Network management device, transfer device, network system, and transfer schedule setting method

Abstract

A transfer device (10) calculates a synchronization time on the basis of a communication frame for time synchronization. The transfer device (10) calculates a time update amount, which is the difference between the synchronization time and an internal time that is managed by the device. The transfer device (10) transmits, to a network management device (20), network information (51) which indicates the time update amount. The network management device (20) uses the time update amount indicated by the network information (51) to calculate a transfer schedule (52) that defines, for each communication frame priority, a period in which the transfer device (10) performs data transfer. The network management device (20) distributes the transfer schedule (52) to the transfer device (10).

Description

Network management device, transfer device, network system, and transfer schedule setting method

[0001] The present disclosure relates to a technique for setting a transfer schedule that determines a period to be allocated to each of a plurality of communication streams when the communication streams are transferred by separating them in time.

[0002] IEEE 802.1Q-2018 (see Non-Patent Document 1) defines TAS as a specification for network devices to ensure the transmission quality of each communication stream in a network where communication streams with different required quality levels coexist. TAS is an abbreviation for Time-Aware Shaper. In TAS, the network device stores communication streams in queues for each priority class, and performs scheduled queue readout control based on the synchronized time within the network. This allows each communication stream to be transferred while being separated in time. The setting value related to the scheduled queue readout control is called the transfer schedule.

[0003] Patent Document 1 describes a transfer schedule setting technology aimed at improving the accuracy of the transfer schedule. In Patent Document 1, network devices such as a network switch and a PLC acquire propagation delays between the devices, and a network management device calculates a transfer schedule based on the propagation delays. The network management device then distributes the calculated transfer schedule to the network devices. PLC stands for Programmable Logic Controller.

[0004] Japanese Patent Application Laid-Open No. 2022-136722

[0005] IEEE 802.1Q-2018 - IEEE Standard for Local and Metropolitan Area Networks--Bridges and Bridged Networks.

[0006] In Patent Document 1, propagation delay between devices is used to calculate a transfer schedule. However, due to a timing discrepancy in the network device's transmission of a communication stream, the communication frame may not be transferred in the expected time slot, and the expected communication bandwidth or delay may not be achieved. The present disclosure aims to make it easier to achieve the expected communication bandwidth or delay even when there is a timing discrepancy in the network device's transmission of a communication stream.

[0007] The network management device according to the present disclosure comprises: a network information acquisition unit that acquires, from a transfer device that calculates a synchronization time based on a communication frame for time synchronization and performs time synchronization, network information indicating a time update range, which is the difference between the synchronization time and the internal time managed by the transfer device before time synchronization using the synchronization time; a transfer schedule calculation unit that calculates a transfer schedule that defines a period during which the transfer device will transfer data for each priority of the communication frame, using the time update range indicated by the network information acquired by the network information acquisition unit; and a schedule distribution unit that distributes the transfer schedule calculated by the transfer schedule calculation unit to the transfer device.

[0008] In the present disclosure, a transfer schedule is calculated using a time update interval. The time update interval is a parameter that affects the timing difference between when a network device transmits a communication stream. Therefore, by calculating a transfer schedule using the time update interval, it becomes easier to achieve the expected communication bandwidth or delay even if there is a difference in the timing when the transfer device 10 transmits the communication stream.

[0009] 1 is a configuration diagram of a network system 100 according to a first embodiment. A functional configuration diagram of a transfer device 10 according to the first embodiment. A hardware configuration diagram of the transfer device 10 according to the first embodiment. A functional configuration diagram of a network management device 20 according to the first embodiment. A hardware configuration diagram of the network management device 20 according to the first embodiment. A diagram outlining the operation of the network system 100 according to the first embodiment. A flowchart of processing from when the transfer device 10 according to the first embodiment receives a communication frame for time synchronization including time information, to when the transfer device 10 notifies the network management device 20 of a time update width, etc. An explanatory diagram of the relationship between network information 51 and a transfer schedule 52. An explanatory diagram of the relationship between a synchronization error and a time slot margin. A flowchart of processing from when the network management device 20 according to the first embodiment receives a communication frame including network information 51, to when the network management device 20 distributes a transfer schedule 52 to the transfer device 10.

