Communication system, communication control device, communication control method, and program

Abstract

A communication control device 20 comprises: a control unit 22 that preliminarily lists alternative routes available on a network, sets a priority for each of the listed alternative routes, and calculates a preliminary gate control list corresponding to each of the alternative routes in descending order of the priority; and a storage unit 23 that stores a predetermined number of the alternative routes in association with the preliminary gate control list in descending order of the priority, wherein when the network configuration is updated, the control unit 22 acquires a preliminary gate control list corresponding to the updated route from the storage unit 23 and sets the preliminary gate control list in the communication device 10.

Description

Technical Field

[0001] The present disclosure relates to a communication system, a communication control device, a communication control method, and a program.

Background Art

[0002] Conventionally, in each node of a network, a technique is known in which transmission and reception timings are ensured and frames of priority traffic are transferred according to a Gate Control List (GCL) in which priority traffic is scheduled to satisfy delay / jitter requirements on the network.

[0003] Non-Patent Document 1 describes Amendment 25 that defines enhancement of functions of scheduled traffic in IEEE 802.1Qbv-2015, which is an IEEE standard for local / metropolitan area networks.

[0004] Non-Patent Document 2 describes a routing algorithm in a network compliant with IEEE 802.1Qbv.

[0005] Furthermore, Non-Patent Document 3 describes a discussion on how the communication schedule of the Gate Control List defined in IEEE 802.1Qbv can be formulated as a constraint system expressed via the Theory of Arrays (TA).

[0006] Figure 12 illustrates a change in network configuration. As shown in Figure 12, a network with a gate control list set on each node may have its configuration changed due to physical routing, such as route failures or planned route switching. In Figure 12 (i), planned route switching is performed on a route marked with a "Road Closed" sign, and frames of priority traffic ST (ST#1, #2) are forwarded by bypassing the "Road Closed" route. In (ii), a route failure occurs on a route other than the one where planned route switching is taking place. In (iii), a "Road Closed" sign is set on the route where the route failure occurred, and the route forwarding frames of priority traffic ST#1, #2 is changed. In addition to physical route switching, "Road Closed" may also be performed by the Spanning Tree Protocol (STP) to avoid logical communication loops.

[0007] Thus, when the network configuration changes, it becomes necessary to update the gate control list to meet the latency / jitter requirements on the new network. By updating the gate control list, even if the network configuration changes, frames of priority traffic STs can be forwarded with low latency on the modified network. [Prior art documents] [Non-patent literature]

[0008] [Non-Patent Document 1] IEEE, “IEEE 802.1Qbv-2015”, Approved 5 December 2015 [Non-Patent Document 2] Naresh Ganesh Nayak et al., “Routing Algorithms for IEEE802.1Qbv Networks”, Institute for Distributed and Parallel Systems, Stuttgart, Germany. [Non-Patent Document 3] Ramon Serna Oliver et al., “IEEE 802.1Qbv Gate Control List Synthesis using Array Theory Encoding”, TTTech Computertechnik AG, Vienna, Austria [Overview of the project] [Problems that the invention aims to solve]

[0009] If the gate control list calculation begins after the network configuration has been changed, it becomes impossible to forward frames of priority traffic (ST) with low latency until the solution is found. To solve this problem, it is desirable to store the gate control list calculated for the updated network configuration so that the gate control list can be quickly set when the network configuration changes.

[0010] However, in addition to the difficulty of covering all network path failure patterns, there is a problem with insufficient memory resources if we were to maintain a list of alternative paths for each path failure pattern, calculate a gate control list for each alternative path, and sequentially store all the calculated gate control lists in memory as a backup gate control list. Hereafter, the gate control list created as a backup to handle path switching will be referred to as the backup gate control list.

[0011] Therefore, there was room for improvement in the technology for forwarding priority traffic frames on the network.

