Communication system

Abstract

This control device (20) sets a shared time slot for passing, as a flow of data communication performed along a path that passes through a port of at least one transfer device among a plurality of transfer devices, both a flow of a limited class including a first class and a flow of a second class different from the first class, to the port through which the path passes. The at least one transfer device, by monitoring the data communication, when detecting the start of the flow of a first class of the data communication, switches the shared time slot to a dedicated time slot for passing only the flow of the limited class, and, by monitoring the data communication, when detecting the end of the flow of the first class of the data communication, returns the dedicated time slot to the shared time slot.

Description

communication systems

[0001] The present disclosure relates to communication systems.

[0002] Non-Patent Document 1 defines TAS. "TAS" is an abbreviation for time aware shaper. Non-Patent Document 2 discloses a technology that applies TAS to allocate time slots according to VLAN ID and priority. "VLAN" is an abbreviation for virtual local area network.

[0003] IEEE Computer Society, IEEE Std 802.1Qbv-2015, IEEE Standard for Local and metropolitan area networks -- Bridges and Bridged Networks - Amendment 25: Enhancements for Scheduled Traffic, 2016-03-18Yuhei Kawakami, et al., “Applying Time-aware Shaper Considering User Identifier to Service Provider Network”, IEEE 19th Annual Consumer Communications & Networking Conference, 2022

[0004] By constructing a network with multiple nodes with TAS functionality, it is possible to achieve deterministic communication with little delay and jitter. In this case, it is necessary to assign time slots dedicated to deterministic communication to the output ports of all nodes that are passed through end-to-end.

[0005] The mechanism of TAS is shown in Figure 6. TAS performs priority control by determining the traffic to be transmitted according to a time-shared schedule. Specifically, TAS stores frames in FIFO queues for each VLAN-CoS or IP-ToS, and allows transmission from queues with open gates according to the GCL. "CoS" is an abbreviation for class of service. "IP" is an abbreviation for Internet Protocol. "ToS" is an abbreviation for type of service. "FIFO" is an abbreviation for first in, first out. "GCL" is an abbreviation for gate control list.

[0006] An example of a GCL is shown in Figure 7. TAS can control the overlapping of best-effort traffic and delay-guaranteed communication. In the example shown in Figure 7, four ST flows and one NST flow are multiplexed. "ST" is an abbreviation for scheduled traffic. "NST" is an abbreviation for non-scheduled traffic. ST flows correspond to delay-guaranteed communication. NST flows correspond to non-guaranteed communication, i.e., best-effort traffic. The GCL shown in Figure 7 specifies that STs with CoS "7" are permitted in timeslots 1 and 3, STs with CoS "5" in timeslot 2, STs with CoS "4" in timeslot 4, and NSTs with CoS "3" or less in timeslot 5. This GCL further specifies that the duration for which communication is permitted in each of timeslots 1 through 4 is 15 microseconds, and the duration for which communication is permitted in timeslot 5 is 100 microseconds.

[0007] To avoid collisions end-to-end, all nodes in the network must be time-synchronized and the timing of opening and closing the GCL gates at each node must be coordinated. The GCL is either centrally managed by a controller called a CNC, or managed individually at each node. "CNC" stands for centralized network configuration. Each node opens its gate taking propagation delays into account, preventing collisions with other communications and enabling communication without queuing delays. The transmitting terminal is also time-synchronized and periodically transmits frames in accordance with the GCL timing, enabling communication without queuing delays.

[0008] As described above, by having a frame for deterministic communication occupy a time slot that matches the time at which it passes through a node, transmission waits due to collisions with other frames are eliminated, and deterministic communication with little delay or jitter can be realized. However, time slots for deterministic communication are consumed even when no frames for deterministic communication are flowing.

[0009] The present disclosure has been made in view of the above circumstances, and aims to make effective use of a band for deterministic periodic communication when it is not in use.