[0010] First Embodiment. ***Description of Configuration*** The configuration of a network system 100 according to the first embodiment will be described with reference to FIG. 1. The network system 100 includes a plurality of transfer devices 10, a network management device 20, a time distribution device 30, and a plurality of terminals 40. The plurality of transfer devices 10, the network management device 20, the time distribution device 30, and the plurality of terminals 40 are connected via a transmission path 90. Each transfer device 10 is a device that transfers a communication frame received from an adjacent device to another adjacent device. Specific examples of each transfer device 10 include network devices such as a network switch, a router, a hub, a bridge, a gateway, and a PLC. The network management device 20 is a computer that manages the operation of the network system 100. The time distribution device 30 is a computer that distributes communication frames for time synchronization. Each terminal 40 is a computer or the like used by a user.

[0011] The functional configuration of the transfer device 10 according to the first embodiment will be described with reference to Fig. 2. The transfer device 10 includes a communication port 11, a timestamp acquisition unit 12, a communication control unit 13, and a setting unit 14. The communication control unit 13 includes a transfer unit 131, a time synchronization unit 132, an internal device delay calculation unit 133, and a notification unit 134. The time synchronization unit 132 includes a propagation delay calculation unit 1321, a synchronization time calculation unit 1322, and a time update width calculation unit 1323.

[0012] The hardware configuration of the transfer device 10 according to the first embodiment will be described with reference to Fig. 3. The transfer device 10 includes a processor 101, a memory 102, and data communication hardware 103. The processor 101, the memory 102, and the data communication hardware 103 are connected via a bus 104.

[0013] The communication port 11 is realized by data communication hardware 103. The data processing units, namely, the timestamp acquisition unit 12, the communication control unit 13, and the setting unit 14, are realized by hardware, software, firmware, or a combination thereof. The software and firmware are written as programs and stored in the memory 102. When the data processing units are realized by software or firmware, the data processing units are realized by the processor 101 reading from the memory 102 and executing the programs for operating as each of the data processing units.

[0014] The functional configuration of the network management device 20 according to the first embodiment will be described with reference to Fig. 4. The network management device 20 includes a communication port 21, a network information acquisition unit 22, a synchronization error estimation unit 23, a setting unit 24, a transfer schedule calculation unit 25, and a transfer schedule distribution unit 26.

[0015] The hardware configuration of the network management device 20 according to the first embodiment will be described with reference to Fig. 5. The network management device 20 includes a processor 201, a memory 202, and data communication hardware 203. The processor 201, the memory 202, and the data communication hardware 203 are connected via a bus 204.

[0016] The communication port 21 is realized by data communication hardware 203. The data processing units, namely, the network information acquisition unit 22, the synchronization error estimation unit 23, the setting unit 24, the transfer schedule calculation unit 25, and the transfer schedule distribution unit 26, are realized by hardware, software, firmware, or a combination thereof. The software and firmware are written as programs and stored in the memory 202. When the data processing units are realized by software or firmware, the data processing units are realized by the processor 201 reading from the memory 202 and executing the programs for operating as each of the data processing units.

[0017] The processors 101 and 201 are CPUs, system LSIs, etc. CPU stands for Central Processing Unit. LSI stands for Large Scale Integration. The processors 101 and 201 may also be called processing devices, arithmetic units, processors, microprocessors, microcomputers, or digital signal processors.

[0018] The memories 102 and 202 are non-volatile or volatile semiconductor memories such as RAM, ROM, flash memory, EPROM, or EEPROM. RAM stands for Random Access Memory. ROM stands for Read Only Memory. EPROM stands for Erasable Programmable Read Only Memory. EEPROM stands for Electrically Erasable Programmable Read-Only Memory. The memories 102 and 202 may be portable recording media such as magnetic disks, flexible disks, optical disks, compact disks, minidisks, or DVDs. DVD stands for Digital Versatile Disc.

