of edge 2 fault l is included in the main path leading to the destination node and the other edge of edge 2 fault l is included in the redundant path leading to the destination node is satisfied, and takes 0 if the condition is not satisfied. In this way, the number of users N downstream of the destination node d ｄ When considering factors such as N ｄ ×U ｌ takes a finite value greater than or equal to 0.

[0073] The communication path calculation device of this embodiment can also be realized by a computer and a program, and the program can be recorded on a recording medium or provided via a network.

[0074] Although the embodiments of the present invention have been described in detail above with reference to the drawings, the specific configurations are not limited to these embodiments, and include designs within the scope of the present invention that do not deviate from the gist of the present invention.

[0075] REFERENCE SIGNS LIST 1 communication route optimization device 2 NW management device 3 network 11 database 12 route calculation unit 71 processor 72 storage unit 73 communication interface 74 user interface 121 input unit 122 failure event occurrence probability calculation unit 123 optimization calculation unit 124 output unit

Claims

1. A communication path calculation device comprising: a path calculation unit that calculates communication path candidates consisting of a main path and a redundant path from a multicast start node to each of the end nodes included in a multicast end node set based on information on the nodes that constitute a network, the edges representing the links between the nodes, and the physical topology representing the failure rates of each of the edges, such that the main path and the redundant path leading to the same end node do not include the same edge, calculates an evaluation value for each of the calculated multiple types of communication path candidates that represents the impact on a user of an event in which an edge included in the main path and an edge included in the redundant path fail, and selects a communication path to be used from the multiple types of communication path candidates based on the calculated evaluation value.

2. The path calculation unit calculates, based on the information of the physical topology, a failure event occurrence probability q ｌ a process for calculating a plurality of types of candidates for the communication path based on information on the physical topology; and a communication cutoff information U which takes a value of 1 when a condition is satisfied that one edge of the edge 2 fault l is included in the main path leading to the end node and the other edge of the edge 2 fault l is included in the redundant path leading to the end node, and takes a value of 0 when the condition is not satisfied. ｌ The value ΣU obtained by adding ｌ The fault event occurrence probability q of the edge 2 fault l ｌ Multiplying by the partial evaluation value q ｌ ΣU ｌ Calculate the partial evaluation value q of the edge 2 fault l in the network. ｌ ΣU ｌ and a calculation unit that selects a communication path to be used from among a plurality of types of candidate communication paths based on the calculated evaluation value.

3. The calculation unit calculates the communication cutoff information U ｌ The communication path calculation device according to claim 2 , wherein the weighting factor is determined based on the number of users downstream of the end node.

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