[0010] A communication system according to one embodiment comprises a plurality of transfer devices; and a control device that sets a plurality of time slots for each port of the plurality of transfer devices, wherein the control device sets a shared time slot for a port along a route that passes through a port of at least one of the plurality of transfer devices, the shared time slot allowing both a flow of a limited class including a first class and a flow of a second class different from the first class to pass as a flow of data communication that is performed along the route; wherein the at least one transfer device monitors the data communication, and upon detecting the start of a flow of the first class of the data communication, switches the shared time slot to a dedicated time slot that allows only flows of the limited class to pass; and upon detecting the end of the flow of the first class of the data communication by monitoring the data communication, switches the dedicated time slot back to the shared time slot.

[0011] According to the present disclosure, it is possible to effectively utilize a band for deterministic periodic communication when it is not in use.

[0012] 2B is a block diagram showing the configuration of a communication system according to an embodiment; FIG. 2C is a diagram showing a frame flow according to an embodiment; FIG. 2D is a table showing time slot allocation corresponding to the embodiment shown in FIG. 2A; FIG. 2E is a block diagram showing the configuration of a control device provided in a communication system; FIG. 2F is a diagram showing time slot allocation according to a comparative example; FIG. 2G is a diagram showing time slot allocation according to an embodiment; FIG. 2H is a flowchart showing the operation of a communication system; FIG. 2I is a diagram showing the mechanism of TAS; and FIG. 2J is a table showing an example of GCL.

[0013] An embodiment will be described below with reference to the drawings.

[0014] In each drawing, the same or corresponding parts are denoted by the same reference numerals. In the description of this embodiment, the description of the same or corresponding parts will be omitted or simplified as appropriate.

[0015] The configuration of a communication system 10 according to this embodiment will be described with reference to FIG.

[0016] The communication system 10 includes a control device 20 and a plurality of transfer devices such as transfer devices 31, 32, and 33. The control device 20 and each transfer device are connected by a monitoring and control network and can communicate with each other via the monitoring and control network. The plurality of transfer devices form a communication network and can transfer frames between any user terminals, such as between fixed period communication terminals 41 and 42, between high priority communication terminals 51 and 52, or between low priority communication terminals 61 and 62, via the communication network.

[0017] The control device 20 is a computer that monitors and controls each forwarding device. Each forwarding device accommodates users and forwards frames to a port designated for each destination user terminal. The number of forwarding devices is three in this embodiment, but it may be two, or four or more. Each user terminal is, for example, a mobile terminal such as a smartphone or tablet, a general-purpose terminal such as a PC, or a dedicated terminal for a specific purpose. "PC" is an abbreviation for personal computer. Each user terminal can be either the start point or the end point of a flow.

[0018] In this embodiment, the transfer device 31 is connected to the defined period communication terminal 41. The transfer device 31 is connected to the high priority communication terminal 51. The transfer device 31 is connected to the low priority communication terminal 61. The transfer device 33 is connected to the defined period communication terminal 42. The transfer device 33 is connected to the high priority communication terminal 52. The transfer device 33 is connected to the low priority communication terminal 62. The transfer device 31 is connected to the transfer device 33. The transfer device 32 is connected to the transfer device 33. Therefore, a communication frame sent from the defined period communication terminal 41 addressed to the defined period communication terminal 42 passes through the transfer device 31, the transfer device 32, and the transfer device 33 in this order before reaching the defined period communication terminal 42. A communication frame sent from the defined period communication terminal 42 addressed to the defined period communication terminal 41 passes through the transfer device 33, the transfer device 32, and the transfer device 31 in this order before reaching the defined period communication terminal 41. The path of communication frames between the high priority communication terminals 51 and 52 and the path of communication frames between the low priority communication terminals 61 and 62 are similar to the path of communication frames between the fixed period communication terminals 41 and 42, so description thereof will be omitted.

[0019] An outline of this embodiment will be described with reference to FIG.

[0020] In a communication system 10 in which frames for deterministic period communication, frames for high priority communication, and frames for low priority communication are mixed, a start trigger is detected when the circulation of frames for deterministic period communication begins, and an end trigger is detected when frames for deterministic period communication have not been circulated for a predetermined period. During the period from the start trigger to the end trigger, a predetermined time slot for deterministic period communication is allocated exclusively for that deterministic period communication, and during the rest of the period, that time slot is also allocated to high priority communication. Therefore, according to this embodiment, it is possible to effectively utilize unused bandwidth for deterministic period communication without requiring user operation.