[0019] The data communication hardware 103, 203 is a network card for Ethernet (registered trademark) or the like.

[0020] The data processing units of the transfer device 10 and the network management device 20 may be implemented using dedicated hardware. Examples of dedicated hardware include a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC, an FPGA, or a combination of these. ASIC stands for Application Specific Integrated Circuit. FPGA stands for Field Programmable Gate Array. A portion of the data processing unit may be implemented using dedicated hardware, and the remainder may be implemented using the processors 101, 201 and memories 102, 202.

[0021] ***Description of Operation*** The operation of the network system 100 according to the first embodiment will be described with reference to Figures 6 to 10. The operation procedure of the network system 100 according to the first embodiment corresponds to the transfer schedule setting method according to the first embodiment.

[0022] **Outline of Operation** An outline of the operation of the network system 100 according to the first embodiment will be described with reference to Fig. 6. In the network system 100, data transfer is controlled in accordance with the TAS defined in IEEE 802.1Q-2018. Specifically, the network management device 20 sets a transfer schedule 52, which is a setting value related to queue read control. Each transfer device 10 reads the queue in accordance with the transfer schedule 52, thereby transferring data in accordance with the transfer schedule 52.

[0023] A communication frame for time synchronization including time information is distributed from the time distribution device 30. The communication frame for time synchronization is distributed to each terminal 40 via the transfer device 10. Each transfer device 10 and each terminal 40 performs time synchronization based on the time information included in the communication frame for time synchronization.

[0024] When performing time synchronization, each transfer device 10 measures the propagation delay between adjacent devices and the internal delay within the transfer device 10. Furthermore, each transfer device 10 calculates a time update width, which is the difference between the synchronization time calculated from the time information during time synchronization and the internal time managed by the transfer device 10 before time synchronization at the synchronization time. Each transfer device 10 transmits network information 51 indicating the propagation delay, internal delay, and time update width to the network management device 20. The network management device 20 uses the network information 51 transmitted from each transfer device 10 to calculate a transfer schedule 52 that defines a period during which each transfer device 10 will transfer data. The network management device 20 then distributes the transfer schedule 52 to each transfer device 10. Then, each transfer device 10 performs data transfer during the period defined in the transfer schedule 52.

[0025] **Operation of Transfer Device 10** The operation of the transfer device 10 according to the first embodiment will be described with reference to Figure 2. The communication port 11 transfers frames constituting a communication stream received from an external device to the timestamp acquisition unit 12. The communication port 11 also transfers frames constituting a communication stream received from the timestamp acquisition unit 12 to the external device. The timestamp acquisition unit 12 transfers communication frames received from the communication port 11 to the communication control unit 13. The timestamp acquisition unit 12 also transfers communication frames received from the communication control unit 13 to the communication port 11. At this time, the timestamp acquisition unit 12 acquires the reception time of the communication frame received from the communication port 11 or the transmission time of the communication frame to be transmitted to the communication port 11, and notifies the communication control unit 13.

[0026] In the communication control unit 13, the transfer unit 131 transfers a communication frame received from the timestamp acquisition unit 12 to a corresponding destination communication port. If the communication frame received from the timestamp acquisition unit 12 is a communication frame for time synchronization, the transfer unit 131 transfers the communication frame to the time synchronization unit 132.

[0027] When transferring a communication frame to a communication port, the transfer unit 131 assigns a priority and an identifier to the communication frame based on the setting information received from the setting unit 14. The priority and identifier are determined by pattern matching between the received frame's attributes, such as the receiving port number of the received frame, header information, payload information, and error information, and the setting information received from the setting unit 14. For example, assume that the setting unit 14 is configured to assign a priority of 7 and an ID of 1 to a communication frame received on port number 1 when the destination MAC address is 12-34-56-AB-CD-EF and the EtherType is 0x0800 (IP communication). In this case, the transfer unit 131 determines whether the communication frame matches this setting, and if so, assigns a priority of 7 and an ID of 1 to the communication frame. The transfer unit 131 stores the communication frame in a queue corresponding to the priority. The transfer unit 131 then controls the reading of the queue scheduled based on time in accordance with the TAS defined in IEEE 802.1Q-2018. Here, the time in the transfer device 10 is synchronized with other devices by the time synchronization unit 132. This allows scheduled transfer to be realized, and each communication stream is transferred separately in terms of time.