[0012] In light of these circumstances, the purpose of this disclosure is to improve the technology for forwarding priority traffic frames on a network. [Means for solving the problem]

[0013] To solve the above problems, the communication control device according to this embodiment is a communication control device that causes a communication device to transfer frames of priority traffic, and comprises: a control unit that pre-lists alternative routes available on the network, sets a priority for each of the listed alternative routes, and calculates a reserve gate control list corresponding to each of the alternative routes in order of decreasing priority; and a storage unit that associates the alternative routes and the reserve gate control lists and stores a predetermined number of them in order of decreasing priority. When the network configuration is updated, the control unit retrieves a backup gate control list corresponding to the updated route from the storage unit and sets it in the communication device.

[0014] To solve the above problems, the communication control method according to this embodiment is a communication control method that causes a communication device to forward frames of priority traffic, comprising the steps of: a communication control device pre-listing alternative routes available on the network; setting a priority for each of the listed alternative routes; calculating a reserve gate control list corresponding to each of the alternative routes in descending order of priority; associating the alternative routes with the reserve gate control lists and storing a predetermined number of them in descending order of priority; and when the network configuration is updated, obtaining the stored reserve gate control list corresponding to the updated route and setting it in the communication device. Execute this.

[0015] To solve the above problems, the program according to this embodiment causes the computer to function as a communication control device. [Effects of the Invention]

[0016] This disclosure makes it possible to improve the technology for forwarding priority traffic frames on a network. [Brief explanation of the drawing]

[0017] [Figure 1]It is a block diagram showing a configuration example of a communication system according to this embodiment. [Figure 2] It is a diagram showing a configuration example of a network connected in a grid pattern. [Figure 3] It is a flowchart showing an example of a communication control method executed by a communication control device according to this embodiment. [Figure 4] It is a flowchart showing an example of a communication control method executed by a communication control device according to this embodiment. [Figure 5] It is a diagram for explaining the update of the network path. [Figure 6] It is a diagram for explaining the occurrence of the confluence of priority traffic. [Figure 7] It is a diagram for explaining how to measure the total number of confluence nodes of priority traffic. [Figure 8] It is a diagram for explaining an example of measuring the total number of confluence nodes of priority traffic. [Figure 9] It is a table for explaining the priority of an alternative path based on the total number of confluence nodes. [Figure 10] It is a table showing a preliminary gate control list in order of priority of the updated network. [Figure 11] It is a block diagram showing a schematic configuration of a computer functioning as a communication control device. [Figure 12] It is a diagram for explaining the change of the network configuration.

Mode for Carrying Out the Invention

[0018] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings.

[0019] (Configuration of Communication System) Figure 1 is a block diagram showing an example configuration of a communication system according to this embodiment. Referring to Figure 1, an overview of the communication system 1 according to this disclosure will be described. The communication system 1 comprises a plurality of communication devices 10 and a communication control device 20. The plurality of communication devices 10 and the communication control device 20 are connected to a network 2, including, for example, the Internet and a mobile communication network. Figure 2 is a diagram showing an example configuration of a grid-like network. In this disclosure, for example, as shown in Figure 2, the plurality of communication devices 10 (10A, 10B, 10C, 10D, 10E, 10F, 10G, 10H, 10I, 10J) are connected in a grid-like network 2, but the network topology is not limited thereto. The communication devices 10 transmit and receive frames of priority traffic ST (ST#1, ST#2, ST#3, ST#4).

[0020] (Communication equipment configuration) The communication device 10 is a network node such as a switch or router. The communication device 10 comprises a communication unit 11, a storage unit 12, and a control unit 13. The communication device 10 performs communication using the Time Aware Shaper (TAS) technology in the Time-Sensitive Networking (TSN) standard. TAS is a technology that outputs frames over the network 2 according to a gate control list stored in the communication device 10 (configured in the communication device 10). Multiple communication devices 10 are connected to each other on the network 2 so that they can communicate with one another, and forward frames of priority traffic ST based on the control of the communication control device 20.