[0021] In this embodiment, the control device 20 calculates time slots for definite period communication and sets them to each of the transfer devices 31, 32, and 33 on the route between the definite period communication terminals 41 and 42. The control device 20 also sets time slots for high-priority communication and low-priority communication. The time slots for definite period communication are set so that they can also be used for high-priority communication. In other words, the time slots for definite period communication can also be used for communication between the high-priority communication terminals 51 and 52. However, it is also possible to set them so that they are not shared with high-priority communication.

[0022] Each transfer device monitors the circulation of frames for deterministic periodic communication. When each transfer device detects the circulation of frames for deterministic periodic communication, it switches the time slot for that deterministic periodic communication to an exclusive one. The high priority communication terminals 51 and 52 are no longer able to use the time slot for that deterministic periodic communication, and the deterministic periodic communication terminals 41 and 42 communicate using the exclusive time slot. If there is no circulation of frames for deterministic periodic communication during the protection time, each transfer device switches the time slot for that deterministic periodic communication to a shared one. With this switch, the high priority communication terminals 51 and 52 also return to a state where they can communicate using the time slot for deterministic periodic communication.

[0023] The high-priority communication terminals 51 and 52 communicate using time slots allocated for high-priority communication in addition to time slots for fixed-period communication. The low-priority communication terminals 61 and 62 also communicate using time slots allocated for low-priority communication.

[0024] The flow of frames within each transfer device will be described with reference to Figures 2A and 2B. Figure 2A shows the flow of frames according to one example of this embodiment. Figure 2B shows the allocation of time slots corresponding to the example shown in Figure 2A. In Figure 2B, the rows correspond to deterministic periodic communication "DG", high priority communication "HP", and low priority communication "LP", respectively, and the columns correspond to time slot numbers. "C" is an abbreviation for closed. "O" is an abbreviation for open.

[0025] Each time slot can be set to any interval, but in this embodiment, the first, third, fifth, and seventh time slots are set to be shared by both fixed-period communication and high-priority communication, and the second, fourth, sixth, and eighth time slots are set to be shared by both high-priority communication and low-priority communication.

[0026] A frame for deterministic periodic communication is transmitted in the first time slot. Therefore, the flow of frames for deterministic periodic communication is detected at the timing of the first time slot, and the third, fifth, and seventh time slots, which are time slots for subsequent deterministic periodic communication, are no longer shared with high priority communication. In other words, the third, fifth, and seventh time slots are switched over to be exclusively used for deterministic periodic communication. If a frame for deterministic periodic communication and a frame for high priority communication flow in simultaneously at the timing of the first time slot, the frame for high priority communication will wait to be transmitted.

[0027] In the second time slot, a frame for high priority communication is transmitted.

[0028] In the third time slot, a frame for deterministic communication is transmitted. That is, at the timing of the third time slot, a frame for deterministic communication is transferred using an occupied time slot.

[0029] In the fourth time slot, a frame for low priority communication is transmitted.

[0030] No frame is transmitted in the fifth time slot. That is, at the timing of the fifth time slot, no frames for deterministic communication are circulating, and the reserved time slot is not in use. Then, since no frame flow for deterministic communication is detected even after the protection time has elapsed, the setting for the seventh time slot, which is the time slot for the subsequent deterministic communication, is returned to being shared with high-priority communication. That is, the seventh time slot is switched to being shared by both deterministic communication and high-priority communication. The protection time may be of any length, but in this example it is set to be less than the length of the sixth time slot.

[0031] In the sixth time slot, a frame for high priority communication is transmitted.

[0032] In the seventh time slot, a frame for high priority communication is sent out. That is, at the timing of the seventh time slot, a frame for high priority communication is transferred using a shared time slot.

[0033] In the eighth time slot, a frame for high priority communication is transmitted.