[0028] Here, the transfer unit 131 receives setting values ​​related to read control of the scheduled queue, i.e., the transfer schedule 52, from the setting unit 14. The setting unit 14 holds two transfer schedules: the transfer schedule 52 currently being executed and the transfer schedule 52 to be newly applied. When the application time of the transfer schedule 52 to be newly applied arrives, the transfer unit 131 adopts the transfer schedule 52 to be newly applied.

[0029] The time synchronization unit 132 performs time synchronization processing in accordance with a time synchronization profile, such as PTP defined in IEEE 1588 or gPTP, which is based on PTP. PTP stands for Precision Time Protocol. gPTP stands for generalized PTP. The propagation delay calculation unit 1321 exchanges the reception time or transmission time of the time synchronization frame acquired by the time stamp acquisition unit 12 with an external device and calculates the propagation delay between the device that supports external time synchronization. The propagation delay is the delay of the communication stream that occurs on the transmission path between the devices. In the case of a wired network, the propagation delay is a cable delay or fiber delay. The synchronization time calculation unit 1322 calculates the synchronization time based on the propagation delay calculated by the propagation delay calculation unit 1321 and the time information included in the communication frame for time synchronization distributed from the time distribution device 30. The time synchronization unit 132 synchronizes the internal time, which is the time managed by the transfer device 10, with the calculated synchronization time.

[0030] Here, an error occurs in the calculated synchronization time due to factors such as an error in acquiring the timestamp and a deviation in the clock frequencies between the time distribution device 30 and the transfer device 10. As a result, a time jump occurs when synchronizing with the synchronization time calculated by the synchronization time calculation unit 1322. The time update width calculation unit 1323 calculates this time jump, that is, the time update width, which is the difference between the internal time, which is the time that the transfer device 10 was running before synchronizing with the time of the time distribution device, and the synchronization time, which is the time to be newly synchronized.

[0031] The in-device delay calculation unit 133 calculates the delay of each communication stream within the transfer device 10. The delay of a communication stream is calculated by subtracting the reception time of the same communication stream from the transmission time of the same communication stream acquired by the timestamp acquisition unit 12. The in-device delay calculation unit 133 calculates the in-device delay for each communication stream identifier assigned by the transfer unit 131.

[0032] The propagation delay calculated by propagation delay calculation unit 1321, the time update width calculated by time update width calculation unit 1323, and the intra-device delay calculated by intra-device delay calculation unit 133 are transmitted to notification unit 134. The propagation delay, intra-device delay, and time update width may be reported as the most recent measured values, or as statistical values ​​such as the minimum, maximum, average, or variance over a certain period of time. Notification unit 134 stores the received propagation delay, time update width, and intra-device delay in a communication frame addressed to network management device 20, and transmits the frame to an external device via transfer unit 131, timestamp acquisition unit 12, and communication port 11. As a result, the propagation delay, time update width, and intra-device delay are reported to network management device 20.

[0033] The setting unit 14 notifies the transfer unit 131 of the transfer schedule 52 that it holds and the application time of the transfer schedule 52. The setting unit 14 acquires and holds the transfer schedule 52 distributed from the network management device 20 via the communication port 11, the timestamp acquisition unit 12, and the transfer unit 131. The setting unit 14 may also hold a transfer schedule 52 that has been set by the user.

[0034] 7 , a process will be described in which the transfer device 10 according to the first embodiment receives a communication frame for time synchronization including time information, and then notifies the network management device 20 of the time update interval and the like. As described above, the transfer device 10 receives the communication frame for time synchronization. The transfer unit 131 then transfers the communication frame for time synchronization to the time synchronization unit 132.