[0021] The communication unit 11 includes one or more communication interfaces connected to the network 2. These communication interfaces support, but are not limited to, communication standards such as Ethernet®, FDDI (Fiber Distributed Data Interface), and Wi-Fi®. In this embodiment, the communication unit 11 transmits and receives frames of priority traffic ST.

[0022] The storage unit 12 includes one or more memories. The memories are, for example, semiconductor memories, magnetic memories, or optical memories, but are not limited to these. Each memory included in the storage unit 12 may function as, for example, a main memory, an auxiliary memory, or a cache memory. The storage unit 12 stores any information used for the operation of the communication device 10. For example, the storage unit 12 may store system programs, application programs, embedded software, gate control lists, etc. The information stored in the storage unit 12 may be updateable with information obtained from the network 2 via, for example, the communication unit 11.

[0023] The control unit 13 includes one or more processors, one or more programmable circuits, one or more dedicated circuits, or a combination thereof. The processor is a general-purpose processor such as a CPU (Central Processing Unit) or GPU (Graphics Processing Unit), or a dedicated processor specialized for a specific process, but is not limited to these. The programmable circuit is an FPGA (Field-Programmable Gate Array), but is not limited to this. The dedicated circuit is an ASIC (Application Specific Integrated Circuit), but is not limited to this. The control unit 13 controls the operation of the entire communication device 10.

[0024] (Configuration of the communication control device) The communication control device 20 comprises a communication unit 21, a control unit 22, and a storage unit 23. The communication control device 20 causes the communication device 10 to transfer the frame of priority traffic ST.

[0025] The communication unit 21 includes one or more communication interfaces connected to the network 2. These communication interfaces support, for example, Ethernet®, FDDI (Fiber Distributed Data Interface), Wi-Fi®, etc., but are not limited to these, and may support any communication standard. In this embodiment, the communication control device 20 communicates with a plurality of communication devices 10 via the communication unit 21 and the network 2.

[0026] The control unit 22 includes one or more processors, one or more programmable circuits, one or more dedicated circuits, or a combination thereof. The control unit 22 controls the operation of the entire communication control device 20.

[0027] The storage unit 23 includes one or more memories. Each memory included in the storage unit 23 may function as, for example, a main memory, an auxiliary memory, or a cache memory. The storage unit 23 stores any information used for the operation of the communication control device 20. For example, the storage unit 23 may store system programs, application programs, databases, alternative gate control lists associated with alternative routes, etc. The information stored in the storage unit 23 may be updatable with information obtained from the network 2 via, for example, the communication unit 21.

[0028] (Operation flow of the communication control device) Figures 3 and 4 are flowcharts illustrating an example of a communication control method performed by the communication control device according to this embodiment. The operation of the communication control device 20 according to this embodiment will be described with reference to Figures 3 and 4.

[0029] Step S101: The control unit 22 sets a gate control list in the communication device 10 via the communication unit 21 and the network 2.

[0030] The control unit 13 of each communication device 10 stores the gate control list for the normal network configuration, which is obtained from the communication control device 20, in the storage unit 12.

[0031] Step S102: The control unit 22 causes the communication device 10 to forward the frame of priority traffic ST.

[0032] Each communication device 10 forwards frames of priority traffic ST on the network according to the stored gate control list. The communication device 10 performs communication using the Time-Aware Shaper (TAS) technology in the Time-Sensitive Networking (TSN) standard. TAS is a technology that outputs frames via the network 2 according to the gate control list stored by the communication device 10.

[0033] Step S103: The control unit 22 pre-lists the alternative routes available on the network.

[0034] The control unit 22 searches for available alternative routes within the network in advance and lists them while the network, to which the multiple communication devices 10 are connected in a communicable manner, is operating normally. In this disclosure, a list means a composite data type (container / collection) that can store multiple data in an ordered manner. A list in which each piece of data has reference information (link / pointer) indicating the location of the next piece of data is called a linked list, but a list in this disclosure may also be a linked list.