[0034] According to this example, it is possible to switch between exclusive and shared time slots for deterministic periodic communication without the user having to notify an operator or a system separate from the transfer device of the start and end of use of deterministic periodic communication. In other words, the effort of notifying the start and end of use of deterministic periodic communication is eliminated, and the transfer device autonomously controls the allocation of time slots, while effectively utilizing time slots for transferring high-priority communication frames during periods when deterministic periodic communication frames are not flowing. By allocating high-priority time slots rather than low-priority time slots, it is possible to transfer the start frame that detects the start of distribution of deterministic periodic communication without loss and with little delay.

[0035] In this example, a time slot for deterministic communication is shared with a high-priority communication, but it is also possible to share a time slot for deterministic communication with a low-priority communication. However, in order to reduce the possibility of loss or delay, it is desirable to share a time slot for deterministic communication with a high-priority communication.

[0036] The configuration of the control device 20 according to this embodiment will be described with reference to FIG.

[0037] The control device 20 includes a control unit 21 , a storage unit 22 , and a communication unit 23 .

[0038] The control unit 21 includes at least one processor, at least one programmable circuit, at least one dedicated circuit, or any combination thereof. The processor is a general-purpose processor such as a CPU or GPU, or a dedicated processor specialized for specific processing. "CPU" is an abbreviation for central processing unit. "GPU" is an abbreviation for graphics processing unit. An example of the programmable circuit is an FPGA. "FPGA" is an abbreviation for field-programmable gate array. An example of the dedicated circuit is an ASIC. "ASIC" is an abbreviation for application specific integrated circuit. The control unit 21 controls each part of the control unit 20 and executes processing related to the operation of the control unit 20.

[0039] The storage unit 22 includes at least one semiconductor memory, at least one magnetic memory, at least one optical memory, or any combination thereof. The semiconductor memory is, for example, a RAM, a ROM, or a flash memory. "RAM" is an abbreviation for random access memory. "ROM" is an abbreviation for read only memory. RAM is, for example, an SRAM or a DRAM. "SRAM" is an abbreviation for static random access memory. "DRAM" is an abbreviation for dynamic random access memory. ROM is, for example, an EEPROM. "EEPROM" is an abbreviation for electrically erasable programmable read only memory. Flash memory is, for example, an SSD. "SSD" is an abbreviation for solid-state drive. Magnetic memory is, for example, an HDD. "HDD" is an abbreviation for hard disk drive. The storage unit 22 functions, for example, as a main storage device, an auxiliary storage device, or a cache memory. The storage unit 22 stores information used in the operation of the control device 20 and information obtained by the operation of the control device 20 .

[0040] The communication unit 23 includes at least one communication module. The communication module is, for example, a module that complies with a LAN communication standard such as Ethernet (registered trademark). The communication unit 23 communicates with each transfer device. The communication unit 23 receives information used in the operation of the control device 20 and transmits information obtained by the operation of the control device 20.

[0041] The functions of the control device 20 are realized by executing a program according to this embodiment on a processor serving as the control unit 21. That is, the functions of the control device 20 are realized by software. The program causes a computer to execute the operations of the control device 20, thereby causing the computer to function as the control device 20. That is, the computer functions as the control device 20 by executing the operations of the control device 20 in accordance with the program.

[0042] The program can be stored on a non-transitory computer-readable medium. Examples of the non-transitory computer-readable medium include flash memory, magnetic recording devices, optical disks, magneto-optical recording media, and ROMs. The program can be distributed by selling, transferring, or lending portable media such as SD cards, DVDs, or CD-ROMs that store the program. "SD" is an abbreviation for Secure Digital. "DVD" is an abbreviation for digital versatile disc. "CD-ROM" is an abbreviation for compact disc read only memory. The program can also be distributed by storing it in the storage of a server and transferring it from the server to another computer. The program can also be provided as a program product.

[0043] A computer temporarily stores a program stored on a portable medium or transferred from a server in its main storage device. The computer then reads the program stored in the main storage device with its processor and executes processing in accordance with the read program. The computer may also read the program directly from the portable medium and execute processing in accordance with the program. The computer may also execute processing in accordance with the received program each time a program is transferred from the server to the computer. Processing may also be executed using a so-called ASP-type service that realizes functions simply by issuing execution instructions and obtaining results, without transferring the program from the server to the computer. "ASP" is an abbreviation for application service provider. A program is information used for processing by a computer and includes something equivalent to a program. For example, data that is not a direct instruction to a computer but has properties that define computer processing falls under the category of "something equivalent to a program."