[0035] (Step S11: Synchronization Time Calculation Process) The synchronization time calculation unit 1322 calculates the synchronization time based on the propagation delay calculated by the propagation delay calculation unit 1321 and the time information included in the communication frame for time synchronization.

[0036] (Step S12: Initial Calculation Determination Process) The synchronization time calculation unit 1322 determines whether the synchronization time calculation in step S11 is the first calculation of the synchronization time. If it is the first calculation of the synchronization time, the synchronization time calculation unit 1322 ends the process. On the other hand, if it is the second or subsequent calculation of the synchronization time, the synchronization time calculation unit 1322 proceeds to step S13. If it is the first calculation of the synchronization time, it is expected that there will be a larger difference between the calculated synchronization time and the internal time, which is the time managed by the transfer device 10, compared to the second or subsequent calculation of the synchronization time. Therefore, if it is the first calculation of the synchronization time, the process from step S13 onwards is not performed, and notification of the time update width at this timing is stopped.

[0037] (Step S13: Time update range calculation process) The time update range calculation unit 1323 calculates the time update range, which is the difference between the internal time and the synchronized time. In other words, the time update range D is expressed as D = TM - TS, where TM is the synchronized time and TS is the internal time.

[0038] (Step S14: Time update range notification process) Time update range calculation unit 1323 transmits the time update range calculated in step S13 to notification unit 134. In response, notification unit 134 transmits to network management device 20 network information 51 indicating the propagation delay transmitted from propagation delay calculation unit 1321 and the intra-device delay transmitted from intra-device delay calculation unit 133, in addition to the time update range.

[0039] **Operation of Network Management Device 20** The operation of the network management device 20 according to the first embodiment will be described with reference to Fig. 4. The communication port 21 transfers communication frames received from external devices to the network information acquisition unit 22 and the transfer schedule distribution unit 26. The communication port 21 also transfers communication frames received from the network information acquisition unit 22 and the transfer schedule distribution unit 26 to the external devices.

[0040] The network information acquisition unit 22 acquires network information 51 from the communication frame transferred from the communication port 21. When the network information acquisition unit 22 acquires the network information 51, the network information acquisition unit 22 notifies the synchronization error estimation unit 23 of the time update width indicated by the network information 51, and notifies the transfer schedule calculation unit 25 of the propagation delay and in-device delay indicated by the network information 51.

[0041] The synchronization error estimator 23 estimates the statistical value of the time update interval in the most recent reference period as the synchronization error. As a specific example, the synchronization error estimator 23 estimates the maximum value of the time update interval in the most recent reference period as the synchronization error. The synchronization error estimator 23 may also calculate the standard deviation of the time update interval in the most recent reference period and estimate a range of 2σ as the synchronization error.

[0042] The setting unit 24 holds system specification information that indicates the specifications of the network system 100. The setting unit 24 notifies the transfer schedule calculation unit 25 of the system specification information. The system specification information includes topology information required for calculating the transfer schedule 52, as well as the transmission period, frame length, priority, and delay constraint of each communication stream.

[0043] The transfer schedule calculation unit 25 calculates the transfer schedule 52 using the synchronization error, propagation delay, and internal device delay for each transfer device 10, as well as the system specification information held by the setting unit 24. Specifically, the transfer schedule calculation unit 25 sets a margin before and after each time slot using the synchronization error for each transfer device 10. A time slot is a period during which the transfer device 10 transfers data, determined for each priority of a communication frame. In other words, the transfer schedule calculation unit 25 extends the period allocated to the transfer device 10 for each priority of a communication frame forward or backward by the amount of the synchronization error. Then, the transfer schedule calculation unit 25 calculates the transfer schedule 52 by searching for a combination of setting values ​​that satisfy constraints such as the delay of each communication stream, based on the propagation delay, internal device delay, and system specification information, while taking the margin into consideration. The transfer schedule calculation unit 25 transmits the transfer schedule 52, in which the application time has been set, to the transfer schedule distribution unit 26.