[0035] Step S104: The control unit 22 sets a priority for each of the listed alternative routes.

[0036] The control unit 22 wants to store a list of spare gate control paths corresponding to all available alternative paths in the storage unit 23. However, since the amount of memory resources that can store the spare gate control list is finite, setting an appropriate priority for the alternative paths to be stored becomes a challenge.

[0037] Therefore, the control unit 22 calculates the total number of combined flow nodes for each alternative route, which is the total number of nodes where frames from two or more priority traffics merge, and sets the priority of the alternative routes in descending order of combined flow node count.

[0038] Figure 5 illustrates the updating of network routes. As shown in Figure 5, when the network routes to which ST#1 and ST#2 are forwarded are updated, the merging of each priority traffic may occur or decrease at nodes other than nodes 1, 2, 3, and 4 where the route switching occurred. Therefore, looking only at nodes 1, 2, 3, and 4 involved in the route switching does not reveal the complexity of calculating the gate control list for the entire network.

[0039] Figure 6 illustrates the occurrence of mergers in priority traffic ST. As shown in Figure 6, using priority traffic ST#2 as an example, if we search for cases where mergers occur at nodes other than nodes 1, 2, 3, and 4 where route switching occurred, we can see that a merger between ST#1 and ST#2 occurs at node a, which is connected to node 1. Therefore, it is necessary to count the increase or decrease in the number of mergers not only for nodes 1, 2, 3, and 4 involved in route switching, but for all nodes in the updated network.

[0040] Therefore, in this disclosure, we have decided to compare the total number of merged nodes for each preferred traffic with the available alternative routes, and to set the priority of the alternative routes higher in the order of the total number of merged nodes.

[0041] Step S105: The control unit 22 calculates a list of spare gate controls corresponding to each of the alternative paths, in order of priority.

[0042] Figure 7 illustrates how to measure the total number of flow nodes for priority traffic. In Figure 7, in the pre-update network, other priority traffic merges with priority traffic ST#1 at nodes 3 and 4, resulting in a total of 2 flow nodes. On the other hand, in the post-update network, other priority traffic merges with priority traffic ST#1 at nodes 2, 3, and 5, resulting in a total of 3 flow nodes.

[0043] Figure 8 illustrates an example of measuring the total number of flow nodes for priority traffic. (i) is the network before the update, (ii) is network #1 after the update, and (iii) is network #2 after the update. Priority traffic ST#1, ST#2, ST#3, and ST#4 are forwarded to each network. Below, the total number of flow nodes in each network is calculated for each priority traffic.

[0044] In the pre-update NW (i), ST#1 merges with ST#2 at node 3. Also, ST#2 merges with ST#1 at node 3. Therefore, the number of mergers for ST#1 is 1, and the number of mergers for ST#2 is 1, resulting in a total number of flow nodes of 1 + 1 = 2.

[0045] In the updated NW#1 (ii), ST#1 merges with ST#3 at node 3, ST#2 at node 4, and ST#4 at node 6. ST#2 merges with ST#1 at node 4. ST#3 merges with ST#1 at node 3. ST#4 merges with ST#1 at node 6. Therefore, the total number of flow nodes is 3+1+1+1=6.

[0046] In the updated NW#2 (iii), ST#1 merges with ST#2 at node 8. Also, ST#2 merges with ST#1 at node 8. Therefore, the total number of flow nodes is 1 + 1 + 0 + 0 = 2.