[0044] Some or all of the functions of the control device 20 may be implemented by a programmable circuit or a dedicated circuit as the control unit 21. In other words, some or all of the functions of the control device 20 may be implemented by hardware.

[0045] In this embodiment, the control unit 21 has a time slot calculation function 24 and a time slot setting function 25. The time slot calculation function 24 is a function that calculates in advance the time slots to be allocated to definite-period communication. The time slot setting function 25 is a function that allocates time slots to definite-period communication, high-priority communication, and low-priority communication, and allocates the time slots allocated to definite-period communication so that they can also be used for high-priority communication.

[0046] The storage unit 22 stores information about the time slots assigned by the time slot setting function 25 as time slot information 11 .

[0047] The communication unit 23 transmits information about the time slots assigned by the time slot setting function 25 as setting information 12 to each transfer device.

[0048] Each transfer device holds both a table that sets the allocation of time slots for transferring frames for deterministic periodic communication, and a table that sets the allocation of time slots that are shared by deterministic periodic communication and high priority communication. Upon receiving the setting information 12, each transfer device generates or updates a table in accordance with the received setting information 12.

[0049] 4A and 4B, the allocation of time slots in the table held by the transfer device 31 will be described. Fig. 4A shows the allocation of time slots according to a comparative example. Fig. 4B shows the allocation of time slots according to an example of this embodiment.

[0050] In both examples, the transfer device 31 includes an input port 34, a frame distribution unit 35, and an output port 36. Assume that definite-period communications D1, D2, and D3 are performed between definite-period communication terminals 41 and 42, high-priority communications D4 is performed between high-priority communication terminals 51 and 52, and low-priority communications BE, such as best-effort communications, is performed between low-priority communication terminals 61 and 62. While the definite-period communications D1, D2, and D3 may be identified based on priority alone, they are identified here based on VLAN ID and priority, similar to the technology disclosed in Non-Patent Document 2. That is, the definite-period communications D1, D2, and D3 are communications for each user. On the other hand, the high-priority communications D4 and the low-priority communications BE are communications between multiple users.

[0051] In the comparative example shown in FIG. 4A , the control unit 21 of the control device 20, upon operator trigger, calculates a time slot that is a combination of a period and a bandwidth that matches the time at which frames of the deterministic period communications D1, D2, and D3 pass through the transfer device 31. As the number of transfer devices on the communication path or the number of flows of deterministic period communications with different periods or bandwidths increases, calculating the time slot to be exclusively used takes time. Therefore, the control unit 21 of the control device 20 calculates the time slot to be assigned in advance and sets it in the transfer device 31. In the table 70 held by the transfer device 31, the time slots calculated according to the flows of deterministic period communications D1, D2, and D3 are set as those for the deterministic period communications D1, D2, and D3, and the other time slots are set as those shared by the high-priority communication D4 and the low-priority communication BE. Specifically, the first, fifth, ninth, and so on are set as those for the deterministic period communication D1. The second, seventh, and so on are set as those for the deterministic period communication D2. The sixth, ..., time slots are set for fixed-period communication D3. The third, fourth, eighth, ..., time slots are set for shared use by high-priority communication D4 and low-priority communication BE. The transfer device 31 references the identification information of each frame received from the input port 34, and allocates each frame to an assigned time slot according to the table 70 in the frame allocation unit 35, and sends out the frames carried by each time slot from the output port 36.

[0052] In this example, frames for deterministic periodic communication exclusively use time slots that match the times at which they pass through the transfer device 31, eliminating transmission waits due to collisions with other frames and enabling deterministic periodic communication with little delay and jitter. However, time slots for deterministic periodic communication are consumed even when frames for deterministic periodic communication are not flowing.