[0044] The relationship between the network information 51 and the transfer schedule 52 will be described with reference to FIG. 8 . The transfer schedule 52 is calculated based on the propagation delay between the transfer devices 10 and the intra-device delay that occurs inside the transfer device 10, while taking into account a margin based on the synchronization error between the transfer devices. Specifically, there is a propagation delay X between transfer device #2 and transfer device #1. Furthermore, there is an intra-device delay Y between transfer device #2. Therefore, the time slot assigned to transfer device #2 starts at a timing that is propagation delay X + intra-device delay Y later than the time slot assigned to transfer device #1. Then, from this timing, a period that includes a margin for synchronization error Z before and after the required period P determined based on the system specifications is assigned as the time slot for transfer device #2. The synchronization error between the transfer devices 10 affects the error in the timing of transmitting communication frames from the transfer device 10. Therefore, as shown in FIG. 8 , it is desirable to set a margin for the synchronization error before and after the time slot.

[0045] The relationship between the synchronization error and the time slot margin will be described with reference to Figure 9. The transfer schedule calculation unit 25 sets the maximum synchronization error in the transfer process as the time slot margin for each transfer path of the communication stream. For example, in the case of transfer device #6, the transfer path passes through transfer device #1, transfer device #2, and transfer device #5, so ±30 ns (nano second), which is the maximum synchronization error among these, is set as the margin.

[0046] The transfer schedule distribution unit 26 distributes the transfer schedule 52 sent by the transfer schedule calculation unit 25 to each transfer device 10 via the communication port 21. Then, in each transfer device 10, the distributed transfer schedule 52 is set in the setting unit 14, and is adopted by the transfer unit 131 at the application time.

[0047] 10 , a process will be described from when the network management device 20 according to the first embodiment receives a communication frame including network information 51 to when the network management device 20 distributes a transfer schedule 52 to the transfer device 10. As described above, the network management device 20 receives a communication frame including network information 51. Then, the network information acquisition unit 22 acquires the network information 51, notifies the synchronization error estimator 23 of the time update width, and notifies the transfer schedule calculator 25 of the propagation delay and the in-device delay.

[0048] (Step S21: Synchronization Error Estimation Process) The synchronization error estimation unit 23 estimates the statistical value of the time update width in the most recent reference period as the synchronization error. The synchronization error estimation unit 23 notifies the transfer schedule calculation unit 25 of the estimated synchronization error.

[0049] (Step S22: Information Determination Process) The transfer schedule calculation unit 25 determines whether or not information necessary for calculating the transfer schedule 52 has been collected. The information necessary for calculating the transfer schedule 52 is the synchronization error, propagation delay, and intra-device delay for each transfer device 10, and the system specification information held by the setting unit 24. If the transfer schedule calculation unit 25 has collected the necessary information, it proceeds to step S23. On the other hand, if the transfer schedule calculation unit 25 has not collected the necessary information, it ends the process.

[0050] (Step S23: Margin Setting Process) The transfer schedule calculation unit 25 uses the synchronization error estimated for each transfer device 10 to set a margin before and after each time slot.

[0051] (Step S24: Transfer schedule calculation process) The transfer schedule calculation unit 25 searches for a combination of setting values ​​that satisfies constraints such as delay of each communication stream, based on the propagation delay, the delay within the device, and the system specification information, while taking into account the margin set in step S23. In this way, the transfer schedule calculation unit 25 calculates the transfer schedule 52.

[0052] (Step S25: Transfer Schedule Distribution Process) The transfer schedule distribution unit 26 distributes the transfer schedule 52 calculated in step S24 to each transfer device 10.

[0053] ***Effects of First Embodiment*** As described above, in the network system 100 according to the first embodiment, the transfer device 10 periodically notifies the network management device 20 of the time update interval with the time distribution device 30. The network management device 20 then sets the transfer schedule 52 using the synchronization error obtained from the time update interval. This makes it easier to achieve the expected communication bandwidth or delay even if there is a discrepancy in the timing at which the transfer device 10 transmits the communication stream.