[0047] Figure 9 is a table illustrating the priority of alternative routes based on the total number of flow nodes. In this disclosure, a list of alternative routes in the network is maintained in fields named "updated NW#1", "#2", ... and priority is assigned based on the calculated total number of flow nodes for each alternative route. In the example shown in Figure 9, updated NW#1 has 6 total flow nodes, while updated NW#2 has 2 total flow nodes. Therefore, updated NW#1 is assigned a priority of 1 and updated NW#2 is assigned a priority of 2. Priority is assigned in descending order of numerical value. Then, a list of spare gate control paths is calculated in descending order of priority, and the calculated list of spare gate control paths is stored.

[0048] Step S106: The memory unit 23 stores the alternative path and the reserve gate control list in association.

[0049] Figure 10 is a table showing the priority-ordered list of backup gate control paths for the updated network. The storage unit 23 stores the alternative paths and the backup gate control lists in the format shown in Figure 10. In Figure 10, the updated network configuration corresponds to the alternative paths.

[0050] Step S107: The control unit 22 determines whether the storage unit 23 has stored all the spare gate control lists.

[0051] Step S108: If the memory unit 23 cannot store all of the spare gate control lists, it stores a predetermined number of alternative paths corresponding to the network configuration in order of priority.

[0052] Step S109: The control unit 22 monitors for updates to the configuration of the network 2, which consists of multiple communication devices 10.

[0053] The control unit 22 monitors whether an update has occurred in the network configuration, for example, from (i) to (ii) or (iii) as shown in Figure 8.

[0054] Step S110: When the control unit 22 detects an update to the network 2 configuration, it searches for the updated route.

[0055] Step S111: The control unit 22 checks whether the storage unit 23 has stored an alternative route corresponding to the updated route.

[0056] Step S112: If the storage unit 23 does not store an alternative route corresponding to the updated route, the control unit 22 calculates a gate control list corresponding to the updated route.

[0057] Step S113: When the network configuration is updated, the control unit 22 retrieves a list of alternative gate control paths corresponding to the updated path from the storage unit 23 if the storage unit 23 has stored alternative paths corresponding to the updated path.

[0058] Step S114: The control unit 22 obtains the newly calculated gate control list or the spare gate control list stored in the storage unit 23 and sets it in the communication device 10.

[0059] The control unit 22 obtains a newly calculated gate control list or a spare gate control list stored in the storage unit 23 and sets it in each communication device 10. When the network configuration is updated, each communication device 10 needs to update its gate control list to meet the delay and jitter requirements on the new network. By updating the gate control list, each communication device 10 can perform priority traffic forwarding by TAS on the new network.

[0060] Step S115: The control unit 22 determines whether the transfer of priority traffic by the multiple communication devices 10 will continue.

[0061] The control unit 22 returns to step S102 if the transfer of priority traffic by the multiple communication devices 10 continues, and terminates processing when the transfer is completed.

[0062] Furthermore, whenever the network configuration is updated (an update is detected), the control unit 22 updates the list of alternative routes corresponding to the updated network configuration, updates the priority of each of the updated alternative routes, and calculates a list of spare gate control routes corresponding to each of the updated alternative routes in descending order of priority.

[0063] As described above, the communication control device 20 according to this embodiment lists the alternative routes available on the network, assigns a priority to each of the listed alternative routes, calculates a spare gate control list corresponding to each alternative route in descending order of priority, associates the alternative routes with the spare gate control lists, stores a predetermined number of them in the storage unit 23 in descending order of priority, and when the network configuration is updated, retrieves the spare gate control list corresponding to the updated route from the storage unit 23 and sets it in the communication device 10.

[0064] This invention achieves memory resource savings by pre-calculating the number of merged priority traffic for alternative routes, assuming network failures, and preferentially storing a reserve gate control list for nodes with a large number of merged traffic.

[0065] With this configuration, when a network path is updated, instead of a reactive process that recalculates the gate control list after the update, a proactive process is possible in which a list of alternative gate control lists for available paths on the network is stored in advance. This allows the communication device 10 to quickly set the alternative gate control list corresponding to the updated path. This improves the technology for forwarding frames of priority traffic on the network by reducing the likelihood that the calculation of the gate control list will take time and delay the recovery of low-latency services.