[0053] In the embodiment shown in FIG. 4B , similar to the comparative example, the control unit 21 of the control device 20 calculates the time slots to be assigned in advance and sets them in the transfer device 31. However, the time slots calculated to match the flows of definite-period communications D1, D2, and D3 are not dedicated to the definite-period communications D1, D2, and D3, but are set as shared with the high-priority communication D4. The time slots calculated to match the flows of definite-period communications D1, D2, and D3 are also set in the first table 71 held by the transfer device 31. The other time slots are set as shared between the high-priority communication D4 and the low-priority communication BE, similar to the table 70 of the comparative example. Specifically, the first, fifth, ninth, and so on are set as shared between the definite-period communication D1 and the high-priority communication D4. The second, seventh, and so on are set as shared between the definite-period communication D2 and the high-priority communication D4. The sixth, and so on, are set as shared between the definite-period communication D3 and the high-priority communication D4. The third, fourth, eighth, and so on time slots are set as those shared by the high-priority communication D4 and the low-priority communication BE. In the second table 72 that the transfer device 31 holds separately from the first table 71, the time slots calculated in accordance with the flows of the definite-period communications D1, D2, and D3 are set as those exclusive to the definite-period communications D1, D2, and D3, as in the table 70 of the comparative example.

[0054] In this example, the control unit 21 of the control device 20 calculates in advance the cycle, bandwidth, and protection time required for deterministic cycle communication, designs a time slot allocation table, and sets it in the transfer device 31. The control unit 21 of the control device 20 sets the bandwidth through which the first frame of deterministic cycle communication flows as a high-priority bandwidth and then opens the path. Unlike the comparative example, the transfer device 31 further includes a communication monitoring unit 37 and a table switching control unit 38. The communication monitoring unit 37 of the transfer device 31 monitors the distribution of deterministic cycle communication flows. When the communication monitoring unit 37 detects the start of distribution of deterministic cycle communication frames, the table switching control unit 38 of the transfer device 31 switches the time slot for deterministic cycle communication to an exclusive one. If the monitored deterministic cycle communication flow does not flow during the protection time, the communication monitoring unit 37 of the transfer device 31 determines that the distribution of the deterministic cycle communication frames has ended, i.e., detects the end of distribution. When the communication monitoring unit 37 detects the end of frame distribution for definite-period communication, the table switching control unit 38 of the transfer device 31 switches the time slots that were switched to exclusive use to shared use with high-priority communication. For example, when the communication monitoring unit 37 detects the start of definite-period communication D1, the table switching control unit 38 of the transfer device 31 switches a part of the first table 71 to the second table 72, thereby switching the time slots shared by the definite-period communication D1 and the high-priority communication D4 to dedicated time slots for the definite-period communication D1. When the communication monitoring unit 37 detects the end of the definite-period communication D1, the table switching control unit 38 of the transfer device 31 restores the part of the first table 71 that was switched to the second table 72, thereby returning the dedicated time slots for the definite-period communication D1 to shared time slots for the definite-period communication D1 and the high-priority communication D4.

[0055] According to this example, when switching between dedicated and shared time slots, recalculation of the time slot is not required, enabling switching in a short time without affecting frame forwarding. While realizing low-latency and low-jitter deterministic period communication as in the comparative example, it is possible to utilize communication resources for high-priority communication during periods when deterministic period communication frames are not flowing. Furthermore, by monitoring deterministic period communication, it is possible to switch between shared and exclusive time slots without the user having to notify the start and end of use. In other words, no procedures are required before or after using deterministic period communication. Furthermore, by pre-setting the bandwidth through which the first frame of deterministic period communication flows as a high-priority bandwidth, it is also possible to transfer the detected frame with little delay when the first frame of deterministic period communication is detected.

[0056] The communication monitoring unit 37 and table switching control unit 38 of the transfer device 31, like the control unit 21 of the control device 20, include at least one processor, at least one programmable circuit, at least one dedicated circuit, or any combination of these. The communication monitoring unit 37 and table switching control unit 38 of the transfer device 31 may be integrated and implemented as a single processor, a single programmable circuit, or a single dedicated circuit. The functions of the communication monitoring unit 37 and table switching control unit 38 of the transfer device 31 may be realized by software, by hardware, or a combination of software and hardware.

[0057] The allocation of time slots in the tables held by the transfer devices 32 and 33 is similar to the allocation of time slots in the table held by the transfer device 31, and therefore a description thereof will be omitted.