[0054] By estimating the maximum value of the time update interval in the most recent reference period as the synchronization error, it becomes easier to achieve the expected communication bandwidth or delay even when there is a deviation in the transmission timing of the transfer device 10. However, if the synchronization error is set too large, bandwidth utilization efficiency deteriorates. By calculating the standard deviation of the time update interval in the most recent reference period and estimating a range of 2σ as the synchronization error, it is possible to achieve the expected communication bandwidth or delay while improving average bandwidth utilization efficiency.

[0055] Furthermore, in the network system 100 according to the first embodiment, the processes from the transmission of the network information 51 by each transfer device 10 to the distribution of the transfer schedule 52 by the network management device 20 are automated. This makes it possible to reduce the labor required for setting the transfer schedule 52, and to reduce the costs of introducing and operating the system.

[0056] ***Other Configurations*** <Variation 1> In the first embodiment, the network management device 20 calculated the synchronization error from the time update interval. However, each transfer device 10 may calculate the synchronization error from the time update interval and notify the network management device 20. In this case, the time update interval calculation unit 1323 of each transfer device 10 calculates the synchronization error from the time update interval using a method similar to that of the synchronization error estimation unit 23. Then, the time update interval calculation unit 1323 notifies the notification unit 134 of the synchronization error instead of the time update interval.

[0057] 10, in the first embodiment, transfer schedule calculation unit 25 recalculates and distributes transfer schedule 52 upon receiving network information 51. However, transfer schedule calculation unit 25 may recalculate and distribute transfer schedule 52 at least one of the following times: at periodically determined timing; when network information 51 changes by more than a standard; and when data transfer is performed in violation of the period determined in transfer schedule 52.

[0058] When periodically determined timing is adopted, the network management device 20 is provided with a periodic timer. When the periodic timer expires, the transfer schedule calculation unit 25 recalculates and distributes the transfer schedule 52.

[0059] When adopting the case where there is a change in network information 51 that is greater than the standard, transfer schedule calculation unit 25 determines whether network information 51 acquired by network information acquisition unit 22 has changed by greater than the standard compared to previously acquired network information 51. When there is a change that is greater than the standard, transfer schedule calculation unit 25 recalculates and distributes transfer schedule 52.

[0060] When adopting the case where data transfer has occurred in violation of the period defined in the transfer schedule 52, the notification unit 134 of each transfer device 10 notifies the network management device 20 that data transfer has occurred in violation of the period defined in the transfer schedule 52. When this notification is received, the transfer schedule calculation unit 25 recalculates and distributes the transfer schedule 52. Here, data transfer occurring in violation of the period defined in the transfer schedule 52 means a case where a communication stream that is not permitted to be transferred at the current time is stored in the queue of the transfer device 10, and a case where a gate closes while the communication stream is being output from the transfer device 10 (a time when output is not permitted has arrived). Whether or not there has been a violation may be determined taking into account the degree of the violation, such as the number of violations and the number of bytes exceeding the time slot of the violation frame.

[0061] By adopting the case where there is a change in the network information 51 that exceeds the standard, or where data transfer is performed in violation of the period specified in the transfer schedule 52, it is possible to reduce the processing load on the network management device 20 and the transfer device 10 and reduce the network bandwidth usage.

[0062] In addition, the word "unit" in the above description may be read as a "circuit," "step," "procedure," "process," or "processing circuit."

[0063] The embodiments and modifications of the present disclosure have been described above. Some of these embodiments and modifications may be combined and implemented. Furthermore, one or more of them may be implemented partially. Note that the present disclosure is not limited to the above embodiments and modifications, and various modifications are possible as needed.

[0064] 100 Network system, 10 Transfer device, 11 Communication port, 12 Time stamp acquisition unit, 13 Communication control unit, 14 Setting unit, 131 Transfer unit, 132 Time synchronization unit, 133 In-device delay calculation unit, 134 Notification unit, 1321 Propagation delay calculation unit, 1322 Synchronization time calculation unit, 1323 Time update width calculation unit, 101 Processor, 102 Memory, 103 Data communication hardware, 104 Bus, 20 Network management device, 21 Communication port, 22 Network information acquisition unit, 23 Synchronization error estimation unit, 24 Setting unit, 25 Transfer schedule calculation unit, 26 Transfer schedule distribution unit, 201 Processor, 202 Memory, 203 Data communication hardware, 204 Bus, 30 Time distribution device, 40 Terminal, 51 Network information, 52 Transfer schedule, 90 Transmission path.