[0066] Although the embodiments described above are representative examples, it will be apparent to those skilled in the art that many modifications and substitutions are possible within the spirit and scope of the present invention. Therefore, the present invention should not be interpreted as being limited by the embodiments described above, and various modifications or changes are possible without departing from the scope of the claims. For example, it is possible to combine multiple component blocks shown in the configuration diagram of the embodiments into one, or to divide one component block.

[0067] In this disclosure, the number of total flow nodes, which is the sum of the number of merging nodes for each preferred traffic, is compared with the number of total flow nodes for each available alternative route, and the priority of the alternative routes is set higher in order of the number of total flow nodes. However, the indicator for setting priority is not limited to the number of total flow nodes, and other centrality indicators such as degree centrality, adjacent centrality, eigenvector centrality, and betweenness centrality may also be used. Centrality is an indicator used to show the importance of each node in a network.

[0068] Degree centrality is an index that uses the degree of each node (the number of edges connected to that node) as an indicator. According to degree centrality, nodes that are adjacent to more nodes are considered more important. Proximity centrality is an index that uses the reciprocal of the average distance (shortest path length) from a given node to all other nodes as an indicator. According to proximity centrality, nodes that have a small sum of distances to other nodes are considered more important. Eigenvector centrality is an index that reflects the centrality of other nodes associated with a given node in the centrality of that node. According to eigenvector centrality, the centrality of each node is proportional to the sum of the centrality of the nodes adjacent to that node. Betweenness centrality is an index that uses the proportion of times a given node is included in the shortest path between any two other nodes. According to betweenness centrality, nodes that have many shortest paths passing through them are considered more important.

[0069] To enable the above-mentioned communication control device 20 to function, it is also possible to use a computer capable of executing program instructions. Figure 11 is a block diagram showing the schematic configuration of a computer 100 that functions as a communication control device 20. Here, the computer 100 that functions as a communication control device 20 may be a general-purpose computer, a dedicated computer, a workstation, a PC (Personal Computer), an electronic notepad, etc. Program instructions may be program code, code segments, etc., for executing the required tasks.

[0070] As shown in Figure 11, the computer 100 comprises a processor 110, a memory unit consisting of a ROM (Read Only Memory) 120, a RAM (Random Access Memory) 130, and a storage unit 140, an input unit 150, an output unit 160, and a communication interface (I / F) 170. Each component is connected to the others via a data bus 180 so as to be able to communicate with each other.

[0071] ROM 120 stores various programs and data. RAM 130 temporarily stores programs or data as a working area. Storage 140 consists of an HDD (Hard Disk Drive) or SSD (Solid State Drive) and stores various programs and data, including the operating system. In this disclosure, the program related to this disclosure is stored in either ROM 120 or storage 140.

[0072] The processor 110 is specifically a CPU (Central Processing Unit), MPU (Micro Processing Unit), GPU (Graphics Processing Unit), DSP (Digital Signal Processor), SoC (System on a Chip), etc., and may be composed of multiple processors of the same or different types. The processor 110 reads a program from the ROM 120 or storage 140 and executes the program using the RAM 130 as a working area, thereby controlling each of the above configurations and performing various calculations. At least a part of these processes may be implemented in hardware.

[0073] The program may be recorded on a recording medium readable by the communication control device 20. Using such a recording medium, it is possible to install the program on the communication control device 20. The recording medium on which the program is recorded may be a non-transitory recording medium. While not particularly limited, non-transitory recording media may include, for example, CD-ROMs, DVD-ROMs, or USB (Universal Serial Bus) memory. Furthermore, the program may be downloaded from an external device via a network.

[0074] The following additional information is disclosed regarding the embodiments described above.