[0058] The operation of the communication system 10 according to this embodiment will be described with reference to Fig. 5. The operation described below corresponds to the time slot switching method according to this embodiment. That is, the time slot switching method according to this embodiment includes at least steps S1 to S4 shown in Fig. 5.

[0059] Prior to S1, the control unit 21 of the control device 20 sets multiple time slots for each port of the multiple forwarding devices. Specifically, the control unit 21 of the control device 20 sets, via the communication unit 23, a common time slot for a port along a path passing through a port of at least one of the multiple forwarding devices, a flow of a limited class including the first class and a flow of a second class different from the first class, as a data communication flow performed along the path passing through the port of at least one of the multiple forwarding devices. The "limited class" may include only the first class, or may further include classes other than the first class, but does not include the second class. For example, when CoS "7" is the first class and CoS "3" is the second class, CoS "6," CoS "5," CoS "4," or any combination thereof may be included in the "limited class" as a class other than the first class. In this embodiment, the control unit 21 of the control device 20 sets, as a common time slot, a time slot for passing only a flow of the limited class and a flow of the second class. The control unit 21 of the control device 20 further sets, via the communication unit 23, time slots for passing one or more other class flows different from both the limited class and the second class as data communication flows to ports along the route. The "one or more other classes" may be any class, or may be limited to a few classes, such as CoS "2" or lower. In this embodiment, the control unit 21 of the control device 20 sets, as shared time slots, time slots for passing only limited class flows between a specific combination of terminals and second class flows between any combination of terminals. When the ST flow with CoS "7" between the fixed-period communication terminals 41 and 42 is the flow of fixed-period communication D1, and the NST flow with CoS "3" between any terminals is the flow of high-priority communication D4, in the example shown in FIG. 4B , the control unit 21 of the control device 20 sets the first, fifth, ninth, ... time slots to the output port 36 of the transfer device 31 as shared time slots for the fixed-period communication D1 and the high-priority communication D4. When the transfer device 31 is set as "at least one transfer device," the communication monitoring unit 37 of the transfer device 31 starts monitoring data communication when the time slot setting is completed.

[0060] When the communication monitoring unit 37 of the transfer device 31 detects the start of a first-class data communication flow by monitoring data communication in S1, the table switching control unit 38 of the transfer device 31 switches the shared time slot to a dedicated time slot that allows only flows of a limited class to pass in S2. In this embodiment, the transfer device 31 holds both a first table 71 containing settings for shared time slots and a second table 72 containing settings for dedicated time slots, as tables containing settings for multiple time slots. Therefore, the table switching control unit 38 of the transfer device 31 switches between the first table 71 and the second table 72 to switch between the shared time slot and the dedicated time slot. In the example shown in FIG. 4B , when the communication monitoring unit 37 of the transfer device 31 detects the start of a flow of determinate period communication D1, the table switching control unit 38 of the transfer device 31 switches a part of the first table 71 to the second table 72, thereby switching the shared time slot for the determinate period communication D1 and the high-priority communication D4 to a dedicated time slot for the determinate period communication D1.

[0061] When the communication monitoring unit 37 of the transfer device 31 detects the end of the first-class data communication flow by monitoring the data communication in S3, the table switching control unit 38 of the transfer device 31 returns the dedicated time slot to a shared time slot in S4. In this embodiment, after the table switching control unit 38 of the transfer device 31 switches the shared time slot to a dedicated time slot, the communication monitoring unit 37 of the transfer device 31 detects the end of the first-class data communication flow when the first-class data communication flow is not resumed even after the protection time has elapsed since the first-class data communication flow was interrupted. In the example shown in FIG. 4B , when the communication monitoring unit 37 of the transfer device 31 detects the end of the deterministic period communication D1 flow, the table switching control unit 38 of the transfer device 31 restores the portion of the first table 71 that was switched to the second table 72, thereby returning the dedicated time slot for the deterministic period communication D1 to a shared time slot for the deterministic period communication D1 and the high-priority communication D4.

[0062] Steps S1 to S4 are repeatedly executed. Similar steps are also executed in the transfer devices 32 and 33. According to this embodiment, by executing steps S1 to S4, it is possible to effectively utilize the band for deterministic periodic communication when it is not in use.