Claims

1. a network information acquisition unit that acquires, from a transfer device that calculates a synchronization time based on a communication frame for time synchronization and performs time synchronization, network information that indicates a time update width, which is the difference between the synchronization time and an internal time that was managed by the transfer device before time synchronization based on the synchronization time; a transfer schedule calculation unit that calculates a transfer schedule that defines a period during which the transfer device transfers data for each priority of a communication frame, using the time update interval indicated by the network information acquired by the network information acquisition unit; a schedule distribution unit that distributes the transfer schedule calculated by the transfer schedule calculation unit to the transfer device; A network management device comprising:

2. The network management device further a synchronization error estimation unit that estimates, as a synchronization error, a statistical value of the time update interval indicated by the network information during a reference period acquired by the network information acquisition unit; Equipped with The transfer schedule calculation unit calculates the transfer schedule using the synchronization error estimated by the synchronization error estimation unit. The network management device according to claim 1 .

3. The transfer schedule calculation unit calculates the transfer schedule so as to extend the period allocated to the transfer device forward or backward for each priority of the communication frame by the amount of the synchronization error. The network management device according to claim 2 .

4. the network information indicates an in-device delay for the forwarding device; The transfer schedule calculation unit calculates the transfer schedule using the in-device delay. The network management device according to claim 1 .

5. The transfer schedule calculation unit recalculates the transfer schedule at a periodically determined timing, when there is a change in the network information exceeding a standard value, or when data transfer is performed in violation of the period determined in the transfer schedule. The network management device according to claim 1 .

6. a transfer device that transfers data according to a period allocated in a transfer schedule distributed from a network management device; a synchronization time calculation unit that calculates a synchronization time based on a communication frame for time synchronization; an update width calculation unit that calculates a time update width, which is the difference between the synchronized time calculated by the synchronized time calculation unit and an internal time managed by the device; a notification unit that notifies the network management device of the time update interval calculated by the update interval calculation unit; Equipped with a transfer device.

7. The transfer device further comprises: a synchronization error estimation unit that estimates a statistical value of the time update interval during a reference period as a synchronization error; Equipped with The notification unit notifies the network management device of the synchronization error estimated by the synchronization error estimation unit. The transfer device according to claim 6.

8. The notification unit notifies the network management device of an internal delay for the transfer device. The transfer device according to claim 6.

9. The notification unit notifies the network management device that a data transfer has been performed in violation of the period defined in the transfer schedule. The transfer device according to claim 6.

10. The network management device calculates the transfer schedule based on the time update interval notified by the notification unit. The transfer device according to claim 6.

11. A network system including a transfer device and a network management device, The transfer device a synchronization time calculation unit that calculates a synchronization time based on a communication frame for time synchronization; an update width calculation unit that calculates a time update width, which is the difference between the synchronized time calculated by the synchronized time calculation unit and an internal time managed by the device; a notification unit that notifies the network management device of the time update interval calculated by the update interval calculation unit; Equipped with the network management device, a transfer schedule calculation unit that calculates a transfer schedule that determines a period during which the transfer device transfers data for each priority of a communication frame, using the time update width notified by the notification unit; a schedule distribution unit that distributes the transfer schedule calculated by the transfer schedule calculation unit to the transfer device; A network system comprising:

12. The transfer device calculates a synchronization time based on the communication frame for time synchronization, The transfer device calculates a time update width, which is the difference between the synchronized time and an internal time managed by the device, the transfer device notifies the network management device of the time update interval; the network management device calculates a transfer schedule that defines a period during which the transfer device will transfer data for each priority of the communication frame using the notified time update width; The network management device distributes the transfer schedule to the transfer device. How to schedule a transfer.

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