[0075] (Additional note 1) A communication control device that causes a communication device to transfer frames of priority traffic, A control unit that pre-lists available alternative routes on the network, assigns a priority to each of the listed alternative routes, and calculates a list of spare gate control routes corresponding to each of the alternative routes in order of priority, The system includes a storage unit that associates the alternative routes with the reserve gate control list and stores a predetermined number of them in order of increasing priority, When the network configuration is updated, the control unit retrieves a backup gate control list corresponding to the updated route from the storage unit and sets it in the communication device. (Additional note 2) The control unit calculates the total number of nodes where frames of two or more priority traffics merge for each of the alternative paths, and sets the priority of the alternative paths to be higher in descending order of the total number of nodes, as described in Appendix 1. (Additional note 3) The communication control device according to Appendix 1 or 2, wherein, each time the network configuration is updated, the control unit updates the list of alternative routes corresponding to the updated network configuration, updates the priority of each of the updated alternative routes, and calculates a list of spare gate control corresponding to each of the updated alternative routes in descending order of priority. (Additional note 4) A communication system comprising a communication control device described in any one of the appendices 1 to 3, and a plurality of communication devices that are interconnected on a network so as to be able to communicate with each other and that transfer priority traffic frames based on the control of the communication control device. (Additional note 5) A communication control method that causes a communication device to transfer frames of priority traffic, By the communication control device, A communication control method that pre-lists alternative routes available on the network, assigns a priority to each of the listed alternative routes, calculates a spare gate control list corresponding to each of the alternative routes in descending order of priority, associates the alternative routes with the spare gate control lists and stores a predetermined number of them in descending order of priority, and when the network configuration is updated, retrieves the stored spare gate control list corresponding to the updated route and sets it in the communication device. (Additional note 6) A non-temporary storage medium storing a program executable by a computer, the non-temporary storage medium storing a program that causes the computer to function as a communication control device as described in any one of the appendices 1 to 3. [Explanation of Symbols]

[0076] 1. Communication System 2 Network 10,10A~10J Communication device 11 Communications Department 12 Storage section 13 Control Unit 20 Communication control device 21 Communications Department 22 Control Unit 23 Memory section

Claims

1. A communication control device that causes a communication device to transfer frames of priority traffic, A control unit that pre-lists available alternative routes on the network, assigns a priority to each of the listed alternative routes, and calculates a list of spare gate control routes corresponding to each of the alternative routes in order of priority, The system includes a storage unit that associates the alternative routes with the reserve gate control list and stores a predetermined number of them in order of increasing priority, The control unit is a communication control device that, when the network configuration is updated, obtains a spare gate control list corresponding to the updated route from the storage unit and sets it in the communication device.

2. The control unit calculates the total number of nodes where frames of two or more priority traffics merge for each of the alternative routes, and sets the priority of the alternative routes to be higher in descending order of the total number of nodes, according to claim 1.

3. The communication control device according to claim 1 or 2, wherein the control unit updates a list of alternative routes corresponding to the updated network configuration, updates the priority of each of the updated alternative routes, and calculates a list of spare gate control routes corresponding to each of the updated alternative routes in descending order of priority each time the network configuration is updated.

4. A communication control device according to claim 1 or 2, Multiple communication devices are connected to each other on a network so as to be able to communicate with one another, and forward frames of priority traffic based on the control of the communication control device, A communication system equipped with these features.

5. A communication control method that causes a communication device to transfer frames of priority traffic, By the communication control device, The steps include: pre-listing available alternative routes on the network, The steps include setting a priority for each of the listed alternative routes, The steps include calculating a list of auxiliary gate controls corresponding to each of the alternative routes in order of increasing priority, The steps include associating the alternative route with the reserve gate control list and storing a predetermined number of them in order of increasing priority, When the network configuration is updated, the communication device obtains a stored list of spare gate control corresponding to the updated route and sets it in the communication device. A communication control method that performs this action.

6. A program for causing a computer to function as a communication control device according to claim 1 or 2.

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