[0063] The following additional notes are provided regarding the above-described embodiments.

[0064] (Supplementary Item 1) A communication system comprising: a plurality of transfer devices; and a control device that sets a plurality of time slots for each port of the plurality of transfer devices, wherein the control device sets a shared time slot, which allows both a flow of a limited class including a first class and a flow of a second class different from the first class to pass as a flow of data communication performed along a path that passes through a port of at least one of the plurality of transfer devices, to a port passed through the path; wherein the at least one transfer device monitors the data communication, and upon detecting the start of a flow of the first class of the data communication, switches the shared time slot to a dedicated time slot that allows only a flow of the limited class to pass, and upon detecting the end of the flow of the first class of the data communication by monitoring the data communication, switches the dedicated time slot back to the shared time slot. (Supplementary Item 2) The communication system according to Supplementary Item 1, wherein the control device sets, as the shared time slot, a time slot that passes only the flow of the limited class and the flow of the second class, and further sets, as the data communication flow, a time slot that passes one or more flows of other classes different from both the limited class and the second class, to the port passed through on the route. (Supplementary Item 3) The communication system according to Supplementary Item 1 or Supplementary Item 2, wherein, after switching the shared time slot to the dedicated time slot, the at least one transfer device detects, as the termination, that the flow of the first class of data communication has not resumed even after a protection time has elapsed since the flow of the first class of data communication was interrupted. (Supplementary Item 4) The at least one transfer device holds both a first table containing the settings of the shared time slots and a second table containing the settings of the dedicated time slots as tables containing the settings of the multiple time slots, and switches between the shared time slots and the dedicated time slots by switching between the first table and the second table. This is a communication system described in any one of Supplementary Item 1 to Supplementary Item 3.

[0065] The present disclosure is not limited to the above-described embodiments. For example, two or more blocks shown in the block diagram may be integrated, or one block may be divided. Two or more steps shown in the flowchart may be executed in parallel or in a different order, instead of being executed in chronological order as described, depending on the processing capabilities of the device executing each step, or as needed. Other modifications are possible within the scope of the present disclosure.

[0066] REFERENCE SIGNS LIST 10 Communication system 11 Time slot information 12 Setting information 20 Control device 21 Control unit 22 Storage unit 23 Communication unit 24 Time slot calculation function 25 Time slot setting function 31, 32, 33 Transfer device 34 Input port 35 Frame allocation unit 36 ​​Output port 37 Communication monitoring unit 38 Table switching control unit 41, 42 Fixed period communication terminal 51, 52 High priority communication terminal 61, 62 Low priority communication terminal 70 Table 71 First table 72 Second table

Claims

1. A communication system comprising: a plurality of transfer devices; and a control device that sets a plurality of time slots for each port of the plurality of transfer devices, wherein the control device sets a common time slot for a port along a route that passes through a port of at least one of the plurality of transfer devices, the common time slot allowing both a flow of a limited class including a first class and a flow of a second class different from the first class to pass as a flow of data communication that is performed along the route; wherein the at least one transfer device monitors the data communication, and upon detecting the start of a flow of the first class of the data communication, switches the common time slot to a dedicated time slot that allows only flows of the limited class to pass; and upon detecting the end of the flow of the first class of the data communication by monitoring the data communication, switches the dedicated time slot back to the common time slot.

2. The communication system according to claim 1, wherein the control device sets a time slot that allows only the limited class of flows and the second class of flows to pass as the shared time slot, and further sets a time slot that allows flows of one or more other classes different from either the limited class or the second class to pass as the data communication flow at the port passed through on the route.

3. The communication system of claim 1, wherein the at least one forwarding device detects the termination as the failure of the flow of the first class of data communication to resume even after a protection time has elapsed since the flow of the first class of data communication was interrupted after switching the shared time slot to the dedicated time slot.

4. A communication system according to any one of claims 1 to 3, wherein the at least one transfer device holds both a first table containing settings for the common time slots and a second table containing settings for the dedicated time slots as tables containing settings for the plurality of time slots, and switches between the common time slots and the dedicated time slots by switching between the first table and the second table.

Images